Chevy 6.5 Turbo Diesel REVS Out of CONTROL?! (Part 1 - Throttle Diagnosis)

[@paulbrown3180]

Fuel is by-passing inside the injection pump itself . Worked a large GM dealer in Toronto , changed literally hundreds of these pumps , just get another one and don't forget new fuel filter , set TDC offset with scanner when engine is at operating temp and add Standayne fuel conditioner , yeah and move that driver module off of the pump using the resistor that came with the driver module as they were calibrated together . A higher resistor number meant more power but to the expense of fuel mileage , Aftermarket harnesses and mounting plates usually came with a number 9 resistor , high fuel consumption with those , usually had a 4 stamped on the resistor when looking inside the bottom of the the driver module wire connector . Good luck , reminds me of the good old days when life was simple .

[@PineHollowAutoDiagnostics]

I still don't understand why the PCM ramps up the fuel solenoid duty cycle through the roof if you touch the throttle 🤔

[@aleskyfinis1025]

Wo man 🧍‍♂️

[@colchronic]

​@@PineHollowAutoDiagnostics It's a hard call to make perhaps try a used pump out of a Pick-n-Pull

[@jonnycando]

@@PineHollowAutoDiagnosticsDiesels are like helicopters, there is no way they should work at all…so making them work is pure luck!

[@dnlmachine4287]

Cummins has a detailed and fairly simple fuel system test, requires a couple of fittings, fuel pressure gauge, some tubing and measuring "cups". Will show confirmation of pressures, leaks, sensors, fuel bypass, pump efficiency etc. Is there a similar procedure for the GM 6.5? I would like to think so? Stay gold.

[@JREACHER1954]

Bought mine new in 94. Still have it. They don't take kindly to abuse and are prone to electrcal gremlins. I have a local shop that actually has a younger tech that works on these so very fortunate as they are not welcome in a lot of diesel shops. This is the first deep dive video on the electrical side of the fuel control system that I've seen. My hat is off to you and to boldly go where no one likes to any longer. Looking forward to Part 2.

[@Bizija123]

This thing I love about Ivan's diagnostics is that he doesn't just sit down and Google stuff. He does a step by step process of elimination and scope wizardry to get to answers. This one's tough because you know the ecu is decades old but you don't want to condemn it right away.

[@CedroCron]

You have the patience of a saint Ivan. Amazed by your cool level head and the "let's see what we can do" attitude. Hat off to you sir.

[@DukeRivers]

St. Ivan.

[@ronaldwilkinson6685]

Make sure that the resistor that calibrates the pump is inside the connector of PDM's, they slide onto the pins. We were told that those were important back in the days of replacing these injection pumps under the GM special policy.

[@brandongarnold]

Be careful on that call on the PCM. I had a 97 3500hd with 6.5 with the same issue and it was the pump. I luckily had a sister truck beside it I was able to swap the PCM and PMD due to it already being remote mounted on both trucks. I was for sure it was the PCM but to my surprise it was not. I didn’t go as far in depth on the diagnostics as you are doing so you may be more confident on your call but the truck I had surged horribly when trying to drive to the point it could not be driven and in park any touching of the throttle would send the engine to full rpm. I believe it was an issue with the fuel metering solenoid that comes in the back of the pump.

[@kennthb6590]

It will be the fuel pump itself not electrical

[@brandongarnold]

⁠​⁠@@kennthb6590Not so much the electrical side but the mechanical side. Like a broken or weak poppet valve spring or a poppet valve that hangs up in the bore under the high fuel pressure. I’m not sure because I’ve never had a pump apart but it seems to me whatever meters the fuel is hanging up under the higher pressure. It seems the popped valve is closed at the beginning of injection and opened at the end of injection so the longer it’s closed the more fuel delivered the faster the engine runs. So if the poppet is hanging up there will be issues.

[@jeffmiller6100]

Love the variety of vehicles. Equipment etc Ivan brings to his channel ! Keep it coming Ivan !👌

[@jaredpaulsen3]

You give me faith Ivan! Everyday I go into work, I feel better prepared for whatever is next, and a lot of that confidence is directly from you. Never stop learning people!!!

[@AP9311]

Love those 6.5s the problem is the modules sitting on the engine are prone to failures like overheating the modules. That's why the RPM is ramping up. I've seen this issue before. The pump fuel is bypassing that, causing issues. Some injection pumps need to be rebuilt with upgraded parts that'll take care of the problem.

[@QuadstarTuningLLC]

You did a great job of applying advanced diagnostic principles to this platform that you've never worked with before. All normal EFI control principles apply until you get into the actual DS injection pump that's its own beast.

[@bombardier3qtrlbpsi]

Older guy's all retired working on these things. Ivan you will be able to retire early if you just get a few more of the old chevy 6.5's😆😆 Great work ethic as always. Have a geat summer 👍

[@tomwagner4516]

I had a Cutlass Supreme diesel in college. Honestly the best car I ever owned. When I moved I sold it to a friend because I needed the money. Bad move on my part. But it did act up exactly as this one. It was the injector pump. Only thing that ever went bad.

[@mtebaldi1]

This is the first 6.5 I've seen diagnosed using a scope. Ivan, you are a true electronic technician. Most just parts cannon these engines known by history on internet Q&A.

[@JoseSilveira-newhandleforYT]

Pretty advanced diagnostic, Ivan! And on an older school diesel! I think Paul Brown comment is hitting the problem root.

[@kerrylewis2581]

Holy highs and lows Batman. This beast needs to be soothed

[@andrewbrown4975]

Hi Ivan, There is a braded copper ground strap that runs from the firewall behind the exhaust downpipe from the turbo to the back of the left bank head, when it corrodes it sets up all kinds of crazy feedback to the computer behind the glovebox and the pmd, I’ve had a couple of 94’s with this problem, I went back to a 93 five speed 4x4 no computer never been a problem and still going strong,

[@gazoline7093]

Try hooking up a frequency generator up to the injector control line on the pcm that will tell you for certain if it’s a bad pcm putting out a bad signal to the IDM

[@philh9238]

I said the same thing. We’re the only onescc by who said that.

[@mikechiodetti4482]

You've got a good one here Ivan. Looks like one of the comments had an answer for this problem.

[@philh9238]

Which is what?

[@gags730]

@@philh9238 LOL I was thinking the same thing when I read that comment...haha.... I would say the best answer would probably be the comment with: Fuel is by-passing inside the injection pump itself, change the pump and move that driver module off of the pump using the resistor that came with the driver module as they were calibrated together. Set TDC offset with scanner when engine is at operating temp. Change fuel filter. Have a great day.

[@kevinbarry71]

The Duramax was such an enormous step forward over this old Detroit diesel design

[@80SWoods]

I’m nearly sure that the Duramax is an Isuzu design they picked up when they merged.

[@kevinbarry71]

@@80SWoods it is

[@bags4]

What kind of Detroit is in this truck?

[@Ilikeryche]

@@80SWoods It is.

[@bm03431]

Interesting you mentioned detroit. I've seen several faulty fuel metering valves cause idle oscilations in the dd15

[@philh9238]

If you had a signal generator you could dial it in the correct duty cycle when the engine actually idled for that few seconds. Eliminate computer control. Not sure if that’d work but would be an experiment

[@bags4]

Smart suggestion. Would love to see Ivan try this

[@lvsqcsl]

This could be worse; this engine could be a 6.2 liter diesel. I drove one on a delivery route that was a C-30 Chevrolet with a 20' box on the back. Those engines didn't have turbos and 130 horsepower wasn't enough to "pull a sitting hen off a nest." The company eventually got some 6.5 liter diesels that were somewhat trouble-prone and the 6.6 Duramax was an improvement over those engines. I am wanting to say the Duramax was an Isuzu design IIRC. I own 2 6.0 liter Ford diesels and I have a newfound respect for those upon viewing this video. Ivan, you are getting down to the nitty-gritty when it comes to waveforms; I don't think you have gotten this technical before. Good to see it. GREAT VIDEO!

[@billziegmond4943]

I love how you talk us through your thought process. I wouldn't be ready to call the pcm just yet. Need some further data gathering.

[@BoatDiesel82]

Love your work Ivan! thank you for sharing your knowledge Sounds like the injection pump. Low and ultra low sulfur fuel really wears out those Stanadyne/Roosa-master pumps. I'd change the nozzles and glow plugs out too while it's apart and insist the client runs Power Service additive in every tank. Those were junk new, really junk now.

[@farmermiyagi1338]

When I was in the military, serving in Japan, I worked in the heavy equipment shop, we had a detroit runaway one day. GI's scattered. It was a genuine runaway though, not just 2k rpm. I got out of the service and went into automotive and left the heavy equipment field.

[@richb419]

Hi the Detroit diesels were 2 stroke units that had that problem, when they were worn, they would burn the crank case oil until the oil was gone or the emergency stop cover closed of the intake air

[@kevin9c1]

That's ok, they have a natural rev limiter: valve float.

[@MarcusKeeler]

Just the idea of a Diesel runaway frightens the life out of me

[@tedstantz1185]

No doubt. Gotta have a plan!!!

[@tonep3168]

A diesel runaway is when the engine starts burning and consuming its own engine oil. You simply cannot stop it. I’ve always owned diesel cars and never experienced one, and I know nobody who has either. I think it’s something that happened to old and industrial stuff that’s not maintained. This old truck has been electrically and electronically messed with, so it’s shall we say, a controlled runaway with too much diesel being commanded into the engine.

[@luckyguy600]

Well. It wouldn't be my choice of vehicle to take a date to the drive-in.

[@robertsmith2956]

@@luckyguy600 I think that bed is big enough for the chaperone as well.

[@phprofYT]

@@tonep3168 Plug the air inlet.

[@renj6531]

18:37 i think that was the rev limit , and the tach was bouncing for sure

[@supersteveize]

Replacement of the injection pump is needed. I bought a 97 GMC van with 188 k + the same issue. . Replace the injection pump and be done with it. I called Antein Diesel in Pa and they diagnosed the problem over the phone. Anteim Diesel is known nationally and is run and owned by the Meninites. I bought a used pump I found on Craigslist that came from Antrim with 30k on it. The crank snapped and it was to expensive to fix so the guy put in a 454 he had lying around and everything bolted up with no issues. The guy said that the gas mileage sucks but the power was better. I installed the pump and I gotta say it was a total nightmare. If you ever peeked under the hood of one of these vans I'm sure you'd agree. Never again . After twerking the timing and changing the lift pump to a Carter it ran great and got almost 20 mpg on the highway at 65 mph. Over 65 mph fuel mileage drops off. 4.10 rear was the reason for that. I installed an adjustable oil pressure switch and set ir to 4 psi with an indicator light for the dash. I also added a liquid filled pressure gauge on the firewall to keep an eye on the lift pump pressure. If the lift pump quits the injection pump will die quickly from not having a lift pump. Clean all the ground connections and add an extra ground for cheap insurance. I'm not a fan of the electronic version of the injection pump I gotta say..... I'm currently thinking about venting the cdr tuna can from it's stock routing to an oil catch can.

[@edwinlomonacofoolsend]

This is where I'd break out my decade box. Add resistance to mimmic ambient temperature. And see it makes a difference.

[@poweredbyford87]

Why are they called Decade Boxes I wonder?

[@edwinlomonacofoolsend]

@@poweredbyford87 They are known as decade boxes because they have controls that correspond to the digits in a decimal number - a control for the tens position, a control for the hundreds position, and so on.

[@Notsostuck]

Old Detroit two cycles had an emergency shutdown flap held open by a cam lock operated by an electrical solenoid, when they ran away (every chance they got) you could hit a switch or manually hit the cam and shut off the intake but it was scary as heck.

[@vdivanov]

Every trip to the Pine Hollow is an adventure, requires one to be brave, smart, resourceful, but also humble and cautious. No wonder why people drive or worse, tow there for hundreds of miles to get help.

[@frankjohn4302]

Had a couple of these back in the day with same issues.seems like the pumps were over fuelling injectors.Replacing pumps and setting the TDC offset always fixed the problem

[@jessicav2031]

In the first test the pump command at 4k RPM is LESS than at 1k, and so is the feedback, and the solenoid is tracking the command. How could a smaller command result in more RPM? It has to be a mechanical problem. Fuel must be coming in outside of the command, or the pump is producing too much pressure, or something like that.

[@T-Hogie]

There's your problem. A diesel with a gas pedal. 😁🤣

[@josephwash109]

Another variable that still remains is the coolant temperature sensor circuit. The temperature/resistance chart shows that the PCM should register -40 degrees with the sensor unplugged (maximum resistance), but your reading only went to -7 degrees. The circuit still has a problem with the sensor unplugged, and the only answer is a partial short-circuit or internal PCM problem. Wherever the problem is located, it seems logical to conclude that the fuel injection system may be affected by it as well, whether it be corrosion or a pinched/chafed harness.

[@chekelley6861]

I’ve had a couple of these trucks with similar issues and they all had glow plug codes even tho the glow plug system all tested good. They all had pad PCMs

[@terryjackson2998]

Fantastic video! Loved everything about it.....diagnostic skills top notch! Love your channel!

[@vg3430]

Trying his hardest to use a 4 channel scope to identify an electrical malfunction when the problem is simply a bad injector pump. ECM is not in complete control and doesn’t know how to handle the situation. Fuel is bypassing internally. Touching the throttle commands even more fuel, hence the high revs. Rebuild or replace the injector pump. Relocate the module and put a computer fan on the heat sink.

[@DukeBlade-ol6pm]

A bad input to a computer gives a bad output. On a Powerstroke, the IPR (Injector Pressure Regulator) (a fuel pressure sensor) output (like gasoline engine MAP) tells the computer how much energy is going into the engine. If that signal is indicating low, the computer will over command for the desired result. Possibly a bad pressure sensor regulator on the Duramax causing bad commands. The 7.3 PS goes dragster crazy when the IPR fails indicating low fuel rail pressure. Scary to drive it because accelerator pedal becomes hyper sensitive.

[@cullenmiller8170]

Interesting case study. I have never worked on one of these. I had a K5 Blazer with the 6.2 liter Diesel many moons ago.

[@freeride202]

I will post more later but this is most likely a worn injection pump from the poor fuel filter I see installed. The other two causes are the PMD or lack of a calibration resistor in the PMD connector. I doubt this is the issue as he had tried so many PMDs.

[@carloserazo1286]

Thanks!

[@richardcranium5839]

never worked on that system but .... dont worry about the temp. yeah its off but it really makes very little difference on fuel delivery except maybe on start up. it has a seperate shutdown sollenoid so if you unhook everything but that on the pump it should start at idle and run smooth. if not check for sucking air and if not sucking air and still erratic change the pump, a sticky timing advance will cause elevated idle rpm. that most likely is a stepper motor running the fuel metering controls. it is fast and precise. any binding in the mechanical side will cause what this thing is doing. you could depin the stepper and monitor the throttle circuits and output to the stepper if thats all good change the pump. the mechanical version of that pump was real finicky and does not like low sulfer diesel fuel.

[@freeride202]

To continue on the injector closure time PID on these early truck is misleading. It is actually the fuel solenoid closure time. Just like a gasoline injector hump, this is measuring the time it takes for the solenoid to close and start injection. That is why the value does not change much with RPM or load. It is not the on time of the solenoid. In your waveform if you measure the difference between the command red signal and closure signal green, you will get the same reading that the PID displays. Also if you look at the scan data you will notice the shutoff solenoid will be activated to bring the RPMs down. Anything is possible but I have yet to see a PCM cause this fault. The introduction of the black plastic fuel filter ended up destroying these pumps. Stock filtration is 5 micron and the black plastic one is closer to 20 micron absolute. 5-7 micron particles cause the majority of damage to a diesel fuel system.

[@atikovi1]

GM went to an electronically controlled IP in 1994 which introduced a new level of complexity to the system compared to the mechanical pump of 1993 and older models. When they run right, they run great, but can be a pain to diagnose and repair when they act up. I have that engine in a 1992 truck with the mechanical pump and it's been pretty much trouble free.

[@randyr.parker2698]

LOL! 10 minutes in, and best be tearing apart the engine computer and checking for bad/leaky capacitors, and corroded traces. 29 yrs old, I can guarantee there are bad capacitors! 😉

[@robertoruiz7069]

This was my thought also,a bad cap in the pcm that is not regulating the voltage in a gradual amount.Allowing a full 12 volts to jump to the solenoid opening it all the way.The feedback circuit must be working in that it reads full open for too long and then it shuts it down.I know jack crap,about this unit and am finding this very interesting.WHERE'S the crusties???a corroded wire at the fuel plug or is it the solenoid?? STAY TUNED for more BATMAN,haha IVAN what is the voltage going to the solenoid leads and scope it to watch it VARY in length of pulse or voltage?great video so far.

[@joevaagen6170]

This is why I LOVE my 1995 Ford F250 4x4 with a 5.8l ALL PRIMITIVE PETE, cabled throttle, crank windows, no cruise control, manual transfer case, manual hubs and only electronics is fuel injection and transmission which I can deal with that!!!!

[@volvo09]

You are just missing the manual transmission :) Probably slow as a dog compared to a modern diesel, but you can't beat the simplicity.

[@joevaagen6170]

@@volvo09 I bought what 1, I could afford and 2 what was available at the time!! But manual transmission are good but their fun runs out at about 5000 miles. Yes I do love CV the simplicity of not having more modules than the space station!

[@rhkips]

Call me crazy, but just purely as a thought experiment, I can kind of create a scenario where extra fuel bypassing in the injector pump could cause a situation like this. 2000 RPM is probably a comfortable place for this truck to live on the highway, it's a '95, and so depending on how the injector pump is designed, wear on the flow control pintle, seat or orifice could favor this RPM, and continue to bypass at higher RPMs, causing it to hit the rev limiter. Further, with these being old mechanical function design with a rudimentary ECM and some electronic controls and monitoring slapped on top, it's entirely feasible that the ECM doesn't have as much control as we're thinking it does, and instead, it's really just following basline maps for expected behavior at certain data points. As per usual, this is entirely speculation, and the only tests I can think of to alter behavior in a predictable manner are insanely dangerous on this design of diesel. About the only "safe" thing I can think of is a thick piece of steel to partially block off the intake and a 5-gas analyzer to look at combustion and fuel mixtures. Even then, without a known good, I have no idea what I would do with this data. Man, this is a really good one!

[@snoopyshea]

I can't wait for part 2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[@willemstreutgers1154]

Cars of that age might have electric problems due to leaking capacitors in devices (ECU, ) Anyway i see more good comments here, follow them you will succeed i am convinced you fix this one Ivan

[@Sandmansa]

I used to work on the shops old 96 chevy tow truck with the same engine. And it would sometimes cut off while coming back down to idle. Replace the injector pump driver module and it would run fine for 6 months or so. Then start doing that random stalling again. This truck already had the module relocation kit installed behind the driver side battery. So, it made swapping the module a breeze. But I suspected there was a high resistance problem in the injector pump itself. But the shop owner didn't want to replace it.

[@jeffco908]

I would do a TDC offset learn and then see what it reads. If someone moved the pump and did not do this it wont change the reading in scan data. It will look in spec but its not. If its + or - 2.46 it needs to be timed. I always found -2.38 to be the sweet spot but hard to hit.

[@scrappy7571]

We had pallets filled with old 6.5 pumps. Nobody wanted them for cores, sent all to scrap.

[@TJ1855]

Wow Ivan! That must have been a big Hammer that you hit your thumb with! Ouch

[@marcusmohorco380]

And I liked how he must've relieved that pressure build up under the nail: With a red hot pin/nail/steel wire end. Goes through the nail like butter, so you're better careful. He's a real hero, he didn't even lose a single comment over it. He just soldiers on. A real man.

[@davidturner4639]

Good morning Ivan, another mystery one with the parts cannon. I am very suspicious of the PDM relocation wiring.

[@ecaparts]

Leaking capacitors in the PCM corroded several PCB traces causing the erratic operation...

[@topher8634]

That loping idle reminds me of a Honda with a bad idle air valve.

[@darrendouglas4796]

Blower surge ? 🙂

[@maui6446]

The Flying Wings of Despair!

[@BigEightiesNewWave]

Our 1980 Cutlass Supreme Diesel never had such problems, just blown head gaskets!

[@josephkober3324]

I know this is s diesel but I owned a 1997 Chevy Monte Carlo Z34 that did this same thing . No one could figure it out at GM dealer . Finally I closely checked the MAF it had a cracked wire that would intermittently do this same symptom you are having because the heater wire would intermittently make contact and drive the computer nuts.

[@lowbagg]

"The flying wings of Quality".... 🤣😂

[@unclea8148]

I’ve had a few of these trucks. Does sound like the injection pump, had some good luck with Pensacola diesel reman pumps and good price. However, had an issue that took me forever to figure out similar to yours although truck would go into limp mode. Theres a harness that runs in the intake valley front to rear that goes to the pump and other sensors, mine melted together and ended up shorting the ECM as well, there are well made and insulated harnesses available. Only found it while changing the injection pump as intake has to come off but I was at my wits end and thankfully found it.

[@shidukirider]

I won’t buy anything from Pensacola diesel anymore. Got 4 injectors to do one side on a 7.3 powerstroke. Had to reject 2 injectors right off because one had a cracked solenoid and the other was built from a rough core that the connector was all chewed up. Immediately got a check engine light that flashed on and off after installing just the two remaining injectors. Figured it was air still in the system. Let the truck go to the customer. Later the #8 I installed had a dead miss. Replaced with injectors direct injector. Check engine still flashing on and off. Ohmed injectors, Ohmed harness from idm everything checked out. Moved suspect injector to another cylinder and the fault moved to that cylinder but only while running. Replaced with injectors direct injector and no problems. So 4 injectors, 2 rejected one replaced within a year and the other caused a check engine light immediately. 4/4 injectors were crap and naturally this was the first time using them.

[@brianw8963]

Interesting for sure. Have to review a bit and do some more head scratching…. Never laid a hand on one of these, but what Paul said sounds pretty logical. I’ll go with that theory. 👍👍🇺🇸

[@calebfarley9101]

I had a similar issue with a duramax, i replaced the cam and crank sensor and no more issues after that.

[@MrJet30]

That thing is a Beast!

[@CUSTOMWORKS7.3PSD]

Last time I fixed one of these it was the pmd extension wire harness and it rubbed through

[@Djriggs-f8q]

I have had to deal this problem about four or five times on the 65 Detroit diesels. 90% of the time it is ECM. But there is one odd time. That the old PMD went crazy and cause it to fry the ECU. But that was one time of multiple trucks I have had this problem with. Also too make sure that it's the PMD has a calibration resistor right into the pigtail there are resistors you can get from 1 to 10 5 and 7 limit the max fuel rate. If you don't you can be shooting excessive fuel into it it's not much of a problem you can get them from Rally's from dorman for like 35 bucks.

[@pdzh]

Ince in a truck shop I watched an 84 year old man in a wheelchair telling s younger tech what to do, after chatting with them, they told me that they got an old suv, 1985 ford, new guy had no idea what he was doing, and old fella on his pension, was begged to come and assist.

[@jessecarbajal8932]

Drain the water out of the engine mounted fuel filter through the petcock mounted on the front of engine. Take filter out and check bottom of filter for sediment

[@2packs4sure]

Yeah getting a quality part these days is brutal,, recently my 2002 F250 power stroke accelerator pedal was acting up and I thought no problem I'll get a Motorcraft,, well no,,, it doesn't exist.. Apparently for about 20 months between 2002 and the 2003 change over to the 6.0 was the only period that used that particular accelerator pedal and it's only available in the aftermarket.. Fortunately the one I got works fine... So far......

[@markricketts-qm6xu]

since the old pdm is still on the pump it is likely they didn't transfer the resistor to the new pdm. This will cause the exact problem, just look into the plug on the pdm to see if it's in there.

[@redtopberries]

My guess on the fuel rate being 0 is the pcm is trying to drop the rpm, but with the injection pump bypassing it can't.

[@PineHollowAutoDiagnostics]

But the duty cycle of the fuel solenoid doesn't drop below 30%...weird! 🤔

[@tomtom1541]

​@@PineHollowAutoDiagnosticsmaybe that's a preset minimum in the ecu tune.

[@abdouallahuniverse5689]

I was about to say idle air control valve, vacuum leak, but diesel may different.

[@daveunbranded]

You bashed that finger really good

[@southhillfarm2795]

These 6.5 diesels have the PDM installed in the wrong location where there is a lot of heat. There are aftermarket PEM suppliers that make a better unit and it needs to be relocated to a cool spot. Good engines but faulty electronics.

[@GraditelMacedonia]

9:31 IAC valve... probably, because my Volvo 850 doing same...

[@mydogpeaches1]

this is very interesting it’s acting like both an electrical problem but it could be a mechanical issue as well im very interested to see what you find

[@somerandomguy3868]

If it's mechanical Injection is it a balance point system, incorrect balance point can definitely cause a lope at idle

[@RussellBooth1977]

It sounds like brothers Subaru Forester when it had an air leak at the throttle body & it was fitted with a MAP sensor like that 6.5 litre diesel V8 engine is. I don't think that it would be the PROM inside of the ECU that's at fault unless someone has mucked around with it !

[@colchronic]

These are notorious for bad pumps and it could be an ECM but I'm thinking there's something broken in the pump

[@mickeyingram4400]

Boost PSI showed 14.0 when engine not running. Time stamp 5:34

[@baxrok2.]

Thanks Ivan!

[@luckyguy600]

This machine is 'possessed' too!

[@greggc8088]

"Flying wings of quality" 🤣🤣 We call them "the wings of disappointment".

[@kevin9c1]

My now brother-in-law had one of these when we were in college so I got to learn a little more about them. I remember the 3 potentiometers in the throttle pedal. I think you need to compare PCM output to a known good. If it's commanding a fuel solenoid duty equivalent to 2000 rpm when it should be idling, that suggests a PCM problem. Also have to check the feedback because I presume it uses the feedback to modify its output to achieve the desired fuel quantity.

[@MrTonyPiscatelle]

Intermission,,, where's my popcorn !

[@samchrome-g8v]

Remove the feedback line, it is oscillating, that is mean the feed back is wrong, the computer is good. It is a mechanical problem for sure.

[@cumminsbanks]

Do not overlook the ecm behind the glovebox or whatever they call it. I’ve seen two instances where a 6.5 wouldn’t run right because of a pin that backed out on the connector.

[@bigblocklawyer]

My dad bought a new '94 Silverado 6.5 TD, 4x4, ECLB, and after about 3 years, he put it in reverse one day and it died. It ran flawlessly up to that point, and it was a constant issue after that. The dealer was very attentive and did a lot of work out of warranty to keep it going with Stanadyne pumps and remote PDMs. My dad and the owner of the dealership were Korean combat veterans, so I guess it was a bit of professional courtesy. I ended up working on it myself and kept it going. It's been so long ago, it's like a different life. True to form, with hundreds of thousands of mechanical 6.2 and 6.5s in military service, where lives depended on them, leave it to the epa and government regulations to eff it up for consumers. Again. Having done a bunch of upgrades on my '03 LB7, and owning it since new, it's amazing the progress GM made in light diesels.

[@scottmendoza8989]

The duramax diesel is made by azuzu.They just love to put that name on it to get credit

[@bigblocklawyer]

@@scottmendoza8989 Not true. Try Google. I hear it's free.

[@tomtke7351]

would be helpful for a shop declining a problem to suggest one that will. Doesn't mean the 2nd shop is better than first or first worse than second but that a foot doctor doesn't do nose and mouth work.

[@billsmith5166]

Fuel pump, fuel injectors, fuel filter, blow out the fuel line to tank, wiring harness extension, PCM, wiring harness. Has he been running any performance chips? Looking forward to this one.

[@Paul-lp6kt]

Could it have had Corrosion Resistance to the Coolant Temperature Sensor? The Engine is Reading a higher Air Temperature and so it Overfuels on tickover to provide an erratic R.P.M. Under Throttle it Overcompensates Markedly! The P.C.M. and P.D.P. signals are Correct and the Fuel Delivery Solenoid is not thought to be at fault because of the R.P.M. changes! If it were Corrosion and with bad batteries as is evident then the Extra Power from the Alternators was Overcoming the Corrosion by a Far Stronger Electric Signal and the Temperature was then read as Markedly Higher! The Fueling is then Increased because the Engine thinks that the Fuel Density is Less at High Temperature and thus is Overcompensating! This Would Explain the Spikes that the Engine Displays Without the P.D.P. and P.M.D. showing a Fault and Whose Data seems to be Concurrent! Regards! Paul

[@jeffryblackmon4846]

I wonder if you could remove the PCM driver signal from the PDM and substitute your own? If the engine behaves, it's a PCM. If not, it's the pump itself. It has 160K miles' use.

[@stevevogelman3360]

Boy you sure did a number on that thumb….ouch!

[@Bigtbuilder]

Ivan every time I see that left thumb nail…boy I cringe!! Been there done that many times.

[@ajautoanddiesel8576]

I’ve done ton of these things and 90% of where the wiring harness is shorted underneath the fuel filter runs along the valley of the engine fuel disintegrates the installation on the wiring, major problems and they will do all kinds of crazy things

[@richardnilsen5]

Notice : guages stay up with the key off ? Powers and grounds?

[@hightttech]

Comments really interesting on this one. I'm siding with anyone that says black magic is involved 😁👍

[@kenmelrose3429]

what was added to cause this problem, possible miswired harness , other common problems cracked intake,cracked hose, water in fuel

[@Sean_Diagnostics]

The first part of the video i was thinking a clogged fuel filter or bad fuel filter. along the way i'm guessing a pump not timed correctly or out of time

[@mechniack]

Normally there's a pump adjustment to stop surging, but as it's electronic I do not know have to look up info, the engine shouldn't surge up down up down then something are wrong

[@frankmasters3796]

Man YOU are so right .!!!