Cold no-start Case Study: '95 Ram V10 -Part 2

In Part 2 I finish up this weird diagnosis, but we have a couple options on the repair...
Enjoy!

[@vikingjoe93]

I loving watching these case study videos but they are way over my head, lol.

[@ElectronicWorkshop]

I would not leave a permanent/switched 12V supply to a 8V circuit, it would be better to use the 7808 or 7908 regulators mounted on a small heat sink.Looking at the 8V o/p and it is heat related, I suspect it is capacitors in the pcm. I normally use a hair dryer to heat up and a can of freezer to cool down components on a pcb. This isolates a fault to a componentGreat videos, thanks for sharing them

[@wyattoneable]

Now this is getting interesting! I'm sure the customer will appreciate that your trying to save his money by suggesting alternatives.

[@MCHNCTCH]

About 5 minutes into the first video I was thinking it is a classic Dodge, Chrysler, Jeep PCM problem of a cracked solder joint on the circuit board. I like to wiggle the connectors on the PCM because it puts strain on the solder joints sometimes. I have seen these PCMs put into the freezer over night to duplicate the problem. Good video.

[@rooanashan]

always remember to cycle the key between unplugging sensors. I know some vehicles go into like a fail safe when the reference circuit is shorted and they don't always go to zero volts

[@PineHollowAutoDiagnostics]

+Tim Waterhouse Yup that's a great tip! I have seen this on ScannerDanners channel as well.

[@stuzman52]

Nice find Ivan. The only thing about using a resistor is that the voltage would still vary to the sensors. But as you've proved with a 12V test light on there and with the truck running having the higher charging voltage, it doesn't seem to be an issue. Looking to see what you finally come up with.

[@theoldwizard998]

I have to wait another day ! Taking video tips from Eric. Probably not required, but I would like to see what voltage is on the 8V ref pin from the PCM **without** the 8V wire connected !

[@HUBBABUBBADOOPYDOOP]

*Definitely autopsy the PCM before shunting any external power to a solid state circuit. It could easily be a cracked solder joint on a ground rail.*

[@12volttech5]

Great job Ivan. Much better than the Power Window Extravaganza video on the 04 Dodge Ram (no back handed compliment intended) just being honest. The main problem I've experienced with older Chrysler vehicles is where the PCM is mounted. The PCM is mounted directly in the drain channel with very little or no protection from water with the exception of the seal on the PCM itself. 9 out of 10 times if there is sheet metal protection from the rain channel it is rotted out allowing water from the windshield to run directly onto the PCM. I have seen internal damage (solder points, capacitors, corrosion) due to moisture that voids the seal then freezes because of temperature drop. In addition, The location of the PCM was intended to protect it from heat but inadvertently another issue was created.

[@leebarnes655]

8 volt regulator is likely to be just a zener diode that is no longer functioning possibly due to burnt bias resistors inside the PCM. 200 milliamps is well within the capacity of them as well. Plugging in the ICM helped boosts the 8 volt buss due to backfeeding of that circuit with 12 volts where I was entertaining for at least some time that the ICM was the source of the 8 volts in the first place. Ivan's sleuthing however shows this thinking to be in error. 30 ohm, 1 watt resistor is required between the 12 volt and 8 volt system to get the 8 volts back up to where it should be without burning up THAT resistor - what this is doing inside the PCM is a crap shoot until you go in there and check up on what's going down inside there. To bad the PCM remains on the pricey side, nice one Ivan.

[@grzegorz16100]

3:54 Wow! I like the battery clamps;)

[@547Rick]

You and Eric and your trilogies. LOL! Love the videos though. Please keep them coming.

[@zerskier]

it's a dodge so I say a old school ceramic ballast resistor would look right at home under that hood.

[@franksoliday5510]

Great job Ivan. The resistor bridge idea sounds good to me. You need a simple 1 to 2 ratio bridge, example: 10 ohm and 20 ohm resistors in series would give you a 4 volt to 8 volt drop across a 12 volt source. Use a couple of 15 watt or more wire wound resistors for safety and they will last for ever. Connect the 10 ohm side to 12 volts , the 20 ohm to ground, and the junction to the PCM. Cost two resistors.

[@willemstreutgers1154]

Why not clean the battery connenctions first.

[@FinalStopMobileAutoTech]

Great video my friend! lovein those symptoms!

[@offtwoaces]

I had my fingers crossed when you connected battery to the 8V supply. I was hoping you weren't going to let the smoke out of the PCM ;-). As someone mentioned, using a resistor bridge would allow the voltage to fluctuate with variations in the battery voltage. The sensor/PCM might not be tolerant of that much fluctuation. I have my money on a cold solder joint inside of the PCM.

[@eddiemartinez265]

Thats good ivan cheap repair set up your own 8 volt supply see what the owner wants to do.

[@fieldsofomagh]

. An L7808CV will give 8v[1.5 amps] with input 5 to 24v. The internal reg might be replaceable ? The comments on the truck having a history of dodgy pcm's proved to be correct.With the sensors unplugged, it was checkmate.Tis time to get out the bugle in part three and play "call to quarters" and rest for the night.

[@ericcorse]

Well done and interesting

[@cjames4957]

Good old Eric O .

[@ziggassedup]

Nice analyzing..

[@feeneysmechanical6215]

I also was thinking in the beginning of video what the battery voltage might be. you know as if it was too low to shut anything off or the alternator wasn't shutting down. but then again it's Ivans video. so knowing him he probably already covered the basics.

[@PineHollowAutoDiagnostics]

+GREG Feeney Battery voltage is always a variable for sure! In this case the truck cranked over normally, and as you saw it put out 14.4V when running, so nothing wrong with the battery or alternator here...

[@ozzstars_cars]

nice find. wonder whats going wrong inside the pcm pulling the voltage down on the 8 volt reference? looking forward to part 3

[@upallnight888]

+Ozzstar High resistance due to a cold solder joint.

[@ozzstars_cars]

Upallnight Anything is possible until true evidence is discovered

[@jsohn18436572]

I wouldn't recommend using a resistor but rather a l7808 voltage regulator. it is a linear voltage regulator.

[@jeffl398]

Good job on the diagnosis Ivan. Most shops wouldn't think of a way to get 8v on that wire and just replace the ecm. That's surely what I would (give it the 8v) if it was my truck. As long as the customer is ok with it, thats a great fix. looking forward to how you do that. Old dodge looks pretty good for a Pa truck. Mine's newer and got eaten up by the salt.

[@Clete88]

Thank you Ivan for following up.....I was really interested in this case. A big question: What kind of design would pull up the 8 volt rail by plugging in the ICM module? That seems unnecessary as part of the design....So the ICM was pulling up the 8 volt rail, but just not enough....that's crazy as hell! These things are complex enough without designing each system to be independent of one another. Kudos to you man! Now then, what caused the relays to chatter? The 8 volt output of the ECM? So plugging in the ICM raised the volt rail enough to stop the chatter from the ECM's internal voltage regulator?

[@Clete88]

+Clete88 Again, sorry for blabbing so much on your project, but it intrigues me......I would have never guessed the possibility that the ICM could pull up the 8 volt circuit.....Next, if you go to dig into the computer, and you are able to isolate the 8 volt regulator, concentrate on the current limiting resistor, which will be found on the input of the semiconductor of the final output....since high impedance voltage sources are used to protect the computer...... This truck was made before lead-free solders were used....could be an easy fix...

[@PineHollowAutoDiagnostics]

+Clete88 Fantastic questions and reasoning...are you an electrical engineer? The relay chatter might be explained by the PCM going crazy when the voltage from the 8-volt regulator is at the threshold of "waking up" the logic, resulting in a resonance between "on"and "off" states :)

[@mikebrennan4534]

Two questions. 1. i was always under the understanding applying voltage to reference wires on the pcm will take out the pcm, is this not correct? 2. would it not have been easier to remove the pin for the 8 volt wire at the pcm first to determine if a sensor was shorted instead of going sensor by sensor?

[@joshausterlitz3798]

+Mike Brennan 1. it is, if this was a 5 volt ref, it would have cooked the driver, though with a 8 volt here, apparently not, in a way, it makes since, though thats a risk you take as we don't know what that driver can handle. I like watching Ivan's videos, but this is something i would have never ever EVER!!! have done, an adjustable DC power supply unit would be the right thing to have used for this, dial in 8 volts, and safely see if its a bad computer. 2. I've always started by unplugging sensors and watching voltage for change when my ref is low, best way (for me) to determine sensor or ref problem, a bad/shorted sensor can/will pull the whole reference down.

[@Clete88]

+Jason Warkin I don't know for sure, but the outputs of the ECM should be diode protected.....In other words, you can't back-feed current into them....remember though, this is an older vehicle....I may be wrong.

[@joshausterlitz3798]

+Clete88 You could be right, there's a lot of variables here we don't know, and from year to year, all depends on what the manufacturer put in there to do and not. I've seen cars with bad drivers because of crossed wires, corrosion ECT... and others, after repair came back to life like nothing ever happened. In my case though, i'm not interested in testing/finding this out, why i always use a adjustable power supply for testing, last thing i ever want to do is tell a customer they need a computer because i "thought" it could handle a little more, and then find out it couldn't. just my ¢2

[@PineHollowAutoDiagnostics]

+Jason Warkin Hey Jason, in fact I just recently obtained a 5-Amp regulated DC power supply for use in cases like this! Have always wanted one, they are quite useful for bench testing as well. Definitely agree that jumping straight battery voltage to the 8-volt ref was a bit unorthodox, but I figured since the PCM was on its way out anyways, and the truck dead in the water, what's the worst that could happen? :)

[@joshausterlitz3798]

+motoYam82 I figured as much seeing as it was a computer problem, just something i wouldn't do. Great videos though, really enjoy seeing your case studies.

[@jameshill2008]

a litte ign on relay sending power to that 8 volt wire will do just fine ;)

[@cbsctomh]

I'd look to transform 12 volts down to 8 volts outside the PCM but what could you possibly use. May have to turn to ohms law...however, what else will be affected??

[@pedrolriveranegron5178]

seeing it now !!!

[@feeneysmechanical6215]

I would try a different ignition module.

[@Clete88]

+GREG Feeney I'm wondering that myself.....

[@williegillie5712]

Something tells me maybe the relays aren’t getting a good ground. The computer try’s to engage them and they lose their ground when they reach a certain threshold

[@feeneysmechanical6215]

I agree. I made that battery comment before I continued watching your video.

[@wtbm123]

Cool

[@CajunShrek]

Who puts a cpu pins up in an area that prone for water intrusion? Ya chrysler that's who!

[@derekrobbins3833]

Having crowded battery terminals won't help any electronics especially on a Ram. Lol. I'm like 5minutes in on watching this video. Let's hope you figure this out. Lol

[@sara78130]

nice vidoeee

[@garyjohnson2879]

that's a clean machine. how many miles on it?

[@broncowrangler]

Looked like 80,XXX. It's definitely a clean low mileage truck.

[@whatdoyouthinktodd]

keep it OEM

[@feeneysmechanical6215]

how's the battery?

[@Bryankrall8090]

Eric O

[@tomsawyer4776]

Congratulations of shortening the life of all the relays by one half while you make a video. No regard for machinery.

[@PineHollowAutoDiagnostics]

How did I shorten the life of the relays? Truck is still running great BTW 👍

[@scotttucker4075]

What?

[@samrugtiv3839]

Do it right buy a pcm

[@mminc81]

The problem is in the title of your video :p

[@gbowne1]

-40° lol

[@PineHollowAutoDiagnostics]

+gbowne1 haha I noticed that too! Was someone diagnosing the coolant temp sensor or IAT? No idea.

[@gbowne1]

+motoYam82. not sure either Ivan. 40 below 0 is not a common temp. not sure why someone would scribble that on the bottle. IAT maybe. unless thats the rating of the coolant they use(d).

[@mmiller1188]

+gbowne1 Pretty common here in NY - usually if you go to garage or dealer to get service work done they will check the freezing point of the coolant.

[@SteveRobReviews]

Ok I'm game , on to the next part. 👍👍

[@undaya]

moisture in something?

[@goodguy555]

If the internal 8v regulator is inoperable how is it that applying 12v doesn't damage the system? If you were to apply the same test to the 5v reference would you damage the system? Awesome vids as usual!