Porsche 911 Carrera Engine, 3.2L - WILL IT RUN? Or WILL TOM BE STUMPED?

[@tomperazzo2758]

What would you suggest to try next? #nospark

[@klassikats]

Tom, Ignition control is by the ECU, Check to make sure that both of your impulse signals, (speed and reference signals), are present at the control unit. Next using your oscilloscope connect to terminal 7 on the ignition coil. The waveform should be switching from Ground to Battery Positive, similar to what a set of points look like. Terminal 7 should be normally grounded to charge the coil and go to battery positive when it fires. DO Not use a test light anywhere near the coil, this can result in DME damage. If you are not seeing the square wave signal at the coil and the DME is getting power, ground, and the two speed/reference signals replace the DME.

[@GarageTimeAutoResto]

Thank you Kurt! I'll repeat that signal test on the DME connector. This pins do have 1000ohm impedance, but will try the scope too. The test light I used is just a light bulb. Not active power, so I don't see how that can harm the DME. I got nervous about putting my scope on the green coil wire due to high energy feedback. Do I need a special resistance probe for that? I don't want damage the scope obviously.

[@klassikats]

@@GarageTimeAutoResto Terminal 7 is low voltage so no you do not need an inductive pickup. The problem with a standard light bulb type test light is that they act like a set of points when they are opening. Because the current draw to power the light bulb is an amp or two what can happen is as you pull the test light away the current will continue to try to power the bulb. Just like a set of points when they are opening the energy will try to jump the gap. This creates a large rise in energy and current that can damage an ECU. Best practice is to never use any tool that requires a current to drive it as it can send a pulse back down the circuit causing unwanted damage. When you measure the resistance on the switching circuit you are just reading the switching transistor and or any protection networks built around it. This means nothing to us as we don't know how the circuit has been designed. The only way to confirm operation is to see the waveform on your scope. good luck and let us know if you need any help Kurt

[@GarageTimeAutoResto]

Gotcha, I was using the light on term 15 to confirm (+) power. I understand what you are saying about the points side of the coil. Also just be clear, the same energy you are talking about damaging the ECU can also damage an oscilloscope too? Are you suggesting connecting the scope on the wire after it's been removed from the coil? #7 terminal. I know with a points system there can be some pulses on that one.

[@klassikats]

@@GarageTimeAutoResto You will need to leave it all connected to the coil. The power flow is from the fuse through the coil into the ECU where it will be shunted to ground. To fire the coil the ECU will go open circuit on terminal 1 of the ECU, causing the current flow going through the primary side of the coil to collapse through the secondary side of the coil and fire. If the waveform looks good, replace the coil.

[@GarageTimeAutoResto]

@@klassikats Thanks Kurt, will do.

[@1ocean515]

great video, as always. And bonus input from Kurt, which is very cool, and speaks to the community that surrounds your efforts. 👍👍

[@GarageTimeAutoResto]

Yes, love this community! I wish I could fit all of you in my garage. Would be a cool hangout.

[@jimmydunham4013]

Great video Tom - I have a 3.2L I plan to put in an early car so glued to the TV set on this one....

[@GarageTimeAutoResto]

Very cool, once I get this running, I will make it clear exactly how to connect the wire harness to the car. This is such a popular engine swap!

[@danwood1047]

Glad to see Kurt and others weigh in on this. I’m sure you’ll figure it out. Thanks for another solid video.

[@GarageTimeAutoResto]

Very grateful! I love this car community! Will get it figured out. So much easier on the test stand!

[@KeithShafer]

Wish I could help. Only thing I’ve seen online for no start issues with motronic is a bad relay.

[@GarageTimeAutoResto]

The relay is still a likely culprit. I have two of almost everything except this relay. So I ordered one. The one I have doesn't have a very solid click to it. And there is actually two relays in there!

[@joycedcruz3015]

tom, great video as always! i'm crossing my fingers that it's nothing serious...

[@GarageTimeAutoResto]

Thank Benji, I made this extra dramatic and sensational for the KZbin gods. Just kidding. Will get it sorted out soon.

[@joycedcruz3015]

@@GarageTimeAutoResto and it worked! hahah! thank you tom!

[@bertmorris9976]

Have you checked for an injector pulse? No spark and no injector pulse is almost always DME trouble. Most commonly the DME not receiving speed/reference sensor signals but could also be internal. You mentioned checking the power and ground at the DME connector but I would test all pins there to be safe. If you narrow it down to the DME always test your DME in a know good car and not the other way around to prevent potentially damaging the good DME.

[@bertmorris9976]

Also forgot to add, bad solder joints are a common failure point in the DME so wouldn’t hurt to pop it open and check.

[@GarageTimeAutoResto]

I haven't checked the injector pulse, but will do. Thanks for your great advice. I have another DME and harness, but like you say I don't t want to just swap stuff. I did measure some impedance on the various pins on the same connector. About 1000ohms on both speed sensors. Will continue my testing. Thanks again for your help!

[@rsrguy]

Love the shirt!

[@DoubleRRestorations]

Very cool Tom. I'm curious to find out what it is. Some great suggestions already. Its been awhile since I have used a scope, I'm amazed at how small they are from the ones I used to use.

[@GarageTimeAutoResto]

Hi Russ! Yay no more CRT tubes!

[@joew1803]

Here's to hoping it is something simple like a ground or a relay. While you are troubleshooting the DME, it would be interesting to do a compression and/or leak down to see if it things are tight. Good hunting, you'll get it I am sure.

[@GarageTimeAutoResto]

Will do leak down once the engine warms up!

[@CrispysProjects]

You have signals of sorts, as all the other comments have said various great suggestions, is the negative of the coil switching and causing a spark? Fuel being delivered to the cylinders, don't overlook the obvious, diagnosis is the same as a carb Main thing is you know how to use a scope 👍 If we have spark in the right place little 'easy start' spray should let it chuckle in the right place. Voltage dropping below 11.5V when cracking will effect the engine electronics, as well as crank speed being higher than 250rpm, basic Kjet 4pot can start on 100rpm!

[@GarageTimeAutoResto]

I agree that there have been great comments here! I'm still a bit nervous about checking the negative side of the coil signal, but will figure it out. Right now I'm focusing on the no spark issue, but I like your idea of a little start juice. Your point about dipping voltage while cranking could be the issue too. A new battery is on my list to try. Thanks so much for being here and helping!

[@CrispysProjects]

@@GarageTimeAutoResto You've already looked it up, scope + to T15 (12v) of the coil and - of scope to switched point (-) of the coil and should get some form of Square wave all being well, this would show the voltage while cranking in the same hit unless there's a ballast resister (shouldn't be) Diag from there poor voltage or no pattern leading back to ECU pins in & outs- Good luck Tom 👍

[@jeffdanner3194]

Maybe no fuel ? I have heard the injectors can stick when they have sat for a while . After I reinstalled mine it seemed to have no fuel . I removed the fuel rail test port and check ball and made sure I had fuel . Put back together and problem was solved. Maybe there was air trapped in the line . Love your channel

[@GarageTimeAutoResto]

Thanks Jeff, The injectors may need some TLC too. Right now I'm trying to chase down the no spark issue and then I'll work on the fuel injectors if it still won't start.

[@gregorysinclair4873]

Worth checking wether or not this ECU is from a car with an immobiliser, the DME may be expecting a signal from the immobiliser unit before it will allow power to the coil.

[@GarageTimeAutoResto]

Good point . I'm sure it's something simple like that. The harness does have some non factory tape on it.

[@marklangren3142]

Definitely check this it was a problem on a 928S4

[@marklangren3142]

If can bus the voltage peak to peak is 5 volts

[@GarageTimeAutoResto]

Must be a coincidence!

[@johnthrossel9981]

Do you access to a break out box (bob). It’s the easiest way to diagnose a no start

[@GarageTimeAutoResto]

I don't, unless someone in Orange county wants to stop by. Bring your own Bob!

[@franckn8338]

Hope you will solve the trouble ASAP. Do injectors receive signals from ecu? Is there others functions that could not allowed the ecu to start the engine.? Like a anti starting mode, or a security/rescue mode that cut the engine like a kill switch, a wrong battery voltage, a lower gas pressure that cut the engine and the fuel pump. My car doesn't start when the voltage is under 10V, with starter on for example. New cars have anti starting mode if you don't have the good key. Other thing, the signal from crank position trigger sensor could be at the wrong place du to a different bracket. I hade the problem when I transferred an engine from a car to an other that wasn't the same year and model. Keep your scientist way of working and you will find.

[@GarageTimeAutoResto]

Thanks for all your ideas! My battery isn't in great condition and the power pack may be dipping too, so a fresh battery is on my list. I can check the voltage while cranking too. The ECU/harness is from an 84, but the engine is an 87. Supposedly it came from a running car. The harness does have some non factory tape on it so a previous alarm system is likely. This is a little bit like a detective mystery.

[@markdaugherty6378]

I thought at one time you had two of these engines, if so it would be easy to switch coils for a confirmation. my two cents

[@GarageTimeAutoResto]

You are right! I have two of everything except for the DME relay. Will be trying a bunch of stuff later this week including swapping the coil. Thanks!

[@marklangren3142]

Tom do you have a factory shop manual with the electrical drawings?

[@GarageTimeAutoResto]

Kind of. I have the Bentley manual which has all the electrical diagrams. I also have factory manuals, but not for the Carrera model.

[@marklangren3142]

@@GarageTimeAutoResto I have an electronic version of the 84 - 89 manual. What is size limit on your email account? Could send the electrical section in pieces

[@GarageTimeAutoResto]

Thanks Mark, email is 25MB I think. [e-mail]

[@djice000]

Can you hook up a scan tool and see If you have any codes?

[@GarageTimeAutoResto]

No obd port in 1984 unfortunately

[@marklangren3142]

Get a magnetic spark plug socket

[@GarageTimeAutoResto]

Not a bad idea👍

[@marklangren3142]

Plugs didn’t look wet so if that is true you have no fuel

[@GarageTimeAutoResto]

That was before I tried to start it with fuel pressure, but I don't think the fuel injectors are firing either.

[@TeunS133N]

Did you replace the fuel filter aswell?

[@GarageTimeAutoResto]

Yes, the fuel filter is new and you can see plenty of fuel corsing through the fuel system and returning to the tank.

[@jockellis]

What about your crank position sensor - if it has one?

[@GarageTimeAutoResto]

That was the second signal I tested I believe

[@jockellis]

Is that one of those Chinese ultrasonic tanks on eBay? What size is it. I want one to clean the small gears snd pinions I crack check at work. Whatever chemicals are in out huge parts cleaner reacts with whatever is on the used gear teeth snd under UV light, turns them bright blue - about like your shirt - and prevents me seeing any of the fluorescent magnetic particles. But I want to own it so I can use it on my 944 and 914 but keep it at work so my wife won’t know I’ve bought it.

[@GarageTimeAutoResto]

Yep, it's a 10L size and clearly not big enough for this oil tank. Good for most everything else. I linked to the one I have in the description of this video. Please buy from that link!

[@marklangren3142]

Sure looks like a can bus signal

[@fgjf1079]

Just make it carbureted and be done

[@GarageTimeAutoResto]

I knew someone would make this comment. I do love carbs too, but this will get sorted out too. Each have advantages!

[@rsrguy]

I've never had any luck with my webers... I can't wait to swap to megasquirt