At Wit's End w/ Dad's 3.2
 

Hello gentlemen,
Never thought I could say this, but right about now, I love my CIS-equipped 1986 930!
I have my dad's 1988 Carrera 3.2, all stock, trying to figure out a peculiar issue that has, in hindsight, been a potential progression to its current state:
1. Couple months ago, on freeway, just exceeding 80 mph, there was a studder, rpms fell towards zero, engine just died. Popped the clutch while coasting, engine fired up, kept on as if nothing happened. I stayed under 80, and came to forget about the event.
2. Since, car runs like a dream - until it reaches temp, that is. When temp is reached, engine will sputter if cruising, and die while coming to a stop with clutch in - rpm's drop like a rock.
Here's what I've done thus far.
Replaced DME relay under seat.
Replaced o2 sensor, both position sensors, CHT sensor, plugs, cap, rotor.
I've played musical red relays up front, rotating them around into different positions.
Per Bentley, tested most of the accessible sensors for Voltage, Continuity, etc.
Now, I'm guessing there's something just precariously loose in its fitment, and the slightest bump jars it out of its seating and pffft!!!

Thanks for your time guys. It sure would be nice to get this thing going for dad again.

It sounds like it could be a bad ground somewhere?

I had that issue on my old 2012 Mustang. It would hit a bump and the entire vehicle would die then fire back up. Turns out one of the grounds was not hooked up from the factory.

I would replace the CPS sensors. They are almost a maintenance item.

If by CPS sensors, you mean the 2 neighborly sensors down behind the left rear wheel by the CHT sensor, then those have been done...The fuel filter was replaced as well, just forgot to mention earlier...

Sounds like he did that already, as well as the CHT and O2 sensors.

If only happens once warmed up, what about a vacuum leak? The CHT would create a rich condition at cold startup which could mask it. Then, once operating temps are reached, the DME will lean the mixture out, which if there is a vacuum leak, then you'll be too lean?

I had a problem similar to yours, but mine ended up being deteriorated ref sensors. But you said you've replaced those.

I feel your pain. 6 months of hell on my 3.2 never figuring out why mine cut out, backfired, and stuttered at random times and random RPM's. Nothing was repeatable except the cutting out itself.

Ripped all the DME parts out and went MegaSquirt.

You can read my misfortunes to make you feel better under the search phrase as "pushing my Carrera 3.2 off a cliff", or something to that effect. :mad:

GL!

I have read that, Tippy, through the times of confusion...I am unfamiliar with the 3.2 Motronics - it seems so hi-tech compared to CIS!
Any particular areas for common vacuum leaks?
I do have a couple concerns but need to post pics for ya'll. That way I don't need to get to wordy...
Be right back.

Have the spark plug wires been replaced? What brand DME relay did you use?

OK, CPS already done.

It sounds electrical.

Agree with checking the ground straps. Also, check every connection in the harness. Clean them out with contact cleaner.
Swap in a known working ECU.

It sounds like you have addressed many of the usual suspects with no change. My money is the DME itself, perhaps a component on the way out or a solder joint that opens when warmed up. Any chance you have a buddy that you can play swap the DME game? Otherwise there are some fine people on the forum that can inspect and repair your DME. ischmitz is the user name (on this forum) of one that has a good reputation.

Check the ground for tight on the #1 intake runner.
Bruce

I concur with max, sounds electrical. If it shuts off suddenly at speed after getting warmed up, then starts up from cold like nothing happened, could be the ignition coil. That happened to us in our VW Westfalia last fall, but we had a good place to sit along the interstate while it cooled back down!

https://photos.smugmug.com/Other/197...7820525-XL.jpg

Years ago my 2.7 Carrera displayed the same symptoms on a weekend trip to Las Vegas.

Friday afternoon at 4:40pm it gave up the ghost and I coasted into an independent VW mechanics shop in Baker.

I was desperate, the old mechanic listened intently for 10 seconds and disappeared to the field out behind the shop, pulled the coil wire off a Bug. He plugged it into my coil and distributor cap.

Saved me a weekend in Baker California, an expensive tow and hundreds in diagnostics......wouldn't let me pay for the old coil wire.

Hope it's this simple, Scott

Sounds like coil issues to me too

OK, I'll bite. Browsing thru your thread(s), I stopped after reading this ...

"w/turbo (T60-1) 447whp"

Might wanna mention that little detail in your next rant.

I recall a past issue with the DME itself getting hot and needing work. Any local pcar friends able to loan you their DME to test?

I'll try anything...All suggestions are considered...Except posting pics...I've failed 5 times now, each time losing everything I typed up...
So, w/o pics, does anyone know the vacuum line coming off the oil related unit above the oil filter?
Where does it go, or does it float around?
Another new development - In removing the air filter half-housing to replace air filter, I noticed the rear bottom clips - the PITA one - isn't able to clamp that corner down as tightly as designed. Could this be the culprit? It looks as though I will have to replace the removeable half, as the plastic tab has busted off. Thanks again...

The air filter box clips shouldn't make a difference in the cars running, just that some unfiltered air could sneak in where the lid isn't fastened down. My 964 developed a nasty intermittent running problem, and the problem turned out to be a bad main battery ground wire, so electrically testing all the ground straps and wires would be wise.

Cool story - Baker of all places!

Why? It was ran with 100% stock DME and associated bits minus larger injectors and chip.

I feel your pain but unfortunately have no suggestions. Following hoping for a solution.
Johan

I would check all of your grounds:

Battery neg to chassis
Behind fuel filter
Intake runner
i think 2 others in the frunk
Transmission ground strap

Only happening at operating temps sound like heat expansion - could also be ecu internals related?

What is the syndrome called when a car won't restart while warm?
Owner has to let it cool down and then it starts fine?
Heat soak? What is that?

Sounds like you are overheating a component in the DME. I'd send the ECU to Ingo

My personal list of what I would suspect when a 3.2 suddenly dies when hot but runs fine otherwise:
- DME relay
- Speed and reference sensors
- Head temp sensor esp. if original 2 wire type.
- DME
Since you've replaced the 1st 3, I'd suspect the DME at this point. Swap DME's with a friend. the idle speed changed over the model years but for testing purposes, you should be fine.

Note: If you have a black ignition coil, keep it unless you know it is bad. Replacing it with a newer silver coil "while you're in there" is a downgrade in reliability in my opinion.

Just an update - and an opportunity to thank all those who have chimed in with experiential suggestions - I am in midst of cleaning all ground connections while waiting for new plug wires...If the problem persists, its time for a DME check up...Who is Ingo, where can I find him? Sounds like he's the place to go...Thanks again you all, immensely...

ischmitz on the forum, he helped me a ton with a DME issue and a very nice guy.

Subject matter expert Ingo Schmitz

I'll PM him for you, Scott

Here you go:



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I had a mysterious engine misfire, and was stumped. I finally looked at the coil itself. It was oozing black goo. The real pain is no one really sells a new perfect replacement coil for the 3.2. The Porsche dealer will sell you a new coil in a Porsche box that is a total waste of money, Bosch branded coil made in Brazil. Those are oven NFG right from the box. The aftermarket coils are all the wrong voltages.

I finally located a OEM Bosch black coil from a junkyard. It has been perfect. Check your plug wires, especially the coil wire, and the coil.

And get a solid state DME relay sold by on of the members of the board.

Update: Cleaned ALL grounds, changed out plug wires with new set. Initial reaction was positive, car felt zippy and tight. Upon reaching temp, she burped a bit just to warn me she was about to cut out...And she did. I sat for 30 seconds, fired her up and she got me back around the corner where I started - and died upon applying the parking brake. I know all about the silver coil from brazil, er I mean Bosch...TWICE before! I am not ruling out heat soak of the coil, which occurred before with my 930...Not knowing squat about the DME I will get it ready to send to Ingo...
As soon as I figure how to post pics, I have some "where does this wire go" questions for the group. Thanks again all.

I would also double check the resistance of the CHT sensor you fitted - appreciate its new but Bosch (?) quality hasn’t been the best for a while, I had a brand new one changed out within 50-100 miles a few years ago.

In fact I believe there is a way of jumping the CHT, to remove it from the ECU circuit, purely for testing.

See ChrisBennet’s post from another thread:

http://forums.pelicanparts.com/porsche-911-technical-forum/213741-engine-cuts-out.html

Just because you replaced the Crank Positions Sensors with new doesn't mean that a new part is not faulty. A new part can and will be faulty out of the box...

There are a couple of solder joints in the DME that you could check for yourself if you can solder. I would check the fuse and fuse connections to the fuel pump. In my case there was a bad connection to the hot wire to the fuel pump that was intermittent when run more than 30 minutes.

I could not fix the problem until it failed completely. It's hard to diagnose a problem if it is working when you are testing it.

I traced a lot of wires, checked harness continuity, cleaned a lot of grounds and tested and retested. I did send the DME out, and it was worth it just to eliminate that as the problem. I had a bad AFM on another car. It would cut out, but only at specific RPMs where the resistor strip was worn out.

It was worth it to me to work on it myself. How is a mechanic going to diagnose it any better if it doesn't fail while he is working on it ?

But less likely, and the symptom would most likely be total failure, does not run. It seems like something is getting hot and failing under hot load.

I had this happen with crank sensors. Failed when hot, then cooled then OK. Replaced with new Bosch (now made in the Peoples' Republic of China) - failed soon after. Finally got a good one in there...

Sure sounds like cracking solder joints on the DME circuit board.

One other thing I’ve seen is a tachometer that would heat up and short out the primary ignition circuit. Try unplugging the tach next time it dies, just go rule it out.

This probably isn't your issue, but in the interest of providing more options than none...I had a similar issue, and it turned out to be the ignition module overheating due to a lack of heat sink. This was on a 3.6, though:

http://forums.pelicanparts.com/porsche-911-technical-forum/966521-whats-smell-wait-why-isnt-my-car-running.html

It looks like the 3.2 ignition module is built into the heat sink, but maybe the internal connection isn't great anymore, or the engine bay is getting too hot now...I dunno.

86 3.2 here...had similar issues a few years back. Wasn't DME relay...wasn't grounds...wasn't wires or the coil. It turned out to be a bad solder joint in the DME that allowed it to run fine untill the unit heated/expanded. I took out and had to look twice before I found the crack. I re-flowed the solder and all has been good for years now.

Ok this is an easy one. Only because it’s happened to me with customer cars a few times.’ You have done all of the right things so far but I am seeing this more often. Open the rear deck. Look to the drivers side where the three sensors on the rail plug into the main harness. As the main harness makes a 90* turn under the outer shielding is where you will probably find cracking on the crank sensor wiring. Most but not all, I have found all three cracked. This problem will only get worse till it won’t run at all. That’s when they usually get towed in.