Stumbles Intermittently

[Jhalsey]

My 1989 930 which has under 50k miles and is stock other than a CAT bypass pipe and a Permatune CDI box, stumbles under acceleration until around 4000 rpms when it clears and pulls. Seems to be happening more frequently. I drive it every two weeks, maybe 20 miles round trip. Motor and turbo were rebuilt 7 years ago. Other than this stumbling problem, runs great, excellent acceleration, good idle (does go to high idle when restarted when warm but it is my understanding this is normal until the ICV gradually bleeds off rpms to reach normal idle speed). Appreciate any suggestions on how to go about trouble shooting the problem.

[mark houghton]

I don't know what an ICV is, but I suspect you're referring to the AAR...auxiliary air regulator and yes it's normal to cause a high idle at cold as well as for a minute or so after restarting a warm engine.
To your stumbling, may take some trial and error to sort out. It almost sounds like you're not getting vacuum advance and only seeing mechanical advance as the rpms get beyond 4000. Or perhaps your Permatune or coil are starting to fail, rotor or bad plugs or wires. Of course, could be fuel delivery related to WUR or fuel pressures. Just have to be methodical to check all systems, connections, vacuum lines, pressures, IC o'rings, etc.

[gsxrken]

Any time these cars don’t run right is a good time to verify your cold and warm fuel pressures. That said, I wouldn’t be surprised if your plugs are fouled with the way you use the car. The stock plugs run cold anyway and need a good Italian tuneup now and then, but 20 mile round trip trips will barely warm the car up. Your oil is probably a bit foamy too by not getting hot enough for long enough to burn off the condensation produced by all those short tips.

If you know your plugs are clean, and your timing advances properly (not stuck at one #), it’s worth checking your intercooler orange o-rings for boost leaks. It’s more common for these cars to run ok until 4k and then have issues at higher RPM levels, whereas you are saying the opposite. Perhaps you have a leak that affects lower RPM but is immaterial or less noticeable at full boost.

Be sure to come back and let us know what it eventually turns out to be… we’re all here to learn.

[mark houghton]

Agree with Ken 100%. Pull a plug to look at the burn, and verify that you have power to the WUR (same circuit as the rear fuel pump). If no power, then blown fuse (which would also take out your rear pump, dropping system pressure and causing low control pressure at the WUR = rich running. The WUR won't warm up properly and be stuck in warmup mode.
If all is good then proceed to checking pressures for which you'll need the gauge setup. A good place to start for ruling out fueling.

[Jhalsey]

I’ll guess I should invest in a set of pressure gauges, can i get some recommendations on which ones to buy??

[mark houghton]

Originally Posted by Jhalsey

I’ll guess I should invest in a set of pressure gauges, can i get some recommendations on which ones to buy??

Everyone needs one of these in their tool box

https://www.pelicanparts.com/More_Info/TOLSGT33865.htm?pn=TOL-SGT-33865

[Jhalsey]

Thanks Mark, just ordered. Will advise when I have measured pressures.

[Jhalsey]

Ok, I finally have some information to report. I received my CIS gauges from Pelican. After struggling to remove the air cleaner (could not loosen the right rear bolt on the AC compressor even with a crows foot) I finally resorted to removing the intercooler, I was able to hook up the gauge and follow the WSM procedures for cold, warm and system pressures. My pictures seem to be over the 5 mb limit so here is what they showed:

Cold control pressure:1.5 bar
Warm control pressure (after 5 minutes): 2.8 bar
System Pressure: 4 bar

These all appear low so I’m thinking my fuel pump(s) may be at fault. They both appear to be operating based upon the listening to them so I will test the output flow tommorow. Will advise.

[Jhalsey]

Well, after some missteps, I now have some pressures that look ok, as follows:

Cold cp: 2.0-2.1 bar
Warm cp: 3.72 bar after 5 min
System pressure: 6.4 bar

Along the way I decided to test some relays. All the red and black round relays tested good. However, the yellow relay on the left side behind the cover appears to be dead. When I apply +12v to 86 and Gound to 85, I get no clicking which i hear with the other relays. What are the symptoms of a failed yellow relay? Checking quickly I see Pelican’s price for this relay is over $300, it must be gold inside.

Another thing i noticed is that there is a sensor with a red plastic boot in the intake manifold and there is no wire on the GND terminal and no evidence of a disconnected wire in the vicinity, see below:

Perhaps it is grounded through the body of the sensor to the intake? Should I run another GND wire to that terminal?

I also recalled (hasn’t happened lately) that it occasionally backfired during cranking. Afterwards it would not start for 30-45 minutes but then it would start and run normally. Any thoughts why it wouldn’t start until 30-45 minutes? Perhaps connected to my other “stumbling” symptom that started this thread.

I went to check the rotor but wasn’t sure how to access the rear clip on the distributor. Is a rotor failure visually detectable?

Anyway, I still need to check that the timing advances correctly. I presume that now that the control pressures are verified ok, that rules out other fuel supply issues related to the fuel system, such as fuel filter and fuel accumulator?

I wanted to test fuel pressure in the manner shown in the WSM but the special Porsche tool to connect the gauges to the rear fuel pump is not available anywhere that i could find.

Anyway thanks in advance for your feedback.

[mark houghton]

Your system and control pressures look fine.
The infamous yellow relay: When they die, your car will not run at all. Period.

And as for the orange booted sensor; that's the sender to your boost gauge. Yes it has a post for a ground connection but not necessary since the body of the sensor where it screws into the manifold provides sufficient ground. I've never had a ground wire connected there.

The rear clip on the distributor cap is a royal PITA. Swear words usually work to pop it off and on.

I'm starting to think, from your symptoms, that you have an ignition problem. As for not wanting to start back up until 45 minutes of cooling down, kind of speaks to a heat soak issue 'maybe' with your CDI. Try putting a bag of ice on top of it when you shut down and see if she'll start back up in a few minutes. Maybe just a long shot diagnostic.

[Alan L]

There have been heat soak issues with the coil too - it is not in a favourable spot for heat soak.
May pay to try and swap a coil.
As for the rear clip on the dizzy... words fail most of us. But I have a simple piece of flat bar - about 10mm wide and 1mm thick - curved to slip around the back of the dizzy and flick that clip off. Special tool # 1234a. As for getting it back on - another story. But the flat bar does prop it up near where it is supposed to go, so I can flick the top of it in place.
Alan.

[mark houghton]

Comment regarding coils: I've noticed over the last few years that when shutting down and re-starting hot a few minutes later, I crank the starter for a couple seconds for which should normally fire right up...but as soon as I let go of the key, i.e., no longer cranking the starter...she will light right up everytime. My thoughts are that my coil might be going south on me, not producing the high voltage when the starter is engaged and pulling huge amps. As soon as I stop the starter and the engine is still turning over from its own inertial momentum, she fires up. Something I never experienced in my first 930.
Stone cold, she lights right up in a half a second even after weeks of sitting.

[Alan L]

The Brazilian replacement coils are famous for unreliability. There are some threads on this. But the original black Bosch coils were filled with asphalt type material - as a heat soak. It melts under normal operating temps, hence any air bubbles trapped in the filling of the coil body, disperse themselves to the top. Which is why that coil is mounted 'upsidedown'.
The Brazilian (and most others probably) are filled with epoxy. So any bubbles are trapped. Then you get hotspots in those windings and finally the coil starts to break down.
If the coil is not an original black Bosch, heat soak is something to consider.
Alan

[Jhalsey]

Well, while i wait for a new yellow relay, I have some other issues that may need addressing.

I have read that a Permatune unit should be used in conjunction with a Permatune coil. It may be marketing hype, don’t know. I have a Bosch coil, see below:

l

So i have probably the improper coil that may be bad anyway, or its not an improper coil and its possibly good. Given that a new Permatune coil is a lot cheaper than a new Permatune ignition, perhaps i’ll buy a new Permatune coil.

I also noticed that the wires into and out of the sheet aluminum tray in the left front corner of the engine bay (next to the yellow relay) appear to have been burned by excessive current sometime down the line. The wires show burned insulation but seem to be functional. I would like to remove the tray and investigate. The three fuses there also look beat but test ok. Can anyone advise the steps to remove the tray, looks like I will have to remove the Permatune unit.





Thanks for any assistance, I appreciate it greatly.

[Alan L]

That coil looks like the proper Bosch coil, but as for a Permatune one I have no experience.
If you try searching for some threads on Permatune I suspect you will find this has been answered. But I have a sneaking suspicion there is a difference in the coil specs.
Alan

[flightlead404]

That discoloration on the wires that look "burnt" may not me. I had it on every 911/930 and never had an issue. Maybe its the rubber grommet that's breaking down, or from external heat. It's work cleaning and recrimping down the the screw terminals but the wires look fine to me.

regarding the yellow relay, I've has a standard relay in that spot for donkeys and works fine for me. Long discussion threads in here regarding what the smarts in that yellow relay are, but for me at least unnecessary. I can't remember off the top of my head if you need a relay with a quenching diode though (red for Porsche). If it's an inductive load (ie pump motor) then yes.

[mark houghton]

Yeah, lots of discussion over the years on those yellow relays. For kicks I once tried plugging in a standard red relay in my '87...no workie. Perhaps there are some years where it does work.
I just keep a jumper wire on hand, just in case.

[Jhalsey]

More info to report. I managed to remove the three bolts holding the Permatune unit. That bottom right one was a *****. I followed the trouble shooting instructions for a Gen 4 unit on the Permatune web site and got the following:

Pin 1 to Pin 3 measured at .1 ohm. Spec = 0
Pin 1 to housing measured at .8 ohm. Spec = 0-.5 ohms
Pin 1 to Pin 4 measured at 3086 ohms Spec = 3300 +- 100 ohms
Pin 2 to Pin 5 measured at .3 ohm. Spec = 0
Pin 1 to Pin 5 measured at 244 ohms. Spec = 200-575 ohms

While most are out of spec, they are not wildly so. I will call Permatune tomorrow to see what they recommend.

I also measure the coil resistances as follows:

Primary measured at .6 ohm. Spec = .1 - .165 ohms
Secondary measured at 687 ohms. Spec = 390-630 ohms

So I have ordered a new Permatune coil.

I tried to remove the engine compartment relay tray after removing the Permatune. I have it loose and moving around but I can see no way to remove it, the wires connecting below prevent it. Perhaps if I could remove the rubber round base for the Yellow relay? I tried to push upwards on it from below, will try some lubricant tomorrow.

I finally managed to remove a spark plug. W3DP0 gapped at approx .023”. It was dirty but cleaned up easily. See below:

Given the difficulty of removing plugs from the right side of the engine I can only assume the left side will be impossible without substantial further disassembly. In any case I don’t think the plugs are causing my symptom, just need a little “Italian” tune up when I have it back together.

The rotor, on the other hand, did not look good, a heavily burned area was evident where it contacts the cap lugs. See below:






So I have a new rotor on the way and a new fuel filter as the access is great now that the Permatune is on the bench.

So in total I’m waiting on: new yellow relay, new coil, new rotor, new fuel filter. I have yet to check the ignition timing, will have to wait until I have it running again. Will advise what Permatune says tomorrow.

Thanks for all the help.

[Jhalsey]

Whoops, the measurement from Pin 1 to Pin 5 was in microfarads not Ohms.

[Alan L]

What is the spec for the gap on those plugs? Seems tight. They don't look flash - based on 1 plug. I think you need to pull them all - there could be worse ones. You are looking for a miss.
It pays to organise a simple way to pull the plugs. There is a Porsche tool that works pretty good. On the other hand I use a regular spark plug tool - but the socket extension kept separating when trying to withdraw the socket sometimes - hung on to the plug. So I welded part of a bolt to the plug - cut the shank so the bolt head just sticks out more or less flush with the heads. Drop a socket over it. Works great. If it was a few mm too long it would be tight to drop in some of the plug holes. Too short and sits inside the head and hard to extract. Trial and error sort of thing.
Alan