1990 928 GT with chronic 4 cylinder mode issue

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02 Aug 2011 13:07 #5774 by srshaw3
I am planning on picking up my 1990 GT from a service shop tomorrow. It has been there for 4 months. A number of problems have been resolved, but there is a nagging and disheartening problem still with the car. While I appreciate any thoughts, I ask that any potential respondents read carefully what has been checked, or changed, on the car, in an attempt to resolve this issue.

I will review, and revise the below description as my memory and testing clarifies the issue.

The Ignition Monitoring System (IMS) relay triggers putting the car into 4 cylinder mode ( by cutting fuel as I recall). This happens often and without knowledge as to why at this time.

There is a IMS bypass relay. I have one, and have used it. The symptom of 4 cylinder mode still occurs just less often.

Prior to the problem, I had a complete intake refresh done, with every part replaced except one vacuum hose. Since then the vacuum hose has failed and been replaced (twice).

I have tested much, but as it is a 20+ year old car, I have also replaced many parts in an effort to resolve this issue. Including the ignition modules and the ignition coils.

The shop doing the recent service did find a problem wire near the EZK, and thought it resolved the problem when repaired, but optimism was misplaced.

I did have a known good EZK sent from Rich Andrade swapped in, and it did not resolve the issue.

I have owned this car for 4 years, and driven it just a few thousand miles due to these issues.

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02 Aug 2011 15:49 #5776 by 928mac
Hi Stan;
Here is the way I would go after this problem.
The Ignition Monitoring System (IMS) will have values and tolerances that need to be met or maintained.

Here is a link
www.landsharkoz.com/tech/rich/ticmr.htm

Other then following the test,
What I see in this link is the response to the ignition is given by the Exhaust prob.
I would disconnect the probe to stop the shutdown issue,
But, as you can see from the doc, the ign. over heats and fails, then the exhaust cools and the fuel is turned off by the prob.

Soo either the ign. is over heating or the probe is malfunctioning.
I am not using my probes if you want them?
of coarse I will need to cap the ports. Right now my probes are just tied out of the way.

Is this possible that this is the problem Stan or did I miss something.
Brad

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02 Aug 2011 15:56 #5777 by srshaw3
When the bypass relay is in place, the IMS is not monitoring exhaust temperature, so even if there was a different in temperature it would no longer be recognized and acted on.

Essentially with the bypass relay in place the car would function as a pre0IMS 928.

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02 Aug 2011 16:34 #5778 by 928mac
Have you went through this document to see if it sheads any light on your issue

www.porsche928forums.com/download/928EngineControl.pdf

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02 Aug 2011 16:42 #5779 by srshaw3
I provided that document to the repair shop that has my car. They used it to identify the bad wire. The author of the document, Rich, is who sent the known good EZK unit to test in my car. I anticipate starting at the begining when I get the car back, but it is distressing.

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02 Aug 2011 18:03 #5781 by SeanR
I know this is frustrating and really hard to track down especially since most everything most of us can think of has been covered. For now, I'd keep the relay jumper in place.

Once again, I'd go and pull the boots back on the Temp II, MAF and O2 and make sure that the wires are in no way touching each other. The O2 won't have a boot per se, but you can check the grommet where it enters the car for misplacement or fraying. If you don't have an X-pipe, you might need a mirror to see the wires going in to the O2.

I'll keep looking at this thread, and if I can come up with any thoughts, I'll add them.

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02 Aug 2011 18:32 #5783 by 928mac
Stan, I wish you luck. I see you have all the best people on this as is what I would do after 4 years.

Let me know if it is a standard and if it is for sale. Sorry,

I guess this is one of those stories that people ask when they say "I here the 928 can be a nightmare"
You can answer Yes! want to buy one

Still, you have to remember that it is just a machine.
If you put power to the end of a good wire, the other end will have power.

Speaking of which, I have come across wire that had been probed with a test light, looked good, showed voltage, but only had 1 or 2 strands left inside and would not handle current.
Pulling on wires helps find these ones.

Anyway, good luck.
Brad

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02 Aug 2011 18:45 #5784 by srshaw3
Thank you both, I don't anticipate it being for sale, I have been a 928 owner for 20+ years, and getting a GT was a long term goal. (yes, Brad it is a manual, as always with a GT).

I don't expect to get to it until at least next week, as I have a day at Lime Rock Saturday with the M3.

I am nothing, if I am not persistent. I have never been beat by a problem, and don't plan on starting now. I have always claimed my greatest technical strength is problem determination, this will be just another one.

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03 Aug 2011 19:29 #5789 by 928 Go Go Joe
Hi Stan,

Sorry you are having trouble with your car. I'm not an expert, but if you have checked out/swapped out all major components, I'd strongly suspect the wiring harness itself. Is it possible to swap the IMS harness with another one? Or carefully inspect the wiring and determine it is able to carry the required voltage. Often, it's the simplest thing that is the culprit. Remember, that is 20 year old wiring in there.

Best regards,

Joe B.

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03 Aug 2011 19:44 #5790 by srshaw3
After getting the 928 back, I was driving to a racquetball club @25 miles away.

In the first 3 miles of driving it went into 4 cylinder mode perhaps a dozen times while the IMR relay was swapped out and the bypass relay swapped in.

I had given up, and was almost back home when it no longer had the issue. I turned around drove to the club and back without it ever going into 4 cylinder mode again.

On the way down, I went off a random bump, and warnings that the anti-lock brakes and locking differential were disabled. This error did not reoccur on the way back.

On the way back, I did notice the alternator gauge dropped to @12 a few times. I recall this doing so before I brought it in the shop and testing the battery at such times showed 13+, so perhaps one issue might be a connection to the dash cluster. I do have a replacement pod to install too.

On the way back I stopped about halfway and swapped the IMR relay back in. I had no issues.

Like others have suggested, the shop suggested it could easily be a connection somewhere or even just a wire.

I don't expect to get a chance until after Saturday, but I will review the components Sean suggest first, and document what and when I check each.

Thank you all.

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03 Aug 2011 20:45 #5791 by the flying scotsman
Stan.......by the last description the intermittent issue indicates wiring or the CE to me.

I'd completely remove the fuse/relay panel and all fuses and relays. Inspect thoroughly and replace anything suspect........I'd replace all common relays they're cheap.

Also inspect the back side of all the 'grey'wiring and the associated wiring harness.

good luck

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04 Aug 2011 10:31 #5792 by SeanR
Yes, sounds like bad ground, intermittent ground and I think I know which one it is.

Pull the air box and MAF. Right side in the V, under the throttle cable pulley is a block ground that is the grounding point for the EZK/LH. There is also the ground for the MAF and a CPS on the left side, in the V. Check those and ensure they are grounded.

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04 Aug 2011 11:10 #5793 by 928mac

Yes, sounds like bad ground, intermittent ground and I think I know which one it is.

Pull the air box and MAF. Right side in the V, under the throttle cable pulley is a block ground that is the grounding point for the EZK/LH. There is also the ground for the MAF and a CPS on the left side, in the V. Check those and ensure they are grounded.


Man I wish I had your knowledge.

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04 Aug 2011 13:50 #5794 by the flying scotsman
Brad.....you were there also.........under the intake, back of the v in the block the throttle cable is there, the CPS just beyond thats where the grounds are that Sean references......they get very warm due to location and also are under the fuel lines and close to coolant ports....all contaminate the grounds as well age.

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04 Aug 2011 19:47 #5795 by 928mac

Brad.....you were there also.........under the intake, back of the v in the block the throttle cable is there, the CPS just beyond thats where the grounds are that Sean references......they get very warm due to location and also are under the fuel lines and close to coolant ports....all contaminate the grounds as well age.


Except I no longer have a stock harness and my grounds are on the back of the head.
nothing in my V except Knock sensors. even the crank sensor loops back towards the firewall and all three attach level with the right head just under the AC line.

I guess I should doc my harness into a schematic so that if the car ever goes to a different owner they will have a map to follow.

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One of the knock sensor connectors

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04 Aug 2011 23:02 #5796 by the flying scotsman
Had thought the stock harness was on before the mods?

Stan.....whats the current draw on the battery with everything off?

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04 Aug 2011 23:56 #5797 by 928mac

Had thought the stock harness was on before the mods?

Stan.....whats the current draw on the battery with everything off?



Yes the car was stock when I got it before the mods and I do remember some grounds there.

The current draw should not be above 100 mil volts.
I think I have mine down to 23 mil volts and will last for 3 or 4 months easy
but I have seen caddys has high as 320 mil and the bat will be to dead to start it in 10 days or less

Most modern vehicles will shut down the modules with in 20-40 sec after the key is removed and will drop to 20-70 mil volts

here is a good step by step
www.aa1car.com/library/battery_runs_down.htm

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05 Aug 2011 09:28 #5801 by SeanR
Here's another thing to consider, and would not have given it a 2nd thought if it had not happened to my car yesterday.

The ignition modules. My car just started to do what you you are experiencing. Now I know everything on my car is new and these are not, so I swapped a new set in and the car ran great. For $40.00 each, cheap insurance.

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05 Aug 2011 10:02 #5802 by the flying scotsman
where did you buy them Brad?

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05 Aug 2011 12:57 #5804 by srshaw3

Here's another thing to consider, and would not have given it a 2nd thought if it had not happened to my car yesterday.

The ignition modules. My car just started to do what you you are experiencing. Now I know everything on my car is new and these are not, so I swapped a new set in and the car ran great. For $40.00 each, cheap insurance.


I haven't got to any of these tests yet, trying to prepare the M3 for a Lime Rock track day tomorrow.

Just a quick note, that I had previously swapped ignition modules with varied results, as well as the coils. I ended up replacing all of them for both sides (20+ year old car why not). The varied results might be indicative of one of the wiring issues previously suggested. I am particularly interested in checking the O2 sensor, as I replaced it, but haven't looked at it in some time, and did at one time install an RMB, so perhaps tweaked some wiring then.

I am hoping the grounds were previously checked, as it is one of those items I paid to have done, and the intake has been off 3 times since. Nonetheless, I am taking *nothing* for granted, and will check everything one item at a time.

Thanks so much for the suggestions so far!

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07 Aug 2011 20:38 #5806 by srshaw3
I had a few minutes, so I:
1. Cleaned the ground by the ignition modules, the one that has 4 brown wires coming to it.
2. Swapped the cable connectors from ignition module 1 to ignition module 2 and ignition module 2 to ignition module 1.

I started the car and nearly immediately the green light lit on the IMS relay (as it has been). This indicates the problem is in ignition circuit 2 (cylinder 2,3,5,8. I would conclude the ignition module is not the problem.

As a side note the dash voltage gauge started working again, this has been an intermittent problem.

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07 Aug 2011 22:24 #5807 by 928mac
Good news, that will be $928.43 split 3 ways please. :D

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08 Aug 2011 05:18 #5812 by srshaw3
I think you misunderstand Brad, since both ignition modules are new, I didn't expect they would be bad anyways. Finding the cause is what will make me happy, not eliminating as suspect known good parts.

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08 Aug 2011 10:27 #5814 by 928mac
It was a joke Stan.
That you owe us all some money for helpng you fine your 4 year gremlin :D

I thought $928 was a nice number ;)

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08 Aug 2011 11:19 #5815 by srshaw3
I would happily pay the $928 if someone found it, as it seems I have already paid many times that for it *not* to be found.

But it still hasn't been found....

I did know your payment comment was a joke though.

I checked the coil wire connections on the driver side. They seem fine, as expected since I replaced the coil before the car went in for service.

Trying to find the ground mentioned in the above comments, so spent @15 minutes trying to access the MAS/MAF band clip head. No joy there yet.

My 53 year old back will feel like it is 83 by the time I get through this and will impede ever step of this process, so bear with me, it will be slow and get slower. I have been down this road before, thus why I was willing to pay a service shop to do work I can do.....

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08 Aug 2011 14:01 #5818 by srshaw3

Yes, sounds like bad ground, intermittent ground and I think I know which one it is.

Pull the air box and MAF. Right side in the V, under the throttle cable pulley is a block ground that is the grounding point for the EZK/LH. There is also the ground for the MAF and a CPS on the left side, in the V. Check those and ensure they are grounded.


I found a ground on the driver side at the back edge of the block, not in the V itself, this was just to (driver) side of the throttle cable pulley. it was tight and when removed was shiny, so was apparently checked and cleaned at some recent point.

I would like to review the other ground as well, if I can find it, but I haven't seen it yet.

Perhaps noteworthy, but I will reserve optimism, is the MAF boot is cracked and I can see the wires have broken coating, thus there is a chance they could be arcing to each other. (photo below) What is the suggested repair? Just wrap them with electric tape? Shrink wrapping them might be feasible if there is shrink that can be wrapped, so I don't have to splice the wires. Or I could get another boot and splice it in. Thoughts?

P.S. laying on the motor worked well, and my back appreciated the position lmao

Attached files [img]media/attachments/5964=668-maf_wires_small.jpg[/img]

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08 Aug 2011 22:50 #5823 by the flying scotsman
Stan......you found one of two grounds, the other is real close to the first :)

If it were my car I'd find a harness that has a good MAF connector and wiring and do the splicing far away from the connector. I know who has one :D

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09 Aug 2011 04:24 #5824 by srshaw3

Stan......you found one of two grounds, the other is real close to the first :)

If it were my car I'd find a harness that has a good MAF connector and wiring and do the splicing far away from the connector. I know who has one :D


I think the MAF is the same connector since '85, do you know? I may have an '85 harness in the shed. Otherwise I will see who has one.

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09 Aug 2011 14:09 #5827 by 928mac
I cut my harness at the firewall and both ends are hanging up.

I have robbed some connectors off of it and will have to see if the MAF connector is any good.

I don't know if Malcolm was suggesting me or if he has one.

Brad

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09 Aug 2011 16:16 #5830 by the flying scotsman
Didnt know what you did Brad and wouldn't presume anyway.

Stan, I do have a harness off a '87.....let me know.

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09 Aug 2011 16:21 #5831 by srshaw3

Didnt know what you did Brad and wouldn't presume anyway.

Stan, I do have a harness off a '87.....let me know.


I have an '85 harness that might have the right connector. I started the shrink wrapping yesterday, so will finish that up and see where I am afterwards.

I am wondering how different the harness is from year to year. If someone had a real good harness, I would consider the task of swapping it in :(

Thank you for the offer, I will keep it in mind.

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10 Aug 2011 21:42 #5834 by srshaw3
First, thanks to those who have made suggestions so far :)

Today I finished putting shrink tubing on the MAF wires that had broken coating. I then wrapped that section with electrical tape as a replacement for the cracked boot, and to further hold the shrink tubing in place.

I started the car and it idled well, even when I put the A/C on. I drove it 1/2 mile or so, with no issues. I then drove @60 miles round trip tonight without the limp mode symptom occurring at all. Perhaps I will jinx myself, but I would rather have it happen again and know, then have false optimism.

I do have (at least) two problems to address *if* the limp mode problem is gone. Sometimes my gauge cluster warning will flash “anti lock brake disabled” and “locking differential disabled”, this has often been after a bump in the road. My volt meter also will drop to 0 for long periods of time. Prior to taking the car in for service, the volt meter symptoms existed, but not the other symptoms. When tested in the past the battery was getting charged when the volt meter was 0. I am guess this might be a ground issue, maybe in the pod… I am interested in hearing other's thoughts.

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10 Aug 2011 22:54 #5837 by the flying scotsman
good job Stan.....hopefully you have the 4 cyl issue fixed.

The loosing signals on the pod is perhaps one issue a 3 or more. I'd start by looking at the ignition switck then pull the pod and inspect the wiring and circuits.

When was the PSD serviced?

Has any of the ABS relays been replaced? Does the ABS work?

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10 Aug 2011 23:38 #5838 by srshaw3

good job Stan.....hopefully you have the 4 cyl issue fixed.


I am hoping and am concerned that I am overly optimistic :)

The loosing signals on the pod is perhaps one issue a 3 or more. I'd start by looking at the ignition switck then pull the pod and inspect the wiring and circuits.


I have a replacement pod in hand to address the splits in this one, so it gives me another reason to take this task on.

When was the PSD serviced?

In the 2010 service.
The PSD light comes on often enough when accelerating in corners with slipage that I am confident it was working.

Has any of the ABS relays been replaced? Does the ABS work?

I have not replaced any relays.
I believe I have had the ABS kick in when on wet roads.

Since these problems are not present at startup, except for the volt meter issue intermittently, I can verify PSD and ABS before proceeding.

Thank you again for your thoughts.

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11 Aug 2011 09:21 #5844 by SeanR
Good news on the MAF connector. This can absolutely be the cause of the issue and for some reason I thought we'd been through that. Hope it fixed the issue.

On the PSD/ABS, check the barrel connectors at each wheel for condition, a broken ground wire can cause this. If those are all good, get under your seat and check the inertia switch, these can get unplugged, or inside they need to be cleaned. Don't think about buying a new one, they are expensive. Search on R-list for inertia switch in both the 928 and the 964 sections.

It also could be a crappy relay, that has a loose component when hitting a bump.

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11 Aug 2011 14:08 #5845 by 928mac
Hi Stan, I have a different idea.
Since you are having more then 1 gauge problem, try this.
Well driving, put your right hand under the pod and feel for the wires where they go into the pod.

Move them around, push them tight, and see if this changes the volt gauge issue.
I know that I have a bad contact on 1 of my connectors as well as when I squeeze the right side of the cluster, my problem goes away.

I’m not saying anything but this is a quick check that will help locate loose wires if there are any in that area.

I need to pull mine apart and tighten the pin grip as mine looses connection as the dash and wires warm up.

Brad:)

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12 Aug 2011 06:23 #5846 by srshaw3

Good news on the MAF connector. This can absolutely be the cause of the issue and for some reason I thought we'd been through that. Hope it fixed the issue.


Before the most recent service attempt I had swapped MAFs. I do not recall a cracked boot, so never checked the wires beneath.

On the PSD/ABS, check the barrel connectors at each wheel for condition, a broken ground wire can cause this. If those are all good, get under your seat and check the inertia switch, these can get unplugged, or inside they need to be cleaned. Don't think about buying a new one, they are expensive. Search on R-list for inertia switch in both the 928 and the 964 sections.


Will check these, thanks.

It also could be a crappy relay, that has a loose component when hitting a bump.


I will re-seat the relays in play, thanks.

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12 Aug 2011 06:24 #5847 by srshaw3

Hi Stan, I have a different idea.
Since you are having more then 1 gauge problem, try this.
Well driving, put your right hand under the pod and feel for the wires where they go into the pod.

Move them around, push them tight, and see if this changes the volt gauge issue.
I know that I have a bad contact on 1 of my connectors as well as when I squeeze the right side of the cluster, my problem goes away.

I’m not saying anything but this is a quick check that will help locate loose wires if there are any in that area.

I need to pull mine apart and tighten the pin grip as mine looses connection as the dash and wires warm up.

Brad:)


Sounds like a simple enough idea, and fortunately my under dash bolster is still off, so should be possible. Thanks.

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12 Aug 2011 12:16 #5853 by srshaw3
My optimism was inappropriate, @10 miles of driving today and 3-4 limp mode occurrences withe one separate ABS and PSD light. If these were somehow connected it would seem more likely to be a ground, or at least a fuse panel issue, thus the suggestion to review and clean it all (by Malcolm as I recall) might be next on the list....

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12 Aug 2011 13:46 #5855 by the flying scotsman
If nothing else cleaning the fuse/relay panel eliminates it from the tshoot equation.....good luck.

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