anyone know the flowchart for startup?

[Icedt]

I'm looking for the culprit that keeps shutting off my engine.
The car will always start cold. It runs at 1600 rpm until it reaches 30-40C and then just dies. I can start it again if I partially dperess the throttle. It will run after a while until about 80-90C and then die again, after that, once you get it going it runs.
Temp sensor II tests good through the whole range

Does anyone know what else senses the engine temperature and then talks to the LH or EZK? Those modules seem ok.
Would an MAF that isn't burning off do this? (also affect the idle speed at fast idle?) II tried to test that once but maybe didn't have the engine hot enough?

Does the O2 sensor have that kind of input authority?
Does my car, 1991 GT Canada, have a cold start valve? The manual isn't great once you get past 87 models, the pictures aren't even updated for many of the procedures.
Can a malfunctioning idle stabiliser actually shut off the engine instantly? (there isn't even a sputter)
Thanks for any answers you may have, the dealer doesn't have a diagnostic tool in their shop, so ............

[Shark_GTS]

the maf is important of course, but usually will cause a no start or difficult to start. unplug the MAF and you can run in limp mode.

the engine runs on the O2 sensor, a immediate switchover when the engine warms up to xx degC. that is the most efficient measure of combustion, closed loop as it is known in control. i would start there.

idle stabilizer causes hunting and poor idle control, but it will run half decent still.

there is no cold start valve with LH, the injector pulses are longer. temp sensor II is over-rated!!

[Danglerb]

Throttle position switch maybe?

[Normy]

Intermittent nature makes me think about the fuel pump relay. Can a relay overheat? Try changing it first.

[Icedt]

Well, I have replaced the O2 sensor, the Temp II sensor and now the MAF. The new MAF did fix the hunting idle problem so now I have a new one.
The car will always start. It runs about 1300 until about 40-50C and then just dies. It will restart by depressing the throttle a bit and then runs until warm. If you rev the engine at all it responds fine but then it won't idle, it just dies when you take your foot off the gas.
EZK? LH? Fuel pump? fuel pump relay? (I can't see how, it always restarts.) But it is like something just kills the fuel or the spark and then resets. My Hammer says there are no faults.

[Normy]

Originally Posted by Icedt

Well, I have replaced the O2 sensor, the Temp II sensor and now the MAF. The new MAF did fix the hunting idle problem so now I have a new one.
The car will always start. It runs about 1300 until about 40-50C and then just dies. It will restart by depressing the throttle a bit and then runs until warm. If you rev the engine at all it responds fine but then it won't idle, it just dies when you take your foot off the gas.
EZK? LH? Fuel pump? fuel pump relay? (I can't see how, it always restarts.) But it is like something just kills the fuel or the spark and then resets. My Hammer says there are no faults.

Let me give you some sage advice. I've been dealing with the vagaries of LH-Jetronic Bosch injection since May 4, 1999. That means about 10 years.

Are you aware that there is a "suitcase" tester produced by Bosch that can be hooked into the fuel injection and the ignition via their plugs and it can diagnose your system to a basic degree?

Have you tried calling any local Porsche shops and asking them if they have this tester? I did. I had so many problems with my '85 hesitating that I had Zotz garage in Orlando hook their sensor to my car. They found one serious problem. It didn't solve my issues, but it helped.

-It's not uncommon for there to be several small issues that cause a car to run rough. In your case, I think you are dealing with a fuel pump that is dying. Why else would an engine that run fine at idle, but then as soon as more horsepower was required [that is, more FUEL]...suddenly die? At idle, and for the first few thousand RPM's there is little change in ignition, and this is certainly either an ignition or a fuel issue.

Can I ask you a question? Have you smelled your cars' butt?

[Sorry; there I go again. Yes, I sniff my car's "butt"]

Though that might seem be something for the off-topic section... it has real meaning. Do you smell fuel when you sniff your 928's exhaust fumes? If you do then something is really! wrong! That thing is either missing on a cylinder or the injection is pulsing and your ignition isn't working. If you DON'T smell fuel...then you have no injection. EITHER you have a blown LH computer, a dead fuel pump relay, or a dead fuel pump. This last isn't likely, since your car runs at idle, which means that the pump is running.

-How long did this car sit? And I wonder if your fuel pump is covered with crap? A funkalated fuel filter would probably still flow enough gasoline to allow the engine to run, but all the crap blocking it might be an issue if the engine needs more fuel.

-Spock would call that a "hypothesis that fits the facts"

Good luck-

N

I'm of the the opinion that your fuel pump is blown, or that your

[Danglerb]

Pretty sure this car tested clean with a Hammer, no errors.

If you have an extra Temp II sensor, hook it up, but don't install it so you can test with the motor hot, but sensor in a cooler cup of water (brain doesn't know its hot) and vice versa engine actually cool, but sensor in a cup of boiling water.

[DanielDudley]

Check your throttle position sensor. Just a hunch.

[DanielDudley]

Sorry, missed that Danglerb.

Many Ljet cars have an Auxilliary Air Valve, an AAV, that bypasses the throttle to raise the idle. It is a small can with a 3/4 inch tube going in both ends, and a small two conductor wire coming in from the harness.

If your car has one, it is closing too fast. The wire runs to a heating element that causes a bimetallic spring to close off the aux air. Try unplugging it.

[MPDano]

AAV will look like this.



PM me, I have a working one for cheap.

[Danglerb]

I think its a Canadian market 91 GT, which uses an ISV, but I think that has also been replaced. This is a LONG term problem the poster has been working on for MONTHS with little change. He has a Hammer tester, and John Speake is already in the loop, but its still not on the road.

This is a case where having a second car is extremely helpful. By swapping parts we can verify good and bad, which substitution by new parts doesn't really do. Knowing you found a bad part by it not working in a second car lets you make progress incrementally.

Anybody know if the Hammer does any kind of CRC type checking of the eproms in the brains?

[Mrmerlin]

first question i have is, what was the last thing you fixed??
Has the intake ever been removed?
Have you run some techron in the fuel system, or changed out the fuel filter ( blow it out the other way into a catch can to see if its dirty)
Have you ever checked the dampers and FPR for a fuel smell ( pull off the vacuum lines and sniff the end or rub the end on your finger, if you smell fuel its probably leaking) Also get a Myti Vac and see if they hold vacuum
Have you inspected both of the coil leads for corrosion at their ends?
Have you replaced the 2 plastic hose connectors at the MAF boot?
If you replaced the ISV hose, then there is a chance that the hose has split where it bends around to come to the MAF.
Please answer as much as you can

[lizard928s]

MPDano,
The AAV you have there is only used on 16V motors, 85+ USA and 87+ ROW cars use something completely different. He has a 91 GT, nothing to do with the engine is the same as yours.

IcedT,
First off what part of Canada are you in?
The issues you describe do not sound like a brain failure, or a bad relay as you can keep it running with holding the throttle open.
As well it is unlikely to be the TPS that is causing the engine to stall as if the idle loop doesnt engage then it doesnt return to idle very fast. The fact that it idles high at 1600RPM is enough of a reason to check it though.
I would disconnect the LH brain and check the manual for the pin out. I would then find out/confirm that your TPS is activating with a DVM. Once you confirm this have a helper hold the throttle wide open and verify that your WOT part of the TPS is working too.
Your stalling issue, and the high idle issue sounds like a bad ISV though. This requires the intake to be removed. However this part is controlled by the LH which can have some funny failure modes. Due to this I would recommend finding someone in your area with a 87+ car and putting your brains into their car and seeing if their car has the same symptoms. Then put their brains in your car and see if that changes anything. If it does not then remove the intake replace the ISV, TPS (if it doesnt check out), knock sensors, and gaskets. This job runs around $1k in parts and you may want to have the intake powdercoated while off. You may consider though replacing the TempII at the same time or before just for ****s and giggles as it is a very cheap part.

The other thing which there is a faint chance of it being is the Reference sensor on the engine these have funny failures. But if it is this and you continue to live with it, it will get worse and not restart at times.

If you live on the west coast pm me privately and I can add you to our emailing list and there are a ton of guys who will let you swap the brains around.

Normy,
He has already put the hammer on his car, the Porsche dealership will not be able to do any more for him except rack up a very large bill trying to find the problem.

[MPDano]

Sorry, my bad. I kinda jumped in the thread after seeing AAV, then offered it up. Disregard AAV post as it was for an early 928.

Yes, heed the advice of not taking to the Porsche Dealer. Way too many experts her to give into that route. Costly and un-necessary.

[Danglerb]

Does the GT also have that EGT sensor thing that detects a temperature difference between the exhaust banks and shuts half the motor down?

[lizard928s]

Danglerb,

Yes the 1991 928 GT does have the EGT and ign monitering system you are speaking of.

But this would not cause the engine to stall.

I am 99% sure that the ISV will 100% cure this problem.

[Icedt]

Wow, thanks guys!
I am bad, should have read my post more thoroughly, it dropped all the latest info. Arrggh.

It drove last year fine. I thought it had lots of power. It was parked for the winter (Edmonton, lizard) and this spring I have been fighting this.
I have: replaced the Temp sensor II, no change (I had tested the old one it worked through all ranges but it was a cheap replacement.)
I have replaced the O2 sensor, some improvement so was probably needed. I then sent the MAF to JDS's rep in Toronto and he put it on his M5, said it ran but poor power, so I got them to send me a rebuilt. Vast improvement but still dies. I will try to explain this dying better, please bear with the verbosity.

It will always start cold. runs at about 1200-1300 now until it warms up and then gradually drops to about 900. If I leave it alone, sooner or later at any given temp above 40-50C it will just die. (Yes I have sniffed it's butt, dad taught me that years ago, nothing abnormal). I can always restart it by depressing the accelerator a bit. It will go back to that idle state. Now here's the hard part to explain.
If I rev it up, it will rev fast and smooth and stay wherever you hold the throttle, no shortage of fuel, but if I take my foot off the gas, it dies. I can restart it again immediately by depressing the throttle a bit.

I have pulled the vacuum lines off at the 4-way connector by the master cylinder (i think that's what it is) and even after 1 or 2 days it still is holding vacuum. I assumed that was connected to the whole system so I did not vac check any further. (Is that a safe assumption? I thought if anything leaked, it would drain the whole reservoir.)
No the intake has not been off since I bought it.
Dangler, it does have the dual exhaust bank sensors (I started to remove one when I couldn't find the O2 sensor (read duh) and realized what it was ). And thanks for the vote of confidence, I'm losing hope.

The Hammer checks all the flaps as well as the WOT and idle switch , everything seems to be perfect. That was why I went after the MAF first as it doesn't really check the MAF unless it is gross failure (JDS said).
The local dealer doesn't have anything, I talked to the Porsche tech and I think they might want to start renting my Hammer, so no help there. They said they would just have to start replacing parts.....

This car was sitting in a police compound for 6 years before I bought it, so yes the fuel filter probably does need love (never thought of that!) but it ran excellently last year so I figured that that kind of stuff was ok. I put some stabiliser in the fuel last fall too.

I hate to say this but after doing some investigating (asking questions of people) it may have been boosted reverse polarity (long story). That is why I am leaning towards a blown electronic component.
Thanks again for all the ideas, I will do the fuel filter next anyways but I doubt that would kill the engine since it will run at high revs as long as I want it to. Maybe I should just take it out on the road and DRIVE it. That might give it the love it's looking for......

[Danglerb]

I was thinking you also changed the idle control valve, if not, put it at the top of suspects.

928-606-161-01 Idle Control Valve, 928 (1987-95) $357.75 here on Pelican, but shopping around will find it closer to $300.

Not an endorsement, but $242 here, http://www.worldimpex.com/parts/genuine-part-isc-valve_28873.html

[lizard928s]

OK Travis,

This is much more to go off of.

I am going to suggest something that will help to solve the issues, but eventually you will have to pull the intake and replace the ISV.

The hose that attachs to the drivers side intake cover, and goes to the brake booster has the hose which runs to the ISV. disconnect the hose which runs into the manifold and cap the line to the booster. Then make an adapter to go down to a small vacuum line to limit the amount it can suck in.
You will have to hold partial throttle or the car will stall as it needs this air to run (reason it is stalling). Once the engine is at full operating temperature take a 1 litre bottle of tap water and take this small vacuum line and put it in the bottle of water while holding the rpms between 2500-3000 the engine will bog down slightly as the water is sucked in. TONS of white smoke will come out the tail pipe dont worry this is normal. The water droplets will pass through the ISV knocking ANY carbon built up out of it. This carbon build up is what is most likely preventing it from working properly. Get it to suck the entire 1L bottle of water through the system. Once it has keep the engine running at around 1000rpm (will need someone operating the throttle the whole time). for around 5 min. This will ensure it has all gotten out.
Once this is done return the hoses to how they were before hand and take it out on a back road and give it a good italian tune up (drive hard). This will make sure that everything has been flushed/knocked out of the system. Not only will this clean your ISV but it will clean your valves as well. And the S4/GTs always have a fair amount of build up on the intake valves.
If that does not cure your problem, then you can try the brain swap. I gave you a contact via PM.

BTW I drove my 87 auto to Edmonton just this past february. It was bad as my blizzaks that I had on it, one of the rears had a problem a couple days before I went so I had my Fuzion ZRis on the rear. I could stop and turn, but getting started was tough! Then I came back in a blizzard. No problems starting the car in the morning though, and no problems once I was moving.

HTH

[Icedt]

I will try that this weekend and let you know, thanks everyone so far!