Yep, the FPR/Dampner has been suggested several times now. It's on the list of things to check. The MAF boot is new as well as all the stuff under the intake. Not sure how unmetered air would cause extra fuel to be pumped in???

Okay... maybe not a myth, but people seem to jump on injectors when more often than not it's something else. But you're point is valid.

 

D'Oh! Sorry. It's a yes on the DMM and a NO on the Mity-Vac.

Ahh, okay, I thought the LH/EZf had the same/similar fuel maps. I'm surprised no one has latched onto a flaky Temp II sensor reading. That's where I'm leaning.

One other cuplrit that no one has suggested so far is the TPS.

And if you go back and read Tony's thread, it turned out to be a "cocked" W plug.

 

GHi Andrew
What's an "idle gauge" ?

When you floor the throttle, you do not shut off the injectors, just let more air into the engine. The cranking pulse width is a fixed pulse width, so opening the throttle wide lets in more air in, weakening the mixture, helping a partially flooded engine to start.

Qualifier:- the cranking injector pulse width is varied by temp 2 reading.

So check LH temp 2 readings hot and cold at LH ECU connector

 

Can you plug an ST2 into the diagnostic port of a car that has stock chips and read out just sensor data?

Dan
'91 928GT S/C 475hp/460lb.ft

 

Hi Dan
No, only if PEMs are fitted.

 

Don't know. Did I say that? I must have meant to say FP gauge?

Good stuff there. I always thought it turned off the injectors. I will correct myself from now on.

I'll check the temp II readings at the LH, cold and hot.

 

The tech documentation for 1987 suggested that the reason for uprating fuel pressure was avoidance of hot start problems due to vapor lock. (service info by year, 1987, pg 2-05 which is about 33 pages into the document).

This is a cool hunt.

 

But Andrew has re-start problems even when engine hasn't had time to get hot enough for fuel vapourisation... or at least that's how I read his initial post.

 

+1 (FPRs first, then fuel damper, and finally fuel pump check valve last in the line of possibilities)

 

My thought also... and it fits the symptoms. That's why I wrote:
There are two opportunities for a ground problem: coating getting down the threads where the Temp-II sensor mounts, insulating it; and coating insulating the whole water-bridge from the engine block. A quick ohmmeter check between the Temp-II body and the engine block will eliminate that as a possibility (but it is still worth checking the resistance from the LH connector, as described in the WSM).

And what's the first thing we do before disconnecting the LH or EZK connectors??

 

I hate to be a "me too-er" but leaky injector is very probable. I had the same problem with my 89 18 months ago or so. Ask Paul - it drove us nuts. It was an aggervated problem by bad CPS signal (swapped out all the CPS items, including the kickdown relay), the problem improved, but persisted.

I had a completely failed injector. The body was leaking inside and out. I didnt catch the problem until it started leaking enough to set off the EGT probes, and trigger the ignition protection circuit. About 45 minutes after we figured out that it was doing that, and then testing the EGT probes to make sure they were testing correctly, we started to smell gas, and the injector started leaking out of the body into the valley.

So, I can personally attest that a bad injector can do this, and that if I was driving instead of poking around in the garage, it could have been disastrous. Its a fire hazard you wouldnt see coming.

Hans

 

Broken bi-metallic spring on the choke.

 

Andrew,
If you are looking for a logical sequential test plan procedure to find the fault and fix the problem I would suggest that you refer to the Porsche Service Test Plan for the EZK - Ignition and LH-Jetronic '87 for the 928S4, document WDK 493 921.

I used this document and supplemented this test plan procedure with Porsche LH-EZK-Diagnosis / Trouble Shooting for the S4 and GTwhich is contained in the WSM section 24/28.

I also did extensive reading on the Bosch Jetronic Fuel Injection System together with Bosch Technical Information from their web site and many other references that I have accumulated together with JDS manual for his 928 Spanner and other post that I located on Rennlist's "search".

From this information if you follow Porsche's test plan procedure in WDK 493 921 and you can eliminate each item by testing circuits, sensors etc., until you locate and rectify the problem that you have.

By using this method I was able to eliminate circuits in a logical sequence, knowing when I moved on that what I had tested were OK and operating to specification requirements.

Tails 1990 928S4 Auto

 

Where is this document?

 

An obvious case of thrust bearing failure.








Just kidding.

At this point, my real first guess would be the temp-2 sensor either being bad, or not being grounded properly due to the powdercoating, as was already mentioned. The coolant temperature gauge also acting up helps to point to this as being a pretty good suspect. The resistance of the sensor goes up as temperature goes down. If the sensor's not grounded well, it would have the same effect as the sensor being at a very low temperature. The LH will then provide a lot of fuel, like it would for a cold start on a very cold day.

I'd say that a leaky injector is pretty unlikely to be the sole cause of the problem. A leaky injector only affects one cylinder. The other seven wouldn't be affected, and the engine would still start pretty much normally. For the problem to be injector leaking, it would have to be mutiple leaky injectors, and it wouldn't just be a hot start problem then either.