AO

I thought this might be fun for some of the newer members out there (and some of the "old guard" too.) I've got an early '87 S4 auto with 92k miles. This is my project car I work on weeknights while in OH - so there will not be any work on the weekends.

Symptoms: The car seems to start fine when cold. After it's been running even for a few minutes, if I shut the car off and try to restart it, sometimes it starts right up. But often, if it doesn't catch right away, it floods the engine (I can smell the gas). I've learned that if it doesn't start in about 2-3 seconds, I need to mash the gas pedal down (this turns the injectors off to clear the flooded engine) and crank away until the car clears the flooding, catches and starts - about 10-15 seconds, sometimes more.

Background: The wires, caps, and rotors are all new. New TPS, and if I recall a new ISV. Plugs are not new, but looked okay when I redid the top-end. The intake, water bridge, and cam covers have all been powder-coated. I recently posted about a problem where the idle and the coolant gauge were erratic and it was postulated that maybe the coolant bridge was not grounding properly - sending an erroneous temp signal to the LH/pod.

I have not checked anything on this yet. I would like to tackle this without the use of my sharktuner/928DT.

What is causing the problem? You make the call!

Calgary Ole

Fuel pressure regulator or one of the dampners leaking into a vacuum line.

Cosmo Kramer

Leaky injectors? Do you have a fuel pressure gauge on the rail?

R.Pires

Hi,

I have a very similar issue with my 83S Euro, for a very long time.
When cold, but real cold, like overnight it starts fine on first crank.
After shut down, it also starts on first crank on the next 10, 15 minutes.
More than that, say even 4 or 5 hours, I must smash accelerator down.
Sometimes I smell fuel, sometimes don’t.
From what I read on the Forum, I guess it’s leaking injectors.
Some day, I’ll take care of them…

Regards

aaddpp

Ditto

jcorenman

Andrew, what other tools do we have at our disposal? Multimeter? Miti-vac? Any known-good spare parts on hand?

A good first step would be to list the possible suspects, and then put together a test plan (using whatever tools and parts are available) to eliminate the various suspects.

Also, did this problem start after any particular work? Is this a new problem after your intake refresh?

the flyin' scotsman

Too little air?

As well as the fuel related items I'd ensure there's no air restriction and inspect the MAF.

AO

I have looked at the fron dampner, and it was fine. Have not looked at the rear dampner/regulator.

No FP gauge, but he problem does not seem to be too little fuel, but rather too much upon hot start up.

I highly doubt leaky injectors. It seems to me that injectors are more of an urban myth than an actual problem. I have seen the reverse, however, where teh injector would not actuate - causing a mis. We'll keep this one on the list, but it will be way down on the list.

I've got a DMM, but no DMM. I may have a FPR from my GT laying around.

That's what I wanted this thread to do. I've done the test plan for this in the past for Tony Harkin when he had a similar problem. I thought it would be good for some of the newer people out there to scratch their brain a bit a see if they could come up with other possibilities.

Great question. Unfortunately the car came to me with one of the heads off. So I can say for sure if it was somethign I did or not, but let's assume it's a "new" problem as a result of top-end/intake work.

I'm not sure how we'd get too little air. The intake is stock and once the car is running it runs great. It's just the hot start issue.

Calgary Ole

If the FPR is leaking, the car would probably run a little rich and foul the plugs. I think you said the plugs looked okay but it might not hurt to check one or two now that the car has been running.
I had similar symptoms that The Flyin' Scotsman help me repair last year.

shmark

Fuel check valve? Putting a gauge on the passenger rail will tell you pretty quickly if your hot pressure is off. This wouldn't be an overly rich condition, but if the plugs look good it's a possibility. Have you checked the plugs since this happened? Another thing, does the '87 have a cold start injector? If so it could leak, causing a hot start problem too. I've also heard of people hacking the cold start injector in a misguided effort for more power, any chance the PO did something like that?

AO

85-95 do not have a cold start injector. They do have other ways to add fuel, however.

One is the Warm Up Enrichment map with utilizes input from the Temp II sensor to enrichen the fuel mixture when cold.

There is also a Cranking Map that gives a little extra gas while cranking. Can't recall off the top of my head if that is temperature dependent or not.

AO

I have not checked the plugs recently, but you're right, that should be checked. I will try to do that tonight (if I stick around - May go home tonight).

Mrmerlin

first check the dampers and FPR vacuum lines simply pull the line off and smell the end if you smell fuel the part is bad , if none of these indicate fuel then inspect the 2 plastic connectors that plug into the MAF connector boot usually the right one will crack with old age letting in air.
best to put new ones on anyway they are about 5 .00 each. Next replace the fuel injectors .
and inspect the fuel filter for plugging

dprantl

Leaking injectors is not a myth. If you have ever experienced the sound of an intake blowing off (usually denting the hood in the process) due to fuel leaked into the manifold from injectors, you will think otherwise.

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

jcorenman

So that's a definite "yes" or "no" on the DMM?

A leaking check-valve at the fuel pump would cause pressure to leak down quickly when the engine was shut off. That would not cause an overly-rich hot-start problem however. A leaky injector would also cause a pressure leakdown with engine off, but only into one cylinder-- which could probably be identified by pulling the plugs after it failed to hot-start.

No, the '87 was the first year for the LH2.3 / EZK combo. The MAF determines airflow (corrected for temperature) and the temp-II sensor on the water-bridge tells the LH (and EZK) how to fiddle things for cold start-up (i.e. add more fuel at colder temps by making the injector pulses longer).

The Temp-II is a dual sensor, one wire for the LH and a second for the EZK. The attachment to the (freshly powder-coated) water bridge is also the ground connection for both sensors. ...