[s-cars] Hot Start: Episode III, Revenge of the Sbitch (longish)

Tue Jun 12 00:00:47 EDT 2007

Paul,

Regarding the engine running too rich, I always play with the gas pedal when
an engine doesn't start right away, an old habit I kept from my old
carburated cars, and it doesn't help. Beside, if the engine was not starting
from a too rich air/fuel mixture, I would have a heavy gas smell exhaust
after cranking the engine for several seconds, like 10-15 sec, which is not
the case.

There's something additional I realised today: When I stopped the hot
engine, it will restart in the next 5-10sec but won't restart if I wait 5
minutes. This, AFAIK, would rule out any electrical problem but kind of
confirm my vaporizing ethanol theory.

I checked ethanol vapor pressure and it reach 40psi at 105C and 58psi at
118C. With the fuel filter being heat soaked by the turbo below it, I
suspect the problem has to do with the fuel pressure dropping to 40psi when
I stop the engine then slowly rising to 55 psi, probably on ethanol vapor
pressure.

Now the question is, who is the culprit for this pressure drop just after I
shut off the engine?

Vincent.

-----Message d'origine-----
De : Paul Gailus [mailto:gailus at mindspring.com] 
Envoyé : 11 juin 2007 09:20
À : Vincent Frégeac
Objet : Re: [s-cars] Hot Start: Episode III, Revenge of the Sbitch (longish)

Vincent,

It's possible that you could be running too rich, so that the engine won't
start when it's warm, but it'll start when it's cold due to the incomplete
fuel evaporation. To check this, try feathering the throttle open just a
little bit (i.e., push a little bit on the accelerator pedal) when you're
trying to start it with a warm engine. If this helps, then you might be
getting too rich of a fuel mixture from a bad coolant temperature sensor or
some other reason.

If this doesn't help, you might want to verify that you're getting
electrical pulses at the fuel injector connectors when the engine is warm. A
"Noid light" tester such as the one listed below can be hooked to one of the
injector connectors to verify that you're getting pulses.

http://www.sjdiscounttools.com/ta36330.html

If you're getting pulses on the injectors, then the next thing to check is
the ignition. If you have a cheap analog Volt-Ohm-Meter (VOM) with a
mechanical meter movement, you can check the signals on the input side of
the POS (Power Output Stage) that come from the ECU. Backprobe the connector
with the red positive lead of the meter, and then ground the black lead to
the chassis. Start with a higher voltage scale like 10 volts, and see if you
can get the needle to wiggle when turning the engine over with the starter.
Keep turning the meter range down to a more sensitive setting (lower
voltage) till you get the needle to wiggle. You might try this first on a
cold engine with the injector connectors pulled off (so the engine doesn't
start and begin to run), just to verify that you can detect the pulses at
the POS input when the engine is being turned over by the starter.

Regards,
Paul

-----Original Message-----
>From: Vincent Frégeac <s.sikss at gmail.com>
>Sent: Jun 9, 2007 6:31 PM
>To: "'S-Car-List at Audifans.Com'" <s-car-list at audifans.com>
>Subject: [s-cars] Hot Start: Episode III, Revenge of the Sbitch 
>(longish)
>
>Summary of the last episodes
>The Patient: A '96 S-Bitch
>The Symptoms: Do not start with warm engine, idle has a hard time to 
>keep up load (A/C or power steering).
>The cure so far: New CPS, ISV marinated one night in carb cleaner then 
>pressure cleaned.
>The results: None, as you cold expect from an S-Bitch.
>
>After waiting 6 weeks to finally get my fuel tester on the third 
>shipment attempt, I was able to diagnose the fuel system, expecting 
>that the tester will be worth the wait. In a way, yes. It's an Equuus 
>Pro Series Fuel Injection Tester I got for 40$ on eBay and the nice 
>feature is it includes a
>12x1.5 banjo bolt adapter that fit perfectly on the front of the fuel 
>filter, so no need for a home made adapter. Air box removal help a lot 
>for the installation but can be reinstalled once the fuel pressure 
>tester is in place.
>
>Once installed, I run the tests as per Bentley using a half-fuse for 
>VAG
>1348/3 A remote control, first on a cold engine:
>- Fuel pump running: 58 psi (spec 58-61psi)
>- Fuel pump stopped: 54 psi (spec 49-55psi)
>- After 10 min.: 52 psi (spec no more than 7 psi drop)
>- After 60 min.: 45 psi (no spec, I just run out of cigarettes. Yes, I
know:
>gas+cigarettes=BOOM)
>Then I warmed up the engine until coolant and oil reach 90C and re-run 
>the
>tests:
>- Fuel pump running: 57 psi (spec 58-61psi)
>- Fuel pump stopped: 55 psi (spec 49-55psi)
>- After 10 min.: 55 psi (spec no more than 7 psi drop) The I runned a 
>flow test:
>- 470ml @ 12.45V;15 sec. (spec 700ml at 12.45V;15sec.)
>
>So the check valve works even better when the engine is hot (with no 
>reason as it's a bit far from the engine) and the FPR does its job 
>perfectly. The fuel pump is on the low side but this should affect high 
>rpms, not the start.
>
>Then I run a few non-Bentley test. I replugged the fuse 17 and tried to 
>start the engine to make sure it was in no-start condition. And it was, 
>pressure was at 57 psi but no start. First, I poured water from the 
>fridge
>(3-4C) on the fuel rail because I'm still suspecting some vapor problem 
>due to the 10% ethanol we have in summer gas. The pressure drop to 40 
>psi. Some more water on the fuel filter made it drop to 25 psi. Then, 
>the engine start after 3-4 turns, as it does when it's cold. So, at 
>least I know the problem is related to gas temperature.
>
>With the engine idling, the pressure is steady at 55 psi. At 3-4Krpm, 
>it drop to 50psi and stay steady there. When I release the gas pedal, 
>it doesn't raise as fast as the rpm drop, so the engine fall at 
>6-700rpm where the pressure rise above 55 psi then it surge as usual 
>after an rpm drop below 700rpm. The most noticeable phenomena happens when
I stop the engine.
>The pressure fall at 40psi the rise slowly to 55psi in 30-45sec. I 
>suspect the pressure is rising on vapor as the fuel pump is stopped at this
time.
>
>But, at the end, I still have the same conclusions:
>- FPR is OK.
>- Check valve is OK.
>- Fuel pump is on the low side but has no problem keeping up with the 
>2-300rpm of the starter as expected.
>So what?
>
>I know I could go the dealer way, replace every fuel related part until 
>it works but I already tried this way on a few other problems and each 
>time it just lightened the wallet without any improbvement of the patient
condition.
>
>So, if you had the courage and perseverance to read so far, any idea of 
>a logic-backed solution with these numbers?
>
>TIA,
>
>
>
>
>
>
>Vincent.
>'96 S-Bitch silent when hot
>'81 Fiat Spider noisy whatever the temp but at least running
>
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>
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