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

[Jerry Scott]

The vaporizing alcohol in the fuel rail may be causing a vapor lock.   
How about draining off the rail pressure before trying to start when it 
is hot. Don't know how you would safely do this, but maybe at the banjo 
to rail fitting.  Be very careful with the spilled fuel around a hot 
engine.  See how long it takes to build pressure back to 57 psi.on the 
next start.  Alcohol boils at a very low temperature, so the hot rail 
may be causing the vapor lock.  Try insulating the rail so that it does 
not get radiant heat from the engine. 
Just an idea.
Jerry

Vincent Frégeac wrote:

>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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