Riddle me this 92 Cabby won't run after start

[Briano1234]

Ok, I have to air This out.

My 92 Green Cabby has an issue:

The car when cold starts fine and runs like a champ.
Turn it off, and restart it after 3-4 minutes no problems.
Turn it off and wait 20 minutes, and it will start, you hear the pumps prime.
When it starts it runs for about 10 seconds great, then starts bogging down, and dies
it is like getting flooded. If you give it gas it will try but continue to bog down till dead.

Now if you start it 3 more times it runs like a champ.
If you wait for an hour, it starts and runs like a champ.

What I have done.
Replaced Gas Cap (Yeppers Some one stole it again So I got the Famous Stant Locking cap.)
Replaced the in-tank pump (it was noisy).
Replaced the Fuel Pump relay
Replaced the CTS and o2 Sensor
Checked timing it was right at 6 BTDC (dropped timing light and broke it right after...)
Plugs are Great no fouling white ashy colored.

The ISV wires were broke, and I fixed those about 3-4 weeks ago, and issue wasn't present.

Only thing that was different between repairs was my crappy broken 5-Star gas cap, which I replaced, and a fresh tank of QT gas.
The fuel tank has pressure, and both gas lines were replaced about 2 months ago.

I am leaning to a leaky injector, main pump (Changed it with my spare, and my spare leaked all the fuel out the case joint) or the FPR, but decided to give yall a go.

[Calimus]

Shot in the dark here, but I've read about the coolant temp sensor causing issues like this on early MKIV's. Basically it throws wild readings causing the ecu to go lean or super rich. I don't know enough about DigiII to say that this could be a factor.

[Briano1234]

Changed it already.
Checked for Vacuum leaks none detected.

[gull]

I forget, is this a CIS car or a Digi car?

[Briano1234]

DIGI..............

[gull]

Right, guess I should have guessed that when you mentioned the ISV.

[Briano1234]

Well since I have to watch a 4yr old I am limited in my troubleshooting but today I did measure the
Fuel pressures to eliminate the main pump and to check for a leaky injector.

Spark Plugs have a nice knock your privates in the Dirt Arc. It bridged a 1/2 inch gap and was a cool blue/white.


My fuel pressure gauge is in 5lb/psi increments, but I was also watching the KG/cm2.

45psi at idle.
55psi at no vacuum hose attached
Bleed off was non-existant if then it was less than 1/2 needle at 10 minutes.

Testing the bleed off pinched return line.
45psi at idle
after 10 minutes no drop at all it actually increased to 50psi, so that basically sums up that the FPR is Deceased.

Fortunately I have a spare...

As I was really considering the Single pump conversion, as 50 bucks is easier to choke on than damn near 300.

[Calimus]

Odd that it was the FPR, those don't generally crap out from what I've seen. As long as a swap out does the trick, thats good news. But for it to be intermitten is whats bugging me. It's a vac controled unit in the Digi-II if memory serves, so if it has a tear in the diaphram you would think it would cause problems the entire time.

Keep us posted, I'm still scratching my head a bit.

[Briano1234]

Odd that it was the FPR, those don't generally crap out from what I've seen. As long as a swap out does the trick, that's good news. But for it to be intermittent is whats bugging me. It's a vac controlled unit in the Digi-II if memory serves, so if it has a tear in the diaphragm you would think it would cause problems the entire time.

Keep us posted, I'm still scratching my head a bit.

Has me going too, the Bentley states that if there isn't a bleed off when pinched it is bad. Yes it is Vacuumed controlled, and you remove the vacuum it jumps 10psi? I can see that as there is nothing to
pull the diaphragm to the engine speed.

Too much pressure on a warm engine I guess would tend to flood it more easily as the volume is there but at the increased pressure of the fuel rail more gas can flow through the injector flooding it? Or is it causing a decrease in fuel after start because internally it has failed somehow... beats the dog snot outta me.

I am assuming that since it takes a bloody long time to bleed that there is a problem with the valve internally, to it. I mean it is almost 20 years old.... So parts are gonna crap out...

[Briano1234]

It was the Fuel Pressure Regulator, who'da thunked that one.

I installed the new one, drove it about to get it up to temp and simulate the drive to "Tar Jay" Waited 20 minutes, and presto it fired right up, and ran great no stumble.

I drove it about a bit got it up to temp, waited the 20 minutes and presto if it didn't work good again.....

[Calimus]

Good deal Brian. An yea, your inscription would make sense. Glad it was a nice simple fix.