dm3k

So my 88 5.7 is showing the classic signs of a bad cold start valve. It cranks and starts but then dies right away. If you do this 3 or 4 times it will stay running and run great until I let it sit again for a few days. Fuel pressure is perfect. Anyways I'm doing the cold start valve circuit test from my service manual and it states: "If cold start valve is functioning properly the fuel pressure should drop more than 3psi." Any one know how much it should drop? Mine drops exactly 3 psi. That's pretty close. Which way would you swing? Thanks. cold start.pdf

paulo57509

Have you followed the flow chart for both "OK" and "NOT OK" after you performed the pressure drop test?

I doubt it's the cold start injector. The injector only operates with the key in the start position (and the coolant below 95F). Your engine starts but then dies; by this time, the you've released the key and it is now in the run position, yes?

Try this: Connect your fuel pressure gauge, start the engine and let it run for a few minutes. Shut off the engine and note the fuel pressure. Monitor the fuel pressure for the next 30 minutes. It should hold pressure. Report the pressure drop.

dm3k

That was the 1st test I did. Fuel held steady pressure. I did go through the flow chart as if it didn't drop more than 3 psi because technically it didn't. It was just so close I was hoping to see how much of a drop they were looking for. When I say it starts it's only for about 1 or 2 seconds before it stumbles off.

Bob88GTA

iTrader: (2)

Paulo is correct^^^^
That sounds to me like a IAC/ TPS setting. Have you checked them out. Start, Stumble and die are classic syptoms of these two sensors out of adjustment or bad.
Follow this to a T

https://www.thirdgen.org/tpimod2/

Tuned Performance

iTrader: (92)

https://www.thirdgen.org/forums/tpi/...old-start.html
I'm not sure why the fsm says no pressure drop. In a 10min period you can get bleed off back through the pump. Pinching off the supply and return line then watching for a pressure drop might be a better way of testing for pressure drop.

dm3k

I've been chasing this for about 6 months. Tps and iac were actually on top of the list and the 1st tests I did. They are normal.I might still change them. I just hate "throwing parts at things" I like to know the problem. . I know a mechanic who worked on these in the late 80's and 90's at a chevy dealer. Apparently this was a common symptom to come in with. Like I said it's only on a cold start after sitting a few days. Usually After 3 tries she runs like a champ with no issues. I hope I get it. It's more of nucence than anything.

Bob88GTA

iTrader: (2)

If you know a Mechanic that worked on these in the 80's and 90's, and you got the money, buy that man lunch and have him work it! I'm not a big guy on having people work on my cars, but if he's good, go for it. MY guy passed away 10 years ago. And HE WAS GOOD!!

paulo57509

Yes. Do the test I described but pinch off the fuel supply lines to the fuel rail. This will isolate the injectors from the rest of the fuel supply system (thanks for that, TP).

I suspect you have injectors leaking into the cylinders after the engine sits for a while. Pressure should bleed off eventually but not through the injectors. Isolating the injectors will tell you if you have injector leakage. Unfortunately, it won't tell you which ones are leaking without some disassembly.

I don't recall if the FSM has a bleed off spec with un-pinched lines; the next best thing was to ask the OP if it holds pressure - OP would have reported if there was a drop in pressure within 30 minutes (I think a few psi is acceptable). IIRC, mine will hold pressure minus a couple of psi for ~30 minutes.

dm3k

The car is garaged but this gets worse in the winter when it sits out there in the cold. I don't notice as much in the summer. Maybe because it gets used a little more. But it's definitely not tps or the iac. And there is no check engine light. Newer mechanics look at this car like wtf was chevy thinking?

Tuned Performance

iTrader: (92)

You might be able to have it serviced ultrasonic/ flow tested.
Or just block it off and go with 89 programming.