98 5.7 starting problems

[demps101]

I've got a 98 tahoe with a 5.7. Having some starting issues but runs great once its finally starts. I just did a complete tune up plugs, wires, cap, rotor, coil, icm, fuel pump and filter. All A/C delco parts. The vats system has been disabled in the pcm with a tune. After sitting all night I have to use starting fluid to get it to start but then it starts fine on its own after that. I havn't been throwing parts at it tho. The fuel pump had been getting loud and the tune up was just planned maintenance. Now when this all started I was pretty positive about it being thats vats system. It would try and start for a second or 2 then go back to just cranking. I could see on my scanner that it was shutting the injectors down which is typical of the that stupid security system. Now I'm running out of ideas. Any help would greatly appreciated.

 

[Schurkey]

What is the fuel pressure during the 2-second "prime"?
What is the fuel pressure when running?
What is the fuel pressure if you push the button on the side of the pressure gauge, to flow fuel down the hose simulating high-fuel-demand?

 

[demps101]

At shraeder valve 62 while cranking. Key on before cranking no pressure i could read. Thats using the scope on my scanner.
I dont have a gasser set up for fuel injection. I'm a diesel mechanic so most of what i"ve got is for those.

 

[demps101]

I'm gonna grab a gasser set up tomorrow. what numbers should i be lookin for?

 

[Schurkey]

Key on before cranking no pressure i could read.

MOST importantly, you need 60-ish psi during the 2-second "prime" when the key is turned from "Off" to "Run".

No prime = failed fuel pump relay system which could be the relay itself, or it could be the wire harness or the PCM = long cranking because the engine has to crank long enough to build oil pressure before the fuel pump will build pressure. No fuel--no starting.

After that, the service manual will have the test pressures. I don't remember what they should be except it's around 60 psi. The old poppet-style injectors are more sensitive to that than the upgraded electronic injectors.

 

[demps101]

Thanx. I'll Have to check that tomorrow evening and sunday. Appriecate your help

 

[east302]

Here is the procedure from the 1998 manual. PDFs of the manual can be downloaded here:

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

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[east302]

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[demps101]

Thanks for the manuals. I gotta find sometime this week to try and get some of this testing done. Its drivin me nuts!

 

[demps101]

Well shes up runnin good again! Wanna say thanks for all the help. After all the testing narrowed it down to the regulator or an injector. So i t replaced the cpfi with updated mpfi set up. After getting the cpfi injectors out 2 of them had broken poppets. Thats what was causing the pressure problem on cold starts. Once again thanks for all the help