GM Techs: 1995 G30 Hard Start Issues

5.7 TBI engine 105k miles with hard cold start issues that started last week. Requires much more cranking time after sitting overnight/few days than usual. Van is generally driven 2-3 times a week and taken on longer trips (500 mi.) every two weeks. Hot starts seem fine, drives down the road fine. This morning the CEL came on. Have not had a chance to have it plugged in at the auto parts store, but wanted to get some ideas before I head there later today. Thanks in advance.

 

Umbrella valve in fuel pump bad causing fuel pressure in the line to drop?

 

FYI, auto smarts store likely won't be able to pull codes.

'95 is pre-ODB-II.

 

Yeah. Might have to buy a cheapo scanner. Although I thought they could still pull OBD I?

 

Cheapo scanner won't do it either. You're talking big bucks for a scanner that will pull ODB-I codes.

 

Shit's never easy. Or cheap.

 

Be a shit-ton easier if it was a '96.

 

I forget how, but I think theres a way you can get flash codes on the old OBD.

 

Nah, it's a one ton....

 

https://www.truckforums.com/forum/gm-how-tos-tutorials-84/obd1-codes-how-pull-code-list-13297/

 

Thank you! Awesome.

I just pulled the codes:

39: TCC Error
54: Fuel pump circuit low voltage
68: AC clutch switch
85: PROM

I am thinking fuel pump relay? I cannot hear the fuel pump run when the key is switched to the ON position.

 

There is a single 1/4" female spade connector with a red wire under the hood near the fuel pump relay. If you put 12V to that connector and the pump runs (and the engine can be started quickly) then the relay is bad.

 

This thread is a prime example of why I love the BBS.

 

Google is pretty awesome too.

 

Heart me some google solutions.

 

Thank you! I replaced the relay and saw that connector all by its lonesome there. It has never been plugged in since I've owned the van, but I always wondered.

 

That is the "fuel pump prime" and is only used for diagnosis or to run the pump independent of the ignition circuit.

Did replacing the relay fix the problem?

 

I won't know until tomorrow. Problem only seems to manifest under a cold start condition. Engine cranks until oil pressure builds, then it starts. Hot starts have not been an issue.

 

The relay is energized by the ECM for a few seconds when the key is turned on to pressurize the fuel injectors. Unfortunately there isn't an easy way to de-pressurize the TBI system on that van, so you'll have to wait until it leaks down overnight. In other words, it's not a "cold start" problem as much as it is a "starting from zero fuel pressure" problem.

The relay and the oil pressure switch are in parallel, so if either one closes the fuel pump runs.

You can also put a 12V test light or meter on the prime connector to verify when the pump is being energized.