Hard to start and runs rough when cold?

DANNYG

MEMBER
1990 CHEVROLET TRUCK
V8
2WD
AUTOMATIC
235,000 MILES

I have a 1990, 2500 series chevy truck with a 350. Check engine light came on. Next morning hard to start and runs rough when cold (Its been in the 30-40 in Chicago at night). Truck runs great after it's warm. No trouble starting the remainder of the day. We had a few warmer nights (50s) and it started much better but still not right,

Sound like a sensor to me but if you had to guess what would you try first. I hate to drop 85 bucks on a scan unless neccesary.

Thanks,

Dan

1 Reply

SQM

MECHANIC
6,383 POSTS

Hello,

It sounds like you might have a faulty fuel pressure regulator.
Over time the diaphragm inside of the regulator can become stiff and prevent proper fuel flow when cold. But as the engine or ambient temperature warms up it will work as designed.
You can do a fuel pressure test first thing in the morning to see what is the output. If it is low when cold but goes to normal range when warm then it is a bad regulator.
This vehicle should have 9-13 PSI of fuel pressure with the key On and engine Off.
You can rent the fuel pressure test gauge from your local auto parts store.

Here is a helpful video on how to check fuel pressure:

https://youtu.be/aITQclp7zIE

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

I have attached diagrams for your reference.

Please let me know of any questions.
Thank you.

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