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1990 Chevy S10 fuel pump

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New User

Mar 31, 2012, 8:49 PM

Post #1 of 8 (2829 views)
1990 Chevy S10 fuel pump Sign In

1990 Chevy S10 pickup 4.3V6 170K miles automatic. Truck was running fine. Had a mechanic install a new fuel pump, fuel pump relay, tank strainer, and in-line fuel filter a week ago as a preventative measure because of age and milage. Mechanic used all NAPA parts.
Problem: engine will not crank in afternoon without manually pouring gas into trottle body.

Info: Trucks sits at night at work for 13 hours and cranks fine in morning. Truck sits at home 10 hours during day and will not crank in afternoon without adding gas.

What I've done: Replaced new fuel relay with another new fuel relay. Have inspected, cleaned, and performed continuity tests on all wiring connectors (except the actual connection at the pump). Checked continuity of applicable fuses. Have performed all diagnostic tests per a Haynes manual. They indicate an open in the circuit between relay and pump. I believe the problem to be either a defective new fuel pump or the wiring connection at the pump is bad. Mechanic is not sure but will take truck back and trouble shoot problem.

Wanted to get you guys opinion/advice before preceding further. Thanks, FredM

Tom Greenleaf
Ultimate Carjunky / Moderator

Mar 31, 2012, 8:57 PM

Post #2 of 8 (2825 views)
Re: 1990 Chevy S10 fuel pump [In reply to] Sign In

Let you mechanic trouble shoot this but know that there are plenty of defective new parts. Seems by your description that the fuel pump just is pumping borderline pressure. Stinks to pay more but with those one from GM - OE seem to do the best,

Long retired now

Hammer Time
Ultimate Carjunky / Moderator

Mar 31, 2012, 9:09 PM

Post #3 of 8 (2809 views)
Re: 1990 Chevy S10 fuel pump [In reply to] Sign In

All you can do is test the fuel pressure during this failure.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

New User

Mar 31, 2012, 9:31 PM

Post #4 of 8 (2795 views)
Re: 1990 Chevy S10 fuel pump [In reply to] Sign In

Thanks for the reply. I agree about the GM parts. NAPA was $40 for the pump and Chevy dealer was $78 for AC/Delco. At my age, it's not the money but avoiding aggravation as much as possible. Only reason I let mechanic use NAPA was that he was adament about using their parts. Wish I had insisted on the AC/Delco.

Tom Greenleaf
Ultimate Carjunky / Moderator

Mar 31, 2012, 11:07 PM

Post #5 of 8 (2772 views)
Re: 1990 Chevy S10 fuel pump [In reply to] Sign In

I have had great luck with parts from NAPA but have noticed in this dog-eat-dog world that some stuff has lost some quality to lower prices or lose market share. Still unknown if this is the whole trouble but not unheard of as said,

Long retired now

New User

Apr 3, 2012, 12:19 PM

Post #6 of 8 (2702 views)
Re: 1990 Chevy S10 fuel pump [In reply to] Sign In

To All:
This info is per the mechanic.
The sending unit in the tank that the pump mounts to was bad. It was causing the pump voltage supply to be 11.6V instead of the 12V required.
He said it could have happened due to its age or simply from being jostled around while replacing the pump. I haven't gotten the truck back yet, just a phone call, but I am assuming at this time that he is correct.
(For info, because the "new" NAPA pump has been apparently trying to operate at low voltage and that I simply don't like NAPA, I got the new ACDelco pump from Chevy and told him to install that while the tank is out!)

Tom Greenleaf
Ultimate Carjunky / Moderator

Apr 3, 2012, 12:49 PM

Post #7 of 8 (2697 views)
Re: 1990 Chevy S10 fuel pump [In reply to] Sign In

Not sure 11.6 would be the total problem but your mechanic seems to have found the trouble there. Whole unit from GM has the least troubles so far to me and said by others here all over the place. No bargains in doing something twice to save a buck as we know,

Long retired now

Veteran / Moderator

Apr 3, 2012, 5:06 PM

Post #8 of 8 (2687 views)
Re: 1990 Chevy S10 fuel pump [In reply to] Sign In

They did have problems with the electrical pass thru terminals on the top of the sender melting causing high resistance in the pump circuit.

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

1990 Chevy S10 fuel pump

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