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low fuel pressure: causes? 01 Sub.

mike g 09

By mike g 09
in Ask A GM Technician

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mike g 09 Enthusiast

mike g 09

Posted
Posted

OK. Having problems with starting when it is below zero degrees F outside. A brief history:

 

2001 Suburban. 5.3 liter 150,000 miles. Bought in '08. Ran fine, but would not start at -20 F (would turn over fine). Same problem occurred in winters of '08 '09 and 10 - then fuel pump died altogether.

 

Replaced fuel pump, filter, and fuel pump wiring plugs in Dec 2010. With new Airtex pump in place, it ran fine, except still would not start when temps were <-10 degress F. Replaced FPR. Note: used previous FPR's small o-ring,due to losing new FPR's small o-ring. Swapped FP relay with adjacent (identical) relay in fuse block. Removed grounding lug near fuel filler neck: scraped off undercoating to bare metal, and re-tightened.

 

This problem is still occurring. When it was about -5 degrees F a few weeks ago, I noted the following:

 

- key cycled 4-5 times, no start.

-Tested pressure, KOEO: spiked to 55 for just an instant, then fell.

-cycled key 2-3 more times, engine started.

-pressure, engine running: 50

-pressure, vac hose pulled on FPR: 58

 

I have pulled the vac hose on the FPR to boost pressures for starting, and sometimes that does the trick.

 

This morning, at -12, the FPR vac hose trick didn't work. I could hear the fuel pump running, but it sounded weaker to my ear.

 

I haven't had any problems with the new pump, except for the really cold start issue.

 

Being that I had a very similar problem with the old pump, I thought maybe the problem was outside the fuel pump (and, I didn't really want to drop the tank...) I called Airtex Tech support, and they suggested the FPR, but then also the ground connection. They also suggested I do a voltage drop test. They suspected that the cold temps resulted in either a bad connection or increased resistance in the wiring, thus lowering voltage at the pump.

 

1. Is it likely to be a supply voltage problem?

 

2. How can I perform a voltage drop test without dropping the tank?

 

3. Is it possible I have a voltage drop occuring at or near the relay? How to check this, as the relay contacts aren't readily accessible to a probe?

 

4. Anyone seen this before? Other possibilities?

 

Many thanks!

Coolmaker Enthusiast

Coolmaker

Posted
Posted

Just had a 2000 GMC Sarari do this to me. Turns out that the starter was turning to slow and taking the voltage way down. Replaced the starter (original) and the three year old battery. Now she spins like a new one and starts instantly.. ;)

 

take a volt meter and check it while the starter is spinning...

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