1999 GMC Suburban Hard Start Cold Only

Tiny
MADMOOSE
  • MEMBER
  • 1999 GMC SUBURBAN
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 214,000 MILES
I have an odd starting problem - it takes 3-5 attempts to start my Suburban in the morning (more on colder days), runs rough for about 5 seconds then smooths right out. However, it starts just fine the rest of the day, even if its cold. It appears to be starving, as adding starting fluid lets it fire right up the first time. Once it runs there is no lack of power, rough idle, poor acceleration - it runs great. At no time does the Check Engine light come on indicating a code has been thrown. Also, my fuel pump was replaced about 11 months ago.

Things I have done: new plugs, wires, rotor, cap, air cleaner, O2 sensors. Pulled upper intake manifold (plenum), replaced CSFI fuel regulator, pressurized system and checked for injector tube or other leaks - all good.

My manual and everything I read online says that when checking fuel pump pressure at the fuel rail, you should have 60-66 psi when the pump is running, cranking should be 50-57 psi or it won't start, running should be a minimum of 55, and after the car is off it should hold 45 or better for 5 minutes. If it drops to 0 within 15 seconds, you have a leak under the plenum or in the fuel line. If it doesn't have at least 50psi, the pump is bad.

Here's the thing - my symptoms are right in the middle of all this information. When the pump is running, I only get 54-58 psi. Cranking, I only get 44 psi (which according to everything means it won't start but mine does), and then while running I DO get the recommended minimum of 55 psi. After it is off, it doesn't drop to zero within 15 seconds (indicating a leak), but it doesn't hold above 45 psi for 5 minutes, either. I get: 48 psi after 1 minute, 40 after 2 min, 36 after 3 min, 33 after 4 min. And 32 psi after 5 minutes.

Since the fuel pump is fairly new, I hate to replace it again just to find the issue was with something else. Do you have any ideas of what else might cause these peculiar cold hard start symptoms?

Thanks for your help!
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Tuesday, January 13th, 2015 AT 12:00 PM

3 Replies

Tiny
HMAC300
  • EXPERT
Some of these pumps that are on the market are for crap airtex being one. You should get 60-66 psi with key on engine not running. If not it s' a fuel problem which yours certainly sounds like. If replacing pump filter should have been replaced as well you can check for blockage on return line or blocked intake line. It should hold with in 10 psi for 5 minutes. Also when you replaced the new pump there should have been a harness that came with it to replace as it should take a different connector and about a foot of harness all of that should have been replaced. As the harnesses at the end and connectors were bad
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Tuesday, January 13th, 2015 AT 12:11 PM
Tiny
MADMOOSE
  • MEMBER
Yes, I did replace the harness and filter, and even changed the filter again just recently to make sure something didn't get lodged in it.

So, to be clear, you don't think there's anything else I should try first, just get a better pump and install, correct?
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Tuesday, January 13th, 2015 AT 12:30 PM
Tiny
HMAC300
  • EXPERT
I don't know what kind you put in but delco seems to do ok and check the sock on pump if it wasn't replaced. Also scan for codes and take crank sensor out and seeif there is a lot of gunk on it if there is clean it off and see if it does anything also clean the throttle plate on both sides. Do the easy stuff first and see ifit clears it up. Use choke cleaner for throttle plate then check for a vacuum leak with same.
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Tuesday, January 13th, 2015 AT 1:39 PM

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