97 CHEVY S10 P/U GIVES ME LEAN FUEL WHEN WARMED UP

  • Tiny
  • twd22285
  • 1997 Chevrolet S-10
  • 6 CYL
  • 4WD
  • automatic
  • 128,000 miles

Ok, here it goes.. A little backround first: fuel pump is a yr old, changed out fuel pressure regulator, fuel filter, and all spark plugs, fixed vacuum leak, fuel pressure gauge reads 55 psi when running. When I first start it up it runs fine when its cold, not a sign of problems. After about ten minutes it starts to act as if its not getting fuel, step on gas and nothing happens. It wants to die. Check engine comes on and reads p071, running lean on fuel. When its having trouble fuel pressure will drop when I step on the gas but after I let off gas it goes right back up to good pressure. That tells me fuel pump is good. Where I get confused is why does it run fine when cold and it takes a while to start having trouble. What would cause this? I'm 600 dollars deep and still have no solution. Please help! Thank you in advance

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Thursday, March 17th, 2011 AT 5:16 AM

9 Replies

  • Tiny
  • mhpautos
  • Expert
  • 30,591 posts

Air flow meter tell the ECU how much fuel to supply for correct ratio, could be a problem here or a map sensor if fitted, check this out first, most Air flow meters can be cleaned this may be an option.

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Thursday, March 17th, 2011 AT 6:35 AM
  • Tiny
  • twd22285
  • Member

What would cause it to run poorly the longer it runs? Would air flow meter, map sensor respond differently the longer the vehicle runs? Do you think there is any way this is catalytic convertor?

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Thursday, March 17th, 2011 AT 3:09 PM
  • Tiny
  • hmac300
  • Expert
  • 44,378 posts

If it's a catylitic converter you should have low vacuum at idle. Also if you have one of thoseperformance air filters like K&N put the old system back on and see if it cures it. Alot of times it does.

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Thursday, March 17th, 2011 AT 8:47 PM
  • Tiny
  • twd22285
  • Member

I'm back :( well i've changed out the throttle body positioning sensor, map sensor tests out at 5 volts, and replaced air flow meter. Still same issues. Could this be a engine control computer thats bad?

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Monday, March 21st, 2011 AT 7:49 PM
  • Tiny
  • twd22285
  • Member

Oh and you were right hmac300, was not catalytic convetor

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Monday, March 21st, 2011 AT 7:51 PM
  • Tiny
  • hmac300
  • Expert
  • 44,378 posts

If you haven't had the codes read then you are doing stuff blind. What is your fuel pressure? It shold be 41-47 psi, if it's lower than thatthen tha may be your problem. If you aren't getting the proper amount to the injectors it will leanout. This could also include your fuel filter. Or a vacuum leak.

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Monday, March 21st, 2011 AT 10:51 PM
  • Tiny
  • twd22285
  • Member

Well I did have the codes read. Thats how I know its lean on fuel. Changed out fuel filter (first thing I did), replaced two gaskets that created small vacuum leaks, haven't been able to find any other vacuum leaks. At this point i'm asking anyone if a bad engine control computer could do this. Thank you in advance

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Tuesday, March 22nd, 2011 AT 12:09 AM
  • Tiny
  • twd22285
  • Member

Oh and I bought a fuel pressure gauge and its at 55 pounds

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Tuesday, March 22nd, 2011 AT 12:10 AM
  • Tiny
  • hmac300
  • Expert
  • 44,378 posts

It could be the ecu but I also asked if you had a filter like a K&N or performance type filters as they can cause you grief and set some of these codes. I'd check for a bad connection or similar before I would go to the ecu. Also checkfor bad grounds first. Roule out all other things before the ecu.

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Tuesday, March 22nd, 2011 AT 12:14 AM

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