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98 chevy k2500 5.7l hesitates when gas pressed

Mikeflach91

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Mikeflach91 Enthusiast

Mikeflach91

Posted
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Every time it gets hot outside my truck hesitate after stopping at a stop light and has little get up and go when I press the gas petal. I have replaced fuel pump a year ago. I replaced plugs and wires 15,000 miles ago. I replaced fuel injectors to the upgraded mfi about 3 months ago.I have no idea what it could be. Any help would be great thanks!

ifixedit Enthusiast

ifixedit

Posted
Posted

When it gets warm out (and the engine is warm), if it is losing power in these conditions, to me anyways would indicate the fuel mixture is likely going very lean for some reason. Regardless of whether it's warm outside or not, how does the truck run before the engine comes up to full operating temp? Usually the way it works is an overly rich condition will improve as the engine comes up to temp, a lean initial mixture may seem fine until the engine gets hot, then just gets worse.

Mikeflach91 Enthusiast

Mikeflach91

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I guess it makes sense that when it's cold out the engine takes longer to warm up so it seems to run better. When it's hot out it seems almost instant that it starts to hesitate with the engine hardly warmed up. So yes it does seem to run better before it warms up and starts to hesitate once it gets warmed up. And ideas what could cause the fuel mixture to become lean?

ifixedit Enthusiast

ifixedit

Posted
Posted

I'm not an EFI expert, but you mention doing some upgrades to the injectors, etc. My only guess would be that there's now a fuel mapping / calibration issue. Unless the EFI system is 'self learning' which the available aftermarket ones are (and I don't think yours would be), then your computer likely needs to be tuned for your current set-up, something only a competent shop with the equipment and knowledge can do.

 

Did this problem occur prior to the upgrades as well or just after you did them?

1997SierraSLT Enthusiast

1997SierraSLT

Posted
Posted

because the CSFI system was such a crappy design utilizing the poppet valves that would gum up and get stuck, GM came out with the MFI retrofit unit which bolts right into place where the injector is located directly at each cyclinder intake. Both types still utilize a central "spider" with plastic tubes however.

ifixedit Enthusiast

ifixedit

Posted
Posted

because the CSFI system was such a crappy design utilizing the poppet valves that would gum up and get stuck, GM came out with the MFI retrofit unit which bolts right into place where the injector is located directly at each cyclinder intake. Both types still utilize a central "spider" with plastic tubes however.

 

Is the retrofit MFI supposedly plug and play or is does the computer need to be re-flashed as well?

Mikeflach91 Enthusiast

Mikeflach91

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The problems were happening before I switched the injectors, I was hoping it would fix the problem. It does run a bit better though. Some people told me to try changing the oxygen sensors and if that doesn't work then the catalytic converters. Any thoughts? Besides that I'm at a complete loss and have no idea what could cause this.

ifixedit Enthusiast

ifixedit

Posted
Posted

If it was doing this before, it certainly sounds like the converter(s) could be plugged. It is a 1998 truck and depending on miles and the use it's seen I could believe the lack of power is due to a bad converter and would indicate excessive back pressure in the exhaust, the condition would likely get worse as it warms up as well. I've read elsewhere if you bang on the converter with a rubber mallet and if you hear rattling, the structure inside the converter is likely collapsed rendering it junk which would plug it up good. I'd probably be eyeballing the converter as the main culprit next. You might find this useful >> http://www.aa1car.com/library/exhaust_backpressure.htm

 

If you take it out on the road and floor it, if it's slow to rev or just doesn't want to rev, I'd say it's pretty much guaranteed the converter is plugged.

Mikeflach91 Enthusiast

Mikeflach91

Posted
  • Author
Posted

Thanks ifixedit. I will try and look for a pressure reader for my exhaust and also I will try a rubber mallet. Hopefully I can get this issue fixed. While driving it yesterday I notices out of 5 stop lights it hesitated 3 times.

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