Engine backfires and sputters when floored

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HotWheelsBurban

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When was the fuel filter last changed? Most fuel pump warranties require that you replace the filter when you replace the pump. One of the things I have to do to the Burb yet....
 

SUBURBAN5

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I had this issue before on my vortec. New ac delco fuel pump less then a year old. Turn out the sock in the pump was clogged. I agree with the others. Throw a guage on it and stomp it. You may see the fuel pressure drop down drastically until you let off the gas. I would of never thought that at the time.....
 

Komet

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When was the fuel filter last changed? Most fuel pump warranties require that you replace the filter when you replace the pump. One of the things I have to do to the Burb yet....
Gotta do it, clean fuel going to the injectors is very important. They come out pretty easy, last one I did didn't even spill much fuel. I won't tell you it takes ten minutes because it takes ten minutes for me to get under a car with wrenches in my hand, but honestly if you booked an hour of your time, you'd probably be able to wrap it up in less than that.
 

HotWheelsBurban

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Gotta do it, clean fuel going to the injectors is very important. They come out pretty easy, last one I did didn't even spill much fuel. I won't tell you it takes ten minutes because it takes ten minutes for me to get under a car with wrenches in my hand, but honestly if you booked an hour of your time, you'd probably be able to wrap it up in less than that.
Yup I just gotta get to the shop, get the jack out from behind the junk that got put in front of it, etc.... I can do the filter on the one ton by sliding under it, but the Burb is too low with the running boards.
 

Schurkey

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Yes, fuel pressure test, preferably WHILE THE VEHICLE IS ACTING UP. A less-effective but still reasonable "cheat" is to use the bypass button included with most fuel pressure testers, so that fuel flows down the cheap-junk vinyl tube into a drainpan while the engine is running. Simulates increased fuel demand by the engine.

Also, as usual, verify ALL the sensors and computer outputs by connecting a scan tool. In particular, assure that the TPS and MAP sensors are working properly. Wouldn't surprise me to find that a heavy-throttle misfire is caused by a failed TPS that doesn't transmit a proper signal at large throttle openings.

How old are the usual "tune-up" items? Distributor cap 'n' rotor, plug wires, spark plugs, PCV, and ignition timing/timing advance checks, fuel and air filters, etc. Pretty common for weak ignition systems to run OK at low- and mid-throttle, and fall on their face when voltage demand goes up due to higher cylinder pressure when the engine is working harder.
 

greenz97

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Yes, fuel pressure test, preferably WHILE THE VEHICLE IS ACTING UP. A less-effective but still reasonable "cheat" is to use the bypass button included with most fuel pressure testers, so that fuel flows down the cheap-junk vinyl tube into a drainpan while the engine is running. Simulates increased fuel demand by the engine.

Also, as usual, verify ALL the sensors and computer outputs by connecting a scan tool. In particular, assure that the TPS and MAP sensors are working properly. Wouldn't surprise me to find that a heavy-throttle misfire is caused by a failed TPS that doesn't transmit a proper signal at large throttle openings.

How old are the usual "tune-up" items? Distributor cap 'n' rotor, plug wires, spark plugs, PCV, and ignition timing/timing advance checks, fuel and air filters, etc. Pretty common for weak ignition systems to run OK at low- and mid-throttle, and fall on their face when voltage demand goes up due to higher cylinder pressure when the engine is working harder.
The cap and rotor are less than a month old spark plugs are 30k miles or so old pcv is clear timing I have not checked new fuel filter and pump, air filter is clean.

Basically all this tells me that it's probably in the fuel but I need to get my hands on a pressure tester and go through the full shop procedure. Do you agree with that statement?
 

Schurkey

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Basically all this tells me that it's probably in the fuel but I need to get my hands on a pressure tester and go through the full shop procedure. Do you agree with that statement?
You should check fuel pressure. That part I agree with. This certainly could be a fuel pressure/injector issue.

I don't think you have evidence that it's a fuel problem vs. ignition problem. As said, this could be a faulty coil (or other cause of weak ignition), similarly it could be a failed TPS, failed MAP sensor, or some other computer problem. 30K isn't high-mileage any more; it used to be in the era before O2 sensors, and especially before unleaded gasoline. Still, it'd be worthwhile to pull a few and see what they look like.

Since you say it runs good at idle and part-throttle, it's probably not a mis-timed camshaft or low compression.
 

PlayingWithTBI

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Since you say it runs good at idle and part-throttle, it's probably not a mis-timed camshaft or low compression.
See post #11, at 1st he said only at WOT, then later said it stalls at idle too. It's pretty hard to diagnose when you don't get the full story. :33:
 
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