Having a problem with my '99 4.6l Expy, no check engine light, but hesitation @ 45-50 mph(1500 rpms). Took it to autozone, no codes showed up on scanner. Plugs ,wires and fuel filter all new since fall '03. 90,000 miles, any ideas???? Thanks!
Possible Misfire?? No check engine light
- Thread starter Bootlegger
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There are many things that might be causing that but one that comes to my mind is the PCV valve. If you have never replaced it, at 90,000 miles the PCV valve is probably pretty gummed up, which could be causing the bogging.
I doubt it's the PCV valve. People put way too much stock in the PCV valve causing problems. If you had any kind of regular oil change schedule, it'll be clean.
Hesitation could be so many things. If it was a true misfire, your ECU would detect it and trip a code if it was actually a misfire that was bad enough to be felt as a hesitation. Perhaps starting with a can of complete fuel system cleaner would help you narrow it down. If that doesn't help, then moving on to more complex things like vacuum analysis and then having it analyzed on a scope at a repair facility would point you in the right direction.
Hesitation could be so many things. If it was a true misfire, your ECU would detect it and trip a code if it was actually a misfire that was bad enough to be felt as a hesitation. Perhaps starting with a can of complete fuel system cleaner would help you narrow it down. If that doesn't help, then moving on to more complex things like vacuum analysis and then having it analyzed on a scope at a repair facility would point you in the right direction.
Have you ever changed your fuel filter? Not everything trips a code. I would check obviuos things first like vaccum,compression,fuel pressure and volume, and take a few voltages or resistance reading at key sensors!
Nope, not on all cars all the time. Several times I have had mine stumble when I went through too high water, and had the light come on about 1/2 the time - maybe 2/3 the time but not every time. When I took it to a mechanic, yes it was misfires but not enough to trigger the light. His scanner could read the ones getting ready to trigger, and AutoZones, the ones I have been to, CAN NOT... they read only if the light is on.
A wild guess the pot in the throttle, body not sure of the proper name of the part.
Can you explain a little better? You say it does it at 45 to 50 mph. Does it do it when you push down on the gas pedal, or is it missing and chugging when you are just cruising?
If it hesitates when you push on the gas it sounds like a throttle position sensor.
If it hesitates when you push on the gas it sounds like a throttle position sensor.
Found the problem, bad plug wire #3 cylinder.Boot was damaged, Possibly didn't get it pushed down all the way when I changed the plugs.
Glad you found it. I have seen the CAP, thw mwtal thing inside the cap, EAT in two parts, caused me headaches for some time, it was not until the mechanic pulled it apart til we discovered the thing.... burned everything up in there.quote:
Originally posted by Bootlegger:
Found the problem, bad plug wire #3 cylinder.Boot was damaged, Possibly didn't get it pushed down all the way when I changed the plugs.
Are you getting new WIRES or just repair the one boot>?? What kind of wires went bad-OEM?
Wire was aftermarket that was bad, always seemed to be hard to install on plug. Replaced with OEM,(full set) much easier to install on plugs. Just like you said CAP shorted out (arched).
I would also have thought that a misfire would have triggered a check engine light on an OBDII vehicle. Obviously this is not the case. My sister in laws '01 Grand Am (2.4l) was acting funny at around 55-60mph whenever she hit the gas pedal. She was sure it was the transmission but the dealer diagnosed it as a #2 cylinder misfire, even though the check engine light never flashed. Turned out to be a bad ignition coil.
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