Misfire and Hesitation issues when cold.

Tiny
BIGREDDMACH1NE
  • MEMBER
  • 1997 PONTIAC BONNEVILLE
  • 3.8L
  • V6
  • FWD
  • AUTOMATIC
  • 262,000 MILES
Please note it's the Supercharged 3.8 engine.

A few days ago I did some maintenance and repairs on my car including:

Transmission Fluid + Filter
PCV Valve
Fuel filter
Valve cover gaskets.
One vacuum line was replaced.

A small misfire issue popped up after this was done. Also the fuel pump went out a day later. The fuel pump was replaced and the gas tank was cleaned out. New spark plugs were installed to help with the misfire issue. Which didn't fix anything sadly.

This misfire mostly occurs when the engine is starting from cold (Upper 40's this week). Idles fine with an occasional hiccup. Mid-high throttle is when the hesitation and misfiring occurs. However when the car warms up after a little bit the car will run fine NO problems whatsoever. I have no check engine lights unfortunately.

All the vacuum lines are fine I checked for damage or a botched install and they all look fine. Spark plugs didn't fix the problem. Checked the plug wires and they all seem connected right and free of damage. I also cleaned the MAF sensor and IAC. No changes. Fuel pressure is good after replacing the failed one.

What is the next thing I should check and inspect?


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Sunday, October 4th, 2015 AT 10:04 PM

2 Replies

Tiny
BIGREDDMACH1NE
  • MEMBER
Please let me know if there is any other information I can provide. I have a code scanner (only for codes though nothing else.).
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Sunday, October 4th, 2015 AT 10:10 PM
Tiny
CAR-MAN145
  • EXPERT
Well it sound like you need to take it to a shop and at least find out what cylinder is missing I can not thing of anything that would do what you are saying except a coil but they usually start the miss after warm. Could also be an injector problem.
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Sunday, October 4th, 2015 AT 10:52 PM

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