Weird engine stumbling past 3k RPMs ??

[11B2V_Mike]

Weird engine stumbling past 3k RPMs


(on a 99 gt 5 speed)

a week ago i put on a mac o/r h pipe, 2 new o2 sensors, and new ngk plugs. now lately after about 30 minutes of driving the engine starts stumbling and wont go past a certain rpm. also gas mileage took a 4 mpg or more nosedive.....

in 1st gear rpms won't go past 5k, 2nd gear past 3.5 - 4k, 3 rd gear past 3k rmps. the longer i drive the worse the stumbling/stalling problem gets. i can floor it in neutral and it goes to redline no problem, only happens under load.

also, if i turn the engine off for around 5 minutes then start driving again the problem goes away for 15 or so minutes (when it's restarted it still is at normal operating temperatures)

i can hear a sound kinda like a small tiss tiss tiss(kinda like small exhaust leak) when the engine is stumbling. when it is working fine (first 30 minutes of driving) no sound at all.

my guess is a coil pack not igniting the chamber, and that sound is from the fuel flowing right by (explains gas mileage drop). can anyone shed some light on this problem? how can i test the coil packs to see which one is missing/ not firing? thanks

 

[DC-GT]

This may sound odd and it certainly shows my age but it sounds to me like the old potato in the tail pipe maybe? I mean, maybe something is stuck in your exhaust blocking it partially. I am only guessing that due to the fact that you just replaced some exhaust components and the symptoms you describe are similar.

Hope you get it figured out soon. Engine stumbling is harder on rods than a booster is.

Bo

***edit*** Wait a sec, you said you changed the O2 sensors, have you tried putting the old ones back in? Makes me wonder since you gave the impression that it resets after shutting down for a bit. Also, check for pinched wires leading to the sensors.

 

[11B2V_Mike]

This may sound odd and it certainly shows my age but it sounds to me like the old potato in the tail pipe maybe? I mean, maybe something is stuck in your exhaust blocking it partially. I am only guessing that due to the fact that you just replaced some exhaust components and the symptoms you describe are similar.

Hope you get it figured out soon. Engine stumbling is harder on rods than a booster is.

Bo

***edit*** Wait a sec, you said you changed the O2 sensors, have you tried putting the old ones back in? Makes me wonder since you gave the impression that it resets after shutting down for a bit. Also, check for pinched wires leading to the sensors.

i doubt it's the potato thing.. it runs awesome for about 30 minutes then just starts stumbling, missing, etc. i can check about the pinched wires though..

 

[11B2V_Mike]

ttt

 

[11B2V_Mike]

just drove it again, now anytime it goes over 3000 rpms it bucks hard (like if i slammed on the gas) this is bringing it up to speed slowly (not the traction cotrol kicking in) i have no idea what the hell it is but it can't be good

 

[DC-GT]

just drove it again, now anytime it goes over 3000 rpms it bucks hard (like if i slammed on the gas) this is bringing it up to speed slowly (not the traction cotrol kicking in) i have no idea what the hell it is but it can't be good

Im my opinion, I would stop driving it around. I was told that engine stumbling is VERY rough on the motor.

If you must though, have you tried putting the old O2 sensors back in? Are you getting an SES light?

Bo

 

[11B2V_Mike]

Im my opinion, I would stop driving it around. I was told that engine stumbling is VERY rough on the motor.

If you must though, have you tried putting the old O2 sensors back in? Are you getting an SES light?

Bo

i don't have the old o2 sensors, not getting a ses light or any check engine lights for that matter. had autozone scan the car but came up clean. still have no idea.

 

[98BLKHRSE]

Not like this is gonna help you, but i dont want you to feel alone. I have the same exact problem going on with my car. Funny thing is it started right after i put my o/r X pipe on too. I bought the MIL eliminators, but my ses still comes on even after i reset the computer. I thought the bucking could of been from a bad fuel filter, so i changed it, and still bucks. Like you said it happens around 3k. I too also changed my plugs and wires. No change. Sometimes it does it to me when im cruisin at highway speed. Seems like the car loses power even if i push on the gas harder.

 

[98BLKHRSE]

Anyone have any ideas????? please

 

[SVTSTEEDA]

my car did this when the cats were going bad. Once the honeycomb broke up it was fine. I know you all have o/r pipes (no cats) but my point is it sounds like something has to be in the exhaust. Mine would run fine one day and then act up (no power, more noise, etc.) Good luck.

 

[DC-GT]

my car did this when the cats were going bad. Once the honeycomb broke up it was fine. I know you all have o/r pipes (no cats) but my point is it sounds like something has to be in the exhaust. Mine would run fine one day and then act up (no power, more noise, etc.) Good luck.

That was my original thought too. Problem is, now that you have been running it, anything that was in the pipes might now be in the muffler?

I hope you guys figure it out and let us all know what was up!

Bo

 

[01'TRUE BLUE GT]

Disconnect your battery for a bit and then try it ... that will reset the computer. It may help or may not but it's worth a shot if you haven't tried already. Look in your owner's manual and it will tell you the simple procedure how to make your car re-learn the idle trim after you disconnect the battery.