Backfire under wot and lost idle
- Thread starter Timbuick
- Start date
Check all the hoses to see if one didn't rupture or blow off.
I had one of the intercooler hoses blow off under wot on my fmic and it did as you described,it was hard to see because the hose didn't come all the way off the piping.
i Checked the IC hoses first as I have had these blow off before. They are all sound, wished it was that easy, but not so lucky this time.
I can change the coil pack as I have a spare, but i'm guessing thereafter.
Went from perfect running to prety poor.
The only area seemingly unaffected was mid range throttle which seemed ok until any attempt at WOT.
I can change the coil pack as I have a spare, but i'm guessing thereafter.
Went from perfect running to prety poor.
The only area seemingly unaffected was mid range throttle which seemed ok until any attempt at WOT.
Red Regal T
Senior Member
- Joined
- May 24, 2001
Changing plugs or wires as suggested above is a possible direction. If you have another coilpak, try it, but that doesn't rule out the other more expensive component, the ignition module.
I have a spare coil pack to change and will give a visual inspection to the ignition module too.
I just unplugged the MAF and it idled smoothly. keen to test it further, I swapped in a spare MAF and no change. if I revved the motor it tended to soar up to 2000rpm. Cant have 3 bad MAFs i'm sure
Can I test drive with the MAF unplugged/ I thought the MAF readings sent the ECM fuel requirements based on air flow. Trying to fix stuf as well as learn more theory
I just unplugged the MAF and it idled smoothly. keen to test it further, I swapped in a spare MAF and no change. if I revved the motor it tended to soar up to 2000rpm. Cant have 3 bad MAFs i'm sure
Can I test drive with the MAF unplugged/ I thought the MAF readings sent the ECM fuel requirements based on air flow. Trying to fix stuf as well as learn more theory
Nasty Wendy
Perverted Lurker
- Joined
- May 24, 2001
Check your camsensor. I had one loosen up and spin and cause havoc.
berserker6
Assistant to the regional manager
- Joined
- Oct 1, 2009
i hope i dont sound like a broken record but if you have a scanmaster, monitor your AF readings. it may be locked in on a particular number and anything above or below that number the cars not going to run right. below that number its rich, above it and the motor leans out. i had an ls1 MAF do that to me. it locked in on 23grams.
Nasty Wendy
Perverted Lurker
- Joined
- May 24, 2001
Mine spun while the car was up in rpms. It backfired and I let off, it came down to a stupidly rough idle. I found the problem before I fired it back up but it's not likely that it would have started.
Thanks for the heads up. I'm the only Buick guy around (UK) so i'm dependent on this fine board and its members advice
I have a scanmaster and it show 4 on AF with ignition off. I thought it should be 3. Not sue if that means its out of synch. That said, i have changed MAFs without significant change.i'm trying to deal with the erratic idle before finding the backfire
I have a scanmaster and it show 4 on AF with ignition off. I thought it should be 3. Not sue if that means its out of synch. That said, i have changed MAFs without significant change.i'm trying to deal with the erratic idle before finding the backfire
ELLISDALLASWE4
Member
- Joined
- Nov 7, 2005
I had the "S" hose expand and crack the cam sensor cap. You might want to check that and look real close. also make sure the hose does not touch the cap..
Thanks, i did check the cap this weekend, looks to be fine. I've fixed the rough idle now and the car runs as it did with numbers o the scantool as they should be.
However, under hard acceleration the car still nose dives. I've checked that fuel pressure is correct and rising with boost, i've changed coillpacks. Not sure what is next
However, under hard acceleration the car still nose dives. I've checked that fuel pressure is correct and rising with boost, i've changed coillpacks. Not sure what is next
berserker6
Assistant to the regional manager
- Joined
- Oct 1, 2009
How did you fix the rough idle? And monitor your AF on scanmaster to be sure the number rises in relation to throttle input.
I fixed the idle by finding a ground that had come lose (thre grounds on one bolt on the passenger inner wing) and replacing the PCV/Check valve/vac hose plus retightening the uppipe connections. That bought it into line.
The MAF numbers do appear to be correct, although its dificult to check now as I dont want to push the car if it is malfunctioning.
It feels like the 'plug' is being pulled form the car and yet returnns instantly once I get off the throttle. TPS is correctly set too.
The MAF numbers do appear to be correct, although its dificult to check now as I dont want to push the car if it is malfunctioning.
It feels like the 'plug' is being pulled form the car and yet returnns instantly once I get off the throttle. TPS is correctly set too.
berserker6
Assistant to the regional manager
- Joined
- Oct 1, 2009
Make sure nothings touching your headers. Particularly the drivers side. Any codes?
Generally from prior threads that I've read it is either the crank sensor or the TPS sensor. My TPS sensor was set correctly at idle, but under load at WOT there was a dead spot. If you have a scan tool that records, make a run (not too fast or too far) and then play it back and see what the TPS volts show.
Check the TPS connector with the key on / engine off, sit the scanmaster on the dash where you can see it of course and wiggle the connector. If that's not the problem start the car and let it idle and check all the connectors and see if one is causing the problem.
I had a bad TPS connector and it would go from .42 to 4.00 instantly just by me barely touching the wires on the connector. A new TPS connector / pigtail from O'rielly's was $9.00
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