LS1 runs rough, sounds cammed, rich, LTFT pegged
06-20-2011, 10:23 AM
#1
LS1 runs rough, sounds cammed, rich, LTFT pegged Friends car is having issues we can't seem to sort out.
It sounds cammed with a stock 98 cam, sometimes dies on start up, runs rich enough to smoke on hard accel, LTFT are pegged at 25% at idle/light throttle. Fuel mileage in town is terrible (single digits) with a 6 speed and stock gears.
01 Trans am with rebuilt engine using 98 cam, but pcm information for the 98 cam was flashed into the tune.
SLP lid, 1 7/8" longtubes, LM1, stock ls6 intake.
Car is throwing codes for o2 sensors but it runs like **** on cold start before it should be reading them so we are pretty sure that could be counted as a symptom of the over fueling more than the culprit.
Things we have tried so far:
1) replace all rubber hoses which could have vacuum leaks
2) check fuel pressure (constant just at normal)
3) check all intake gaskets (new fel pros)
4) tried alternate IAC motor
5) MAF signals look good in logs
6) silicone sealed the MAP sensor to intake just to be sure
If we don't get any other ideas we could swap in the o2 sensors from my car and clean the pcm memory, but the car has run this shitty long enough o2 sensors aren't likely the cause.
It sounds cammed with a stock 98 cam, sometimes dies on start up, runs rich enough to smoke on hard accel, LTFT are pegged at 25% at idle/light throttle. Fuel mileage in town is terrible (single digits) with a 6 speed and stock gears.
01 Trans am with rebuilt engine using 98 cam, but pcm information for the 98 cam was flashed into the tune.
SLP lid, 1 7/8" longtubes, LM1, stock ls6 intake.
Car is throwing codes for o2 sensors but it runs like **** on cold start before it should be reading them so we are pretty sure that could be counted as a symptom of the over fueling more than the culprit.
Things we have tried so far:
1) replace all rubber hoses which could have vacuum leaks
2) check fuel pressure (constant just at normal)
3) check all intake gaskets (new fel pros)
4) tried alternate IAC motor
5) MAF signals look good in logs
6) silicone sealed the MAP sensor to intake just to be sure
If we don't get any other ideas we could swap in the o2 sensors from my car and clean the pcm memory, but the car has run this shitty long enough o2 sensors aren't likely the cause.
06-20-2011, 11:47 AM
#2
Let's put it this way...if the car runs like **** and gives you o2 sensor error when fully warmed up, then it's your o2 sensors.
Sure you might have a combination of problems other than the o2 sensors that's causing issues when the engine is cold and out of the hands of the o2 sensors...but when warm it's definitely them.
I would swap them out and reset your pcm by pulling the battery.
Sure you might have a combination of problems other than the o2 sensors that's causing issues when the engine is cold and out of the hands of the o2 sensors...but when warm it's definitely them.
I would swap them out and reset your pcm by pulling the battery.
06-20-2011, 12:05 PM
#3
thanks for the reply, the only problem with that is it will kill the new sensors in short order if the underlying problem is not also corrected, so we are trying to find some other likely culprits to start diagnosing ASAP after the new sensors go in
06-20-2011, 02:57 PM
#5
TECH Apprentice
Join Date: Nov 2003
Location: Houston, Tx
Posts: 309
Likes: 0
Received 0 Likes
on
0 Posts
I was running around at -10% LTFT. Cleaned the MAF and disconnected the battery for an hour and it was running +-2% afterwards.
If its still running rough in OL then I think you can rule out the O2 sensors
06-20-2011, 03:08 PM
#6
It's my car. I have also replaced the timing chain and checked my base cam timing 4 times. The car doesn't always throw 02 codes (about once every other week or so). The car doesn't really seem to be too down on power. Ran a 13.3 @108 with a pretty high DA a few months ago. I'm about at the end of my rope here trying to figure this problem out. Does the MAF come in to play at idle? We were getting readings from the MAF during data logging but I'm not sure the readings were where they needed to be, but I'm no expert.
06-20-2011, 03:13 PM
#7
It's my car. I have also replaced the timing chain and checked my base cam timing 4 times. The car doesn't always throw 02 codes (about once every other week or so). The car doesn't really seem to be too down on power. Ran a 13.3 @108 with a pretty high DA a few months ago. I'm about at the end of my rope here trying to figure this problem out. Does the MAF come in to play at idle? We were getting readings from the MAF during data logging but I'm not sure the readings were where they needed to be, but I'm no expert.
.
Trending Topics
06-20-2011, 03:35 PM
#9
TECH Apprentice
Join Date: Nov 2003
Location: Houston, Tx
Posts: 309
Likes: 0
Received 0 Likes
on
0 Posts
Unplug your MAF and set to mil on first error to eliminate it as a potential issue. Your car should be able to run fine off of a proper VE table. May stumble for a second at start. If its still running poorly then look elsewhere beyond the MAF
Last edited by OnyxY2KSS; 06-20-2011 at 03:45 PM.
06-20-2011, 03:45 PM
#10
Just went outside and started the car with the MAF unplugged and let it idle for a few minutes. The car ran exactly the same and didn't throw a trouble code. Is that normal?
06-20-2011, 03:48 PM
#11
TECH Apprentice
Join Date: Nov 2003
Location: Houston, Tx
Posts: 309
Likes: 0
Received 0 Likes
on
0 Posts
06-20-2011, 03:50 PM
#12
TECH Apprentice
Join Date: Nov 2003
Location: Houston, Tx
Posts: 309
Likes: 0
Received 0 Likes
on
0 Posts
Curious, what are your STFT's reading?
also, seems there is a bit of information left out...
What are the exact codes you are throwning?
When did this start? Following the 98 tune flash?
also, seems there is a bit of information left out...
What are the exact codes you are throwning?
When did this start? Following the 98 tune flash?
Last edited by OnyxY2KSS; 06-20-2011 at 03:55 PM.
06-20-2011, 04:04 PM
#16
TECH Apprentice
Join Date: Nov 2003
Location: Houston, Tx
Posts: 309
Likes: 0
Received 0 Likes
on
0 Posts
06-20-2011, 04:05 PM
#17
I have had insufficient switching as well has heater circuit I believe. This has been a problem since second start-up on this engine. Haven't been able to fix the problem. Car currently gets about 12 MPG in town and 25 MPG on the hwy. I don't think the logs were saved, but we could always run new ones.
06-20-2011, 04:46 PM
#19
-check MAF fuse
-check maf itself by unplugging it to see if there is a change
-check coolant temp sensor
-still have a vacuum leak somewhere
pegged LTFTs make me think the last two more than any other.
-check maf itself by unplugging it to see if there is a change
-check coolant temp sensor
-still have a vacuum leak somewhere
pegged LTFTs make me think the last two more than any other.
__________________
800-456-0211 / PM / Facebook
WHIPPLE Superchargers, Procharger, Magnuson, Powerbond Sale, HPTuners packages!, Trickflow, AFR, PRC, CHE Trunion upgrade, $100 7.400" pushrod set, Custom Cam of your choice
800-456-0211 / PM / Facebook
WHIPPLE Superchargers, Procharger, Magnuson, Powerbond Sale, HPTuners packages!, Trickflow, AFR, PRC, CHE Trunion upgrade, $100 7.400" pushrod set, Custom Cam of your choice