Lt1 running rich but the PCM says lean?
11-28-2007, 01:03 PM
#1
Lt1 running rich but the PCM says lean? Sorry for the repost, this is in the Lt1 section as well but I thought mayby someone in here that doesn't venture into the Lt1 forums would see it.
--------------------------
Hey guys, my car has been running extremely rich the past few weeks. I got it finished earlier this summer, broke it in, and drove it 700 miles to Ocean City MD in the same day. It was running good except every once in a while it wouldn't idle when you came to a complete stop. Say you were rolling to a stop, it would be idling fine but as soon as you stopped it would just die. You would start it and it would be fine till mayby 15 minutes of cruising and do it again. If you caught it dieing and kept it alive and flicked the key off then back on (without turning the motor off) it would start idleing like a champ.
Eventualy that stopped happening on its own and it just started having a rough idle sometimes and a quick key off then back on would solve it. Then my friend scanned my car and we found a o2 was bad and my MAP was bad. We replaced them. Car still acted the same (bad idle sometimes).
I figured it was because my IAC counts were probally high and my tps needed adjusted. I was going to fix that when I got a cable and datamaster.
Then it started throwing a little bit of black smoke one day, this was after the o2 and map replacement. It progressively got worse untill the smoke was bad. REALLY BAD. Just cruising you could see a hint of black smoke, but at WOT lookout, it poured black smoke! Then it started getting some blue smoke at WOT with the black smoke which I'd vote it from some reall bad wash down.
Fast forward to a few days ago. My car is on jackstands with no trany when I received my cable so I could only datalog it at an idle basicaly. So I hooked it up to datamaster. (which I don't have the log on this computer.) Here's what I observed.
Fuel trim cell- Stayed in 16 from open to closed loop .
Map- stayed around 58kps at idle the whole time.
RPM- managed to stay at around 1000 (which is the target idle)
IAC-Pegged at 160 on cold start. Around 80 at operating temp.
TPS- 0.84v
AFGS ~17 at cold start ~12 once at operating temp
Left o2- consistently switched between ~.700-.160MV
Right o2 consistently switched between ~.650-.180Mv
Inj. duty- Left bank ~3.0, right bank ~2.0 at operating temp
BPW- Left bank ~3.5, right bank ~2.5
S term counts- Varried between ~127-135 with the left bank tending to be about 5 higher most the time.
L term couns- Left bank stayed at 160 and the right at 127. Once or twice they changed by one for a second then back to 160 or 127
Should it have stayed in fuel trim 16 the whole time? Whys me left bank ltfs pegged at 160.
After I shut the car down I pulled the motor. The plugs were dark as can be. I did compression test and the numbers came back between 135 to 160 for all the cylinders. Not so good for ~12.5:1 compression. My battery died before I could squirt oil in the cylinders. I'll try that and report back. I also found that the headers were leaking, the 2 middle cylinders on each bank has a lot of black exhaust around the exhaust ports.
I had a high res opti code when i first started it t I cleared it and it did not come back. I think it's from when i tried to start the car without the opti hooked up by accident.
All my specs are in my sig, It's a new coil, opti was new when the car hit the road. All the wires are good, and the plugs were recently changed. Checked for vaccum leaks and nothing. Fuel pressure is at stock levels. It's a pcmforless mailorder tune.
So does anyone have any ideas? Is it going to be as simple as getting my IAC counts, TPS voltage, and exhaust leaks fixed or is it going to be way more?
--------------------------
Hey guys, my car has been running extremely rich the past few weeks. I got it finished earlier this summer, broke it in, and drove it 700 miles to Ocean City MD in the same day. It was running good except every once in a while it wouldn't idle when you came to a complete stop. Say you were rolling to a stop, it would be idling fine but as soon as you stopped it would just die. You would start it and it would be fine till mayby 15 minutes of cruising and do it again. If you caught it dieing and kept it alive and flicked the key off then back on (without turning the motor off) it would start idleing like a champ.
Eventualy that stopped happening on its own and it just started having a rough idle sometimes and a quick key off then back on would solve it. Then my friend scanned my car and we found a o2 was bad and my MAP was bad. We replaced them. Car still acted the same (bad idle sometimes).
I figured it was because my IAC counts were probally high and my tps needed adjusted. I was going to fix that when I got a cable and datamaster.
Then it started throwing a little bit of black smoke one day, this was after the o2 and map replacement. It progressively got worse untill the smoke was bad. REALLY BAD. Just cruising you could see a hint of black smoke, but at WOT lookout, it poured black smoke! Then it started getting some blue smoke at WOT with the black smoke which I'd vote it from some reall bad wash down.
Fast forward to a few days ago. My car is on jackstands with no trany when I received my cable so I could only datalog it at an idle basicaly. So I hooked it up to datamaster. (which I don't have the log on this computer.) Here's what I observed.
Fuel trim cell- Stayed in 16 from open to closed loop .
Map- stayed around 58kps at idle the whole time.
RPM- managed to stay at around 1000 (which is the target idle)
IAC-Pegged at 160 on cold start. Around 80 at operating temp.
TPS- 0.84v
AFGS ~17 at cold start ~12 once at operating temp
Left o2- consistently switched between ~.700-.160MV
Right o2 consistently switched between ~.650-.180Mv
Inj. duty- Left bank ~3.0, right bank ~2.0 at operating temp
BPW- Left bank ~3.5, right bank ~2.5
S term counts- Varried between ~127-135 with the left bank tending to be about 5 higher most the time.
L term couns- Left bank stayed at 160 and the right at 127. Once or twice they changed by one for a second then back to 160 or 127
Should it have stayed in fuel trim 16 the whole time? Whys me left bank ltfs pegged at 160.
After I shut the car down I pulled the motor. The plugs were dark as can be. I did compression test and the numbers came back between 135 to 160 for all the cylinders. Not so good for ~12.5:1 compression. My battery died before I could squirt oil in the cylinders. I'll try that and report back. I also found that the headers were leaking, the 2 middle cylinders on each bank has a lot of black exhaust around the exhaust ports.
I had a high res opti code when i first started it t I cleared it and it did not come back. I think it's from when i tried to start the car without the opti hooked up by accident.
All my specs are in my sig, It's a new coil, opti was new when the car hit the road. All the wires are good, and the plugs were recently changed. Checked for vaccum leaks and nothing. Fuel pressure is at stock levels. It's a pcmforless mailorder tune.
So does anyone have any ideas? Is it going to be as simple as getting my IAC counts, TPS voltage, and exhaust leaks fixed or is it going to be way more?
11-28-2007, 09:44 PM
#2
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
This is the nature of closed loop control; when you have a bad
feedback it overcorrects the other way. Like a fouled O2 sensor
or something that fakes the exhaust oxygen sensed quantity
making it look lean, the PCM (wrongly) compensates it rich
because it knows no better.
feedback it overcorrects the other way. Like a fouled O2 sensor
or something that fakes the exhaust oxygen sensed quantity
making it look lean, the PCM (wrongly) compensates it rich
because it knows no better.
11-28-2007, 09:53 PM
#3
Yeah, I understand that, so do you think starting with new O2s is a wise place to start? How did they get fouled so quickly?
Could my MAF be slightly off and tell the pcm im getting more air then I actualy am, making the motor run rich also?
Could my MAF be slightly off and tell the pcm im getting more air then I actualy am, making the motor run rich also?
11-28-2007, 10:48 PM
#4
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
Offhand I'd point the finger more at the big-***, high overlap
cam. The other things, air or fuel side errors, would be easier
to just compensate and get back to balanced O2 switching.
Unless your tune was so far off that trims run out of range.
But the cam lets air through to the exhaust through the
overlap and that musses up the O2 sensors' "input". I don't
know how the L, S "counts" work on a LT1 system (the min /
max range). If it's not at the limit then it "thinks" it's doing the
right thing.
The intermittent nature of it is peculiar. Another thing that
can whack closed loop is a misfiring cylinder, bad spark or
bad injector. But the odds are low that that would hit both
banks. Catching scans of normal (if normal happens anymore)
and abnormal, and comparing the various sensors' data, might
show you where to look closer.
cam. The other things, air or fuel side errors, would be easier
to just compensate and get back to balanced O2 switching.
Unless your tune was so far off that trims run out of range.
But the cam lets air through to the exhaust through the
overlap and that musses up the O2 sensors' "input". I don't
know how the L, S "counts" work on a LT1 system (the min /
max range). If it's not at the limit then it "thinks" it's doing the
right thing.
The intermittent nature of it is peculiar. Another thing that
can whack closed loop is a misfiring cylinder, bad spark or
bad injector. But the odds are low that that would hit both
banks. Catching scans of normal (if normal happens anymore)
and abnormal, and comparing the various sensors' data, might
show you where to look closer.
11-29-2007, 11:38 PM
#5
128 is perfect, 160 is as high as it goes. 129-160 is saying the PCM is detecting lean so correcting by adding more % fuel the higher the number gets. I forgot what the range number is on the rich side, probaly around 100, I have it wrote down in my notes but I don't have them handy.
11-30-2007, 07:44 AM
#6
Are you tuning it yourself? Can you post your tune or send it to me?
If you have your own cable, buy tunercat, pull your tune and send it to me. You have some of the typical LT1/big cam problems, i.e. split fuel trims. There are cures for it.
tunercat is cheap, and you wont really have any down time. you can email me the tune, I can change it and email it back. You flash it and bada-bing.
If you have your own cable, buy tunercat, pull your tune and send it to me. You have some of the typical LT1/big cam problems, i.e. split fuel trims. There are cures for it.
tunercat is cheap, and you wont really have any down time. you can email me the tune, I can change it and email it back. You flash it and bada-bing.
Last edited by edcmat-l1; 11-30-2007 at 07:59 AM.
11-30-2007, 12:58 PM
#7
I have tunercate and a cable. I have not touched the tune though. it's a PCMforless tune. I'll pull it asap and send it to you. Give me a few days though, I need to find a laptop without vista like mine, tunercate seems to not like vista.
