LT trim is stuck at 24.98 no matter what I do
05-10-2011, 09:18 AM
#1
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LT trim is stuck at 24.98 no matter what I do H/C 383 LT1, Jet-Hot (Hooker) LT headers, dual 3" exhaust with mufflers in the stock location.
LS1 PCM and coils.
94-95-style O2 sensors
I'm having issues with the driver's side of the engine.
The O2 sensor is telling the PCM that it's running lean and it's adding a lot of fuel.
Plug #3 is coated in thick black residue, 1, 5 and 7 are cleaner.
I probed around with my stethoscope, but didn't find a leak.
I double-checked my 3" band clamps with the 1/2" impact.
I replaced the O2 with a new one, no change.
The PCM is not reporting a misfire.
We've altered the tune to see if it will richen or lean out and it did not respond.
Short-term trim moves around, but Long-term stays put.
The passenger side responds exactly as it should and trims are close to 0.
What else could it be?
I'm going to pull the harness back up to check for shorts next because I am out of ideas.
LS1 PCM and coils.
94-95-style O2 sensors
I'm having issues with the driver's side of the engine.
The O2 sensor is telling the PCM that it's running lean and it's adding a lot of fuel.
Plug #3 is coated in thick black residue, 1, 5 and 7 are cleaner.
I probed around with my stethoscope, but didn't find a leak.
I double-checked my 3" band clamps with the 1/2" impact.
I replaced the O2 with a new one, no change.
The PCM is not reporting a misfire.
We've altered the tune to see if it will richen or lean out and it did not respond.
Short-term trim moves around, but Long-term stays put.
The passenger side responds exactly as it should and trims are close to 0.
What else could it be?
I'm going to pull the harness back up to check for shorts next because I am out of ideas.
05-10-2011, 12:02 PM
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I just don't understand why 24.98 is such a constant.
I would expect it to move around more if it were a vacuum, spark or fuel issue.
But if it were a short, the short-term should be steady as well.
Additional info; I should have mentioned this in the original post.
Recent changes:
1) New cam - milder than the old one, but that means that the injectors and intake have been off the motor.
I've noticed a small amount of oil on the plug tips, I wonder if I have a manifold leak between the valley and runner?
I think that I'd hear hissing though.
2) 24x conversion, which means new PCM, new coils, new wires, new plugs and new PCM (and thus the new tune).
Possibly. I could swap left and right to see if the problem follows the injectors.
Those are flow-matched Racetronix injectors with less than 2000 miles on them.
They worked fine with the old cam.
The LS1 PCM would throw a code if it wasn't sparking, wouldn't it?
I'll put my tester on and check.
I would expect it to move around more if it were a vacuum, spark or fuel issue.
But if it were a short, the short-term should be steady as well.
Additional info; I should have mentioned this in the original post.
Recent changes:
1) New cam - milder than the old one, but that means that the injectors and intake have been off the motor.
I've noticed a small amount of oil on the plug tips, I wonder if I have a manifold leak between the valley and runner?
I think that I'd hear hissing though.
2) 24x conversion, which means new PCM, new coils, new wires, new plugs and new PCM (and thus the new tune).
Possibly. I could swap left and right to see if the problem follows the injectors.
Those are flow-matched Racetronix injectors with less than 2000 miles on them.
They worked fine with the old cam.
I'll put my tester on and check.
05-10-2011, 02:17 PM
#5
Almost hate to open this can of worms, but.....
You can "dummy" the O2 sensor reading and see how the PCM reacts. What I did is used a small potentiometer, about 1K Ohm, and a flashlight battery. Wire the battery across the pot and ground the negative end. Wire the center lead to the O2 sensor wire. The PCM supplies some current to the O2 sensor so you need to adjust the voltage while it's powered up. You can trick the PCM to think it's lean or rich. I just used a scan tool and watched the O2 sensor reading. If the PCM sees a high, the PCM will go full lean. On my truck it was pinging to beat the band. Set it lean and the exhaust will turn black and it will get sluggish. On my truck it set a code but did not light the check engine light. BTW: while I was screwing with it I also dummied the coolant sensor. Wanted to see if it would set a code, no light but it did set a code saying the engine was too cold.
Al
You can "dummy" the O2 sensor reading and see how the PCM reacts. What I did is used a small potentiometer, about 1K Ohm, and a flashlight battery. Wire the battery across the pot and ground the negative end. Wire the center lead to the O2 sensor wire. The PCM supplies some current to the O2 sensor so you need to adjust the voltage while it's powered up. You can trick the PCM to think it's lean or rich. I just used a scan tool and watched the O2 sensor reading. If the PCM sees a high, the PCM will go full lean. On my truck it was pinging to beat the band. Set it lean and the exhaust will turn black and it will get sluggish. On my truck it set a code but did not light the check engine light. BTW: while I was screwing with it I also dummied the coolant sensor. Wanted to see if it would set a code, no light but it did set a code saying the engine was too cold.
Al
05-10-2011, 02:54 PM
#6
Does it do it in open or closed loop? Or all the time? If its on start up ECT should be controlling fuel trim. Check the ECT reading with both a multimeter at the sensor and with the scan tool. Double check all connections on the harness. Then if you need to go directly to the PCM and start checking for signals from sensors.
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05-10-2011, 04:53 PM
#8
If you haven't done a case learn the misfire detection may not function properly. It is a constant 24.98 because 25% is the max it can add. If the oxygen sensor is still reading lean then it will always try and add the most amount of fuel possible. If you unplug the oxygen sensor it should default to around 450mv.
05-10-2011, 09:27 PM
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Almost hate to open this can of worms, but.....
You can "dummy" the O2 sensor reading and see how the PCM reacts. What I did is used a small potentiometer, about 1K Ohm, and a flashlight battery. Wire the battery across the pot and ground the negative end. Wire the center lead to the O2 sensor wire. The PCM supplies some current to the O2 sensor so you need to adjust the voltage while it's powered up. You can trick the PCM to think it's lean or rich. I just used a scan tool and watched the O2 sensor reading. If the PCM sees a high, the PCM will go full lean. On my truck it was pinging to beat the band. Set it lean and the exhaust will turn black and it will get sluggish. On my truck it set a code but did not light the check engine light. BTW: while I was screwing with it I also dummied the coolant sensor. Wanted to see if it would set a code, no light but it did set a code saying the engine was too cold.
Al
You can "dummy" the O2 sensor reading and see how the PCM reacts. What I did is used a small potentiometer, about 1K Ohm, and a flashlight battery. Wire the battery across the pot and ground the negative end. Wire the center lead to the O2 sensor wire. The PCM supplies some current to the O2 sensor so you need to adjust the voltage while it's powered up. You can trick the PCM to think it's lean or rich. I just used a scan tool and watched the O2 sensor reading. If the PCM sees a high, the PCM will go full lean. On my truck it was pinging to beat the band. Set it lean and the exhaust will turn black and it will get sluggish. On my truck it set a code but did not light the check engine light. BTW: while I was screwing with it I also dummied the coolant sensor. Wanted to see if it would set a code, no light but it did set a code saying the engine was too cold.
Al
I guess that would at least tell me if it's a leak/misfire or a sensor issue.
Does it do it in open or closed loop? Or all the time? If its on start up ECT should be controlling fuel trim. Check the ECT reading with both a multimeter at the sensor and with the scan tool. Double check all connections on the harness. Then if you need to go directly to the PCM and start checking for signals from sensors.
I installed a new FPR while I had it off.
If you haven't done a case learn the misfire detection may not function properly. It is a constant 24.98 because 25% is the max it can add. If the oxygen sensor is still reading lean then it will always try and add the most amount of fuel possible. If you unplug the oxygen sensor it should default to around 450mv.
In fact, the goal at the moment is just to make it driveable so I can swap in the 4l60e and
take it to the dyno for a complete tuning session.
Can I do that with the O2s unplugged? Sure.
Will that make me feel like my car is running well enough to take to a dyno ? Hell no.
05-10-2011, 09:33 PM
#11
I'm working on getting the idle working before I tune cruising or WOT.
In fact, the goal at the moment is just to make it driveable so I can swap in the 4l60e and
take it to the dyno for a complete tuning session.
Can I do that with the O2s unplugged? Sure.
Will that make me feel like my car is running well enough to take to a dyno ? Hell no.
05-10-2011, 09:41 PM
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If I find find anything while checking plugs/wires/coils and injectors .. I'm going to try re-seating the intake.
Headers are last on my list.
If I have to go to all of that trouble, I'm putting a new set of Kooks in while I am at it.
05-12-2011, 10:33 PM
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I pulled the passenger side plugs out and found that they were all as black as #3 was.
I replaced all 8 with new ones.
Then I installed my widebands in the narrowband bungs and fired it up.
Sure enough, both sides are running at 17:1, but I could see both needles swinging from 16:1 to 18:1.
The driver's side did seem to hug the 18 slightly more than the passenger side did.
Manifold pressure holds steady for the most part at 64KPa ~975rpm idle.
I have not swapped or removed injectors yet.
If I'm taking the rail off, I'm going to redo the manifold gaskets while I am at it.
The black on the plugs appears to be oil, not carbon.
If that doesn't work, I guess it's time to run another leak-down test, but with so few
miles on a fresh motor I just don't see that being an issue. Especially since it did so
well when I ran the test last year. But I alsonoticed that the inatake has a nice coat of oil in it.
That thing was clean when I put it on after the cam swap (< 2 engine hours ago)
I replaced all 8 with new ones.
Then I installed my widebands in the narrowband bungs and fired it up.
Sure enough, both sides are running at 17:1, but I could see both needles swinging from 16:1 to 18:1.
The driver's side did seem to hug the 18 slightly more than the passenger side did.
Manifold pressure holds steady for the most part at 64KPa ~975rpm idle.
I have not swapped or removed injectors yet.
If I'm taking the rail off, I'm going to redo the manifold gaskets while I am at it.
The black on the plugs appears to be oil, not carbon.
If that doesn't work, I guess it's time to run another leak-down test, but with so few
miles on a fresh motor I just don't see that being an issue. Especially since it did so
well when I ran the test last year. But I alsonoticed that the inatake has a nice coat of oil in it.
That thing was clean when I put it on after the cam swap (< 2 engine hours ago)
Last edited by James Montigny; 05-12-2011 at 10:48 PM.
05-23-2011, 03:58 PM
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I tried swapping the O2s, but it didn't change anything.
So I installed new manifold gaskets, a generous amount of RTV and cleaned
every bolt and thread to make sure it sealed properly. I also gave the intake a nice
scrubbing with B12 to get all of the oil out. I fired it up and found that I am still
maxed out at +24.98.
ST B1 -5.47%
LT B1 -8.60%
ST B2 +41.39%
LT B2 +24.98%
RPM 928
MAP 71kPa
Then I swapped the injectors left to right.
ST B1 +50.76%
LT B1 +24.98%
ST B2 -0.79%
LT B2 +0.77%
RPM 1034
MAP 65kPa
AHA! So I'm working with Racetronix to get them cleaned and tested.
Hopefully, that solves at least some of my problems.
So I installed new manifold gaskets, a generous amount of RTV and cleaned
every bolt and thread to make sure it sealed properly. I also gave the intake a nice
scrubbing with B12 to get all of the oil out. I fired it up and found that I am still
maxed out at +24.98.
ST B1 -5.47%
LT B1 -8.60%
ST B2 +41.39%
LT B2 +24.98%
RPM 928
MAP 71kPa
Then I swapped the injectors left to right.
ST B1 +50.76%
LT B1 +24.98%
ST B2 -0.79%
LT B2 +0.77%
RPM 1034
MAP 65kPa
AHA! So I'm working with Racetronix to get them cleaned and tested.
Hopefully, that solves at least some of my problems.
05-23-2011, 06:45 PM
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Yea well its my sense of humor really , some times my posts.. their kinda like batch fire with random misses. and i was only a couple away from 1,000 but thanks So,...c'mon joe don't hate 
your post was also irrelevant to topic and upped your post by one Hoe lol.. hell sometimes "more often than not, you just chime in with nothing more to offer than sarcasim.. like.. ( :facepalm: ) 
your post was also irrelevant to topic and upped your post by one Hoe lol.. hell sometimes "more often than not, you just chime in with nothing more to offer than sarcasim.. like.. ( :facepalm: ) 
