Need help, poor acceleration
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 426
Likes: 4
From: Austin, TX
Need help, poor acceleration I just got my LS2 conversion running and it has incredibly poor throttle response. It runs very smooth, but it picks up additional throttle very slowly.
I have visually checked the throttle blade and it is going wide open and very quickly.
The throttle position angle only shows 88% at full throttle even though the throttle position shows 100%. The long term fuel trim on bank 1 and 2 are about - 16%. The short trim from O2 sensor 2 on both banks is 99%. Should I be showing anything at all if the 2nd O2 sensors have been edited out?
The short term fuel trim is about -0.8 on both banks.
I have logged some operation, so ask for any parameter, and I will look them up.
I am used to these engines just starting right up with no problems, but this thing feels like a 4 cylinder engine!
I pulled the MAF off my truck and tried it, to assure that the MAF was not bad, and it did not improve it.
Thanks, John McGraw
I have visually checked the throttle blade and it is going wide open and very quickly.
The throttle position angle only shows 88% at full throttle even though the throttle position shows 100%. The long term fuel trim on bank 1 and 2 are about - 16%. The short trim from O2 sensor 2 on both banks is 99%. Should I be showing anything at all if the 2nd O2 sensors have been edited out?
The short term fuel trim is about -0.8 on both banks.
I have logged some operation, so ask for any parameter, and I will look them up.
I am used to these engines just starting right up with no problems, but this thing feels like a 4 cylinder engine!
I pulled the MAF off my truck and tried it, to assure that the MAF was not bad, and it did not improve it.
Thanks, John McGraw
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 426
Likes: 4
From: Austin, TX
Unfortunately, I only have autotap. The timing is all over the place when I run a data log. It goes from a high of about 39 degrees to as little as 4 degrees. The steady short term fuel trim suggests to me that the A/F is probably pretty good, but I am pretty stupid on the parameters. I have always just pluged the harness in, and it ran well. What could be causing my timing to vary so much? The only reason that I questioned the relative throttle angle position was that the help screen on autotap said that idle should = 0% and full throttle should equal 100%. My idle = 15% and full throttle = 88%.
Any advice would be truly appreciated.
Regards, John McGraw
Any advice would be truly appreciated.
Regards, John McGraw
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 426
Likes: 4
From: Austin, TX
I went out and ran some graphs on the ignition timing vs the engine speed, and it appears the timing is tracking the engine speed well. The timing is all in by about 2200 rpm and tops out at 40 degrees and stays there above 2200.
The O2 sensors track each other very well, and the pattern is very similar to my daily driver pickup truck.
One glaring difference that I see between my daily driver and my conversion, is that the calculated engine load at idle on my truck is about 2%, while my conversion runs about 21%. Does this make any difference in operation?
Thanks, John McGraw
The O2 sensors track each other very well, and the pattern is very similar to my daily driver pickup truck.
One glaring difference that I see between my daily driver and my conversion, is that the calculated engine load at idle on my truck is about 2%, while my conversion runs about 21%. Does this make any difference in operation?
Thanks, John McGraw
Unfortunately, I only have autotap. The timing is all over the place when I run a data log. It goes from a high of about 39 degrees to as little as 4 degrees. The steady short term fuel trim suggests to me that the A/F is probably pretty good, but I am pretty stupid on the parameters. I have always just pluged the harness in, and it ran well. What could be causing my timing to vary so much? The only reason that I questioned the relative throttle angle position was that the help screen on autotap said that idle should = 0% and full throttle should equal 100%. My idle = 15% and full throttle = 88%.
Any advice would be truly appreciated.
Regards, John McGraw
Any advice would be truly appreciated.
Regards, John McGraw
Being that this is an ETC, there is no IAC motor. So, the throttle must be open in order to run properly.
What controller are you running? Where did you get it? You might be running into a torque limit on the setup. I know some of the ealry GTO stuff was really soft as to lengthen the drivetrain components life.
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 426
Likes: 4
From: Austin, TX
Mark,
This is a 05 GTO motor with the factory computer. Once the car gets moving, it goes pretty good, but off-the-line performance is pitiful. It is in a 65 Corvette with a tube frame, a 4L65E trans and a C4 Corvette Dana 44 rear end, with 3.45 gears. I have a 59 corvette with a stock LS1, and it would run away and hide form this car. My 4.8 liter chevy truck pulls harder off the line than this car does! It only weighs in at about 2900 lbs, so it ought to scream.
I take it that a good tuner should be able to wake this car up? The computer was programed by Speartech, and the harness is from them as well. No Cats, and a large, free flowing exhaust system. The drive train should be bullet proof.
How did the torque limiting get it's input to soften it up? Could the skewed calcualted engine load at idle have an effect? I presume that it is displaying a high calcualted engine load at idle because it does not have an input for barometric pressure, and that is used to calcualte the engine load. The Barometric pressure reads 99 at all times.
Thanks, John McGraw
This is a 05 GTO motor with the factory computer. Once the car gets moving, it goes pretty good, but off-the-line performance is pitiful. It is in a 65 Corvette with a tube frame, a 4L65E trans and a C4 Corvette Dana 44 rear end, with 3.45 gears. I have a 59 corvette with a stock LS1, and it would run away and hide form this car. My 4.8 liter chevy truck pulls harder off the line than this car does! It only weighs in at about 2900 lbs, so it ought to scream.
I take it that a good tuner should be able to wake this car up? The computer was programed by Speartech, and the harness is from them as well. No Cats, and a large, free flowing exhaust system. The drive train should be bullet proof.
How did the torque limiting get it's input to soften it up? Could the skewed calcualted engine load at idle have an effect? I presume that it is displaying a high calcualted engine load at idle because it does not have an input for barometric pressure, and that is used to calcualte the engine load. The Barometric pressure reads 99 at all times.
Thanks, John McGraw
Last edited by John McGraw; Jan 28, 2008 at 09:57 PM.
Trending Topics
The 99% you're showing on the rear o2s that have been deleted is normal. That's the fixed value when when o2 is removed. Is it possible that you have a traction control programming interfering. I had that happen one time and it killed the off the line performance. Can you see your speed signals?
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Topdon ONE vs. Artidiag 800 BT2: Which is the Diagnostic Tablet For You?
Pouria Savadkouei
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 426
Likes: 4
From: Austin, TX
Robby,
Yes I can see the vehicle speed on Autotap. What should I be looking for? does the torque management kill the timing to control torque? I have not been able to find out how the torque management control works. I contacted John at Speartech , and he said that he doubted it was torque management, and suggested the problem was fuel supply, but I checked the fuel pressure , and it was a steady 60 psi regardless of engine speed or throttle position.
Once I know what to trend the vehicle speed against, I will make another couple of pulls with the laptop graphing the parameters.
Thanks, John McGraw
Yes I can see the vehicle speed on Autotap. What should I be looking for? does the torque management kill the timing to control torque? I have not been able to find out how the torque management control works. I contacted John at Speartech , and he said that he doubted it was torque management, and suggested the problem was fuel supply, but I checked the fuel pressure , and it was a steady 60 psi regardless of engine speed or throttle position.
Once I know what to trend the vehicle speed against, I will make another couple of pulls with the laptop graphing the parameters.
Thanks, John McGraw
The torque management pulls timing and fuel pulse width on the injectors to control power, hence the "Traction Control". Will your Autotap show any data concerning traction control,meaning traction control enabled or disabled. I'll be somewhat free this weekend if this problem still persists,I could come over w/ my scan tool. Another thing to look at is your O2s. Is it fluctuating under throttle or is the voltage stuck low or high under throttle?
What you should watch is throttle opening. On the newer cars like yours with the ETC, it controls all that through the ETC. Log and watch your throttle position. It should be following your foot. If it is slowly coming open, then that is what is going on.
Thats right. You wanna log pedal position and actual throttle blade position, and if you stomp on it and the pedal position goes to 88% and the blade position slowly comes up, its most likely a torque management problem. The blade position should very closely match the position of the pedal.
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 426
Likes: 4
From: Austin, TX
The torque management pulls timing and fuel pulse width on the injectors to control power, hence the "Traction Control". Will your Autotap show any data concerning traction control,meaning traction control enabled or disabled. I'll be somewhat free this weekend if this problem still persists,I could come over w/ my scan tool. Another thing to look at is your O2s. Is it fluctuating under throttle or is the voltage stuck low or high under throttle?
Unfortunately, I only have the basic Autotap and not the extended codes. I can not see any parameters that pertain to traction control. If you get a chance, I would appreciate you stopping by with your tool.
The O2 sensor pattern is pretty normal, and the two sensors pretty much track each other. The fuel trims, both short term and long term, are modulating well and never get anywhere near minimum or maximum value.
Thanks, John McGraw
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 426
Likes: 4
From: Austin, TX
Thats right. You wanna log pedal position and actual throttle blade position, and if you stomp on it and the pedal position goes to 88% and the blade position slowly comes up, its most likely a torque management problem. The blade position should very closely match the position of the pedal.
Regards, John McGraw
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 426
Likes: 4
From: Austin, TX
I went out an made some pulls tonight with the data logger hooked up, and the problem is real obvious, but the source is still a big question mark.
I graphed the pedal position, commanded throttle position and the actual throttle position as well as both O2 sensors and Engine RPM.
The throttle is commanding correctly and the actual throttle position goes wide open as well. The O2 sensors fall off the face of the earth as soon as you nail the throttle! They hover down around the 0 mv level until the throttle position is dropped back, or the engine speed builds. The fuel pressure at the rail is rock steady the whole time. It would appear that either the program is not enriching the mixture when the throttle is opened, or the injectors are really clogged. I guess I will go to the auto parts store tonight and get some cleaner, but it is hard for me to believe that they could be clogged enough to cause this problem, but still have normal fuel trim values at all times except under high throttle position. What do y'all think?
Regards, John McGraw
I graphed the pedal position, commanded throttle position and the actual throttle position as well as both O2 sensors and Engine RPM.
The throttle is commanding correctly and the actual throttle position goes wide open as well. The O2 sensors fall off the face of the earth as soon as you nail the throttle! They hover down around the 0 mv level until the throttle position is dropped back, or the engine speed builds. The fuel pressure at the rail is rock steady the whole time. It would appear that either the program is not enriching the mixture when the throttle is opened, or the injectors are really clogged. I guess I will go to the auto parts store tonight and get some cleaner, but it is hard for me to believe that they could be clogged enough to cause this problem, but still have normal fuel trim values at all times except under high throttle position. What do y'all think?
Regards, John McGraw
Is it still MAF? Did you log the maf? And the injector DC? I've seen really dirty mafs cause pretty bad driveability problems. I would log those 2 along with some of the others you already have on. Also the MAP. Does it go right to 100 or 105 Kpa when you hit it?
Sounds like you're on the right track. Shouldnt be too hard to figure it out from here.
Sounds like you're on the right track. Shouldnt be too hard to figure it out from here.
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 426
Likes: 4
From: Austin, TX
The MAF looks real linear and smooth. I made another pull, and found that the comanded equivalency ratio never moved off of 1. From this, can I assume that the PE routine is not running at all? This would certianly explain the problems!
Regards, John McGraw
Regards, John McGraw
Thread Starter
TECH Regular
Joined: Jan 2004
Posts: 426
Likes: 4
From: Austin, TX
OK, I found a description of the Equivalency Ratio, and found that it only changes when the ECM is operating in the open loop mode. Back to the drawing board! I have exhausted everything I can think of, so I guess it is time to pull the ECM and send it back to John at Speartech and see if he can figure out what is wrong. It is goes extremely lean when the throttle is opened wide under load. The O2 sensors go below 25 mv at full throttle, until the engine speed builds.
Regards, John McGraw
Regards, John McGraw