Hesitation Under Load. Backfires.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,683
Likes: 1
From: Houston Texas
Hesitation Under Load. Backfires.
I took my car in for a dyno tune 2 weeks ago and had problems on the dyno. It was throwing Traction Control, ABS, and Active Handling codes at WOT on the dyno. My car has a mild cam (228/230 112lsa), headers, and a Vararam. Nothing crazy. I've had it like this for about 2 years with another dyno tune and no major WOT problems.
Here's what the dyno looked like from 2 weeks ago:
I have since replaced the clutch because my slave cylinder was leaking and took the car out to test it. The car idles fine, takes off fine, but putting any load on the car will cause it to stumble and hesitate. It will even backfire! For the most part it still has good power but is very inconsistent.
The codes I had were C1221 and C1222 and C1248. I reset these earlier today and they have not come back on.
I read that it was a good idea to check the ground wire plugs. Did that tonight. They looked ok but I rubbed the connection with some sandpaper for good measure. NOW, my headlights won't go down!!
I don't know what to do. Any suggestions would be much appreciated.
Here's what the dyno looked like from 2 weeks ago:
I have since replaced the clutch because my slave cylinder was leaking and took the car out to test it. The car idles fine, takes off fine, but putting any load on the car will cause it to stumble and hesitate. It will even backfire! For the most part it still has good power but is very inconsistent.
The codes I had were C1221 and C1222 and C1248. I reset these earlier today and they have not come back on.
I read that it was a good idea to check the ground wire plugs. Did that tonight. They looked ok but I rubbed the connection with some sandpaper for good measure. NOW, my headlights won't go down!!
I don't know what to do. Any suggestions would be much appreciated.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,683
Likes: 1
From: Houston Texas
I took it to work this morning. Somehow magically the headlights went down on their own at some point overnight 
Car will still backfire occasionally. I start noticing the problem at highway speeds. I can be cruising in 6th at 60-70 and give it half or so throttle and it will start to hesitate and bog down. Doing this will cause it to backfire occasionally.
No codes at all, no warnings, nothing.
Could it be something simple like a bad spark plug or wire? Wouldn't that throw codes?
Need some help please!
Car will still backfire occasionally. I start noticing the problem at highway speeds. I can be cruising in 6th at 60-70 and give it half or so throttle and it will start to hesitate and bog down. Doing this will cause it to backfire occasionally.
No codes at all, no warnings, nothing.
Could it be something simple like a bad spark plug or wire? Wouldn't that throw codes?
Need some help please!
Tech Contributor
Joined: Jan 2007
Posts: 19,350
Likes: 1,124
From: Dyer, IN
I took it to work this morning. Somehow magically the headlights went down on their own at some point overnight
Car will still backfire occasionally. I start noticing the problem at highway speeds. I can be cruising in 6th at 60-70 and give it half or so throttle and it will start to hesitate and bog down. Doing this will cause it to backfire occasionally.
No codes at all, no warnings, nothing.
Could it be something simple like a bad spark plug or wire? Wouldn't that throw codes?
Need some help please!
Car will still backfire occasionally. I start noticing the problem at highway speeds. I can be cruising in 6th at 60-70 and give it half or so throttle and it will start to hesitate and bog down. Doing this will cause it to backfire occasionally.
No codes at all, no warnings, nothing.
Could it be something simple like a bad spark plug or wire? Wouldn't that throw codes?
Need some help please!
You said you examined the plugs, I hope the sandpaper was not used on the electrode.......
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,683
Likes: 1
From: Houston Texas
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,683
Likes: 1
From: Houston Texas
Since you had your car at a tuner, and he had the ability to read all the sensors in real time, what feedback did he provide on the cause? What is the history with the car, and when did this start exactly? What is your fuel pressure? Have you inspected the AIR connections for security and leaks?
You said you examined the plugs, I hope the sandpaper was not used on the electrode.......
You said you examined the plugs, I hope the sandpaper was not used on the electrode.......
As far as the history of the car, I've had this cam in for over 2 years with an OK tune that did not cause any problems. Maybe it was just a coincidence that it happened on the dyno with a new tune.
I did find a loose wire in the front passenger side O2 sensor plug while I was swapping my clutch this weekend. I pushed it back in and it stayed, but that didn't change anything. Could be a good place to start.
The sand paper was not used on the spark plugs, just on the ground connections to the frame.
Not sure what my fuel pressure is, but I have replaced my fuel filter within the last 6 months.
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
In regards to the dyno run, I'm not an expert or anything similar but, the PCM looks at the wheel speed sensors in comjunction with the EBTCM and so on all making determinations if the wheels are turning as expected. So on the dyno, hopefully you turned off the AH/TC systems otherwise they will indeed try to put on the brakes and so on due to the front wheels not moving and the rears are. This would throw codes like crazy for those systems and induce lots of engine control issues. If I missed something you said, feel free to tell me to be quiet...lol
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Tech Contributor
Joined: Jan 2007
Posts: 19,350
Likes: 1,124
From: Dyer, IN
I'm really suprised your tuner was not able to provide more insight.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,683
Likes: 1
From: Houston Texas
In regards to the dyno run, I'm not an expert or anything similar but, the PCM looks at the wheel speed sensors in comjunction with the EBTCM and so on all making determinations if the wheels are turning as expected. So on the dyno, hopefully you turned off the AH/TC systems otherwise they will indeed try to put on the brakes and so on due to the front wheels not moving and the rears are. This would throw codes like crazy for those systems and induce lots of engine control issues. If I missed something you said, feel free to tell me to be quiet...lol
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,683
Likes: 1
From: Houston Texas
I'm not sure what pin lock are you talking about? The wire that was pulled out was part of the male connector of the wiring harness that leads up to the engine, not part of the O2 sensor itself. I shoved it back in and it held snug, but it's possible that it's not getting a good connection. What is involved with replacing this? Does GM sell these plugs/connectors or do I have to trace the wiring harness back to the computer?
I think my first step tonight is to swap out the plugs with some new TR55's. If that doesn't do the trick, then wires. If not that, then the O2 plug.
After that it's back to the tuner.
Not sure what else it could be.
Tech Contributor
Joined: Jan 2007
Posts: 19,350
Likes: 1,124
From: Dyer, IN
A slipping clutch was one of my thoughts at the time too b/c I had a leaking slave. This was the main reason I swapped clutches this weekend. That should at least take that portion out of the equation.
I'm not sure what pin lock are you talking about? The wire that was pulled out was part of the male connector of the wiring harness that leads up to the engine, not part of the O2 sensor itself. I shoved it back in and it held snug, but it's possible that it's not getting a good connection. What is involved with replacing this? Does GM sell these plugs/connectors or do I have to trace the wiring harness back to the computer?
I think my first step tonight is to swap out the plugs with some new TR55's. If that doesn't do the trick, then wires. If not that, then the O2 plug.
After that it's back to the tuner.
Not sure what else it could be.
I'm not sure what pin lock are you talking about? The wire that was pulled out was part of the male connector of the wiring harness that leads up to the engine, not part of the O2 sensor itself. I shoved it back in and it held snug, but it's possible that it's not getting a good connection. What is involved with replacing this? Does GM sell these plugs/connectors or do I have to trace the wiring harness back to the computer?
I think my first step tonight is to swap out the plugs with some new TR55's. If that doesn't do the trick, then wires. If not that, then the O2 plug.
After that it's back to the tuner.
Not sure what else it could be.
Tech Contributor
Joined: Jan 2007
Posts: 19,350
Likes: 1,124
From: Dyer, IN
I know you said the traction control was off during the dyno run, but is there a chance the tuner forgot initially?
The codes you posted are consistent with the system sensing two wheels moving(on the same axle), in conjunction with two wheels stationary(on the same axle). A C1221 & C1222 will precipitate a C1248.
The codes you posted are consistent with the system sensing two wheels moving(on the same axle), in conjunction with two wheels stationary(on the same axle). A C1221 & C1222 will precipitate a C1248.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,683
Likes: 1
From: Houston Texas
I know you said the traction control was off during the dyno run, but is there a chance the tuner forgot initially?
The codes you posted are consistent with the system sensing two wheels moving(on the same axle), in conjunction with two wheels stationary(on the same axle). A C1221 & C1222 will precipitate a C1248.
The codes you posted are consistent with the system sensing two wheels moving(on the same axle), in conjunction with two wheels stationary(on the same axle). A C1221 & C1222 will precipitate a C1248.
Tech Contributor
Joined: Jan 2007
Posts: 19,350
Likes: 1,124
From: Dyer, IN
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,683
Likes: 1
From: Houston Texas
When I took it in for a dyno tune 2 weeks ago, the tuner had it on the dyno. That graph is on my first post.
The tuner and I talked about the traction control issues. He purposefully turned off the TC/AH and it would still throw warnings during the pull.
The tuner and I talked about the traction control issues. He purposefully turned off the TC/AH and it would still throw warnings during the pull.
Tech Contributor
Joined: Jan 2007
Posts: 19,350
Likes: 1,124
From: Dyer, IN
