Miss under WOT... help
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Heel & Toe
Joined: Aug 2017
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Miss under WOT... help
Long story short. I purchased a c6 off of a close friend that he had wrecked. Minor consmetics and the intake along with maf is all that was damaged. Everything is new including the maf and under wot it falls on its face around 3k rpms and will stay there until I slightly lift the throttle. 90% throttle it’s fine and will pull all the way to redline. If I’m running above 3k and floor it, it falls instantly. No cels other than a rear o2, which I’m told will not affect performance and cause this issue. It was running perfect before the accident. Fuel pressure holds 60 psi at all times. Plug wires have been swapped. I’m swapping the maf port with a new one because I feel it’s maf related. Anything else I should look into ?
Race Director
Joined: Sep 2007
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From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
Long story short. I purchased a c6 off of a close friend that he had wrecked. Minor consmetics and the intake along with maf is all that was damaged. Everything is new including the maf and under wot it falls on its face around 3k rpms and will stay there until I slightly lift the throttle. 90% throttle it’s fine and will pull all the way to redline. If I’m running above 3k and floor it, it falls instantly. No cels other than a rear o2, which I’m told will not affect performance and cause this issue. It was running perfect before the accident. Fuel pressure holds 60 psi at all times. Plug wires have been swapped. I’m swapping the maf port with a new one because I feel it’s maf related. Anything else I should look into ?
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
Long story short. I purchased a c6 off of a close friend that he had wrecked. Minor consmetics and the intake along with maf is all that was damaged. Everything is new including the maf and under wot it falls on its face around 3k rpms and will stay there until I slightly lift the throttle. 90% throttle it’s fine and will pull all the way to redline. If I’m running above 3k and floor it, it falls instantly. No cels other than a rear o2, which I’m told will not affect performance and cause this issue. It was running perfect before the accident. Fuel pressure holds 60 psi at all times. Plug wires have been swapped. I’m swapping the maf port with a new one because I feel it’s maf related. Anything else I should look into ?
Thread Starter
Heel & Toe
Joined: Aug 2017
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Changed plugs today and the maf is a new acdelco. Spliced in a new plug for the sensor and it still remains. If I let it sit and it gets really warm in the engine bay I can floor it and it bogs and sits at 3k rpms. If I slightly let off then it climbs to redline. There’s been a few instances while checking fuel pressure that the throttle is completely unresponsive like it’s not getting any fuel at all but the fuel pressure is at 60psi. Cut off and restart and it’s back to normal. He said the car had no issues at all before the accident.
Le Mans Master
Joined: Mar 2006
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From: Texas
Check for intake and exhaust leaks. The car runs in closed loop most of the time, getting feedback from the front O2 sensors. But at WOT it goes into open loop, calculating the amount of fuel based on the amount of air going into the engine. I would check all over for intake leaks. The accident may have knocked a hose loose from the intake, letting a large amount of air in. You could have an exhaust leak as well that might be causing this, so check for intake and exhaust leaks.
Another thing I would do is floor it so that it bogs like you said, then shut it off immediately. Check all the plugs and see if it's a particular cylinder or bank of cylinders.
Another thing I would do is floor it so that it bogs like you said, then shut it off immediately. Check all the plugs and see if it's a particular cylinder or bank of cylinders.
Thread Starter
Heel & Toe
Joined: Aug 2017
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System too lean bank one code now. I’ve checked all over the intake and I’m not seeing any leaks. I can’t see bad o2’s causing a wot issue because they aren’t used wot. I’m goin to look back over it again. Mayb I missed something
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
at the MAF I’d check for 12volts, the 5 volt reference and the signal ground( <100 Mv) !!...you can unplug the MAF and let it run off “speed density”...the MAP sensor...see if it bogs at 3000 !!
Last edited by C5 Diag; Nov 30, 2018 at 06:40 PM.
Thread Starter
Heel & Toe
Joined: Aug 2017
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Maf unplugged has the same issue. I can replicate the issue and have the throttle to the floor and it sits at 3k rpms just bogging but holding a steady 60 psi. I haven’t tested maf voltage but I will first thing tomorrow. A good scanner would be really nice. A friend has blue driver and I’m gunna try it out tomorrow or Sunday and see what I can come up with.
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Thread Starter
Heel & Toe
Joined: Aug 2017
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What’s sorta strange tho is ever so often when I’m checking fuel pressure, it will sit at idle and I will have no throttle response at all. Nowhere. I had play with the throttle and find a few spots but it will just sit there and idle normally. That makes me think tps but I haven’t had any codes there. All while still holding 60 psi
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
Ok, like I had said I’d check the fuel pressure under snap throttle...if the throttle isn’t responding yes you can may have issues with your TPS sensor...you can check the signal wires at both sensors with a multimeter but it’s best to check it with a scope...muti meter isn’t fast enough to see those quickly changing voltages...I’ll include a video I did with my ‘01 (TPS Sweep)...one signal wires goes up as the throttle is increased and the other decreases...a Blue Driver will work..I keep one plugged into my daily driver...I’d concentrate on your O2 sensors ( maybe bank 1 upstream O2 sensor signal is low (lean) and way below 450 mv’s ) and your long and short term fuel trims...see if that bank 2 long term fuel trim is also high.
Thread Starter
Heel & Toe
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I’ll check it tomorrow. I’ll also make a video of what’s going on so you can get an idea. It’s like 3k rpm is the redline at wot. If at 5k rpms I go wot it just bogs down till It reaches 3k unless I slightly lift up off the throttle then it carries on to redline as normal. I’ll check the snap throttle in the morning and see if I can get more data.
Thread Starter
Heel & Toe
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So it won’t let me post the videos of the issues. But I did test the throttle positions and it all looked good except for throttle actuator control motor command. At wot it sees 30 percent and sometimes 20. It’s different at wot every time. It could be normal but I’m not positive. I removed upstream o2’s With no luck. I plan one switchin injectors and coil packs to the opposite bank because now I get a lean bank 1 code.
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
So it won’t let me post the videos of the issues. But I did test the throttle positions and it all looked good except for throttle actuator control motor command. At wot it sees 30 percent and sometimes 20. It’s different at wot every time. It could be normal but I’m not positive. I removed upstream o2’s With no luck. I plan one switchin injectors and coil packs to the opposite bank because now I get a lean bank 1 code.
Thread Starter
Heel & Toe
Joined: Aug 2017
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And I removed upstream o2’s to make sure cats weren’t clogged and it still stopped at 3k. I was goin to swap banks with injectors and coils to see if I got lean bank 2 and it would point me towards bad injector or coil.
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
Oh, OK...can you show your O2’s and fuel trims at idle and 3000 RPM ??...my TAC data doesn’t show a motor data PID... I’ll have to look at my live data !!
Thread Starter
Heel & Toe
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Finally found it. Something stupid. Clutch position switch. Wasn’t pushing in all the way when the clutch was released. May have been user error by me or may have been just gunked up from sitting for a year without being driven. Found it scrolling through the computer and took it out and played with it a bit and runs like a dream now. Thanks for all the help guys I appreciate it. Thought I’d relay the msg for anyone who had similar issues.