Intermittent acceleration problem--request advice!
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Joined: May 2009
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From: San Antonio TX
Intermittent acceleration problem--request advice!
I have an '07 Z51 manual with 11K miles that occasionally exhibits some strange behavior under moderate to hard acceleration. The vehicle's only mod is a BB Bullet cat-back; I purchased the vehicle used with 4600 miles and in my best estimate, this problem began when the car had more than 6K and has occurred 4 or 5 times since: Under acceleration load, typically in first or second gear, the car will not accelerate smoothly; rather, it almost acts as if it hits an artificial rev limiter anywhere between 3K and 5K rpm. At this point, the car bucks fairly violently as it would when you hit the normal rev limiter (alternating slowing/revving) despite the gas pedal held constant. This problem seems to only occur early in a drive; that is, after some shifting and a few minutes, I can resume any acceleration I want with no issues. However, it seems to be independent of warm-up--ie, it can happen following a brief shut-down period after a warm-up cycle (like a return trip from the post office or something). None of these occurrences has resulted in a CEL. Any help short of "take it to the dealer" would be appreciated. Some pointed questions for the experts: could this be a result of water in the gasoline? Engine knock retardation? Something else entirely?
Tech Contributor
Joined: Dec 2006
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From: Van Buren Arkansas
Wounded Warrior Escort '11
If it was water in the gas, when you next filled up, it would probably have gone away. Assuming it didn't go away, you need to get a code reader and see if any codes are present in the onboard systems. This could be as simple as a MAF sensor needing cleaning as already mentioned to a wire grounding issue with the coil circuits. I too have an '07 Z51 but no such problem with mine. On the C-5's, the coil wires and so on, all ground to the driver's side head in the rear of it. Now I don't know and have not looked to see if GM continued that on the C-6's but if they did and it was lose, that would cause this. Also, you should look at the battery connections and especially the battery to solenoid connection as that is the electrical center for the power from the alternator to battery and battery to the car's systems. I found mine wasn't as tight as it should have been, but not quite lose either. Maybe your's has loosen up a bit.
Team Owner
Joined: Jun 2005
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From: Northern, VA
St. Jude Donor '15
"In honor of jpee"
can't always hear pinging, right? also, have you done a disconnect/reconnect of the battery cable? I doubt it's water in gas, but you could try a bottle or two of isogas (isopropyl dry gas---red bottle).
some other good suggestions in this thread to look into.
some other good suggestions in this thread to look into.
Racer
Joined: May 2006
Posts: 471
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From: Overland Park Kansas
A lot of good suggestions already here...
My first thought was a dirty MAF sensor, then a glitch in the throttle by wire, plugged cat?, or fuel delivery system...but since it not throwing the CEL on...
perhaps an active handling/TM concern?
Electrical gremlins can be hard to track down (I assume no water damage or some new fangled electronic gizmo wired in lately?)
Corrosion and ground issues are sneaky at best.
I think (unless someone has a really good answer, or had it happen to them), your only choice is to take it in and have it checked out before it possibly harms you, itself, or someone else.
g/l and keep us posted
My first thought was a dirty MAF sensor, then a glitch in the throttle by wire, plugged cat?, or fuel delivery system...but since it not throwing the CEL on...
perhaps an active handling/TM concern?
Electrical gremlins can be hard to track down (I assume no water damage or some new fangled electronic gizmo wired in lately?)
Corrosion and ground issues are sneaky at best.
I think (unless someone has a really good answer, or had it happen to them), your only choice is to take it in and have it checked out before it possibly harms you, itself, or someone else.
g/l and keep us posted
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Joined: May 2009
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From: San Antonio TX
I haven't noticed any pinging in normal driving or hard acceleration, but I suppose that doesn't rule it out. I do use 91 or 92 octane gas, depending on what I can find--haven't really seen 93 out here. Tomorrow I'll check/reset electrical connections and check the MAF. In another note, I do have a code reader, but strangely it won't power up even when the car is in the ignition on/engine off mode, yet it powers up fine in other vehicles. Certainly something I will be looking into. As far as water damage, there has been none during my ownership and I haven't found any evidence in the engine compartment or beneath any of the floor carpeting.
Thank you to all for the advice thus far. Updates as this develops...
Thank you to all for the advice thus far. Updates as this develops...
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Thread Starter
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Joined: May 2009
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From: San Antonio TX
Today I borrowed a different code reader and found no pending codes or stored memory codes. With that, I disconnected the neg cable and continued on. Removal and inspection of the MAF sensor revealed a clean honeycomb and all filaments intact and without debris or residue. No corrosion on the connection either. I then inspected all connections to spark plugs/fuel injectors/coils and all seemed in good shape. I could not find any loose grounds from the battery or any loose connections near the ECU. I reconnected the battery cable, went and filled my tank, and poured in a bottle of isogas.
Time will tell... also, the possibility that I have a faulty MAF remains...is there a good way to test this?
Time will tell... also, the possibility that I have a faulty MAF remains...is there a good way to test this?
Somba master
Joined: Mar 2005
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Cruise-In 7, 9 & 12 Veteran
Wounded Warrior Escort '11
St. Jude Donor '07-'08-'09-'10-'11
I have had a similar problem with moderately spirited acceleration.
I was instructed to disconnect the battery for a few hours, and reconect.
To my amazement, the problem was gone. It has been a few weeks since, and all is still well.
GM
I was instructed to disconnect the battery for a few hours, and reconect.
To my amazement, the problem was gone. It has been a few weeks since, and all is still well.
GM
Burning Brakes
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From: BROOKLYN NY TO SOCAL CA
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Joined: May 2009
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From: San Antonio TX
Would you attribute the fix to disconecting the battery or something else?
