2007 GMC Sierra 1500 (MAX) #6 misfiring

Hi all,

This had happened before 3x, but was about to turn truck off and wait 10 second and turn back on. Then truck would run fine for months. I found this on my truck manual.

My truck is riding differently. Here’s the story - I put new tires on Friday, an hour later, my truck started to ride rough. The light on dashboard is; Check engine, Engine power lost (truck would not get up when this was shown on dash. This error has not come up again), stibilitrac check. Truck’s driving performance; Idle sputters (like RPM rising, but they are not, it’s just the engine shaking), once driving when it shifts hard at 3000 RPMs (only 2nd gear). I took my truck to Advance, and this was the error code I received; #6 Cylinder Misfiring and Actuator module. I changed all spark plugs and number #6 was very dirty compared to the other and smelt very much so like gas. I have not driven this truck only cracked and it stayed in park. I had a person look at it, and he said that the #6 cylinder was the only problem he could find when he hooked up his code thingy. Now he played with everything and took out the #6 spark plug (this is now Tues) and said that it didn’t smell of gas like it should have. At the end. he stated that we first should change the Injector for #6. and if that did not correct the problem, then he would recommend the lifters to be replaced. I asked how confident he was about “his” diagnosis. and he stated… I am not a GM mechanic… wow. now I am confused as to what I should really do! BTW, he never cleared the error codes. :-/

Please anyone please advise!


It sounds like the only person who has looked at the truck was the guy from Advance Auto Parts. Have you had an actual mechanic look at it?

Check the “Mechanics Files” section of this site for a recommended local mechanic and get a professional opinion on it before you start replacing parts randomly.

I really was asking for suggestions as I do have an appt with a shop, but was hoping I could have figured it out with help to save money. :frowning:


For starters, how about telling us what engine you have

Please post the exact fault codes . . . you had at least 2 codes, correct?

Once you do that, I can post a thread which shows the parameters for those codes

How many miles?

Ok I took it to a GM certified service shop. This is what they told me on the phone. I had 49 error code pop up which after having that many they could not exactly pen point the problem. They said that # 6 cyclinder has NO compression and that the truck was running off only 5 cylinders. Given the above and still not certain they recommend me repairing the camshaft, lifters and V-LOM @ $4,950. He said transmission was fine. I asked how certain they felt on this being the problem and they said that they couldn’t answer. I asked If I could get a print out of all 49 error codes and he hesitated and said I will see what I can do. My husband went there to pick up my truck and they told him something different. Here is the new story is - when retesting the error codes only one code came up, P0306 (cylinder #6 misfire). And that 175lb was the compression on #6. Also they told him that they could not provide the error codes they once told me as there system did not print.

I know I heard him correctly when i talked with him earlier because I asked for him to hold on so I could get a pen and paper. I wrote everything down while he was on speaking… Another person heard the details.

The truck is not knocking or tapping… It’s just sputters @ idle and hard shifts in 2nd gear. The lights on the dashboard are still the same as my first post.

Truck description: 2007 GMC Sierra Vortec Max, 6.0 4x4.

& 107,000 miles


It disturbs me that the shop told you and your husband 2 different stories

And it also bothers me that they couldn’t give you a printout of those codes

But at least we know you got P0306

It sounds as if the compression for that cylinder is acceptable

If it were my truck, the first thing I’d do is change all of the spark plugs, as they’re due at 100k. I would install the AC Delco parts that are listed in the owner’s manual. A bad and/or worn plug can definitely cause a miss.

If that doesn’t help, I’d suggest getting somebody to perform a fuel pressure test and a fuel injector balance test.

I was just rereading your original post, and it seems that you had a throttle actuator code at one point. There are many possible causes, but the first thing I would do is clean the throttle body.

A 175 pounds of compression is perfectly acceptable. If there’s a miss on that cylinder then it’s going to be ignition related (spark plug, coil, etc) or fuel injector related.

How they go from zero compression with 5 grand worth of guesswork repairs to 175 PSI of compression is reason enough to get the truck away from them.

The odds of the camshaft or lifters causing the problem are very, very slim; or zero.

Did the person who pulled the No. 6 spark plug reinstall that plug?

Update: we have another mechanic checking the compression and grounds later today. As soon as we were pulling up the truck started to shift fine and the idle was almost prefect. The mechanic got in the truck to feel and hear what we were talking about and he said it does seem to be any cam or lifter problem. He thought is was the fuel injector. He ask us to leave the truck at his shop and will start looking at it later. We did. Oh by the way… I turned off the radio and it came back on - this happen mulipule time while driving to the mechanics shop. When the mechanic first got in I had the radio off after a few seconds of the truck being on the radio came on again.

I have changed the spark plugs and wires. The new spark plug for 6 doesn’t smell of gas either. The Battery died which we replaced yesterday.

I cleaned the throttle body or the butterfly before we took it to the GM service shop. “Cleaning” to me is cleaning all the black stuff off.

The spark plug was put back in after testing.

I will post back once we talk to the other mechanic.

Thank y’all for helping a girl out!


Thanks for the update

It sounds like you’re on the right track now

BTW . . . I just looked up your maintenance schedule on a GM website. It seems your transmission is due for service every 50K under “severe” driving or every 100K under “normal” driving

If you’re going to get it serviced, I suggest a pan drop, with fluid and filter replacement using only Dexron 6. I am against the transmission flush.

I’m not sure if the transmission service will fix any shifting complaints, but it should be done anyways.

Just heard back from the other mechanic.

Cannot find any issue with the cam nor the lifters. Compression was 90lbs every time he tested, and believe the reason for 90lbs was cause by the following finding. —> #6 cyclinder (the one that was misfiring) was soaking wet in gas. He believed that the fuel injector is stuck open and suggested us to replace. Will are going to pick the truck up and replace. Please cross your fingers, on one hand though, for that to be the solution!

What are your thoughts?

Thank you!


A cylinder flooded with fuel is going to have low compression

I hope that he diagnosed that stuck open injector . . . versus just guessing

With the right tools, and the knowledge of how to use them, faulty injectors can be diagnosed

Ummm, great point. I don’t think he tested the injector… I think he is assuming due to the amount of fuel. If i would have known there is a test that could havr been done i would have asked. What else would cause heavy fuel in the injector?

Replacing 1 injector is not expensive. Any reason why u don’t want shop to do it? They keep saying it is issue. Tell them to guarantee repair? New injector= fix or no charge?

Ok problems have occurred again today. Went to O’reillys and bought the part. Took the fuel injector out and right before I was going to put in the new injector it was not the correct one. I went back to O’reillys to exchange, I took the original one with me, but they stated it was the correct one. I’ve called every part store around while for my year is the same as O’Reillys. I cannot/ they cannot figure it out. There is a part number on the original Delco part that Parks Auto Parts was able to reference the part number to another fuel injector (not for my year on style… GMC light duty… It something). But they didn’t have any in stock to purchase. I call another GM here in Charleston… They wanted me to explain what’s going on, I did. They said that I should bring it to them as they believe low compression would be a sign that the cam and or lifter problem and not a fuel injector. They also stated the if I being it to them they will run the text and fix the problem… If they misdiagnosed i would not have to pay for they service.

I am soooo confused. How can I not find the part for one? Two, what should I do?

Sorry you are having this frustrating problem. You may have to order the correct injector from a dealer and just wait for it to arrive from their warehouse or distributor. Don’t try to speed things up by using the wrong part.

I can’t tell what is wrong by the posts above, but one time I had a problem w/a VW Rabbit that – after I had tested the fuel injectors then put everything back together – it wouldn’t start no matter what I did. It turned out that the test I had done had squirted a lot of gasoline into the cylinders, and the engine was so flooded it wouldn’t start. The remedy? Remove the spark plugs and just let the gas evaporate. I did that, and it ran fine.

What I’m saying is that part of this problem may be a result of the various tests that have been done, rather than something wrong with the vehicle. Pro’s w/experience w/this engine have tests to verify if an injector is working or not, with no ambiguity. At this point, suggest to find one and get their help. At least to diagnose the exact problem.

The dealer you talked to should realize that if an injector is stuck open or is being held open electronically then low compression could be for the very reason db4690 stated; the cylinder wall has been washed down with gasoline.

The odds of low compression being due to a worn cam lobe or faulty lifter are miniscule at best.

Had same exact symptoms 2007 gmc z71. Replaced number six spark plug. Gas smell is from spark plug not igniting fuel. Ran fine afterward.

Hi, did you ever solved this issue? I am running into the same exact issue like yours. Same stories from mechanics, etc.

Our prob ended up being the camshaft and all the lifters, but once they were working to fix those they seen the oil pump was bad which they told me that was probably the cause of the the cam and lifters going bad.

Hope this helps.

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