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Discussion Starter #1
Hi,

I have a 2009 Acadia SLT and lately it has been running a bit rough.

Previously it had a misfire code for cylinder 5. I replaced all the plugs, as well as the boots for the coils.

It ran well for a few weeks, but now I am getting some hesitations under load, but no misfire codes -- In fact, no CEL light or codes at all. I have a Thinkdiag OBD2 scanner, so I can look for fault codes in every system of the Acadia, but even with than no actual or pending codes are showing up in either the Engine or transmission.

Any ideas where to look to help resolve?

Thanks,

Tom
 

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how many miles?
 

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Has it run rough with multiple tanks of gas? Maybe try some fuel system cleaner as a simple start.
 

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The Acadia has 220k miles. Previous owner had the timing chain done, but that was likely 80 to 100k miles ago. Transmission was rebuilt at about 160k, and I replaced the TEHCM pressure discs about a year ago (Tranny seems to be running fine, with no fault codes present) I have run several tanks with Techron fuel cleaner, but I can always do that again or switch to a different fuel system cleaner. Most of my driving nowadays is 2 to 5 miles, with the occasional trip to the hardware store that requires a trip over a large bridge. It is usually when driving over the bridge that the hesitation occurs, although it also runs rough (slight misses) at idle until warmed up. I can manage if I step on the gas and the transmission kicks down a gear, but it will hesitate when traveling at 60 to 65 and it comes upon an incline.

I changed the oil a few weeks ago. Low oil levels have produced multiple misfires in the past, as it affects the variable valve timing mechanism, but that will trigger the CEL. I will check oil level again today, but I don't think that is the issue as this problem preceded the last oil change.

I replaced a catalytic converter a couple of months ago, and that CEL has not tripped since. There was no rough running with the Cat, just the CEL light tripping.

It looks like I have a couple of small pinholes in both the mid muffler and the rear muffler on the passenger side, which I will probably just patch up until I can find used replacements.

About a year ago I had an issue with a shorted high-pressure sensor on the AC line that cause all sorts of problems. Apparently a bunch of the the low voltage sensors share a common power supply, so if one shorts the computer gets all whacked because the throttle body positioning sensor voltage, throttle pedal positioning sensor and about 10 others are also thrown off. That one took weeks to sort out, and was finally resolved with a trip to the auto electric shop.

I hesitate to replace the coils and plugs again without first getting a misfire code, but I am running out of ideas.

If this is a fuel-related issue, does anyone know what the pressure at the fuel rail should be? I can get that data (and just about anything else) from my ThinkDiag scanner.

Thanks,

Tom
 

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Have you scoped the intake valves and looked for excessive carbon deposits on them? Carbon deposits in the GDI engines can cause running problems and may or may not set misfire codes.
 
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Have you scoped the intake valves and looked for excessive carbon deposits on them? Carbon deposits in the GDI engines can cause running problems and may or may not set misfire codes.
Following as your problem sounds exactly like mine ....
 

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The Acadia has 220k miles. Previous owner had the timing chain done, but that was likely 80 to 100k miles ago. Transmission was rebuilt at about 160k, and I replaced the TEHCM pressure discs about a year ago (Tranny seems to be running fine, with no fault codes present) I have run several tanks with Techron fuel cleaner, but I can always do that again or switch to a different fuel system cleaner. Most of my driving nowadays is 2 to 5 miles, with the occasional trip to the hardware store that requires a trip over a large bridge. It is usually when driving over the bridge that the hesitation occurs, although it also runs rough (slight misses) at idle until warmed up. I can manage if I step on the gas and the transmission kicks down a gear, but it will hesitate when traveling at 60 to 65 and it comes upon an incline.

I changed the oil a few weeks ago. Low oil levels have produced multiple misfires in the past, as it affects the variable valve timing mechanism, but that will trigger the CEL. I will check oil level again today, but I don't think that is the issue as this problem preceded the last oil change.

I replaced a catalytic converter a couple of months ago, and that CEL has not tripped since. There was no rough running with the Cat, just the CEL light tripping.

It looks like I have a couple of small pinholes in both the mid muffler and the rear muffler on the passenger side, which I will probably just patch up until I can find used replacements.

About a year ago I had an issue with a shorted high-pressure sensor on the AC line that cause all sorts of problems. Apparently a bunch of the the low voltage sensors share a common power supply, so if one shorts the computer gets all whacked because the throttle body positioning sensor voltage, throttle pedal positioning sensor and about 10 others are also thrown off. That one took weeks to sort out, and was finally resolved with a trip to the auto electric shop.

I hesitate to replace the coils and plugs again without first getting a misfire code, but I am running out of ideas.

If this is a fuel-related issue, does anyone know what the pressure at the fuel rail should be? I can get that data (and just about anything else) from my ThinkDiag scanner.

Thanks,

Tom
I had similar issues with my 2009 GMC Acadia which has about 220k miles. I had a local garage look at it but ended up taking it to the dealer. It ended up being the rear wiring for the fuel pump that had rusted through -- at least that's what I recall. It was a fairly simple fix which the dealer repaired.
 

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Discussion Starter #8
I had similar issues with my 2009 GMC Acadia which has about 220k miles. I had a local garage look at it but ended up taking it to the dealer. It ended up being the rear wiring for the fuel pump that had rusted through -- at least that's what I recall. It was a fairly simple fix which the dealer repaired.
Electrical problems can be frustrating. Glad yours got taken care of.
 
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