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Hi, I'm trying to diagnose a problem with my 2011 Acadia. I've had some codes set and long term fuel trims seem to stay pretty negative -25 to -30. Short term bounces around +/- 10% maybe. Both banks run about the same. Doesn't seem to matter if its idle, cruising or hard accel. I'm thinking its probably the MAF. However, my scanner (Torque Pro on Android) is showing like -40 (if I remember correctly) for maybe ambient air 2. So I'm not sure if this is an incompatible sensor definition in torque or a real reading of a faulty sensor. DIC external temp seems about right. I've checked for vacuum leaks (though that seems pointless). Fuel pressure is reading in the 700+ psi at idle and runs >1000 when engine revs (its been a few weeks, I think it got up to maybe 1300-1400)

Background:
Car is at about 130k miles. Recently changed plugs, cleaned the MAF (with MAF cleaner), cleaned the throttle body, and changed the air filter. Also been fighting an AC issue, leaks then more leaks then compressor..... Still not working right but I don't think AC is related to the engine. However, engine could be related to the AC. If it thinks its way colder outside I'm thinking it might open up the expansion valves because less cooling would be needed and it might try to run at a lower high side pressure. I'm not really sure what the control for expansion valves are this is just a wild guess. In any case noticed codes after compressor was replaced but this is all within maybe 300 miles.

Might be a little sluggish off idle but I think this thing has always been that way but I haven't been driving it since its hot and AC isn't working. Its always felt a bit heavy handed with the filtering of the throttle.

Other random background bit, its always been a little "hunty" at idle. Doesn't really feel rough but tach is just +/- maybe 50 to 100 RPM. Been this way since I got it at 60k miles. Only reason I mention it is maybe this has been a long running issue with the MAF or temp. Rich codes are recent though.

Even now it still seems to drive pretty well, I think acceleration is normal but I don't have a metric to compare it to so could be down 10-15% and I probably wouldn't notice.

Questions:
Is the DIC temp sensor the same as the one used in combination with the MAF?
Is there some other thing I'm not thinking of that can cause a lack of metered air?
Injector doesn't seem like the problem since both sides are off. Pressure seems right from what I've seen on the internet. Anything else I should check before getting a new MAF?
 

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Questions:
Is the DIC temp sensor the same as the one used in combination with the MAF?
Is there some other thing I'm not thinking of that can cause a lack of metered air?
Injector doesn't seem like the problem since both sides are off. Pressure seems right from what I've seen on the internet. Anything else I should check before getting a new MAF?
The DIC displays ambient outside temperature reading. Intake air temperature is monitored by the IAT sensor. Check performance of the IAT sensor before changing the MAF.
 

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The DIC displays ambient outside temperature reading. Intake air temperature is monitored by the IAT sensor. Check performance of the IAT sensor before changing the MAF.
I thought it was probably different from the one shown on the DIC. Any idea where the IAT is? I'm assuming it has to be somewhere in that air stream, I would assume close to the MAF. Looked for something like that last time I was messing with it. Is it integrated in the MAF module?
 

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... Is it integrated in the MAF module?
I believe it is. Wiring for the IAT along with troubleshooting info should be available in the service manual. Links to download a manual are available in other threads of the forum - any Lambda platform model year after 2009 should be OK, since the engine variant is the same. Replacing parts without checking out the basics (wiring, connectors, fuses, etc.) doesn't always resolve the problem.
 

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Discussion Starter · #5 ·
Well I checked the IAT and the sensor seemed fine with an ohm meter. Also looked around on Torque and found what looks like the actual intake sensor and it also seems to read about right.

Anything else I should check before replacing the MAF? Fuel pressure was being reported at 550-680 idle (using ODB2 sensor). I can't think of anything else that really makes sense other than the MAF.
 

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You stated you had some codes set, what codes? There are a few test procedures for the maf on the web, see if you can test it. Sounds like the car runs fine and such a negative fuel trim does not match that. Check for vac, exhaust leaks. O2 sensors could be faulty. Clear all data and start checks again. did all of this happen before or after you changed plugs, cleaned maf? List all codes then can offer more advice.
 
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