GMC

GMC Troubleshooting Questions? Ask a Mechanic for Answers

Ask an Expert,
Get an Answer ASAP!

GMC

I have a customer with a 2010 GMC Acadia. Codes have been

Customer Question
I have a customer with...
I have a customer with a 2010 GMC Acadia.
Codes have been set for misfire on cylinders 1, 3, and 5 (essentially bank 1) and P0300 random/multiple misfire. Codes also set for P2097 (post cat fuel too rich). LT fuel trim is showing about -20%, more negative under load than at idle. Engine runs rough with obvious misfire.
Historical data shows tens of thousands of misfires on cylinder 3, with about a thousand on 1 and 5. My thoughts are cylinder three is my true misfire and 1 and 5 are either registering wrong or being affected by the performance of cylinder three. I am able to command cylinder 3 off with my scan tool and the rate of misfires on cylinder three increase, so I do not believe cylinder 3 is a "dead cylinder", but it does misfire with great frequency. Cylinder 3 has good compression (~180 PSI) that matches it's neighboring cylinders.
02 sensors all show appropriate voltage and voltage gently moves between .1-.9 V as expected. All 02 sensors respond appropriately when I induce rich or lean condition with starter fluid or causing vacuum leak.
So, cylinder 3 misfire with tons of unburned fuel on that bank. Dealership changed spark plugs and recommended catalytic converter replacement (horrible idea, obviously cat inefficiency is result of misfire and raw fuel). I swapped ignition coils and plugs but the misfire did not change cylinders. Good spark present at cylinder 3 at spark plug. So...I replaced fuel injector on cylinder 3, with absolutely no change in any codes or live data. Also, the resistance on the old fuel injector was within spec and matched all other 5 injectors. I have perfect 60 PSI on fuel Schrader valve.
I read up some on direct fuel injectors and found a TSB for the intake valves being dirty on the intake side due to fuel not being present to "clean" the valves and causing misfires due to "tumbling of air". I cleaned the back of the intake valves thoroughly, but to no avail.
Reading my scan tool all of the bank 1 cylinders have a narrowed pulse injector voltage, as to be expected by the fuel trim numbers. Honestly, it seems to me like cylinder three fuel injector is just "dumping gas" like crazy, but the strange thing is I've replace it, and also the fact that I can command it off with a scan tool which makes me think wiring is at least (partially?) functioning.
My next thought it to backprobe cylinder 3 fuel injector with oscilloscope, capture what it looks like, and compare it to a backprobe of cylinder 1 or 5 and see if the suspect fuel injector (cylinder 3) is actually receiving the appropriate pulse width/voltage. If not, maybe wiring issue or PCM not actually sending appropriate signal? Am I missing something I should do first, because this is getting kind of drastic and my customer is unhappy with diagnostic costs (I don't feel like I've screwed the pooch or been sloppy in diagnosing, though).
I'm not very familiar with modern direct fuel injection, so I am hoping to find a GM guru to help me out with this one. I will pay for you to help enlighten me.
Submitted: 1 year ago.Category: GMC
Show More
Show Less
Ask Your Own GMC Question
Answered in 9 minutes by:
3/11/2016
GMC Mechanic: cloe0626, Auto Mechanic replied 1 year ago
cloe0626
cloe0626, Auto Mechanic
Category: GMC
Satisfied Customers: 824
Experience: was a mechanic in the army for four years and have been working at a dealer ship the past five years
Verified

honestly i do believe you have covered all the bases and the only thing that makes since at this point is the pcm not sending the correct signal but you havent missed anything you have covered everything i can think of

Ask Your Own GMC Question
GMC Mechanic: Ryan Schott,
 replied 1 year ago
Ryan Schott
Category: GMC
Satisfied Customers: 83
Experience: technician at Demarois Buick Gmc
Verified

Ground wire at the back of bank one cylinder head. Its the ground for your coils on that bank. You have spark but its insufficient under compression and leaving fuel unburned therein playing hell with your fuel trim. Ground 112.

Ask Your Own GMC Question
Customer reply replied 1 year ago
Ryan that sounds like a good bet, I'll get back to you after I take a look-see tomorrow...
GMC Mechanic: edhunt0r, ASE Certified Technician replied 1 year ago
edhunt0r
edhunt0r, ASE Certified Technician
Category: GMC
Satisfied Customers: 506
Experience: GM B Tech ASE Certified Master Tech ASE Certified Master Medium/Heavy Truck Technician New Jersey
Verified

Hello. Welcome to the site. Thanks for coming. I'm ***** *****.
I'm here to provide as much information and insight as I can, to best answer your question.

Can you give me your VIN# ***** I can see if there are any Service Bulletins?

Thank you for posting your question.

Your business is very valuable to us.
Thank You
***** *****

Ask Your Own GMC Question
Customer reply replied 1 year ago
VIN # *****I visually inspected ground 112 today, does not look like the issue. With key off engine off I have no resistance between black wire (ground) on fuel injector 3 plug and battery negative. With engine running I have no resistance on brown wire to ground telling me the ECM is opening a ground as it should.Also, I pulled cylinder 3 spark plug and used test light to ground to see how strong arc was, I was able to pull an arc over an inch away from the spark plug tip. It looked similar to other cylinders spark plug too which could also pull an arc about an inch, so I'm doubting it's a spark issue (unless spark delivery timing is off).My guess is my fuel or spark delivery is occurring at the wrong time on cylinder 3. I can visually see I have good spark, and I know fuel is making it into cylinder because I have unburned fuel being read on that bank by 02 sensors.Maybe a bad crankshaft position sensor (like bad teeth not reading on tooth reluctor wheel) is giving ECU bad timing info for spark?
GMC Mechanic: Ryan Schott,
 replied 1 year ago

Any cam or crank issue in this will almost always after 08 throw a DTC. Chain issues are consistent in these but usually will throw a cam code( not always the right one but whatever). Try doing a leak down at low psi and let me know what you find. Sorry about the delay in response its the weekend so my dirt bike was calling.

Ask Your Own GMC Question
Customer reply replied 1 year ago
I don't have an AFIT...will do a leak down...when you say low PSI what are you talking?
GMC Mechanic: Ryan Schott,
 replied 1 year ago

I was just commenting on one that I was working on that was similar. Keep your psi at about 80 for the leak down. Look mostly for valve leakage and let me know what you find. I've replaced quite a few heads on 3.6l.

Ask Your Own GMC Question
Customer reply replied 1 year ago
I ran a leak down compression test on cylinder three and it held 80 PSI perfectly. Uggg. One thing I saw in Alldata's explanation of the fuel system is the the ECU sends a high voltage (~65V) signal to the fuel injectors to open up high pressure to overcome cylinder compression. My thought is to back probe cylinder 3 at ECU (which I believe is super easy to get to) and see if I'm getting that high voltage peak regularly on o-scope. If it was only sending the low voltage it's never overcoming compression so there could still be raw fuel in exhaust and spark present and a cylinder misfire. Other ideas?
GMC Mechanic: Ryan Schott,
 replied 1 year ago

you can check if you have a good scope, you can switch the pins for injector one and three at the ecm then swap the plugs At the injectors to verify you have no drop in your circuit. if you weren't getting sufficient power to the injector though i would suspect you'd see a lean condition. did you get a look at your cam lobes when you did the leak down? That one i mentioned the other day needed a cyl head, luckily it didn't ring wash too bad. let me know if alldata doesn't have the connector views for the ecm and i will shoot them too you after you scope it if you want to swap those circuits. what is the mileage at on the vehicle i will call GM TAC and have them check all closed cases for cyl 3 misfires and see if there is something im overlooking.

Ask Your Own GMC Question
Customer reply replied 1 year ago
Have you seen them hold good leak down compression and still need a head?
Customer reply replied 1 year ago
92,000 miles
GMC Mechanic: Ryan Schott,
 replied 1 year ago

yah if it had a physical cam issue,let me check resolved cases and ill regroup with you shortly.

Ask Your Own GMC Question
GMC Mechanic: Ryan Schott,
 replied 1 year ago

called and checked same story there he said most of their cases for this end in a cylinder head assy. always a right bank too. do you have it together enough or a quick road test?

Ask Your Own GMC Question
Customer reply replied 1 year ago
Customer has vehicle but I could get it back, what are you looking for in a road test? Also, how would a physical cam issue cause misfire but with good compression - are you thinking physical cam damage threw mechanical timing off?
GMC Mechanic: Ryan Schott,
 replied 1 year ago

a worn lobe will let you have compression but not open sufficiently, if you can monitor the misfires live with your scan tool at a pretty hard acceleration and it doesn't miss id say it still looks like a valve issue.

Ask Your Own GMC Question
Customer reply replied 1 year ago
I recall hard acceleration did reduce misfire. Trying to get vehicle back and I'll tear the valve cover over and look at cam
GMC Mechanic: Juan Crespo, Tech Trainer replied 1 year ago
Juan Crespo
Juan Crespo, Tech Trainer
Category: GMC
Satisfied Customers: 1,529
Experience: A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
Verified

After reading about all the troubles GM is having with "cam walking" and other such mishaps, I'm with Ryan in thinking this is most probably a cam issue and the cure will be none other than a new head - the customer also mentions a well known malady with these direct-injection systems; and that is carbon buildup. An issue worth discussing with the customer post-repairs.

So, how about performing a dynamic or "running" compression test on that No. 3 cylinder? At idle, compression should be about 50-60% of static or "cranking" compression. Snap-throttle compression should be about 80% of static compression - a lot less than 80% would indicate problems with the cam and/or carbon buidup.

Best Regards ***** *****

Ask Your Own GMC Question
GMC Mechanic: Ryan Schott,
 replied 1 year ago

Let me know and try and monitor that live again too before you tear it down.

Ask Your Own GMC Question
GMC Mechanic: Waverly Lorello, ASE Certified Master Automotive Technician L1, L replied 1 year ago
Waverly Lorello
Waverly Lorello, ASE Certified Master Automotive Technician L1, L
Category: GMC
Satisfied Customers: 25
Experience: ASE Certified Master Automotive Technician L1, L2
Verified

Have you been able to command the o2 sensors on that bank full rich with propane or full lean with o2 sensor

Ask Your Own GMC Question
GMC Mechanic: Waverly Lorello, ASE Certified Master Automotive Technician L1, L replied 1 year ago

Also what is you thought on pulling the engine down?

Have you found a reason other then a groove in cam lobe?

have you ever seen carbon build up in a direct injection engine?

I have pulled so many 3.6 gm apart but never for any of the problems you are thinking

timing chains, carbon build up, cam phasers

Never heard of cam walking in head

This question has been open for 20 days lets get this car fixed

Ask Your Own GMC Question
GMC Mechanic: Waverly Lorello, ASE Certified Master Automotive Technician L1, L replied 1 year ago

Also after looking at your first post you say the cyl 3 injector you replaced did you check to see if the injector is stuck on by a shorted driver in the pcm

Ask Your Own GMC Question
Customer reply replied 1 year ago
Hey Waverly, thanks for your ideas. If you read my original posting I have verified 02 sensors by introducing lean and rich conditions and the voltages respond appropriately. Also, I found a TSB on carbon buildup (and read up more on the internet) on DFI systems and thoroughly cleaned the back of the intake valves. I was able to command the injector on and off with my birectional scan tool, and the cylinder became a "dead miss" when turned off. However, the condition has worsened and the cylinder is essentially a dead cylinder now. I am more concerned by the "groove" in the cam lobe than the gouge, although I must admit a little skepticism that is the root cause...I've seen much rougher cam lobes running better than this thing...however that was on older style fixed camshafts, so I'm left to wonder if the variable cam timing exasperates the cam lobe wear.
GMC Mechanic: Waverly Lorello, ASE Certified Master Automotive Technician L1, L replied 1 year ago
What kind of scan tool are you using so i can send you some vvt information
Ask Your Own GMC Question
GMC Mechanic: Waverly Lorello, ASE Certified Master Automotive Technician L1, L replied 1 year ago
if it is snapon what version of software is it
Ask Your Own GMC Question
GMC Mechanic: Waverly Lorello, ASE Certified Master Automotive Technician L1, L replied 1 year ago

I think you need to focus on the high pressure fuel pump

Ask Your Own GMC Question
GMC Mechanic: Waverly Lorello, ASE Certified Master Automotive Technician L1, L replied 1 year ago

here is the picture of the pump

does that cam lob that is damaged correspond with where the pump bolts in the head

Ask Your Own GMC Question
GMC Mechanic: Waverly Lorello, ASE Certified Master Automotive Technician L1, L replied 1 year ago

And here is the fuel system overview go to the hi pressure pump description

Ask Your Own GMC Question
Customer reply replied 1 year ago
The high pressure fuel pump is on the #2 bank so no it is not on the bad cam. I am using a MaxiDas 708. The fuel rail pressure sensor is reporting appropriate data, and bank 2 and cylinders 1 & 3 generally do not misfire. So I don't really see how the high pressure fuel pump could be issue and effect only 1 cylinder, and I know it's getting fuel as I have a rich condition in the tail pipe. The ECU could be not supplying the high voltage signal, or wiring could be bad. As Ryan said a bad ECU high voltage would most likely cause a lean condition, and I can command the fuel injector on and off on cylinder 3 so I know the wiring is good and the ECU can command on and off the cylinder.
Customer reply replied 1 year ago
Also,I thought I would note for general reference that the misfire occurs in open and closed loop. It starts immediately with the car and the ECU can't hold the RPM's steady, it run's +/- 75 RPM with the misfire although it does smooth out a little at higher speeds as we discussed.
GMC Mechanic: Ryan Schott,
 replied 1 year ago

Yep that's a valve sealing issue and not a fuel one if load improved it, a groove isn't good but shouldn't totally kill it if you can get in there with a mirror or boroscope pry the springs around on the valves as sometimes they fracture and still hold shape makes them very hard to spot. end o the day though the cam should not have a groove period, the head assy is an updated unit GM couldn't really specify the change when i asked though but obviously they have issues, might not be a terrible time to throw that leak down back on and manually turn it a few times and tap on some things and see if it decides to show some leakage. but most all fuel or spark management misfires will be static under load when monitored via scan tool, all misses 'feel' better at high rpm but when monitored will be consistent. but there should definitely not be a groove in the cam, i'd still service it as an assembly though, wouldn't look too hard at that fuel pump.

Ask Your Own GMC Question
Ask Ryan Schott Your Own Question
Ryan Schott
Ryan Schott
Ryan Schott
Category: GMC
Satisfied Customers: 83
83 Satisfied Customers
Experience: technician at Demarois Buick Gmc

Ryan Schott is online now

A new question is answered every 9 seconds

How JustAnswer works:

  • Ask an ExpertExperts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional AnswerVia email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction GuaranteeRate the answer you receive.

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help.

Mary C.Freshfield, Liverpool, UK

This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!!

AlexLos Angeles, CA

Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult.

GPHesperia, CA

I couldn't be more satisfied! This is the site I will always come to when I need a second opinion.

JustinKernersville, NC

Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around.

EstherWoodstock, NY

Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know.

RobinElkton, Maryland

He answered my question promptly and gave me accurate, detailed information. If all of your experts are half as good, you have a great thing going here.

DianeDallas, TX

< Previous | Next >

Meet the Experts:

Gm Tech (Cam)

Gm Tech (Cam)

GMC Mechanic

1,696 satisfied customers

GM Grand Master Technician 2007. 14 year experience.

Gary

Gary

ASE Certified Technician

1,557 satisfied customers

GCM master tech over 25 years

Dave Nova

Dave Nova

GMC Technician

929 satisfied customers

ASE Master Certification. GM World Class Certification

Chris (aka-Moose)

Chris (aka-Moose)

GMC Technician

583 satisfied customers

16 years of experience

Ron Z.

Ron Z.

- GMC Tech -

259 satisfied customers

18+yrs experience. State Inspector & GMC Diagnostics/Repair

George H.

George H.

ASE MasterTechnician

227 satisfied customers

15+ Years ASE Master Technician with Level 1 Certification

Don - Mo Lurch

Don - Mo Lurch

ASE Certified Technician

218 satisfied customers

GM, GMC, Chevrolet Cert., Heavy Line Mech, Race Shop Owner, Mobile Electronics

< Previous | Next >

Related GMC Questions
The o2 sensor seem to me be switching quickly and mirror
The o2 sensor seem to me be switching quickly and mirror each other when your looking at them on a graph… read more
Pete
Pete
Independent Auto Technician
Vocational, Technical or Trade Scho
138 satisfied customers
Battery will not charge. new battery and new alternator. The
battery will not charge. new battery and new alternator … read more
Cesar Jimenez
Cesar Jimenez
Owner/CEO
Vocational, Technical or Trade School
108 satisfied customers
I have a brand new battery in but my battery level sits at
I have a brand new battery in but my battery level sits at about 11 on the cluster and won't turn on, if I boost it the truck starts and runs normal but if I turn the truck off the truck immediately w… read more
Mechanic01
Mechanic01
1,736 satisfied customers
New battery drains overnight. No but the battery is new. The
No but the battery is new. The same thing happened before the battery was replaced. … read more
AMEDEE
AMEDEE
AUTOMOTIVE TECHNICIAN
Vocational, Technical or Trade Scho
9,105 satisfied customers
I just bought a new battery at autozone and they put it in
I just bought a new battery at autozone and they put it in but the next day when I tried to put 2006 gmc envoy into two wheel drive from auto it just flashes and then moves to four wheel drive high. I… read more
tim37857
tim37857
Mechanic
High School or GED
71 satisfied customers
It will Not start. We tried a new battery- its not the
We tried a new battery- its not the battery, nothing is corroded … read more
David Craig
David Craig
OWNER/MECHANIC
Associates
4,420 satisfied customers
Is it normal for a car battery voltage increase after trying
Is it normal for a car battery voltage increase after trying to unsuccessfully start the car and then letting it sit for several moments?… read more
Gary
Gary
ASE Certified Technician
Vocational, Technical or Trade Scho
1,557 satisfied customers
Idle engine. 285000 VVM envoy 2003 XL. Also battery not
This just happened todayhvnt had a chance to do anything as yet… read more
Chris (aka-Moose)
Chris (aka-Moose)
GMC Technician
Vocational, Technical or Trade School
583 satisfied customers
Battery saver light came on. Battery test with the engine
Battery saver light came on. Battery test with the engine off at 12.7 VDC, With the engine running at an idle 15.7 VDC. Trying to locate the issue … read more
Mechanic01
Mechanic01
1,736 satisfied customers
Diesel exhaust system service? speed limited to 4mph and i
diesel exhaust system service? speed limited to 4mph and i am 20 miles from town … read more
Chris (aka-Moose)
Chris (aka-Moose)
GMC Technician
Vocational, Technical or Trade School
583 satisfied customers
2013 gmc duramax diesel: service exhaust fluid system
2013 gmc duramax diesel: service exhaust fluid system warning light and states will reduce speed. Filled DEF tank, warning persists … read more
Chris (aka-Moose)
Chris (aka-Moose)
GMC Technician
Vocational, Technical or Trade School
583 satisfied customers
Getting a service message on my exhaust fluid system and is
getting a service message on my exhaust fluid system and is transitioning to 65mph … read more
Gabriel Grey
Gabriel Grey
Master Service Technician
Associates
375 satisfied customers
Battery is dead all of a sudden. symble on dash = Battery
battery is dead all of a sudden. symble on dash = Battery malfunction It's a 2013 Acadia … read more
AZTechBrian
AZTechBrian
ASE Certified Technician & Shop Owner
Vocational, Technical or Trade School
732 satisfied customers
How much does it cost to replace a timing solenoid exhaust.
how much does it cost to replace a timing solenoid exhaust … read more
Gunvir Singh
Gunvir Singh
1,817 satisfied customers
Hard starting. New battery, it cranks great, acts like no
New battery, it cranks great, acts like no fuel or no spark.. Changed plugs,wires,both O2 sensors, throttle position sensor, mass air flow sensor. Hasn't changed the start. Runs great after a few seconds running rough … read more
Chris (aka-Moose)
Chris (aka-Moose)
GMC Technician
Vocational, Technical or Trade School
583 satisfied customers
Battery light was on this am but alt is charging. Battery
Battery light was on this am but alt is charging. Battery was dead but is 6 years old. … read more
Pete
Pete
Independent Auto Technician
Vocational, Technical or Trade Scho
138 satisfied customers
Need an exhaust pressure differential pipe for a 2013 GMC
need an exhaust pressure differential pipe for a 2013 GMC 3500HD... … read more
Chris (aka-Moose)
Chris (aka-Moose)
GMC Technician
Vocational, Technical or Trade School
583 satisfied customers
Replace o2 sensor reset engine lite, lite went off. Lite
replace o2 sensor reset engine lite, lite went off. Lite came back on again, reset lite again, afther you stop and start again engine lite comes on. It,s been 4 days now drove for over 250 miles and e… read more
roy
roy
Associate Degree
3 satisfied customers
Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Show MoreShow Less

Ask Your Question

x