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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1667
Experience:  GM Grand Master Technician 2007. 14 year experience.
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I have a 2008 gmc with the 6.6 LMM duramax that i just

Customer Question

I have a 2008 gmc with the 6.6 LMM duramax that i just rebuilt because the crank broke. Complete rebuilt bottom end, all new gaskets, seals, everything. Cranks over fine, busts off for split sec then nothing. If you hold key in crank it continues to bust off then crank, bust off then crank. After that i can pull code p0336. Have replaced all fuel lines that appeared to be pinched, new fuel filter block, nee crank and cam sensor, ohmed out both those harnesses, pulled glow plugs, disconnected injectors and spun over, no fuel shooting out, plug inj back in and get fuel from glow plug ports, checked timing of cam/crank gear, reluctor ring is on correct, not backwards or off. Can start and run off gas soaked wrag at intake pipe but wont pick up and run. While cranking have rpm reading, running w gas rag i have none. Stuck and have run out of ideas????
Submitted: 15 days ago.
Category: GMC
Expert:  Chris (aka-Moose) replied 15 days ago.

Welcome, I'm Chris (aka Moose), my normal schedule online is around lunch and after dinner till early morning.

What is the injector pump actual and desired pressure reading while cranking?

Customer: replied 15 days ago.
Usually the desired reading is 6500 while not cranking, when you crank it raises with the actual fuel pressure. Im getting close to 10,000 while turning it over but it jumps from around 6 to 10,000 while cranking. Drops back to around 140 psi rather quick after you stop spinning it over. Hg vaccuum is between 2.5-3 on the test port. Pump primer up to 10psi, doesnt drop below 7psi within the test time of one minute. Dont know what im missing on this and stuck.
Customer: replied 15 days ago.
Late and have to get off, will respond back in the morning to your next question
Expert:  Chris (aka-Moose) replied 15 days ago.

Those pressure readings are they actual or desired?

Have you done the diagnostics for code 0336?

Customer: replied 15 days ago.
The desired fluctuates with the actual. While not cranking, the desired sits around 6500, actual sits around 140. Cranking it jumps around for actual between 6500-10000, desired jumps up around 9-10000
Expert:  Chris (aka-Moose) replied 15 days ago.

Thanks, ***** ***** and desired match when cranking at 10k.

Have you done the diagnostics for code 0336?

Have you done a compression test manually or with a scan tool?

Customer: replied 14 days ago.
diagnosed and checked all possibilities for 0336. Replaced crank sens, ohmed out that part of circuit from sensor to computer. Replaced cam sens and test that circuit, put noid light on and checked random injector plugs for pulses, check reluctor ring for correct placement, everythings good there. Compression is good as well on all cylinders. If you crank it over, it hits but doesnt fully start. No codes set at all. If you crank it over but continue to hold it it hits over and over but still doesnt start then it sets P0336. Maybe like a pre-detination missfire or something. Leaking injector possibly?
Customer: replied 14 days ago.
No code set if you just crank and let off ignition when it bust off, only sets code if you continue to spin it over as it continues to try to bust off over and over
Expert:  Chris (aka-Moose) replied 14 days ago.

I do not believe I can figure this one out. I will opt out so another can try.

Customer: replied 14 days ago.
Ok
Expert:  Gm Tech (Cam) replied 11 days ago.

Hi there, I am Cam. Do you still need assistance?

Does your scanner show engine RPM while cranking?

Customer: replied 11 days ago.
it shows rpm while cranking but if u run it off gas rag at intake it will run but shows no rpm, but as it sucks all the gas fumes from the rag and starts to die the rpms start working again and jump around till it completly dies
Expert:  Gm Tech (Cam) replied 11 days ago.

Ok, it should show RPM. Is there damage to the reluctor wheel?

Customer: replied 11 days ago.
Not that i can tell, had a friend turn it slowly as iinspected reluctor, ensured it wasnt wobbling byeayching it as he spun it over using starter. Used fiber optic scope to check that it wasnt on backwards, and in correct possition. But it shows rpm when it hits off, but wont run, if you hold key it hits over and over but wont run.
Customer: replied 11 days ago.
I did pull sensors for crank/cam and scoped it after i got the ballancer to the TDC notch on front cover. Checked crank/cam marks, checked cam reluctor plate, checked position of crank reluctor notch, replaced both cam/crank sensors, ohmed harness, not routed near injectors or solonoids, all checks good. Im wondering if while starting i have signal but when it hits off and i guess the computer would supose to start managing it it loses signal. Only reason i could figure why it shows rpm while cranking but lose rpm on gage when running off gas rag.
Expert:  Gm Tech (Cam) replied 11 days ago.

My first thought is that there is a loss of signal but why, is it the PCM not recognizing it? Is it a bad connection? Loss of power? Loss of ground?
If you crank it for the 15 seconds, does it set any codes?

Customer: replied 11 days ago.
If i crank and release when it hits, it will never set a code, but if i hold it in crank and it continues to spin over and hit over and over it sets p0336. And thats all it does set.
Expert:  Gm Tech (Cam) replied 9 days ago.

Ok, have you followed through any set diagnosis for the no start?

Customer: replied 9 days ago.
p0336 diagnosis and checks from internet. Maybe fuel injectors or cp3, vac hg is low at 2.5 and high side is around 6500-7000 when cranking. If you prime pump it tries to hit more than if you dont. Im wondering if because i had it out for a while i may need to get computer reflashed.
Expert:  Gm Tech (Cam) replied 9 days ago.

The computer should not need refreshing, it does not loose its programming.
Let me ask this, is your scanner able to read body codes?

Customer: replied 9 days ago.
i borrowed a solus pro and accessed all the modules, body, anti-theft, trans, engine. All accessed fine, and showed no codes except engine with p0336 only