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View Full Version : LQ4 won't rev up. Idles fine, chokes under throttle (video)


bubba68ss
September 21st, 2015, 06:28 PM
Anything in the PCM or tune (12212156) that would cause engine to cut out like this under throttle? Injector driver? It sounds like he is bumping the throttle up and down but looking closer I think he bumps it a few times then holds it open and it oscillates up and down. Why would the noid light be cutting out like that? I built this harness for these guys but they are 5 hours away. PCM does not have relearn done but I've never seen this before with other setups without a CASE.

FF to :25

https://youtu.be/S0Kmg7LjSgw
joecar
September 22nd, 2015, 02:42 AM
Check crankshaft endplay (too much endplay moves CKP reluctor away from CKP sensor when sudden load is applied to engine).
joecar
September 22nd, 2015, 02:46 AM
If injector circuit noid light cuts out, also check if spark cuts out, use something like this: Lisle 19380 (http://ecx.images-amazon.com/images/I/31iDgca-27L.jpg).
bubba68ss
September 22nd, 2015, 03:48 AM
Very good idea. I'll have them check.
bubba68ss
September 22nd, 2015, 08:43 AM
Apparently spark does not cut out. Only injector pulse.
bubba68ss
September 22nd, 2015, 06:33 PM
What else should I check?
joecar
September 23rd, 2015, 03:00 AM
Apparently spark does not cut out. Only injector pulse.
Ok, this eliminates CKP/CMP problems, and nowpoints to the following:
- fault in injector wiring to battery power;
- fault in injector wiring to ECM;
- fault in ECM ground(s);
- fault in ECM injector drivers (injectors ground thru here).
joecar
September 23rd, 2015, 03:01 AM
What else should I check?Check the wire harness terminal crimps with an ohmmeter, you want to see 0.1 ohm or less.
bubba68ss
September 25th, 2015, 10:01 AM
Joe, I sent my customer another Pcm with the same 12212156 os flash and he still had the problem. He then grabbed an ls1 Pcm I flashed for him a while back and it runs fine (except fuel trims off of course). Ideas? Corrupt tune? CRank relearn problems?
joecar
September 26th, 2015, 08:03 AM
Joe, I sent my customer another Pcm with the same 12212156 os flash and he still had the problem. He then grabbed an ls1 Pcm I flashed for him a while back and it runs fine (except fuel trims off of course). Ideas? Corrupt tune? CRank relearn problems?POssobly corrupt tune...

Flash the tune from the running PCM onto the failing PCM, does the failing PCM now work...?

Open the working tune, open the failing tune as alternate, copy the differences from the the failing tune to the working tune, see if this new tune runs on any PCM.
joecar
September 26th, 2015, 08:05 AM
Lack of Crank Relearn will not cause these problems (it will cause misfires to be falsely detected, which then causes PCM to do special things during misfire, such as protect the catalysts, protect the TCC, and some other protective things).
joecar
September 26th, 2015, 08:08 AM
I was going to say check that the terminals in the wire harness connectors make good contact on the plug pins...

but you said another PCM works ok running a different tune...

flash that different tune into the failing PCM and observe if the PCM works or not... if not, then the PCM's connector terminal pins are faulty (open the PCM and check for water damage);

otherwise if the PCM now works with the different tune then you may have a corrupted tune file... are you using any .cax files...?
bubba68ss
September 30th, 2015, 10:53 AM
Must have been a corrupt tune. I sent another PCM with 6.0 12212156 OS and it runs great.... Except fans do not turn on now. Ugh. Thanks for the advice. I haven't had a corrupt tune before. Unless both pcms with the same tune happen to have messed up injector driver
joecar
October 1st, 2015, 04:03 AM
Open the PCM's and inspect their harness connectors/terminals for water damage.
bubba68ss
October 1st, 2015, 11:28 AM
They sent back another 6.0 pcm that I did (same flash, not knowing it was bad) and it does the same thing. I put all three on my test stand 5.3 and they all cut out when throttled. Weird.
bubba68ss
October 1st, 2015, 11:32 AM
Any idea why the fans wouldn't be turning on in the 'new' tune? This is becoming a nightmare for me.

Heres the tune

18888
joecar
October 1st, 2015, 05:59 PM
Does vehicle have Series-Parallel fans...?
bubba68ss
October 1st, 2015, 07:07 PM
Single fan relay controlled by blue pin 42
joecar
October 2nd, 2015, 10:56 AM
Which PCM connector/pin is driving the fan relay...?
bubba68ss
October 2nd, 2015, 11:13 AM
C1 42
joecar
October 2nd, 2015, 11:36 AM
That's odd, in the GM Service Manual the PCM schematics don't show any fan...!?

What year/model/vehicle is the PCM and/or OS and/or tune file from...?
bubba68ss
October 2nd, 2015, 11:45 AM
The trucks did not have dual fans. C1 42 is fan 1 and c2 33 is fan 2.

I made a new tune and flashed and they all three run like they're supposed to and fans now turn on. I think I have a bad bench flash tune that was cutting out when reading or writing which corrupted the tunes. I used a tune from gearhead and flashed with tunerCats and all seems well now.
bubba68ss
October 2nd, 2015, 11:46 AM
The trucks did not have dual fans. C1 42 is fan 1 and c2 33 is fan 2. Optional on the 0411.

I made a new tune and flashed and they all three run like they're supposed to and fans now turn on. I think I have a bad bench flash tune that was cutting out when reading or writing which corrupted the tunes. I used a tune from gearhead and flashed with tunerCats and all seems well now.
joecar
October 3rd, 2015, 10:20 AM
Ah, ok, good deal.