I have a 2004 Sierra 1500 4x4. 2 years ago, and 30,000 miles ago I swapped in an lq4- 6.0l from 3/4 ton truck. The motor was bought from ATK performance engines.The truck is having issues with breaking up/ missing. It is more noticable in higher RPMs and gets worse as engine heats up. Wondering if any one has some advice on how to begin diagnosing the problem
Vacuum guage shows good. But I'm going to pull the plugs, see how they look. Then the valve covers and have a look under them. Lastly pull the rockers and do leakdown on all cylinders.
See if see any anomaly.
Have head gaskets on the way and a new set of heads sitting on the bench going on it Monday if I don't get it running good this weekend.
[This message has been edited by LitebulbwithaFiero (edited 12-03-2016).]
Was the old engine a 6.0 or a 5.3? Has it done it ever since the swap? (Edit - After rereading the O/P, I'm guessing this is a "new" thing.) Is it getting enough gas? If it was a 5.3 and you didn't change the tune (or used the same injectors) I'm thinking it may be "starving". Is it setting a "misfire" code? Perhaps a fuel pump or regulator?
Edit - Possibly a crank position sensor? Was a "CASE learn" performed when the engine was swapped?
[This message has been edited by Raydar (edited 12-05-2016).]
The truck had a 5.3 before the 6.0l. I got a tune from Black Bear Performance to run the bigger motor. Truck has ran good for the 30k miles I have on it. So I am sure it is not in the tune. Fuel pressure checks okay and there is no check engine code for misfire, just for rear o2 sensors. I am unsure what a case learn is.
Thanks, Josh
[This message has been edited by LitebulbwithaFiero (edited 12-05-2016).]
Blew the cats out almost exactly a year ago. It feels like, when it currently misses, like when I broke the cats and they would plug off the exhasut. The main difference between then and now, is the sound. Busted cats are loud like a rod knock. I am sure what you mean bt o2 known-ness. I did have an msd plug wire arcing to the manifold. I was happy when I saw that thinking I had it licked. But new plugs and wires seem to of made no difference.
Thanks for replies, you are helping to make me think more on it
[This message has been edited by LitebulbwithaFiero (edited 12-06-2016).]
The truck had a 5.3 before the 6.0l. I got a tune from Black Bear Performance to run the bigger motor. Truck has ran good for the 30k miles I have on it. So I am sure it is not in the tune. Fuel pressure checks okay and there is no check engine code for misfire, just for rear o2 sensors. I am unsure what a case learn is.
Thanks, Josh
CASE Learn is usually performed whenever a crank sensor is replaced. It also is frequently done when an ECM (or engine) is replaced. It's kind of like a "fine tune" thing. The 3800 guys do it a lot. It helps to optimize the timing of the Crank Position Sensor, engine, and PCM. I poked around a bit, and some people say that it needs to be done in order for the misfire codes to even work, but I don't know how true that is. In any event, if yours has worked fine for 30K miles, I'm pretty sure it's not the problem. Or at least not contributing to the poor running.
Is it possible that it's something as simple as bad gas? How is it at low RPM, high throttle? (i.e., lugging - if it's even possible to do that.)
If a relearn is necessary, there is a dtc for that. I never got the dtc for needing it. But I have had misfire codes pop up. I was low on gas so I filled it up yesterday. Drove around for a half hour. It starts out only at higher rpms, but once heat soaked it becomes more problematic. Lower rpm with load and it starts missing.
[This message has been edited by LitebulbwithaFiero (edited 12-06-2016).]
My understanding with coils is they either work or they don't. I look up testing for them, and all people say is to see if it sparks. Mine are definetly sparking
Anyone have experience with EFI Live? I have a V2. I thought I couldn't use it as my laptop is broke, but from early searching, it seems to be capable of stand alone data logging. Biggest problem while searching on how to use it, most info out there is for diesels
Bought a new laptop and got efilive all installed on it and working, I think. I will find out tomorrow. My tuner set me a pid list to use while doing a datalog to see if the miss can be isolated to a certain cylinder or condition.
Computer shows all cylinders randomly misfiring. No obvious correlation.
So, I cleaned the throttle body and the MAF. Replaced the air filter and a cracked hose for the crank vent. Even poured a bottle of seafoam in the gas tank. Cleaning the throttle body lowered the throttle position at idle from 14% to 6%.
But no difference in the missing and still no cel for it.
I am moving on to the power side of things. Going to put a new battery to block ground cable on and check all the harness grounds I can find.
[This message has been edited by LitebulbwithaFiero (edited 12-13-2016).]
I think it is fixed. Computer connector had some corroded pins. Cleaned them and couldn't replicate the symptoms on a test drive. Will lnow tomorrow for sure with the commute home from work
Well, the truck has been acting up again the last couple weeks. I pulled the ecm connector and cleaned it spotless on both ends, made no difference. Ended swappimg in a clean ecm, again no difference. After the truck getting bad enough to not even start, it magically went away. Drove fine for a week, then yeaterday started acting up. Time to start grasping for straws again.
[This message has been edited by LitebulbwithaFiero (edited 01-07-2017).]