Carguyrob598

My new ls376/480 crate engine will not run right. It idles very rough and surges quite a bit and is pretty unresponsive with the dbw pedal. It threw 2 codes for low voltage on o2 sensors on both sides, so they are both reading extremely lean. I figured exhaust leak but I have changed the header gaskets and all other exhaust seals and it has not fixed the problem. I am running 60psi fuel pressure as recommended and the MAF readings are ok. The tech who looked at it said the MAP sensor readings were low, I think he said 1.5-2 volts where it should be 3-4?? We also unplugged the o2 sensors and tried to restart and that did nothing also. The only mods I have made to the engine are a rev extreme catch can which I thought may be responsible for a vacuum leak but I have bypassed the can and that did not fix it either. Does anyone have any ideas? I will try to get a video link to youtube up in a little bit. Thanks

Carguyrob598

Here's a link to the motor running:

http://www.youtube.com/watch?v=WMA4j...ature=youtu.be

Carguyrob598

No ideas? Another thing I thought of is I have the o2's mounted pretty far down the system, probably 3 ft from the exhaust ports. Could that be a problem?

Old Geezer

iTrader: (3)

Did you use the GM installation kit? [IE: harness, etc]
Data log it with the MAP reading in KPA...Helps to see if there's problems there.
The sensors being that far from the heads could allow them to cool off some. What do you see at hot idle? Are they toggling?
Posting the tune and data logs would allow the gurus to look for issues....

Carguyrob598

Thanks for the replh! Yes I did use the recommended gm computer and harness. I wish I had data to post, I took it to a local dealership since it has a "gm warranty", but that turned out to be a joke. Engine temp doesn't really seem to affect it much, it may smooth a little bit with heat but not significantly. It was running 180 in the video. Are the o2s heated? And if they are would the distance from the heads be a problem? I have seen a lot of mixed reviews about heated and non heated o2 sensors and how important their location is. Thanks for the help!

Old Geezer

iTrader: (3)

The O2's are heated. I was referring to exh gas temps, not engine water. Water temp will determine when the system goes to closed loop, and the O2's start working.
Without a scanner, it'll be difficult to tell what's going on. NE1 around you that has a scan tool such as EFILIVE??
Where are you located?
[That ECM may not be the most "user friendly" to tune...]

Carguyrob598

I'm in Columbus Ohio. I'm probably going to take it to dyno tune motorsports, they seem to have some good reviews on here. I was hoping to take it there running ok to get a tune but he can probably save me a lot of time with a proper diagnosis.

Carguyrob598

Got it all straightened out yesterday. Local tuner got it up and running, turned out the MAF was acting up and the pre-tuned fuel curves were way off. Good to go now, 456hp/430lb ft to the wheels!

daniel76309

Good to hear, especially the dyno results! I have the same engine with GM controller package. A year or so ago I was having a lot of problems getting mine to run right. I am new to this and have a lot to learn, and have not messed with the "tune" (yet). I replaced a few sensors with no effect, and eventually replaced the ECM. (The first one I had apparently was defective in some way.) I was going to suggest the MAF sensor as a potential problem for yours. I found that the MAF sensor configuration can make a lot of difference. A longer intake with an "airflow straightening device" upstream from the MAF sensor helped a lot with mine. At this point it runs great and has a lot of power. The only thing is that the idle is still a bit unstable--will stall sometimes with the AC on. I am going to try to tune myself but haven't gotten there yet.