LS-1 lagging and throwing codes

**ws6Poncho** · 07-24-2014, 04:15 PM

On acceleration up to about 3k rpm there is a definite lack of power, after about 3200 rpm the power will kick in. On a hard run tonight the service engine soon light came on, I checked it with my Actron 9580, and it was p0137 and p0157. This is the second time these codes have appeared, indicating a problem at the rear o2 sensors. I have cleaned the MAF twice, new plugs and wires, new fuel filter, and new PCV valve, plus all new vacuum lines for the PCV system. I checked the fuel pressure, it holds at 56psi up to about 5k rpm. Could this have something to do with the secondary air/ EGR system? I'm running out of ideas.

**FORD RECOVERY EXPERT** · 07-24-2014, 09:19 PM

Have you cleaned / replaced the o2's?

**ws6Poncho** · 07-25-2014, 01:08 AM

I don't think replacing the rear o2's will do anything to correct the lagging problem. They are reporting a problem, I can't see how they are causing it, but I may be wrong. Another thing to note, when I let up on the throttle I am getting mild-moderate backfiring.

**pajeff02** · 07-25-2014, 03:06 AM

Can you see live sensor data with your scanner? Sounds like you have a fueling issue that is either caused by the MAF misreporting airflow, the front O2 senders not working properly, or a vacuum leak. I would check the front O2 senders to see if they are operating correctly. A good sensor should rapidly cycle up and down from about 150 mV to 850 mv. The rear O2 senders simply tell the PCM if the cats are working correctly - they have nothing to do with how your engine runs.

**ws6Poncho** · 07-25-2014, 06:05 PM

I tried to figure out how to monitor the o2 sensors with the Actron tonight without much luck. Its been a long week at work, and I have all day tomorrow to try and get some readings of the o2 sensors.

**pajeff02** · 07-26-2014, 04:02 AM

In addition to your O2 sensor data - take a look at your fuel trims. Ideally, the trims should hover around zero, plus or minus 3 or so. If the trims are running high, the PCM is adding fuel. Negative trims depict a subtraction of fuel. There are both short term fuel trims (STFT) and long term fuel trims (LTFT). I accidentally crossed up my O2 sensors after some work on our car (they are the 13111's with the really long harness) and our car immediately went to +25 on one side and -25 on the other... ooops.

**RONS98TA** · 07-26-2014, 05:06 AM

Could be a long shot, but maybe your cats are beginning to go bad. They may be falling apart inside causing a clogged up exhaust system. If the car cant get the exhaust out, it will fall on its face. Besides seeing them glow from excessive heat, or having a buddy give it some gas and checking exhaust flow out the muffler, you can disconnect the exhaust from just before the cats (kinda of a pita, btw) and see if power returns. I've had clogged up cats cause a car to not even start.

**ws6Poncho** · 07-26-2014, 10:33 AM

First thing I tried this afternoon was unplugging the MAF and see what happens. Its got tons of power and no backfiring now. I had cleaned the MAF twice previously and the lack of power went away briefly, but returned soon after. Have I found the problem? I was going to send the PCM to Frost for a tune, would this be a good time to delete the MAF for the speed density option, or replace the MAF with a stock unit? I have to pass emissions here in New York. Sorry if I'm a little clueless, still pretty new at this, and learning as I go.

**pajeff02** · 07-26-2014, 04:03 PM

Can you borrow a MAF sensor from a friend's car? If not, a stock replacement from GM Parts Direct is the way to go. It'll have a plastic body and an adapter harness.

**ws6Poncho** · 07-26-2014, 04:10 PM

I bought a remanufactured OEM unit at the parts store this afternoon, and put it in this evening. Just got back from a 20 mile run-WOW! Tons of power, smoother starts, no backfiring, what a difference. Thanks a million guys!