PWagon

I had a pinched O2 sensor wire which gave a bad O2 code. I replaced the O2 sensor and soldered in a new wire section to replace the damaged wire. The check engine light (solid / not blinking) went off and stayed off. All was good.

About this time I noticed a small fuel leak at the metal pipe that connects both fuel rails. I replaced it and its rubber o-rings with a genuine GM part (not cheap). I was careful not to let any dirt/crud into the fuel rail, but a tiny amount may have fallen into a rail while moving the connector out and the new one back in. I put everything back together, and now it idles rough, slightly backfires (pops) at the intake, and runs very sluggish. I took it to a mechanics shop, and they ran every test they could. They did a smoke test for vacuum leaks – no leaks. They did seek error codes P0101 and P0106 which indicates a MAF and/or MAP issue. They replaced both MAF and MAP, and the problem remains. They then opened my up wire harness loom and traced out each MAF and MAP wire back to the PCM to rule out a wiring problem – no wiring problems. An interesting thing they noticed is that the MAP sensor gives a constant reading of 28.3 Hg at all times (when it should be fluctuating). Like I said they replaced it, but no dice. If a small amount of sludge around the fuel rail connector o-ring came loose and fell into the fuel rail while I was replacing it, would it cause this type of behavior? Maybe it’s clogged up some injectors? Any ideas?

i r teh noobz

iTrader: (4)

How did they check the harness? Visual only? Did they confirm that the wires run to the correct pins? Check signal/power/ground from each sensor? Did the codes go away? Was fuel pressure ever tested?

Did it run fine before? I highly doubt any small amount of debris in the the rail could be causing this.

Check the intake manifold gaskets for leaks. Monitor short term fuel trims with the engine running, spray carb/brake cleaner around the base of each runner, watch for sudden spikes in STFT activity (should go negative if the gaskets are leaking). Check for leaks at the MAP sensor and between the MAF and throttle body this way as well.

PWagon

Yes, the shop did check voltage, ground, fuel pressure, vacuum, wiring (opened wire loom and tested voltage/ground), sensor readings. They also put the original MAP and MAF back in since it didn’t change anything. They use current professional testing equipment and follow the computer’s recommendation on what to check in sequence. They ruled out a vacuum leak by doing a smoke test and checking manifold vacuum with a gauge. No injectors or rails were removed (ever), only the connecting rail that supplies gas to both rails was replaced (see attached picture (part #1 in red was replaced)). Also, they tried clearing the codes, but they (P0101 and P0106) come back immediately. What would a hard/immediate code return come from?

64post

iTrader: (5)

Fuel pressure reg. or vacuum line to it, restriction in fuel return, 02 sensor or wiring to them grounded or shorted are the most likely culprits to a rich condition. Check short term fuel trim with engine data and ALL 0-5v references, one item gone bad can create problems, even a coolant level sensor. Popping through the intake sounds like a lean condition though, retrace your steps, everything you touched or unplugged. Try unplugging the MAF while running and see if it smooths out.