S10 with a 408 swap. We've been having issues with the driver side O2 sensor not cycling back and forth and just sitting at .1 volt, unless you rev up the engine to around 2200+ then it will start to cycle and the STFT will come down to around zero, but the LTFT will stay pegged at +25 but only on the drivers side, the Passenger side O2 cycles back and forth like its suppose to at idle just fine and LTFT is right about zero, and STFT has gone in the negatives to right around zero.

I replaced the drivers side O2 sensor plug on the harness the other day, and the sensor started to cycle at idle, truck seemed to run alittle better, but still not great. Took it for a drive around the block and only went maybe 5-6 miles, but the longer i drove the worse the truck ran, the O2's were cycling, FT's were down except for drivers side LTFT of course and the truck was acting like it was out of gas, but it has half a tank, and i had severe back firing out the exhaust and was shooting flames at idle. and buy this time the drivers side STFT was in the +50's, yet the WBO2, which is on the drivers side was showing 18-20 or lean.

I pulled all the plugs, and #1,3,8 were very dark black and very sooty, and the rest were all a light tan/brown and looked halfway normal. I had TR55's in there. I went ahead and replaced them all with stock delco iridium plugs. Fired the truck back up and it didnt really make any difference. The drivers side o2 is back to just sitting at .1 volt and STFT will go up to the mid +50's after a few mins of running and LTFT stays pegged at +25. passenger side has always stayed close to zero on both and the O2 cycles fine within a few seconds of the truck running. Once again, if you hold the revs at 2200+ the drivers side O2 starts the cycle and naturally the STFT comes down to zero or close too it and LTFT stays at +25.

This engine has been checked about half a dozen times for vacuum leaks, and only found that the TB was leaking around the IAC due to there not being an O-ring, then around the Injectors which last time at the shop you modified the fuel rail to straighten up the injector angle and that fixed that vac leak.

We did have the stock L76 intake ported, and the company that did it is no longer in business, can you think of anything inside of the manifold, that could have been messed up or gotten cracked that could cause an internal vac leak that would only affect the drivers side? With the drivers side being affected at idle, but then it clears up a bit above 2200 rpm, im still inclined to believe there is a vac leak somewhere, but if it were internal to the manifold would that affect the FT's?

Sorry this is kinda long and winded, but i need to find some answers and find them fast. Thanks for your help.

 

Time for a smoke test.

 

That's just it, truck has been smoke tested 3 times, and the last test after fixing the injector angles it tested all clear on the intake side. Ive also checked the exhaust side several times, and am 99% sure there are no exhaust leaks between the O2 sensor and the header flange.

 

Sounds like a wiring problem with that 02 sensor.

 

That's what i thought at first, but the wiring harness has been checked several times, and i just replaced the O2 sensor plug on the harness itself, and before that the harness was removed and sent back to CP in FL to have it checked just to make sure, and they said all was good.

 

Ok, well today, i decide to check the brake booster, and when i remove the hose from the booster, the air its sucking in affects both sides of the engine, and the booster seems to be holding vac just fine, so im pretty sure thats not the issue. I decided to double check the collector bolts, and even though i used all metal locking nuts, it seems that they are pretty loose on the drivers side, i really couldn't see any sides that there was an exhaust leak, i tightened then up good and snug, both sides were loose, the drivers side way more than the passenger side, but sadly it didnt change anything.

I reset the PCM so it would have a fresh start, and while it did seem to run alittle better at first, and it did take longer, almost 5-6 mins for the LTFT to start coming up and sit at +25, and the driver side O2 will not cycle at idle, but when i rev up the engine to 2K+ the O2 cycles, and the LTFT drops to 0, and the STFT will slowly drop from the mid 50's down to about 10 or so, and go back and forth from about 8/10 to 15/18 and the LTFT will stay at 0, but as soon at it goes back to idle no cycle and the FT's start to go up.

I tried unhooking the #1 injector, and there really wasn't a change in sound with it idling, but on the data all the FT's dropped to 0 on the drivers side. Plug it back in and they go back to where they normally are. When i unhooked the #2 injector there was a noticeable change in sound and the engine started to shake a bit, and the passenger side FT's all went to 0, and the O2 stopped cycling.

Tried unplugging the coils for the #1, #3 and #2 coils, and pretty much the same result.

With these new test, im starting to think there is an injector problem on the drivers side, and these are suppose to be brand new injectors too. What are some of yall's thoughts?

 

I would spray carb cleaner around the manifold at idle and watch for your numvers to change.
Whoever ported the intake might have taken to much meat out of it and with vacuum it's distorting enough to leak.

 

Could be badly underfueled, could be misfiring or could
be that your heater power isn't enough (or present at
all).

One injector delivering short fuel can throw enough
air to really whack readings. So can a runner leak.

 

Yeah, the injectors are new, but im thinking it may be worth it to pull them back out and have them flow checked just to be sure.

 

If it were me, I would swap sides with the injectors. I usually recommend swapping O2s side to side first, then injectors to see if the trims swap sides. Might first unplug one O2, and watch the scan tool to verify it's mvs stay about 450 mvs, and never move. I had one come in once wired up wrong, the left O2 was wired to the PCM as right side, etc. PCM wasn't adjusting the bank it "thought" it was.

 

In addition to Ed's strategy and checks, verify that ignition coils/plugs are firing (use a spark tester like ST125).

Usually air leaks make a significant difference when rpm are low, and make less difference when rpm are higher.

LTFT pegging positive indicates excess oxygen, i.e. too much air, not enough fuel, poor/no combustion... (each of those has various root causes).