1997 5.7 Misfire under load, bunch of parts replaced

[Nad_Yvalhosert]

Ok, it seems to be the O2 sensors, but I cant get bank 2's off. All the nuts decided both to round off and rust weld themselves to the exhaust (understandable) and the O2 on bank 2 won't come out. I replaced bank 1's and it's running a lot better. Not perfect, but a whole lot better. I'll probably end up just replacing the whole exhaust on this thing just to get rid of the cats, the rusted out hardware, and all that good stuff.

My '00 Denali had the same problem with bank 2 upstream O2 sensor. I broke off the end of it, heated the bung with a torch, and put on a 24mm spline drive socket, with a fluted extractor socket as a backup.
It came out, but mushed the threads. Thankfully I have an O2 sensor tap socket to play cleanup. 18x1.50.

 

[Dud1f3r]

Re: P1345 code, did you adjust the distributor to eliminate the code? You hinted at this in your prior post (#13).

The process is described in the factory service manual and elsewhere. See the LAST page of the attached .pdf, although the rest of the pages are relevant for a distributor re-install.

As you may already know, the distributor can be installed WAY off its optimal position and the engine will still run, but it may run poorly under certain conditions. The procedure described in the 1st and later pages of the attached .pdf describe one method of installation that avoids the issue. While you OP may not benefit from this information, some other reader may. I hope this helps

FWIW, the contents of the .pdf came from the 1998 FSM.

So, turns out the timing marks on the dizzy are incorrect, and I was putting it in a tooth off. After that, I got it as close as I could, then used my new scanner to set cam retard. Goofy truck for sure.

 

[Dud1f3r]

My '00 Denali had the same problem with bank 2 upstream O2 sensor. I broke off the end of it, heated the bung with a torch, and put on a 24mm spline drive socket, with a fluted extractor socket as a backup.
It came out, but mushed the threads. Thankfully I have an O2 sensor tap socket to play cleanup. 18x1.50.

I can't even get the pipe that it's on off, much less the O2 itself

Gonna replace headers/cats back to the muffler and let her chooch.

 

[Laredo1307]

My guess is you're off by a tooth when stabbing the distributor or......Are you using the new distributor hold down bracket or the original one? The new aftermarket distributors come with a hold down that locks the distributor in-place and allows no adjustment. Need to use the old one so that you can advance or retard the distributor a few degrees. No sure how many miles are on the truck but if the timing chain has stretch it can cause the P1345. That was the case mine. I replaced my chain at 300K.

If you're getting the P1345 code it means you're more than 14 degrees out otherwise the computer will try and compensate. Also, check the crank sensor and make sure it's not damaged. it's on the underside of the time cover.

 

[Laredo1307]

Somehow I didn't see you last post before I wrote this.......Looks like you figured it out. I'll leave it up for someone else.

 

[Dud1f3r]

last update for anyone having this same issue. It ended up being both upstream O2s. Been driving it a lot hauling stuff and whatnot, and yeah it hasn't been acting up after I replaced the O2s.

Word of advice, even if you don't have O2 codes, check what your upstream sensors are doing. Mine would start at about 1v, and slowly drop to 0.14v and stay there, causing the truck to have no acceleration and jerk at idle like a big cam.

Oh, and last update, because I can't replace my bank 2 O2 without destroying the exhaust, I'm just gonna fab up a whole new exhaust for it. Long tube headers, 3" pipe back to the muffler, true duals. Should net me some nice top end, but more importantly let me actually have functional O2s.

 

[Dud1f3r]

My guess is you're off by a tooth when stabbing the distributor

I was for a while, the timing marks on the new dizzy were off by a tooth. But now that it's fixed we're all good to go. O2s man, they're weird. Makes me wanna go carb and just say **** it

 

[Road Trip]

last update for anyone having this same issue. It ended up being both upstream O2s. Been driving it a lot hauling stuff and whatnot, and yeah it hasn't been acting up after I replaced the O2s.

Word of advice, even if you don't have O2 codes, check what your upstream sensors are doing. Mine would start at about 1v, and slowly drop to 0.14v and stay there, causing the truck to have no acceleration and jerk at idle like a big cam.

Oh, and last update, because I can't replace my bank 2 O2 without destroying the exhaust, I'm just gonna fab up a whole new exhaust for it. Long tube headers, 3" pipe back to the muffler, true duals. Should net me some nice top end, but more importantly let me actually have functional O2s.

Dud1f3r,

First of all, Welcome to the GMT400 forum. Although these trucks are older and can
accumulate 'tough to troubleshoot' issues if they suffered from benign neglect by the
PO, once you get them sorted out they can be a hard working faithful traveling companion,
and a hoot to drive to boot.

Second, a sincere thank you for returning to share what the final fix was. So many people
pop in, ask for troubleshooting assistance, and then never return to share what the machine
decided was the actual solution to the problem. That's too bad, because every person who
shares the results provides valuable feedback/insight to all of us trying to do our best with
the remote troubleshoot art.

And, yet again the solution supports @Schurkey's recommendation to gain access to the
real-time data for these tough 'resisting repair' scenarios.

Again, thanks for closing the loop and sharing the fix. Hope we get to cross paths down
the road.

Cheers --

 

[Dud1f3r]

So many people pop in, ask for troubleshooting assistance, and then never return to share what the machine
decided was the actual solution to the problem. That's too bad, because every person who
shares the results provides valuable feedback to all of us trying to do our best with the remote
troubleshoot art.

There's a special place in Hell for people like that. Can't count how many times I've read a forum post looking for an answer and it went dead for 10+ years with no fix listed

 

[Dud1f3r]

To anyone going the route I did and going header dump, just as a word of warning, leave at minimum 5" of exhaust tubing past the upstream O2 sensors. This helps prevent them from reading ambient air and saying you're running too lean.