Hi guys, I've been having some issues with the monte lately and wanted your opinions. The other day I was opening it up on the highway, and soon after shifting into 4th gear the engine bogged down and I got a flashing check engine light. I slowed down and everything seemed normal and the light turned off, and checking my scan gauge I had a P0300 code. I did it a couple more times, this time looking at the misfires. After it shifts into 4th I get a couple thousand misfires and I loose all acceleration and begin slowing down. Driving normally though shows no misfires and everything seems to be normal.

The next day I get in it and there is a noticeable exhaust gurgling and popping when decelerating, and the engine feels like its misfiring under normal acceleration. Later I try driving again and now it has a rough idle and very noticeable misfiring at all times, with the P0300 code included.

I checked the fuel pressure on the rail and it was at 40psi with the car off. I went ahead and replaced the fuel filter and that brought it up to 48-50psi. When I went and replaced the plugs I found the source of the obvious misfiring, the #4 cylinder plug was completely melted away and was loose. Luckily, I think it melted over enough time to prevent any large chunks from ending up in the cylinder, although I am probably going to need to do an oil change now. I uploaded pictures of the three worst plugs below, the worst being the melted #4 plug. I don't remember the cylinders of the other two, but I remember one of them was #1. I put new Autolite 104s in it and opened it up on the highway again. This time it seemed to be better, getting well into 4th gear above 115, but it started bogging and misfiring a little bit. I didn't keep it pushed down so I don't know how badly it would have gotten, but I think the plugs are a symptom and not a cause.

Does anyone have any advice for me? To me it seems like I am running lean and getting too hot, but the dealership I took it to to get checked out said the AFR was normal, granted this was checked in park though without making boost.

 

To start, I'd really avoid 4th gear WOT pulls in general. The transmission is going to die quickly if you keep doing that. 3rd is fine, 4th not so much.

I really am worried its something in the tune given your last thread. The tuner said neither AFR changes nor timing changes had any impact on power output, and couldn't even check for knock.

I really worry the tune could have issues because of that - maybe theyve got the fueling too skewed on that cylinder, maybe theyve got a weird fueling / timing modifier that's making too much of a change over time? Hard to tell for sure without seeing some scan data.

Lean and detonation can both cause the issue, I'm afraid it could easily be one or both given the previous thread...

 

Bumpin,
I am wondering the same thing. I have been meaning to get my own tuner since I still plan on switching to E85, but I need to get this sorted out first clearly. Would you recommend I call them and tell them something isn't right and see if I can convince them to retune it for free or discounted, or should I just stay away from them and get a correct tune elsewhere?

As for the pulls, good to know. When you say stay away from WOT 4th pulls, do you mean ease off the pedal before it shifts? My PCM is still a overkill motorsports canned tune (it has since been tuned of course), and I seem to remember the feature list for that mentioning something about it being programmed to let off the throttle when shifting into 4th (website says he is done doing 3800 tunes so I can't check ).

Edit: I should also mention that I do see anywhere from 3-6 degrees of knock on my scan gauge

 

Based on your last post, I'd stay away. I dont get the feeling they know what they're doing and it could cost you an engine (if it hasn't already).

I mean I would not let it shift into 4th at all at WOT. I'd either run it it 3/D or let off before the shift. The stock clutch hub splines are trash and can strip off, and that clutch pack has only 2 friction disks (compared to 10 on 3rd) so it cant hold near the power. TBH theres no reason to be running a bolt on 3800 that fast anyways.

That's way too much, especially on a 'tuned' setup. I'd quit getting into boost at all until you can figure out what wrong or you're going to cook the engine.

 

I have to agree with you on that one. Is there a canned tune that I could do instead of paying for another dyno? I have heard mixed things about ZZP, and it looks like overkill is done doing canned 3800 tunes. My other option would be getting an HP tuner and fixing it myself, do you think this would be a relatively easy thing to find and fix in the tune, or am I better off letting someone who knows what they are doing fix it? What would you be concerned about as far as damage already done? Is there anything I should be checking?


Duly noted


Will do. Do you have an recommendations on a way to lower some knock? Like I said I am still planning on doing E85, but I don't know that I will get that done soon, especially since I need to pay for a canned tune, tuner, or dyno tune. For reference I've done all the entry stuff on your stickied mod plan (CAI, plugs, 180 tstat, rockers) plus 3.4" pulley, headers, ported blower and northstar tb. Obviously I can just go back up to a 3.5" pulley, but do you have any other recommendations that could eliminate KR instead?

 

Downside in your situation is that it already sounds like you've got more mods planned (E85) meaning itll cost more money to have it tuned yet again.

I really think this is a great way to go given your situation (that or a used DHP Powrtuner would do the same for a fraction of the cost if this is the only platform youd want to tune). Other upside is that it would give you a full blown scan tool and the knowledge to deeply understand how the readings interact.

I hesitate to say its easy though. Your setup is certainly the easiest level of 3800 to tune. None of the stuff has been changed that makes it harder to dial in. But I also wouldn't just tweak the issues, I'd start the tune completely from scratch / stock file (available online for free) so you know its good and that there isnt some random table they played with thatll continue to cause issues. Itll definitely take some time commitment to leane how to do that though.

I'd suggest poking around on google a bit for 3800 tuning guides so you can get a feel for level of difficulty compared to your ability.

Pistons mainly, secondarily rings and valve sealing. Ideally, I'd rent a cheap borescope to stick in each one to make sure the pistons arent chipped, then would do a compression test to make sure they're all still sealing up nice. Probably a bit overkill as it's not highly likely on just a 3.4", but it would give you 100% confidence that the engine is GTG.

I think the pcm / tune is the key here. That setup should be able to run knock free after a tune with reasonable timing.

The big culprit seems to be that lean condition on the one cylinder. That one cylinder could be causing all of your KR.

I'd also not rule out a maintenance issue. I focused a lot on the tune as that whole last thread you posted seemed so sketchy, but there could be a legitimate problem too. I'd definitely pull the other plugs to see how they look compared to normal. If they look good, I'd probably swap the injector from the bad plug cylinder to a known good one to see if the issue moves too.

 

I think buying a tuner and learning to do this is probably the best route. I need to eventually do it anyways, and then I can do it myself and make sure it gets done right.


I have access to a snake camera that should fit down the spark plug hole, and I'll see about getting a compression tester.

Sounds good. Is there a way to see AFR for each cylinder? My only concern about moving injectors would be this issue only cropped up after 6 months, and only after I finally left town and opened it up on the highway, so it might take a while to see any difference in the moved cylinders plug. For reference, here are the other three plugs + one temporary one that was put in to get me home where I could change out all six for new 104s. The 4th temporary one was driven about 40 miles in cylinder #4.

 

If nothing else, they probably rent them at Autozone. Realistically though, the snake cam will cover the biggest concern. The top of the piston above the upper ring land is pretty thin, so if the ring over expanded from heat or the knock was too much, itll usually show up as broken off pieces of piston edge.

Not without a lot of expense. Youd need a modified header/manifold with ports for EGT or wideband on every primary tube. You can pick up a totally dead cylinder with an IR temp gun, especially with headers - but that doesnt sound likely here.

The bad thing about the stock O2 setup is its using 1 narrow band sensor to read a blend of both banks. So if 1 cylinder was doing something odd, it could be globally adjusting fueling via the trims and masking the problem. Definitely makes diagnostics a bit harder.

Are you getting any misfires? If you're picking up a notable amount of cylinder misfires on that cylinder with a good plug then maybe you could use the cylinder misfire counter to see if that moves.

Otherwise, you're already on the right track with replacing the plugs and then checking how they look. That's certainly served plenty of old school racers and mechanics well.
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Sounds good, I'll post pictures if anything looks out of place, especially on #4.

I am getting some misfires WOT, even after new plugs and a new fuel filter. When I try using the misfire reading on my Aeroforce interceptor it just shows xxx for every cylinder, which was part of my difficulty with finding the source of the misfiring originally. The misfire reading when scanning seems to work, but I cant get per cylinder counts.

 

Drove the 5 hours home from my parents the other day, stayed off boost the whole way and things went pretty smoothly. Yesterday grocery shopping around town I had a couple misfires idling, I checked the plugs and all but Cylinder #1 were in nearly identical condition. #1 was whiter and had more corrosion on the ground electrode. I went ahead and replaced it, still had a few misfires on random occasions though. My HPTuner comes in tomorrow, I'm hoping to get started it on it then. Does anyone have any good starting resources or guides for tuning a modded L67? I've watched some videos on the basics of using their software, but I'm having a bit of trouble finding good guides on tuning the L67 specifically.

Also, so I don't accidentally use up the stupid credits HPTuners require, I should use them on my current canned PCM and then use a stock file and copy all the stock values over, right? Or should I leave my current PCM tune read only and save it, and then use the credits on the stock tune and flash that instead?