5.3 swap weird stalling issue

[wildkard]

It's been a while since I did any tuning as I got my own swap running great, but a few weeks ago I did a harness and basic swap tune for a buddy putting a bone stock lm7 in his 63 chevy truck. Only mods are the air intake and headers really. When I first set up the tune I removed all the unneeded stuff, and set up his fan and the like but he didn't know his rear end gear so I told him to bring it to me when he had that figured out so I could set up the speedo and shift points. He brought it back a couple fo days later said it ran great, I set up the WOT shift points using a formula I found on here that worked great for my Nova swap.

That's when the weirdness began, right after he left he came back saying that every time it shifted the engine fell flat on it's face. I double checked everything, even did the speedo calibration math manually and came up with the same thing as the wizard did. SO I thought maybe it didn't take the write correctly, and rewrote the calibration. This time i went on the drive with him and no stumbling on shifts, but it did sometimes hit a wall about 5000 rpm like it was hitting a rev limiter there. But only about 30% of the time, the rest of the time it would happily rev to the 6k it was set at. I didn't have time that day to get into that and told him I would look into when I had a chance.

Well today he wanted me to stop by and look at his fan, he finally got it hooked up to allow the ecm to control it but said it wasn't coming on even at 230 degrees, well that turned out to be his dash gauge reading about 10 deg higher than the ecm. But he wanted me to lower it to 200 degrees and bump the shift point a couple hundred degrees, and reduce the shift times like I did my nova to make it shift crisper. I made those changes, and flashed the ECM, we took it for a drive and it started falling on its face again, though I noticed it wasn't just a shift points.

We got back to the shop so I could grab the laptop and start scanning, I noticed that whenever it would fall on its face it would be at high manifold pressure, and it would absolutely gut the spark advance, like down to 6-8 deg at times. I logged knock retard, torque management advance everything I could think of that might be pulling the advance and couldn't find anything causing the issue. Re-flashing did not help this time.


AT this point I was stumped, so I went back to the stock tune and just made the mods I needed to make to make it run, vats disable, fans, speedo calibration and MIL deletes. No more falling on it's face, but it still seems to hit that rev limiter at ~5k sometimes.

This is the calibration and a scan for when it was falling on its face

bobbys modified file.hpt
timing log 3.hpl

And here is the "milder" tune that just has the odd rev limiter

bobies modified tune 2.hpt
stockscan.hpl

I am at a loss of where to even start or what other things I should be logging to figure this out so any insight would be greatly appreciated.

[5FDP]

It's pretty easy to spot problems with both tunes.

First one has the commanded AFR stuck at 12.4 for the entire log, that isn't helping you any. The fuel trims are all over the place and you aren't logging enough information. You need o2 sensor data, intake air temps, coolant temps, injector data. All that stuff can point towards problems.

The 2nd tune has the commanded AFR back to somewhat normal but the fuel trims are still pretty bad. It needs VE and MAF tuning for sure.

What size fuel injectors does this have? You say it's a bone stock LM7 but are the injectors really flex fuel injectors like the computer is saying it is? If you aren't running flex fuel, disable that feature to prevent the computer from commanding different AFR's on you.

[flyingfool]

yup always run stoich when "not" under heavy loads

[wildkard]

It's pretty easy to spot problems with both tunes.

First one has the commanded AFR stuck at 12.4 for the entire log, that isn't helping you any. The fuel trims are all over the place and you aren't logging enough information. You need o2 sensor data, intake air temps, coolant temps, injector data. All that stuff can point towards problems.

The 2nd tune has the commanded AFR back to somewhat normal but the fuel trims are still pretty bad. It needs VE and MAF tuning for sure.

What size fuel injectors does this have? You say it's a bone stock LM7 but are the injectors really flex fuel injectors like the computer is saying it is? If you aren't running flex fuel, disable that feature to prevent the computer from commanding different AFR's on you.

Well crap, that's what i get for taking him at face value and not making sure he knew what he was talking about. It is a flex fuel, L59 with no flex fuel sensor, I'll have to get that disabled and see if that makes a difference. I was so focused on it gutting spark advance I didn't even notice the commanded AFR. I'll get the O2s and injectors back in the scan after I get the flex fuel sorted out i needed the room for all the spark stuff I was looking at.

Though I think I may not have been clear enough, by bone stock I was meaning that it has no engine mods other than air intake tube and exhaust. And that I haven't made any changes to the engine tuning. That first file, the only tuning changes are to lessen torque management and some changes to shift times and WOT shift points. The second file is the tune as pulled from the ECM except for VATS disable, speedo calibration, electric fan calibration and disabling some MIL parameters.

I know he's going to need a tune to get the most of the motor but it should still run pretty good "stock". Hopefully its just some artifact with not having flexfuel disabled, this will be the first one of those I have done out of half a dozen like this I've done for members of my car club.