tune too aggressive?

[SSandman]

I have had a strange problem with my 94 for a long time now.

The car runs SIGNIFICANTLY better in humid weather. Now I know humidity will always have an effect on power, but in the rain the car feels like a totally different animal. On any given day, even in the winter it often feels like a dog...very loose and sloppy and sluggish. No noticeable misfires but just real lazy. In high humidity, like a rainy/foggy night, the car feels like it should...tight and has some power.

While I don't currently have my scanner, when I was trying to diagnose the problem a few years ago I noticed my knock count was up pretty high. I never hear any ping though.

I am just wondering if you tuners believe it is feasible that the PCMforless tune I have is too aggressive, possibly leading to knock and then to pulled timing making the car feel like a dog. In the humidity, the water vapor acts to cool the combustion temps possibly fixing the problem.

I know it sounds crazy, but I can't think of any other cause for this. It's done this after new opti, opti harness, injectors, plugs, wires and swapped MAP, MAF, coil and ICM just for ****s and giggles with no change. I did the PCM when I first got the car, while I was still chasing around some drivability issues such as misfires from bad injectors, bad pigtails and tons of other problems...so the PCM is the one thing that has really stayed constant after so many parts have been replaced/swapped for various reasons.

The car has flowtech long tubes, deleted cats, 2.5" pipes w summit turbos and turndowns, RAISS, deleted EGR and a bryan H PCM tune for 91/3 octane.

[1slow96]

Don't you have another PCM you could try. I doubt Brian would ever admit his tune is the problem. So,there you are. What to do? I'd swap in a known good PCM,and see.

[4DoorSS]

Much easier to at least try another ECM and see what that does. I doubt it will be the cause but worth a shot.

Looking at your list of items you replaced, that is 1 long list of possibilities. Being that you described this issue being affected by moisture in the air, the areas I would be looking in would be vacumn/hose connections and checking electrical connections/componets.

It is very similar but actually opposite of what I've seen with faulty electrical componets like a cracked coil cover on a DOHC 4 cylinder recently. On damp days the car ran like crap, remove the humidity and she ran fine. The problem was a cracked coil cover buried down inbetween the cams and I guess shorting out the firing of the plugs.

[Rocko350]

Also keep in mind that higher air temperatures have a drastic effect on power. Poor air quality will make performance suffer. It has been damn hot this summer, the IAT sensor will remove timing to richen the mixture slightly. This makes it sluggish. I've seen wideband data on a car make a swing from pull to pull, where IATs went up to 110F from sitting for a minute or so and the wideband was reporting 10.9 AFR where previously the IAT was at or slightly below ambient air temperature when the engine was cooler, and running at a steady 12.9. Car dropped 5 or 6 hp across the curve and it looked like it was smoking out of the pipes. You could even hear it in the engine, it sounded "flatter".

Log it if you can and post it.

Chris

[SSandman]

4doorSS, did all new vacuum lines and resealed the intake manifold back when I got the car with no difference, but it can't hurt to maybe check some of the evap lines that aren't so noticeable.

As far as electrical, that's what I was thinking; most electric problems are worse in humidity, not better. Plus, I swapped the engine harness to a known good one and it made no difference.

Rocko, I will definitely try to get some logs! It's strange, temperature wise it doesn't seem to matter. It'll run way better on a foggy, humid, rainy warm night than on a cool/cold dry one. Other than on crazy humid/rainy days or nights, it feels just as you described, flat. Almost feels like the car is under load all the time. I know LT1s do seem a little sensitive to temps, but my 96 when it was bolt ons was predictable. The cooler it got, the better it ran. It didn't ever feel like a dog unless it was really hot out.

thanks for the help

[Rocko350]

The 96's handle the IAT calcualtion differently than the 94's adn 95's. The also run leaner with lower targeted o2 switch points as well. They could with the faster processor.

Chris

[xxxmalosoxxx]

I see you mentioned that you are getting pretty high knock counts on the scanner. I think its normal to get knock counts on startup and then they go away after a minute or two. If you think the knock is messing with the timing you might want to install a LT4 knock module. I have one installed in my LT1 Camaro because of headers/loudmouth exhaust. If you're not getting false knock then you probably don't need to install a LT4 KM.

This is from Summit Racing - These modules are less sensitive than stock modules which eliminates retarded timing from false knock created by noise from modifications such as larger cams, roller rockers, or headers. Not recommended for use with N20 or boost.

[defdaboss]

Originally Posted by xxxmalosoxxx

I see you mentioned that you are getting pretty high knock counts on the scanner. I think its normal to get knock counts on startup and then they go away after a minute or two.

i would be FREAKING out if my knock count were climbing at start up for a minute or TWO! the knock count should stop immediately RIGHT after the key fall back into ignition.

[Ram Air 383]

I would not be surprised if you have a mail tune. I had the best results lowering the timing as much as 5* in some tunes that I had from reputable tuners.

The 2 biggest indicators (in addition to the obvious timing retard) if the timing is screwed up are cam surge when the converter is locked in the 45-50 mph range; and a noticeable transition (and possible surges) during deceleration when going from open to closed throttle.