Soma07

Need some assistance guys, I'm trying to tune a car which appears to have an fairly consistant misfire on the passenger side bank only.

The car is a 93 Z28, with all the bolt-on's plus a CC XE 230/236 cam. The opti is a 95+ vented unit and its new, as are the plug wires (MSD 8.5, over the valve covers) and the plugs (NGK TR5).

I believe its a misfire for two reasons, first the BLM's are split drastically from left to right, we're talking 108 on one side and 140+ on the other. Second, during WOT the O2 readings on the right side are very inconsistant. They go from 900's down to the 200-400 range, then back up to 900 again and so on while the driver side is fairly steady in the mid 900's. IMO that is representative of unburnt mixture going past the O2's signaling a false lean condition.

I've recorded some ECM data for you guys to look at, hopefully it will shed some light on the situation. The first file is a TTS Datamaster file. You'll need the 93 LT1 version of Datamaster to read it properly. The second file is part of the same file exported to an Excel spreadsheet.

http://pegasus.cc.ucf.edu/~ja389166/jim93z28.uni

http://pegasus.cc.ucf.edu/~ja389166/jim93z28.csv

Any ideas? All of the plug wires look fine and none appear to be burnt. We pulled two of the plugs from the pass side (#2 & #4) and they didn't appear to be much different from the ones on the driver side.

Soma07

Don't everyone try and help at once now...

96speed

I'd swap the O2s (side to side) for grins, and/or injectors.

Nothing looks ridiculously out of place from the .csv file, besides the fuel trims (obviously). This leads me to believe its a hardware problem.

Ryan

turbo_Z

93s are weird.. just had to get that in the open first.

now looking at your csv file a few strange things i noticed were that you were in cell 18 a lot. i thought cell 18 was an open loop cell like 16, 18, 17 but you are in 18 quite often and it seems to have a lot less of a split as well.

next you have a major split in most cells which again is strange. i would say its your cam but your splits are not consistent. what is hard to determine is cause and effect. if you look in the 280-290 rows while in cell 15 (WOT) the O2 sensors are not very still on the pass side... the drivers side they are in the upper 900 consistently. now what is hard to decide is if the O2s are messed up or if something else is causing them to appear that way... misfires for whatever reason. did you do the heated O2 conversion? if not then that might help you out some.

next notice how your TPS % looks a bit low while cruising.. only 2-3% going 25-30 mph seems off but ill have to check that tomorrow and maybe someone else will disprove me.

Soma07

First, I should have mentioned this isn't my car. It actually belongs to a friend and I'm just trying to help him tune it.

Injectors maybe, I doubt its the O2's. They are brand new GM 3 wire heated units and the old single wire sensors exhibited the same split.

I'm pretty sure its hardware realted as well, I'm just looking for ideas on how to narrow it down.

Weird, but simple. No MAF BS to mess around with

From what I've gathered cell 18 can be either open or closed loop depending on certain parameters. The .csv file doesn't show it but the car was in closed loop the entire time according to Datamaster.

Yes, the car has heated O2's now. It was converted because we were seeing the same huge BLM split with the stock O2's and we figured one of them was bad/too cold. Unfortunately the heated sensors haven't helped any in this situation (although they are still good to have).

If the BLM's were just split at idle/low load then I might write it off as the cam but it does it everywhere which leads me to believe something is causing a misfire. This would also account for the high BLM's on the passenger side since the unburnt mixture going across the O2's would be interpreted as a lean condition by the ECM (hence the sky high BLM's). This would also explain for the erratic O2's at WOT.

Never really paid any attention to that. I figure as long as its getting +4v at WOT and ~.5v at 0% TPS the sensor was fine.

Thanks guys!

shoebox

Try swapping the injectors from side to side (or a new set). You said something in an email to me about having some bad gas (rusty looking you called it). Maybe just clogged injectors.
A new fuel filter and maybe purging the lines could help.

And what's up with all the DTCs in the log? Definitely, the IAT code (23) should be taken care of.

[edit] It could be my Datamaster is not properly reading the uni file, so I may have seen something that was not there.

Soma07

Thanks for the reply Rob.

I believe that was Jim (car owner) who e-mailed you. I wasn't there when he installed the FPR so I didn't see what he described. I can say the car has been driven a decent amount lately and any bad gas should be gone by now. That doesn't eliminate a clogged/dirty injector though.

Right now I'm thinking swap the injectors, wires, and plugs from side to side to see what happens. That would eliminate the cheap/easy stuff first.

The car could probably use some bigger injectors too but I'd hate to change them right now unless we're sure thats the problem. The last thing we need is to change too much at once and create more problems than we already have.

Yeah, thats what happens if you try to read the file with the 94-95 version of Datamaster. I'm getting no DTC's at all here.

Pro Stock John

A guy on my board recently had that problem on an LS1 and it turned out the his intake manifold was not completely bolted down on one side of the motor. I'd also check the injectors and make sure they are firing... clicking.

ryaskovic

Jason, did you ever figure this out?