I just got DataMaster up and running and could use a bit of help with weeding through the Data. Can I send someone my uni file?

I installed LT's and a 3" CB a month or so ago. Since then the car has been down a bit on power. There is a miss in the idle, a new Opti helped, but did not eliminate this. And at WOT the car surges noticeably, but not excessively, this is more apparent at higher RPMs in 2nd and third gear.

I have read the great tutorial by Injuneer, and with my Novice eye picked out a few things that I don't like. First, at the top of 1rst gear injector DC is nearing 100%. Second, O2's go rich from idle to 3200 or so then dive lean and stay lean with the exception of shift points and spikes. I realize that the O2's are not in the loop at this point, and can be inaccurate, but I would expect them to be pegged high. In my unskilled opinion I think this is showing a cylinder missfire. I am close?

Any help would be greatly appreciated.

 

I'll take a look. PM sent with email address.

Dan

 

emailed you

 

Well, your MAF is reading about 13-15% higher than it should, which is making the car run rich in open loop. The computer is correcting for it in closed loop, but it would be good to get the MAF tables corrected.

I'm not sure what is going on with your O2 mV readings at WOT. They are either running super lean, or jump around all over the place. Your injector duty cycle gets close to 100% near the upper RPM, which shouldn't happen with your mods. You should be closer to 80%. Also, your short term fuel trims are calling for a lot of fuel at WOT, even though the long terms are locked at 128 like they should be.

Since you are able to get a datalog, you should be able to get a flash of your tune. If you can get that to me, I can verify that nothing is off with the tune at least. I think you can use pcmread.exe from the LT1 edit site to get the flash of your tune and then email it to me.

I think you may have a bad connection or ground somewhere when your engine hits WOT. Other than that, it looks fine, but with your MAF reading a little high.

Dan

 

Thanks for looking at the data for me. I will try to do a data dump later today and get it to you.

When I am @ WOT in the higher gears the car surges a bit. I think this shows up as the O2's going all over the place.

All of these issues showed up after the header install. I plan to block off the EGR soon, I think that this could be causeing some of my problems.

BTW when you look at the data how can you tell the MAF's are high? Is this a comparison to other normal cars? Thanks again for the help.

 

Assuming the engine is in good working condition:

If you look at your long term fuel trim, if the numbers are somewhere between 100 and 128, then your MAF is reading high. If the numbers are somewhere between 128 and 156, then your MAF is reading low. 128 is ideal. In datamaster, these are the two cells listed as LTerm Counts. Yours range between 108 at idle and 112 partial throttle. This means that the engine is being told to take fuel out by this amount (1-108/128)*100 = 15.6% at idle, and (1-112/128)*100 = 12.5% partial throttle.

This is happening because your MAF is reading more air than is really entering the intake of the engine. Since the PCM uses the MAF to initially gauge how much fuel is added to get the desired A/F, it adds too much fuel because it thinks there is more air. The MAF reading is used in open loop, closed loop, and Power Enrichment. In open loop, the PCM can't cut fuel, so for the first couple of minutes after cold startup, you are running 12-15% rich.

To fix this, your entire MAF table could be reduced by about 12% and 15% at idle. Mine was similar to yours before I calibrated the MAF. I descreened my MAF, and I'm not sure if that is what did it, but it seems that a lot of bolt-on LT1 have a MAF that reads a little rich.

Dan

 

I just tightened a plug and went to do another data run. I noticed that mt S Term Counts start to change when my O2's dip while I'm in PE mode. Reading Injuneer's Tut I thought they were supposed to lock.

I am working on getting the tune data, I will fwd it to you when I do. For now though I think I have a few mechanical kinks to work out.

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