I am at a loss on where to look next and could use some help.

My 95 LT1 developed it's own rev limiter at 2500 rpm.

I've established it's closed loop computer related as it will rev to shift points above 5500 if I disconnect the computer and let it reset. The TPS seems to some accurate movement however it does fluctuate a bit when trying to hold it steady.

I am not getting a check engine light for this problem, I am getting code 97 4000 ppm signal out of the pcm. In the datamaster file it also shows a MAF code as I had it unplugged when I started it. I am admittedly not great with the datamaster information so if someone could take a look and advise I'd appreciate it. The tune is a mail order from madtuner.

DataMaster file

 

It's running extremely lean at WOT.... may be running out of fuel. O2 sensors are at about 100mV, when they should be closer to 900mV. Running lean is probably the reason for the high knock retard.

Funny thing is it's running rich at idle and low loads. The long term fuel corrections are closed to being bottomed out with regard to the amount of fuel they are able to subtract to prevent it from running rich.

Get the VSS fixed to the PCM is getting the correct vehicle speed.

 

Fred, thanks for responding.

I will look into the VSS, previously I thought it was just the output but saw some mph spikes in the linked file which should not be there since I was in park. It's grouped with a bunch of other wires so I'm guessing it's getting interference. I'll see if I can get a pigtail for the speed signal and isolate it.

Is it "normal" for the O2s to be opposite of each other like it seems they are? I have an innovate wideband on the right side providing the stock signal and running a digital gauge in the dash which doesn't bounce around like I seem to remember. I have cables on order to be able to look at that. Some else installed it and kept the serial cables.

I have another file from a time I'm actually driving the car and it is having the same issues. Maybe that'll help.

Datamaster Driving File

 

In closed loop, the PCM intentionally toggles the A/F ratio back and forth from slightly rich to slightly lean - it does that to allow the cat to store the O2 from the NOx reduction reaction so it can be used for the HC/CO oxidation reaction. The O2 sensor readings reflect that. Since each bank of the engine is fueled independantly, it is possible for the reading on the left and right banks to be totally opposite, fairly close, or anything in between.

Check your fuel pressure. If the engine wasn't actually being driven, and under a decent load (from the MPH spikes I thought it was actually on the road) it shouldn't run out of fuel at 2,500RPM.

 

I do have a fuel pressure gauge in it and while I don't recall the actual number it was in the mid to upper 30's, 36-38 i believe. I'm running an Aeromotive regulator currently set at 43 with the vacuum hose off.

 

Fred or anyone-

Any ideas on where to look other than tune on this? I was going to test the injectors (and prob will) but don't think that's it as it's ok in open loop. Are there any guidelines on MAF readings based on RPM?

 

I don't know if your MAF readings are out of whack because your vss is not working and there's only a few seconds of a log, but it thinks there's something wrong with it - maybe for an experiment you should unplug it and see if it runs any better on speed density. If it does, look for a broken wire near the connector or borrow another MAF from someone, or try some spray cleaner for it. If you have a fresh K&N filter, make sure it's not overoiled and getting oil on the MAF. Also check for vacuum leaks and exhaust leaks near your headers, collectors, and O2 sensors -

Your pulsewidths do seem to go right up when you open the throttle, though... It looks like it's trying to give you fuel

 

My K&N has not been oiled within a year so I don't think it's that. I may try some cleaner on the maf or try swapping one in. If you look at the driving files the VSS does not have the issue it does in park. I tightened the header bolts the other day but I will did not check the collectors, I will do that as well.

I am posting a much longer file than I had before. I didn't want to post something non relevant but I guess it may help. After looking at it a bit more I see that I was able to make it over 2500 a few times in closed loop.

Rec #'s around 1410, 1910 & 3075 show over 2500 with only 1410 being in open loop. around Rec #4300 is where it starts acting up. See screenshots or download the whole file.

Datamaster 7/17 long file

 

Do you have a cam installed, your idle MAP is 52.8 Kpa, low vacuum for a stock setup. Your vacuum only goes to 41 Kpa when decelerating again looks like a vac leak. The DTC 97 is an open unterminated line from the PCM to the speedometer, hang a 1/4 watt 10K resistor on the line to ground if you don't have a speedometer hooked up. Hate to say it but the trace liiks Ok AFGS is about right for RPM and MAP, injector BPW looks OK I can't see why no RPM unless its mechanical, cam, lifters etc..

 

Bob,

I do have a cam, Comp 07-466-8 (218/224 & .570/.565).

Thanks a bunch for the tip on the speed signal. I think I have my dakota digital speedometer hooked to it but it was a few years ago when I hooked it up so don't recall exactly.

My thoughts on mechanical or vacuum is it should do it all the time a computer reset shouldn't have an effect. Not saying it couldn't happen, just trying to wrap my head around it.

I tested the injectors tonight, all were 12.1-12.3 ohms. I found out my truck has the same maf so I can swap that just to rule it out.

 

As Kevin stated in post #7 you can pull the MAS connector off then start it up and it will run in Speed Density (with a MAS DTC present). If your VE tables were set up with the tune it should run w/o any problems. Your AFGS flows looked pretty close to mine (I have a 214/228 112 LSA) so the MAS readings did not look way out of wack. Some DTC 97 info http://www.mifbody.com/DTCs/DTC%2097.jpg

 

Well I went for a drive tonight without my laptop as it's giving me issues. First 10 minutes or so went fine then the car started acting up. I pulled the plug on the MAF, no change. Plugged it back in and I unplugged the cooling fan just out of curiosity, thought it may be a trigger, no change. Plugged it back in and pulled the vac hose off the regulator, minimal or no change.

Thanks again for everyones help and suggestions. I will look into that link.

 

I noticed on screen shots 2 & 3 that the TPS % is 100 on both but the voltage is different at 3.80 & 4.53. Is that normal?

 

Yes it's normal at least it's the same on my car. I can't explain the reason, but during WOT runs I hit TPS=100% between 3.88 and 4.55 (4.55 is the actual wide open voltage). The PCM must have some magic in the S/W that calculates the TPS%. Been replacing pistons and rings in one of my Waverunners so have not been on a while..love 2 cycle engines.. I looked at your logs again and I'm baffled.. I compared your run at record 4659 with a log of one of my runs.. everything looked perfect till you hit 2500 or so RPM then your car just froze. TPS hit 100%, MAP was perfect at 98.2 Kpa (same as baro), AFGS was 116.7 (mine was 110) , timing is 27* (retarded 5* due to knock) but it's not your problem at this RPM and load. Your injector pulse width is 17.96 (mine is a tad lower), your injector duty cycle is only 37 so you must have bigger injectors than mine as I am running stock and the DC is 50%. You enter kickdown mode the car shifts into 1 st gear injector BPW is still solid at 18Ms and then you just stay there doing nothing, your speed actually drops from 20 to 18 MPH when you hit first and the RPM stays around 2500, the rest is history. In my trace injector BPW stays the same width and the RPM keeps climbing fast, the PCM shifts to 2nd and speed increases fast. You got correct air flow, BPW and injector DC indicate good fueling, what kind of ignition are you running, any chance you are cutting the spark.. could be the MAS is stuck at 116 and below , but you swapped that out and tried SD mode, if not ignition or mechanical I'm stumped..

 

Just an afterthought, any chance your crank to cam timing relationship could have been set up incorrectly during the cam install. Or the Opti out of timing. One tooth off on the cam sprocket would be 9* or 18* for one tooth on the crank sprocket. Serious retarded timing could cause it to bog out at 2500.