This is a repost from the LT1-Based Engine Tech but I received little feedback so I figured I would give this section a shot.

Datalogs:
http://www.mediafire.com/?dyqyydmm2rn
http://www.mediafire.com/?vy0jgymg1y2
http://www.mediafire.com/?yjyzywymom2

These are all the datalogs I took of my car. The second link is a .csv file so anybody can look at it; the other two are .uni files.

The Car:
-1994 Camaro z28, ~138k miles on the odometer
-Stock A/C Delco plugs, ~6k miles since replaced
-Taylor ThunderVolt 8.8 plug wires, ~8k miles
-MSD Pro-Billet Distributor, ~8k miles

Modifications:
-Edelbrock Mid-length headers, no A.I.R, EGR is still hooked up
-Open Y-pipe
-BBK 58 mm TB
-Ebay CAI
-Descreened MAF
-TH350 with 3k stall
-Wait4Me Performance mail-order tune
-Powerdyne Elbow

Symptoms:
-Bad hesitation from idle, meaning I can go full throttle but it takes a few seconds before the car actually takes off.
-Surging on deceleration. Jumps RPMs in increments of 300 to 500 RPMs.
-Just an overall lack of power. I dynoed the car back in November of last year, and my best pull was 204 rwhp, and somewhere in the 240 range for rwtq. This was on a DynoDynamics dyno, SAE corrected (I believe).

Recent Maintenance:
-Replaced the air filter.
-Cleaned MAF with MAF cleaner.

As I said above, the car dynoed at 204 rwhp, 240-something rwtq. A/F Ratio during the dyno pulls was fairly normally, nothing alarming to the dyno operator. I have the dyno sheet if anybody would like to look at it.
The best time I have gotten out of the car was a 14.1@94 mph, on a cold October night.
I have owned the car since 2005 and have only put about 10k miles on the car due to many issues (opti and transmission, mostly).

I am just looking for some insight on what to repair/replace, or if the car is just in need of a rebuild. I will try to answer all questions to the best of my knowledge, if I need to do more datalogging I can; if there is something particular you are looking for.

 

Your .csv file is only a single line of data. When you export, you have to specify the full range of records you want to export, or it will only export the first line.

 

I took a quick look at first.uni.. 1- Your throttle is cracked open a little to much. TPS voltage is .88 IAC is at 0 and your idle is running above desired setting. I think you surging during deceleration is partially caused by the tune. Your main timing table is jumping radically. In first1.uni record 2860 you are at 32 MPH, 7.5 % TPS, 1900 RPM and 46* timing. You then go hit the throttle TPS=25% and your timing actually drops 9* to 37*. Then you let off to TPS=0% and your timing drops down to 10* by cycle 2871, and your RPM dipped 400 then timing started to increase back to to 25* and your RPM recovered by cycle 2880. (all within 3 seconds) . To verify look at a trace and map your acceleration and deceleration MAP Vs RPM and circle each cell in the main timing table to chart your path during accell and deaccel. Make sure there are no large timing gaps. You also have to see where you come out of closed TPS timing table and transition to the main timing table. There should be no big gap there. Overall you are running pretty advanced at 46* you don't have and knock so it may OK but that's a lot of timing for a stock block and valve train. If you are not a tuner and have purchased this tune I would contact the tuner and insure it's correct for your setup. .. ALSO have you looked into the DTC 11 MIL indicator circuit code that is set ?.

 

I thought I had done this, I am new to Datamaster so I have no clue on how to do it! Any pointers?

I have not looked into the code, as I said above I am new to Datamaster so I was not sure which codes were set. What steps do I need to take to look into this code?

 

All of these comments are from log first 1

With the screen out your maf is just not very sensitive to changes in airflow, and it may be possible that you have some sort of a vacuum leak. Look at record 1790 and just after when you step on the gas both o2 sensors bottom out lean for a second which is probably your stumble. It happens again at record 2031, 3912, 3989, in fact nearly every time you step on the gas it has a LEAN stuble which there is no pumpshot setting in the lt1 pcm to cure it.

If I saw the tune I could make better guesses as to why it had the lean stumble other than some sort of mechanical problem (vacuum leak, descreened maf, too much throttle exposure and inactive iac).

Your problem in decel is because your DFCO tables need adjustment. The engine is worn from all the mileage and is not quite so happy to relight at the very low rpm that it does with the current trans and engine condition.

For log 2: you can see pretty well after record 6256 the lean bog and the change in the rpm slope as it corrects.

The timing curve in both logs seems to be very agressive to me although I dont see any knock being reported that doesnt mean it hasnt been disabled. These cars alot of times will drive alot smoother and better with a smoother timing table with less overall timing in it to keep the timing more consistant.

Turn up the speed that datamaster makes the logs at.

I wouldnt mind seeing copy of the tune, and perhaps bit of wot run. Too much timing at wide open will kill hp just as bad as too little. The lack of power could just be that the engine is worn and tired in any different number of areas though.

 

I am running a descreened MAF and it is a good possibility that vacuum is being affected, being that I am taking vacuum from the egr vacuum source and splitting it for use with the th350 transmission and MSD distributor.

 

ws6t3rror, I was wondering if that BBK 58 Mm TB is to much input air for a stock 138K mile setup, causing a bog when the throttle is hit. W/Current throttle stop setup the IAC is not controlling the idle, I am not familiar w/BBK TB operation.

 

Its not too much tb it just needs adjustment so the blades are shut more and if the iac still isnt open after that then the blades are poorly machined or the air is getting in some other way. Although the idle airflow from the maf does not suggest a vacuum leak until he hits the gas. Then there is about a half second lag before the maf reports any increase in airflow at all and the engine stumbles because the airflow has in fact increased and the engine is dead lean.

 

So I need to adjust the TB a little?

 

Yep.. crank it shut till voltage goes between 5.5 and 6.0 and see where your IAC counts go. The IAC counts for your setup should start running above 25 or so at idle. That signals the PCM is correctly controlling the idle speed not the TB. Secondly your timing at idle is 15* that's -5* (-25%) from stock setting of 20*. Getting the TB/IAC in range and upping idle timing should improve your vacuum (lower your MAP) a few KPA. Did you load that tune yourself. I just don't like your low timing at idle and the high timing 35-46* coming off idle when accelerating. Can you reload your stock tune to see if it helps the bogging. Each of these pieces, descreened MAF, 58MM TB, incorrect TB Stop adjustment, low timing, slightly lower vacuum (39.9 KPA at idle) and 138K on the motor may be collectively causing the bog. That would be my guess at this point..

 

The reduced timing at idle is because of the idle rpm being too high and the overspeed tables pulling it out trying to slow the car down. Its not always that way.

Try to get the tps to 0.6-.67 volts or so andwith the car warmed up the iac counts into the area of 30 or 40. You may not be able to depending on how well the tb is machined.

 

The tune that the car is currently running on is a mail order tune, just for clarification. And thanks for the direction, I will see what I can do!

 

ws6, you're right , I thought idle overspeed timing correction would be a couple of degrees but it's actually -5* at 100 RPM in the table. That accounts for the 15* at idle.