I had time this weekend to get my datamaster up and working along with a fuel pressure test.

Basic problem is after about 15-20 minutes of warming up driving I develop a stumble under acceleration starting at about 2k rpm all the way up. Way worse at 3500-5000rpm. If I hold the gas constant about half throttle I can get the stumble at least one a second if not more where the car will buck. Occasionally at full throttle no problem will show or it will last only a split second and carry on. Per suggestions on several similar threads I checked fuel pressure.

At initial prime approximately 42psi then drops to 36psi and holds steady.
About 36psi at idle
40-42psi with blipping the throttle
4-42 psi under load/full throttle even with the stumble. The needle bounces a little when the car bucks but the pressure is steady.

So here are my datamaster logs;

This is just a log of idle. had a EGR fault code 32 stored with no SES light. I cleared this one after this log.

http://myfreefilehosting.com/f/7b77d2b9b4_0.06MB


Here is a bit of mild cruising after idling. I was not expecting any problems yet but towards the end it is stumbling.

http://myfreefilehosting.com/f/21345efbba_0.05MB


So here I payed a bit more attention and started with a wot through 3rd and the stumble occured at 1710-1730secs at 4-4500rpm. Then again at 1749secs.
http://myfreefilehosting.com/f/12440250c6_0.02MB

Please enlighten me with any insight. I am prepared for it to be the opti but I dont want to throw a $500 dollar fix and a weekend at it if its something else. Thanks a bunch.

 

Just did a run with the 02's unplugged to rule them out and still had the stumble.

I also did the shbox voltage test of the ICM plug which was normal.

 

In to see what you find. I am having the exact same problem. I cleaned the MAF to no avail. I pulled the EGR off and cleaned it and that helped for a while, but it started back up again. I just bought another egr off the boards and hope that will help. I'll let you know.

 

Your speed is messed up on the datalog. It will go from 50 to 191 mph and back down to 50. This is causing the spark advance to go from 36 to 18 in the exact instance the mph go throught the roof. You getting knock retard at several points which messes with the spark advance. Figure out why the computer is not reading the speed correctly and you might solve a lot of the problems. You are running very rich it appears in most of the cells and that will screw up many things & could damage cylinder walls by washing them off. Don't drive this to far until you solve these issues. Your O2's appear to be working and it looks like the right side is much richer (around 50+) then the left and even when the cars rpm's smooth out your in the 950+ for the right side and thats bad. It looks like the car is dumping fuel and its not getting burnt so it could be a number of things. I would pull the plugs and see if any are wet with fuel. Your maf reading are all messed up also and your injector duty cycle reached 1120 at point. I don't know what a fried pcm looks like but theres something going on here.

 

I was wondering what would happen if the ground to the pcm was not on right, would it cause the weird readings? It appears that out of nowhere at any given time it would come up with numbers that were 2X to 10X what they could be. Maybe its loose and would lose the ground for just second. Just a guess.

 

I answered this on another site/forum. The data logs are filled with data errors. That's why there are crazy readings like 200+ MPH, 8* of knock retard, 3000mSec injector pulse widths, etc.

I suggested that he look at the MSD (which appeared in the mods list on the other site, but not here???), make sure it was grounded, and possibly use the MSD noise filter in the power supply line. Most Cells are closed to being max'd out at the amount of fuel they are pulling, except for Cell 15. That Cell is actually adding fuel, and its running a bit rich at WOT, particularly on the right side, if you believe the stock O2 sensors.

 

Its been suggested to me on fbody.com that the erratic reading may be the result of all the data errors in the log. This could be a bad ground or noise from the msd.

Looks like fred(injuneer) just made note of that. Someone is fast.

Please tell me what tells you my MAF readings are hosed up. I did just clean this thing in hopes that might be my problem but it did not help. Im obviously a complete novice and don't really understand most these PCM paramaters, but am trying to figure it out. Thanks.

 

I just drove home from work with the MAF disconnected. I started the car then unplugged with a quick drop in rpm. I then developed the stumble after about 15 minutes. So I guess I can rule out a bad MAF.

I will clean up and check my grounds as soon as my 8 week old stops going ballistic. Mom is going back to work...oh no's.

 

Yeah, I did the same to no avail. Same result with unplugging my EGR, however, after cleaning the valve, The car drove perfect for about a week. You might try that. It is really easy to do and a simple thing to at least try.

 

The problem is your car is seeing real eratic signals from some issue so until you fix that its hard to say what your maf is doing. If the knock goes crazy and then the car thinks your injectors are maxed and your air flow jump out of this world your going to have performance issues and stumbles.

 

Besides the battery terminal what other grounds to I need to check? Does the PCM have a separate ground back under the box? I will check/clean these and if that does not help I will try the MSD noise filter fred suggested.

 

The "car" is not necessarily seeing erratic signals... the ALDL is putting out bad data. That doesn't mean the PCM is running the engine based on that data. From the DataMaster help:

 

Suggestions for me from another forum
http://www.fastlouis.com/forums/view...709039#p709039

What would be the best way to test the O2s?

 

Did the OP figure out anything?

 

Not yet. Waiting for my summit order to get here to do a basic tune-up (plugs/wires, coil, fuel filter). Also going to install the MSD noise filter that Injuneer suggested in an attempt to get a better datalog without errors. Might get rid of the annoying speaker hum I have too.

I'm just going down the list eliminating stuff until I get to the Opti really, as I suspect thats what the problem is. I just dont really understand why if its the opti why my car does not show symptoms from the very start.