F-Body drivers are: SMARTEST ON THE PLANET


So Gentlemen, here is my problem.
I did several searches to see if anyone has this same problem and found a lot of similar things. I fixed or replaced everything you all suggested. I've made several runs with autotap and plotted the graphs on just about everything, but nothing jumps out at me.
I purchased the car from a dealer with all the mods in the sig except the pullies. I have never been able to reach the previous owner, he's in IRAQ.

PROBLEM: The car runs great, nice and smooth and then the sound of the exhaust will change and it gets real growelly and the power drops like it's running on 7 cylinders. After a while it will change back and run great again. When it switches to the bad mode, it seems to be running rich. If it's running in this mode and I get on the freeway, it will take about a mile or so and you can hear and feel the difference when it changes and runs smooth. I ran it through several changes while driving around with autotap connected and logged no misfires on any cylinders, O2's swinging properly, AFR seems OK, KR never exceeded 0.8. When the car is smooth, the power is amazing and I want it like this all the time.

Things I've changed:
Opti, Water pump, Plugs and wires, O2's, MAF, MAP. I did seafoam and deep creep. None of these have made a perminant change.

Every time I make a change, the car will run without a problem for a week or so and I think OK I fixed it and then it will start this crap again. Sometimes, when I start the car It will start out in this mode. If it's running crappy and I go WOT, you can feel and hear the change and it halls a$$ but when you let off, it's back and a little worse.

Things I don't know:
I don't know if the previous owner has had any PCM tuning done or what kind of cam he put in. The cam is not heavy, you can feel and hear the lope. I don't know what else was done to the car and removed before he traded it in on a 03 cobra. Could PCM tuning cause this if it's set up for mods that are not there anymore. This is not an all the time problem, it's just every now and then.

WHAT ELSE COULD IT BE?
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Polo Green 96' z28, M6, Some kind of Cam, 52mm BBK TB with bypass, K&N CAI, 160 Stat, Flowmaster cat-back/no Cats & 3” pipe, Vortech Elbow, B&M ripper, NGK TR55's, Accel super coil, March pulleys, 3.73’s. BMR STB. Pro Mag 1.6RR, Comp’s Hardened pushrods with LT4 Springs, LT4 KM.

 

Come on guy's, with all the brains on this board someone has got to have some ideas.

F-Body drivers are: SMARTEST ON THE PLANET
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Polo Green 96' z28, M6, Some kind of Cam, 52mm BBK TB with bypass, K&N CAI, 160 Stat, Flowmaster cat-back/no Cats & 3” pipe, Vortech Elbow, B&M ripper, NGK TR55's, Accel super coil, March pulleys, 3.73’s. BMR STB. Pro Mag 1.6RR, Comp’s Hardened pushrods with LT4 Springs, LT4 KM.

 

If you have the AutoTap logs in .csv format, one running well, and the other running poorly, I'll take a look at them. Either post them with a link, or send me an e-mail with the files attached, identifying your screen name clearly in the subject.

 

Fuel pump kind of comes to mind.

 

Thanks for reminding me, I left that off. I replaced the fuel pump with the Walpro 255 and P&P harness.

F-Body drivers are: SMARTEST ON THE PLANET
____________________________________
Polo Green 96' z28, M6, Some kind of Cam, 52mm BBK TB with bypass, K&N CAI, 160 Stat, Flowmaster cat-back/no Cats & 3” pipe, Vortech Elbow, B&M ripper, NGK TR55's, Accel super coil, March pulleys, 3.73’s. BMR STB. Pro Mag 1.6RR, Comp’s Hardened pushrods with LT4 Springs, LT4 KM, Walpro 255.

 

Injuneer,
I try and get you the Data for the two runs, it will be easier to E-mail. My E-mail address is john.gloyd@spectra-physics.com. send me a message and I'll reply back with the data.
Thanks, I'm an engineer for a big laser company, I designed and built the lasers that dock the space shuttle to the space center and I can't even figure out what is going on with my car.



F-Body drivers are: SMARTEST ON THE PLANET
____________________________________
Polo Green 96' z28, M6, Some kind of Cam, 52mm BBK TB with bypass, K&N CAI, 160 Stat, Flowmaster cat-back/no Cats & 3” pipe, Vortech Elbow, B&M ripper, NGK TR55's, Accel super coil, March pulleys, 3.73’s. BMR STB. Pro Mag 1.6RR, Comp’s Hardened pushrods with LT4 Springs, LT4 KM, Walpro 255.

 

The coil may be faulty. How about your fuel filter?

 

My e-mail address is visible in my profile.

 

Coil, coil wire, and maybe ICM (Ignition Control Module). Have you checked for the f-body "fireworks show" under the hood yet? IF not, then do. Intermittant problems are almost always ignition related. It's one of the only items on a car that can be "broken" and still work fine.

Dave C.

 

Thanks Guys,
I haven't checked the coil, Ground wires, or ICM. I did replace the coil wire and checked for the light show from the top and bottom. I'll check these this weekend.

F-Body drivers are: SMARTEST ON THE PLANET
____________________________________
Polo Green 96' z28, M6, Some kind of Cam, 52mm BBK TB with bypass, K&N CAI, 160 Stat, Flowmaster cat-back/no Cats & 3” pipe, Vortech Elbow, B&M ripper, NGK TR55's, Accel super coil, March pulleys, 3.73’s. BMR STB. Pro Mag 1.6RR, Comp’s Hardened pushrods with LT4 Springs, LT4 KM, Walpro 255.

 

Sounds very similar to the problems I have been experiencing. Unfortunately I havent figured it out either but I am pretty sure it is ignition related. Can you post or send me your autotap logs so I can take a look at what is happening?

 

Odd, my guess is the ignition.
I'll take a look. Send them to dan@helicoptersafety.com