First of all, it's a 1998 Z28 A4 with lid/MAC's/TCI 4000 stall/bullet muffler on the end of the i-pipe.

Ok, here is the long drawn out story of my car. (I am seriously thinking of trading it in after all this!). My car has had a rough idle ever since I have owned it,so I was assuming that is normal for a LS1. The car pulled 305rwhp on the dyno with a lid, headers, and catback through a 3200 stall while pulling 8.1's. Anyway, last time I dyno'd, I pulled an amazing 225rwhp. Now, my transmission was on it's last legs at the time so we assumed it was the tranny slipping. Swapped in new tranny along with a 4,000 stall and then ran the car at the track to make sure I got that power back (dyno is 4 hours away). I did not get that power back. I usually run a 8.1 or 8.0 @ 86-87 mph. Well, this Friday, I ran a 8.8 @ 76mph! I did break loose every shift and almost hit the wall on the 2-3 shift (bald nittos), BUT it shouldn't be THAT bad of a mph, should it? I JUST changed the plugs (went with Bosch platinums, then read about them on here, oops) I pulled out NGK TR 5's (not 55's) and some looked perfect (brownish), some looked lean (white) and two looked reddish (not sure what that means). Jeff Creech (my tuner) thinks something in my motor is giving out even though it looked great on the dyno run that only showed me putting down 225rwhp (all engine readings were good). Now my question is where do I start looking? The coolant looks good, the oil isn't frothy, and the car cranks and runs fine. Could it be a head gasket leak even though it doesn't overheat and there are no other signs? Will a compression test alone tell me everything I need to know or will I need to do a leakdown test as well? If it could be valve springs or something, should I just put the new comp 918's on and see if that helps? Or do I trade it in on something else? LOL, and before you say stroke it, remember that I don't have a big budget! There is no suction or blowing coming from the oil cap, so what do I check now? There was a bad vibration at 1100 RPM's, but I rotated my stall one hole and it went away. Another change I made was that I went from a 3" I-pipe with a cut-out to a 3" I-pipe with a bullet super turbo muffler that dumps right in front of the axle. Could this be THAT big of a restriction? Thanks for any help.

PS
This is a long list of wierd things that have happened in my car. Local guys think it's possessed!

 

car go slow.




















lol, j/k kevin.. ttt for ya.

 

damn saounds like me man i had bad luck with my carever since i got it to. if it's posses man and you are short on funds just cut it loose man and get your self a newer one.

 

Tell me about it! The car ran stronger bone stock than it did with a ton of mods to include computer tuning on a dyno Thinking about abandoning it and trying to get a newer one if I can get a good interest rate. Only problem is, this one will be paid off within a year

 

Dude, I am about STUMPED with this car. Everything I check checks good, even with a Tech II scanner from GM. The only thing is that it won't get up and go!

 

Have you checked for false knock ? Do a compression test for sure and post up the numbers .

 

Will try that after work..... What will false knock cause? I do have a lot of knock retard showing in A-tap, but everything else is fine. Could it be a rusted knock sensor or something? Would this cause me to be THAT much down on power?

 

dude, ive scanned your car...you've scanned it... milkman has scanned it.... the computer cant tell you everything.

its time to start looking at mechanical things.
id start with doing a compression and leakdown test...

 

So why didn't you break out the compression tester when I was at Todd's house? Oh yeah, we didn't have one! LOL, so now I have to go buy one. If the compression tests are all good, do I need to do a leakdown test?

 

might as well do it at the same time since the spark plugs are a bitch to get to.. ask PJ or Joey or Jeff... someone probly already has one you can barrow...

also, stick a vac gauge on it while its idling... just to see what its upto.

 

bingo we found our culprit the 98 cars are renound for having bad knock sensors this causes the computer to pull alot of timing killing your performance, i never heard of it as bad as you have it but you did say the comp was pulling alot of timing. easy fix just change the knock sensors.

 

A-tap has shown as much as 4.1* of knock retard driving at 1400 RPM's and 15.6* at 5800.. I will do a compression check AND check the knock sensors. Thanks for the info.

 

how come the PCM isnt showing a ton of knock retard?

 

holy hell thats alot at 1400rpm

 

1. why didnt you tell me that sooner?

2. why didnt that show up when i was riding in your car the othernight?


armed with this new knowlege, i say, go replace your knock sensors... lol.

 

It doesn't show it all the time, only while driving. And I don't think you had it turned on that night did you?

 

Well, honestly I had forgotten about it It was when I was having lots of misfire issues. I changed out my wires and the misfires went away. I totally forgot about the knock retard as I assumed it was related to the misfires. And I didn't think you had that parameter running the other night?

 

OOPs! My bad, it was 4.1* @ 1400 RPM's and 15.6* @ 5800 RPM's. I just looked back at my logs.

 

it was one of the things i was watching...

anyhoo, i did a search for you..

the GM part number for the knock sensor is :10456222
$74.45 for TWO at GMpartsdirect.com

the Equivalent Part Number:
Delco 213-298
GP Sorensen KS116



you can probly get the GP one at advance... athough id goto Parks(main store) and see if they have the delco one in stock.

 

I e-mailed Jeff to see if my knock sensors were turned off (although I don't know why they would be) and I will run A-tap on the car again today to make sure I still have the knock retard. Can I tell if the sensors are bad by just pulling the intake? Will they be good if they look good? I don't want to just throw parts at this car anymore, i want it to run again!