breathment

i noticed today that when im accelerating, whether it me 1\8 throttle or 1\2 throttle. when i get to about 2500 rpms (+- 100 rpms) it feels like the engine misses. or has a lack in power for that area.. and it seems like its more then just a slight miss. cause it last for like 200 rpms or more. and when im accelerating slowly enough, you can feel the car kinda slow down, and then speed up once you get to about 2700 rpms... it always seems to do this at the same RPMS. and with a 6 speed. it gets anoying really quickly... i was wondering if this is some weird property of the TPI system. with the TUNNED runners...

i also have noticed that when im accelerating at WOT. i seem to get alot of knock retard (upwards of 15*) that seems to start right around 2700 rpms and goes to around 4000... and then after that i can go all the way up to 5400 with no more then like 5* of retard.. why am i getting MORE knock retard at lower rpms??

i

Sena'sIROC

Have you advanced the base timing at the distributor? Assuming that this is a stock motor with EGR, it's possible the EGR valve is stuck open. When's the last time you visually inspected the cap/rotor, spark plugs, plug wires? Man, it could be any number of things. But you need to ante up more info, like did the car just start doing this out of the blue or after a modification you made?


Brian P
89 IROC-Z 355

breathment

the car has always done this i believe. it is just more noticeable with the 6-speed. but it is just starting to **** me off now. the cap and rotor are about 6 months new. and their both high quality accel pieces.. but ill inspect them both.

so u think EGR might be causing this? i have been meaning to replace my EGR because of my bad gas milage. 14 MPG with a 6-speed.. thats with 50% highway driving.. could an stuck open EGR also cause excessive spark knock? the plugs and wires are brand new as of last march. and iv pulled two plugs so far just out of curiosity and they just seem a little black from carbon. but not bad, just running a tad rich.. even though my BLMS are around 140+. so i think im getting a false reading from the O2 which is causing the ECM to THINK im running lean, and therefore enriching the mixutre. but i am almost positive that it is because of an exhaust gasket leak and is letting in air. the O2 is about a year old. but i have been having this problem before i put my headers on and get the leak... sp should i replace the EGR?

if u need any other info just let me know. i can also hook up my scan tool if u need info fromo that.

tamu130

ive got an idea. shift before you get to 2500 rpms. that will keep you out of that annoying range.

jacob

p.s. i didnt say it was a good idea!

Bort62

EGR is a possibilty.

It is likely this problem is related to your cold start problems, as well.

Sena'sIROC

I think that the EGR is a possibility but don't change it just yet. Does your scanner record in an Excel format or the like? If so send it to me at sena@team.camaroz28.com I'd like to see it. I can get a ton of information by reading the datalog you make.


Brian P
89 IROC-Z 355

breathment

no its a gay scanner.. so i have to enter all the information manualy into the computer and i only get like 3 seconds of it.. but here are two WOT runs that i made. and tonight ill make another like 1\4 run that will show the weird stuff at 2500 rpms


http://www.fbody.com/members/david88...tool/Book1.htm
http://www.fbody.com/members/david88...tool/book2.htm

Sena'sIROC

Looks like you're running seriously lean. When you nailed the throttle at 2500 RPM your load variable jumped from 69 to 130 and your 02mV's were 500mV's then they fell to 60mV's. The highest the 02mV's went during this run was 720 mV's....very lean. You need to find out why you are running so damn lean. Looks to me like you have a bad 02 sensor. I can help you test this theory if you want; it'll be easy and quick and you can do it in the dark. Make a light run and record the areas you are getting knock retard and let me see those as well.

FWIW, I have an aftermarket camshaft in my car and had the EGR function enabled in the PROM and saw stuff just like this. Turned off the EGR function and the 02mV's look a helluva lot better and the knock retard went away (but I was getting a maximum of 1.2* of knock retard). But I really don't think that is the problem for you.

Brian P
89

breathment

i have a theory about the learn condition. but it doesn't explain the cold running problems..

i think my drivers side header gasket might be leaking causing a little bit of air to be getting into that side and making the O2 see more air then what is coming out of the engine. makeing it THINK i am running lean.. which in turns richens the mixture.. but then again if my cold running problems are because im running lean.. when im in open loop. i wouldnt be getting readings from the O2 anyways, so the leak wouldnt effect it. so maybe i really am running lean.

Sena'sIROC

Are you running hot? If your head gasket was blown trust me, you'd know it. A vacuum leak would introduce air which was unmetered past the MAF/MAP which would make you run lean but at WOT there is no vacuum. And at WOT your 02mV's were only 720mV's and that's the highest they got.


Brian P
89 IROC-Z 355

breathment

no, exhaust HEADER gasket..