CO99Z28Vert

iTrader: (30)

I need some help and I have tried numerous things to help remedy this problem by searching the forums.

The car is an automatic, it has 65,000 miles on it and has the awesome faint piston slap noise in the morning.
It has a miss when it idles and nothing I tried has changed it, when you are driving around 30-40 or so and try to keep it there it will sometimes surge...

The car is stock except for a SLP lid, K&N filter, NGK plugs, cat back Flowmaster muffler (I know this wasnt the best for this car but it sounds good for now).
Keep in mind that the missing started before I did these things to it and its still there.

My overall performance is crap right now and I dont think its the Flowmasters...or maybe it is.

On top of the plug change I also cleaned the maf with CRC cleaner and have checked to make sure the oil from the air filter did not get on it since, I cleaned the throttle body, changed out the PCV valve, cleaned the IAC valve and changed all fluids and even with the miss it never triggered the SES light.
Keep in mind that it seems like the car runs great except for the miss and the overall performance.

The limiter kicked in around 115.
This video was made late at night on a 85M.P.H 4 lane freeway, sorry about the dark video because of this.
http://www.youtube.com/watch?v=Sw4CXRduHf4
Should have probably rolled up the window lol

So what do you guys think I should try next? I have seen many videos and my car seems extremely slow and will probably run a 1/4 in 16 seconds. lol


Thanks in advance for any help.

orangeapeel

iTrader: (18)

Stupid work filter. I can't get to the video.

Hell Ride

how many miles did the car have on it when you bought it? I have only seen this kind of problem in cars with cracked pistons so maybe you cracked one or more? Good luck!

Hell Ride

a friend of mine has an 07 STi and cracked 2 pistons............no smoke. I dont know how it would be with an N/A V8.

CO99Z28Vert

iTrader: (30)

Whoa somehow I screwed up the last reply lol.

Hmm thats interesting.

Cruz28

I just have a question. It may seem like a stupid question, but I would like to know why is your speed limited at 115? Is it because it's a Convertible? I have a 99 Z28 with t tops and I've done over 155 in it. My speedometer tops at 155 but car still goes.

SLP Firehawk

iTrader: (9)

did you try changing the fuel filter ? either that or cat converter could be clogged cause it seems like ur engine is really straining

Alt

iTrader: (6)

He hits the limiter because his vehicle did not come with Z rated tires from the factory and thus the limiter was set to what appears to be 115-118. This has popped up in a few threads and thats the only answer I can muster. Apparently there were some 98 and now 99's from this thread, Z28s that did not roll off the lines with Z rated tires and that limiter is GM's remedy to doing so.

Da Swami

iTrader: (6)

Have you checked your fuel pressure?

A lot of fuel related problems can cause symptoms like this without any SES code or warning.

That's my guess considering you have no other symptoms.





I would think a cracked piston would, if not smoke, lead to a fairly large increase in oil consumption....

CO99Z28Vert

iTrader: (30)

Forgot to mention I changed out the fuel filter when I did the tune up,
but one thing I also forgot to mention was the fact the car sat for 11 months or so before I got it. I ran it pretty low a few times already since I changed that filter and even added stuff like seafoam to the tank, do you think the filter could have clogged up? I guess the pressure test should tell me.
I'll get a pressure tester tomorrow and try that.

I can tell you that when I first got the car a month ago it idled smoothly and only began to miss after a few hundred miles so thats when I started changing stuff and doing what I thought would help.
I checked the car in a dark garage and didnt see any kind of arching that would cause the miss.

Thanks for the help and I will let you know what the pressure comes back at.

Cruz28

I would change the fuel filter too, it seems like you took care of most of the things I would have checked already. Let us know what the outcome is. Good luck. Also thanks for the reply on my question Alt. My father has a 95 with the limiter problem. I checked his door and it's exactly what you said his Z28 did not come with Z Rated tires, you would think that would be standard equipment. How do you get rid of that limiter? Would GM do it if you buy Z Rated tires from them?

CO99Z28Vert

iTrader: (30)

Ok so I got the fuel pressure back and its at 45 psi with key on and when cranked its at 60-63. One thing though that seems odd is the fact that when its just sitting the gauge shows the pressure spiking from 60-63 violently, the reading was shaking between 60-63 and I know its not the gauge itself because I tested my other car and it worked fine, also when I gave it some gas it would stop shaking? Is this normal?...

Thanks for the help so far guys.

Da Swami

iTrader: (6)

Well damn. Those numbers are pretty much on the money for a normal LS1.


But the spiking sounds somewhat disconcerting. At idle it should be anywhere from 57ish up to about 65ish, but it should be fairly constant.

CO99Z28Vert

iTrader: (30)

Ok so I changed out the fuel filter again hoping by some chance in hell it may fix the problem but it didnt.

I read on the forum that I should get the car scanned even if the light is not on so I went and got that done, no codes found.

One thing I have noticed is the fact it seems to idle rougher after I have been driving.
In the morning when I crank it, it runs fine smooth. After driving it for awhile and when I come to a stop you can feel it miss, almost like it has an aftermarket cam.



Im going to just keep changing crap out until I eventually find the problem. Do you guys think O2's could cause this and not throw a code? also with the pulsing of the fuel pressure from 60-63 is this normal..could it be the strainer getting clogged up?

Thanks again for any help.

Da Swami

iTrader: (6)

From my experience (which is one car that had it) a clogged strainer causes a constant drop in pressure, not a variable one.

I still say it's fuel related. Maybe the fuel pressure regulator or an injector. Maybe run some cheap fuel system cleaner through it?

renxwar

I'd check the cylinder compression, and test the coils. The misfire is where you should focus first. If your getting fuel pressure at all, that means fuel probably isn't the problem with that.

The shaky fuel pressure doesn't sound normal, I wonder if the fuel pump could be going out (Seems kind of odd with only 65k miles).

Just to let you know, my 99 SS with similar mods (M6) runs about twice as fast as the video. Something definitely is NOT right.

ROLLN

i am dealing with the exact same problem to the tee right now, minus the surging. tommorro i am going to compression test it and work my way up from there. i am watching this thread closely and will also update you with anything i found. i also threw no codes but when i scan it on a genesis live scan, it says it has missfires throughout the scan cycle, but will not throw a code. my car is completly stock. after the compression test, i am taking the injectors off and taking them to this place by my house that cleans them for 3 bucks an injector, i already changed plugs wires and fuel filter. so after that i am going to try testing the coils. i ll let you know what i come up with and maybe i can help your problem too!

Sharpe

iTrader: (7)

If it were me, I'd change them. but yeah, should throw a code I'd think. If you do, might want to get Bosch 13111's. About $140 for the pair. I don't know though; i got them cause I have long tubes and they go all the way to the harness without extensions.

CO99Z28Vert

iTrader: (30)

Ok I finally got some free time to mess with this.

My bro hooked me up with some new plug wires and Denso iridium plugs for $27...dont ask

At work I decided to get these done and while I was there I was going to do a compression test, well after trying to get it threaded in the hole on the easiest plug to get to I gave up on the compression test since it was pissing me off and it just wouldnt thread in.

I was going to test the coils but I was clueless how to test them.

So anyways I took my time and spent 2 hours changing the plugs and wires and when I went to crank it I was shocked....It was not missing at all and the throttle response was alot better. I was not surging at all while cruising and even my friend noticed the difference right away.

In the video it seems just as slow as before but take off is alot better, I cant find any videos showing what a stock Z28 can do from inside the car to compare mine to. Anybody have a video? I would appreciate it alot.
I had to shut it down this time at around 100 because they did something weird with the freeway and there were grooves everywhere, I lost some traction on take off...damn pebbles in the road

http://www.youtube.com/watch?v=QWkne_hwD-k

I am happier with it now since it doesnt rumble me out of my seat when it starts to miss.

Thanks for all the info and I guess I lucked out on the iridium plugs and wires getting rid of that damn miss and surging issue...now I need alot more power...I gotta get rid of this exhaust next.