marshall51875

I have a 1996 Z28. It has

1. Manual fan switch. For 160 Thermostat that is installed.
2. Long tube headers with off road Y-pipe (no cats) code needs taken out for rear O2 sensors.
3. Flowmaster Muffler
4. Throttle Body Bypass
5. A.I.R Removed
6. K&N Cold Air Intake
7. LE Elbow with Air Foil
8. 2800 Stall Converter
9. MAF de-screened
10. Feed tube is unhooked for off-road headers. There is no plate on it at this time.

The computer has not been tuned yet. At the track it ran 13.66 with street tires and stock 2.73 gears spinning bad. I got some slicks and put in some 3.73 gears and now it bounces off the rev limiter bad before it will shift and now (not sure if bouncing off rev limiter caused this) it has a miss. Specially in OD mostly from 1500-2000 RPM. I checked car running at night and saw no arcs. I took out a few plugs (not all of some are very hard to get to and require loosening the headers) and they looked fine. I had a parts store hook up a hand held computer to it and it threw codes p0133, p0160 (I think these are the rear O2 sensors which are unhooked cause I have no cats) also threw codes p0133, p0153 ( I think these are the front O2 sensors which I replaced brand new a few months ago when I put on new headers?) also codes p0400, p1441 ( I think these have to do with the feed tube being unhooked and not blocked off cause off-road headers have no place for the feed tube?) Any ideas where I should start to correct these problems would be greatly appreciated.

96z28_lt1

take a look at spark plug wires maybe one burned cut up or even came off, first thing, also look up what all those codes are actually i honestly don't know them at all. also check out the icm i hear they have a pretty good failure rate and also they can cause some similiar symptoms

Injuneer

P0133 and P0153 are for slow response from the pre-cat O2 sensors. Are your headers cera-metallic coated? How long have they been on the car? Often the coated headers seem to contaminate the O2 sensors when they are initially run.

P0133 and P0160 - the first number appears to be a typo. I think you mean P0135. Yes, those are for the missing after-cat sensors.

What are you calling the "feed tube"? Do you mean the corrugated riser tube for the EGR that runs from #8 primary to the back of the intake manifold? Assuming you still have the EGR valve bolted on, the valve should be sealing off what would otherwise be a huge vacuum leak. P0400 is for the non-functioning EGR system. If you did not tune the EGR out of the PCM, or at least remove the vacuum line from the valve, you will have a vacuum leak when the PCM activates the EGR valve. That won't make it stumble at high RPM or hit the rev limiter, because EGR does not activate above 3,500 RPM.

P1441 indicates there is vacuum in the EVAP system when the EVAP purge solenoid is supposed to be closed. Either the EVAP purge solenoid is stuck open, or you have the lines reversed on the EVAP purge solenoid:

http://shbox.com/1/evap_sol.jpg

Problems with the EVAP system can affect high RPM operation, because EVAP is used at high RPM.

marshall51875

The headers where coated and the coating burnt off fast they have been on the car for a few months and I put brand new O2 sensors in at that time for the front. There is no telling how long the codes have been in there cause the check engine light has always been on ever since I got the car cause it has never had cats. What I am refering to as the feed tube is the thing beside the EGR on the back of the intake that runs to the passenger side exhaust manifold. The off-road long tubes dont have an area to put it. I took it off long ago and it ran just fine without it forever. I have an EGR block off plate but I was not going to put that on untill I got a computer tune. I tried the vacuum unhooked and plugged that goes to the EGR and I still had a problem with the surging so I have now hooked the vacuum back up to the EGR. As far as the EVAP is concerned I have not ever messed with any of that. I do know when I fill up the gas tank gas comes out the top of the tank and the gauge don't work (I think someone fooled with that and didnt put it back together properly) and I read that tank pressure can cause that code? I have no idea. Tomorrow I'm going to get a new filter for it cause it is due for one anyway and I'm going to hook a gauge up the schrader valve. As you posted in my other post I have starting issues as well. Other than the starting issues none of this happened untill I put the 3.73 gears in it and bounced it off the rev limiter a bunch of times cause it does not want to shift in any gear at WOT without bouncing off the rev limiter a few times.

marshall51875

http://shbox.com/1/egr1.jpg calls it EGR exhaust gas feed pipe. Mine is unblocked just like on this intake >> http://shbox.com/1/fp_reg.jpg

97WS6SCharged

Are the headers coated or painted? Coating should not burn off under normal circumstances.

It's likely that the EGR valve itself has started to develop a leak. Install the block off plate and see if that helps the surge problem.

As far as banging the rev limiter you're going to need to recalibrate the PCM for the gears and stall by changing the shift points and line pressures.

You really should invest in a laptop with a cable and scanning software before you go any further.

marshall51875

The headers where painted cause it burnt off fast and there was smoke every when I first started the car. I think thats why the front O2 sensors where reading. I reset computer and took it down the highway making it surge in OD at low RPM till the check engine light came back on. Then went back and hooked it up to the computer and it read codes for rear O2 which aint even hooked up so no biggie there. It also read p0300 which is random cylinder misfire and it read p1441which is the EVAP and I'm going to remove all that crap anyway and have it programmed out. I hooked a fuel pressure gauge to it and when I turned on the key the first time it would shoot up to 30 psi and rapidly drop back to 5 psi. Turning key off then on again it would shoot to 40 then drop rapidly back to 5 and then doing it one more time it would shoot to 45 then rapidly drop back to 5. At idle the pressure read 36-38 psi and when I unhooked the the vacuum it would shoot up to and maintain a pressure of 45 psi. Reving the motor in park with vacuum hooked up (I coudnt leave parking lot cause I didnt have $200 for a loan fee) it read 32-38 psi. Does this mean I have a bad regulator or a bad check vavle in fuel pump or both?

timnfxr

Sounds like the check ball in the fuel pump. The pump should prime to 41-47 psi, and should hold (within a lb or 2). My son's 95z had similar problem, primed to 42lbs, then dropped to zero within a second. Changed pump - fixed.

marshall51875

I'm sure the check vavle is bad that's why I have to prime it 2-3 times to start it but my big issues is the car missing. I can live with having to prime it to start it. Went today and bought a multimeter and a fuel pressure gauge. Drove car with guage sticking out of hood it read 32-36 cruising in overdrive with cruise control on. When u let of throttle it would drop to 32 and it had 38-40 at wide open throttle. Miss was still there. I unhooked the vacuum to the regulator and drove it some like that. The pressure stayed at 42-44 and the car still had the miss in it. Came home unbolted fuel rail and lifted injectors out enough that I could see them. Key off and on none leaked and cranking the motor over they all seem to spray a nice cone of gas evenly. So I don't think my missing problem is fuel related. Where should I start next? The opti and coil are only about six months old. The plugs are only about a month old. I don't think its a single miss cause the whole car surges when it does it in overdrive.

marshall51875

ICM connecter A and D read 12 volts on DC. B cranking read 3.0-3.4 on AC. C was grounded. Stock coil ohm at 8500.Didnt check the opti harness as its to hard to reach with water pump on car. So this means I have a bad opti? Also before I checked it with multimeter I got a new ICM. Now it surges throught the rpm band.

marshall51875

ICM connecter A and D read 12 volts on DC. B cranking read 3.0-3.4 on AC. C was grounded. Stock coil ohm at 8500. Checked the opti harness. A&B read 5.05 volts. C read 12.1 volts. And D ohm at 9.6 at 200k settting. Does this tell me I need a new opti? If so do I just need new cap and rotor or the hole thing? I'm not getting much vacuum if any at the line that goes in after MAF maybe I'm not getting the right ventilation. If I have to change the opti I'll make sure I double check my vacuum and vent houses to make sure they are clear and make sure the vavles in the vaccum line are working properly.

marshall51875

Replacing the opti fixed both issues. Shifts fine now. I guess if car is missing the computer gets confused on how and when to shift it. After doing an AC delete for the life of my now I cannot find my power steering pump harness.