Hello everyone i'm kinda new to this site. So i'm not sure if this will help me or not. I have a problem that i really need some help on. Before every one tells me to do a search i already did and the topic was covered but they were slightly different then my problem. I have a 1995 z28 and just did a top end rebuild because my headgaskets had blown. When i had the engine apart i added pacesetters long tub headers a 3 inch off road y-pipe, MSD cap and rotor, new NGK spark plugs, MSD 8.5 wires and 1.6 roller rockers. I sent the heads out to be rebuilt and trued and they were ported and polished. I also added a new K&N FIPK and a trick flow 90 degree elbow, a airfoil and hypertech 160* thermostat. My problem is that when my car get up to operating temp it starts bogging down like it is low on fuel but it is not i have 3/4 of a tank and this is my second tank of fuel so that eliminates bad gas. I thought maybe fuel pressure but i have 38 psi with vaccum and 44 psi without vaccum so that not it. I thought bad wires but they all checked out good. I also sprayed them down with the car running so they would arc if they were bad but they did not. The temp of the outside air has no bearing on when or how much the problem happens. The problem is somewhat visable at idle but not to bad unless you are at speed and slow to a stop at a light or stop sign then i almost stalls and on really special ocasion it will stall. Then when i go to pull away from stopped it will bog down then if i blip the throttle just a little a couple of times it will clean up and drive normally for a little. Then if i hold the throttle steady say just off the stop or maybe mid throttle it will bog down and lose lots of power and if i give it just a blips on the throttle it cleans up again. As it heats up it gets worse so i have limited down to a bad opti, ignition coil, and ignition moduel. I dont think that the fuel system is to blame but i could be wrong. I have no codes in the computer so i cant use that to help. Oh by the way it runs great if i stand on the gas. Which has me thinking it cant be the ignition because it should get worse in the upper rpms so this really has me stumped. I sure could use a helping hand. Thanks

 

Well i would look into o2 sensors, since it happens when you get warmed up. Any codes being thrown? Have it scanned at all? Possibly clogged injectors?

 

Yes....look into the O2's....mine did the same exact thing after i put my L/Ts on...for some reason the coating on hte headers has a tendacy to take out the O2's...

 

Is it hard to start when the engine is already warmed up?

 

Thanks for the info guys. It starts up fine wether it is hot or cold just has the bogs after it warms up. There is no codes in the computer that autozone can pull. I had to extend my o2 sensors wiring could i have messed that up. Maybe i should buy new ones and just resplice them and try it again. Would the 02 sensor be able to cause this kinda trouble i thought they were just a triming function. Add a little fuel take away a little fuel. my vaccum is kinda low about 15-16 instaed of the 17-22 that it should be. I checked compersion and they all tested out ok a little lower than the high rating but that is to be expected out of a motor that has just over 100000 miles on it. Anymore help would be great

 

Oh by the way i eliminated the egr valve system and the AIR system bought the block off plates for the egr and jery rigged the headers i was stuipid and bought the emmision headers then decided to get rid of those item anyways. So no egr is stuck open and the air system is gone.

 

Yes O2s can cause this...I though the same thing when it happend to mine....I had spliced my wires and to extend them and it ran like that after a bit of running.Didn't throw O2 codes or anything either...was just a process of elimination for me to figure it out...

 

o2's can cause this but there will be a code. If there is no code then will will be your optispark. These things just like to go bad and if you blew a head gasket it probably caught alot of moisture.

 

Oh yea, and I'll never do that again. Next time I will be smart and extend the engine harness connector because the o2 wires can get messed up and when you have a warranty on the o2's it is void when you cut the wires. OUCH

 

I just oreder 6" extentions from summit

 

I hope it is not the opti that would suck i just put all back together. It ran good before i pulled apart. i hope o2 sensors are bad maybe i can change them without to much trouble. Is there any know test for the opti besides pulling it off and testing it off the car. What kills our optis so fast heat or water?

 

I hope it is not the opti that would suck i just put all back together. It ran good before i pulled apart. i hope o2 sensors are bad maybe i can change them without to much trouble. Is there any know test for the opti besides pulling it off and testing it off the car. What kills our optis so fast heat or water?

 

For instructions on how to test the opti, click here http://shbox.com/1/4th_gen_tech2.html#opti_test. Dampness and the opti are mortal enemies. Well, that and because it's the opti. Certainly not one of GM's brighter ideas. Your ICM can suffer from heat related maladies though. For a fix on that issue, click here http://shbox.com/1/4th_gen_tech2.html#ICM_cooling That Shoebox is a God-send!