Here's what has been done. Last April - heads, cam, lifters, timing set, SVO injectors, hardened push rods, COMP promag rockers, PCMforless tune, LT's, EGR tube block/tune out - but I left the valve on because I had to get it out from my parent's garage. I also replaced the plugs - and wires with a set of Taylor's with fire sleeves (been down the burnt wire route). The car ran like a bat out of #### until last weekend. It started surging slightly at around 1800rpm and now it's missing/bogging from idle up. With the hood up, if you give it gas you can hear/feel a slight miss. It's much more pronounced when driving. I pulled the #4 plug and it's black indicating a very rich condition. Checked the O2's and they are bouncing between 200 and 700mV which they should?? The maf, coil, ICM and opti are also brand new. Any ideas anyone?? This thing is driving me nuts!!!!!!!!

Edit: Forgot to tell ya - this is in a 96Z and there are no codes being thrown - yet.

Thanks all

 

My 95 started stumbling as I accelerated from an idle and occasionally it would bog down and run extremely rough. It turned out to be the fuel pump. It was putting out only 10 PSI when checked and should have been up above 40, I think.

 

Quick update: I checked fuel pressure last night and have at least 40psi. I took the car to a buddies garage and hooked his Snap On scanner to it. Went for a drive with him riding checking the data. The scanner registered no misses and all sensors operating properly while the car was missing and bogging like crazy. Two things - it doesn't act up until the engine heats up (something in closed loop I'm guessing) and we noticed that under mild acceleration it goes full rich.

Any more ideas???

 

I'm thinking you may have an opti issue... They don't always throw a code when they're on their way out. Before you go through all of that trouble though I would double check all of your wires at both the plug and the opti end. I've seen them burn even with the fire sleeves, and it's also pretty common to slice them on a pulley.

 

The opti is new (less than 300 miles) and no wires are sliced. The #6 plug boot is real close to the header. I'll check the wires again anyways. It only acts up when the PCM goes into closed loop. Seems if a wire was arcing it would miss all the time.

 

It's more than likely not an issue with plugs since it's only in closed loop.

Look at the O2 wiring and particularly were it goes down the passenger fender toward the starter. Thought mine could hold up to the heat of the header there since it was wrapped with protective foil. But the wires there were fried. Causing a closed loop problem.

The way I found mine was monitoring the O2s. Once I saw that it was never going below 450, I tested the wiring and found an open wire.

 

O2's are fine, checked them on my bud's scanner. MAF is good, IAT registered 88F on the scanner. I checked the output voltage from the MAP sensor and could not get it to go above 1.5V while raising the rpms. I wound it up to about 4500 while testing the output voltage. This seems a little low from what I've read??? I'm still real suspicious of that #6 plug boot. When I say it's close, I mean it and the fire sleeve are actually touching the header. No clearance, the header is too close to the plug unless I go over the valve cover!!! In driving it more the miss at times is not constant. It drives like whichever cylinder(s) are missing, occasionally decide to come back on line. I'm gonna replace the MAP and if that doesn't do it, pull the #6 wire and see if the boot is charred under the firesleeve.

 

Well, I'm about 90% certain that I found it. I took it out and drove it until it really started to miss (fading in and out but mostly missing), brought it home and pulled the #6 plug wire. This guy has been suspect since it's right next to (nearly touching) the header. Took it back out for another drive and the miss wasn't any worse. Other than it wasn't fading in and out, just steady. What do you want to bet that I'll find a burnt plug boot inside the firesleeve? I guess I'll find out tomorrow.