pboxfun

As the title states I知 having a pretty bad WOT misfire. This problem happens when I WOT from a dead stop it値l immediately start missing and won稚 stop till I let off the gas, and it値l also happen if I知 moving and I hit the gas it値l work fine until I get above 5k and it値l start missing and breaking up bad until I let off the gas. Other than those times the car will drive normally. It痴 only under WOT I have a problem. I replaced the opti, plugs, wires, and tps less than a year ago. But for all I know one of those things might have gone bad. I知 also not throwing any codes as well. Does anyone have any idea what the problem might be? I知 planning on checking the wires, coil, icm, plugs, and opti. Is there anything else I can check or I知 missing? Everything that痴 done to my car is in my signature. Any help would be great.

parkers Z28

You say that your not throwing any codes what scan tool are you using ??
cam position sensor ?? just taking a guess

pboxfun

I'm using freescan. No cam postion sensor I'm OBD1.

slick1hunting

I would look at your plug wires might have burned near your headers. A quick look in the dark might be useful. Ive heard of others with similar symptoms with a bad coil wire also. Did you loctite your rotor screws when changed the opti? Im not sure what the symptoms would be if rotor was starting to get loose.

slick1hunting

Might also check fuel pressure to eliminate it since its easy to do.

pboxfun

Thanks for the help. I'm going to try running it at night to see if I can see anything that shouldnt be lighting up. I have an extra coil i'm going to throw on there just incase. I did loctite those screws. I've got a fuel pressure gauge in the car and i'm pretty sure thats fine, but i'll look at it more closely.

Zfbod94

My 94 had the same problem. Exactly. What fixed my problem was a new OEM coil(not MSD junk) ans some new wires while I was at it. Check out Shoebox's website for how to test the coil.

My MSD was showing 5.xx ohms on 3 terminals and on the 4th terminal it read 17.xx ohms, and this was after only 10k miles of running it.

So if you have another coil, throw that on there and see if its any better.

Hope this helps.

Injuneer

You're thinking of the CRANK position sensor - added for misfire detection in OBD-II.

Your car has a CAM position sensor. It's the optical module in the distributor. If it's faulty, it will set DTC 16 and or DTC 36. But DTC 16 shuts down the fuel system. DTC 36 may cause some firing irregularities. It sounds like the ignition is breaking down under load - plugs, plug wires (burned by headers?), coil, coil wire, IC Module, Opti cap/rotor.

pboxfun

Due to the nice weather today I’ve finally been able to datalog my car. The car was in closed loop during these runs. The first file labeled misfire 1 is from a dead stop. I had a little trouble getting traction at first but once it hooked you can see it immediately started missing really bad, I had to let off the gas because it wasn’t going anywhere. The second file labeled misfire 2 was from a roll. I had the car manually in 2nd gear from the beginning of the roll. The car took off fine but as soon as it got around 5k it started breaking up bad and wouldn’t shift into 3rd. Once again I had to let off the gas because it wasn’t going anywhere. Also I checked my electronic fuel pressure gauge I have in my car during these runs and it was fine. Does anyone have any ideas or can see something I’m missing????? Any help would be greatly appreciated.


Missfire 1

misfire1.xlsx

Missfire 2

misfire2.xlsx

pboxfun

Anyone???

parkers Z28

So the plugs , wires, ICM , and everything else that Fred listed ???? are fine and you have checked
the opti ??????? Is there any chance that something is not right with the MadZ28 tune ???

LowRyter

plug wires? opti? coil?

popo8

Exactly what i said on our site...and what i still feel.


Larry (Popo8) Co-owner
LTXtech.com

Injuneer

Just looking at the first log, it appears to shift at record 261, RPM drops to 4375, and both the left and right O2 sensor readings drop fast.... at 6250 RPM the left O2 is indicating 0.040V and the right side is indicating 0.329V - very lean. Appears to be running out of fuel.

pboxfun

I changed the coil and ICM and it didn%u2019t fix the problem. I also used a millimeter to check the fuel injectors and the wires going to them to make sure they were getting power and functioning properly, which they were. The reason I checked for that is because in my datalog my left o2 senor was reading very lean compared to my right one when the car starts acting up. So I thought it might be a fuel problem. But according to my fuel pressure gauge and testing out the injectors and wires it seems like everything is working right. I can also hear the fuel pump kick on when I turn the key. I also looked under the hood at night to see if I could see any arching but I didn%u2019t. I%u2019m going to take the wires off to get a better look. Anyone else have an idea what might be going on or what I should check for next? What could be causing my left o2 to be reading so lean? I also replaced the o2 sensors about a year and a half ago. Is this a fuel or electrical problem???