New to DOHCS HELP!!

[Zboy]

Ok guys here goes. I'm new to Dohcs but have been working on GMs for longer than I care to remember. I just got my first DOHC a 92 Z-34. Runs like shit. Terrible fuel mileage, no power, horrible vibration at 60 miles p/hr.Feels like its running on 5 cylinders. Snap-On scanner says O2 sensor open shorted or bad. I've never had an o2 sensor make a car run this bad. Just for kicks I checked the Injector resistance. Alls well except for rear bank #3 seems slghtly low, 11.9 ohms to 12 flat for all others. Plug wires appear to be fine, but I haven't removed them yet. Had too many plug wires come apart removing them. Going to change O2 sensor first chance I get, but I have the feeling this won't fix the problem. Any Ideas?

[SappySE107]

What codes is it throwing. There are so many things that it could be at this point. Fuel Pressure and Compression check would help, so you gotta remove the plug wires. Just twist them and pull up, they shouldn't come apart. I havent had any do that, and thats including my cheap ass autozone wires. The O2 sensor can and will fuck up the way this engine runs.

Is it an auto or a manual?

[Zboy]

What codes is it throwing. There are so many things that it could be at this point. Fuel Pressure and Compression check would help, so you gotta remove the plug wires. Just twist them and pull up, they shouldn't come apart. I havent had any do that, and thats including my cheap ass autozone wires. The O2 sensor can and will fuck up the way this engine runs.

Is it an auto or a manual?

I don't remember what number the code was, just that it was the O2 sensor. the car is an auto. 160,000 miles. No thats not a typo. I also checked the cam belt just for kicks, it looks ok. No hairs, fibers or chunks missing, looks resonably clean.

[pontiac92gp]

Is it possible a bad ignition coil/module could cause this? I had same symptons and that was the devil. Just a possibility. But Bens the guru here ..

[Zboy]

Thats what I'm thinking since the plug wires look fairly new.

[Juglenaut]

Is it possible a bad ignition coil/module could cause this

No, not to throw a o2 code..

ICM fault will override.

12 Ohms is about normal 11.9 is not much different. Resistance on the injector inductor coil can either increase or decrease in resistance.

Injector Pulse is what to look for.

What is the Air/fuel ratio thru RPM???

What is the IAC steps at idle??

What is the Mean Value Injector Pulse at idle??

What is the throttle angle thru TPS voltages??

What is the TPS voltage at idle, 1/2, 3/4 to WOT (engine off but heat soaked)

Does the map respond to engine status???

Vac lines leak??

Upper/lower gasket leaks??

EGR status at Idle not moving, at idle in gear, while going 30MPH, while going 65???

[SappySE107]

The coil pacls can cause crap idle,pulsations at speed, and overall poor running There is too much going on with this engine at once though so its easier to start at 1 pointand work you way around. Ive been through bad EGRs, Bad O2s, and plenty of bad coils...and the symptoms are all relative in some aspects.

[Zboy]

I know the coil going to shit won't throw an O2 sensor code. I've got a gut feeling the o2 sensor is junk. My question is will replacing the o2 sensor fix what is pretty obviously a miss? Unbelievably enough, the engine still idles well. The problem is absolutly no power at any RPM and the occasional backfire. A failing coil could coat the o2 sensor with carbon and make it fail. I first thought the injectors were junk, but they appear to be operating normally. I don't believe the catalytic convertor is plugged, there is no rattling or exhaust leaks although I have not removed the cat to check it. The weather here in Duluth sucks this time of year and i don't have a garage so I work on the car when I can. As for the other information concerning the scanner, I'll have to bring it back to my friends place and hook it back up.

[Cotton]

the lower intake gaskets tend to leak when cold, after they get old.
this style of plug wire should not brake, but i know what you are talking about.
with a strange/not obvious eng miss condition, first step is to pull the plugs, and inspect carefully, they tell the story of whats going on in the eng.

wet the plug wires with a squirt bottle of water, load the eng (brake torque), and you will find a bad plug wire if indeed they are going bad.

FUEL FILTER-is a good item to replace just for elimination.

then, check the fuel pressure. 35-45psi at idle is ok

[Zboy]

the lower intake gaskets tend to leak when cold, after they get old.
this style of plug wire should not brake, but i know what you are talking about.
with a strange/not obvious eng miss condition, first step is to pull the plugs, and inspect carefully, they tell the story of whats going on in the eng.

wet the plug wires with a squirt bottle of water, load the eng (brake torque), and you will find a bad plug wire if indeed they are going bad.

FUEL FILTER-is a good item to replace just for elimination.

then, check the fuel pressure. 35-45psi at idle is ok

Thanks alot, I'll try that as soon as the weather gets warmer.