bigbadrat

ok here it goes.i have a 92 Z28 with the tune port 305 5 speed.last week my check engine light came on for 5 minutes and went out.2 days later i notice the car was missing and running rough.also it was smoking at the exhaust.kind of like gas smoke.gray in color.replaced the spark plugs and noticed the right side ones where black.did a scan and got a code 44.so i replaced to O2 sensor like the book said and still not right.checked vacumn lines,fuel pressure which is at 35psi.replaced ECM,MAP sensor and still the same outcome.i was watching the readings on the scanner for the O2 and it was around 0.47-0.86.but once it was about at operating temp,it would jump around from 0.27-0.87 and when u hit the gas it would drop to 0.06 at times.i am lost at this and have searched on here for answers but dont know where else to go.

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burnout88

Very possible the ECM itself is bad or the wire running from the O2 to the ECM is bad.

Using a digital volt meter test the voltage reading at the wire right before it goes into the ECM (should be a purple wire) If your reading there is good (0.47-0.86) but the scanner shows the output as a different reading (ie 0.06) then you know the ECM is taking a good signal and turing it into garbage and the ECM is bad.

To test for a bad wire check the signal on the wire just coming out of the O2 if the signal is good (0.47-0.86) and then you check it right before going into the ECM and it is bad (0.06). Then you know your wire is taking a good signal and turning it bad.

It also could be a bad ground wire in the O2 circuit by the ECM. But do these tests first and report results. Both the bad wire and ECM are very common problems on the O2 circuit and easily fixed.

SystemX

I had this same problem and it took forever for me to find it. Turned out to be 3 bad fuel injectors.

With the car running use a test light (what I used) to short out each cylinder one at a time at the distributer to find out which cylinders are missing. Then get those injectors tested or replaced. (after you've investigated the O2 sensor first of course). Also, check each injector plug with a noid light ot verify you have pulse at all the injectors.

bigbadrat

ok did the purple wire test.it is the same at the O2 sensor and right at the ecm.also checked the the injectors.they were reading13.50 and u could feel them working.i also did another ecm and map sensor.nothing has changed and driving myself crazy with this.i also sprayed carb cleaner around intake runners and throddle body but no change.i unpluged the map sensor and really didnt change anything.so does that mean something?

burnout88

Can you have a scanner, correct? What is your TPS readings? What happens to your fuel pressure on the guage when you rev the engine?

Also what are your BLM readings?

bigbadrat

i have a good scanner from matco.i am not sure about my tps sensor.have not looked at that.the fuel pressure moves up to like 40 when i hit the gas.it stay at 35 while idle

bigbadrat

ok still havent figured it out.the car has 134000 miles on it.do u think that the timing chain is wore out and causing the issues?the motor will rev up and sounds like it has the power.just a thought.

burnout88

Can you post a copy of your data scan? Not to pick on you but I am not confident you troubleshoot your O2 circuit properly. Also what are your block learn readings aka BLM?

bigbadrat

i can try to do that.have to see if i can get it downloaded to the laptop.i am still learning the scanner.just pisses me off that i cant drive my car because of this and might burn out the cats.

bigbadrat

OK I THINK I FOUND A PROBLEM.SO FAR ONE INJECTOR HAS A READING OF 0.06.THE OTHER FEW THAT I CHECKED WERE AT 0.16.SO LETS HOPE THAT IS IT.

bigbadrat

ok replaced the one injector and seems to be fine.just weird how one injector would cause all that.i bought a whole tune port motor that runs for 200 bucks and used the injector.now i have spare parts to do the 350 changeover.

bigbadrat

ok replaced the one injector and seems to be fine.just weird how one injector would cause all that.i bought a whole tune port motor that runs for 200 bucks and used the injector.now i have spare parts to do the 350 changeover.

burnout88

.06 OHM reading on an injector is basically a dead short. That's going to cause all alot of problems.

bigbadrat

yeah once i did the reading yesterday during work and found that out,i knew that had to be the problem.so i was thinking that since one injector was not working,the ecm was trying to adjust for the lost cylinder.am i thinking right on that?