Problems with a 1990 Q (aus GM 18le engine)

[ozpulsarQ]

Hey, I have a 1990 pulsar Q (Aus model) and the other day it decided not to start. i checked for spark checked fuel pressure and injectors(spray pattern and for leak), checked valve timing from the timing marks and again with the rocker cover off and a screw driver to find TDC. did a cylinder leakage test and everything was fine. but still no start. i thought the spark my have been a little weak so i replaced the HT leads distributor cap rotor button and spark plugs. still no start. then i went through everything again and after i got it back together it started, but was misfiring on all cylinders and backfiring out the intake when it was revved. while it was running i hooked up the timing light only to find the timing was way to far advanced, but even adjusting the distributor all the way could not retard it enough. Knowing that the advance is controlled electronically i tried another control unit and distributor(with ignition module), still the same. i tried my control unit on the car i pinched the other off and it ran perfect. i have now also tried a MAP sensor and throttle position sensor just for the hell of it and cause im running out of ideas. there are no faults in the system and the ECU light does not come on. Anyone who has any idea please let me know. im going insane thinking about it all the time. thanks

[jc58nc]

When you say you swapped the control unit I asume you mean the ECU?

[ozpulsarQ]

"When you say you swapped the control unit I asume you mean the ECU"

Last time i checked ECU stood for Engine Control Unit. What do you think?

[jc58nc]

If you have a read your own text you had " changed control unit", I just wanted to make sure we are talking about the same thing. I can only suggest to make sure that the valve timing is 100% correct. If that's out then the ignition timing is out. And as you said you have changed the distributor ect. theres nothing else left! Check the fuse link and power for the ECU, I wonder if it's going into limp home mode, they run a bit rough when that happens. Make a test link and check the ECU for an error code.

[ozpulsarQ]

ok heres the G.O.
I found although the valve timing was correct the belt was looser than it should of been so i tightened the belt and the car ran better but not perfect. still misfiring and carrying on. I then swapped the coil again. more improvement and the car seemed ok. But after driving it home it started playing up again. since i was low on fuel i tried to use as much as possible up and put a fresh tank in. better again, but still not running perfect. I then received fault 13(O2 sensor i believe). i disconnected the O2 sensor to find the car now running perfectly(although a little rich) except a slightly rough idle. i drove the car like this all weekend and it ran well except for a slight miss at partial throttle, never full throttle and never no throttle and only sometimes at partial. whether or not this is due to the vehicle running rich im not sure ill have to look into pricing up a new 02senor i think. So thats it, thats my story.

[jc58nc]

That's good well on the way to a fix. With a new O2 sensor it should be fine.

[ozpulsarQ]

you reckon that will fix the intermittant misfire?

[jc58nc]

Yep, good chance! As you said it's running rich which would tend to foul the plugs. Once the new O2 sensor is in and reset the ECU (remove 3rd fuse link I think) should be OK!