Engine prob on petrol

Hi all I have a 1995 navara 3.0lt vg30 auto, it runs ok on gas but on petrol it has a bad flat spot or bogs down and at times may pop or back fire through the air box, if I hold it at 2000 rpm it can vary from 1500rpm to 2500rpm its like it finds the problem fixes it then dies off again, idle is ok just a bit up and down very minor, I put this motor in because the old one had water in the oil and heads tested ok found a small crack in the bore so out she went, it still ran ok and did not have this problem even with water in the oil, just came back from mates who checked the codes there was a air flow code but after we cleared it went for test drive came back and retested it there was no codes but still runs the same.

Sounds to me like the AFM is buggered.

Seen a few TF Rodeos act like that, the 3.2L V6 model.

Dave.

I had this happen to my car when the ignition advance was bodgy and needed replacing.

Maybe squirt some WD40 in the dizzy? Also check all the HT leads for blackening or greying, indicating a split in the insulation.

Any idea where to get AFM to try or buy if I have to.

Ask the wreckers if you can try it before you buy.

A VG33E AFM might work.

Dave.

Will be trying AFM on sat, but not sure it can be that there is no codes comming up

Disconnect the AFM and see if it changes.

Do it while turned off though and then start it.

Dave.

Done that it runs but hunts or surges at about 2000rpm

Sounds like to me the afm is stuffed.

Dave.

Ok will let you know on sat

Went to wrecker today tried AFM and no good, tried oxy sensor and all good, the sensor I tried was not the right one for my car as the fitting is smaller but the plug was the same, so ran it without the oxy sensor and runs ok, so now just need to get new one and all should be good I hope, thanks for your help

Oxygen sensors usually only work at cruising speeds to get the engine to run most efficiently.

Dave.

Thats kinda what I thought it was only to help out the AFM, but its gunna hurt to pay over $150 for oxy sensor and not fix the problem, but it runs ok without it, so can it be a short in the system, I checked each wire on the oxy sensor and they were not broken(with tester)

Considered asking a auto electrician.

Dave.

Fitted second hand oxy sensor today (cant afford new one) car runs good, but tested old and it was -volts and I think thats trying to make it rich but the computer cant do it, I was told that the old sensor was contaminated from a stop leak stuff that was put in to stop the water problem it had with old motor and because water was going into the piston it got to the oxy sensor, and when the car sat for over two weeks it must have dried out in the sensor

Just one other thing, how do I reset my ecu

I'm not sure I follow the reasoning for the oxy sensor failure, but anyway ...

To reset the ECU the easy way: unload the car (empty tub, no towing). Take the negative lead off the battery, press the brake pedal for a few seconds, put the negative lead back on. Then take the car for a gentle drive.

That works with diesels. Don't know if it'll make much of a difference to yours. It can't damage the car - but it might also do nothing.

Cant be sure why it failed just know its better now

Disconnect the battery for say 3 hours and it should reset the computer.

Dave.

Will try that, one more thing how do I set the timing it runs ok but want to make sure, there is a wire to unplug then check it with timing light but what wire