My Z (81 N/A) has a misfire from 4500 RPM and above. Idle is smooth and revs are smooth till 4500 then blah. Been doing this since I got the Z. I had to replace the head gasket when I got the car and I just fixed an exhaust/intake leak and replaced a few vacuum lines. If I remember right it was doing it since I got the Z, just not as bad as it is now... I can't figure it out.

What I've done since is the AFM deal, replaced the fuel injector harnesses, replaced the cap, rotor, coil, plugs, wires. Replaced the CHTS and TPS. I belive timing is set to 10* but I will have to check that. The distributor has some play in it, but I can't afford a new/reman one right now.

I'm stumped as to what it could be. If anyone has come across this and has fixed this problem please enlighten me.

 

mine is doing the same...is good but than starts to cut and bogg..but stills accel's slower tha normal than all of a sudden goes back to normal?

 

I'm ready to chuck this motor and find another that I can get to almost run good haha

I wish mine would go back to normal. I need to find someone with a good running N/A L28 so I can have a benchmark to shoot for.

 

Um, Your fuel pump and or regulator isnt going out is it? And you've check all the sensors right?

 

thought about the pump and would like to replace it if I could find a decent priced one, and the regulator is new. The pump doesn't shut off when priming the system. it used to before the head gasket change, and didn't after.

 

I wonder what your fuel pressure is as well. Checker had a cheap one for like $170 before. Fuel pump that is

 

So on the AFM adjusting, you did the carbon track & also adjusted the spring? With or without an a/f gauge?

Replaced the FI harness means the entire ecu harness or just the fuel injector clips?

Did you reset the tps using an Ohmmeter?

I have an 81 dizzy somewhere in my garage. I'll try to find it.

Also, pull your spark plugs & inspect / compare the tips. It's likely just one cylinder causing the prob & the spark plug will tell you which.

 

Not the harness, sorry. I ment the fuel injector clips.

TPS adjusted using ohmmeter. I did the carbon track and the AFM shows good readings with the A/F gauge so I didn't adjust the spring...

I replaced the plugs recently they all looked the same.

I will be back to working on it Friday, I will check the plugs and the A/F readings again and make adjustments accordingly if needed. I'm going to pull the valve cover off again to make sure the cam isn't 1 tooth off or something (and hopefully I won't drop the chain if I need to adjust it haha).

 

Well, put a timing light on the Z last night and could only get a random timing mark to show up. Pulled the distributor gave it a spin and the air gap was null as the reluctor would hit the stator(?). Replaced it timed it (could actually see the timing mark!!) but got a random misfire while driving so I replaced the wires. All seems good now except the 1500 RPM idle speed after driving. I'll give it a week of driving to see.

Gotta check timing one more time, check the a/f ratio, double check the TPS and all "should" be right...

 

timing is at a weird spot, adjust it down a hair and the high idle will go away. but try and adjust the idle speed first. someone could have bumped it up trying to overcome the headgasket problem before you got it. it could also be that the throttle plate is being held open by the adjuster.

 

My car had a problem when I first got it running where it wouldn't pull barely to 5k even in first gear, but it seemed to free rev fine... I eventually got a new (MSD Blaster 3) coil for it and it solved my problem...