New here, but Ive had the car for quite a long time. Its a 1983 280zx turbo, all original with 127,000 miles on it.

About 6 months ago, it started misfiring under cruise conditions. Light steady throttle, most noticable around 15-2000 rpm, though can feel it anytime the throttle is held steady to maintain speed.

If I floor it, the miss goes away, and the car pulls great. So I cant imagine this to be a major issue, I just don't know enough about the vacuum setup to accurately troubleshoot this thing.

Ever since the misfire started, the following items have been replaced:
All fuel injectors with new fuel lines
Fuel filter
Fuel Pump
AFM
Spark Plugs
Distributor cap/rotor
Spark Plug wires
Various vaccum lines.


I have also tested the Throttle switch, egr valve and a few other items.


Any help on this would be GREATLY appreciated..
And just for kicks, a few pics of the car:

 

Is your boost gage showing decent vacuum when idling? you pretty much hit everything else easy. On a dark night in a garage you might look the engine over when idling and see if you see any extraneous sparking going on. Maybe something loose in the dizzy cas system?

 

Welcome to ZDriver!

I would check your ecu connections for corrosion. Clean and use some dielectric grease to protect the pins. Also check for loose wires. The 280zxt ecu plugs are notorious for crappy connections that cause funky / random problems (I know from personal experience).

 

I will check the connections as mentioned and will also be putting a timing light on it to triple check the base timing. I love the car, but this drivability issue is making me crazy.

 

look up the definition and use of dielectric grease before you use it. People on these forums don't seem to understand that it is an insulator and in many instances will cause contacts to stop working. it is for the purpose of protecting rubber boots.

 

Hum... you talking about yourself?

From the intrawebs (Roger said to look it up.........): http://www.wisegeek.com/what-is-dielectric-grease.htm

So... thanks for clarifying.

 

Still haven't check the electrical connectors yet but I have started replacing the original vacuum hoses...yeah, 27 year old vacuum lines still holding in there...sorta.. Hope that will atleast help the issue a bit, but am also going to be checking the connectors and such while I am at it.

 

Remember that there are 265 vacuum lines under the dash. Not really. but there are alot of them, probly like 20 for man, 35 for auto(climate control not trans) that feed off the engine. The ones going from the engine to firewall might be good, but those could be bad. easy way to check is to run threw all the functions of the system, defrost, heat, cold etc... See how well and fast it might go from floor to vents and vents to defrost. these are allot more in detail then most will go, but another step if the simple ones fail. Leaky intake gasket, check this with a can of ether(starting fluid) spray slowly in small bursts on each runner with car idle, Liston for a pick up in RPM's. check the flat parts too, excp around #6, that damn cylinder is havoc. Also check for exhaust leaks around the exhaust mani, and lower flange, should not cause problems as large, but hey, why not. look for black soot. EGR as well. Remember to check for air leaks around the T/B, its gasket and rubber boots AFTER the AFM, use the starting fluid. GROUNDS GROUNDS GROUNDS!!!!!!!

 

Much appreciation to this forum and for the replies.

I have gotten the car straightened out and the misfire is gone now. I went through and replaced a bunch of vacuum lines (about 25 ft worth), corrected the ignition timing (was at 36* advanced, put it back to 24*), and bypassed the VCM as the large diaphram in the back was leaking. I also found the O2 sensor to be bad, but that will have to wait for now.

 

Nice finds!

 

Just going through old posts. What does he mean by bypassing the VCM??

 

VCM = vacuum control module.

Controls the AAC and EGR on the turbo model.

 

You can bypass that? Does that make it so you don't use the AAC and EGR and can remove them?