Hesitation/Hunting At Operating Temperature

[Guest incalescence]

I'm a long time lurker/reader.. I finally have something I haven't been able to search out.. the symptoms just don't seem to match up.

 

Okay..

 

This seems to be defying some logic, and I'm hoping someone may have some insight.

 

I bought this car with the conversion already done, so I don't have a full history. Observation tells me that this conversion was done with the N/A dizzy, no CAS to be seen. I haven't had a chance to pull the kick panel, and check the ECU yet, so I don't actually know if the ECU is in fact a turbo ECU.

 

System appears to be set up to run in Open Loop.

 

Problem: The car runs great when it's cold. Once it is at operating temperature, the car loses power, and seems like it's hunting, possibly missing, only when under load. Idles with no trouble. The turbo doesn't have that nice whistle it should have. It seems to sound right when cold, though. A vacuum line had come loose, and the turbo had overboosted. I had an idea that this could have been part of the cause, but why is it okay when cold?

 

When driving with car warmed up on a quiet back road, I hear what sounds to be that distinctive "spark" pop. I replaced cap, rotor, plugs, and wires. No seeming change. Once heated up, I can see what appears to be arching from the plug boots (have to be looking in the dark, though). I pulled the J-Pipe to check and see if I could see any indications, and I saw a little oil pooled at the top of the turbo, but didn't really see indication that there was some IN the turbo. I didn't have a chance to pull the inlet connection to check shaft play yet. However, when I pulled the J-Pipe, I noticed the oil seemed to be all the way up it.. so I pulled some of the accessories off the intake manifold and found that there seemd to be a fair amount of what appeared to be oil in the intake manifold itself. Running with that, I checked the oil immediately. I cannot see any indication of oil consumption, except for some oil physically in, some on the intake. I had a good friend and mechanic take a look at my plugs so he could read them. He said they aren't burning rich or lean. They look great according to him. I changed 'em anyway, and the new ones look the same, had him read 'em too.. he agrees.

 

I have NO smoke. My coolant doesn't seem to have any oil or any crap in it. The oil doesn't have any coolant in it. Once again... no smoke.

 

I also replaced hoses, etc.. verified NO vacuum leaks but same symptoms exist.

 

Any ideas? If you need any other info to diagnose, please ask. I could have not mentioned some things I checked.

 

Thanks

 

I'm not 100% sure.. I'm thinking that maybe my ground to the engine block isn't up to snuff so this is causing trouble for me at the spark plugs and causing them not to fire well?

[z-ya]

It sounds to me like detonation. What is your full advance ignition timing set to? If it is an NA distributor, and the timing is set as if it were an NA, the total advance will be around 30deg. Way too much for a stock turbo motor. What boost pressure are you running? If you are running more than stock, yank the boost controller out for the time being and see if the problem goes away.

 

I've seen people use NA electronics with a turbo motor, and we couldn't get it to run just right. We also had to back off the timing a lot to prevent detonation. This made the sluggish when not under boost.

[Guest incalescence]

I'm not 100% on the timing currently. I don't have the car at the house right now, and won't really be able to get my hands on the car to take a look at the timing until thursday or friday. I'll definately be checking that. I was also considering that possibly I should plug up the vacuum advance on the n/a dizzy? I personally haven't had a car that is having detonation, so this is a bit new to me.

 

One other symptom as well... when it bogs down, if I don't either drop the throttle, or push the throttle (if I just hold it steady), it will slow down more and more, and a couple times I heard a "pop." I couldn't identify if it was from the intake or exhaust, but I definately heard a pop. Reminded me of a backfire. I've still gotten NO smoke even when this occurs, however.

 

I'll check on the timing, for sure. I was considering taking and doing the z31 ECU conversion, but I need to get my hands on a 280zx turbo dizzy, still. I have the z31 dizzy, but I don't believe they are compatible, as all indications say to swap the guts from the z31 dizzy to the 280zx dizzy.

 

Please let me know if any other ideas.

 

Thanks

[Guest incalescence]

I still don't have access to the car right now, but I was brainstorming. Could it be as stupid as the AFM or something like that? This kinda reminds me of my 81 n/a that had the AFM go out. This was when I'd try to rev it, but it would try and go, and if you held the throttle steady trying to get it to inch higher in RPM, it would often pop.

 

Any input?