280zx missing at 1/3 throttle

[Brian1]

Hi, this is my first post, but i have been searching on this site for a long time. I have a 1983 280zx turbo, 5-speed.

 

Basically, I got two problems. First of all, when i go to start my car when its cold, it has to warm up, if it doesn't, then i will try to leave the driveway or something and as soon as the turbo starts to spool, the car will bog out like its not getting enough fuel to compensate with the extra air. after a few minutes of warming up, the problem will completely go away. (Maybe carbon build up on the valves?)

 

The next problem, is that even if the car is warm or cold, when im driving down the street trying to hold a constant speed (at about 1/3 throttle or so, regardless of rpms) the engine will kind of have a steady miss it feels like. But if im accelerating or decelerating, everything is normal.

 

What I have done so far is replace fuel filter, air filter, fuel pump, fuel pressure regulator, spark plugs, plug wires, checked cap and rotor (look great) checked compression (I think they were all like 125), checked fuel pressure(Normal), checked vacuum lines(look crappy, but no leaks from what I can tell) replaced head temperature sensor, checked air flow meter (flap opens and closes fine), checked ECU (all the wires are securely connected to it), reset the timing, and checked the throttle switch(which from what I understand isn't like a TPS, in that it only sends two signals to the ECU, one for off throttle and one for on throttle). Also, the connectors that hook up to my fuel injectors are a little melted, i ordered some new ones which should be here any day now. The car sounds like it has a loose lifter (doubt that has anything to do with it, but im pretty fresh out of ideas, haha)

 

So if anyone can give me some more ideas, I would appreciate it very much.

 

Thanks,

Brian

[nismopick]

Welcome!

 

What did the orig spark plugs look like when you took them out? What did you set the timing to? What do the metal connections to each sensor look like? Any corrosion?

[Brian1]

I changed the original spark plugs a while ago when i first got the car about 8 months ago, but from what i can remember, the gaps where fine and they didn't have any bad coloration or anything. I just went out and checked all my connections and they aren't corroded or anything, except for the fuel injector wires which are a little melted and look pretty crappy. But I also held a screwdriver up to them and listened to it and they are all opening and closing. As for the timing, I set it with a timing light to whatever the book said it should be(like 20btdc or something like that i don't quite remember).

 

One other thing I was thinking was that even though I checked the Air Flow Meter, all I did was feel how the flap moved, but today I was told that the spring can stretch out and the flap will open too easily, and that it also may have dead spots in the voltage it sends to the ECU. I haven't checked this yet, because I think I have too pull the whole AFM out to check it. But does that sound plausible?

 

Brian

[RUZN]

I have the Same issue. I have been asking around here for awhile.

 

I switched even to 300zxt ECU, 300zx MAF, sparkplugs, wires, coolant temp sensor, thermostat, vacuum lines,removed even EGR, AAC, friggin tried everything so let me know what you find. Cause I have the exact same issue

[nismopick]

^^^ So even after the Z31 ecu swap you have the same prob? Have you run the diagnostic codes?

 

Most of my issues went away when I did my Z31T ecu swap, except for crappy idle & random misses. Running the diagnostic codes helped. I was actually getting random sensor codes. After racking my brain I finally found that the culprit was the bottom ground wires on the lowest ecu plug. They were very loose in the plug itself, and the massive ground collector joint about 4 inches in was really half assed by Nissan. Those grounds control all the major sensors. I cut out and replaced that entire plug w/ one from an 89 Z31, then made my own ground connections. If you do this, pay attention to the wiring schematics, because one ground cannot be grounded to the body as the ecu controls it directly.

 

Now my Z idles & revs great.

[VinhZXT]

The ECU connectors on the 300ZXT and the 280ZXT are the same type. These are famous for not making good contacts over time which causes all kind of running issues. Clean up the connectors real good and put conductive grease in the connectors. Good luck

[Brian1]

So today, I checked the grounds on my ECU, which were fine, and then I checked my AFM at the ECU, and all the terminals were giving the correct voltage.

 

So now I am really stumped, haha. I am going to try to get a fuel pressure gauge and check to see if i drop pressure when ever the engine misses... might point me to the fuel system or not. except it smells rich when it misfires.

 

I don't know.

anymore ideas?

I am about 10 seconds away from driving it to a Nissan dealer and paying the 100 bucks for them to tell me everything I already know... haha

 

thanks,

Brian

[roger.svoboda]

you might check around with the portland z club they got a bunch good guys down there can probably help out if you make contact. sounds like you hit all the stuff that should be the problem. There is a post on zbum or atlanticz on checking and readjusting the air flow meter. yes it can get a dead spot on the potentiometer from driving a lot at one opening (speed). and it can get out of position.

[RUZN]

So yeah I wiggled the ECU connector and car turned off LOL. guess ill get in that rats nest and clean that up next LOL. But yeah I dont have a code scanner. How do you reset the Z31 ecu again? Unplug bat for like 20 mins isnt it?

 

Yeah I had issue with 280zxt ECU and the Z31 so must be grounds. Just finished cleaning up stereo stuff with all new wires and grounds then Rigged in a Dual Electric Fan off a caravan (with much chopping to make it fit haha) made a nice little switch by my stereo to turn it off and on (glows green when on yay!) then proceeded to rivet some crap on so it didnt come loose ect ect.

 

Soooooo yeah it happens only when I first turn on car idles rough for the first 3 mins gotta keep a tiny bit of throttle. Then every so often as I said at a stop sign I go to Go and puffs smoke hesitates almost like the coil is shutting off or something but like I said I wiggles the ECU cable and car shut right off so gonna try to get it greased up see if that helps and then cleean up those grounds..

 

DO YOU KNOW EXACTLY WHAT PIN is that ECU ground im not supposed to BODY GROUND

[Brian1]

Alright, I will try to get a hold of the Portland Z club.

 

Also I noticed today that the car smells really rich.

I don't know if that helps anything, but is there a way to bring down the fuel mixture? Maybe thats why my car is running the way it is?

 

Also, I took the cat off my car, so its just an open down pipe so maybe it is supposed to smell that way, haha.

[nismopick]

DO YOU KNOW EXACTLY WHAT PIN is that ECU ground im not supposed to BODY GROUND

 

Sorry... Pin 28 & 36 are gounds & pin 27 & 35 are switched +12v power. I was thinking of a diff connector when I said one ground needs to stay separate. Here's a pic of my new ecu connector.

[RUZN]

^^^^ awesome ty Ill try that out and maybe clean up all my wiring again make it all nice and fancy

[Brian1]

Alright guys, figured out what was wrong..

And I feel kinda stupid, haha.

 

I originally brushed off the idea of my plugs being bad because i figured since I changed the plugs and wires when I got the car, there was no way they could be bad already.

Well one thing I forgot was, that one of the plug wires broke, and I just replaced it with one of the old wires.

 

So I was out checking my plugs on my lunch break one day just for the heck of it, and realized that I didnt bring the right socket to pull the plugs out, so I just shut my hood and went back to work, forgetting that I didnt plug that wire back in (which just so happened to be the old crappy wire).

I go start my car after work and notice that it is holding normal idle, and there dont seem to be any dead spots in the throttle. Except for the fact that I had lost a cylinder, haha.

 

So this started worrying me even more than when my car was acting crappy, so I looked under the hood, and noticed the wire was unplugged, Once I plugged it back in, the car went back to its normal self.

 

Hmm, I thought, funny how the car drives better when cylinder #6 is completely not firing.

So, I went and bought new plugs and wires again, installed them and the number 6 cyinder is no longer cutting in and out.

 

haha, So basically I think what happened, was that the old crappy spark plug was giving a weak spark, and not burning all the fuel or something, with eventually fouled out the plug.

 

Anyways my car drives great now, and thanks for all your guys' help, I figure even though it was just a spark plug problem, I still learned alot from going through the steps to check out all the other possibilities.

 

Thanks,

Brian

[C-Dawg]

did the rich smell go away as well?

[Brian1]

you know, now that you mention it, it does smell a lot better, but I can still smell a hint of richness, maybe because of the open down pipe? I don't know.

[ZLadie2000]

you know, now that you mention it, it does smell a lot better, but I can still smell a hint of richness, maybe because of the open down pipe? I don't know.

 

why is your downpipe open?