# "New" '85 NA Bogging/Choppy running?



## TheTygur (Jul 26, 2009)

New to the forums....
I'm working towards getting a 300ZX off my friend, its an '85 Naturally Aspirated, manual tranny, but its got one small problem. I'll get the car either way but I wondered if you could help me out a bit here.

Its an intermittent problem, which is awful but the details are:

1. When started cold and idling, it runs slightly choppy. Only sometimes, not every time, could be cold or hot weather. Usually when it warms up a bit, the idle returns to normal, but there's #2:

2. When accelerating, it really bogs down, gets quite choppy and has barely any power. Again, only sometimes (but this has been getting progressively worse and now does it almost every time) 

3. I've been troubleshooting it with him and don't know what all he's changed but pretty sure about cap/rotor button/wires/plugs/fuel filter. My current pondering is leaving me wondering about EGR, MAF, plugged cat or fuel pump on its way out.

Anyone got any ideas?


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## TheTygur (Jul 26, 2009)

Urgh. 

Replaced plugs/wires/cap/rotor, muffler, cat, timing belt, timing belt tensioner, FPR, fuel filter and more. Still randomly bogs. No rhyme or reason to it. It can do it on acceleration, stopped or slowing. 

Today I fixed a harness that plugs into something, I had thought it was part of the EGR, it sticks out right under the PCV valve on the passenger side of the intake manifold. Anyway the plugin was melted and wouldnt stay on, so I had bought some of those quick connect crimp on wire ends which fit perfectly, (and also were gold plated expensive mer fers). 
Since then, it hasn't acted up but I've only driven it once. Hopefully this is the solution, as the plugins on it when I got it were all falling off, none of em have clips anymore. In fact, the MAF sensore plugin is held on by a couple zip ties (although they managed that pretty well actually). 

The wiring under the hood is a small nightmare that looks like someone was randomly cutting and splicing things. I have a couple wires (red and green I believe) running down the passenger side over the valve cover that are completely cut and some random harness is wired to the end of one but not plugged in. Just thoroughly confused.

Its not my first rodeo, I've worked on many a car, had the full ASE training course (in mechanic and parts pro) and manage an auto parts store, but this thing at the moment is mind boggling.


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## pulsar86 (Aug 13, 2009)

Have the coil tested the problems match a faulty coil.


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## TheTygur (Jul 26, 2009)

Thanks for the reply, I'll test it at work tomorrow 

EDIT: btw just wondering if theres an aftermarket coil available for these. can you wire in one of the canister-style ones? usually when I replace parts, I go for an upgrade to the best thing I can find, slowly building up all my vehicles. couldn't find a listing for a performance or better one at the auto parts store where I work.


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## TheTygur (Jul 26, 2009)

HAHA the little stopper plugs for the brake lights/cruise control switches shattered out last night. It never ends does it. But its worth the work.


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## TheTygur (Jul 26, 2009)

Bah, coil was fine, replaced with a new one, no difference. However, the module looks like its wearing away/cracking on the back after closer inspection. I was under the impression that if modules went bad, they would just die and the car wouldn't start? hmmm


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## pulsar86 (Aug 13, 2009)

Sorry it wasn't the coil. Always test any electrical parts before going to the expense of replacing them. I have had cars with faulty coils that have caused intermitant problems and bogging down,they don't always just fail outright.


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## TheTygur (Jul 26, 2009)

Yeah. Thanks for your help. I'm checking into what I suspect will be the pickup in the distributor. Any particular way to test that? I'd like to find some way to make sure before I yank off the distributor.

I've got a module coming in tomorrow. I really don't worry too much about replacing parts, I get a good discount, and I'd rather have the assurance that its fresh even if it doesn't need replacing. But the module was in pretty bad shape, all corroded and cracking out the backside. I heard the same of modules as I did with coils though: if it goes bad, the car will just die and not start, or possibly just run until it warms up the module again. 

For intermittent issue like this, it seems more likely something is loose or off in the pickup, I'd just rather not go that route yet, its just out of my price range at the moment.


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## TheTygur (Jul 26, 2009)

Well, the module yielded almost nothing, although in the condition it was in, I'd rather have it replaced either way. Still running a fast idle when its running smoothly, at about 800-1100RPM. Sounds like one or possibly a couple cylinders are missing at low RPMs. I know when the idle drops to about 600 and you actually almost stall when you hit the gas before it catches itself and the revs climb slowly with what seems like only 3 cylinders firing, that's "suck mode".


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## pulsar86 (Aug 13, 2009)

Check that your vacuum hoses are in good condition and also ckeck that intake manifold is tight and not sucking in extra air, that can increase idle and also cause missing.


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## TheTygur (Jul 26, 2009)

Roger. Already done the rundown of vacuum hoses and electrical connectors, apart from the fuel injector connectors, and cleaned what needed it, and put dielectric in em. No leaks as far as I can tell without bringing a smoke machine into the picture. A few of the connectors looked marginal, but after a thorough cleaning, none have changed anything.

I'm trying to get my hands on a fuel pressure tester but its hard to validate the price for what will probably be 10 minutes of usage. It really does feel like the fuel supply gets cut off and it runs very lean. Thats probably the best way to describe what happens. I know a lot of things can cause that sort of behavior but I know the plugs he had put in were only in for mebbe a month and when I changed em they had what looked like a white powdery buildup on em, which I believe means a lean mixture. And since I've changed the fuel filter and pressure regulator, and went through all of those ignition components, my next guess is that the fuel pump is going out. Thats why I'm loking for a pressure tester, but since the problem is erratic, it may be hard to find a time when its acting up, if that even is the problem.


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## manuelrys60 (Nov 29, 2008)

have you cheked your codes? on your ecu that could tell you a lot


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## TheTygur (Jul 26, 2009)

Thanks for the suggestion. Haven't done that yet, was gonna do it in the morning, but I don't get much time to work on it. I'll definitely try that next. Hopefully it will yield some information, but from what I gather from the codes it gives, its still probably going to be hard to pin down.


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## manuelrys60 (Nov 29, 2008)

well it sound's to me like your mas is gone but like i said CHECK your codes an save some $$$ and take the guess work of what it could be ........ well best of luck on you project!!!!


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## TheTygur (Jul 26, 2009)

Yeah, the MAS/MAF whatever is on this car, though, was just replaced a couple months ago by the previous owner who said it didn't help anything so he returned it and put the original back on. 

Tomorrow is my first day off in a while, I'll check codes then.

I randomly tried squeezing the fuel line after the filter to see how much pressure there was since I have no access to a pressure tester for this thing. It felt like there was absolutely nothing and I could fairly easily pinch it off. Not sure if thats the way it would normally be, though.

And thanks everyone, for your input.


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## TheTygur (Jul 26, 2009)

Results of the ECU diagnostic:

First off, I followed instructions at z31.com

1. turned ignition to on without starting it
2. turned ECU screw thing fully clockwise
3. As far as I can tell it gives 1 green, 2 red, 3 green, 3 red repeating. It said after it blinks 3 times to turn it counter clockwise again and read the codes, but after I turn it back, the lights just stay on.
If those codes are repeating the actual trouble codes then I dunno how to go on that.

I guess it would be 23 and 31 or something?
Apart from that I can't figure it out, I'm gonna keep trying here...

EDIT: It looks like the ECU itself is from a junkyard, it has the telltale yellow writing on it, and most of the lines have been spliced to oblivion. I dunno what somebody did but they made a mess of things.

EDIT2: Full reading.
Turned ignition to on position.
Turned dial fully clockwise and got these codes:
11
13
21
23
31
33
43

Very confused.

I know the MAF/TPS/O2 sensor were just replaced in the last couple months by previous owner.


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## TheTygur (Jul 26, 2009)

Results: here I am, quite a while and a few new parts later. I think I found most of the issues.

1st: car came from Cali. Has California Emissions
2nd: junkyard ECU from around here, Federal emissions

as far as I've heard, that won't really make a difference except that the Cali one has wiring for an extra sensor.

Since it was all spliced, I started checking all the wiring. He has 3 red/green leads which I think I've tracked down to be injector wiring, on the passenger side. Makes sense.

He had all 3 injectors hooked to one wire. After some research, I found this is basically OK as thats pretty much how its wired in the ECU and the extra wires aren't needed.

After checking the wires, the butt connectors this previous owner used were loose and corroded. On top of that, one of the injector leads was spliced into a harness for the EGR control solenoid.

I found that I could, with some degree of constant, replicate the bad condition of the car by shaking the EGR wire he had spliced and later discovered even more noticability shaking the injector wires, which is what lead me to this discovery.

Found the correct EGR control wires and hooked that up. Re-wired the injectors to a different lead with a direct connection.

Now its not running perfect, but it is idling at the correct RPM and its not missing and shaking like it used to. It still has a slight pop which could be a very unpronounced miss or possibly from what I believe is a leak in a downpipe.

Anyway I'll drive it for a while now and see if the bad conditions reappear, but they were there when I turned the car off (initially to clean the MAF) but cleared up immediately after the re-wiring.

Thanks for everyone's input on this.


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## Floridapaisan (Feb 8, 2010)

Wow, you just described my problem exactly. I just took it to a mechanic as I don't have time to deal with it. I know it will 90% be related to either the coil/plugs,wires/dist./worn cam/ etc. 
Waiting to hear from him tomorrow to tell me what he thinks. The only difference I see in my symptoms and yours is mine revs up and maintains at 2000rpms when cold starting, then suddenly drops to 1000rpms and jumps right back up to 2000rpms and repeats every few seconds. once the clutch is pressed in, it lowers the rpms to about 1500rpms.


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## TheTygur (Jul 26, 2009)

Well I do want to mention the problem has been solved. It was the ECU. It was fried. Good luck with yours.


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## turbotim (May 10, 2010)

i had a problem with my z and changed everything under the hood trying to fix it and it wouldnt fix! Afer a while of scraching my head saying its got to be the fuel pump but i get no code for it. car diagnostic check would come out good. so i finally checked the o2 sensor and that was the problem, changed it and its fixed.


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