# Running rich



## nism0nicK (Jul 11, 2007)

i just bought a 86 n/a 300zx and the car sat for about a year. i tried starting it and everything was there (spark,gas,signal to the injectors, and timing was on). the next day i came back and changed the fuel filter and the spark plugs. the plugs were black, and soon as i changed them it fired first click. the car was running like crap, missing and the exhaust was black and burning my eyes. it had no power under load and kept dying. the TPS has the plug missing and the ground for it and the idle contact were wired to it. but my biggest concern was the MAF cover was off and exposed to the weather. i pulled off the MAF and it was all charcoal inside but the filaments were intact. can somebody please help me out with why my car is running rich and missing..


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## Zen31ZR (Mar 24, 2004)

The MAF needs to be cleaned or replaced, for one. The TPS is less important, it does not serve the same function as on more modern vehicles. It is only a switch to tell the ECU whether the throttle is in the idle position or not., so it will probably work OK the way it is. It would seem, however, that your O2 sensor (Oxygen Sensor) is bad. It has the single biggest impact on how the engine runs, failure can make it run very rich or very lean. 

So I'd start with cleaning the MAF with electrical parts cleaner, available at the auto parts store. See how the car runs after that. If it is still too rich, replace the O2 sensor. It should be located on the driver side exhaust manifold, towards the very back. You will need a special tool to remove it and replace the new one with. The tool is a large bore deep well socket with a long slot on the side. The slot is for the sensor wire to hang out of. It may be initially expensive to purchase, for a small tool, some stores charge around $20 for it. However you can always return it afterwards.


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## nism0nicK (Jul 11, 2007)

i cleaned the MAF and bought a new o2 sensor, changed them both and still had the same outcome. its like its in a limp mode and showing no codes, but when i give it gas it misses and only revs to like 2k. he also gave me some more information that when you put the headlight fuse in the door locks and headlights go up and up down over and over. i also took the cat off thinking it was restricting the air flow. any different ideas to help me out??
thanks for the info so far. i also took of the neg battery terminal and reset the computer.


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## Zen31ZR (Mar 24, 2004)

Sounds like this car has some serious electrical problems. The thing with it only revving to 2000 rpm, thats what happens when you unplug the MAF on one of these cars. So your MAF is probably dead, or it's a wiring issue. The headlight thing is kinda strange, sounds like an alarm malfunction, but the factory alarm system in these cars isn't that extensive. Unless another aftermarket alarm was installed.....


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## nism0nicK (Jul 11, 2007)

there isnt anything aftermarket on the car, the was a power cable for the amp from the previous owner but i took it out....


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## nism0nicK (Jul 11, 2007)

i was just looking over the car, and the previous owner told me it was in a light accident on the left side and he replaced the fender and bumper cover. the harness to the drivers side door must of been pinched and shorted out cause its all melted together. thats the door and light problem but, could that cause the running richb and miss problem? tomorrow ill replace the timing belt and wire up the door properly, if you have any other suggestions tell me....


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## nism0nicK (Jul 11, 2007)

i fixed the wiring and replaced the timing belt today with no luck..... if anybody has any suggestions tell me......


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## Zen31ZR (Mar 24, 2004)

I guess try some tune-up basics, clean or replace the cap and rotor and pull the spark plugs and see what they look like. Also make sure the firing order is correct and check the condition of the plug wires. Check all fuses in both fuseboxes. Pull the plug on the MAF and see what it runs like that way. Should be no change. Pull some wire connectors apart and check for corrosion. Clean them with the electrical parts cleaner I mentioned before. I'll think more about possible causes for your situation over the weekend.


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## nism0nicK (Jul 11, 2007)

it ended up being the MAF afterall i talked to another guy with a z31 and he unpluged the MAF and it ran just like mine. the filaments were good it just went out. thanks for your help.


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## brodymulry (Sep 16, 2007)

nism0nicK said:


> it ended up being the MAF afterall i talked to another guy with a z31 and he unpluged the MAF and it ran just like mine. the filaments were good it just went out. thanks for your help.


Sorry for bringing up the past here; i've recently posted a similar/if not same problem.
Did you check the (defective) MAF with a Multimeter?
Do you remember the voltage readings?

Cause I have a Spazzy ZX with the MAF attached, but without it it runs fine.. however no more that 2000rpm, and kinda stalls when no throttle is open.

Thanks Mate


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## Zen31ZR (Mar 24, 2004)

You came to the right thread. For voltage values, check with the FSM.


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## brodymulry (Sep 16, 2007)

Okay, here is the thing.

I've checked the workshop manual for the voltages.
It only has two voltage readings; one for being the voltage the MAF is using, and the other, the sensor to the ECCS which increases in voltage as the air flow through the unit increases.

These are all 100% dead on to the values, in reguard to the manual.

The only thing the manual does not state, is the Lean/Rich selector. I cannot work out the 'default value' as I suspect, tampering with that would technically cause the ECU to flood it.

Any ideas?

Connect the MAF, engine backfires through intake and wont start.
Disconnect the MAF, engine Starts and runs rich, however conks idle if left to go to 500 RPM.
Cause yes, i agree.. its pointing to the MAF, but the MAF seperately works (it meters flowed air) however I am unable to check/optimise the default lean/richness.


And that ISNT in the Factory Workshop. It tells you how to change it, with no reference to what the default position is. Says Left is Lean, Right is Rich.

However the thing does 360's in both directions!! :|

It's close im sure!


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## Zen31ZR (Mar 24, 2004)

I'm tempted to say the L/R screw is either broken or is simply a cover for the real screw. If it is broken, the MAF is toast and likely needs to be replaced.


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## brodymulry (Sep 16, 2007)

Zen31ZR said:


> I'm tempted to say the L/R screw is either broken or is simply a cover for the real screw. If it is broken, the MAF is toast and likely needs to be replaced.


Humm.. is there any way to check this?
The screw on the outside, DOES turn the resistor/whatever it is on the circuit board on the internal MAF. 
(i.e is the Screw supposto turn 360 degrees to infinite?)

I've pulled the MAF appart, and it all seems good, no broken bits or etc.

JUST THEN:
I run the ECCS diagnostic test.

I got Error 12 (MAF)
and Ocassionaly? Error 13. (Cylinder Temp Sensor)

Error code 12 happens reguardless to wether i have the MAF plugged in or not. :\

I'm going to check the wiring harness to the MAF tomorrow, as I think that may be the cause. I doubt the MAF is dead, as the resistor that the screw is attached to, looked in good condition when i pulled the MAF apart.

I suppose if the wiring harness to the MAF is dead, then it probably wont work. However, why does it start up rough with it ISNT connected?
Perhaps half the harness is stuffed? Humm.


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## Zen31ZR (Mar 24, 2004)

The CHTS may keep the car from starting, I seem to recall that. Certain parts of the MAF may be dead, but not others. The hotwire assembly may be functional but it's controller may not be or vice versa. As I recall the MAF can be grounded externally and this may help it work properly, as long as everything else is working right. You may wish to check the harness where it passes near the headers, or anywhere within a couple inches of the engine, I've seen problems in those areas before.


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## brodymulry (Sep 16, 2007)

Zen31ZR said:


> The CHTS may keep the car from starting, I seem to recall that. Certain parts of the MAF may be dead, but not others. The hotwire assembly may be functional but it's controller may not be or vice versa. As I recall the MAF can be grounded externally and this may help it work properly, as long as everything else is working right. You may wish to check the harness where it passes near the headers, or anywhere within a couple inches of the engine, I've seen problems in those areas before.


Please excuse my ignorance, what is the CHTS?

I'm about the check the harness, no idea where it connects into the ECCS.
If i could unplug it, and run some small voltage (nothing on both ends) and see what the opedance is and voltage loss. Wish me luck.


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## Zen31ZR (Mar 24, 2004)

CHTS = Cylinder Head Temperature Sensor. I think it might have been on the turbo cars only, though. There's been a few threads in this section about it, maybe you can find them.


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## brodymulry (Sep 16, 2007)

Arr all these acronyums.

ok.
Your a Smart Man!!
Okay, did the diagnostic check (been meaning to do for a while now :\)

I get error 12, and error 13 (occasionally...as in, appears once in the 'eccs flashing sequence', and then does not appear again). So thats the Temp Sensor.

Error 12, is still the MAF. Error appears even with the MAF disconnected, then connected (blah blah, all varibles checked).

Tested the wires (in the cable) running to the MAF. All seems fine.
(yes i removed the ECCS 
Just run 5volts DC through the cable, and checking continutiy with a multimeter selecting the color wire for + and testing to the common 'black' with -.

I got 100% through all the ones i was able to test in a closed 'loop'.

There are two colored (from memory) and then rest are all various thickness black. I dont really quite get it yet.. cause near the ECCS connectors inside the car, there are quite a few black wires, crimped together. Sorta forms a lumpy buldge *dont read outside the context * with electrical tape around it. I'm assuming thats the ground.

> So my question is, looking at getting another MAF:

Does the temp sensor contribute to bad combustion (and backfiring), with the MAF on?

I'm going to say no, but please prove me wrong! I'd love to know what specifically it is.


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## Zen31ZR (Mar 24, 2004)

It might, but I don't remember all the details about the CHTS. Consult the factory service manual. I don't recall a whole bunch of wires crimped like that on my car. Maybe you should check that out. The FSM also has wiring diagrams. Really, at this point the service manual is more useful to you than I would be. Remember: RTFM (Read The #!%@^* Manual) Then ask any questions it doesn't answer.


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## cool34 (Dec 19, 2007)

Where is the MAF located I am a new Z owner


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