Possible MAFS issues or detonation sensor

[SKILANDSZ]

Hello I have a 1991 300zx NA. were trying to turn it into a track car we removed the Air bag system heater system seats dash and all the wiring along with it we've also deleted A/C system the AIV system we didn't plug the exhaust when we did though the problem we're having is the car will not stay running when the mafs is plugged in. It pulls a mafs code and a detonation sensor code but it is running extermly rich. We have tried replacing the MAFS Coil packs Temp coolant sensor and all those harnesses. While it was running we pulled injector harness one by one all but one made the car hesitate immediately the last one hesitated not as bad though. Any thoughts on what might be happening?

[PapaSmurf2k3]

So everything runs fine, and then you plug in the MAF and it stumbles and runs super rich?

I would start by doing a MAF voltage check with the key ON (car not running). Maybe something is shorted out, causing the MAF to sense like its sucking a ton of air.

[Ace2cool]

Are you sure you used an N62 MAF? I'm with James on this one. Make sure you're getting proper voltage. My money would either be on a wrong MAF or a shorted or disconnected wire.

[SKILANDSZ]

So I'm getting .4 with the ignition on but not running?

[PapaSmurf2k3]

I want to say that's correct. I THINK its supposed to be under .5v. I don't suppose you can check it at the ECU can you? Just to rule out any shorting.

[SKILANDSZ]

Yes I jumpers it straight from the ecu to the mag

[SKILANDSZ]

Also it is the right mafs I have an identical z same year and car and we swapped the mafs and it worked fine in the other car but not in the race car

[PapaSmurf2k3]

Do you have another ECU in the race car? Or is your fuel pressure higher? Or are your injectors bigger?

[SKILANDSZ]

Sorry about the long responce time I was out of town working

I don't know what the fuel pressure is in the other car but the race car is running around 43 lbs witch if high from what im reading on line but both injectors are stock and i have two ecus the stock one from the race car and the performance ecu from the other car its an ash-spec ecu.

Also we found part of the richness problem. We had vacuum lines going to the wrong places after doing the carbon canister delete but the car will only stay running in safe mode now. When we start it now it revs up then dies no engine codes nothing.

Any help would be greatly appreciated thank you for all the ideas so far

[Ace2cool]

So wait, are you switching between the tuned ECU and the stock? Cause it doesn't work like that. The two ECUs have different duty cycles for the injectors.

[SKILANDSZ]

No we tried the tuned ecu but we put the stock ecu back in. But im cruius what do you mean by differnt duty cycles? Im not very familer with tuned and untuned ecus.
Thanks for the reply

[Ace2cool]

For a bigger injector, the duty cycle will be shorter, so the injector won't have to stay open as long. It's like putting bigger jets in a carburetor. So if you're using an ECU tuned for other mods, it'll meter the fuel differently.

[SKILANDSZ]

Ok we did put the original ecu back in though

[PapaSmurf2k3]

Ok so original ECU, original injectors, original fuel pressure regulator, original timing, original MAF (should be N60, no?), no funky wiring and no loose couplers in the intake tracks after the MAF?

How do the plugs look? Super wet from running so rich?

[SKILANDSZ]

It's an n62 the wiring I'm still checking I removed a lot of wiring from the main harness inside the car speakers heater blower wireing and relays ac wiring ect also we removed the ac condenser and belts and the radiator fan I replaced the harness on the tps it was coreded

[SKILANDSZ]

Also it runs fine if it's in safe mode

[Ace2cool]

No, James. N62 MAF is correct for Z32. The Maxima with the VG had the N60 and a funny looking plenum.

And what are you calling "safe mode?" Just running with the MAF unplugged? If so, that's technically limp home mode. But regardless, if that's the case, I would 100% suspect a problem with the MAF or the wiring. My first step would be reading continuity of the wires to the ECU individually. Just curious, when you say you jumpered the MAF directly to the ECU, did you disconnect the old wires, or just "piggyback" them? Cause if there is a short somewhere, it will still cause the issue if the wire isn't disconnected.

[SKILANDSZ]

Yes limp mode if i plug the maf in and clear the ecu codes it will start the die if i unplug the maf it pulls a code and goes into limp mode and runs ok.But I don't know at this point if it is a maf issue or if thats the code coming up because thats the sensor im pulling. when i jumpered it from the ecu I cut the signal wire out on both ends 1in from the ecu and the harness and ran a new wire.

[Ace2cool]

So you just ran 1 wire? There's 3 others there. Are you getting 12V from the red wire to the green and black wires? Because It's still sounding like a short to me. Also, check the black and green wires to a good chassis ground.

Also, according to the FSM, the signal voltage is supposed to be .8V - 1.5V. Yours is low, which is making the engine dump loads of fuel.

[SKILANDSZ]

So from the hot wire to ground is 11.9 on each ground the signal wire for ecu is still .48

[SKILANDSZ]

Also I tried checking for continuity between the grounds and signal wire there wasn't any

[Ace2cool]

Still sounds like a bad MAF to me. If you've got 12V going in, and only .4 on the signal, then there's only one place it could have "gone."

Only other option is a bad ECU that's internally shorted and draining the voltage.

And no continuity between signal and ground is a good sign. How about ground continuity? Are you 100% sure the connector isn't corroded?

[SKILANDSZ]

Ground continuity is good if I built my own connector took the two blacks to ground and jumpered the wire going to the ecu and brought my own wire from the battery would that eliminate any possibility of it going to ground and would it work?

[SKILANDSZ]

Also i did have continuity from the power wire to the grounds I'm not sure if this supposed to have it the key was on

[Ace2cool]

Ground continuity is good if I built my own connector took the two blacks to ground and jumpered the wire going to the ecu and brought my own wire from the battery would that eliminate any possibility of it going to ground and would it work?

Yes. But from what you're telling me, there's no real way it's the wiring at this point, unless it's some freak issue that only shows when you try to start the car, which I can't 100% rule out, but is very unlikely. You said you cut the old signal wire, and the hot has 12V, and both grounds are good, with no continuity from anything else. That sounds like a good harness to me.

It would be very uncommon for the ECU to be the issue, but it's still possible it's got a drain in there. You'd have more issues than just that though, I'd think. I'm still leaning on it being the MAF or the connector, despite you already having swapped a MAF in from another car.

[PapaSmurf2k3]

No, James. N62 MAF is correct for Z32. The Maxima with the VG had the N60 and a funny looking plenum.

For some reason I thought the NA got the N60, and the TT got the N62.

Also, according to the FSM, the signal voltage is supposed to be .8V - 1.5V. Yours is low, which is making the engine dump loads of fuel.

His is low because he did it with the engine not running. Also, lower MAF voltage = less fuel commanded by the ECU.
He should be able to follow your steps and check the MAF voltage at the ECU while its running to verify if its the MAF or not (ideally, CONSULT would be great so it takes all wiring and connections into account too).

Pulling the MAF to get it into limp very possibly could disable input from many other sensors, taking the ECU out of closed loop mode and just running off safe maps. If the MAF checks out, I'd start looking elsewhere.

[SKILANDSZ]

I have a consult it's saying the maf is at .08 volts with the key on not running my volt meter says .48 and it is showing that the O2 sensors are showing lean

[PapaSmurf2k3]

Yeah, it SHOULD show lean on the O2 sensors when it isn't running.

What does it show when you have the car running?

[SKILANDSZ]

Does it matter if it's in limp mode when I have it running it's the only way the car will run right now

[Ace2cool]

Also, according to the FSM, the signal voltage is supposed to be .8V - 1.5V. Yours is low, which is making the engine dump loads of fuel.

His is low because he did it with the engine not running. Also, lower MAF voltage = less fuel commanded by the ECU.

You're right. My bad.

And if you disconnect your MAF, as James said, it could send the ECU into "safe map" mode, which would more than likely run rich, but it's worth a shot, just to get readings from somewhere else.

This is a rough one, I'm not gonna lie. Have you done a vacuum leak test? I mean, I'm reaching at this point, but there has to be something we are missing.