MAF proper voltage at different rpms.

[emiliog2276]

Im trying to narrow down a hesitation issue. Currently im looking at the MAF. I know the proper voltage should be between 0.8-1.5 at idle. My first question lies when testing voltage with engine off voltage should be at 0.8 but mine is at 0.4V. Does that indicate an issue?

Second comes at idle and an increased rmp range. At idle it is within spec the voltage hovers at 1.18 volts but the question lies when the rpms increase. Going through other posts there seems to be a slight consensus that the volts increase as the rpm goes up, but when the confusion lies is how much the voltage should increase the MAF voltage supposedly peaks at 4.0 volts.

At 2500 rpms my MAF hovers between 1.9-2.1 volts usually staying under 2 volts increasing the rmp to a greater level the voltage still remains at about 2.1 not going beyond that voltage. According to other post the voltage should be at about 3.5 volts at 2500 rpms but i cant find more than two post that states this.
Does anyone know is that voltage is accurate or have ever tested their MAF at different rpms?Thank you.


Some additional info about the issue. A/F from consult is 109%. The only code from ECU is code 45 with is injector leak. The only time i can make this code appear is if i drive and hold the the throttle to keep the velocity constant. If i drive and only use the throttle to reach a set speed let go and only use throttle to accelerate i will never get code, i keep thinking that aside from being an fuel issue it might be an air issue since the only time i get a fault is when holding throttle open constantly therefore letting air flow enter plenum but if the MAF is faulty the ECU cant register the correct airflow, but at this point its just me guessing.

[Ace2cool]

http://www.nicoclub.com/FSM/300zx/1994/ec.pdf

Page 113. Doesn't say anything about revving the engine. .8V-1.5V at idle under no load. What exactly is your issue? Also, if your ECU is calling out code 45, it's in the injector circuit. Guaranteed. The ECU doesn't lie about that. If it isn't a failing injector, it's a clip loose or a broken wire intermittently losing connection. Your harness is 25 years old.

[emiliog2276]

http://www.nicoclub.com/FSM/300zx/1994/ec.pdf

Page 113. Doesn't say anything about revving the engine. .8V-1.5V at idle under no load. What exactly is your issue? Also, if your ECU is calling out code 45, it's in the injector circuit. Guaranteed. The ECU doesn't lie about that. If it isn't a failing injector, it's a clip loose or a broken wire intermittently losing connection. Your harness is 25 years old.

New injector connects, lower and upper insulators, fuel hose, all injectors spec at about 11.5 ohms. Actually the ECU can't really detect when an injector is leaking if it detects a rich condition it assumes its the injector and provides that code.


Reference:
Technical Bulletin NTB95021

Date:
March 8, 1995

POOR ENGINE DRIVEABILITY and/or CHECK ENGINE LIGHT ON (CODE 45- INJECTOR LEAK)
APPLIED VEHICLES:
All Pre-OBD II, CONSULT compatible vehicles

SERVICE INFORMATION
This bulletin outlines procedures and methods to isolate the cause(s) of mixture related driveability incidents. The bulletin also covers incidents where the check engine light is illuminated and code 45 is stored, but there are no driveability symptoms.
SERVICE PROCEDURE
NOTE:
^ ANY SENSOR INPUT THAT CAN CAUSE A "RICH" FUEL SIGNAL CAN CAUSE AN INJECTOR LEAK CODE.

^ ANY CAUSE FOR EXCESSIVE FUEL PRESSURE CAN CAUSE AN INJECTOR LEAK CODE.

The best way to resolve a Code 45 or driveability incident is to carefully go through ALL the following steps:
1. CONSULT ALPHA TEST

2. MASS AIR FLOW SENSOR TEST

3. FUEL PRESSURE REGULATOR TEST

4. INJECTOR LEAK DOWN TEST

5. ENGINE COOLANT TEMPERATURE SENSOR TEST

6. OXYGEN (02) SENSOR TEST

7. QUALITY CONTROL CHECK

[Ace2cool]

Oops, my bad. I was thinking code 51, injector circuit.

Here's a clearing procedure I found on TT.net:
a. Disconnect the battery. Place the terminals so that it cannot come into contact with the battery posts.
b. Remove the gas filler cap. Place it loosely in place, but don’t tighten it enough to create a seal.
c. Remove the Fuel Pump Fusible Link in front of the battery.
d. Crank the car. If it starts, let it run until it dies. When it dies, crank it over a couple of more times until it won’t “catch” anymore.
e. Remove the intake manifold.
f. Mark the position of the Crank Angle Sensor. Leave it connected, but remove it from the head (three 10mm bolts).
g. Turn the key to “ON” (don’t attempt to start it). Slowly rotate the CAS. You should hear each of the six fuel injectors click. If you hear one that’s not clicking, take note of which injector it is, as it’s stuck open and will need to be refurbished or replaced.
h. If they all click, remove all the fuel injectors, an replace all of their O-rings with new NISSAN OEM parts. Lubricate the O-Rings with motor oil when you install them, and be careful not to pinch any. Don’t draw them in with the caps. You’ll also need to do this for the fuel injector you replace, if it’s just one.
i. Reassemble, reset codes, and try again. You may have to run for a while to ensure that this code is gone.

I've actually never even seen that code come up. Consult would be cool, but most of us don't have access to that. Might be worth a shot to look at the FPR as well. ECTS could also cause some funny operation, but usually not on the Z32. Worthwhile to check it for corrosion at any rate.

[Ace2cool]

I wouldn't think you'd have to remove the plenum, though. Not sure why that's in the procedure.

[emiliog2276]

I wouldn't think you'd have to remove the plenum, though. Not sure why that's in the procedure.

ECTS was just replaced with a brand new oem one, Ive done the CAS rotation when the injectors were out and all of them were spraying when rotating and not leaking when not rotating. For the FPR, i just got a fuel pressure gauge connected it after fuel filter, when on pressure at about 35 psi, with fpr vacuum disconnected it jumps to about 45.5. If left gauge connected for an hour while car was off and pressure stayed at about 38 without dropping.

That's why im stumped ive looked at the majority of fuel related things still can't find out why i get the injector leak code plus terrible mpg about 10.6mpg.

[Ace2cool]

There's something wrong with the metering system for sure. Have you tested the O2 sensors using the ECU?

[emiliog2276]

There's something wrong with the metering system for sure. Have you tested the O2 sensors using the ECU?

Yup it doesnt pass. Using consult when the engine stumbles the voltage drops on the left hand one and when the idle jumps back up the voltage jumps back to match the right one (about .8v).

I replaced the o2 with bosch ones, also replaced the o2 connections coming from the harness. O2 sensors pretty much act the same (voltage wise) like before i replaced them.

I have two tps sensors ive set both properly, no change.

Thats why the last thing im looking at is the MAF, but i dont know whether to just risk it and buy another and still be in the same situation im in right now.

[Ace2cool]

That sounds like either a dead short or an open to me. I'd put a meter on the left O2 connection and see if there isn't a short, and if there isn't, make sure you have continuity through the wires to the sensors. One other thing to check is the connection at the ECU. I've seen pins back out of the connector housing before. Give all the wires a slight tug to see if any pins recess. Or you can press on the pins with a scribe, but the wire pull method is a bit safer.

[emiliog2276]

That sounds like either a dead short or an open to me. I'd put a meter on the left O2 connection and see if there isn't a short, and if there isn't, make sure you have continuity through the wires to the sensors. One other thing to check is the connection at the ECU. I've seen pins back out of the connector housing before. Give all the wires a slight tug to see if any pins recess. Or you can press on the pins with a scribe, but the wire pull method is a bit safer.

Would this be the way to test it?

http://troubleshootmyvehicle.com/nissan ... ic-tests-3

On a side not right now with the colder weather in california the hesitation is pretty much non existent in comparison to the summer where it was more than 90% of the time. Does this point to something specifically or just coincidence ?

[Ace2cool]

Yessir, that's how I'd test it.

But the heat being a factor could lead me down a different train of thought. I had an old Subaru with a similar issue, and it would even stall on me. Never did it in the cold. Ended up being loose bolts on the intake manifold either letting air in or fuel out, depending on throttle position. That could trick the ECU into thinking the metering is wrong, and would give you the readings you described on the O2 test. I'd check my manifold gaskets. Spray some carb cleaner, or better yet, starting fluid, around the engine bay to try and locate a leak.

[emiliog2276]

Yessir, that's how I'd test it.

But the heat being a factor could lead me down a different train of thought. I had an old Subaru with a similar issue, and it would even stall on me. Never did it in the cold. Ended up being loose bolts on the intake manifold either letting air in or fuel out, depending on throttle position. That could trick the ECU into thinking the metering is wrong, and would give you the readings you described on the O2 test. I'd check my manifold gaskets. Spray some carb cleaner, or better yet, starting fluid, around the engine bay to try and locate a leak.

So i would need a long multimeter cable to reach the engine bay from the ecu location? If i reading it correctly.

small update.

Also i tested voltage the at the O2 harness left wire on both sides get 12 volts, signal wire gets about .13 volts right wires get no voltage.

I retried the O2 test and i noticed the only way i can get both sensors to alternate between lean and rich at 2000 rpms is to have the opposite one disconnected if both of them are connected at 2000rpms it wont pass and the right hand injectors have a higher injector pulse and duty %.

[Ace2cool]

Sounding more and more like a short to me as we're going along. Either that or a bad ECU....

[emiliog2276]

Sounding more and more like a short to me as we're going along. Either that or a bad ECU....

I think you're right about maybe about a short. Right now im driving with the right O2 disconnected no stumble whatsoever. Another thing when cold if if i would turn on the defroster, lights or anything that would cause and electrical load it would stumble. This past two days with the right o2 disconnected no stumble whatsoever.

How tight should ecu connector be attached to the ecu?All the way down?

[Ace2cool]

Don't crank on it or anything, but yeah, it should be "german spec."

Gudentight. (Good n' tight)

[emiliog2276]

Well i might be back to square one. I checked the 02 for continuity and it does exist. Also replaced the MAF with one i got from the junk yard and also replaced the CTS connector and there is no change whatsoever. Also checked all my vacuum hoses for leaks.

I am still tempted to connect the 02 to the ECU with a new wire but would i just do the signal wire or also the other two wires ( are these the ground and voltage?)

[Ace2cool]

I'd do all three. No telling where the short is. I mean, if that makes it stop, you know what your problem is.

[emiliog2276]

I'd do all three. No telling where the short is. I mean, if that makes it stop, you know what your problem is.

So far I get the center wire is the signal wire, one of the side one is 02 heater ground and the other one is the power going to the fuse box, but on the O2 sensor side does the polarity matter in which i reconnect the ground and 12v power on the wiring harness side?

[Ace2cool]

Yes, on a DC circuit, polarity always matters.

[emiliog2276]

Yes, on a DC circuit, polarity always matters.

Well i connected the signal wires directly to the ecu as well as the heater ground. No change. At this point im out of ideas where to look, i dont know whether to drop the money to buy some 02 sensors directly from the dealer, replace the ecu or just take it to a shop.

[Ace2cool]

Yeah, that's rough, man. But if we've confirmed that it isn't the wiring by running new wires, it has to be one of the two, ECU or O2. Problem is, we're using the ECU to test the O2. Rock and a hard place.

[emiliog2276]

Yeah, that's rough, man. But if we've confirmed that it isn't the wiring by running new wires, it has to be one of the two, ECU or O2. Problem is, we're using the ECU to test the O2. Rock and a hard place.

Before giving up and taking it to a mechanic im going to start from scratch and look over everything again. Starting out with the injectors, ive read that if you take out the plugs on switch the key to on gas will squirt out of the cylinder where there is a leak present, is this true? By squirt out will it be a huge squirt or i really got to look in there to see if any is squirting out?

Granted ive tested the fuel system with the pressure gauge and no pressure was lost after an hour, although i connected the gauge after the fuel filter, would there be a difference if i connect it to the line after the fuel damper or the return line going back to the tank?

[Ace2cool]

Basically the theory is, that with the plug removed, and the key on but not running, you're pressurizing the fuel system and leaving the injectors closed. Nothing should come out at all. You should be able to see and possibly even hear a hissing. If it's got a good spray pattern, you may even get some mist out of the hole. And you can even see what it's supposed to look like by turning the CAS with the plug out and key on. Sucks that you're going through all this though.

[emiliog2276]

Basically the theory is, that with the plug removed, and the key on but not running, you're pressurizing the fuel system and leaving the injectors closed. Nothing should come out at all. You should be able to see and possibly even hear a hissing. If it's got a good spray pattern, you may even get some mist out of the hole. And you can even see what it's supposed to look like by turning the CAS with the plug out and key on. Sucks that you're going through all this though.

If worse comes to worse ill take it to a mechanic. Found this shop http://www.yelp.com/biz/specialty-z-chatsworth seems like a good place. I emailed them and they said it would be about $110 to diagnose it.

I've owned this car 8 years the first 3 years of ownership i was burned too many times by crappy mechanics and since then ive stayed away and done everything myself, and for the most part this car has been reliable in taking me from point A to point B since its my daily driver.

[NolimitZ32]

Thats not just a good shop, that is in the top 5 best Z shops in North America.

[itsa300zx]

Thats not just a good shop, that is in the top 5 best Z shops in North America.

IMHO, they are THE best Z32 shop. Greg, Seb and John know there stuff. They will not burn you, I just wish I lived closer to them.

[NolimitZ32]

I wouldn't go so far as to say best because i"ve never had my car there but I have dealt with SZ, IPP (luckily this one is in my back yard so to speak), Houston Z and Z1, all of whom have provided awesome customer service. Kyle at IPP is extremely knowledgeable and is actually the one decent person left from the pre F&F days shop called SGP here in Houston which fell apart due to some shady practices and disagreements between the partners. And Dane at Houston Z built his shop from the ground up, he has put in his time and paid his dues to make the shop what it is today.

[emiliog2276]

Update:Ended up going to Precision Z(http://www.yelp.com/biz/precision-z-service-canoga-park). Explained pretty much everything ive stated here on the forums. They pulled the car in and within 5 mins they said they couldn't work on it because the wiring is too bad and it would be pointless to try to find what was wrong with it. It seemed kinda harsh but i did appreciate the fact that it wasn't an hour later and having them try to charge be they hourly labor rate.

They recommended just doing the wiring harness which they quoted 850 for the labor plus the cost of the harness. So know i don't know whether to follow their advice but 1350 is quite a good amount to "maybe" fix the issue.

[Ace2cool]

I mean, if the wiring is that bad, it may just be that bad. That sucks to hear, I know, but you can only band-aid something so long. You've got a really good technical head on your shoulders, though. I feel that you could swap your own harness. But like you said, at least they didn't try to jerk you around and "make a buck" off of you.

You never confirmed if you tried a new ECU for troubleshooting purposes?

[emiliog2276]

I mean, if the wiring is that bad, it may just be that bad. That sucks to hear, I know, but you can only band-aid something so long. You've got a really good technical head on your shoulders, though. I feel that you could swap your own harness. But like you said, at least they didn't try to jerk you around and "make a buck" off of you.

You never confirmed if you tried a new ECU for troubleshooting purposes?

I haven't gotten a new ecu , i could only find one at the junkyard from a Z with a manual transmission which would give a check engine light and i have emission testing this month.

I was hoping when i went to the mechanic shop they would try another ecu but like i said they only looked at it less than 5 minutes and told me they could not work on it.

Im still hesitant about a new harness its not like the car is not running at all, the car has steady idle, not stumbling, no hesitation (at the moment since summer time its been gone), all the sensors get a reading when checking with consult, aside from the crappy mpg and the code 45 its ok.

I'm going to recheck all my connections one more time and im thinking of bypassing the PTU's addition harness and connection it directly to the EFI harness see if that helps.