Mass Airflow Sensor and fuel pressure

[quad4z26]

Hi all,

I am helping my roommate work on his 95 auto Max. I'm much more familiar with late 80s early 90s GM FWD stuff, so pardon the inexperience in Maxdome.

First some symptoms.

Idle is intermittently rough, occassional stalling at idle, and serious herking and jerking under load with not much power. Off idle hesitation, too...frequently the worst hesitation comes around 2k or so revs.

Today, I thought the fuel filter may be plugged, so I took it off and backflushed it. No grime there. Next I went looking for a fuel pressure test port, but I couldn't find one. Can any point me to where it is, if there is even one?

Then I pulled one of the plugs, and it was carbon-fouled big time. I pulled the rest and cleaned them off best I could (I know, no substiture for a new set, but I didn't have any to swap at the time). FWIW, the wires look great.

Put her all back together, and fired her up. After a little spit and sputter, it smoothed out a little until I happened to tap the mass airflow sensor -- and it REALLY coughed. That's a test on a GM MAF sensor to see if its dying, indicating the wiring inside is fried. Is that also a suitable test for a Max MAF? (haha).

Are there any diagnostics I can do with a multilmeter to check the MAF before we condemn it? Is this a dealer-only item? Could it be cleaned?

Also, the CE light is not illuminated during engine running. Could trouble codes be stored even without the CE light being on? Can the codes be pulled without a scan tool? (Please feel free to point me to a FAQ.)

I think that's all unless anyone has other ideas. Thanks in advance for any help.

BTW, loved reading that thread on sex in the Max... never done that, but a Camry and a Beretta have been tainted .

[NJMAXSELTD]

From the discription of your plugs, it sounds like you car is running rich. My first question is What kind of plugs are in there? You should be running NGK Platinum plugs. They are OEM plugs and are hands down the best plug for the car. USE THEM! Bosch makes a replacement plug as well but our ignition system EATS the electrodes on Bosch plugs. Don't use them.

Your "tap" on the MAF sensor which caused the car to cough is probably a good sign it's on it's way out. You can clean it, use some alcohol on a q-tip or a squirt of Air Intake Cleaner will do the trick as well. MAF sensors are expensive, like 400 bucks. Search the web for discount Nissan parts. Courtesy Nissan is a good place to look, and if I remember correctly, Discount Nissan Parts - search that exact phrase has cheap MAF sensor prices. You may want to do a search on Maxima.org for MAF sensor. Some guys on there have replaced it and know where to find them cheap.

A few other things you may want to take into consideration -

When was the last full tune up? Every 60K you get a major service.

You back flushed the fuel filter? I'd replace it if I were you after that trick. If any particals get into a fuel injector, open your wallett and dig up $$$ for a new injector.

Clean your throttle body. www.motorvate.co has a nice write up with pics on how to do this.

Tp pull codes from your ECU:
To the right of your gas peddal sits the ECU. You have to remove the plastic trim to get to it. There is a hole in the side of it with a screw in it. Use a flash light and look into the hole to see the screw head. That screw is how you get codes and reset the ECU.

While the ignition key is in the on position, car NOT running turn that screw head clockwise, then counter clockwise. Look at your CEL light on the dash - if there are any codes it will flash. Watch the serier of pulses, there are long and short pulses seperated by a pause. Then it repeats again.

2 long pulses followed by 3 short pulses would be 0203 and so on...
Write down the code that your ECU spits out, if any and I will tell you what it means. Code 0505 means everything is OK.

To reset your ECU, you turn that screw back and forth twice within a few seconds. That clears any codes in your ECU, it also turns off the CEL light if it's been on.

For more information, check the following web sites -
Maxima.org
motorvate.ca
maximadriver.com

[MaxRX7]

nice reply bro

[NJMAXSELTD]

Originally posted by MaxRX7
nice reply bro

Thank you!

[quad4z26]

Thanks, NJ. How about a fuel pressure test port and operating pressure?

I'll see if there are any DTCs stored in the ECU and get back to you on that... I'm guessing not, since the CEL isn't lit, but on some cars, I know there are DTCs that can not light the CEL, so who knows.

[NJMAXSELTD]

You need to put a T fitting on the fuel line right after the fuel filter to check presure.

Fuel pressure readings:

Key on, engine off 43psi
Engine idling 34 - 36psi