Trouble code 12?

[tmorales509]

Hey guys so been trying to diagnose my car for a few days. It will start and die out right away unless i keep my foot on the gas pedal above 2k rpm. So finally decided to try and read the codes on the ecu under the center console(i have never really been able to do it correctly in the past for some reason lol) and i was able to get "1 red blink, 2 green blinks".

From what i read on here that code is the Mass Air Flow Sensor Circuit. I started the car with the MAF unplugged and it stayed running, it idled high but it did stay on. Basically is there anything else that would cause this code or do i just go ahead and buy a new MAF sensor. They are quite expensive so that's why I'm wondering if there is anything else that could cause this? By the way i have already cleaned it with MAF sensor cleaner and did not help.

Thanks in advance.

[centralcoaster33]

Back in the day I had similar issues and found that the car needs at least a TPS or a MAF. So, unplug one and drive up the street and back. Then plug it back in. Unplug the other and drive it up the street and back. Plug it back in. If one works and the other doesn't, then this: When it is not working, the unplugged sensor is fine and the plugged in one is toast. When it is working, the unplugged sensor is toast and the plugged in one is fine. Easy test.

Additionally, I think you need to be sure about the codes you read. Follow the OBD1 code reading instructions, get your grips on an OBD1 scanner, or have it scanned at a parts store or mechanics shop.

So, we don't seem to have the FSM for your 1991, but we do have one for the 1994 (http://www.nicoclub.com/service-manual? ... ma/1994/ec) The EF & EC chapter, starting on Page 195 has instruction for code reading. It only mentions a red light, not green, so I don't know if this would be a perfect match, but figure the method is the same as other ECUs so just give it a go. BTW, you'll notice that the CEL flashes the same as the ECU LED, but in just one color. Long blinks and short blinks are what to count.

Here's a handful of other threads that discuss code reading:
http://www.nicoclub.com/archives/nissan ... ostic.html
post6671015.html?hilit=obd1%20codes#p6671015

[centralcoaster33]

BTW - a google search for "1991 nissan maxima maf" shows some of the cheapest MAFs I've ever seen. What do you mean expensive? For OEM from a dealership I guess? I have a re-manufactured unit in my 240sx and it's been working like a champ for a few years.

[tmorales509]

Thanks. Yeah i seen some as cheap as $40 online. I just meant if i wanted to get one today from a auto parts store like Autozone or oreillys theirs are $150..Anyways as far as the unplug test. the car wont even stay on long enough for me to put it in gear let alone try and drive it with the TPS unplugged. With the MAF unplugged however the car does stay on(albeit not very stable) but it does stay running. Also my ECU does in fact have 2 leds(green and red), I followed the instructions here http://torquespecs.tripod.com/maxima_85-91_codes.htm and came up with the code 12.

[centralcoaster33]

Okay, thanks for the update. Per the unplug test, you have a bad MAF. Per the codes (I reviewed your link) you have a bad MAF.

But! Before you go and get a new one, I believe the FSM will have diagnoses instructions. Those would include checking the ground wires and checking the ECU to MAF wires. So, I'd use a voltmeter for that and do it to be sure you don't have a bad plug, bad ground or shorted wires. Can you dig into that a bit? I know it's work, but it could be the source of your issues. You do have an old wiring harness and they get brittle in some spots, usually where they turn 90 degrees near the engine. That's when people run the car, shake the wire harness and it changes it's attitude while shaking the harness.

Shipping is hella fast these days. Junk yards may have your part. Both usually have a warranty of some sort. Sometimes buying from the local parts store is easiest for purchasing and potentially for returns.

[tmorales509]

Cool thanks for the info. It has crossed my mind that it could be something with the wires possibly. I know the wires are really old. i will try and look further into testing it out this weekend and possibly getting a spare one from a junk yard to test out. I will report back once i make any progress.

[centralcoaster33]

Okay, best of luck! Don't let them overcharge you at the pic n pull and try to verify that they'll take it back if it's not functional or doesn't fit.

[tmorales509]

Hey so i went ahead and bought a new maf sensor. I did test the harness and the ground are good and voltage is good. I got the new maf today and put it on. The car stays on but the idle bounces around at around 2000rpm and not much response when i give it gas if any. Thought maybe i could have a vacuum leak but realized unplugging the MAF has no effect at all as if its not even there/or not doing anything. Any ideas? I did unplug the battery while i replaced the maf as well.

Here is a couple pics and a short vid of what the car is doing now.



https://www.youtube.com/watch?v=ML8pLlPfJE0

[centralcoaster33]

That's a shiny lookin' new MAF! Maybe you have to check the voltage/ resistance on your TPS. Is it adjusted to a specific spot or have you been messing with it? If so, it'll need to be re-set. Have you checked all over the intake side of things for leaks? Vacuum hoses are often a culprit. Brake booster on top, EGR stuff on the back, valve cover vent and EVAP in front, and PCV hoses on the bottom. Also, there's the exhaust O2 sensors that can cause weirdness like this. You would likely get a code... Have you checked for codes after your repair? Last thought from the top of my head is a bad ground wire. I know you checked the MAF wires, so maybe double check the ground wires that go to the chassis and engine block (on my car they're by the exhaust studs, but I don't know where on your car).

[tmorales509]

Yep TPS is good and right on spec. I actually checked the codes again since i actually didn't let it run through, i just stopped after the first code but after waiting it seems there is 2 other codes on the ecu that are popping up. Per the FSM, one seems to be for the Temp sensor(which i don't think would stop the car from running) and the other states could be the power trasistor unit/ignition coil(seems like a more likely culprit). I guess im on to researching how to test it. If anything ill end up running to the junk yard and seeing if i can pick one up to test out. Can't hurt i guess.

[centralcoaster33]

While I wish I knew more about coils, I'm kind of glad I haven't had to mess with them on my cars. I think you're correct to follow up on those codes. I hope you get it going smooth soon.

[tmorales509]

Finally got it fixxed. Turns out it was the fuel injector seals were no good. Finally back on the road again. Thanks for the input.

[centralcoaster33]

Great that it's fixed! What led you to injector seals and how'd you know and how'd you fix it?

[tmorales509]

Well it all started when i changed the 2 fuel lines that connect to each side of the fuel rail(i know i didn't mention it in the original post) because they were leaking. I guess when i put the fuel rail back in the injectors were not seated correctly which i didn't notice right away..Anyways the 3rd time i took everything apart i took the fuel rail back out and noticed 3 of the seals were torn up probably due to the injectors not being seated properly. So bought new seals and put thinner spacers on the fuel rail so when i tighten it down the injectors will seat right and everything worked out after that.