Bad MAFS?

Post by **encasemyheart** » Sat Jun 28, 2003 4:22 am

My car has been behaving rather strangely and I believe it is the MAFS, can anyone confirm?

It starts sometimes and not others. Sometimes after driving and shutting it off for 5 minutes it won't start and sometimes it is a few hours after shutting down and it won't start. The only constant however is that when it doesn't start, if I leave it until morning, it ALWAYS starts, which is strange.

When not starting it cranks fine, I get spark to all cylinders and am also getting fuel. Also once it starts running it acts fine, doesn't stall or anything. It has been stumbling randomly for a second or less occasionally while driving, but not too much and only when cold.

It can't be the ECU because I just swapped my old ECU out for someone else's with a JWT upgrade and it has the same behavior.

All this leads me to believe it is the MAF, what else could it be?!? ANy suggestions would be greatly appreciated.

Post by **PalmerWMD** » Sat Jun 28, 2003 4:22 am

Running a K&N or similiar oil wetted air filter by any chance?

Fred...

Post by **encasemyheart** » Sat Jun 28, 2003 4:22 am

Yes, it's been on there since I got the car about 9 months ago. It's just a cheap open element filter, I have never oiled it but it could have been in the past...

Post by **encasemyheart** » Sat Jun 28, 2003 4:22 am

So I hypothesize that the oil from the filter could be getting on the MAF sensor itself and causing it not to run, but after a night of sitting the oil dries off/evaporates and it works fine?

If this may be the case, why would it do it after all this time?

Post by **NISTECH** » Sat Jun 28, 2003 4:22 am

does it smell like gas when you try to start it? when it wont start that is.

Post by **encasemyheart** » Sat Jun 28, 2003 4:22 am

When it didn't start last week I pulled the plugs and they were sparking when trying to start and it smelled like fuel in the cylinder.

Post by **NISTECH** » Sat Jun 28, 2003 4:22 am

well i was reffering to when you were starting it in assembled condition. what i was getting at was if it was possible the coolant temp was giving the ecm a colder signal then the car really was and it was richening the mixture up flooding it.

Post by **encasemyheart** » Sat Jun 28, 2003 4:22 am

Nah I didn't smell any fuel before pulling any plugs, so I don't think it's flooding the cylinder.

Also I was thinking, could it be the starter itself? Like maybe it's going bad and not cranking the engine fast enough to get started all of the time? Or is the fact that it is cranking at all mean the starter is good? Lately I have been hearing like kind of a grinding noise for a second when the car starts, kind of like when you try to turn the key after the car is started kind of noise.

Post by **NISTECH** » Sat Jun 28, 2003 4:22 am

the next time it acts up try depressing the gas pedal half to w/o throttle. if the car fires and starts you got a rich mixture condition going on and will need to determine if its a sensor giving a bogus input to the ecm. the maxi was the only car i knew to have the starter revolution speed problem from 95 to 97 so i doubt the condition exists on your 240

Post by **encasemyheart** » Sat Jun 28, 2003 4:22 am

ahh...thanks.

When it doesn't start it won't start regardless, but sometimes I can get it to 'catch' and start up to about 400-600rpm and die. During this time WOT is required to get it revved and then it works fine. Would this rich condition affect nothing but starting? ANd how do I determine exactly what is giving the ECM a bogus reading?

Thanks alot for your help so far.

Post by **NISTECH** » Sat Jun 28, 2003 4:22 am

when this condition exists.you need to check the resistance of your coolant temp sensor to see if its within the range for the temp the car is at. if it is the problem it should be way out of spec. also the connector it self on alot of nissans tend to build up corrosion causing the added resistance. if you dont have the specs let me know and i can get it from the fsm at work.

Post by **encasemyheart** » Sat Jun 28, 2003 4:22 am

Yes, please send me the specs and if possible, describe where the coolant sensor is located. I only have a Chiltons, which deals with like 8 different cars and isn't too specific.

Thanks alot.

Post by **NISTECH** » Sat Jun 28, 2003 4:22 am

dude i blew it sorry man. someone had the book out of the dealer ship. got it back today but got real busy and didnt get a chance to grab the specs. i will do it tomorrow. sorry for the hold up .I will have em for ya tomorrow night.

Post by **encasemyheart** » Sat Jun 28, 2003 4:22 am

Hey don't worry about it, you've helped immensely already. Take your time, like I said, it only happens occasionally.

Also today it did it again, I just held the throttle and cranked it for about 5 seconds straight and it started up, there was a puff of smoke from the tailpipe, so I assume that was fuel, couldn't be oil/coolant. So I assume it wasn't starting due to being rich and it just happened to work and the excess fuel was burned and that was the cloud.

Hopefully the problem is what you think it is. Any idea ballpark a new coolant temp sensor is? I may just pick one up new or at the junkyard for cheap to possibly solve the problem.

Again, thank you for the help.

Post by **NISTECH** » Sat Jun 28, 2003 4:22 am

ok guy sorry took so long but heres the specs. you do not need to meet the temp exactly just kinda do the math and figure out where it should be for instance , if you just shut the car off an hour ago and the outside temp is above 70 degrees the temp is probably still around 140 degrees so the resistance should be somewhere around .5 to 1.0 k ohms . if its any where above 1.6k ohms its probably wrong and should be replaced .

Engine Coolant Temperature Sensor TestWith an ohm meter check resistance of sensor at specified temperatures.TEMPERATURE:20°C (68°F)RESISTANCE: 2.1 - 2.7 K ohmsTEMPERATURE:90°C (174°F)RESISTANCE: 0.24 - 0.26 K ohmsTEMPERATURE:! 10°C (230°F)RESISTANCE: 0.14 - 0.15 K ohms

Post by **encasemyheart** » Sat Jun 28, 2003 4:22 am

Okay the water sensor is fine, I just got around to checking it, the car is acting up again. Any other suggestions? Is there a way to verify a bad MAFS? Is there a way to clean it maybe?

Post by **NISTECH** » Sat Jun 28, 2003 4:22 am

i would have told you no about three weeks ago. but since i have seen some interesting things from other members here. these guys seem to be very creative. by factory service manaul there is no cleaning procedure. i dont know an exact thread to anyone that has a procedure here. usually the ones i see get burnt up from moisture or oils getting on the element. there would be no cleaning procedure for that. when you checked your sensor how did the connector look. were the terminals a nice clean brass color or where they growing a green powder coating. also how was its fit is it nice and tight?you could check the voltage output at the air flow meter should be around 1 v off and when cranking around 1.3 to 1.4 v

Post by **encasemyheart** » Sat Jun 28, 2003 4:22 am

I didn't actually pull it off of the car, I left it attached by the wire. I was surprised to see that there was no element in the center of the MAS itself. You know, that wire that usually runs through the middle of a MAF.

I'll unhook it today and make sure the terminals are clean. How many wires are there and which wires should be showing that voltage?

Post by **NISTECH** » Sat Jun 28, 2003 4:22 am

i was referring to the coolant temp sensor connector. the air flow meter has it to the side of the chamber instead of in the mid flow element. i am not sure which wire it is of the ones to it but the black is ground i think the sensor wire is white. if you hook your volt meter to it while the car is running and it says 12 v then its the other color wire.. i beileve red. these wires may have tracers on them and are not just the solid color i mentioned but the primary color of the wire will be one of those. and typically the middle wire is the sensor signal wire on most sensors on nissans

Bad MAFS?

Bad MAFS?

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