mass air flow

[big monkey racing]

Does anyone know how to test the mass air flow to see if it bad. and if so does anyone if there is a way to bypass it. mind all this is for a 1990 240 w/ ka24e in a stock oval racing class so smog and emission ect. means nothing.

[h.240]

Here is how to test the MAF - zerothread/254283. And I don't think it is possible to bypass the MAF since it tells the ECU how much air is going into the engine.

[danielsan]

i got 1v at idle so thats good though. i want to clean it but the thing looks brand new in there.

[gtc_240sx]

if you can't rev it pass 3000 rpm, it is bad

[big monkey racing]

it falls down at all diff rpms in all gears. but it is still consistent of when it falls down

[direktdrive]

Another thing to check is your AIT (air intake temperature) sensor. This goes hand in hand with the MAF. The AIT sensor is located on the air box.

Awhile back I was running a bad MAF/AIT combo. I couldn't drive past 3k. Once I passed 3K the engine would stutter and my car would rock back and forth (A really irritating ride).

[danielsan]

same problem the op (original poster) is having. i didnt know the ait was on the air box. it seems like when i replace one thing the car runs great then after a few minutes it craps out again. did a complete tune up. my car revs all the way to redline but is slow as hell.

bogs mostly at half to full throttle. there is sweet spot where it runs nicely and pulls great but that is barely touching the pedal. big monkey racing is your car doing the same??

[direktdrive]

i didnt know the ait was on the air box.

well for the ka24de's, the AIT is on the airbox. I'm not positive on the AIT location ka24e's.

danielsan, does your car stutter? If not how is your o2 sensors and catalytic? If your catalytic is plugged or ruined it could send wrong signals to your o2 sensors. Thus causing the the slow acceleration you're referring to.

[danielsan]

well when i replaced th o2 the car ran strong, for a minute ran like it should, great power through all gears. then parked started it up again and it started bogging out again.

maybe the cat is plugged up, the bogging issue comes and goes at random. one minute it feels slow and unresponsive and then all of a sudden it bam i get full power and im off. by the look of my spark plugs the engine is healthy, no oil residue, no signs of rich condition, the plugs looks extremely clean.

so a clogged cat will confuse the o2 sensor then? i hooked up a a/f gauge (not wideband) with a healthy o2 the thing sweeps back and fourth constantly from lean to rich very quickly. the old o2 only marked between rich and center readings and was slow to respond. if its the cat i will rip it out and replace it with a test pipe. im in kansas so no emissions testing.

[direktdrive]

Your lucky danielsan you don't have to deal w/emissions. I live in california man, emission is a bugger. If you don't have a functional catalytic you are doomed to fail lol.

The reason a bad catalytic converter throws off the sensor is because the internal honeycomb structure is ruined. So in reality your exhaust is throwing out the leftover debris of the catalytic's honeycomb. This leftover debris can ruin the signal.

But yea since you live in Kansas, just replace it with a test pipe. Then see if it fixes the problem.

[danielsan]

i dont get it the damn thing runs great for a little bit then starts acting up again. i just took the maf off and cleaned it with carb cleaner even though it looked pretty much brand new. car ran great for about an hour but then it starting bogging out again.

it does this every time i replace something, o2, fuel filter, spark plugs, cap and rotor. its seriously pissing me off.

[direktdrive]

one thing i forgot to mention, don't use carb cleaner. Carb cleaner is so strong that is destroys mafs. That's the reason I had to change out my MAF awhile back.

time to look for a MAF replacement. Sorry bud.

Try eBay, they sell used MAFs cheap. You could also look at the junk yards. Getting a brand new MAF will cost you a lot. O and if you don't find a MAF for the 240sx, you can also the get the MAF for the Altima. Since the Altima runs the same motor as 240sx, the MAFs are identical. Just get the MAF for your application.

[danielsan]

i think the maf is still fine. right now its running 80% perfect, 20% a little loss in power. if the maf went bad after the cleaning it would be running like crap all the time but it still runs like it did before but just a tad better. but who knows the maf looked brand spanking new not even dust on on it.

i have no idea what it should read when throttle is applied, i have 1v at idle like it should.

next on the list is the engine temp sensor and adjusting the tps. i think the maf might be whats causing the problem all along...i need more info though. tomorrow to the yard to pick one up.

[direktdrive]

Sounds like a plan.

But yea, my MAF 'looked' really clean but in reality it was busted. What made it worst was the carb cleaner I used. Maybe the carb cleaner that I used was stronger than yours, which ruined my MAF.

But yea for future reference trying using an easier solvent than carb cleaner. Eletrical component cleaners work better.

Keep us updated danielsan and we'll try our best to help you.

ps. From past experience, another indicator of a bad MAF is when you start hitting 2-3k rpm, the car is harder to accelerate or impossible to accelerate. The engine starts shaking with intensity. Also if feel like you're being rocked back and forth between 2-3k rpm. That is worst scenario though.

EDIT: The rpm range was from 2.8k to 3.2k, when my MAF started to mess up. Anything below that range, I could drive regularly.
Modified by direktdrive at 8:31 AM 5/11/2008

[danielsan]

i think i fixed the problem!!!! in unhooked the purge vacuum line from the charcoal canister and plugged it up as the fsm stated for diagnosing hesitation. car now has zero hesitation and pulls hard, great low end torque. i guess you could say it was vacuum leak.

not sure how the canister works but im leaving it like that, screw emissions crap just makes my car run worse when something simple goes wrong.

[direktdrive]

congrats danielsan.

question for you though, do you believe it was the charcoal canister that caused your problem?

[danielsan]

the fsm states to check the vacuum lines if that fixes the problem. so i have no idea if it is the canister or not.
Modified by danielsan at 2:28 PM 5/12/2008

[danielsan]

my car keeps owning me like crazy. damn bastard is toying with me. i thought i had figured it out but im getting sick of everytime i replace or clean something the car runs perfect for a little while then bam starts acting up a bit.

though its not as bad as before, seems like it keeps getting better after replacing parts but im running out of sensor to replace.

last two are the knock and engine temp sensor though the latter will only cause excessive fuel consumption.

[Vegascorbin]

Check this post. Read towards the end about the wireing problem I found near the ECU. Not done fixing it yet but it may give you some ideas.

zerothread/330663

[direktdrive]

danielsan, so what are the symptoms now? Non responsive motor? Hard to accelerate?
Modified by direktdrive at 10:27 PM 5/13/2008

[danielsan]

its not temperature dependent thats for sure. it will do it cold or hot. imagine hitting the accelerator and the car feels good then it feels like your letting off the pedal a little bit even though its at the same spot then it returns to normal. i guess it would be bogging.

it does this randomly but since i have done a full tune up it doesnt do it as much. i hit the gas and it kinda falls on its face at 1/4 half throttle. WOT position sometimes the power loss is felt. i can rev all the way to redline in gear and in neutral, no difference in any gear.

so its either low fuel pressure or a worn out knock sensor. my car takes 3 1/2 rotations for it to start up. while my brothers 86 turbo z cranks right up on the first rotation as did my 90 integra, hell all i had to do was flick the starter.