TrustS13

Okay guys. So as some of you know, I bought a bad (spun bearing) blacktop swap from VA. The guy had a prewired harness and it looks OK, but not perfect. Long story short, I bought a redtop longblock from JDM Of Miami, and it runs awesome. The car is running and driving. But has a small misfire at idle, and runs crappy when it's cold. Ex, it idles about -15 vaccum and is hiccupping. Once it warms up, it drives good, but not great like its supposed too. Once it warms up all the way it pulls perfect -18 or -19 vacuum, and it pulls good but still has a misfire at idle (very slight)

I've done all the required things to check the problem, and last night I did one trouble shooting thing I should have done a long time ago. Unplugged the MAF with the car running.

I cranked it up cold and it starts right up with the slight misfire (at 900 rpm idle) I unplug the maf and it runs PERFECT at 700 RPM with no hesistation and pulls perfect vacuum! I'm like !

-SOO I hope it's just the MAF and swap my roommates perfect MAF on my car.
-Still runs like dookie when I plug in the MAF.
-I also put my MAF on his car and his car runs perfect still.

So my problem is that perhaps the MAF signal is getting a bad reading. I HATE wiring. I did pull the tape to the maf all the way back to the fuel rail and it was the stock white signal wire, so I'm assuming the guy cut it way lower (almost near the firewall?) to extend it. Any input. Do I need to check the wiring back to the ECU?


Checked Ignition Timing - Set to 15* BTDC
Swapped MAF's (Mine and my roomsates)
New Plugs (BKR6ES gapped at .29)
Swapped ignition coils (off my roomates SR)
Boost leak test. (fixed a bunch, made it run better)
Checked IACV
Checked O2 Sensor

But what I'm saying is that the car has a MISFIRE when the MAF is plugged in. When it is plugged up. It's misfiring at idle, especially when cold. Once it warms up, it runs better, but not perfect. Unplug the MAF, it runs perfect.

I'm going on a limb and saying that the MAF signal wire could be the issue.

Ive also swapped the coolant temp sensor to the one off my blacktop. didn't help.

TrustS13

no one wants to make $20.00 easily?

4x4le

The point of the forum is its free help bro.

Im guessing the maf probably has nothing to do with it honestly (or at least shouldnt)

Do you have a working o2 sensor? Its possible that if its not working that your idling lean and your having a lean miss. Another suggestion would be to check your fuel pressure at idle both with your vac lin hooked up to your fpr and with it disconnected. If your not making enough pressure (could be due to a bad line, lazy pump, or a clogging filter) you could be running less fuel pressure and having bad atomization.

I believe that unplugging the maf makes it run rich usually, so lean miss sounds very possible.

TrustS13

I don't think the O2 Sensor is the problem.. But I am looking into possibly replacing it. It seems like a misfire issue not actually an o2 sensor problem, but I may buy a new one for shits and giggles.

Edit - New walbro - new lines and good filter are on the car.

MAF Unplugged makes the ECU think everythings OK (puts ECU into safe mode) so obviously either the MAF wiring has a bad ground.. or a sensor is bad. I've replaced every sensor minus the knock and o2 sensor.

4x4le

There are really tons of possible issues. I dont see how people live without nissan data scan and a wideband.

Diagnosing problems are so simple and it saves you money in the long run replacing all the sensors each time something messes up.

TheWolf

you've got a vacuum leak...

When the car reads how much air it's really pulling....(maf plugged in)
it runs lean and stumbles... (i'm betting it's more a stumble and not a misfire)

When you unplug the maf and the car guesses.. It runs fine..

Take a can of starting fluid and start spraying it around your intake seeing if you can get the idle to flutter when cold. Whatever the leak is, something warms up and seals it up. I'd check around the iacv and the intake flange to the head.

__________________
Eye on the Prize

TrustS13

I've done a boost leak check on it about a week ago.. Had a ton of little ones on the IC pipe, but everything else seemed good. Got the boost gauge to be about 3 psi from the gauge on the air tank gauge.. im assuming the loss is from the massive FMIC. I will boost leak check it again though. Usually a vacuum leak shows way different symptoms but I will boost leak check it and also make a video today or tomorrow.

TrustS13

Trust me, I really want to get NISTUNE and another wideband. I'm trying to save up. I really cant afford downtime on my car so I don't even know how I'd ship out the ECU and everything for NISTUNE.

sr240noob

This was happening to me and it ended up being a bad connection at the ecu. I pulled the plug off and retightened it, after that it idled smooth. Although the plug may seem tight there could be something not seating correctly.

0wn3r

do you have the right MAF. and don't guess.

__________________
97 240sx se

TrustS13

SrNoob. I have swapped out an ECU for another 61 ECU. Ran the same. Tightened up my own a bunch, no fix.

0wn3r. I have the stock SR20DET maf. In my original post, I stated that I swapped my roommates good known MAF for mine, no change, and put my MAF on his car, and his ran perfect still. It's not the MAF.

[email protected]

ive heard about having those sorts of problems from the ground on the battery not being tight enough. check. it could be as simple as that

TrustS13

I will try it out. The main thing that makes me wonder whats going on, is the fact that when I unplug the MAF it fixs everything. WTF

sidewaysstarion

How did your old plugs look? you should look at your new plugs and they should give you an idea if your running lean (lean missfire) or running rich. It could be you have an injector that isn't spraying properly and when you put it in limp home mode it richens up the misture causing it to smooth out.

__________________
Only Shady Tuners Work in the Shadows

blackej7

If he cut away at the shielded wire, that could be your problem....might be picking up interference from something else. You might want to run a new shielded wire, or make sure that the shield covers the whole length of the wire.

__________________

wangan_cruiser

sorry to bring back the thread but

that could be your wiring.

steve shadows

find a local shop that has one of these



then you will find the leak and be done

...honestly if you are a person who does a lot of turbo builds I would just buy one and have it personally

__________________
Like Me on FaceBook !

4x4le

very nice, how much?

HAWAII

change the plugs to Nissan 300zx Twin Turbo from NISSAN parts counter.

Kevdoggyy

-15 is a leak it should idle at 21

jdms14kid

20 bucks is not needed have u checked ur cam angle sensor? Could be that or u could be having fuel issues. What fuel pump are u running?

Mikester

..........................

__________________

Mikester

Umm, this thread is over 3yrs old. Pretty sure it's a done deal by now

__________________