Warning: Long Read...
I've got an issue with my daily driver 240sx that I have not been able to figure out even after taking it to a shop and having multiple people troubleshoot it. I've never dealt with KA cars as I've always had an sr20 since 2008, so I'm lost with the problem I'm having... If it had an sr I would have fixed it as soon as it started running funny
I will pay anybody that helps me track down this problem!
So, it's a 92 s13, ka24de, 140k miles, automatic virgin with no modifications at all. This car has been my daily driver since February and it ran perfectly before this issue started up. It's an auto car and seriously the engine is the most healthy ka24de I've ever driven, its so quiet at idle all you hear is the injectors clicking under the hood.
June 1st I got rear ended
in the right side half at approximatey 40mph according to the kid that hit me. I was stopped at a red light. The collision pushed the rear bumper and crash beam in a bit, and wrinkled the passenger quarter panel a little. I had the frame pulled which fixed the quarter panel and had the crash beam and foam replaced.
The car drove home fine after the collision, but the next time I drove it is when it started running funny:
It no longer idles steadily when either cold or warmed up. It seems to misfire randomly at idle, and sometime is will outright die. It does not do it constantly, but instead it seems to start misfiring approximately every fifteen seconds when idling. Also when driving and coming to a stop it will sometimes shut off. When stopped I now have to heel-toe the gas and brake at the same time or put it in neutral and hold the rpms up a bit so that it does not shut off on me in traffic. Sometimes when doing this in drive it starts bucking pretty bad and I have to put it in neutral.
When cruising holding a constant speed it will randomly hesistate/misfire and not hold speed, and then it goes away and runs fine. A couple seconds later it will do it again, for a few seconds, and again it goes away. This is constantly happening on and off while driving.
Anything over half throttle it does not misfire or hesitate at all and runs perfectly, even flooring it all the way through third gear it pulls hard with no problems. But light/partial throttle it has this intermittent hesitation and misfire.
The weirdest thing. If I sit in the car in neutral, and hold the rpm's at 1500. It will start to misfire CONSISTENTLY literally in 15 second intervals. It misfires for 2-4 seconds, and then runs smooth again for about 15 seconds. Literally 15 seconds later it repeats this same loop. I counted exactly 15 seconds between misfire portions over 10 times in a row and it never varied.
So, since I got hit in the rear you would obviously think that I'm having some sort of fueling issue. However I do not believe it's a fuel issue and I have not checked the fuel pump or pressure for a couple reasons:
a. The fact that anything above half throttle it runs perfectly as it always did before.
b. If I UNPLUG the mafs sensor, it idles DEAD smooth just like it used to and never misfires at idle or hesitates. And it revs strong as it should but of course it won't rev over 2,500rpm with the mafs unplugged since this is a limp mode.
IF it was indeed a fuel issue then unplugging the mafs should not fix the misfiring at idle right?
If I pull the plug wires with it at idle to listen to the spark against a valve cover bolt(mafs plugged in) during the misfires it does not have consistent spark to the number three cylinder. And then the misfire goes away for a couple seconds and it's fine. I tried a replacement plug wire with no effect.
The ecu shows three codes. MAFS Sensor code, Knock sensor code, and speed sensor code (hud speedo doesn't work and it always had the speed code when it ran perfectly before). Resetting the ecu codes does not fix the issue. I did notice that the ecu will not throw any codes at idle no matter how long I let it misfire for, until I actually start to drive and then it will throw the same codes.
This would lead anybody to believe that the collision damaged my mafs sensor and the mafs is bad since it only hesitates and misfires with it plugged in.
Here's the kicker: I tried TWO known good mafs, one of which came off of a 240 that drove to me and runs perfectly so I know it was good. With both known good mafs plugged in the issue did not go away and it was exactly the same!!! So that should throw the mafs sensor being bad out...
Next thing you would think is that there must be a bad intake manifold gasket right? This would cause a similar issue to what I'm having. Well, I went and bought a can of starter fluid, and sprayed it up and down both the runner flange/head gasket and runners/plenum gasket with the engine idling (mafs unplugged so that it would idle steady and not die). If there was a bad gasket the idle should go up when it sucked in the starter fluid. Well there is no bad gasket, spraying the starter fluid never had an affect on the idle no matter where I tried to find a leak.
And this is where I stand. I simply cannot figure out what the problem is! It's my daily driver and it pains me to keep driving it like this. There simply must be a way to fix it.
I've considered buying a consult cable, but I'm not sure if that would help me locate the issue.
I do not want to just start throwing new/replacement parts at this car willy-nilly if they aren't going to fix the problem. Again considering I got hit in the rear you would think that this must be a fuel pump problem, but that does not make sense considering with the mafs unplugged the issue goes away completely...
Sorry for the fucking Novel here, but I just wanted to explain everything as thoroughly as I can to help us figure this shit out. Thanks guys.
And yes, I have researched this online everywhere that I can. Every single thread I have found that is either this same exact issue, or something very similar either had a fix that I have already tried, or was never resolved and the thread died without any fix.