Help my fix my issue and i'll pay you!

[TheRealSy90]

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.

[cotbu]

IF it was indeed a fuel issue then unplugging the mafs should not fix the misfiring at idle right?

wrong, the ecu uses a separate code for limp mode/ and or malfunction.

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

knock sensor had my vote based on your long read essay, lol.

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...

The sensor codes don't have to be a faulty sensor. It could be wiring or the ecu, both or all three(sensor, wiring, ecu)

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.

I never trusted this method alone, clamping the auxiliary air hose or pcv valve line with it, works better.

knock sensor,and wiring, mafs wirng and ecu.
assuming spark plugs, cts and tps have been change or checked.
I'd like to have a listen to the engine...

[kruked]

I'm going to lean on the ECU being shorted. Pull it out and thoroughly look it over, smell it. If everything seems to be ok, borrow someone else's ECU just for added measure.

[TheRealSy90]

Originally Posted by kruked

I'm going to lean on the ECU being shorted. Pull it out and thoroughly look it over, smell it. If everything seems to be ok, borrow someone else's ECU just for added measure.

Oops, I forgot to mention that I did in fact try a different known good ecu already from a friends running 240. It did not fix the issue at idle at all it was the same, but being a 5sp ecu I could not cheek for a difference when driving.


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[KiLLeR2001]

How is the condition of the gas tank after the accident, is it dented in anyway? Especially near the area where the pump resides. Definitely pull the fuel pump assembly out and observe. Check for loose wiring. Does your gas gauge read fine?

Also check the knock sensor out, usually these are cracked up if they are still the original 25 year old unit. Get a timing light out and check your timing. KA24DE is 20* BTDC.

[TheRealSy90]

Originally Posted by KiLLeR2001

How is the condition of the gas tank after the accident, is it dented in anyway? Especially near the area where the pump resides.

From what I can see the tank is not dented at all and only got one scuff on the bottom from the bumper plastic rubbing on it when it got pushed in.
The other stuff I'll have to check on and I'll add it to my list of stuff to check.

How do you get to the knock sensor? It's like in between the manifold runners and the plenum [emoji29]




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[KiLLeR2001]

Originally Posted by TheRealSy90

How do you get to the knock sensor? It's like in between the manifold runners and the plenum [emoji29]

http://www.northwestnissans.com/boar...-sensor-KA24DE

Good luck, haha.

[andisan]

If you are getting all those codes I would start with that first

[TheRealSy90]

Originally Posted by andisan

If you are getting all those codes I would start with that first

I tried two different known good mafs and each one ran the same and still threw the mafs code... So obviously that doesn't work.


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[andisan]

Doing the knock sensor is a bit tricky but getting it done will help it

I can't remember the symptoms of my car but mine had the code and my sensor had a big crack on it and it cleared the code

Also my car had a misfire but it was due to my "high performance nology wires"

But before, I got all OEM replacement parts for the distributor( cap, rotor, and I put my OEM wires back on) and now no misfire

All those parts aren't costly but will help on the long run

[TheRealSy90]

Originally Posted by andisan

Doing the knock sensor is a bit tricky but getting it done will help it

I'll look into replacing the knock sensor i guess.


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[95_S14]

Bring the car to SoCal and I'll have it changed in 5 min

[95_S14]

But really it's not as hard as you think to change

[relaxamigo]

Hi, I just had a similar issue with my car. Replaced the knock sensor and the code went away. I also had an issue with the wiring to the knock sensor which can be a big problem. If you'd like to "test" your knock sensor, you can do so for $5 at radioshack. Wire in a 560K ohm resistor at the ECU pin 27 and it will bypass the knock sensor.

If the car runs well, replace the sensor, and simultaneously check for continuity in the harness AND the subharness under the intake. It's easier than swapping sensors and will tell you IMMEDIATELY if the issue was the sensor.

I don't know if this is for S14 as well, but I'd imagine it would work. Once again, don't keep this resistor pack in. Replace the sensor with an oem one when you get a chance:

http://www.240sxforums.com/forums/ka...24de-obd1.html

[TheRealSy90]

It's an s13 not s14. Was your car running weird like mine and replacing the knock sensor fixed it?


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[relaxamigo]

Originally Posted by TheRealSy90

It's an s13 not s14. Was your car running weird like mine and replacing the knock sensor fixed it?


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Not sure why I thought it was S14. Anyway, short answer, yes. I had a code for the knock sensor, replaced it, and code went away. Car still ran like ass. Essentially tested every goddamn component in the car till I checked the actual wiring to the knock sensor.

Do a little reading about the wiring to the sensor, apparently the design is flawed and the signal can be easily interfered with. Bypass the sensor with the easy solution I sent you. If it fixes your issue, replace the sensor and consider rewiring it.

[hanzbrady]

WS sells a plug and play harness for the knock sensor, and the sensor itself is only held on by one bolt.

[TheRealSy90]

Originally Posted by hanzbrady

WS sells a plug and play harness for the knock sensor, and the sensor itself is only held on by one bolt.

So just those wires on that little sub harness go bad? Not in the main engine harness itself.


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[hanzbrady]

Originally Posted by TheRealSy90

So just those wires on that little sub harness go bad? Not in the main engine harness itself.


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Correct, it's probably the pins coming lose.

[justinbyrant]

a collision can do a lot of unforeseen damage especially anywhere not in the area of the wreck, the initial impact and jarring through the frame could have done any amount of damage, the hit could have cracked the knock sensor, damaged the maf sensor internals which are pretty fragile as it is, and it could still be a fueling issue with the maf unplugged if you have a pinched line and your not seeing proper fuel pressure the maf could be causeing the car to run lean, unplugging it could very well cause it to richen up and idle fine as long as there isn't to much demand, when you tried these working mafs did you clear the codes when you installed the new one?

anyways, start with the knock sensor, if this is an unmolested s13 get a scan tool, knock sensors are generally so sensitive you can monitor them with a scan tool or even a good multimeter at the plug and tap the valve cover with a wrench, you will see it react if its good, a good scan tool can have your problem figured out in a matter of minutes

[sterlinge]

il give you a run down of what i would do.
check fuel pressure never assume anything.
verify a consistant reading on the maf signal wire while idling.
check your compression, do a leak down test if possible
verify your getting constant 12v or more off the battery while idling. could have a bad alternator.
theres alot of stuff you can check but if you dont start with the basics you can waste alot of time
bad ignitor and or distributors are also possible.
also possible you have a bad ground somewhere.
good luck

[kruked]

Jeez. Check the compression? Fucking holy hell.

Before you go chasing your tail, just solve the problem first w/ the knock sensor. It's the best thing to start w/. I wouldn't even bother messing w/ the subharness just yet. Try the resistor trick first. Cheapest thing to try.

[TheRealSy90]

Originally Posted by justinbyrant

when you tried these working mafs did you clear the codes when you installed the new one?

Yes, I didn't elaborate in the OP but yes each time I tried the two different known good MAFs I DID reset the ecu codes before starting the engine. Good catch.

Originally Posted by justinbyrant

anyways, start with the knock sensor, if this is an unmolested s13 get a scan tool, knock sensors are generally so sensitive you can monitor them with a scan tool or even a good multimeter at the plug and tap the valve cover with a wrench, you will see it react if its good, a good scan tool can have your problem figured out in a matter of minutes

I'll be giving the knock sensor troubleshooting a try asap. Unfortunately Mon-Thurs I just don't have any time between work and sleep.

Originally Posted by sterlinge

check fuel pressure never assume anything.
verify a consistant reading on the maf signal wire while idling.
check your compression, do a leak down test if possible
verify your getting constant 12v or more off the battery while idling. could have a bad alternator.
bad ignitor and or distributors are also possible.
also possible you have a bad ground somewhere.

I'll see if I can get a gauge to test fuel pressure.
I'm concerned that if I try to test the mafs signal the unsteady idle itself will not let me get a constant reading, regardless if the mafs is bad or not. Might have to test this in a different way...

I'll hold off on a compression test until there's nothing left, but honestly this motor is very very healthy lol.

Definitely will need to verify alternator voltages. Unfortunately idk how to test the ignitor or distributor aside from outright replacing them and seeing if anything changed

Originally Posted by kruked

.Before you go chasing your tail, just solve the problem first w/ the knock sensor. It's the best thing to start w/. I wouldn't even bother messing w/ the subharness just yet. Try the resistor trick first. Cheapest thing to try.

Yep knock sensor has now been pushed to the top of my troubleshooting list now that so many people have mentioned it. Honestly I never would have thought that it could be a big problem if it went bad. I'll see if I can pick up one of the aforementioned resistors and if it makes a difference.

Again thanks everyone for any and all input. Unfortunately Mon-Thurs I don't have time to do anything to the car itself but we can always guestimate on here until I am able to mess with it Fri-Sun.

[cycloneskate]

I've had the exact issue you're having on a 1992 Fastback ka24de, stumbling every once in a while, and I've found that this is related to there being a vacuum leak. The emissions system can seem a bit daunting to tackle at first, but the FSM explains exactly what each component does. If your vacuum lines are virgin it wouldn't surprise me a bit if they're brittle and the shock of the accident was enough to cause a small leak. Replacement vacuum hose is like $1 a foot at autozone. Snag like 15 feet, work methodically, and replace each hose one at a time so you don't miss anything or accidentally route them wrong. Fyi the spaghetti mess on the back of the head can be a pain to get to. I'd be surprised if replacing your vacuum lines didn't improve your idle stability and overall driving experience. Feel free to pm or text me 480-five28-7771, I've worked with these cars for many moons and love troubleshooting.

[justinbyrant]

Originally Posted by TheRealSy90

I'll see if I can get a gauge to test fuel pressure.
I'm concerned that if I try to test the mafs signal the unsteady idle itself will not let me get a constant reading, regardless if the mafs is bad or not. Might have to test this in a different way...

a good trouble shooting resource I have found for the fuel system is to clamp the return line and check pressure that way, if your having pressure drops afterwards your pump is bad and if you are still having the problem afterwards then its not your fpr quick way to rule out those 2 things

[TheRealSy90]

Shouldn't it just be 43.2psi with the vacuum source unplugged?


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[pacotaco345]

Someone literally just told him that trick in his own thread with his own problem.. He's just regurgitating information with poor grammar.

If you have somewhere around 43 psi (i think its 38 with vacuum) you should be fine. It probably isn't the problem but I would at least start at the knock sensor, it can't hurt. Also just buy a $10 consult port off ebay and hook it up, you'll be able to see all the sensor inputs.. not just the codes.

[TheRealSy90]

I was talking with a friend and we were thinking I could probably buy a new knock sensor and sub harness, bolt it to somewhere easier to access on the engine and plug it in that way I don't have to try to get the one out of the intake manifold. Just to see if it makes a difference.


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[andisan]

It's not that hard just have to have the right tools to take it off, putting it back on all you need is a rod taped to it and help direct it with it and that's it

[TheRealSy90]

Yeah I'm sure I can figure out a way to do it. Might just go ahead and replace it so that I know it's not the issue even if it doesn't fix it.


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