ka24de dies out after warmed up

[thatblackedoutsentra]

After i drive my s13 with a ka24de for about 2 or 3 miles it seems to die out after 2500 or 3500 rpm (my tach doesnt work) i had someone look a it and they thought it was a fuel cut but it drives fine if i turn it off then turn it back on again, i already pulled codes and it reads 55. i have a mishimoto rad a short throw a strait exhaust and and intake. also already replaced ecu

[centralcoaster33]

Hey, I think your transmission position sensors are mixed up. Like, it thinks it's in 5th gear, even though it's not. I think 5th gear and Neutral have the same plugs, so if they get swapped, you get this result. So it's calculating the speed based on gear and RPM and you have a top speed limiter at 115 or 120 that's kicking in. You gotta get under there and sort out your position switch and speedometer wires. This has happened to me and that is what it was. I also had the speedo issue, but it just wasn't plugged in all the way.

[thatblackedoutsentra]

okay but before it started doing this it ran fine like a month ago without all transmission stuff

[centralcoaster33]

Okay, in my past I've had a few things do weird stuff, similar to a fuel cut. The first one was with the S14 and it was my transmission sensors as described above. Yours reads closest to that to me and it's not that hard to check that sub-harness.

On my S13, I had a fuel injector go bad. It wouldn't be super consistent at first, but got worse and replacement fixed the issue. To check those quickly, you can take a volt meter and read the resistance across each injector. They should all be about the same numbers.

Another time, with an S14, I had a TPS go bad, that was a bit more sporadic in the engine bogs, but happened at certain RPMS (as if a portion of the TPS went bad). I was able to verify that with a voltmeter and not seeing a steady climb in resistance as I rotated it.

And finally, the last time on another S14, it was my MAF. I had a spare MAF to swap, but it was also crapping out and I eventually bought one online and all was fixed.

For the TPS and MAF, it's easy to test those two in the driveway with no tools. Unplug the TPS. Start the car. Let it Idle, rev it to the RPMS you describe a bit. Then turn it off. Plug the TPS back in and unplug the MAF. Start the car. Let it Idle, rev it to the RPMS you describe a bit. Then turn it off and plug the MAF back in. If the car won't idle in either situation, then the sensor that is still plugged in is likely bad. Test it with voltmeter.

Also, for position switch tests, you can run the car in the driveway. Push in the clutch and select a gear to make the gear position sensor detect a gear (don't let out the clutch, you don't need to drive around) and rev it up to your suspect RPM. See what happens in Neutral, 5th, Reverse... any fuel cuts?

[centralcoaster33]

You could have fuel pressure issues, or a vacuum leak, or a fouled spark plug, or a bad O2 sensor. But you should be getting more codes for all that... unless your ECU resets on it's own or something.

[thatblackedoutsentra]

Okay cool I've never had to measure any resistance to anything like that with a volt meter so I'll learn how to do that and also with the transmission sensors what should I be looking for

[centralcoaster33]

Hi, sorry for the slow reply... here's a link to a thread that talks about testing your injectors
how-to-test-fuel-injector-resistance-t416697.html

Find them, unplug them, set voltmeter to ohms, maybe 20k, then test the two prongs on the injector.

Similar test for the transmission position switches. Those are just going to be 0 (open circuit) or a number, like any number other than zero (closed circuit). You have to flip each switch while testing each one. Flipping the switch is simply putting the transmission into that particular gear.

You don't need to run the engine for any of the above tests.

[thatblackedoutsentra]

okay sweet so ill test that when i get home but you think its either transmission or fuel injector?

[centralcoaster33]

As far as what to do first, you might start with the easiest and move on down the line.

Testing your injectors is probably the easiest and it will get you familiar with your voltmeter. That could be first. You do not run the car during this test.

Testing the MAF and TPS by using my process of elimination is pretty easy, just try to follow my instruction of when to plug and unplug a sensor and when to run the car. That could be second. You do run the car during this test.

Testing your position sensors will require jacking the car up and getting to the plugs on the transmission... or figuring out which wire is which on the transmission sub-harness plug near your starter would enable testing without jacking the car up. You test for continuity on each sensor twice, once while it is in the gear it's for and once while it's not in gear. Then you look at the plugs and see if they could possibly be mixed with another plug. You should look at the wiring diagram in the FSM and make sure the transmission sensor goes to the proper pins on the ECU. You do not run the car during this test.

[thatblackedoutsentra]

Okay would a coolant temp sensor make it hard to start and cause these problems because my temp gauge went out and it always says the car is cold

[centralcoaster33]

I'm not sure, but I don't think so. You have two temp sensors on your coolant line, near the throttle body. One goes to your ECU and tells it the operating temp (two wires plug). The other goes to your gauge cluster and tells you the approximate operating temp (one wire plug). I think they are completely separate systems.

BTW - that is like a $15-25 part. Just swap in a new one from AutoZone or somewhere. You want to see your temp gauge working. How else will you know if you're running at normal temperature or coming close to overheating?

Anyway, did you do any testing and get some measurements to share?

[thatblackedoutsentra]

Okay so I finally got my hands on a volt meter and some time to look into this thing and I think it's a combination of speed sensor and fuel injector. I ordered new flow matched injectors last night and I already have a speed sensor in my garage so hopefully I can throw that in there this weekend and see if it fixes anything

[centralcoaster33]

I'm not sure a speed sensor can cause the adverse effects you're experiencing. But, if it's not working, like the temp gauge, it's good to get fixed. Hmm, do you have a bad gauge cluster maybe? Or just a few bad sensors? Flow matched injectors. I think I need a set of those for my car coincidentally. I have an odd code to deal with. I'm going to try other things first though. Did you get odd measurements for the fuel injector test?

[thatblackedoutsentra]

I did but to be honest I don't really know how to use the vold meter but cylinder 1 read completely different from the rest when set on ohms but it's still doing it but it's like a hesitation when on throttle but I have a funny feeling that the wire harness that goes from injectors to ecu is fried because of the gauge and no reverse lights anymore either

[centralcoaster33]

Okay, well, bad or odd Ohm reading on that first cylinder tells me that particular injector is faulty. So, you could essentially get away with replacing just that. Having a new and flow matched set will be more peace of mind. Be sure to install new o-rings when you drop these guys in. I assume the set will come with those. Likewise, be sure you got all of the old o-rings out.

Now, you just mentioned reverse lights not working. This is in addition to your speedometer not working. Both of those are parts of the sub-harness. The sub-harness has stuff for your oxygen sensors (would affect engine operation), speed sensor, transmission gear position sensors (these make your reverse lights turn on and they control the engine cut out at rpm in 5th gear), and I can't remember for sure, but I think some starter and alternator wires are mixed in there as well. I'd expect you to have code P0705... among others. This is kind of weird.

You need to jack up the car, mostly the front passenger side, and get into and inspect that whole sub-harness assembly. For all the work you're doing, you might just unplug and remove the whole thing, clean it up at all the connectors, use some dielectric grease, and plug it all in again. That your car runs as much as it does kind of tells me your main engine harness, including the parts to the fuel injectors, is probably fine. The sub-harness connects to the main harness near your starter. You want to check that connection first as it would effect all other connections.

[thatblackedoutsentra]

Okay I checked that last night and it looked fine but I have a whole new harness but by the ecu it only has a brown plug no white also there's no white plug down the line either can I stI'll use this harness to replace it and see if it runs or do I need those white plugs

[centralcoaster33]

I'm not sure without a picture if you can or can not do without a white plug. But it does sound like you're referring to an engine harness and not the sub-harness. It also sounds like they are slightly different engine harnesses. I wouldn't replace it unless you've found an actual fault in it by testing individual wires (typically done from the sensor plug end to the ECU plug end or to grounds).

What I am suggesting you inspect, is your sub harness (as I described above). It is sometimes called the "transmission sub-harness". Coincidentally, you can get a replacement for that one through Wiring Specialties. The "transmission sub-harness" does not connect to your ECU directly. It connects to your engine harness with a large maybe 8 pin connector near your starter motor.

[thatblackedoutsentra]

Okay so you know where the harness plugs into the ecu with the big blue connector and then next to that maybe 4 to 6 inches away there's usually 2 other plugs a brown connector and a white connector well I have a harness with no white connector will that work

[thatblackedoutsentra]

The one that's in there looks like it's brand new like it's the one from wiring specialties the sub harness

[centralcoaster33]

Okay, you can check the sub-harness to make sure all the plugs are in and plugged into the correct sensor. As I first mentioned, in response to your possible engine fuel cut, having the overdrive sensor connected to the neutral sensor wires can cause that. As far as swapping your engine harness and that white plug... can you take some photos of both of them for a visual comparison? Also, if you haven't already, get the FSM and look to the wiring diagram for correct pins and sensor connections.