Redline at 5250 please help

[centralcoaster33]

So I have this '97 240sx se 5-spd and have done some work to it here and there. At some point my car decided the redline of 6500 was too much and now I have a redline of approximately 5250 in every gear. Sure, I have some other things to fix on the car, but this is driving me crazy! I really want my last 1200 rpms back. Can anyone help? So far I've verified that my 5th gear position sensor goes from continuous to discontinuous when I shift in and out (not sure which, but could clarify if needed), but I only traced that up to the relay box behind my passenger headlight... Then I just unplugged the sensor and drove around, but the SES came on saying it didn't know what gears I'm in, so it must be kinda working. I did plug it back in and the code went away, but not the annoying redline.

[centralcoaster33]

I can't be the first person with this problem. Anyone? It's like have the speed limiter at 120mph kick in, but in every gear at 5200+- Isnt it just a wire or sensor like speedo or 5th gear? Is there a "windows safe mode" my ECU could be stuck in?

[centralcoaster33]

Weak. I must have the wrong forum for technical questions. I'll post this elsewhere...

[Brunos14]

I had the same problem. Check the crank position sensor,plug and wire.With mine the wire in the plug backed out a bit and did the same thing. I pushed it back in and my problem was gone.

[centralcoaster33]

Hmm, this is worth checking out. Did yours throw a code or CEL? Because mine is not. But I'll check the connections anyway. This is however the only real advice I've gotten. My post started like a week ago and I got impatient and posted in the 240/180/sil forum. I got a lot more responses, much faster, none of which helped. I'll let you know what happens.

[Brunos14]

Yea there were no codes on mine either.

[centralcoaster33]

Ah good, no light is a sign that I may have the same issue. I fiddled with the wires at the plugs yesterday and went for a cruise. I tried to rev up to redline in third and got the engine cut still at 5250ish rpms. I will test continuity to the ECU tonight or tomorrow. If continuity is good, then I want to test the sensor istself. It kinda sucks 'cause I can really only get to that guy when all is cold or I burn my wrist on the stupid EGR tube or the head. You don't know of a way to test the reading from the sensor do you? Maybe test for Ohms and turn the crank pulley from side to side to move the flywheel teeth a bit? Maybe nows the time to admit I had to replace my stock 5-speed. The inside went to schrapnel and all I could source was an S13 transmission. So I swapped the speed sensor and picked the best looking posistion sensors and plugged them all in. When smog came along, I took the transmission off, drilled two holes, tapped and threaded one and installed a new CAS to clear the code and pass smog. Well, that all worked, but I might not have matched the depth of the sensor perfectly, so maybe the signal it sends is off a bit which is why I would want to test it.

[centralcoaster33]

No dice. I still need help on this one. I checked out the crank angle posistion sensor last night. It tested at about 200 ohms, the ground had continuity to the engine block and the other had continuity to the pin 53. I pulled it and no chips, just some metal dust stuck to the magnetic part so I put it all back. Could there be something wrong with the metal used in a Fidanza lightweight flywheel? What about a Cam angle sensor? My tach shows smooth increase in RPMs from 750-5250 except around 2900-3000 where it kinda shakes and bounces. I often cruise in this 2900-3000 rpm range and the tach needle always bounces. Any other rpms and it is solid and smooth. I'm grasping at straws here and dont' know what to diagnose next. Please help anyone...

[centralcoaster33]

Bump. I still need help.

[16-bit]

the answer is simple. it is your 5th gear rev limiter.

go under your car. you will see a series of plugs that are on the transmission. if you clip the 2 that look the same that are in the middle, you will remove the problem. Right now your car is shorting it and it thinks you are in 5th gear ALL the time, which means the computer (even though your speedo says diff) thinks you are reaching 120+ or something and it cuts you back.

Do a quick search and there might even be pics for ya. I can tell ya this... The plugs for these sensors look exactly the same. The transmission speedo plug looks different, as well as some other plug that is closer to the bellhousing.

If you clip them, you don't throw codes or anything (on an S13 I know for sure).

[centralcoaster33]

Nope, cutting the wires is not going to fix the problem. Also, those are fourth and fifth gear posision sensors on your transmission. Mine only has fifth plugged in because I drive an S14. Why cut wires on a plug when you can just unplug it anyway? I did write that I've already tried driving around with the sensor unplugged and it threw Service Engine Soon codes that said the ECU couldn't tell what gear I'm in. I still had the same redline. So I plugged fifth back in. Now I did test the sensor for continuity, and it goes on and off with the transmission put in fifth and back out. So I think the sensor works, unless it is having the opposite continuity. Do you know what it is supposed to be? Open in Fifth and continuous in all other gears or vise versa? Oh and I only tested that wire up to the relay/ fuse box by the battery, not to the ECU. It could be shorting and you may be onto something. But that was right were I started to look. I just need to know how to look further...

[16-bit]

hunh.. i dunno what to tell ya.. i guess in the S14s they throw codes.. crappy.

the circuit is CLOSED (conducting) when you are in 5th. Thats why when you cut the wires or unplug it, it should remove the 5th gear effect on rev limiting.

Too bad it throws codes for ya... lame. Get an s13???

Good luck fixin it man...

[centralcoaster33]

Solved. Well, I went "all the way" this weekend. I started by suspecting 5th gear posisition sensor. I only got as far as testing wires up to the relay box before starting to diagnose other stuff. I finally tested that sensor all the way up to the ECU and found my pins were wrong. Then I found I had the wrong ECU and none of the pins were right. Then I realized the picture I had was a mirror image and that I had the right ECU and pins. Finally, the truth was revealed. My 5th position sensor and neutral posistion sensors are plugged into eachothers spots in my transmission! Thats what I get for letting friends take my car apart and then trying to put it back together, without the same friends, in a rush, in the dark because the day had long passed. So I gotta drain some fluid, swap the sensors, fill up fluid again and I'll be done. Note to self: If I'm gonna put something together, I better be the one taking it apart.