HELP!!! 240 falls flat around 3500 - 4000 rpm

[oneandonlydp33]

Ok i know everyone is going to say use the search bar this has been covered a hundred times but i have searched, and it has been covered a hundred times... i know because i have read them all and still haven't found an answer to whats going on with my 240. heres my situation. i blew the head gasket on my 91' 240sx hatchback so i took it as an opportunity to do some upgrades, i decided to upgrade my injectors from 270cc to 370cc, got a new timing chain kit, head gasket (obviously), n60 MAF, koyo radiator and new fans, and had my ecu chips re flashed to compensate for the changes made. i slapped everything back together and my baby started right up!!! success... so i thought... the idle was a lil high but i used my consult program to check all my sensors and the timing and everything was reading correctly... maf, throttle position, coolant temp, etc etc... all the readings were good... i gave it a lil gas and it sounded fine so i goosed it up and everything was good... so i finally took the car out for a ride and immediately noticed that the car wouldn't rev passed 3500 - 4000 under load... it just seemed to fall flat and sputter a lil around that rpm and wont go any higher... i hooked back up to the consult and saw it was throwing a knock sensor code so i swapped the knock sensor but it was still throwing the code so i checked the voltage at the knock sensor and it was reading 2.5v which is good so i checked at the ecu pin 27 and it was reading 3.2v... not good... so thinking there was a short i ran a new wire to the knock sensor but still same results... all was done with the car not running so there was no actual knock to throw off the readings... so i got a 1mega ohm resistor to fool the ecu for testing purposes and i got a code 55 all good but the car was still doing the same thing.. in my research Ive looked into the 5th gear sensor and disconnected it, checked the timing chain to make sure it wasn't off a tooth, checked engine grounds... i just cant figure this out and could use some help here. i just don't get why its fine when it isn't under load but once i try to drive it it wont go passed 3500. and if i keep the revs low it drives fine and pulls strong up to 3500. ANY ideas would be greatly appreciated!!!!!!

[oneandonlydp33]

there has to be someone out there that has some kind of idea or suggestion!!!!

[S13_RB25]

Is your knock sensor grounded? Also it can be signs of the fuel pump giving out!

[oneandonlydp33]

Thank you for the suggestions... I was beginning to think I wasnt gonna get any ideas from this... The fuel pump is a few years old but its a walbro 255L/hr and the knock sensor isstill grounded with the resistor... As of right now im trying to get my speed sensor working since my ecu is throwing code 14 but when I replaced the sensor it still isnt working... Iread somwhere that the ecu will go into limp mode if the speed sensor isnt working... I dont know anymore... Im just trying to troubleshoot everything I can.

[S13_RB25]

I don't remember the knock sensor having a resistor, but I grounded mine to the intake mani. Try grounding it to the block or the mani, w/o the resistor your talking about. Also if you have a new speed sensor it could be a short somewhere in the wiring, causing the ecu to go into limp mode.

[oneandonlydp33]

Yeah the knock sensor doesnt have a resistor I just used it for testing purposes... my knock sensor is actually mounted to the back side of the head... So much easier to get to. I think I'm gonna try and run a new wire from the ecu to the speed senson and see what happens.

[dgms240]

yea sounds like its in limp mode. had a broken wire on my maf and it caused it to do the same thing (rev to ~3000 and hit a wall). double check your maf wiring.

[oneandonlydp33]

I already checked my maf wiring and even swapped in other working mafs to test with no result... What I did do lastnight was pull out the gauge cluster and found that the small plug to the speedo was unplugged so once I get everything back together im going to take it for a ride and see what happens.

[dgms240]

any luck figuring it out?

[oneandonlydp33]

Well I finally got around to putting the dash back together and taking my baby for a test drive and there was still no difference... Speedo still doesn't work and I still have no power after 3500rpm... Ugh... On to the next thing... Any suggestions anyone? I'm bout to hook her up to my consult program again and see if anything is off.

[Chaluska]

have you considered that your cams could be a tooth off? even if your timing light is showing you perfect timing, your PHYSICAL timing could be off.. you did remove your head and all that jazz after all... and one tooth can make a world of a difference... IE

Loss of power..

high idle....

[oneandonlydp33]

I actually have thought about that... At one point I type the motor back down and rechecked everything... I also hooked up my consult cable which is showing the timing at 24° btdc which is right where I want it... Not sure if the consult cable would sill read right if the timing was off a tooth... I'm still trying to figure out what's going on with the speedo since that's the only code my ecu is throwing... I'm hoping if I can figure it out it might solve my problem.

[compactfean]

Speed sensor will not cause running issues. The ecu uses the speed signal (not from the sensor, its a converted signal from the gauge cluster) for rev limit/speed gov. having your timing advanced 4 extra degrees will have Ill effects.

[oneandonlydp33]

I didn't really think it was the speed sensor that was the problem since it hadn't worked in years... But this is the first time I have ever seen it throw the code for it... Thought maybe it was throwing the ecu into safe mode... I'm just trying to go through the motions to rule things out I guess... As fast as the 4° extra advice I read somewhere that if your engine is highly modded like mine you could get a lil better performance out of the engine like that... Either way it still won't go passed 3500 with it set at the stock 20°... I'm freaking lost!

[compactfean]

When it hits that 3500 rpm wall is it like a rev limit? If not and it just can't climb past 3500 id say check your coil, or try a different set of injectors.

[oneandonlydp33]

Its deff not like the rpms are bouncing off the limiter... Its more like the power just drops off... Almost like its flooding or something... Its gotta be the timing but I've checked it twice... Maybe I'll tear it down AGAIN and triple check it... I dunno... Is there anyway to check the coil?

[compactfean]

Yes, you have a multimeter?

[oneandonlydp33]

I absolutly do!!

[compactfean]

Look in the fsm on here (just google s13 fsm, first result should be nicos link) because I can't remember the exact way but I think its like 1ohm between pos, and neg. And like 24k ohms from pos, to post.

[oneandonlydp33]

Ok so I tested the coil and from positive to the negative terminal and got a reading of 0.00ohms.... I tested from the positive terminal to the terminal going to the distributor and got 4.64ohms... I should note I have an MSD Blaster 3 coil. I think that's within spec.

[compactfean]

This info was from another forum, im not sure what they mean by ” across the positive” maybe from the positive to post? the blaster 2 and three have the same internals.

"To test your Blaster 2 coil you can check the Primary and Secondary resistance with a volt meter. Your primary resistance that is measured across the positive of the coil and you should get a reading of .7 ohms. The secondary resistance between the negitive coil and the center of the tower should be 4.7k ohms. You should also check and make sure that the coil bracket is SNUG not TIGHT. check theses few thing and it will let you know if the coil is good or bad."

[oneandonlydp33]

the sure I found was a lil diff as fast as testing procedures but I still came up with the same values... 0.00ohms from pos to neg terminals and 4.64ohms from neg to center tower connection... Its not far off... But does that mean its toast?

[compactfean]

No, not that close of numbers for the secondary. But for the primary yes......if its being tested properly than the primary windings would be toast but they aren't clear how to test the primary. They just day ” across the positive”. How do you check the primary on a stock coil? I'm sure its the same way, so I would test the primary like a stock coil and if you get .7 ohms than its good. If your still getting 0 ohms than its toast.

[compactfean]

Btw .7 ohms is not to be confused with .7k ohms.

[oneandonlydp33]

Well I replaced the msd coil and no luck... I did however find that the adjustment screw on my throttle plate was too high and not allowing the throttle plate to close all the way which explains the high idle... Haven't been able to start the car and check though since my starter died. Ugh... Just something else to replace.

[speedeast]

Not only should you make sure the wiring to the n60 is correct, but that the shielded wires are still fully shielded. The 12v source wire will interfere with the return signal wire and give false readings and could cause the symptoms you're seeing.

[StonedRhyder]

I'm having same problem, did u find the fix?