Why cant I rev past 5000rpm's?

[DriftBandit]

I have a 1995 240sx with a s14 sr20 in it. However I cant rev past 5000 rpms when I drive. I thought it was my MAF and swaped it out with a sohc sensor and MAF. It still had the same effects but I could rev to 6000 in 1st gear.

I am running really rich and boosting at about 10psi. I dont think there is a problem with fuel cut, But I could the copper audio wire I used to lenghten the MAF wires have anything to do with it?

Any help would be greatly appericated, and I will try to find another MAF in case the sohc one is bad too.-Jon

[SpeedRacer1]

Usually when the mafs is wrong in some way the engine wont go above about 2400RPM's. But the wire you used would be the first thing I would try and change since gauge and proper connection are very important for the MAFS signal to work properly. Also I would try and get an actual S14 SR MAFS. If you are running the Zenki S14 SR you might as well try to get that MAFS. The Kouki S14 SR MAFS is the same one used on S15's. The SOHC may work, but I am pretty sure your last MAFS was fine unless it wasnt for an S14 SR.

[DriftBandit]

So there is a difference between s13 sr and s14 sr MAFS. I will try running some sheilded wire from MAF directly to the ECU and see if that helps.Thanks

-Jon

[SpeedRacer1]

The difference is the serial numbers, and the connectors vary. I doubt they send seperate signals. But they may, I think the S14 Kouki/S15 have 2 coils, but I havent opened up an S13 MAFS before.

[DriftBandit]

Ok today I disconnected my MAFS and my idle steadied out @1000rpms( before my idle was anywhere between 300 and 1000 rpms), I run really rich so at idle black smoke pours of tailpipe but with MAFS disconnected smoke stopped and my A\F ratio was perfect( or at least it was where it was supposed to be on the gauge and not all the way rich)

Now I know Ive read that this puts your car in safety mode, But I cant remember if it means your MAFS is bad or are there other things?

Does anybody know because I cant find that post again.Thanks-Jon

[SpeedRacer1]

Is it grounded properly? Also it may be the TPS or ignition timing.

Try downloading the FSM's, they will help out. S14 is what you need but S15 has a good troubleshooting section that would be the same as the S14.http://www.zeroyon.com/TheSite/techservice.html

[DriftBandit]

Im thinking its wiring, I have a fsm for s14 so I will look that over

Thanks,-Jon

[Boostedka]

Sounds like a tach signal maybe getting to ECU.

[DriftBandit]

What does that mean?

[DriftBandit]

Would not having a carbon canister be the problem? I just plugged up the vacuum lines. I just thought of it and I dont know if it has any effect on the fuel delivery if boost pressure is not present in the gas tank, just a thought ?

[Supafly]

did you do the shielded wire yet? if you ran audio wire and it goes anywhere near a power carrying wire it will screw with the mafs signal and make all kinds of bad crap happen. i'd try that first and foremost.

[SpeedRacer1]

Chacoal canister has nothing to do with it unless there is a vacuum leak from the way you capped the holes. Tach has even less to do with it.

[Phax]

Change that ghetto stereo wiring job that you did, and hook it up right. I bet the majority of your problems are coming from that.

[DriftBandit]

Ok, when I get paid I will try to find some shielded wire I never thought of an outside power source screwing up the signal.

I am also running extremely rich and I am not sure if that has to do with anything. I think I can fix that soon but I am in debt from this damn car:).

Thanks for your help,Jon

[goldollar]

Use the shielded wire form ur left over ka harness, its the wires commin out of the maf plug.

[Phax]

I am also running extremely rich and I am not sure if that has to do with anything. I think I can fix that soon but I am in debt from this damn car:).

I can't speak for everyone, but I'm running really rich too. I think the ECU runs the motor rich to keep the pistons cool.

[DriftBandit]

would that be a problem with a bad coolant temp sensor? I am pretty sure my FPR is bad, I have the 255lph pump and it might be pushing too much gas for the stock FPR. I have the Nismo adjustable regulator but I need a fuel pressure gauge to install it.

[Phax]

Hang on... do you have the stock exhaust? What exactly happens when you try to go past 5000 rpms?

[DriftBandit]

I have a 2.5 in straight pipe. When I hit 5000 rpms it wont go any higher it will feel like it lunges forward shaking pretty hard, like you are hitting fuel cut or a rev limiter, Sometimes it happens at 4500rpms, others its at 5000rpms. When I am on the freeway in 5th gear and I go WOT my car will lunge every few hundred rpms until it gets to around 5000rpms and will not continue to rise, So im topping out at about 100mph.

I am almost positive my timing is off, and I talked to somebody from a shop that said the s14 zenkie( I have the zenki s14 motor) MAFS is different than s13 or the SOHC MAFS? Is this true, I really havnt had time to work on my car, too busy working on everybody elses, well, at least they pay me.

Thank you for your help, and I havnt got around to trying the shielded wire but i found some off of another harness.

-Jon

[DriftBandit]

Hey guys. I fixed my fuel problem, My pump was pumping too much gas for the stock FPR, it was like 53psi at idle and around 62psi at WOT! I used the Nismo adjustable FPR. It now idles fine and runs 80% better now, and in first gear it pulls hard to redline, but in 2nd gear and 3rd gear it still will not rev past 5000rpms.

Whats going on??Thanks,-Jon

[loudbay]

did you take out your injectors? if so, did you replace the o-rings, when the fuel press. rises, you could be forcing alot of extra fuel into the cylinder.... try draining your oil, and see if it smells like gas... you'll know right away....

[loudbay]

heck, you may have even just caused a leak with those extreme fuel pressures

[DriftBandit]

Ok I will try that, I was thinking there was still a fuel problem, It just dosnt make any sense that I can rev all the way up in first gear, and not the other gears?

[hadokenny]

most liekly a small boost leak

[candela]

It does make sense... It is probably MAF/ECU related then. if you can rev all teh way in first gear and you can't in other gears its most likelt becuse 1st has teh LEAST load on the motor. WIth the load of 2nd+ you are probably getting some kind of weird signal from the MAF (did you change the woring yet?) or you are hitting fuel cut (cause thats what it sounds like to me).

Can you give it LESS than full throttle and rev past 5k? If so then its most likely fuel cut. How much boost are you running? Is the boost creeping?

[DriftBandit]

I am using the apexi AVC-R, and the same thing happens at stock boost or 11psi. I havnt tried reving with less throttle, and I havnt changed the wiring yet, Its hard to find time now. I will try this and get back to you.

[DriftBandit]

Hey I fixed my problem!:ylsuper I was still running too rich, I guess at 5000rpms there was too much gas in the cylinders to combust, I just turned down the knob on my adjustable FPR, And then she revved clean all the way to redline in every gear!!

It still needs some fine tuning, and I can only do this at stock boost, anything higher the same problems exist, I think My injectors are weak.

Just thought I would let you guys know just in case you run into the same problem down the road.

Later,-Jon