onepointone

I posted over on nico and havent really gotten a response. Figured I would give over here a shot..

I have searched around and found some similar stuff, but couldnt find anything exaclty like what I am dealing with.

I bought a 95 S14 off of a co-worker of mine that he attempted to turbo. Two cylinders were low on compression along with some other issues that I sorted out. I am at the point now where I am ready to have it tuned, but am not really sure its running correctly.

The car is a KA-T with a nistune setup in the ecu. Related stuff is SR injectors, stock MAF (switching to z32 before the tune), recently replaced distributor since I broke the one that came with the car, crower cams, 255 fuel pump, and misc other stuff, but that should be the main things related to the concern.

The vehicle idles decently right now, but when you rev the engine with the TPS plugged it in revs like crap. If you slowly increase RPM you can get it to 3500 - 4000, if you stomp the accelerator, it goes to 2000 rpms and stops. If you unplug the TPS, you can rev it to pretty much red line without much drama. I spoke with the guy that loaded the base map on the nistune when the previous owner had it previously to getting to this point. He said it was for NA, stock MAF with SR injectors, and that the car should idle, but told me not to boost it. The TPS was out of adjustment, I was able to get it back into spec per a how-to on here. When setting the timing (at 20btdc), I was having trouble getting a good signal to the timing light from cylinder 1. Cylinders 2 and 4 gave the timing light a good signal and cylinder 3 was decent, but there were some spots that seemed to skip a flash every now and then. I used a different timing light and was able to get a decent signal on cylinder 1, but it wasnt perfect. I got the timing in, but I am curious if I bought a bad distributor? There is a new cap, rotor, and plug wires on there, and I know the plugs arent fouled. When I rev it with the TPS plugged in it just sounds like the ignition is breaking up, but I guess there is a possibility its fuel related. It just doesnt explain why I can rev it with the TPS unplugged.

When I try to drive the car, I cant get it over 1800 - 2000 RPMs, but can get it up to about 35 mph by short shifting it and being easy on the throttle. I did this with the TPS plugged it to check for DTCs. It did have a coolant temp and iat codes that I sorted out and they didnt come back. I unplugged the battery for a while and drove it again and it didnt make much difference. If I drive it with the TPS unplugged it drives better, but like crap if the turbo starts making any kind of positive pressure.

Just wondering if I am wasting my time chasing this down, or if something could be up with the car. I would hate to waste the tuner's and my time trying to get it tuned..


Thanks for the help.

eng

Anytime you get stuck at ~2000 RPMS (the limit is actually 2400) it is almost always because something is wrong with the MAFS and the ECU is cutting fuel.

onepointone

interesting. Ill check that out later today.

If that is the cause, would I still be able to get up to 3500ish by slowly pressing the gas, and be able to rev it higher with the TPS unplugged? Also, if that was the problem, wouldnt it kick a code?

Thanks for the response.

onepointone

Just checked the MAF and it checks ok according to that picture above. .6xx volts engine off, 1.6v idling, and 2.9ish when it starts stuttering with rpm. Also rechecked the TPS and its at .49v with the throttle closed, and goes to 3.6v at WOT.

Talked to Scott Hennessey, who is going to tune it, and he said it might be in the tune. Anyone else have any ideas? I guess Ill get him to try to tune it and see what happens..

GeneStarWindGSW

I've seen this happen to a few people, after they've swapped ecu or go with a different rom tune (entalphy or biki) i've noticed the problem disappear.
my 2 cents

RE-SPECGARAGE

I havent messed with nistune, but if the tps, timing, CTS, and maf all check out then its the tune.

onepointone

i ended up wiring in a good z32 maf and the car runs much much better. I talked to Scott and he said the base map accounted for a stock maf, but since the motor was low on compression with the previous owner, he might of added a lot of fuel to get it to idle. Since the z32 maf is letting a lot more air, it must be matching the extra fuel, in theory.

Either way, just thought I would update the thread. I am getting it tuned this weekend hopefully. Thanks for the responses.

Kouki KA-T

Just got to this, but i would have said maf from the get go. Glad to see you got it running. And hells yeah for going ka-t for sure.

fluxhomemade

Already mentioned but I agree, also if you've tampered with the Fuel Pump any make sure to replace the Fuel Tank Seal with a New OEM or like seal. I swapped a walbro into my cadet and used silicone on the oring until I could get one from Nissan, I hit fuel cut at 3K and couldn't gun it after I swapped it out all was fixed .

Those Mafs are tricky sometimes glad to see you got it worked out