Low RPM Hesitation/Cuttiing out

[rsmithdrift]

93 240sx hatch KADE with 248/232 cam swap. (only real mod other than bolt ons)

Lately I've been noticing it has been hesitating a little below 2k rpm gradually getting worse all the way down to idle. It only does it under load and the more load the worse it is. In first gear at low throttle it's fine. But even just pulling away from a red light slowly if I drop below 2k rpm after shifting it hesitates BAD. Especially in 3rd and 4th gear and 5th gear below 2k just forget it your going to be decelerating.. It started doing this about 4 months ago but just barely. On my 20 mile twisty half city half highway trip home from work each night it would happen like once or twice when I'd leave it in a higher gear after slowing down and trying to gradually accelerate back up to speed without downshifting which I commonly do. I usually only down shift if I drop below 1500 if I'm just cruising around and driving in a way to get the best gas mileage like usual. But the past two weeks its been getting worse. It got to the point that I thought maybe my ignition timing was too advanced at 23* and I backed it off to 18*... This made a huge difference in bottom end torque and got rid of bogging below 2k rpm but the hesitation is still their. So it essentially EXAGERATED the problem. Cause now it'll accelerate nice and crisp momentarily then cut out completely momentarily and resume accelerating... repeat untill your over 2k rpm. And rarely it'll do it above 2k but not as bad. Highest rpm it's ever done it at was 2500. So basically now it gives you whiplash. And worse of all when you let out the clutch to leave from a redlight uphill it will almost 100% of the time cut out and has caused me to stall on more than one occasion. Cause I mean it cuts out HARD. It feels almost like hitting the brakes when it happens. But it will NEVER do it when its not in gear. It revs just fine under no load.

But the last couple days I've been noticing after getting home having come up the mountain the car idles really high. Up at around 1,000 - 1,200 rpm... And not only that but the temperature gauge is up a full notch higher from where it normally runs also. Still 2 notches below the hot mark but still... that's not normal it's NEVER run hot before like this. Even when it had a bad fuel pump and was running super lean it still ran cool...

And mind you that the power is not affected at all it just cuts out. I still pull 6.4 second consistently 0-60 times and no knock at all.

Anybody have any idea what could be causing this???.... I'm very worried it could be something mechanical inside the engine... like cam timing or burnt valve or head gasket or something...

[574-240sx]

I had something similar for about a month before my tps went out completely on my sr. I noticed my tps voltage was very low until it was reading next to noting at wot according to my safc. You may also want to monitor maf voltage too looking for eratic jumps or dead spots.

[-RJ-]

Its off topic but how did you do your 248/232 cam swap? Did you redrill your cam or just twist it ccw 4 teeth?

[Hoffman5982]

Not trying to thread jack, but im having a very similar problem with my sr. The guy above mention TPS, which got me wondering. I've adjusted mine 3 times now. Ill get it right to where it needs to be(.45 volts i think) and tighten it down. After a week ill check it and it's changed, like it moved out of place. Thats not possible because ive tightened it enough to prevent this. The car drove fine for 3 days, then died. The ecu wasn't getting power and the fuel pump wouldnt prime. I got it running again, but now it has the hesitation problem. Im at a loss as to what it is. OP, I tell everyone that has this problem on their ka, tug on you wire harness while its running and see if it shudders. If it does, keep doing it until you find the general area, then go wire by wire. Both of my KA's did this, but it would do it periodically while cruising, not just at low rpms. It turned out a wire had a break in it.Just throwing out ideas for you.

[rsmithdrift]

I had something similar for about a month before my tps went out completely on my sr. I noticed my tps voltage was very low until it was reading next to noting at wot according to my safc. You may also want to monitor maf voltage too looking for eratic jumps or dead spots.

I have an SAFC II just for this diagnosis purpose... My MAF reads PERFECT. In fact it was reading low and inconsistently at low throttle so I rewired it and it runs way better power wise since I did that about a week ago.... had no effect on the hesistation though other than to make it more noticable due to greater difference in power when it does cut out. BTW I run at ~ 14:1 at low throttle and 12:1 at high throttle on the A/F ratio gauge.

And my tps voltage is perfect too. Hasn't changed any since I got the car. reads .490 at idle and 4.5 or something at WOT. % increases very smoothly and accurately.

Also none of that would cause the idle to rise and temp to rise after coming up the mtn either...

[rsmithdrift]

Its off topic but how did you do your 248/232 cam swap? Did you redrill your cam or just twist it ccw 4 teeth?

Twisted ccw ... use a 232 exhaust cam and rotate the old s13 248 exhaust cam ccw... I don't know how many teeth I ended up being rotated because it'll work either 4 or 5 and I lost the mark... and I thought I had gone 4 teeth first time but when I started it it wouldn't run untill 4k rpm so I took it apart and moved it one more tooth... aparently in the wrong direction cause when i turned the motor over it had vavle interference so I didn't even start it I just took it back apart and moved it two teeth the other direction and it was perfect.

So in short... I have no idea how many teeth I'm rotated lol. lesson learned.. mark that s*** for real when you do it. counting the links goes to hell when you have both cams removed simultaneously....

[-RJ-]

how does the car run after you installed, was it a notable difference

[rsmithdrift]

how does the car run after you installed, was it a notable difference

Yea. Much better power band. instead of having a lump of power at 4500 to 5500 and thats it it now makes power from 4000 to redline. and runs just as good bottom end cruising and its nice to be able to have power up high too.

I'd say a 5hp gain atleast throughout the entire power band.
/offtopic

NOW SOMEBODY TELL ME WHY IT"S HESITATING ALREADY!! LMAO

[benz88]

import tuner or superstreet actually did a best bang for the buck mods on a 240 and dyno'd them. The 248 exhaust cam swap made 7whp on an S14 with the 248/232 cams..

[xX RB Xx]

tps. my car was doing the same thing. i changed out my tps and it fixed the problem.

[rsmithdrift]

tps. my car was doing the same thing. i changed out my tps and it fixed the problem.

Well unfortunately my tps works perfectly. I can see the voltage output of it in my SAFC and it works flawlessly.... any body got any other ideas??