1991 240sx Jerky acceleration

[Jiggyfry]

Hey folks, I have a 91 s13 running a KA24DE. Recently ive noticed that upon accelerating the car jerks. I know that my clutch and flywheel are not slipping causing this and I have changed the following: 1. Spark plugs + wires2. Distributor cap and rotor3. Fuel filter4. both coolant temp sensors5. Cleaned out iav and maf sensorI just installed the coolant temp sensors yesterday and noticed a slight improvment. Some of the jerkiness is still there and i also notice that i have a slight stumble during idle. Anyone have any ideas since this is driving me crazy? A lot of people are telling me its my maf but it is hooked up to my SAFC2 and the airflow numbers are fine. Thanks in advance for the help!

[180fan]

have you checked the tps?

[mr_wizard]

have you checked the tps?

Having the same problem, except much worse. I get it under hard acceleration and at certain RPM range. There's ways to test it if you know how. It's somewhere here on NICO. I would do it myself actually if it was a little more detailed. Good news is though it's not too expensive to fix and very easy to install if it needs to be replaced. Good luck.

[Jiggyfry]

ive tested the tps when i rebuilt the engine, everything checked out ok. The other night i did notice that my fuel pump primed quiet loud, sounded like a dying cat. This noise went on for a good minute then stopped. Could my fuel pump be on its way out? Also could this cause my problem?

[180fan]

it sure can (for both questions). The priming should last a few seconds with the key in the on position and if it's an oem pump shouldn't make much of a sound, if it were a walbro it makes a bit of a whine but that's about it.

[Jiggyfry]

ok, my fuel pump has not made any weird noises for aboot a week now, yet I still have this jerky accel. I did notice yesterday that when I step on the gas, aboot 50% throttle, I suffered a noticable power loss at aboot 3200 rpm. The power loss was short lived but was VEry noticable. I have recently replaced my dist cap, spark plug wires, rotor, and spark plugs and both coolant temp sensors. I have also checked for a vacuum leak and checked most of my electrical connectors for corrosion. I'm honestly stumped for now. I rebuilt the engine last feb. and had a power loss for a while cause of a toasted o2. Other than that it has been perfect til recently. Last thing i can think of would be to do a fuel pressure test this week at work. Anyone have any more ideas since I could do all these test in my shop rather than my driveway! So far ive been told its my MAF or fuel pump and FPR. Maf is fine, but not sure aboot fuel pump and FPR.

[znelson]

First thing I would do would be to check and see if your ecu is throwing out any codes, there is a good writeup on that under FAQ. Goodluck.

[Jiggyfry]

already checked the ecu, code 55, so im still stumped!

[znelson]

Check grounds next.. get an ohm resistor check the negative terminal to a unpainted body screw.. over 2ohms and you need to run a jumper ground from the battery to the body. This is a common problem believe it or not.

[Jiggyfry]

awsome, im gonna check that out today, thanks for the info. I'll let you know what i find! I've also heard that adding an extra ground to the MAF sensor could help, any info on that?

[mr_wizard]

Check grounds next.. get an ohm resistor check the negative terminal to a unpainted body screw.. over 2ohms and you need to run a jumper ground from the battery to the body. This is a common problem believe it or not.

ZOMG This was my problem. After replacing the TPS, MAFS, and days of just staring at the motor... it was the f'ing grounds. Specifically the 2 grounding wires on the side of the motor just above the exhaust mani. Make sure all your grounds are secured WELL.

[Jiggyfry]

Thanks a lot for all the info guys! I fogot my DVOM at work so itll have to be done tomorrow, unless i could borrow a buddies.

[znelson]

Post back here and let me know if that works out for you..

[Jiggyfry]

ok, so i tested my TPS today and it was dead on the values found in the FSM. So, I went ahead and tested my chassis grounds and everything is under 2ohms of resistence. Anyone have any more suggestions? I figure my next step is to test my fuel pressure. Anyways, any more info would be greatly appreciated.

[mr_wizard]

What exactly does it do revving in neutral? And how jerky is it? Is it worse at certain RPM ranges? Certain gears?

[180fan]

pull the afc from the loop and see if that problem persists.

[Jiggyfry]

okay, the jerkiness is noticed in 1st and 2nd gear from idle(800rpm) until approx. 3000 rpm. I'll notice it if im accelerating from a stop or if I let off the gas and get back on it. the only time it happens is between those rpm points. As for 180fan's suggestion, I did undo the wiring, and replaced the wires (airflow) as they were before and the same problem persists. It was suggested to me that it could still be the TPS sensor that is messed up and I just cant see the flat spot with my DVOM. Tomorrow im staying after work and doing a proper injector pressure cleaning. Any more suggestions would be greatly appreciated and if any more info is required just ask me. Thanks again folks for all the help so far, greatly appreciated!

[mr_wizard]

If it was the TPS, then the car would run better without it connected up until about 3k RPM. Disconnect it and see how it rev's, just don't do it for too long.
Modified by mr_wizard at 11:34 PM 6/7/2006

[zer0c123]

okay, the jerkiness is noticed in 1st and 2nd gear from idle(800rpm) until approx. 3000 rpm. I'll notice it if im accelerating from a stop or if I let off the gas and get back on it. the only time it happens is between those rpm points. As for 180fan's suggestion, I did undo the wiring, and replaced the wires (airflow) as they were before and the same problem persists. It was suggested to me that it could still be the TPS sensor that is messed up and I just cant see the flat spot with my DVOM. Tomorrow im staying after work and doing a proper injector pressure cleaning. Any more suggestions would be greatly appreciated and if any more info is required just ask me. Thanks again folks for all the help so far, greatly appreciated!

Sorry I need to bring back this old post. Did you ever find the problem to the jerkyness when you "get back on the pedal" while in 1st or 2nd? I have the exact same problem. I can make my car jerk like crazy just by pressing and depressing the pedal in 1st and 2nd.