Surging acceleration fix??

[J Taylor]

I have a 91 240sx I need a little help with. On occasion the car pulls hard all the way through the rpm's but usually it surges and doesn't pull consistently. The car is stock with the exception of a punched out cat. Is there anything that usually causes this on a 240? I'm not too familiar with the little quirks of these cars so any help would be appreciated. JT

[J Taylor]

Oh yeah, the surging seems to be mainly when the car warms up....isn't as bad when the car is cold.JT

[moses]

I believe that is a quirk in the way the ECU is programmed. Something that retards the fuel delivery or timing. Mine does the same. Upgrading the chip is the only fix I have ever heard of.

This is also assuming you're car's in good condition otherwise.

[s0ldats]

if it's due to the ecu retarding the timing, are you using the right octane gas? i heard that if you use lower than recommended in the manual the knock sensor automatically retards the timing to prevent detonation....................but i'm probably wrong

[Syntax360]

my car used to have pratically no power at low RPM and when it hit about 3000rpm it would suddenly take off....and it wouldn't go very well if u were on the gas too little or too much....u had to b right in the middle. That's prolly nothing like ur problem, but eh. There was a spark plug wire that was pretty chewed....after i fixed that it was fine again.

[Luke]

Mine acts like this, i had a vacuum leak around the EGR, it has improved but it still does it to a certain extent, it runs quicker when not warmed up. I'm still wondering what else is wrong

[240SXer]

I'm having the same problem, it sounds like a popular problem with no fix.

[Dattebayo]

maybe maybe maybe its just your injectors gettin clogged. Or something else stupid like your ignition components need changing... and if you dont agree dont mouth off i cant stand children like that...

[240SXer]

...and if you dont agree dont mouth off i cant stand children like that...

?????

I changed the spark plugs and the wires, didnt help at all. Changed the fuel filter, cleaned the trottlebody, mafs, none helped.

[Dattebayo]

sorry i was expecting some trouble, but thats cool. i said some stuff in the other thing you posted checkit out.

[wiwalsh]

O2 sensor is another to check.. Thats usuallly on my list with what you already mentioned 240SXer

[240SXer]

I replaced the o2 sensor. It does not seem to be surging, but still does not have the power it should... I've gotta drive it a bit more to know if the surging is gone, it often comes and goes.

David.

[wiwalsh]

I never did figure out why mine had power issues below 3k. Seemed like from 850-3k it was a lawnmower, and from 3k to 5k it was a real car. Weird, gotta be a sensor, but I dont know which.... knock sensor mabye causing it to retard the timing? any other theories?

[wiwalsh]

BTW, take a look at my parts post to see if you want anything....

[kansas240]

it sounds as though j taylor has an ignition problem. when an engine is cold, the a/f mix is richer and easier to ignite. if you have a bad wire, it will be fine at a rich mixture and worse as things lean out. invest $ in new cap, rotor, wires and plugs.

[Dattebayo]

hey wiwalsh, that sluggishness in the low end could be the aac/iac sensor, cause that can affect the a/f mix in the low end only. Its on the firewall side of the intake plenum (if s13 and s14 design is the same). Someone clued me into that here on the forum like a year ago.

[240SXer]

My 91 was idling at 300rpm and sputtering today. It does not surge when accelerating anymore though with the new o2 sensor. Do you think it might be the fuel pump? What would be the easiest way to check fuel pressure?

David.

[240SXer]

Okay, I changed the o2 sensor, the surguing has stopped. However, it's still pretty slow. It seem to be almost normal after about 4,000rpm. Is that maybe the coil? Fuel pump? It still does not feel right...

[mattback]

Hey johnathon, how's the fuel filter looking ?

[Nismo_Freak]

it sounds as though j taylor has an ignition problem. when an engine is cold, the a/f mix is richer and easier to ignite. if you have a bad wire, it will be fine at a rich mixture and worse as things lean out. invest $ in new cap, rotor, wires and plugs.

Ummmm nice try but not quite. A lean mixture is easier to ignite. Detonation is the result of a lean mixture, making the mixture richer will prevent detonation because of the increased amount of fuel retarding the flame front.

I have a surging problem and it's due to my knock sensor (a $180 sensor from Nissan if you own a 96+ 240). A knock sensor that sends an incorrect signal will cause the ECU to flatline your timing, basically there will be no advancing of the timing.

However if you find the car is surging below 2000 rpms, or under partial throttle then 90% chance it's the 02 Sensor. Other things that can cause surging are the idle control valves sticking and allowing air into the manifold. There are two air valves for idle control, one is engaged all the time for idle control and the other is the auxillery control for the a/c system.

[240SXer]

Would that maybe make my S13 slow? It's got a 130k..

[Dattebayo]

Damn nismo freak you are a fu*king genius man. Thats exactly what i was talking about (iac/aac) but noone listens...sigh. The a/c regulator cant make your car sluggish though, can it?

[240SXer]

My car has no low end power, it pulls past like 4k maybe but before that it sucks. My S14 feels like a big block v8 compared to it in low end. Any ideas on that? Maybe the coil?

[Dattebayo]

you know what? i give up on this thread.

[240SXer]

Sorry.. What is the aac/iac sensor? Do you know how much is costs or if there is a way to clean or test it?

David.

[Dattebayo]

Fine . Just one more try. You said it was an s13, right? If it is DOHC then we're good. If you look at the front of the intake runners, there is a grey plastic plug connecting five or six wires. Take it apart and use a multimeter to test the ohms on the leads of the plug on the right. Just take a reading from any two and give me the results. But test them all. Maybe i can dig up the proper testing order here somewhere...

[240SXer]

Yeah, it's a 1991.. I'll check that stuff tomorrow. I'm gonna have to dig up a multimeter.. I know I had one somewhere around here...

David.

[Nismo_Freak]

Try some carb cleaner in the valves themselves. Worked on a friends 93 S13.

[240SXer]

Sorry.. What valves? Which part exactly? The actual valves in the engine? how would I clean that?

[Ceptos]

always start small and inexpensive, im sure u know, but it cant hurt to do all the stupid things first like plugs and wires, getting ur injectors cleaned even