Strange misfire problem??? - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Negreac · 12-01-2003, 01:23 AM

I've had my SR in and running great for about 3 weeks, then today it started acting up. When I'm not on the throttle the car seems to sputter almost. The car jumps. The throttle response is also very delayed now. I think it is an ignition problem and the car is just misfiring since after idleing for about an hour in my garage the car started to sputter and then after re started the headlights were very dim. My setup is as follows:

S13 SR20DET
KA24DE alternator
Relocated Battery
Aftermark ECU
KA24E MAFS

The last 4 are the 4 things that I think may be causing the problem if it is the ignition. I can't read RPM or speed yet since my gauges burnt out a week ago and I'm still waiting on new ones. The other things I think may be a cause are a bad ground in the rear and a weak battery. Thing is it starts just fine. It also appears to drive fine when I'm driving it hard. Anyone have similair problems? Any ideas on what it could be or any way for me to test wheter it's misfiring? Any info is appreciated. Thanks.

the head · 12-01-2003, 12:56 PM

pressure test the system leaks can cause similar issues

Negreac · 12-01-2003, 01:17 PM

I'll see if I can get the stuff to do it tonight. I also plan to have the battery tested, I'm really not sure how old it is since I got it with the car about 8 months ago. Does anyone know if a local autoparts store can test your alternator in the car? I had it tested out of the car and they said it was fine but it's worth a shot.

Negreac · 12-02-2003, 10:25 AM

More info on the problem:

I realized today that the car only does this when it's under vaccum. The car revs up then bogs down the revs back up then bogs back down almost to the point of stalling. It only happens when the Intake manifold is experiencjing vaccum and there is a load on the engine, It revs pretty good in neutral. It's very bad in first. I have to rev the engine up to 0 psi just to take off. In other gears it's noticable but the momentum of the car keeps the engine spinning and the effect is less intense. The more I think about the issue it seems like either a sensor is bad or my tuned ECU is acting up. I tried resetting the ECU by disconnecting the battery for a minute but it had no effect. Oh the engine also seems to be idling kind of high. The vaccum at idle has reached all the way to -.76 bar (-11psi) It increases as I let the engine idle. Any ideas? I'm baffled.

the head · 12-02-2003, 10:57 AM

are you using an atmosphered BOV? if aftermarket which one are you using

Negreac · 12-02-2003, 04:46 PM

Yes I am using a atmospheric BOV and the ECU is tuned for it (it's a veilside ECU)

I found the problem, and boy do I feel like an idiot for not noticing it earlier. I went to disconnect the TPS and it was wiggling. Upon close inspection one of the screws was missing and the other one was loose. This would explain why it was only bucking at slight throttle, why it had delayed throttle response, and why it only started a few days ago. I disconnected the TPS and the car ran perfect again. I think the dimming of the lights was just a coincidence, afterall the car had just been idleing in the garage for well over an hour.

12-01-2003, 01:23 AM	#1
Negreac Zilvia Member Join Date: Dec 2002 Location: Detroit Age: 40 Posts: 199 Trader Rating: (0) Feedback Score: 0 reviews	Strange misfire problem??? I've had my SR in and running great for about 3 weeks, then today it started acting up. When I'm not on the throttle the car seems to sputter almost. The car jumps. The throttle response is also very delayed now. I think it is an ignition problem and the car is just misfiring since after idleing for about an hour in my garage the car started to sputter and then after re started the headlights were very dim. My setup is as follows: S13 SR20DET KA24DE alternator Relocated Battery Aftermark ECU KA24E MAFS The last 4 are the 4 things that I think may be causing the problem if it is the ignition. I can't read RPM or speed yet since my gauges burnt out a week ago and I'm still waiting on new ones. The other things I think may be a cause are a bad ground in the rear and a weak battery. Thing is it starts just fine. It also appears to drive fine when I'm driving it hard. Anyone have similair problems? Any ideas on what it could be or any way for me to test wheter it's misfiring? Any info is appreciated. Thanks. __________________ Don't pick fights with ugly people, they have nothing to lose...

12-01-2003, 12:56 PM	#2
the head Nissanaholic! Join Date: Jul 2002 Location: in a dark room mastering the art of typing with one hand Posts: 2,164 Trader Rating: (3) Feedback Score: 3 reviews	pressure test the system leaks can cause similar issues __________________ I never knew you could do that with an eggplant

12-01-2003, 01:17 PM	#3
Negreac Zilvia Member Join Date: Dec 2002 Location: Detroit Age: 40 Posts: 199 Trader Rating: (0) Feedback Score: 0 reviews	I'll see if I can get the stuff to do it tonight. I also plan to have the battery tested, I'm really not sure how old it is since I got it with the car about 8 months ago. Does anyone know if a local autoparts store can test your alternator in the car? I had it tested out of the car and they said it was fine but it's worth a shot. __________________ Don't pick fights with ugly people, they have nothing to lose...

12-02-2003, 10:25 AM	#4
Negreac Zilvia Member Join Date: Dec 2002 Location: Detroit Age: 40 Posts: 199 Trader Rating: (0) Feedback Score: 0 reviews	More info on the problem: I realized today that the car only does this when it's under vaccum. The car revs up then bogs down the revs back up then bogs back down almost to the point of stalling. It only happens when the Intake manifold is experiencjing vaccum and there is a load on the engine, It revs pretty good in neutral. It's very bad in first. I have to rev the engine up to 0 psi just to take off. In other gears it's noticable but the momentum of the car keeps the engine spinning and the effect is less intense. The more I think about the issue it seems like either a sensor is bad or my tuned ECU is acting up. I tried resetting the ECU by disconnecting the battery for a minute but it had no effect. Oh the engine also seems to be idling kind of high. The vaccum at idle has reached all the way to -.76 bar (-11psi) It increases as I let the engine idle. Any ideas? I'm baffled. __________________ Don't pick fights with ugly people, they have nothing to lose...

12-02-2003, 10:57 AM	#5
the head Nissanaholic! Join Date: Jul 2002 Location: in a dark room mastering the art of typing with one hand Posts: 2,164 Trader Rating: (3) Feedback Score: 3 reviews	are you using an atmosphered BOV? if aftermarket which one are you using __________________ I never knew you could do that with an eggplant

12-02-2003, 04:46 PM	#6
Negreac Zilvia Member Join Date: Dec 2002 Location: Detroit Age: 40 Posts: 199 Trader Rating: (0) Feedback Score: 0 reviews	Yes I am using a atmospheric BOV and the ECU is tuned for it (it's a veilside ECU) I found the problem, and boy do I feel like an idiot for not noticing it earlier. I went to disconnect the TPS and it was wiggling. Upon close inspection one of the screws was missing and the other one was loose. This would explain why it was only bucking at slight throttle, why it had delayed throttle response, and why it only started a few days ago. I disconnected the TPS and the car ran perfect again. I think the dimming of the lights was just a coincidence, afterall the car had just been idleing in the garage for well over an hour. __________________ Don't pick fights with ugly people, they have nothing to lose...