Misfiring Problem

[KiLLeR2001]

Alright, I'm kind of at a point where I have a few ideas of what could be wrong with my car, but I'd figure I'd ask Zilvia if they've had similar problems and knew the resolution.

I've got a fully rebuilt (to factory spec) redtop SR in my s13 hatchback, everything on it is stock. Injectors, ecu, MAF, SMIC etc. I have a megan FPR, z32 fuel filter, walbro fuel pump, apexi air filter, koyo radiator, stock T25.

I'm having a problem with misfiring. From what I've noticed, when its cold out, it's a lot worse and seems to misfire a lot more than when its warmed up. Upon a cold start, at idle itll occasionally do a slight misfiring every now and then, once its warmed up the misfiring goes away at idle.

The other misfiring problem I'm having is above 4k when I dump the throttle. I've noticed if I gradual the throttle and go above 4k it won't misfire, itll keep gaining in power like normal, but if i go from say 10% throttle to WOT, itll misfire pretty bad (seems to be only one piston), almost feels spark related if I had to say so.

I don't have a boost leak. I've already checked that. I checked the resistance on my injectors and they all check in. I've replaced the o-rings on the injectors. I don't think the problem is fuel related, I'm leaning towards coilpacks or the ignition timing (or maybe even the TPS sensor). Replaced the MAF with a known working one. I did a compression test and got 140psi across the board. When its warmed up it idles steady at about 850 rpm. Occasionally misfiring very slightly every so often. It almost seems at about 1500rpm to 2000rpm somewhere in there itll stumble a little bit for a sec.

Other than this the car is running great, sounds healthy, no leaks of any sort, I know its something simple I'm just trying to pinpoint it.

[makulit054]

I had a similiar problem. my car would misfire around 4-5k. I too checked everything. come to find out the CAS wasn't plugged in all the way. I forgot to push it all the way in. trying check that.

[bmx22]

spark plugs bad or gap is wrong i think i run 34 or 36 gap

[KiLLeR2001]

Originally Posted by bmx22

spark plugs bad or gap is wrong i think i run 34 or 36 gap

For a redtop sr20det? Right now my gap is at .030.

Originally Posted by makulit054

I had a similiar problem. my car would misfire around 4-5k. I too checked everything. come to find out the CAS wasn't plugged in all the way. I forgot to push it all the way in. trying check that.

The harness plug or the actual CAS? I'll have to check that, if this is the problem I'm gonna shoot myself lol.

[ericcastro]

how are the plug wire condition?? the wires between the distributer and the spark plugs?? wiggle each one a little during idle and see if you can get one to skip it??

[KiLLeR2001]

Originally Posted by ericcastro

how are the plug wire condition?? the wires between the distributer and the spark plugs?? wiggle each one a little during idle and see if you can get one to skip it??

SR20DET. I've got coil packs and the CAS.

[ericcastro]

Thats all I can add then, Im a KA guy, sorry.

GL

[KiLLeR2001]

Originally Posted by ericcastro

Thats all I can add then, Im a KA guy, sorry.

GL

I wiggled all the coilpack wires while it was running and there was no change.

Messed with the ignition timing a little. Moved the CAS back to center position and went for a run. Would sputter around like 3k pretty bad. So I went back and advanced it almost all the way... Ran better until after 5k where it began the small subtle stuttering.

[makulit054]

Originally Posted by KiLLeR2001

For a redtop sr20det? Right now my gap is at .030.



The harness plug or the actual CAS? I'll have to check that, if this is the problem I'm gonna shoot myself lol.

It was the harness plug. Make sure it clicks.

[KiLLeR2001]

Messed around with my car a bit more today... Turns out if I gradual throttle (about 1/4 to 1/2 throttle) up in the rpms, it'll never misfire or sputter. But once I go WOT or almost WOT, itll just crap out on me and misfire.

I got to over 6k in 3rd gear today with about 1/2 throttle and it was great. But as soon as I dump the throttle the problem occurs.

I'm assuming this is my TPS malfunctioning? Any other possibilities?

edit: Just checked for resistance on my TPS Sensor, and when I probe the B and C terminals, there is no response at all. Like I'm not even touching the two. Then with the probes still on the B and C I had my dad move the throttle and there was still nothing. Bad TPS? Yes?

[makulit054]

Did you check the resistance while the car was on or off? Have you checked your tps voltages? If you haven't here's a way to check the tps voltages. you could also move the open and close the throttle slowly and make sure the voltage changes. is should go from .45vdc to approximately 5.0vdc.
Step 1:

You will need to put your keys in and turn it to the on position (i.e. brake, engine lights on just before starting).

One click before starting the engine. But you don't need to start the engine for this proces.


Step 2:

Test you TPS before adjusting to ensure that it needs adjusting. Have your multi-meter and push the red

connection pin into the plug coming from the TPS. You will need to push it into the middle pin in he engine side,

then the black connection to the body so it's earthed or a ¼ panel bolt to ground. Doing this you will get a voltage

reading that should be around 0.45 Volts.


Step 3:

If you need to adjust the TPS, get the 7mm socket and the ¼ socket wrench and reach in to the TPS from

the engine side and loosen but DO NOT remove the bolts. Doing this will allow you to rotate the sensor.

Loosen both bolts until only finger tight not too loose.


Step 4:

Rotate the TPS; till you get 0.45 Volts, it may take a few minutes as it is very sensitive.

Tighten the bolts once it's set and double check the volts and away you go.

[KiLLeR2001]

I checked for resistance with the car off. I know on my fuel injectors if I probe both terminals, it came up with 11.5ohms. On the Throttle Position Sensor, when I go to probe the (B) and (C) terminals with the multimeter, nothing happens at all. Then I tried the (A) and (B) terminals, nothing. No matter what two terminals I tried there was absolutely no response.

edit: I just checked the voltage. With the harness plugged into the sensor and the car on... I probed the middle wire with the red probe on the multimeter and the black probe i put on the negative battery terminal...

On closed throttle it read 0.50V, and on WOT it read 4.12V. Still couldn't get it to read resistance on the sensor at all.

So is the TPS good or what?

[KiLLeR2001]

Anyone know if my TPS is bad or not based on the readings posted above?

[JTunedMotorsports]

thats tps is reading is fine both my cars are the same

[KiLLeR2001]

Could this be a possible CAS timing issue at all? One tooth off? If I put the CAS in the center it seems to not run good at all, only when I advance it almost all the way it seems to run its best.

[vutony]

for misfiring, check the following things: coilpacks, coilpack harness, ignitor chip, fuel pressure, fuel voltage, grounds, and even the engine harness which was the case for me.....i missed fire after 5k at woot

[KiLLeR2001]

I'm going to check the coilpacks next. Then probably ignitor chip.

Also, I have a Megan FPR and I've heard mixed reviews about them, is it possible under intense load the fuel pressure is crapping out? When I'm in the engine bay and I rev the engine up the fuel pressure stays around 40psi.

[vutony]

the psi is not suppose to constant at 40psi
it should fluctuate

[KiLLeR2001]

Originally Posted by vutony

the psi is not suppose to constant at 40psi
it should fluctuate

I've noticed when I rev it up, itll dip down then go back to around 40psi. Is it suppose to be at a certain PSI at a certain RPM?

[KiLLeR2001]

Whenever I start my car up after its completely cooled, it will do a small amount of sputtering every now and then until it warms up, then it doesn't do it as much... When I started it up and it was sputtering, I unplugged the TPS harness and viola, it didn't sputter anymore, should I just go ahead and replace the TPS?

[240srhatch]

yea, if its not that im almost 100% sure its the coolant temperature sensor.. i had a similar problem.

[KiLLeR2001]

Originally Posted by 240srhatch

yea, if its not that im almost 100% sure its the coolant temperature sensor.. i had a similar problem.

Replaced the coolant temp sensor not too long ago... So I know its not that.

[makulit054]

check all you sensors. have you checked the ecu for trouble codes.

[KiLLeR2001]

Originally Posted by makulit054

check all you sensors. have you checked the ecu for trouble codes.

ECU throws up 55. No malfunction.

[Lurpin]

Its your coilpacks. I just helped my friend fix his Redtop because he had the exact same problem. We changed the coilpacks and then the problem was solved.

[KiLLeR2001]

Just replaced my igniter chip and most of the bad misfiring has stopped now. It's still a little hesitant at the top end but to me it feels like the ignition timing is a little off.

Put a smile to my face when I could finally dump the throttle and not misfire. It's still not perfect though, gonna check the coilpacks next then the timing. I'll update this thread later.

[DOOK]

yep, check your timing... once you get that spot on you'll be surprised how much more it will come alive.

[KiLLeR2001]

Update: I don't think my igniter chip was messed up because when I started my car up this morning it had the same problems as before. So after work today I went to my friends house and switched my coil packs with his, absolutely no sputtering after this. So it was my coil packs, I'm pretty sure it's just one of them that isn't working properly because the misfire wasn't that bad.

[makulit054]

glad to hear your car is working properly.

[whowutwut]

You can easily find out which coil pack is bad by pulling them out one by one while the engine is idling. If there's no change in the idle, that one is the bad coil pack. I had two bad coil packs in my motor and the car was backfiring like crazy at WOT.