Missfiring after JWT build - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

s13pimp · 06-09-2009, 05:29 PM

After installing msd 72lb injectors (with soldered in resistors) with my JWT ecu on my s13 sr20det, my car seems to be missfiring slightly when it warms up (not at all when it's cold). the missfire does not seem to occur under moderate to heavy throttle, just during idle and maybe very, very low throttle. Any suggestions as to where to start debugging? Thanks!

*4x4le* · 06-10-2009, 07:43 PM

is your o2 sensor hooked up? Jwt ecus run really lean at idle if there is no o2 sensor. The reason its not doing it when warming up is because its running a little richer during warm up. Do you have a wideband? What is your afrs?

This is one of the many reasons that pretuned ecus arnt the greatest things since sliced bread. Each car still wants different things from a tune to run optiomal.

s13pimp · 06-10-2009, 08:27 PM

Quote:

Originally Posted by 4x4le

is your o2 sensor hooked up? Jwt ecus run really lean at idle if there is no o2 sensor. The reason its not doing it when warming up is because its running a little richer during warm up. Do you have a wideband? What is your afrs?

Actually, i think it is running a little rich at idle. However, it is still running the original O2 sensor (i believe). When should those guys get changed? I have no wideband and i dont really know what my afrs are. However, i do have a egt gauge and it reads really low at idle and gets up to about 500 degrees celcius when im just cruising at 55-60mph. Dont know about idle though really.

As for the pre-tuned ecu's not being optimal, i totally agree! However, i have neither the know how nor the money to tune the car myself or run standalone or other such tuning options. The JWT tune is the best i can do at the moment.

steve shadows · 06-12-2009, 02:09 AM

JWT is a preitty good option IMO, I think he does a good job.

I have done some dyno assisted tune ups with cars using JWT ecus and they all made pretty good power.

As long as the tune is ordered by your for the right set up

If you tell JWT you will not be running closed loop (IE using your stock 02) they will take that into account. Pretty basic stuff.

Just most don't think of it when ordering their rom tunes.

either way I would invest in a real standalone eventually. There is nothing like having a solid fully integrated unit in it's own nice case with solid R and D and integrated tuning engineering and history as well as support behind it. But for most who are far from dynos a tuned rom is a good solution.

s13pimp · 06-17-2009, 02:40 PM

So you're saying that my stock O2 sensor is what's causing my car to miss when it's warmed up? I am having a hard time understanding this concept. Can someone clarify/ explain that to me?

*4x4le* · 06-17-2009, 02:56 PM

Because most every jwt map i have looked at is set to idle very lean but if your o2 sensor works it will idle stoich. Too lean will cause it to run bad. And its just a possibility. Have you checked it out yet?

s13pimp · 06-17-2009, 02:59 PM

I think it's running rich only because it smells like it is. This might be because of my vented bov though and catless exhaust. I havent had any chance to do any diagnostic yet. This weekend i will unplug each injector one by one and see if that makes a difference. Then I'll re-trace my wiring and check my solder joints.

s13pimp · 06-29-2009, 02:41 PM

Okay, so after doing a bit of trouble shooting, I realized that the car is not missfiring, but is running rough in a way that resembles miss fire. I found out that this rough idle is actually due to the fact that it is running lean at idle just like 4x4le said. I figured this out when i noticed that after coming off boost and coasting to a stop, my idle goes way down (to like 500) and the car runs rich because of my atmospherically vented bov. At this time, it does not do that "miss fire" like idle because it is running rich. Thanks 4x4le!

*4x4le* · 06-29-2009, 03:21 PM

haha, Well I must say that allot of our customers have actually been jwt ecu users that were not happy with their tune, like you. I have personally seen this issue on my car with a jwt ecu that was supposedly tuned for my setup, and I have seen it on others.

Also when Im tuning peoples cars you get to see what conditions are causing certain problems (such as rich when and lean when) and when it needs more or less fuel or timing.

s13pimp · 06-30-2009, 02:33 PM

Yeah, unfortunately I'm going to have to deal with this setup for a while but on my next setup (which will involve an rb25) i am thinking of going with the nistune system and getting some professional help with the actual tuning of it. I feel that will help me a lot with diagnostics and it will give a more precise tune.

fast-datsun · 07-04-2009, 11:04 AM

You are venting your BOV to atmostphere right.......Computer is looking for air that your expelling and you will have to make changes to allow it to recover from missing the air. IT IS NOT THE JWT TUNE. tighten up bov and raise the idle or get the HKS box to allow the ECU to compensate for the lost air.....

handinpants · 07-11-2009, 08:34 PM

JWT sucks, change your maf and see what happens. I have JWT, I don't even know the tuning parameters, i'm like helen keller, i 'm going nistune.

steve shadows · 07-11-2009, 11:25 PM

Are you sure you are using the correct resistors?

and I also don't understand why you guys all try to use Top Feed low impedence injectors and then soder in resistors

Just buy the Nismo or Tomei high quality side feeds and be done with it?

This is probably part of the issue.

To cause a mis-fire you need a pretty major change in fuel or spark input

*4x4le* · 07-12-2009, 01:08 AM

Quote:

Originally Posted by steve shadows

Are you sure you are using the correct resistors?

and I also don't understand why you guys all try to use Top Feed low impedence injectors and then soder in resistors

Just buy the Nismo or Tomei high quality side feeds and be done with it?

This is probably part of the issue.

To cause a mis-fire you need a pretty major change in fuel or spark input

He already said in post 8 that he is running lean at idle and its not actually a common misfire for-say. Its stumbling due to the lean mixture. That is very common at idle if you have a lean mix, im sure you have seen this.

JWT ecus are programmed to run extreamly lean at idle but the o2 sensor corrects this normally. I feel that his problem is with his o2 sensor.

People use low impedance injectors because they work. I have been running e-85 through mine for over 2 years, no problems.

fast-datsun · 07-13-2009, 11:05 AM

Many sensors effect the idle and how the car runs. JWT has put many hour of R&D into tunning the computer for the average driver, but if all the other parts of the system are not fuctioning correctly it can not correct the problem. Make sure mechanical and sensor are good and and adjusted correctly then car will run correctly. I see cars all the time with what owner thinks is a computer problems and 9 of 10 times its is not....

06-09-2009, 05:29 PM	#1
s13pimp Join Date: Jul 2007 Location: ny Age: 22 Posts: 26 Trader Rating: (0)	Missfiring after JWT build After installing msd 72lb injectors (with soldered in resistors) with my JWT ecu on my s13 sr20det, my car seems to be missfiring slightly when it warms up (not at all when it's cold). the missfire does not seem to occur under moderate to heavy throttle, just during idle and maybe very, very low throttle. Any suggestions as to where to start debugging? Thanks!

06-10-2009, 07:43 PM	#2
4x4le autovaughnperformance.com Join Date: Nov 2008 Location: Manchester, Tn Posts: 467 Trader Rating: (0)	is your o2 sensor hooked up? Jwt ecus run really lean at idle if there is no o2 sensor. The reason its not doing it when warming up is because its running a little richer during warm up. Do you have a wideband? What is your afrs? This is one of the many reasons that pretuned ecus arnt the greatest things since sliced bread. Each car still wants different things from a tune to run optiomal. __________________ NEW/CHEAP s13/14sr CAS Authorized NIStune Dealer

06-17-2009, 02:56 PM	#6
4x4le autovaughnperformance.com Join Date: Nov 2008 Location: Manchester, Tn Posts: 467 Trader Rating: (0)	Because most every jwt map i have looked at is set to idle very lean but if your o2 sensor works it will idle stoich. Too lean will cause it to run bad. And its just a possibility. Have you checked it out yet? __________________ NEW/CHEAP s13/14sr CAS Authorized NIStune Dealer

06-29-2009, 03:21 PM	#9
4x4le autovaughnperformance.com Join Date: Nov 2008 Location: Manchester, Tn Posts: 467 Trader Rating: (0)	haha, Well I must say that allot of our customers have actually been jwt ecu users that were not happy with their tune, like you. I have personally seen this issue on my car with a jwt ecu that was supposedly tuned for my setup, and I have seen it on others. Also when Im tuning peoples cars you get to see what conditions are causing certain problems (such as rich when and lean when) and when it needs more or less fuel or timing. __________________ NEW/CHEAP s13/14sr CAS Authorized NIStune Dealer

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06-12-2009, 02:09 AM	#4
steve shadows In time-out for misbehaving. Join Date: Aug 2003 Location: LA and OC Posts: 7,409 Trader Rating: (3)	JWT is a preitty good option IMO, I think he does a good job. I have done some dyno assisted tune ups with cars using JWT ecus and they all made pretty good power. As long as the tune is ordered by your for the right set up If you tell JWT you will not be running closed loop (IE using your stock 02) they will take that into account. Pretty basic stuff. Just most don't think of it when ordering their rom tunes. either way I would invest in a real standalone eventually. There is nothing like having a solid fully integrated unit in it's own nice case with solid R and D and integrated tuning engineering and history as well as support behind it. But for most who are far from dynos a tuned rom is a good solution.

06-17-2009, 02:40 PM	#5
s13pimp Join Date: Jul 2007 Location: ny Age: 22 Posts: 26 Trader Rating: (0)	So you're saying that my stock O2 sensor is what's causing my car to miss when it's warmed up? I am having a hard time understanding this concept. Can someone clarify/ explain that to me?

06-17-2009, 02:59 PM	#7
s13pimp Join Date: Jul 2007 Location: ny Age: 22 Posts: 26 Trader Rating: (0)	I think it's running rich only because it smells like it is. This might be because of my vented bov though and catless exhaust. I havent had any chance to do any diagnostic yet. This weekend i will unplug each injector one by one and see if that makes a difference. Then I'll re-trace my wiring and check my solder joints.

06-29-2009, 02:41 PM	#8
s13pimp Join Date: Jul 2007 Location: ny Age: 22 Posts: 26 Trader Rating: (0)	Okay, so after doing a bit of trouble shooting, I realized that the car is not missfiring, but is running rough in a way that resembles miss fire. I found out that this rough idle is actually due to the fact that it is running lean at idle just like 4x4le said. I figured this out when i noticed that after coming off boost and coasting to a stop, my idle goes way down (to like 500) and the car runs rich because of my atmospherically vented bov. At this time, it does not do that "miss fire" like idle because it is running rich. Thanks 4x4le!

06-30-2009, 02:33 PM	#10
s13pimp Join Date: Jul 2007 Location: ny Age: 22 Posts: 26 Trader Rating: (0)	Yeah, unfortunately I'm going to have to deal with this setup for a while but on my next setup (which will involve an rb25) i am thinking of going with the nistune system and getting some professional help with the actual tuning of it. I feel that will help me a lot with diagnostics and it will give a more precise tune.

07-04-2009, 11:04 AM	#11
fast-datsun Leaky Injector Join Date: Aug 2002 Posts: 107 Trader Rating: (0)	You are venting your BOV to atmostphere right.......Computer is looking for air that your expelling and you will have to make changes to allow it to recover from missing the air. IT IS NOT THE JWT TUNE. tighten up bov and raise the idle or get the HKS box to allow the ECU to compensate for the lost air.....

07-11-2009, 08:34 PM	#12
handinpants In time-out for misbehaving. Join Date: Feb 2008 Location: los Angeles Age: 27 Posts: 1,563 Trader Rating: (26) Rides Gallery: handinpants	JWT sucks, change your maf and see what happens. I have JWT, I don't even know the tuning parameters, i'm like helen keller, i 'm going nistune.

07-11-2009, 11:25 PM	#13
steve shadows In time-out for misbehaving. Join Date: Aug 2003 Location: LA and OC Posts: 7,409 Trader Rating: (3)	Are you sure you are using the correct resistors? and I also don't understand why you guys all try to use Top Feed low impedence injectors and then soder in resistors Just buy the Nismo or Tomei high quality side feeds and be done with it? This is probably part of the issue. To cause a mis-fire you need a pretty major change in fuel or spark input

07-13-2009, 11:05 AM	#15
fast-datsun Leaky Injector Join Date: Aug 2002 Posts: 107 Trader Rating: (0)	Many sensors effect the idle and how the car runs. JWT has put many hour of R&D into tunning the computer for the average driver, but if all the other parts of the system are not fuctioning correctly it can not correct the problem. Make sure mechanical and sensor are good and and adjusted correctly then car will run correctly. I see cars all the time with what owner thinks is a computer problems and 9 of 10 times its is not....