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Burning Question !

Daboss

By Daboss,
in Engines & Forced Induction

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Daboss Experienced

Daboss

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Hey there forum me again just popping in to ask a quick question about missfire. Car is running 10 psi and in the upper rpm it misses and then the car leans out afr's go up to 17. With throttle wide open and in the 4000 rpm range afr reads 12:1 but as soon as it hits 5000 there is a miss and an instant lean out. Now the plugs on the car are ngk coppers number 5 heat range and gap dropped to .7. Do you think that this is the culprit as I should be running a colder range plug? What I want to know is if the car leans out because of the miss or does the car miss beacause of the lean out and also the spark plugs seem to be at fault right? Fuel pump fairly new walbro 040 hardwired for full voltage, spark plugs might be a little fouled as i ran the car rich a few times and I mean rich as in black smoke out the exhaust and they are the ngk 5 coppers. So what do you think?

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rob82 Mentor

rob82

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Hey there forum me again just popping in to ask a quick question about missfire. Car is running 10 psi and in the upper rpm it misses and then the car leans out afr's go up to 17. With throttle wide open and in the 4000 rpm range afr reads 12:1 but as soon as it hits 5000 there is a miss and an instant lean out. Now the plugs on the car are ngk coppers number 5 heat range and gap dropped to .7. Do you think that this is the culprit as I should be running a colder range plug? What I want to know is if the car leans out because of the miss or does the car miss beacause of the lean out and also the spark plugs seem to be at fault right? Fuel pump fairly new walbro 040 hardwired for full voltage, spark plugs might be a little fouled as i ran the car rich a few times and I mean rich as in black smoke out the exhaust and they are the ngk 5 coppers. So what do you think?

If your getting an ignition missfire then your average 02 sensor reading will look as though it going lean as there is excess oxygen in the exhaust system. Your tuner/dyno operator should know whether or not it is running on less than 6 cylinders above 5000 during a dyno ramp and if it is then I would be willing to bet you have a missfire thats showing a lean condition. In which case you looking for a bad coil or plug or connector blah blah blah.

The heat range of the plug at 10psi will not be of concern. My thoughts are that if you cannot support at least 0.9mm gap at 10psi on a std rb25DET then its time for new coils!

Daboss Experienced

Daboss

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If your getting an ignition missfire then your average 02 sensor reading will look as though it going lean as there is excess oxygen in the exhaust system. Your tuner/dyno operator should know whether or not it is running on less than 6 cylinders above 5000 during a dyno ramp and if it is then I would be willing to bet you have a missfire thats showing a lean condition. In which case you looking for a bad coil or plug or connector blah blah blah.

The heat range of the plug at 10psi will not be of concern. My thoughts are that if you cannot support at least 0.9mm gap at 10psi on a std rb25DET then its time for new coils!

It happened at about 5000 rpm in third gear and boost was about 10 give or take a psi and the wideband showed like 17:1 afrs and it happened when we did it again. No dyno was just doin a road run to set in the boost, when it happened. The plugs are gapped down lower than 0.9 that I am sure of. So I guess it time for new colis then and :wub: I had these set all silicon up as well.

skyguy61 Collaborator

skyguy61

Posted
Posted

Hey Daboss,

I had a similar problem with mine running lean it went to 16 we didnt even go into boost pinging it head off , it turned out to be a dirty afm the wire had some oil on it, cleaned it with brake cleaner waited for it to dry then refitted afr back to normal. cheers

Daboss Experienced

Daboss

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No knocking or anything, just a miss in the upper rpm on wot. Also I noticed that on cruise anything from 3000rpm and above, at partial throttle now as I am cruising, the wideband reads rich meaning my afr's are lower than 10 as it just says rich on the screen of the wideband. Ok here is the deal installed an atmospheric with an antistall kit so the car doesn't stall, the car doesn't stall but now it runs rich at part throttle. Ideal is good varying in between 14.7 and 15 sometimes I see a 17 or 18 but I say thats just the ecu doing its thing to get it to stoich. Now at cruise 2000 rpm and under afr's are great 14.7 to 15. Now I have a stock untuned ecu and a z32 afm that is set up to work through an afc neo that is also untuned. Do you think chipping the ecu will help with the upper rpm rich problem? I cant tune down low because of the stock ecu and it being in closed loop mode.

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