RB25DET backfiring at high rpm full throttle

[Eric0]

Hello guys, first of all, thank you for stopping by and giving this a view! 

Okay so, the car ran perfectly after the tune but about 3 days later under full throttle, when it reaches about 6-8k it will start to backfiire about 2-4 pops.

Things I've done to try to fix the problem:

• Changed spark plugs and gaped to the tuners specification of .02
• Changed fuel filter

Things the car has done to it that relates:

• 550 Walbro (tuned with the car)
• Fuel pressure regulator

When I changed the spark plugs they all looked exactly the same, which makes me believe that the coils are working fine. But the plugs did look fouled as shown in the picture.

I also attached an image showing my gap that was perfectly at .02 without damaging the tip. My fuel pressure is about 38psi on idle. 

Any help would be greatly appreciated!! Thank you!

[GTSBoy]

You need more powerful coils.

[admS15]

0.02? Wow. As above get better coils.

[The Bogan]

I had to google, that's only 0.5mm, wow 

 

How much boost you running? What coils you got?

[Eric0]

8 hours ago, admS15 said:

0.02? Wow. As above get better coils.

I’m running stock rb25det coils. They need to be more powerful? It was running fine with them on the dyno. My fuel/air on idle is 13.7 and under load it’s 14-15psi

[Eric0]

8 hours ago, mlr said:

I had to google, that's only 0.5mm, wow 

 

How much boost you running? What coils you got?

I’m running 19psi of boost at the moment with stock rb25det coils.  

[admS15]

2 hours ago, Eric0 said:

I’m running stock rb25det coils. They need to be more powerful? It was running fine with them on the dyno. My fuel/air on idle is 13.7 and under load it’s 14-15psi

If the coils are 20 years old, they're at the end of their life. Replace with either fresh oem or splitfire coils. Dont bother with any of the other coloured ones. If you can borrow a set of known working coils to verify first, that would be ideal.

[GTSBoy]

2 hours ago, admS15 said:

known working coils

Known working - not at stock boost. At whatever power level you are running the engine at. the more boost, the harder the coils have to work.

[Eric0]

2 hours ago, admS15 said:

If the coils are 20 years old, they're at the end of their life. Replace with either fresh oem or splitfire coils. Dont bother with any of the other coloured ones. If you can borrow a set of known working coils to verify first, that would be ideal.

It’s making 425ho. Since everyone is telling me to change the coils then it has to mean something! Okay, I’ll give that a shot and check in with you guys again! 

Thank you all! 

Eric

[KiwiRS4T]

4 hours ago, Eric0 said:

I’m running stock rb25det coils. They need to be more powerful? It was running fine with them on the dyno. My fuel/air on idle is 13.7 and under load it’s 14-15psi

The official gap is 1.1mm but people often gap down to 0.8mm or .63 if coils are weak. If your tuner is telling you to gap down to 0.5mm he knows you have a problem. What plugs are you using?

Did you get that fuel air the right way round? Idle should be around 14.7 and under load around 12

You've either got a dodgy tuner or you have other problems with your car.

[admS15]

25 minutes ago, GTSBoy said:

Known working - not at stock boost. At whatever power level you are running the engine at. the more boost, the harder the coils have to work.

Yep, all of this.

[Dose Pipe Sutututu]

Splitfire coils (direct drop in) or R35 or 370Z coil conversion kit.

Don't install any coils that aren't black or blue in colour.

[Eric0]

5 hours ago, KiwiRS4T said:

The official gap is 1.1mm but people often gap down to 0.8mm or .63 if coils are weak. If your tuner is telling you to gap down to 0.5mm he knows you have a problem. What plugs are you using?

Did you get that fuel air the right way round? Idle should be around 14.7 and under load around 12

You've either got a dodgy tuner or you have other problems with your car.

Idle is currently 13.6 and load is 14-15. The spark plugs I’m running are NGK 4644. My technician recommended .023 and my tuner .02. I’m running stock coils but will soon install the splitfire. Do you think that will fix my air/fuel and high RPM backfire? My tuner will verify the tune tomorrow, hopefully. 

[Ben C34]

What? Why is it running leaner under load than idle?

Why running 13.5 at idle.?

 

The difference of 3 thou gap won't fix anything.

[KiwiRS4T]

2 hours ago, Eric0 said:

Idle is currently 13.6 and load is 14-15. The spark plugs I’m running are NGK 4644. My technician recommended .023 and my tuner .02. I’m running stock coils but will soon install the splitfire. Do you think that will fix my air/fuel and high RPM backfire? My tuner will verify the tune tomorrow, hopefully. 

No

Yes you need new coils but also a new mechanic and tuner by the look of things.

Do you have any dyno charts you can put up? Particularly interested in the afrs!

BTW how is your car being tuned (what kind of ECU do you have)?

[Eric0]

7 minutes ago, KiwiRS4T said:

No

Yes you need new coils but also a new mechanic and tuner by the look of things.

Do you have any dyno charts you can put up? Particularly interested in the afrs!

BTW how is your car being tuned (what kind of ECU do you have)?

I purchased the coil packs, they were $485 USD! Ouch! 

I’m running a link (AEM) ecu so my tuner can tune the car wirelessly without it being there. I shot him a text earlier today so I’m waiting for him to get back at me. 

 

Unfortunately, I don’t have any dyno sheets. If the car keeps running like hell after the new coil packs, new spark plugs at .02, and after my tuner verifies my numbers look okay, I think my problem will lay something in the fuel system like a fuel controller or something, right? 

[Murray_Calavera]

1 hour ago, Ben C34 said:

What? Why is it running leaner under load than idle?

Why running 13.5 at idle.?

 

The difference of 3 thou gap won't fix anything.

He might not be able to get a nice idle at 14.7 if he is using large old school injectors. Cruising around at 14.7 would be easier to tune as the injectors are out of the low slope range. 

Eric, what injectors are you running?

[KiwiRS4T]

2 hours ago, Eric0 said:

I purchased the coil packs, they were $485 USD! Ouch! 

I’m running a link (AEM) ecu so my tuner can tune the car wirelessly without it being there. I shot him a text earlier today so I’m waiting for him to get back at me. 

 

Unfortunately, I don’t have any dyno sheets. If the car keeps running like hell after the new coil packs, new spark plugs at .02, and after my tuner verifies my numbers look okay, I think my problem will lay something in the fuel system like a fuel controller or something, right? 

So your car is not sitting on a dyno? The tuner is just playing with the maps? Do not gap your new plugs at .02 go to 32 thou (.8mm or .032 in)

The fuel controller is the ecu so if you reckon the pump and fpr are fine that just leaves the injectors so as Murray says what kind are they and could they need cleaning and testing?

Do you have any idea what the duty cycle is on the injectors? I still think your tuner does not know what he is doing.

[tridentt150v]

+1 on resetting your plug gap to 0.8mm/0.032"......the ability of your spark plug providing any sort of meaningful spark at 0.02" would be a real struggle esp. at higher revs.

[Eric0]

6 hours ago, Murray_Calavera said:

He might not be able to get a nice idle at 14.7 if he is using large old school injectors. Cruising around at 14.7 would be easier to tune as the injectors are out of the low slope range. 

Eric, what injectors are you running?

I’m running deatschwerks 740cc fuel injectors. Should I be driving the car at all? I’ve been staying out of boost.