XB9 sudden misfire.

[Fredrikrosen]

Hello.

I got a strange phenomenon today when driving my XB9S on the highway, i had been driving for about 80mph in 20 minutes when the engine suddenly misfired when i gave full throttle and the engine-light flickered. I did press in the clutch and the engine reved nice. And when driving off the highway was everything ok. I know the plug wires rubber caps are cracked, can it be the reason? But i did only happen on the highway.

I did check the system with ECMspy and did notice the AFV value had went from 115 to 135. The misfire did happen a few km from home so it might have gone high and not got back to normal value.

There was no fault codes.

Any ideas? Can it be the very hot weather we have today that affect? About 30 degrees C.

[njloco]

Well, first idea would be to replace your plug wires and then see if it happens again.

[Fredrikrosen]

Well, first idea would be to replace your plug wires and then see if it happens again.

Hi, it seems it was so called ”skip spark”. Probably in combination of very hot weather and speed around 130-140 km/h, but i will for sure change the plug wires any way. Thx for support.

[Cooter]

Probably not "skip spark".
And an AFV of 135 is telling you it has a problem. Most likely an intake leak.

[Fredrikrosen]

Probably not "skip spark".
And an AFV of 135 is telling you it has a problem. Most likely an intake leak.

It had 135 10 min after it happened, it went down till 116 again. Intake seals are new, but it did happen again a few days ago. When giving full throttle does it misfire but when open it slowly is it ok. This only happen on the highway in 5 gear when accelrating from like 140 km/h, not during normal accelration. Strange.

[Cooter]

That high load, high RPM situation taxes the fuel pump to max demand, and will show a weak one or compromised fuel line in the tank (pinholes).

An AFV of 135 is showing the ECM is trying to richen the global fuel map quite a bit, also possibly from a weak fuel pump?

You should test it.

[Fredrikrosen]

That high load, high RPM situation taxes the fuel pump to max demand, and will show a weak one or compromised fuel line in the tank (pinholes).

An AFV of 135 is showing the ECM is trying to richen the global fuel map quite a bit, also possibly from a weak fuel pump?

You should test it.

Sounds like a good theory, is it enough to check the fuel pressure or do i need to remove the pump?

[Fredrikrosen]

Today did i put back the stock Walbro pump, a new hose between the regulator and the metal filter and a new regulator from Quantum. It primes nice, have a good flow when putting the fuel line in a bottle. The fuel pressure was 50psi when the pump primes. Now just waiting for my new ht leads before i will take if for a test ride.

[mike lowary]

Today did i put back the stock Walbro pump, a new hose between the regulator and the metal filter and a new regulator from Quantum. It primes nice, have a good flow when putting the fuel line in a bottle. The fuel pressure was 50psi when the pump primes. Now just waiting for my new ht leads before i will take if for a test ride.

The regulator from Quantum is incorrect. The kpa rating is 300. Stock is 338. You now have less fuel pressure than stock

[mike lowary]

Quantum is 300 kpa=43.5 psi
Stock is 338 kpa=49 psi