BX 22 High RPM misfire

[DOC4444]

I searched for this on this sub-forum, but received mostly unrelated threads. So, I guess I need to post to get a more specific set of responses. Tractor is 10 years old, about 1000 hours, owned by us since new. After a restart while still warm from previous running, it developed a mid, to full-throttle misfire never observed before. The misfire was accompanied with puffs of black smoke out the exhaust. Starts and runs fine up to mid-throttle.

Air filter did not look bad and a new filter made no difference. I plan to change the fuel filter under the deck. Should I also replace the one in the engine compartment at the same time? That was replaced a couple of years ago because it cracked and was leaking. First time there have been any issues with running cleanly.

I live a long way from our dealer. I am having someone pick up parts for me tomorrow AM, so besides the two fuel filters, would anything else be good to pick up for this first pass? Is there a replaceable screen in the fuel pump, etc?

Thanks in advance for your assistance.

DOC

 

[pjbci]

Change the fuel filters first and see what happens. It cant hurt to try. It sounds to me like an injector tip has blown off causing a squirt of fuel each time it fires instead of emitting a fine mist of fuel. A faulty injector can be easily confirmed or ruled out by loosening each injector line one at a time with engine running at high rpm and listening for a change in sound.

 

[csr0831]

Hmmmm.....I'm no machanic, but the fuel filters would be my first step, largley because that would be the cheapest thing to try frist. Failing that.....maybe a bad headgasket that fails only as you reach the pressures generate by the higher RPM,s? are there any signs of a blown gasket in your coolent or oil (soot, foaming, etc.)? Just a though....may be way off base. Good luck and let us know what you find!

 

[motled]

Seat safty switch.

 

[DOC4444]

PJ,

Thanks! If the filter change does not take care of it, could you describe in detail what you mean by "loosening" an injector. Is this not a high pressure system that could cause injury?

Thanks again,

DOC

 

[pjbci]

Not the injector, an injector line or tube that runs from pump to the injector. There will be a nut on each end of it. One at pump and one at injector. Loosen whichever end you can get too easily with a tubing wrench if you have one. Yes it is a high pressure system so just loosen the nut a quarter turn or so. Do not put your fingers near the nut. I wear good leather gloves and hold the wrench by the end. It will spit tiny amounts of fuel each time it fires but it wont soak you. Only loosen it for a few seconds listening for a change in the motor noise. Good injectors will make a very noticeable change in engine noise. A bad injector will only make a small change in noise or no change at all.

 

[DOC4444]

Changed the filter between the tank and the lift pump and it ran perfectly for 10 minutes. However, when it finally got fully up to temp, it started misfiring as badly as before. I suppose the filter could have plugged again, but I tend to doubt it, because it had run fine before from cold and only started to misfire after being fully warm.

Any further thoughts would be appreciated....

Thanks,

DOC

 

[oldnslo]

Valve clearance, once warm a tight valve could be held slightly open causing loss of compression.

 

[pjbci]

Valve clearance, once warm a tight valve could be held slightly open causing loss of compression.

True. Could very be the problem

 

[DOC4444]

Is there a clearance that can be checked and/or adjusted, or are we talking valve job here?

Thanks!

DOC