Occasional Engine hesitation

[sam_uk]

Once every couple of hours the note of my engine changes slightly. Revs drop for 5-20 seconds and then it recovers.

Bleeding the fuel filter shows no obvious air, it seems that diesel comes straight out.

I have recently changed both the 'glass bottomed' and the cartridge fuel filters but the symptoms occured before the change. When changed I didn't see any 'slime' that might indicate diesel bug.

The engine doesn't fail and can be run for several hours at low/half/full revs, just with this occasional hesitation.

Visually the pipework all seems OK.

Although it does continue to run it does make me a bit nervous as _something_ must be causing it?

What's my next step? Is there a way of checking for air holes in the fuel system beyond just looking at it?

 

[Falling Star]

I had something similar once. Turned out to be caused by a blocked tank vent.

 

[sam_uk]

Just checked air in seems clear

Good idea, but just had a look at the air in and it all seems clear.

Any other ideas?

Thanks

Sam

 

[Falling Star]

Hmmm, well it will probably be some kind of fuel starvation IMO.

Are the filters in spec. regarding micron size i.e. if 10 should they be 30?

Or, the only other thing I can think of is a "sticky" injector causing the intermittent problem....

Maybe others have some ideas?

 

[sarabande]

is the pause associated with extra smoke from the exhaust, or is it just revs drop ?

 

[Caer Urfa]

Not saying you have the same problem as I did but awfully simular to yours.

My engine would run for at least 8 hrs then the rev's would just die off and then engine would eventually stop, bleed the fule lift pump then it would go for another 8 hrs and then same again would happen.

I spent 'months' trying to solve the problem including removing and cleaning both tanks, however cutting a long sad story short, check!

Is your filter gravity fed from the fuel tanks/ or are they above the bottom of the tank?

Check the distance from you fuel filter to your lift pump, I had moved the filters and 'increased' the previous distance so much so the lift pump must have been struggling to 'suck' the diesel through at times.

I finally first changed the fuel pipe from 1/4" dia to 3/8" dia to reduce any chances of blockage.

I lowered 'both my filters' to 'below' the tank bottom and moved them 'closer' to the lift pump to reduce the length of main hose to it.

In the picture below both fuel tanks after primary filters run to a diverter valve, then to the 'lift pump' which is on the side of the engine block below the header tank, the return system also has a secondry filter, in this set up I can run from 'either' tank, both tanks' or shut either tank down and change a filter while the engine is still running in emergency, I can also divert which tank the 'return fuel' goes to.

Touch wood this has solved the problem since three years back.

Other than if not any of the above you sound if you have fuel starvation to the pump OR muck in the diesel tank

Good luck
Mike

View attachment 27498

 

[billskip]

You are not demanding high energy power take off occasionally are you? like an electric fridge,air con or some sort of heating? you do not say how many revs it drops.

Does it happen only while under load,or also on tick over in neutral?

 

[KellysEye]

>Revs drop for 5-20 seconds and then it recovers.

It's normally a diesel leak that lets air in. I've mentioned this many time before but to find the leak put talcum powder around any joints/connections in the fuel pipes and fuel filter fittings, bleed screw, filter pump if you have one, and where the bowl screws onto the filter. Run the engine until the revs drop and you will find the leak, the talcum powder will have diesel in it. Diesel can go through a micrscopic hole that you can't see and can also be used to check welds. Please let us know how you got on with that.

 

[savageseadog]

It's an air leak or there might be some debris in the tank like paint flakes or a piece of sealer which may randomly move into position.

 

[sam_uk]

Thanks for the comments all

Falling Star: Filters are the same spec as the old ones I removed, but will double check in the manual

Sarabande: Not noticed any extra smoke but will check..

Caer Urfa: one filter is on the same level as the top of the tank, so I guess it's pump fed. The other is on the actual block. I think I will check for leaks / crud before moving the top one though!

Billskip: we don't have anything fancy like an electric fridge,air con or any sort of heating. We don't even have a rev counter, so can't answer that either! I have only noticed it under load. But as I say its a very occasional thing. I will try running in neutral for a while and report back

kellysEye top tip, thanks will get some talc later

savageseadog: Hope it's not floating ****, sounds like a nightmare to find

This has given me some useful stuff to investigate. Thanks again all

Best

Sam

 

[Juggler7823]

I had a similar problem which took some time to cure. The problem was an air leak into the CAV filter through the central threaded shaft. Make sure you change ALL the seals especially the small one on the shaft.

 

[wotayottie]

exactly those symptoms turned out to be the early stages of diesel bug with the muck temporarily blocking the fuel inlet pipe at the tank. Unlikely to be an air leak which by definition is a constant factor.

 

[essexboy]

Is it the Alternator loading ? The revs will recover as the governor "catches up"

 

[michael_w]

Sounds a bit like a problem I had. Turned out to be a bit of plastic floating round inside the tank; every so often it got sucked into the intake pipe.