Project 8 3CX stopping and starting.

[Scraperman]

I have a problem with my Project 8 3CX that has just started to happen. It is all about the engine momentarily trying to stop at a certain speed.
At about 1200 revs the engine momentarily slows right down almost to a stop but then fires up again. The whole episode only lasts for about half a second and then she runs again for another 30 seconds or so and then does it again. It is just as if I am playing with the ignition key. Turning it off until just before the engine stops and then turning the ignition back on again.
Bizarrely, it only does it at about 1000 revs. It doesn't do it on tickover, nether does it do it if running faster than the one speed. If say she is running at 1400 revs or faster or on tickover it doesn't happen.

It has only started to do it since I had to replace the broken rear window. Because the wiper motor is mounted within the window glass after I had finished the job I went into the fuse box and cleaned it all up. I may have moved fuses, I didn't remove any, I didn't need to.

It almost sounds like an ignition switch problem but I didn't need to touch that.

I wondered if anyone would be kind enough to suggest what might be wrong please. Any help or advice would be greatly appreciated.

 

[topkit]

I Would pull all of the fuses one by one and make sure you have clean connections as those push in fuses get really dusty, I had an electrical intermitant fault on a older Alfa GTV and i went through all of the fuses and found one that looked fine but when you touched the two tabs at the base of the fuse the connection at the top opened up which was causing the problem, Although the way you are describing your problem makes it sound more like fuel starvation to me that usually can throw up a similar symptom, You may have some crap floating around, Funnily enough I changed the fuel filter on my New Holland LB110 last week and I also whipped of the drain trap and sediment bowl, The bottom half of the bowl was full with sludge which came out in one lump, When you look at it You can now see it full of clean fuel.

 

[DaveDCB]

Fuel cut off solenoid maybe? Abit odd given that it’s at very specific revs.. but a fault one gives a similar problem.

 

[Gecko]

A test lamp across the fuel solenoid will tell you if the power is being cut, but the fact it recoveres suggests its not electrical fault.
Check the air hose from the airfilter, and the airfilters themselves (might be collapsing).
Check the sedementor for contamination - when I pulled mine apart, the rubber seal was old and wouldn't reseal.

 

[Scraperman]

I Would pull all of the fuses one by one and make sure you have clean connections as those push in fuses get really dusty, I had an electrical intermitant fault on a older Alfa GTV and i went through all of the fuses and found one that looked fine but when you touched the two tabs at the base of the fuse the connection at the top opened up which was causing the problem, Although the way you are describing your problem makes it sound more like fuel starvation to me that usually can throw up a similar symptom, You may have some crap floating around, Funnily enough I changed the fuel filter on my New Holland LB110 last week and I also whipped of the drain trap and sediment bowl, The bottom half of the bowl was full with sludge which came out in one lump, When you look at it You can now see it full of clean fuel.

Thank you very much for your reply. I am certainly going to have a look at the fuses but it just seems strange to me that it only happens at a certain engine speed. I have never had a digger before that had an ignition key which switched off the engine and to be truthful I don't know how that works. I am only used to an ignition switch to turn the starter motor and a cable or rod to operate the fuel pump to stop an engine. Having said that of course all my pickups have had a system that operates entirely off the key.

 

[Scraperman]

Fuel cut off solenoid maybe? Abit odd given that it’s at very specific revs.. but a fault one gives a similar problem.

Thank you very much for your reply. Yes, I wondered if it might be something like that but I am ignorant of fuel cut-off solenoids. I think I need to get the manual out.

 

[Scraperman]

A test lamp across the fuel solenoid will tell you if the power is being cut, but the fact it recoveres suggests its not electrical fault.
Check the air hose from the airfilter, and the airfilters themselves (might be collapsing).
Check the sedementor for contamination - when I pulled mine apart, the rubber seal was old and wouldn't reseal.

Thank you very much for your reply. All very helpful. I have a funeral today but will get back to the problem tomorrow and will report back.

Thanks guys.

 

[Gecko]

I have never had a digger before that had an ignition key which switched off the engine and to be truthful I don't know how that works. I am only used to an ignition switch to turn the starter motor and a cable or rod to operate the fuel pump to stop an engine.

It's basically the same mechanism - the solenoid serves the function of pulling the stop knob.

 

[Scraperman]

It's basically the same mechanism - the solenoid serves the function of pulling the stop knob.

Thank you. That makes sense. Any idea where the solenoid is on a 3CX or are they always part of the injection pump ?

 

[Mick-the-fitter]

Sounds like a vibration problem to me! A wire rub out maybe, send photo of injection system and pump please

 

[CPS]

Sounds like a vibration problem to me! A wire rub out maybe, send photo of injection system and pump please

I agree, I'd put direct power to the solenoid to rule that out

 

[Scraperman]

Sounds like a vibration problem to me! A wire rub out maybe, send photo of injection system and pump please

Thank you for that. I might be able to get a photo. this afternoon if I get back in time, otherwise I will do it tomorrow.

 

[Scraperman]

I agree, I'd put direct power to the solenoid to rule that out

Thanks very much. I won't tamper until I have got the photo(s) on here.

 

[Gecko]

Any idea where the solenoid is on a 3CX or are they always part of the injection pump ?

There are at least three pumps that might be fitted - in terms of your current problem, it doesn't matter much.

 

[jd6820]

Item circled red in picture 2 is incorrect, the solenoid is marked as number 2.

 

[Gecko]

Item circled red in picture 2 is incorrect, the solenoid is marked as number 2.

Thanks - fixed it.

 

[V8Druid]

Sounds like a vibration problem to me! A wire rub out maybe, send photo of injection system and pump please

was thinking along exactly the same lines .... specific revs setting up a particular vibration movement ... if solenoid is weak it might even be shaking it enough to make it let go, momentarily - cuts back in then repeats letting go ? (ditto scenario with a 'rub through' on a cable - or even a break in a wire)

 

[Scraperman]

Firstly, apologies for not replying to the last two posts. I did look at emails quickly this morning but there were no notifications of new contributions.

I would like to think I have fixed the problem but the most important thing is to say thank you to everyone who has helped me with this problem. I have been working with my own farm machinery and diggers as a contractor for over 60 years and that may give an indication as to my age. Until the contribution appeared on this topic I had never even considered how you stop a diesel engine just on the key. And so it has been a learning curve for me.

Now to the today's progress.

Firstly, I found the solenoid and initially powered it externally after removing the connections and could hear the click when the rod, or whatever is inside, moved into the run position. So I put the connections back on the solenoid and tested for a current at the solenoid using a multi-meter after turning the ignition on. Nothing. So then I went to the fuse box. I took the relevant fuse out and put a new one in but it still didn't work. When you turn the ignition on in this machine a hooter goes off and so I found the fuse for that and swapped it with the solenoid fuse (they are both 5amp) Still no good. I inspected the terminals on the solenoid and one looked a bit dodgy and so I replaced it. I then went back to the fuse box and, long story short, after playing around with the two old fuses and also new ones I got just over 12 volts at the solenoid.

Time to see if the old girl will run. I turned the key and she purred into life. I tried the engine at all speeds and couldn’t get the original problem to re-surface. So, it’s time for a quick trip down the fields, slowing down, speeding up, nearly stalling it, but it ran perfectly.

Mick-the-fitter asked for a photo. of the solenoid and so here it is :

Once again, many many thanks to you all. I don't know where I would have started without the help that I have received from this Forum.

 

[DaveDCB]

To tip, if you want to stop it being taken by anyone just loosely unplug the solenoid slows them down anyway!

 

[Mick-the-fitter]

Many thanks, just for my interest really but that is where I was heading, in this set up the small solenoid covers a hole in the pump with a rubber seal when the power is off, the later Delphi pump was similar in operation, and that said had similar operating issues! Glad you found the issue,