Technical 2.8JTD Ducato motorhome, engine hesitancy

[Washburn]

A similar thing can afflict Moto Guzzi bike engines, viz- at intermediate, low throttle openings, the same symtoms amd also some surging of power and revs. This has now been traced to a weak cam chain tensioner spring and modified parts are feely available and the fix widely known now amongst owners. So, is it possible that a cambelt tension issue is giving a similar thing on the Ducato engines? It need not be loose enough to slip, but it may be the case that it would slip, if loose enough to cause the indicated symtons. Just a thought! The end result being that the timing will wander unless the engine is under load and speed increasing or decreasing; this is the thing with the bike engines= the chain is not being kept tight by an indresing throttle. I own one but have not had this show up yet, but have only done 8 miles on it yet!!

Hi, thanks for these thoughts. The previous owner has changed the cambelt last year, I believe is was a DIY job. Could a cambelt change without changing tensioner affect the balance in the engine in this way? This engine is a common rail diesel with ECU-managed injection. In which way would a "balance" issue around the cambelt affect fuel injection, fuel/air mix etc, would it screw up the valve settings in comparison to the injection perhaps? Appreciate your thoughts on this.

 

[Ocwobio]

Hi,,, no, a cambelt won't affect 'balance' of an engine, as such. and if mis-timed, valve events and injection being off the mark would make an engine run very badly, not at all, or go BANG! If it is that a tensioner was not tensioning correctly, for some reason, it might be possible for symtoms like those mentioned to be apparent. The bike issue involves motors with camchains, not belts, but maybe the same kind of result could come about?
Think thus- an engine under full or increasing load and rpm, the belt would be pulled tight and under tension, decreasing rpm would leave it loose, but as no throttle input (foot off the gas) it might go un noticed. In the mid positon, as indicated, the belt might be neither loose nor tight, and able to let anything driven from it (cams, injector pump- but only a pressure issue as the injectors are time electronically of course) vary in speed related to the crankshaft, either up or down, sloppy if you will. That all said, there will be a crank AND a cam sensor, presumably and one or both wil set injection timing electronically, but if the belt is flapping the 2 sensor outputs to the ecu will vary and conflict, which may be what causes the fault. Imagine the belt as a piece of string,,, pulling = under good tension, push = not so,,, alternating between one state and the other - mayhem. Hope you get the ides, lol! And a fix!!

 

[Washburn]

Ocwobio, many thanks for your elaboration, appreciate it!

I've also learned from another 2.8 JTD owner who too had this issue many years ago that it in his particular case had been caused by the engine being chiptrimmed. That leaves me with 3 possible causes based on forum knowledge so far:

1. Chip trim screwing up mid range power in some way
2. Throttle pedal bad signal quality at mid position
3. Cam belt tensioning issue

In my case, I've just come in contact with the first owner of the vehicle, who had owned it the first 12 years, and he assured me it has not been trimmed. So in my case it's probably not that issue.

I've booked my Ducato for a visit to a Fiat specialist in the area. On Sep 4th they will be able to dig into this a bit more. I'm going to suggest to them testing throttle signal with oscilloscope, and also look at the cambelt tensioner. It's valuable - I hope for them too - to be able to give them these suggestions when I bring in my vehicle.

I'm looking forward to the workshop visit and will report back after Sep 4th with more info on how this develops. Fingers crossed!

 

[corcai]

There are so many things it could be, e.g. dirty high pressure regulator, faulty wiring etc, have you checked if there are any stored codes. Definitely worth looking at the throttle. Does your van have the egr option fitted a sticky egr valve could cause hesitancy. If so try clamping off the egr hose temporarily.

 

[oigle]

Possibly an issue that could be solved with a remap. If the mapping is not exactly right at that rev/throttle/etc point it could be giving a fluctuating fuel flow. I had huge problems with a Benz diesel - big flat spot from idle. A remap fixed it beautifully. Takes off like a petrol engine now.

Ian.