Hi everyone,

I would need you expert opinion on an issue I'm stuck with. At work we have a 2018/19 Transit with the 2.0 TDCI engine that keeps losing power at motorway speeds, at around 120 kph it randomly starts decelerating like you jumped off the throttle. It stays this way 10-15 seconds and then like nothing happened everything carries on. During this "event" it doesn't make a difference if you change gears, or try to do play with the throttle.

Forscan gives no relevant error messages. Tried to log live data, such as boost pressure, delivered fuel, injector quantity deviation, etc. but nothing seemed out of the ordinary. All injectors are providing the same values give or take, no major difference.

Fuel filter has been changed, someone who previously serviced the van in it's previous life used some grease or silicone on the threads of the fuel filter housing. Sadly this didn't make the problem go away, even though it runs smoother and feels more powerful.

The only progress I was able to make is that now I can consistently replicate the fault by driving on the motorway in 5th gear, accelerate up to about 3100 rpm and then it loses power every time. At lower speeds it doesn't have any issues revving above 3100 rpm regardless what gear it's in.

Did you have anything similar? What values would you look at in Forscan's live data that could point me in the right direction? Thanks in advance.

It sounds like someone has put or enabled a Speed Limiter. 

2 hours ago, Tizer said:

It sounds like someone has put or enabled a Speed Limiter. 

Ah!!!

That would make sense 👍

7 hours ago, Tizer said:

It sounds like someone has put or enabled a Speed Limiter. 

Good thinking, I wish it would be that simple. Sadly it also happened at lower speeds, once it started acting up in the middle of a tunnel where I can only do 80 kph due to average speed check.

The issue is quite intermittent, that ~130 kph/5th gear is only a guaranteed way to trigger the issue. But otherwise it happened at 110-120 kph/6th gear as well. I'm quite lost for ideas at this stage.

I'll do a DTC check this morning once again to see if there's any change and post it here. Maybe I get lucky this time and there's a fault code.

I had a, new at the time, 2012 MK3 Focus 1.6 TDCi that was doing this, it would just stop accelerating.

I rejected the car in the end as they could not find the cause

If it's doing it at different speed then it can't be a speed limiter, but it could be a rev limiter.

Get the software reloaded in the PCM as well, in case it's had a dodgy (laptop) remap

Just check it hasn't got a deactivated immobiliser from a previous owner that's causing a CAN issue

Check for good earths and good alternator performance

Other than that, I really don't know, sorry

38 minutes ago, DaveT70 said:

I had a, new at the time, 2012 MK3 Focus 1.6 TDCi that was doing this, it would just stop accelerating.

I rejected the car in the end as they could not find the cause

If it's doing it at different speed then it can't be a speed limiter, but it could be a rev limiter.

Get the software reloaded in the PCM as well, in case it's had a dodgy (laptop) remap

Just check it hasn't got a deactivated immobiliser from a previous owner that's causing a CAN issue

Check for good earths and good alternator performance

Other than that, I really don't know, sorry

Thanks Dave, appreciate it. I'll keep trying for the things you've mentioned.

48 minutes ago, DaveT70 said:

If it's doing it at different speed then it can't be a speed limiter, but it could be a rev limiter.

Just as additional detail, the revs can go above that 3100-ish, but for some reason when that gear/rev/speed constellation aligns up it triggers the fault.

But otherwise you can rev it higher (not that I normally do, but had to rule that out).

Small test drive today, looking at the live data the only thing that stands out is that there's still pressure on the fuel rail, but the engine fuel rate drops to 0 g/s.

Am I right to think that even with the fuel filter repalced there is some sort of blockage in the fuel system? (There was some grease/silicone-like gunk in the fuel filter housing, someone probably used it on the threads... No idea why.)

6 minutes ago, caffeinedealer said:

Am I right to think that even with the fuel filter repalced there is some sort of blockage in the fuel system?

Unlikely, it sounds like the Injectors are being commanded off.

If there is a Commanded and Actual Fuel Pressure PID then bring them both up and compare them. The Pressure in the Fuel Rail should stay high until you switch off where it is normally commanded to dump most of the pressure.

The Grease on the threads is an old school way of checking for Air Leaks in the Fuel System.

Have you monitored what the engine temperature is doing when it happens. Also an oil change/service warning light will cause it to lose power but I think it does it all the time.

3 hours ago, Tizer said:

The Grease on the threads is an old school way of checking for Air Leaks in the Fuel System.

Learned something new today, both about the air leak and how the fuel rail works! The grease also fits the bill with the fuel system issue, likely someone before us faced this issue (and decided to sell).

I'll have a look again tomorrow, see if I actually have this data recorded, and if not I'll take her for a spin.

Thanks for your help and patience. Coming from two older Seats (1.6 petrol, 1.9 TDI) the Transit is an uncharted territory for me.

8 minutes ago, gds1972 said:

Have you monitored what the engine temperature is doing when it happens. Also an oil change/service warning light will cause it to lose power but I think it does it all the time.

The temperature was steady on the dash, no change or fluctuation. I'll add the temp to the live data tomorrow to be able to back it up with numbers.

No service light on the dash, but will double check things with Forscan. Thanks a mill!

Air leaks into the Fuel usually cause starting problems rather than the problems you are having because building up enough Pressure when the Engine is being turned slowly on the Starter is hard enough without air being added to the Fuel.. During normal running the High Pressure Pump might typically only be running at 30% of its full capacity.

The pressure in the Fuel Rail is regulated to its optimum amount, too much or too little can cause problems.

When checking Live Data on a Diesel it is normal to bring up the MAP and MAF as well as Fuel and Turbo PID's and also the Speed, RPM, and Accelerator Pedal position so you can work out what was happening when the problem occurred.

From your descriptions so far I tend to agree with Dave that it is likely to be Software related rather than something physical.

10 hours ago, Tizer said:

From your descriptions so far I tend to agree with Dave that it is likely to be Software related rather than something physical.

Yep, I would be tempted to update or reload the PCM software and check CAN performance

Thanks everyone for taking the time and help. I'll try a fresh log of live data on Tuesday (long weekend), and if we still can't find anything we will have to sit down and figure out if we should carry on chasing this issue or choose another route.

Hope you all have a great weekend!

On 5/2/2025 at 1:54 PM, caffeinedealer said:

Thanks everyone for taking the time and help. I'll try a fresh log of live data on Tuesday (long weekend), and if we still can't find anything we will have to sit down and figure out if we should carry on chasing this issue or choose another route.

Hope you all have a great weekend!

Hi! We are having the same problem in one of our ford transits and we tried eveything but the issue just wouldn't go away

 

Please reach out to me ASAP if you found any solutions regarding this issue thx :)