Power Issues Under Load - Diesel
 

Hi All,
I’m hoping you can help me.
I’m having an issue with, I believe, fuel pressure on my car. When the car is warmed up (also happens when cold but not as early) if I accelerate hard it revs to around 2500-3000 and then jerks and loses power. If I come off the power a little it starts to accelerate again, but if I boot it the same thing happens again.
Providing I’m gentle with the throttle it doesn’t happen. The car revs fine in neutral however, when accelerating or if under load such as a very steep hill where it needs a little more power it happens. It feels like the car loses all power then it tries again and again if I keep my foot hard down.
It’s definitely related to load because if I happen to be doing exactly the speed limit J on the motorway once it gets to a speed where the engine is under a similar load the same thing happens.
Now a little while back PhilT4 told that the pressure on my high pressure fuel pump was a little on the low side, nothing to worry about but just bear in mind. This sounds high pressure fuel related to me, but some other opinions would be great.
If so am I looking at a replacement or rebuild kit or something else entirely?
The two other fuel pumps (being an early diesel) have both been replaced according to the service history and I’ve tested both a little while back so I don’t suspect those initially but open to offers of advice.
This has been going on for some time, but has been much more noticeable with the hot weather.
Sorry for the essay.
Ollie

Wouldn’t be your MAF would it? Somewhere in the bowels of my memory is an idea that the ECM refers to it most from around that rpm range.

I could be talking bolleaux, but you could try unplugging it and see what difference it makes, if any…


Essays are good :D

Ah apologies, should've mentioned that. I had issues with MAF some time back and it's been unplugged since.

Just caused sluggishness. This is a very sudden jerk, loss of power which repeats itself every second or so if you leave your foot on the power. Pretty different to the MAF issues I've had on this, and other cars but thank you for your response.

Ollie

Might be a fault on the low pressure fuel supply side - if you get a drop in HP fuel pressure the engine shuts down.

Try it with the LP fuel pressure sensor unplugged - it is the one on top of the fuel filter.

Thanks Mike, I'll try that tonight and come back to you.
Ollie

worth doing a leakback test on the injectors first and foremost ;)

Brian :D

:wot: Yes I'd be looking at doing a leakback test on the injectors too ;)

Russ

Hi Brian & Russ.
In your knowledgeable opinion which or what is the correct way to do a leak back test.

From cold and run for 2 minutes if so when does the time start as soon as fuel enters the leak off tubes, or when the fuel starts dripping into the containers.

Am I right in saying that 20ml over that period of time is acceptable, I know what we would all like to see is none.

Couple of videos below for the OP to watch and you also please, hopefully this will give members a definitive answer as to how these teats should or should not be run.

Timed from when the car was started and fuel flowing into the tubes, video is for 1 minute as it took a minute for the fuel to flow up the tubes to top of the containers.
https://youtu.be/WfTUFhjOZyQ

Second test the next day timed from starting the car and fuel entering the leak off tube kit, total time 2.02minutes.
https://youtu.be/VnGs_da2o

Third Test same day right after the second test but this timed from entering the container as fuel was already in the tube, total time 2.08 minutes.
https://youtu.be/mcoUSIjus

I later ran an Hawkeye test on the injectors and they were within tolerance, have seen worse

Thanks chaps.

I tried unplugging the pressure sensor and initially I thought that it had made a difference and that the problem only starting kicking in at around 3500 revs however, on the way back home after a little brake it was back to the same 2500-3k.

I'll look up how to do leak back test and do that and report back, it may be some time as I'm pretty busy but will let you know.

I assume this will indicate faulty injectors and therefore replacements with new or recon or good second hand?

Thanks,
Ollie

Running without a MAF is not ideal, replug in the MAF and try again see if it does it, your MAP sensor could be shot or dirty causing it to lose power on boost as thats the sensor it relies on when the MAF is bad.

Personally i'd have a new MAF fitted or get a good second hand one, without the MAF your on base values and really isnt ideal for the engine.