Power Issues Under Load - Diesel

olliewarwick · 26th July 2016, 08:37

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

hogweed · 26th July 2016, 09:44

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

olliewarwick · 26th July 2016, 10:09

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

Mike Noc · 26th July 2016, 10:56

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.

olliewarwick · 26th July 2016, 14:54

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

marinabrian · 26th July 2016, 15:47

worth doing a leakback test on the injectors first and foremost

Brian

26th July 2016, 08:37	#1
olliewarwick Avid contributor MG ZT-T+ Join Date: Jun 2014 Location: Guildford Posts: 143 Thanks: 8 Thanked 20 Times in 13 Posts	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

26th July 2016, 09:44	#2
hogweed I really should get out more....... Vauxhall Insignia CDTi; MG TF 135 Join Date: Jan 2010 Location: Norn Iron Posts: 2,958 Thanks: 942 Thanked 378 Times in 297 Posts	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 __________________ Past cars: MGB GT; Escort 1300 Sport; Vauxhall VX4/90; Marina Coupe TC; Celica ST (1972); Montego Turbo; Astra GTE 16V; Astra GSI 16V; Golf GTI 16V (Mk II); Sierra XR4x4 Estate; BMW 325i (E30); BMW M3 3.0; BMW M3 3.2 Evo. Left some of the more embarrassing ones out. And about 30 motorbikes.

26th July 2016, 10:09	#3
olliewarwick Avid contributor MG ZT-T+ Join Date: Jun 2014 Location: Guildford Posts: 143 Thanks: 8 Thanked 20 Times in 13 Posts	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

26th July 2016, 10:56	#4
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,555 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	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.

26th July 2016, 14:54	#5
olliewarwick Avid contributor MG ZT-T+ Join Date: Jun 2014 Location: Guildford Posts: 143 Thanks: 8 Thanked 20 Times in 13 Posts	Thanks Mike, I'll try that tonight and come back to you. Ollie

26th July 2016, 15:47	#6
marinabrian MG ZT Join Date: Jan 2011 Location: Newcastle Upon Tyne Posts: 20,151 Thanks: 3,565 Thanked 10,837 Times in 5,718 Posts	worth doing a leakback test on the injectors first and foremost Brian