2.0 HDI surging under small load

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kili
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2.0 HDI surging under small load

Post by kili »

So, I have been blessed with a 2001 Dispatch, 93 hp 2.0 HDI engine (BTED w3, RHX), RPO 8950. 340000 km on the clock. Having now sorted out the easier-to-diagnose flaws (leaking head gasket, tank pump not delivering fuel under 1/4 tank), I am at a loss with this last one.
The car surges ever so slightly under small loads like gentle acceleration or climbing a slope. It's like the throttle pedal was slightly pumped, with a frequency of 1-3 Hz. Happens in every gear, noticeable in the 1900-3000 rpm range. Press the pedal some more and the surging stops and the car pulls just as you would expect, without any abnormalities. The surging is so slight, that you can't see it in the clocks but you can definitely feel it. Gets quite tiresome on longer journeys and especially when using the (recently retrofitted) cc.
I have googled and tinkered, but none of the fixes seem to apply. The car has no DPF to empty, and the catalytic converter has obviously been gutted at some point. The car does not consume oil or excessive amounts of diesel nor does it smoke in the least, and otherwise it runs just like you would expect any good 2.0 HDI to run (have had a few of these around over the years). No DTCs unless you deliberately cause them. Turbo pressures are normal.

Things I have tried (and which did not have any effect on this behaviour):
-swapped injectors as a set from a known-to-work 110 hp ATED engine (they had a different number, so I programmed them with Lexia)
-mixed and matched injectors from other engines, too
-unplugged the MAF connector (got the expected DTC, AFAIK the car switches to some default mapping with it unplugged)
-swapped to a known-to-work MAF (old one was clean, too)
-swapped to a known-to-work high-pressure regulator
-swapped to another known-to-work high-pressure regulator
-changed the fuel filter (using the correct procedure, the old one was clean and so was the casing, too)
-checked intake manifold for soot (found very little)
-blanked the EGR pipe on the intake manifold end (got the expected DTC)
-unplugged and sealed the vacuum hose going to the EGR solenoid (got the expected DTCs)
-unplugged the wastegate vacuum solenoid wire (Got the expected DTCs, can't actually remember how the car ran with this disconnected. Should the wastegate be open or closed with the solenoid unplugged?)
-used a bottle of fuel-system-cleaning liquid
-changed the air filter
-gave it the "Italian tune up"

Things I have yet to try:
-change the high pressure sensor/wiring
-change the high pressure pump
-change the ecu (could the cause actually lie there?)
-there is no MAP-sensor on this car to clean, right?
-something else?

Now, there is one thing that actually "fixes" the problem. It is disconnecting the third piston deactivator solenoid on the high pressure pump. That completely gets rid of the surging. This leads me to believe, that the high pressure pump has ingested something it should not have and scored the pistons in the pump, thus the ECU keeps enabling and disabling the third piston in an attempt to achieve the wanted rail pressure, which results in felt surging. Under higher loads the third piston is always in use, and therefore there is no surging. Under even smaller loads the two pistons are enough to maintain the pressure, even if scored.
One problem is, the polling rate on Lexia seems to be so low, that it is rarely if at all possible to connect the surging to the piston deactivator solenoid firing. If the two really are connected in the first place. The high pressure pump is the one thing I do not want to change (yes there are a couple of those around, too) until I am certain that the problem really lies within. (Repairs of that scale are not fun when it is -25°C out and you do not have a garage that you can actually fit a car in.)
The rail pressure constantly oscillates some ±35 bar around the wanted pressure, while on a truly working 110 hp 2.0 HDI Peugeot 406 I had at hand a while ago, the oscillation was about ±8 bar at most (IIRC). The thing is, under full load both cars achieved similar pressures (around 1450 bar). Or maybe that is just because the possibly scored pistons seal better under higher pressures. Or the ±35 bar reading is just normal.

So anyway, what I really wanted to know is, if anybody has had similar behaviour on their HDI that boiled down to the high pressure sensor (the sensor plugged into the underside of the rail) or its wiring, instead of the high pressure pump itself. Or somewhere entirely else. Or if anybody actually has encountered a scuffed high pressure pump, what were it's symptoms. Also, if anybody has paid attention to their rail pressure deviation from the set value, I am interested in those numbers too. Be there surging or not. Since the high pressure sensor is quite a pain to get to, I thought I would ask here first. Thank you, and sorry for making you read all this blabbering.
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Re: 2.0 HDI surging under small load

Post by xantia_v6 »

Your hypothesis regarding the high pressure fuel pump sounds convincing.

I would also suggest investigating whether there is an instability in the turbo waste gate control loop, which could be caused by a sticky actuator, or a faulty waste gate control solenoid or even a partial blockage in one of the vacuum lines or the atmospheric line (filter) on the waste gate control solenoid.
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Re: 2.0 HDI surging under small load

Post by Peter.N. »

When you say you have changed the 'high pressure regulator' do you mean the one on the back of the HP pump? I have had this cause something similar.

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Re: 2.0 HDI surging under small load

Post by picassodad »

Is the throttle cable all ok and not being "influenced" by the engine, a poor cable run with cable lying on the engine and being moved due to engine movement possibly?? From memory the tps is cable controlled and lives by the coolant expansion tank??

From what you have said maybe the 3rd piston is inactive on our 306 as the engine seems to have no guts on heavy throttle pressing but flyies on light load. How are wires from ecu at the flex point, make an=d break contacts in the wires maybe and the devil to find.

The tps can play up and be improved with a good clean inside, the 2 off set quadrants area.
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Re: 2.0 HDI surging under small load

Post by GiveMeABreak »

Pop your VIN up so we can see exactly what you have - there are so many variants of these engines.
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kili
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Re: 2.0 HDI surging under small load

Post by kili »

xantia_v6 wrote: 29 Jan 2019, 07:10 Your hypothesis regarding the high pressure fuel pump sounds convincing.

I would also suggest investigating whether there is an instability in the turbo waste gate control loop, which could be caused by a sticky actuator, or a faulty waste gate control solenoid or even a partial blockage in one of the vacuum lines or the atmospheric line (filter) on the waste gate control solenoid.
Okay, I will give the vacuum system a closer look and check the air filter on the solenoid. I have been meaning to swap the EGR and wastegate electrovalves around anyway. Maybe I could even get hold of a vacuum tester and draw some conclusions, we'll see. The turbo is positioned so awkwardly under the cabin that I don't have high hopes of getting to fiddle with the actuator any time soon, though.
Peter.N. wrote: 29 Jan 2019, 10:48 When you say you have changed the 'high pressure regulator' do you mean the one on the back of the HP pump? I have had this cause something similar.

Peter
Yup, that's it.
picassodad wrote: 29 Jan 2019, 10:54 Is the throttle cable all ok and not being "influenced" by the engine, a poor cable run with cable lying on the engine and being moved due to engine movement possibly?? From memory the tps is cable controlled and lives by the coolant expansion tank??

From what you have said maybe the 3rd piston is inactive on our 306 as the engine seems to have no guts on heavy throttle pressing but flyies on light load. How are wires from ecu at the flex point, make an=d break contacts in the wires maybe and the devil to find.

The tps can play up and be improved with a good clean inside, the 2 off set quadrants area.
I am quite convinced that the problem lies elsewhere, since the throttle percentage reported by Lexia is always what you expect it to be (i.e. never oscillating). The wires in the engine compartment look fine. And since there are no other engine-related problems, I have hope that this is not an electric gremlin. If/when I get around to replacing the sensor, I am going to route new wires from it to the ECU just to rule the old ones out. See, a while back I actually found one case, where the wires going to the sensor had rubbed themselves out, but the symptoms were different (unreasonable rail pressures when decelerating, stalling).
The third piston is easy to "force" to be always active by disconnecting the plug on top of the high pressure pump. It gives a DTC when disconnected.
GiveMeABreak wrote: 29 Jan 2019, 11:01 Pop your VIN up so we can see exactly what you have - there are so many variants of these engines.
VF7**************[VIN obfuscated, can be read by forum staff]
I am quite curious of the differences between the RHX and RHZ engines, since they seem mechanically identical but are some 15 hp apart performance-wise. I have a RHZ ECU with the same connector and seemingly identical pinout lying around somewhere, and I have been toying with the thought of virginizing it and giving it a try on this car.

Thanks for all the replies, guys.
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Re: 2.0 HDI surging under small load

Post by myglaren »

Mine used to do this. On long, straight, flat 30mph road to work it would hunt slightly. Fine under any other conditions.
I cleaned the MAF - no change. Ran it with Redex diesel system cleaner for eight moths (bought a years supply) with no effect whatsoever.
Then began using Torq diesel (cheap, close to home and accessible) and the hunting went away with the added benefit of an improvement in economy.
Torq is no more and I alternate between Sainsburys and Shell diesel with no other noticeable effect. (the Torq station is now Shell).
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Re: 2.0 HDI surging under small load

Post by GiveMeABreak »

I had a quick look, but there is very limited info for 2001 year and I have nothing on the DW10BTED engine you have by way of a comparison or characteristics unfortunately.
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Re: 2.0 HDI surging under small load

Post by MixerFistit »

Apologies if necroing an old post isn't allowed I couldn't see it in the rules.
Was this ever solved?
I have an 06 RHZ Dispatch that is/was doing the same.
I've only ever noticed it at fast idle (3.1k rpm )which isn't exactly something I do often so haven't paid it much attention until now.
I recently changed the seals in my pump due to a leak raining out of the piston access. Is also changed the filter. All good so far but when giving it a bit of pedal I noticed the hunting was still there.
I also noticed a dribble of diesel from my filter housing.
Now when I changed my filter I noticed the previous guy had put 'silly'cone around the threads. I cleaned it all off and just relied on my new o-ring.
When I saw the dribble I undone the ring and this time pushed down hard on the filter while I screwed it up as tight as I could. Since then I haven't been able to replicate the hunting.
It's only been a day and I'm not convinced that could solve it but maybe it was sucking air?
Less than 3.1k not enough to suck air, more than 3.1k sucking hard enough to seal itself?
Not convinced personally, but maybe worth a look. Open to suggestions in case it's the start of something.
Just to clarify, the hunting is approx over 80-100 rpm and occurred before any changes to pump and filter
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Re: 2.0 HDI surging under small load

Post by MixerFistit »

Ah well, spoke too soon. It is still there; however, at least with mine, it happens when the engine hasn't fully warmed up. Somewhere north of 70° C it stops
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Re: 2.0 HDI surging under small load

Post by Peter.N. »

Has anyone mentioned a fuel system air leak?

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Re: 2.0 HDI surging under small load

Post by MixerFistit »

That was my original suspicion and when I saw the silicone around the filter housing and my HP pump started leaking I thought maybe I'm on to something but with no more dribbling from my filter and new seals in my pump the issue remains. I don't really want to call it an issue tbh as it doesn't affect me in any way other than I know it's there and maybe slightly paranoid there's something bigger going on or waiting around the corner.

To add info, if the fuel light is on (even if only just come on) and I park up a steep hill, I will get just cranking but I haven't tested this since I repaired the pump and cleaned up the filter housing.
I didn't realise I had a lift pump at the time so didn't cycle the key from 1 to 2 to keep priming. Fortunately after flushing the hp pump after repair I know my lift pump is functioning - but my diesel catching container placement needs improvement...
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Re: 2.0 HDI surging under small load

Post by Peter.N. »

I don't know if yours has an in tank pump, if so that should overcome the problem but if like my C5 it doesn't can cause problems even with a tiny leak. Do you have clear sections in the fuel line to check for air bubbles? If so have a good look at them while its running. The fuel filter housing was leaking on mine, I changed it and it improved matters but didn't cure it.

Mine was far worse than yours as either it wouldn't start or it would stop after a few hundred yards, I replaced the fuel line from the filter to the HP pump, not an air bubble in sight and it drove fine until you put your foot down hard on a hill then it died, would pick up again with less throttle but was not safely usable. As it needed a clutch and a steering rack it was cheaper to buy another one which I did. I suspect the leak must be on the pump.

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Re: 2.0 HDI surging under small load

Post by MixerFistit »

Yeah I have a lift pump you probably missed it mentioned towards the end of my waffling lol
No clear lines unfortunately.

I may have resolved the fuel issue after fixing the HP pump but I do plan to change the filter housing and lift pump at some point anyway for peace of mind. I understand that just because the lift pump is functioning doesn't mean it's not falling apart. When I first opened the housing to change the filter there was quite a bit of 'gold dust' at the bottom which is from the lift pump. As it's the first filter change for me I don't know if it had been cleaned out prior to the last time it was changed or if they just swapped the filter. Eitherway it's probably best to swap it out at this stage of it's life.

Back to the original thing though, the rev hunting is a very specific tight window of between about 2980 to 3110 rpm.
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Re: 2.0 HDI surging under small load

Post by Peter.N. »

OK, you shouldn't have any air problems if you have a lift pump, any leaks will show up as just that - leaks, unless of course the lift pump is faulty but you sound as though you know what you are doing so I wish you success.

Peter
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