Fuel consumption wandering when coasting in idle and juddering when letting off accelerator

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My Name: Gaston76

Contributor
Posts: 8
Joined: Sun Jul 01, 2018 8:43 pm
Model: C3 2006-2009, Facelift model
Year: 2006 (56)
Engine Size: 1.4 (8v)
Fuel Type: Diesel
Mileage: 124000
Trim Level: NA
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: LHD (Europe)
Engine name: DV4 diesel (70 PS)
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Hi there everyone. Just bought my second 1.4 Hdi 8 valver, although i've had to fix a lot more on this example than my previous one. How i regret selling her.. :oops:

To the problem: When i am coasting (in motion) and put the car into neutral, the instantaneous fuel consumption seems to bounce/wander erratically. it usually bounces from 0,6l/100km to 0,9-> 1,1 -> 2,2 and back at random. If i reckon correctly my previous 1.4 hdi used to stay rock solid at 0,5/100km when rolling in idle to a stop. maybe even lower like 0,3l/100km but always the same number and not bouncing.
The engine also judders when letting go of the accelerator pedal at motorway speeds. for example 1400 revs in 5th on the motorway, giving 100% throttle to build up boost then releasing throttle abruptly causes engine to judder for a second.

the question: Can some kind soul with a 1.4 hdi 8v (preferrably with SID806 injection system) check if their fuel consumption also bounces when in idle and rolling? I just need to know if this is normal or not so i can eliminate it from my worries.
Im wondering if these two symptoms might point to a faulty fuel pressure regulator? just a thought. i do have access to Lexia so i can provide screenshots from there if anyone is interested.

Another thing is that the car is also consuming more fuel than expected. The average fuel consumption sits at 4,5l/100km which i guess is nothing to scoff at, but taking the symptoms into account and considering that my previous 1.4 hdi sat at 3,5l/100km (average!!!) in summer and 3,8l/100km in winter leads me to believe that something is amiss with this one.

A lot has been changed on my car including all new original Siemens VDO injector for all 4 cylinders, glowplugs, turbo, MAP sensor, upper engine mount and lower "gearbox mount", all filters have been changed recently also.
My Name: Gaston76

Contributor
Posts: 8
Joined: Sun Jul 01, 2018 8:43 pm
Model: C3 2006-2009, Facelift model
Year: 2006 (56)
Engine Size: 1.4 (8v)
Fuel Type: Diesel
Mileage: 124000
Trim Level: NA
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: LHD (Europe)
Engine name: DV4 diesel (70 PS)
Has thanked: 8 times

Post

Right, i have also noticed now that the engine is "hunting" a bit at idle. I think this correlates with the hunting fuel consumption i described in the first post.
The idle seems to be hunting between 768 RPM and 800 RPM and then back to 768 RPM. Checking at the Lexia live data i can see that reference fuel pressure is 220 Bar but every ten seconds or so it jumps from 220 to 227 and sometimes but less frequently it dips to 212 from the reference of 220 Bar. The measured air flow also does not seems to match the reference air flow and both these values seems to "jump around a lot", they don't seems to be at a steady value at idle. At most the measured air flow was 50 mg/cp lower than the reference. the measured air flow always seems to be a bit higher or lower than the reference.
Obviously the fuel pressure values and air flow values are connected to eachother. if the engine load increases= more fuel pressure and more air. however since the hunting happens at idle it must mean that something in the fuel system or air system is not working as it should. air leak? fuel pressure regulator? maf sensor?? HP fuel pump knackered??

Does anyone know if the measured air flow can account for air leaks AFTER the MAF? I am asking this because a couple of months ago i took apart the egr pipes, egr cooler and egr valve to clean them and after that i had an exhaust leak on one of the CLIC clamps. i remedied this by wrapping aluminium foil around the egr join before putting on the clic clamp. I havent noticed any soot around the other clic clamp but i am wondering if an exhaust leak there might create the hunting idle and the measured air flow values? Disconnecting the MAF does seem to make a marginal difference in idle steadiness and the engine seems to idle more freely but it might be all in the head.

Also, probably a stupid question but does anyone know if a fault in the ABS can cause fuel injection issues? I am asking because i have a fault code stored in the injection ECU, U0415, Remote fault, Temporary fault - ABS ECU reception incorrect value recieved. error happened at 800 rpm (idle) at 1470s after ignition switched on. I know that the ABS pump is intermittently jamming causing another code but this U0415 code is new. Could it be that the engine raises the revs on/off when it noticed that the ABS pump is jamming?

Any ideas about these issues would be greatly appreciated. Will of course report back if i find anything,

Gaston76 >>
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My Name: Ozvtr

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Posts: 1194
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
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The ABS pump should only run in a breaking Emergency.

In the first case, extreme brake pedal depression may cause the wheels to lock up. So the ABS unit "bleeds" off excess pressure at the wheel brake cylinder lines of the ABS unit. The fluid bled off is "topped up" by the ABS pump to maintain the brake pedal pressure. The brake pedal may "pulsate" as the pump runs.

In the second case, very fast depression of the brake pedal will cause the ABS pump to activate and pump fluid to the brake cylinders and stop the car - fast. The brake pedal will also go straight to the floor!! The ABS system will not allow the brakes to release until the brake pedal is completely released.

So normally, the ABS does nothing.
If you are having communication errors in the ABS unit, you can undo the "bag" over the electrical connector, separate the connector and spray both sides with a contact cleaner or water displacing spray. Being right at the front and at the bottom of the car, it can get effected by moisture and salt ingress.

Sorry but I'm not a "diesel guy" but you could look at the long and short term fuel trims. If the fuel trims are less than +/- 5% that's good. Between 5 and 10% is fair. More than 10% requires investigating.
You will need to see when the airflow is down. If it's at idle it might be a leak after the MAF in the inlet manifold. If it's "on boost" it would be before the MAF like the MAF itself (something stuck in it) or the air filter.

The fluctuations of the high pressure fuel rail seem insignificantly small. +/- 8 BAR is less than 5% of nominal. As I said I'm not a diesel guy but I don't see that as a problem.
My Name: Gaston76

Contributor
Posts: 8
Joined: Sun Jul 01, 2018 8:43 pm
Model: C3 2006-2009, Facelift model
Year: 2006 (56)
Engine Size: 1.4 (8v)
Fuel Type: Diesel
Mileage: 124000
Trim Level: NA
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: LHD (Europe)
Engine name: DV4 diesel (70 PS)
Has thanked: 8 times

Post

Thank you for the reply Oz :)
Definitely need to sort that ABS out ASAP because temperatures have been hovering around 0 degrees C here and hit an ice patch three days ago around a bend and braked. Not sure if it was the ice or the ABS but the car screeched to a halt pretty dramatically and a bit too close to the guard rail for my liking... ABS pump on the way from Poland which will be here in January so i will report back if that changes anything other than fixing the ABS light and ABS function.

About the fuel trim readings - i can't find it when looking at injection live data in Lexia. is it called something else in Lexia-speak or am i looking at live data in the wrong section? :roll: I can see air flow values measured in mg/cp though. When the idle is hunting (which it does on and off mostly when cold) the measured air flow value usually keeps pretty close to reference, at some second it might be off about 20 mg/cp which i dont either reckon is that bad... Dont know if i mentioned it in the first post but engine doesnt have the MIL light on.

Anyways, i took the car to my mechanic yesterday and he told me to check the in tank fuel strainer. i think i will try this first because i've recently had to change the fuel injectors due to running too low on diesel on a couple of occasions. Fuel filter was changed with the injectors but the in-tank strainer might still be clogged. https://frenchcarforum.co.uk/forum/view ... hp?t=52404 this guy apparently solved his hunting idle by cleaning the strainer also so that corroborates a bit.

Will report back if i find anything :)
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My Name: Ozvtr

Moderator
Posts: 1194
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
Has thanked: 59 times
Been thanked: 351 times

Post

Gaston76 wrote: Fri Dec 23, 2022 12:38 pm Thank you for the reply Oz :)
Definitely need to sort that ABS out ASAP because temperatures have been hovering around 0 degrees C here and hit an ice patch three days ago around a bend and braked. Not sure if it was the ice or the ABS but the car screeched to a halt pretty dramatically and a bit too close to the guard rail for my liking... ABS pump on the way from Poland which will be here in January so i will report back if that changes anything other than fixing the ABS light and ABS function.
Sounds like the pump is not working. May be corroded up. In LEXIA there should be a "actuator test" for the ABS pump. See if you can get the pump to run. Did the ABS light come on when you had the skid? The ABS light should come on when it activates. Check that the ABS light comes on when you turn the ignition switch to on.
Gaston76 wrote: Fri Dec 23, 2022 12:38 pm About the fuel trim readings - i can't find it when looking at injection live data in Lexia. is it called something else in Lexia-speak or am i looking at live data in the wrong section? :roll: I can see air flow values measured in mg/cp though. When the idle is hunting (which it does on and off mostly when cold) the measured air flow value usually keeps pretty close to reference, at some second it might be off about 20 mg/cp which i dont either reckon is that bad... Dont know if i mentioned it in the first post but engine doesnt have the MIL light on.
The fuel trims are supposed to be buried in LEXIA, I personally have not found them. :( Silly, as a 15 pound scanner has them. I'll try and find out.
Have you tried to scan the car using Peugeot Planet? I have found some functions under PP that do not appear under LEXIA.
Gaston76 wrote: Fri Dec 23, 2022 12:38 pm Anyways, i took the car to my mechanic yesterday and he told me to check the in tank fuel strainer. i think i will try this first because i've recently had to change the fuel injectors due to running too low on diesel on a couple of occasions. Fuel filter was changed with the injectors but the in-tank strainer might still be clogged. https://frenchcarforum.co.uk/forum/view ... hp?t=52404 this guy apparently solved his hunting idle by cleaning the strainer also so that corroborates a bit.
Take any diesel specific "advice" I might give with a grain of salt. As I said I'm not a diesel guy. :lol:
User avatar
My Name: Ozvtr

Moderator
Posts: 1194
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
Has thanked: 59 times
Been thanked: 351 times

Post

Ozvtr wrote: Sat Dec 24, 2022 12:06 am The fuel trims are supposed to be buried in LEXIA, I personally have not found them. :( Silly, as a 15 pound scanner has them. I'll try and find out.
Have you tried to scan the car using Peugeot Planet? I have found some functions under PP that do not appear under LEXIA.
I found them.

When you open Diagbox and you are given the options of LEXIA or Scantool, choose Scantool. Next choose UCEOBD, then choose Parameters.

With the engine running you will be given the parameters of "Rapid fuel correction (1)" and "Slow fuel correction (1)". It may take a while for the engine ECU to collect the long term trim data.
My Name: Gaston76

Contributor
Posts: 8
Joined: Sun Jul 01, 2018 8:43 pm
Model: C3 2006-2009, Facelift model
Year: 2006 (56)
Engine Size: 1.4 (8v)
Fuel Type: Diesel
Mileage: 124000
Trim Level: NA
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: LHD (Europe)
Engine name: DV4 diesel (70 PS)
Has thanked: 8 times

Post

Thank you Oz!
Well its been a couple of months with the issue and after two sessions with the local indie i've gotten no smarter. I have cross-checked the issue with the wandering fuel consumption on my brothers C4 1.6 hdi non-FAP model and it is also wandering under the same conditions so that pat at least must be normal. Not sure if i mentioned in earlier posts that the idle is/was also slightly wandering when cold starting. That has become less and less noticeable - i assume this was either due to some microscopic crud being left in the common rail lines when my indie replaced all 4 injectors (1400 GBP :twisted:) OR that the fuel pressure regulator is getting tired of being in service. Anywho, the issue with the wandering idle has at least gone away/gotten better with time - or maybe i've come to live with it, so i'll leave it at that until it gets worse or something else breaks. will of course update this thread if i get any further with the issue.
/Gaston76
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