C3 1.1 hesitation at 4000 rpm

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Captainbeaky
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C3 1.1 hesitation at 4000 rpm

Post by Captainbeaky »

Hi,

I'm new here.
My friend has asked me to look at his car because he has had lots of problems with it and has lost confidence in the local mechanics.
I run a small engineering workshop in sunny Madeira, and focus mainly on classic cars, Jags, Landrovers and weird modifications and diagnostics.
I don't have much experience with Citroen/Pug/Ranault Fuel injection systems other than the fabulous BX and Xantia VSX - anyway, thats another story!

I agreed to have a look and here's where I have got to.
The car runs fine all the time - smooth and as powerful as you would expect a 1.1
Fuel economy is good.
But the car hesitates at exactly 4000 rpm - in every gear, under acceleration it always flyers when passing through exactly 4000 rpm.

Does this ring a bell with anyone?
Also, is there a way to clear the engine adaptions without a specialist diag tool?
I'm trying to save the customer money - he's been through enough with this car, so I thought I'd ask here...


Here's the background (sorry its a bit long, but it will explain what I've checked):-
The car presented with the check engine light on, running very poorly / lumpy and poor performance.
The DTC reported was linked to Long term fuel trim out of limits, and the long term fuel trim was -33%
The history of the car is that it had an ECU fault, and has had the parts cannon fired at it before they found the culprit - the ECU.
The car has had a recent service and cam belt, which is when these problems started to manifest.

What I did:-

The car was quite poorly. Other than the Fuel trim DTC, there were no other reported faults, and all the ECU inputs looked sensible, so I suspected some mechanical fault.
No air leaks, intake manifold fine, air filter not blocked, fuel pressure was OK, as was the valve timing, plugs were new.

BUT - cylinder compressions were all over the place.
I checked the valve clearances, they were nearly nil - so I corrected them.
Compressions back to normal - compression good.

The car ran a whole lot better - not lumpy, much smoother and the power was back.

BUT - the fuel trims, while better, were still way out - now around 20%

I whipped out and checked the injectors on my injector test bench - they all worked (no dribbling) and they were all injecting within about 2% of each other (I couldn't tell any difference in inject quantities.)

I checked the part numbers on the injectors (H001 1F002A 04713.)
On an internet search, this shows up as an injector for a 1.1 and 1.4 C3 on the suppliers website.
I think these are cheap chinese injectors (although the spray pattern is good and they are all well balanced - but I digress).
When I checked the Bosch part numbers for these two engines injectors, they show up as different parts, and lo and behold, the 1.4 injector has a 20% higher flow rate than the 1.1!
BINGO.

So - I sourced a set of second hand original injectors, ultrasonically cleaned them, tested them on the injector bench (all fine), and fitted them.

The car runs fine, and the fuel trims are now starting to adapt back to where they should be (I don't have the ability to clear the adaptions with my diag kit)
I have tried disconnecting the battery for a while, but it doesn't seem to reset the engine adaptions, so it will take some time to fully adapt.

BUT - the car has a strange hesitation at 4000 RPM - exactly at 4000 RPM.

It only happens when accelerating up through 4000 RPM
It doesn't happen when decelerating down through 4000 RPM (when driving up a hill with a wide open throttle, but the car is slowing down because the engine does not have the power to accelerate).
(The reason that this is important is that if it was a physical aspect of the engine or ignition etc, it would happen in both of these circumstances - the drop in power would happen at 4000RPM regardless of increasing or decreasing revs.)

Also, its at exactly 4000 RPM every single time.

As I don't have Lexia or similar, I'm flying a little blind when it comes to looking at the internals of the ECU.
Anyone else seen this?
What happens at exactly 4000 RPM???
(Note - no aircon coming in and out - car doesn't have aircon).

Thanks in advance,

Mike.
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Re: C3 1.1 hesitation at 4000 rpm

Post by GiveMeABreak »

Hi and Welcome.

First of all we'll need the VIN and secondly what are / were the fault codes recorded? Third party readers may not be able to interpret constructor-specific codes.
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Marc
Captainbeaky
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Re: C3 1.1 hesitation at 4000 rpm

Post by Captainbeaky »

The Vin is:- VF7**************[VIN obfuscated, can be read by forum staff]

There are no fault codes reported now, and no check engine light.
My third party readers are usually pretty good at teasing out the manufacturers specific codes, but granted, I don't have Lexia or similar.

All the OBD PID's look OK, as do the manufacturer specific pics that I can see. Nothing is out of whack - other than the fact that the Long term fuel trims haven't all fully adapted yet (by definition, they won't have adapted for all load/speed combinations)
So I have the usual condition of the long term fuel trim reading -20% and the short term fuel trim reading +20%... And it seems to take quite some time to get the long term fuel trim load areas to adapt.
(This is why I'd like to be able to fully reset the Engine ECU adaptations).

Putting my ECU designer's hat on for a moment, and simplifying the fuel trim operation description, I wonder if the problem is simply of traversing between poorly-adapted load map areas.
Since the Long term fuel trim is a stored adaptation value (based on short term fuel trim over a longer period of time), and the Short term fuel trim is the actual fuel trim as set by the feedback from the lambda sensor, then if the engine operating area traverses across from one Long term fuel trim area to another (and perhaps this happens at 4000 rpm), then perhaps the hesitation I am feeling is simply that - the fuel trim having a bit of a fit as it changes from the now well adjusted (~0%) sub 4000 rpm area to the original horrendous -33% adapted value from the above 4000RPM area. The short term fuel trim has to make a sudden re-calculation, and might be going momentarily lean (and under large loads, this is when you will feel it most - as the fuelling often goes open loop under large loads).
This would explain why it happens at a specific RPM, and also explains why I don't feel the hesitation as the RPMS drop under load.
(In the case of engine RPM dropping while under load, the change would be the other way around, the Short term fuel trim would have to lean out when it jumps from -33% to 0% long term fuel trim, so the hesitation wouldn't be noticed because the engine is going momentarily rich.)

My previous test drives were carried out alone, so I couldn't concentrate as hard as I would have liked on the diag computer.
I'm going to take it for a longer run when I pop to Funchal later and have a friend driving, and I will monitor the PIDS much more closely while traversing the 4000 rpm barrier to see if that shows anything strange happening.

In the meantime, I think that getting hold of Lexia might be on the cards!!!
I'll have a read around here to see what people think about the various code readers.

Cheers,

Mike.
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Re: C3 1.1 hesitation at 4000 rpm

Post by GiveMeABreak »

So this is a 2004 C3 5 DOOR SALOON 1.1 i (TU1JP) Manual gearbox 5. It will have the Magneti Marelli injection system.

AS far as I know Lexia / Diagbox PP2000 done't support fuel trim functions.

Ok, so if there aren't any codes fault codes present, there's very little I can provide and there are no TSBs I can see relating to any of these issues you describe.
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Marc
Captainbeaky
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Re: C3 1.1 hesitation at 4000 rpm

Post by Captainbeaky »

Thanks for that.

Are you sure that Lexie doesn’t re-set the ECU adaptions?

I’m a bit suprised that the official tools don’t support this - especially since these adaptions are maintained after battery disconnect, and aren’t reset when the codes are cleared...

I can understand if it doesn’t specifically re-set the fuel trims, but I’d be very suprised to not find a “reset ECU” kind of feature.

Cheers anyway, I simply haven’t been out on a long journey to test it.
I’ll post my findings if there are any!
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GiveMeABreak
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C3 1.6 HDi Exclusive Aluminium Grey (The Silver Hornet)
C5 MK II 2.0 HDi Exclusive Obsidian Black
C5 MK I 2.0 HDi SX Wicked Red
Xantia S2 2.0 HDi SX Hermes Red
C15 Romahome White
XM 2.0 Turbo Prestige Emerald Green Pearlescent
XM 2.0 Turbo Prestige Polar White
XM 2.0 SX Polar White
CX 20 Polar White
GS 1220 Geranium Red
CX 2.4 Prestige C-Matic Nevada Beige
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Re: C3 1.1 hesitation at 4000 rpm

Post by GiveMeABreak »

No, there are no reset options on Diagbox. Parameters are preconfigured at factory for the relevant ECU. Any software updates are undertaken online via dealer servers, but are not available to joe public with clone interfaces. We can only undertake live tests, actuator tests, fault tracing, clearing and erasing along with certain procedures required for some operations on PSA vehicles, key coding etc., along with some manual programming for certain areas.
Please Don't PM Me For Technical Help

Marc
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