Baffling Throttle Problem

Questions specifically about a Petrol powered Citroen C3 (usually engine or fuel related problems).
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Petrol engine related faults, like injectors, error codes, overheating.
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My Name: pinvts

Contributor
Posts: 6
Joined: Sat Jul 27, 2019 8:59 pm
Model: Other
Year: 2005 (05)
Engine Size: 1.6 (16v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: RHD (UK)
Engine name: TU5 16-valve (110 PS)

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Ozvtr wrote: Mon Jul 20, 2020 9:50 pm
Edit: LOL! This post is redundant. You posted an answer before me.
:P
Ozvtr wrote: Mon Jul 20, 2020 10:17 pm I believe the crank angle sensor can "fail" and not throw up a code.
Have you cleared the codes on your friend's car? See if the crank angle sensor pops up again?
I wonder if that's what's happening here. I would, if I could - he is in a different country to me, lol! He doesn't have his own Lexia, and I think it costs him quite a bit at the garage he uses. So since the sensor is a cheap part, he says he is simply going to buy a new one, and see if it cures the problem. I am half inclined to sit back and wait for him to report back, since I have become tired of trying to fix this mysterious issue :lol:

One thing to note. My cam cover gaskets were leaking quite badly, so oil managed to make its way down the side of the engine and onto the top/front of the gearbox, exactly where the crank sensor is. I replaced the cam cover gaskets a while ago and cleaned up, but not around the crank sensor area. It's not like there's a pool of oil there with the sensor dripping wet, but the residue is there. Access is made a bit difficult by the coolant hose connecting to the thermostat housing right above it, as well as the radiator fan limiting space in front of it.

Friend has also had an oil leak; he says the sealant on his camshaft housings ("ladders") is failing resulting in a slight oil leak, possibly allowing oil down the same side of the engine to end up on/around the sensor (he hasn't said for certain if he has oil there, but suspects there may be).

So maybe oil has messed up the electrical connector and/or sensor itself? I could try removing the sensor to see what sort of shape it's in, as well as using electrical contact cleaner on the plug and connector. Since access seems a tad awkward though, if I'm going to go to the effort of removing it for cleaning, perhaps I may as well replace it too? I'm running out of things to check/replace at this point!
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My Name: Ozvtr

Moderator
Posts: 942
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: 36 times
Been thanked: 252 times

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I can only tell you that if the crank angle sensor fails I.E. if you pull the plug, the engine wont run. However "sort-of-working" may cause problems.
Because your car is a manual there are only a few sensors to consider.
The engine temp. As your car is a Mk1 you can monitor the temp on the dash.
Coolant loss sensor. Not relevant, throws a warning but does not effect performance.
Knock sensor. I'm not familiar with failure modes with that one. Possible?
MAP sensor. Engine goes into limp mode but still works. Not the right symptoms?
Crank angle. Known to cause random failures. If short or open circuit engine wont run? However what failure was your friend getting?
Speed input. Derived from the ABS on the CAN bus. If ABS Ok unlikely to be the fault. Wont effect he engine at stand still. Unlikely to stop the car, engine just not running at peak efficiently.
Down stream O2 sensor. Only monitors catalytic converter.
Upstream O2 sensor. Used to monitor air fuel mixture. If the values out put by this sensor doesn't match what the computer expects, the computer will complain very quickly. It's monitored very closely so if you don't have an error related to the O2 sensor it's most likely working.

Failure of one or more injectors causes engine to "sputter" in all rev ranges and idle, but still accelerates. Just runs very badly.
Canister purge valve stuck open. Less than optimal performance but not a massive change in performance.
Coil pack. Similar to injectors except more "random". Coil pack failures are usually detected by the ECU, but not all the time.
My Name: pinvts

Contributor
Posts: 6
Joined: Sat Jul 27, 2019 8:59 pm
Model: Other
Year: 2005 (05)
Engine Size: 1.6 (16v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: RHD (UK)
Engine name: TU5 16-valve (110 PS)

Post

Great list, thank you. Putting aside the sensors that shouldn't be relevant in this case:

- Knock sensor: Have not thought about this, will do some digging
- MAP Sensor: Ruled out on the basis that the problem persists even when engine ran with it completely disconnected - if this was at fault, the problem surely should have gone away with it unplugged
- Speed input: No faults of ABS detected by Lexia when global test ran, don't think there is anthing wrong with ABS in practice either
- Upstream o2 sensor: Working at 0.7-0.9v at idle, closer to 0.9v once running for a while, so assume this is ok. Could still be faulty in some way though?
- Crank sensor: No start issues whatsoever. No more information from friend about his crank sensor fault sadly, don't think he has any start issues either though. Rough idle and juddering supposedly possible symptoms of faulty crank sensor - would an idle fluctuating 50rpm be considered rough?

I guess I can do the injector tests on Lexia to see if there is some sort of problem there - not sure what sort of test it is, but can try it out. Coil pack is genuine, heard of issues with cheap replacements. Not sure how to test it.

Not sure where to really go from here, tempted to replace crank position sensor, but quite discouraged at this stage with the whole car
User avatar
My Name: Ozvtr

Moderator
Posts: 942
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: 36 times
Been thanked: 252 times

Post

You can swap the O2 sensors and see. They are identical apart from the colour of the connector and the length of the wires. Not sure the wire length may be long enough though. The chances of both having failed is pretty slim. However if it is putting out a voltage that fluctuates a little and is not constantly 0V or 1V then I would say it's OK.

When the engine goes into closed loop mode the upstream O2 sensor is supposed to oscillate between (about) 0.3 and 0.7 of a volt (about) every second. However I have never been able to observe that on the LEXIA but I have never captured live data while driving. The LEXIA will tell you if it's in closed or open loop mode and if it's in open loop the upstream sensor voltage will remain relatively constant.
My Name: martan

Member
Posts: 2
Joined: Mon Jun 21, 2021 10:46 am
Model: Other
Year: 2005 (05)
Engine Size: 1.6 (16v)
Fuel Type: Petrol
Mileage: 125000
Trim Level: Other
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: LHD (Europe)
Engine name: TU5 16-valve (110 PS)

Post

Have you managed to solve the issue?
I have the same car but LHD, C2 vts Mk1. I changed lots of parts, and all that smoothed out the problem as much as it could probably, but it's still there.

My problem started almost the same as for pinvts. Car would not rev until 2000 rpms. You could say it's a nuisance, but makes it harder to crawl in heavy traffic.

So far what I did.
New crank position sensor (was an error code about it)
New Map sensor (old one was soaking in oil from dirty inlet manifold)
Cleaned the Inlet manifold, changed all three gaskets, new nuts, torqued to spec.
New Throttle body (old one had a bad carbon/oil build up, and I moved the butterfly by hand, big no no here, so changed it)
New Throttle pedal (this made the most significant improvement, as by observing voltage in Lexia, it was dead for first few centimetres of push)
New purge valve (old one was leaking, thus creating a tiny vacuum leak)
Tried blocking the vacuum line to the brake booster (did not help)
New detonation sensor (inlet manifold was taken off, a crime not to changed it due it's location and access to it)
Timing belt kit with water pump, timing is spot on.
New coil pack (Bougicord, mine was the old Sagem crap)
New Bosch spark plugs (previous owner ran on NGKs, heard they are not compatible with Phase detection system)
Removed the catalytic converter (4-1 manifold now, no difference to the problem)
New Upstream O2 sensor
Ecu connectors cleaned (silicone stuff worked it's way down)
Adaptions etc. done multiple times.

What's left:
I kinda hear that my tappets are a bit noisy. I previously had a TU5 lump and tappets were very noisy once I reached 120000 miles with it. This lump has about the same mileage. The cam ladder is leaking in right/end (gearbox end near gear linkage cables) corner. So figured I will fix that leak, and change the tappets as well while I am at it. That's the only thing I have left, apart from complete engine rebuild :evil:
Other thing would be the loom, but broken wires would instantly throw a code. No water/moisture around connectors while replacing stuff. The ecu connectors might have some silicone in there left, that's hard to take out.

TL;DR;

All these new parts, labour and countless swear words later, my car now does not want rev only below 1500 rpm. Sort of. When revs initially drop by themselves, and I press a bit further, I can make the engine rev at 1200rpm, 1300rpm, 1400rpm and so on. Idle fluctuation is still there. Exhaust gas flow is uneven and can be felt. LExia shows ignition timing and fuel injection duration varies as idle rpms move between 760-800 rpms. My previous TU5JP4 lump did not have this issue, while TU5JP4S does.
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