206, 1.4, 2001 idle fault

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Merlin672
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206, 1.4, 2001 idle fault

Post by Merlin672 »

Having trawled the archive here, I can't see the same problem covered so here is the problem. Hopefully, someone will have fixed this one.
Ign on, crank the engine and it runs briefly, and cuts out. The situation improves a little with a warm engine. The way round it is to depress the accelerator pedal when cranking, raising the revs to around 1500rpm for 3 or 4 seconds, and then the car will idle just fine.
There are no fault codes recorded, present or pending. This has been hooked up to PP, and various sensor actuations carried out. We are satisfied that ECU, MAP, Idle stepper motor and TPS are operating within parameters, and that the CTS is reporting the correct coolant temp. The car has genuine bougicord ign coil and genuine plugs, and has the correct oil, at the correct level. Air cleaner is new.
We have set up the Idle motor again, and with a substitute motor have confirmed that it is functioning correctly. Throttle body (PSA651) is clean.
There are many, many similar problems documented with similar symptoms, but none of them quite match this fault, so there you have it. Thoughts, gents?
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spider
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Re: 206, 1.4, 2001 idle fault

Post by spider »

I would of suspected the temp sensor actually reading high so a weaker mixture, in effect the same as starting a carburettor car with little or no choke (mixture enrichment) when cold.

Does the temp gauge on the instrument panel work properly ? , I seem to recall its just single sensor for these and the BSi (your's is post 2000 so its 'plexed) controls the gauge and the signal to the ECU. They can fail although they usually fail at a short resulting in the gauge reading full and the stop light flashing. I'm half suggested to say replace this sensor anyway given they are relatively cheap.

Its worth checking / cleaning the throttle housing too, although not common on the TU check for blocked breathers and general oil fume residue present on the butterfly area.
Andy.

91 205D-Turbo, gone but still missed
02 106D, TUD5B, gone but not really missed apart from the MPG
Merlin672
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Re: 206, 1.4, 2001 idle fault

Post by Merlin672 »

Thanks for the prompt reply Andy, especially on a holiday.
Guage is accurate, and I was thinking along the same lines but 2 things came to mind. Firstly, planet live data shows coolant temp as being correct, and secondly, I only need to raise the revs momentarily for the idle to settle, so there wouldn't be a significant temp change anyway. However, it's still a good call, i'll arrange one when the dealer opens again tuesday.
I was also thinking that electrical interference from the current draw to starter may be pulling voltage down to idle motor? Can't really explain that comment but got to look at the big picture on this head-scratcher......
Throttle body is spotless, breathers clear. I think i've covered all the basics, but will always take note of advice offered.
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Re: 206, 1.4, 2001 idle fault

Post by spider »

You're welcome. I don't really do petrol running faults that well, I prefer to stick to the (now elderly) XUD units but...

Good thought regarding the current drain with the starter, although I'd expect the petrol TU starters are not very heavy on current but then again it is a starter motor. Multiplexed vehicles do not like voltage drops / spikes.

I would expect the dealer to keep the sensor on the shelf given that they can fail reasonably often.

I can understand where you are coming from with the interference thing, a few years ago I had a 406TD where the tachometer would not work *unless* the glowplug relay was disconnected. It was interference from its wiring that caused it to overload and shut it off. Slightly re-routing the wiring to the glowplug relay fixed it.

As a free thing to try for now, I'd whip the battery leads off (both leads, both ends) and check they are clean. Do the same with the gearbox / body earth strap if one is fitted. After that, I'd just try a standard multimeter on the battery terminals and watch what happens to the battery voltage during cranking.
Andy.

91 205D-Turbo, gone but still missed
02 106D, TUD5B, gone but not really missed apart from the MPG
Merlin672
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Re: 206, 1.4, 2001 idle fault

Post by Merlin672 »

Cheers Andy, much appreciated. I'll do that, expecting to see voltage remaining above 9V during cranking.
XUD fan, eh? Arguably, one of the best diesel lumps ever produced.
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Re: 206, 1.4, 2001 idle fault

Post by Merlin672 »

I think i'm getting somewhere with this problem guys. I will post the solution if my theory is right, so hang on.......!!
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Re: 206, 1.4, 2001 idle fault

Post by spider »

Merlin672 wrote:I think i'm getting somewhere with this problem guys. I will post the solution if my theory is right, so hang on.......!!
Will be interesting to hear the theory even if its not correct ( although I'm hoping it is :) ) as it may give rise to other ideas / thoughts etc.
Andy.

91 205D-Turbo, gone but still missed
02 106D, TUD5B, gone but not really missed apart from the MPG
Merlin672
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Re: 206, 1.4, 2001 idle fault

Post by Merlin672 »

It's fixed! Cautionary tale, guys. One I hope you'll take note of.
The battery on this model is enclosed in a case, and although I was aware that it had been replaced very recently, I had not considered it to be the problem until I conducted a volt drop test. The test, involving nothing more than a DMM to measure voltage during cranking, revealed that the reserve capacity of the branded battery was insufficient to power the relevant components at the same time as supplying the starter. Hence, the stepper motor was starved of current during cranking and when the starter was disengaged, the resulting time gap between disengagement and alternator charging was insufficient for the stepper motor to be powered properly, resulting in a stall.
Fitting the correct battery type has solved the issue. I elected to go the dealer route (£38 plus VAT) as the battery is taller than most aftermarkets ones and ensures correct fitting of the terminals. Result!
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Re: 206, 1.4, 2001 idle fault

Post by CitroJim »

Wow :-D Nice one and a supreme piece of diagnosis!
Jim

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