206 8v engine mild hesitatancy plus bonus breakdown story

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pentoman
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206 8v engine mild hesitatancy plus bonus breakdown story

Post by pentoman »

Hi everybody,

I've got a '00 206 with the 1.6 8v which I enjoy although I have always been convinced it is mildly hesitant and not as responsive to the throttle as my girlfriend's '98 106 1.1. I didn't worry about it because, frankly, I try to keep this as a fully functioning everyday car and spend my car-fixing time on my Cosworth Mercedes (old school).

But on the way back from London to my adopted hometown of Cheltenham in the West Country last weekend I lost most power and limped home on maybe 2 cylinders at a maximum of 50 mph. This was quite interesting as you can imagine as I effectively had a 0.8 litre engine and 45bhp. The orange engine light eventually came on. I lied earlier by the way, I didn't really limp home but limpted to my independent garage which - I suppose luckily for me - is run by my own parents. "Yay free repairs," you may think, but the truth is that I pretty much have to fix any problems myself, albeit with the support of a well equipped garage. And I work in IT and am not especially mechanically minded.

So, I plugged in the diagnostic laptop, read the engine's errors and saw:

Double-spark ignition coils 1/4 faulty
Double-spark ignition coils 2/3 faulty
Speed/reference-mark sensor faulty
Oxygen sensor 1 (in front of CAT) faulty

My inexperienced self already suspected the coil pack as the problem, and luckily my parents had a '01 206 1.4 there which I was able to borrow the coil pack from. It instantly solved my problem - great, problem solved new coil pack time for me. But I was interested in the rest of the diagnosis - the oxygen sensor faulty error apparently only came up due to me driving it home with the faulty coil pack and everything being out of expected values. However the more interesting one is the Speed/reference-mark sensor faulty. This apparently could cause the poor throttle response I describe. The new coil pack didn't make any difference to it.

After reassembling the other 206 1.4 I took it for a drive to ensure it was working correctly and it did. Not only that but it was a bit of a rocketship - really sharp throttle response and decent acceleration. By comparison my 1.6 is just as accelerative but has a very unsharp throttle, almost like a diesel but not quite. The difference to drive is night and day.

End of a long story then, but I hope it's been a little bit interesting......
does anyone know the possible cause of this? The car is FSH and last serviced 10k miles ago, just had cambelt, otherwise drives v nice.
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Post by jgra1 »

hi Pento

1 thought.. maybe some of the diagnostic 'leads' were present before you limped.. but you just uncovered them while the coil problem came about..

Others will come along and offer more useful info :)

John
pentoman
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Post by pentoman »

jgra1 wrote:hi Pento

1 thought.. maybe some of the diagnostic 'leads' were present before you limped.. but you just uncovered them while the coil problem came about..

Others will come along and offer more useful info :)

John
I reckon they must have because there were so many. I seem to recall that when you read them, the light goes out - whether or not you cleared them.

By the way, I got the new coil pack and it didn't fit - the connector was slightly different with a bit of plastic plug being a couple of mills bigger and therefore not allowing my connector to plug onto it. The plug was grey where the old one was black I wonder if this was relevant.
pentoman
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Post by pentoman »

Well the right coil came, and it runs again, yay!

The speed/reference-mark sensor warning came up again though so i'll be replacing that.
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Post by AndersDK »

It is the rule that one true failure on the engine, ALWAYS sets a couple of other failure flags.
Thats where the experience and knowledge of a good mechanic comes in to judge whats true and whats fake errors.

Look at it the same way as when you compile a source code for a new program :
a missing THEN in an IF statement may cause hawock in the compiler error report (or did so in earlier systems at least) :lol:
- but you dont go correcting all lines of source code after the initial erroneous if-then statement - right 8)
Anders (DK) - '90 BX16Image
pentoman
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Post by pentoman »

AndersDK wrote:It is the rule that one true failure on the engine, ALWAYS sets a couple of other failure flags.
Thats where the experience and knowledge of a good mechanic comes in to judge whats true and whats fake errors.

Look at it the same way as when you compile a source code for a new program :
a missing THEN in an IF statement may cause hawock in the compiler error report (or did so in earlier systems at least) :lol:
- but you dont go correcting all lines of source code after the initial erroneous if-then statement - right 8)
:D thanks for that.
I'll see if the fault appears again but I'm pretty sure it's the sensor.... the diagnostic comptuer is miles away from my house so I might just replace it anyway as a french parts place is dead nearby.
pentoman
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Post by pentoman »

Well I have fitted a new flywheel sensor, but the problem is still the same.

Just in case my first post was far too long to read, my problem is a hesitancy on initial throttle press - almost like a misfire. Worst at idle when you blip the throttle - the revs actually die before they rise.

I also tried disconnecting the MAP sensor (by the way it's directly mounted to the intake so there's no rubber tube to have split), the throttle potentiometer and intake air temp sensor but no change at all. Each one threw the correct error code when disconnected (and I figured out what each one is because of that!).

These are the values displayed while idle or revving - perhaps someone can say if they're normal?

MAP sensor:
approx 300mbar idle, jumping up to 1000mbar on revving it

IA Temp sensor:
28 degrees

Throttle potentiometer:
500mv idle, maxing out at 4700mv on full throttle.

Coolant sensor read 80 degrees.

Engine correctly identified 'idle', 'partial load' and 'full load' situations.

Throttle angle, whatever that is, went from 0 degrees idle to 75 or 83 degrees on full throttle.

Injection duration was about 3ms at idle.

Any of these seem wrong? Next steps? I'm running injector cleaner through it with this fuel tank.
pentoman
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Post by pentoman »

Injector cleaner did actually clean up a little hesitance/barely detectable misfire the first millisecond when you blip the throttle.

However made no difference to throttle response which is still squidgy.

Next I'm thinking fuel pressure?
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