BX 16v misfire

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citroenesque
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BX 16v misfire

Post by citroenesque »

Hi, although the car's always been lumpy at idle, it has definitely turned into a misfire. I'm intending to change the HT leads (I know the resistance has broken down on them as I got a bit of a shock from them the other day), the distributor cap and rotor and spark plugs. But I'm a bit concerned.

I went through a ford (water not car lol) and it was quite deep but the car was fine, had a bit of a misfire after about 12 miles at a roundabout but I thought it was a one off. Sprayed WD40 around any bits that might've got wet, but the misfire has returned. The reason I'm worried is that I checked the expansion tank and there's some frothing in there. Is this pointing to a head gasket failure? And did I inadvertently suck in some water? I'll check the air filter's not wet: that might be a start.

Anyway I'm a bit worried, so any advice would be welcome.
1992 Citroen BX TZD Turbo Diesel hatch, white, 92k
*SOLD* 1998 Citroen Xantia Ser.1 Turbo Diesel manual, Desire Limited Edition hatch, Mauritius Blue, 118k
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Post by CitroJim »

The usual cause of misfiring on the valver engine is the ignition amplifier. This is the little lozenge shaped Bosch box mounted on a lump of aluminium. They often fail because the heatsink paste between them and the aluminium plate that acts as the heatsink has dried out over the years. This amplifier module is used on a whole raft of XU series engines and is still readily available quite cheaply. Often they betray that they are dying by being OK at low'ish revs and mis-firing as the revs build up. Try to get a genuine Bosch one, the pattern ones are said to be not so good. If you do replace it, give it a good smear of heatsink compound before refitting, but not too much. Too much is as bad as too little.

The coil is suspect as too is the in-line connector from the distributor body to the ignition amplifier. Damp may have got in.

As you've forded recently, it may be worth checking there is no water lying in the valley between the cams where the plugs live; it can't escape easily from there and a bit of damp can cause havoc, as can damp in the distributor cap. It's exposed enough to get a dousing when going through water.
Jim

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citroenesque
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Post by citroenesque »

Thanks for the advice.

The car's much better now. Fitted brand new NGK three prong spark plugs. Fires much better - now that all the water I found between the cam cover sides (as you suggested!) is gone and any moisture in the cylinders was got rid of! The HT wires are cr*p though, so a new set will go on - together with the dizzy cap and rotor that I have here anyway.

Interesting about the lozenge-shaped Bosch box you mention. Where is that precisely? (Sorry, not got the engine bay handy lol!)...
1992 Citroen BX TZD Turbo Diesel hatch, white, 92k
*SOLD* 1998 Citroen Xantia Ser.1 Turbo Diesel manual, Desire Limited Edition hatch, Mauritius Blue, 118k
2003 Rover 75 CDTi Connoisseur SE Tourer auto, BRG, 135k
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Post by CitroJim »

The amplifier is often mounted up on the bulkhead or an inner wing. On the 205GTi for instance, it lives on one of the suspension strut towers and on my Activa it lives on the chassis rail down by the alternator. It might be hiding well..

The froth you see in the expansion tank may be nothing to worry about. The first signs that the head gasket is on the way out is cooling system pressurisation. The gasket usually blows into the waterways and causes the top hose to quickly go rock-hard from cold start-up and for the coolant to be dumped rapidly out of the expansion bottle. Another early sign is that the temperature stays relatively normal during quiet driving but rapidly climbs when you start driving enthusiastically.

Another test is to go to your local MOT man and ask him to poke his emissions tester probe into the expansion tank. If this detects any exhaust gasses in the coolant, the head gasket is on it's way.

If all this is clear and you're not having to top up the coolant frequently then you have nothing to worry about.
Jim

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citroenesque
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Post by citroenesque »

Many thanks. I think my problems were all water/ignition associated (didn't help having plugs past their best and leads leaking current all over the place!).

But I will have a check - I don't seem to be losing any coolant. Fingers crossed.
1992 Citroen BX TZD Turbo Diesel hatch, white, 92k
*SOLD* 1998 Citroen Xantia Ser.1 Turbo Diesel manual, Desire Limited Edition hatch, Mauritius Blue, 118k
2003 Rover 75 CDTi Connoisseur SE Tourer auto, BRG, 135k
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Post by tim leech »

Phil where did you get your leads from in the end?
1994 XANTIA 1.8i SX 132k, From new, Slumbering
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citroenesque
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Post by citroenesque »

A set of K1 Racing (made to order) 8 mm leads. Should get them next week latest. Magnecor OK, but couldn't order them online because I don't have platinum American Express or something!

The ones I'm getting are from a local specialist suppliers.

Those new plugs have made a difference so I'm looking forward to what the rest does! 8)
1992 Citroen BX TZD Turbo Diesel hatch, white, 92k
*SOLD* 1998 Citroen Xantia Ser.1 Turbo Diesel manual, Desire Limited Edition hatch, Mauritius Blue, 118k
2003 Rover 75 CDTi Connoisseur SE Tourer auto, BRG, 135k
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CitroJim
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Posts: 49532
Joined: 30 Apr 2005, 23:33
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x 6163
Contact:

Post by CitroJim »

Phil,

I am likely to have made a small error on the ignition amplifier location. I spent a long time in the world of 205GTis and Mi16 conversions (I still shudder at all those poor BX16s that gave their lives for 205GTi conversions) and forgot they often did not use the stock Mi16 distributor in such conversions, perferring to use an 8V distributor on an adaptor with a different ECU and so on, hence the outboard amplifier module on those.

I think you'll find your amplifier is mounted on the side of the distributor but much the same applies to it as the outboard one.

Sorry for that, I've had a day of silly errors one way or another today :oops: :roll:
Jim

Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
citroenesque
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Joined: 28 Feb 2008, 19:16
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Post by citroenesque »

Jim, it's academic - you haven't wasted my time - it's been too dark to see anything there anyway :lol:

Cheers for the advice. I will have to make sure the amplifier is located before I go messing about changing distributors.
1992 Citroen BX TZD Turbo Diesel hatch, white, 92k
*SOLD* 1998 Citroen Xantia Ser.1 Turbo Diesel manual, Desire Limited Edition hatch, Mauritius Blue, 118k
2003 Rover 75 CDTi Connoisseur SE Tourer auto, BRG, 135k
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