BX refused to start, now backfiring

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NeilGP
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BX refused to start, now backfiring

Post by NeilGP » Wed Jul 09, 2014 9:45 pm

Help
1983 BX 1580cc with electric fuel pump, Weber carb

I took the BX out the garage this evening, stopped engine and closed garage. Tried to restart and it fired and died.
It would then only turn-over with no intention of firing.
The fuel filter showed that fuel was circulating, look in the carb choke and press acc and i see a jet of fuel so there is fuel feed.
Took out plugs and they were all dry, so no flooding.
Tried to do a plug spark test but the sunlight killed any chance of seeing anything.
Checked all wiring and a new ignition module, no joy.
Manually trigger coil to check spark to distributor and got good blue spark.
Out of desperation changed the distributor in case of pickup failure (with an approx timing setting).

I had to get a jump start and eventually during turning was making a weak attempt at firing. I jammed open the choke and managed to get it running roughly with the occasional backfire.
It eventually started running a little better and took out the choke jam. Managed to get the BX back in the garage (uphill ramp), with a few carb spit backs. I turned off the ignition and a seconds later go a carb spit back.
I'm hoping that the backfire/carb spitting are due to the distrib timing being off. But don't have a clue why it refused to start.
Water in the fuel bowl?

Anyone any ideas. (I used the BX last weekend with no problems what so ever and the fuel tank is almost full.)
Sorry for the rambling
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Re: BX refused to start, now backfiring

Post by rutter123 » Wed Jul 09, 2014 11:26 pm

Does this have a pre heater in the inlet manifold?
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Re: BX refused to start, now backfiring

Post by demag » Thu Jul 10, 2014 12:07 am

Sounds electrical to me but I'm not too sure. With all that turning over why are the plugs dry? I would try a couple of squirts of petrol direct into the manifold via the carb and try starting it then. If it starts easier that would suggest no fuel. In that case could the pump have failed with dodgy diaphragm? Place the pump output hose into a bottle and turn it over. Does the fuel spurt out? If it does maybe the timing is out. Backfiring usually sounds like retarded timing turn the dizzy a bit and see if anything changes.
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Re: BX refused to start, now backfiring

Post by NeilGP » Thu Jul 10, 2014 6:26 am

No pre-heater.

It also confused me why the plugs were dry. I did spray some COLDSTART but not even an attempt to fire, this was after I changed the distributor.
I fitted an electric pump a few years ago and checked with there is fuel coming out the feed to the carb.

I'm now suspecting a internal blockage on carb.
I will put the original distrib back on tonight and open up the Weber to clean out.
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Re: BX refused to start, now backfiring

Post by Tinkley » Thu Jul 10, 2014 8:29 am

I would defintely strip the carb and clean all passageways and jets with carb cleaner. Also remove the needle valve and float. Check the float weight, you will need a very sensitive scale for this. The Solex Z1 float weight is 7 gm and if over by even 0.5 gm can sit at the wrong height, or not react correctly. I suspect the Weber you have may be just as sensitive. One specialist carburettor company said that fuel is absorbed by the plastic of the float and becomes too heavy, note not actually leaking into the hollow interior.
The Haynes should give you the setting for height but probably NOT float weight. I believe a refurb kit may be available, which should include gaskets and needle valve assembly, but not float.

The other somewhat ignored thing is any diaghrams in the carburettor, especially on the choke side. I do not know the Weber, but on the Solex, I can assure you that after 20 odd years the 'rubber' diaghrams in eth choke part had become incredibly stiff, compared to a nice soft new part. This is also down to unleaded petrol which has different additives in the last 5% of the blend and some of these are not very sympathetic to older polymers used to make these carb parts. So there can be problems because it was never designed to be resistant to the additives now used in current petrol blends. Note how when the US introduced a % of ethanol into their blends (was 5 now 10%) a whole load of fuel pipes rotted out, especially on outboard motors. There have been a lot of fires started because of this.

One other small point is to check the oil filler cap/breather. Remove and clean any mayonnaise in the wire entrapment part (with petrol) as it may be feeding into the air filter and even into the main jet(s). Not sure of the layout of the early 1.6 but if the crankcase breather pipe can feed into the carb inlet pipe from air filter it might be throwing mayonnaise into the carb from the air intake. Depends if the feed (c/case breather) is before or after the air filter in the system.

Obviously, check the distributor cap (sparking externally?, cracked cap, pitted contacts?) and rotor arm etc. Also do not ignore HT leads, check the ends of all of them, sometimes just one bad corroded end will be the cause especially if the main coil to distributor feed. Last time I had 'rough' lumpy running it was indeed an HT lead. Whilst the 1.4 150C engine eats leads for breakfast the 1.6 unit is much kinder to them, but because they are left in place longer corrosion can occur at the ends, or they get so old the things break down internally.

In conclusion, I would clean carb and check the leads (change set?) as first recourse. Only after that would I start to attack the carb more seriously.

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Re: BX refused to start, now backfiring

Post by Thread Bear » Thu Jul 10, 2014 8:41 am

Not sure what Coldstart is. Easystart ether should prove if sparks are fitted under load. The timing can be roughly checked with one plug out so as to suggest a fuel issue or not.

My only visitation to the carb on these cars suggests they are not very good and ill positioned to work efficiently. The one thing I did not check, having got terminally despondent at the choke and associated emission fittings to give up, is if they have a fuel cut off switch on them. On previously so equipped cars the source of all sorts of problems and another addition to the various bits parasitising the carb that want to be binned. If the car was fitted with a quality fuel pump it would not need a stop cock, would it? So if there is one of these, check it is working, ie energized it allows flow, none energized it does not, and working all the time and not jacking itself off prior to finally not working.
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Re: BX refused to start, now backfiring

Post by Tinkley » Thu Jul 10, 2014 10:44 am

Thread Bear wrote: My only visitation to the carb on these cars suggests they are not very good and ill positioned to work efficiently.
They are not too bad, but agreed I prefer the manual choke versions (of the Solex) at least. One big problem on some of the early cars was isolating the carb from heat from the engine. A lot of problems were cured by double stacking the insulator piece to place the carb higher on the manifold. Citroen themselves changed the gasket thickness ie to thicker on slightly later cars. More fuel frothing/too hot issues, than not starting problems. Generally I would say my 1.4 (150C) and 1.6s' have usually started OK but if you stop them after say between 1.5 and 4 miles, thay can be a pig. This is down to the lean settings and the engine being in between cold and hot, and not quite knowing what mixture it wants!.

So the old lay down 150C engine was worse than the 171 type (and TU) as it lay completely under the carb. You are limited how far you can raise the carb by the bonnet height. Note on the 1.6s' the inlet rubber manifold feed touches the sound insulation on the underside of the bonnet. On an early one, this may not have been fitted. I don't think this is the cause of Neil's problem though.

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Re: BX refused to start, now backfiring

Post by electrokid » Thu Jul 10, 2014 11:20 am

if they have a fuel cut off switch on them.
If it's the original carb then it's a Weber DRTC which IS normally fitted with an electrical cut-off switch (similar in action to the cut-off solenoid on a diesel pump) so although switching the solenoid off is not the only means to stop a petrol engine, it does need to be functional for the engine to run.

Providing there are no petrol fumes around (because this will cause sparks) - switch on the ignition and then disconnect and reconnect the wire to the cut-off solenoid on the carb keeping your fingers away from any of the electrical connections because the solenoid is an inductance and will store energy which is released when you disconnect the wire - this energy in the form of a big fat spark - has to go somewhere - up your finger is not the best place for it to go.

Connect and disconnect and listen for the mechanical activity of the solenoid plunger operating. If it can't be heard then remove the solenoiud and try it again - use a croc-clip lead to earth the body of the solenoid and use the same precautions to avoid electric shock.
The other somewhat ignored thing is any diaghrams in the carburettor, especially on the choke side.
Worth checking but it doesn't sound like a failed diaphram though anything is possible. It should run / tickover without the pump diaphram but it will likely stall when the throttle is pressed unless great care is used. There is an anti-stall diaphram fitted - if this was failing you will have noticed the mixture getting richer / lots of black smoke from the exhaust - they don't usually fail suddenly and when they fail there is serious enrichment - your plugs would be soaked with petrol. To check the anti-stall diaphram, find it on the carb - there will be a vacuum pipe attached - remove the vacuum pipe and sniff it - if it stinks of fuel or if the pipe end is wet with fuel then the diaphram is stuffed and needs replacing - you'll probably only find one in the carb service kit.
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Re: BX refused to start, now backfiring

Post by NeilGP » Thu Jul 10, 2014 12:42 pm

The carb is was new out the box on only about 3years, 15k miles old.

I did think about the solenoids and I only checked the idle cut-off one, I should have checked the float chamber one as well.
There also appeared to be no blue or black smoke from the exhaust when I did get it running

The BX was MOT'd last week with 1.9% CO2 reading so the mixture was OK. The thing that I don't understand is it was running brilliantly then all of a sudden decided not play. I even took off the cambelt cover to make that the belt hadn't broken! (changed 2yrs ago)

Changing the distributor may have added faults, as will change this back tonight, try it, then clean the carb.

The only other thing I can think of is that I had previously put some diesel instead of petrol in the tank, (3gallons diesel and topped up with 7gallons petrol). It did run on this, with the occasional puff of clue smoke, before I drained the tank.

But to me, none of this make sense to the cause.
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Re: BX refused to start, now backfiring

Post by jeremyC5 » Thu Jul 10, 2014 3:26 pm

perhaps not all the diesel drained out, and you've got a 'lock' of diesel in the pipe, might be worth just pumping through the line and make sure you have only petrol in it.
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Re: BX refused to start, now backfiring

Post by demag » Thu Jul 10, 2014 5:56 pm

Neil did you try squirting/pouring a little bit of fuel direct into the carb/manifold? This will prove if you have sparks and they are working. My old Txs played up like this once and it was the idle jet blocked. It wouldn't tick over but with a boot full of throttle it would rev fine. I squirted carb cleaner into every orifice I could see which did the trick.
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Re: BX refused to start, now backfiring

Post by Tinkley » Thu Jul 10, 2014 5:59 pm

Only takes one of the 5 HT leads to go and it will give incredibly similar symptoms to those you describe. Try substituting one by one if you cannot see a corroded end. The last time I had one go, a couple of years ago (1.6 TGS), I limped back home and went through it, at night because I needed to tow the boat somewhere. It could have been anything you mention, but sure enough it was a lead. It popped, banged, ran rough, had to keep revs up etc etc. Change the offending lead, sweet as a nut, off we went down to Penzance some 260 miles away....and had a great weeks sailing at Mounts Bay.

Trouble is, if you just test the spark on the plug with it out and earthed to engine, there is no compression to show up a weakness in the power of the spark. I always tend to work from the simple things backwards, so plugs, leads, distributor cap, rotor arm, ignition coil, distributor in that sort of order. The RAC man who told me 'definitively' that my distributor had gone, when car broke down in Old Street London, was wrong - it was the coil, almost the cheapest and easiest thing to fix on the old 1.4 bar plugs. Not knowing enough about these BX things at the time (I'd had it about 2 years), I learnt my lesson, happy with bikes, but not car knowledgeable, at the time.

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Re: BX refused to start, now backfiring

Post by NeilGP » Thu Jul 10, 2014 8:49 pm

I went back and started it this evening, it started by ran very very rough.
I then put the original distributor back in and it now runs like a dream. I left the carb as is, it works so don't fix it!

I checked the 'replacement' distributor and found the advance vacuum was useless. But I still don't know what caused the original failure. It may have been as been suggested a diesel lock and the many attempts at starting had eventually cleared it.

I've left it in the garage till the weekend and do more of a check of the electrics and change the coil for a new one as a precaution. (also when my brother comes back from hols if I need a tow!)
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Re: BX refused to start, now backfiring

Post by Tinkley » Thu Jul 10, 2014 11:24 pm

Good, sounds like your getting there. It is also possible to get a blockage in the vacuum pipe, like little spiders get in there etc. Don't ask how, it just happens. I have known them block an outboards water system cooling ducts inside a week!.

Just keep a spare lead handy, though!. Coils tend to fail at low speed but high load and also when spinning up high where they lead to a misfiring pattern. So pulling away and cut out is a classic low speed coil fail. It might restart but need more revs than normal, an indication it is failing.

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Re: BX refused to start, now backfiring

Post by B-Hive » Mon Jul 14, 2014 1:24 pm

FWIW

I had 2 very similar issues with both my Mk1s, and to this day have never been able to pin point exactly what happened.

They just worked properly one day after a little rest.
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