novicebuilder
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| posted on 24/7/16 at 10:05 PM |
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Ford Sierra CVH engine fails warm starting - why?
I have completed my Haynes roadster passed IVA and now on the road - Yahey! TH car was built from a Sierra donor with a 1.8l CVH engine with Pierburg
carburettor. I have used everything from original car and only needed to replace the starter motor and HT leads.
During build it always started first time and ran smoothly. Now I am using it on the road it has developed problems starting. It would usually start
first time from cold and drive well, but there have been a few times when it wouldn't restart after being run. I have been able to bumps tart
it OK. Now it won't start at all.
I have check all the wiring and connection from the coil and rotor arm. I have checked the resistance of th primary and secondary wiring on the coli
and this is fine. I have checked that I put the automatic choke on correctly, and I have as the butterfly valve on carb opens up when engine warms
up.
I took it to a local garage and checked the emissions and they said they were all fine and suggested I avoid tampering with the fuel mixture. They
wondered if short trips were leaving deposits on the plugs.
I checked the spark plugs and they were all carbonised and didn't spark. So I cleaned them all and car started fine. I ran it for a while and
the engine just stopped running spontaneously whilst idling. I checked spark plugs again and they were all carbonised again??
This time i cleaned one but it still wouldn't produce a spark.
I had thought that plugs becoming carbonised was the primary problem, So i wondered whether the gases from the cylinder head feeding into my K&N
filter was bringing in oily gases that were fouling spark plugs but the recent failure of spark plug to spark after I cleaned it seems to disprove
this connection. So I am back to square one. Aaarghh!
Advice about possible causes or systematic checks to detect source of problem would be gratefully received.
Thanks
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gremlin1234
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| posted on 24/7/16 at 11:49 PM |
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quote:
able to bumps tart it OK. Now it won't start at all.
ohh.
check the battery first, then the usual earthing points, and any 'cold start' ignition wires, ie 12v to a nominal 6v coil while starting.
also look in most haynes manuals for the (one) colour page that shows typical spark plug failures
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britishtrident
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| posted on 25/7/16 at 05:00 AM |
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A whole load of different symptoms, taking them in some kind of order
Straight off my first reaction is it sounds like the carb float chamber is flooding, you don't say what kind of fuel pump you are using but if
you using a non-standard pump then the output pressure could be to high for the carb or it could just be the usual crap Pierburgh (aka Solex) carb.
The best first aid way to clear major flooding on a carb engine nb (dosen't work with fuel injection) is to take all the spark plugs out and
crank the engine for a couple of seconds with the throttle held flat to the floor. Then replace the plugs and try again, if this works it confirms
carb flooding is the cause.
The other major cause of cutting out when hot or non-starting when hot is an ignition failure (either the coil or associated electronic module) which
is very easy to check f you catch it in the act. All that is required test that the spark will jump 20mm straight to earth from the end of any spark
plug wire (nb check the spark at the wire not the spark plug) when the engines is cranked on the starter. If the spark jumps 20mm + it
is more than enough to fire the cylinder.
If you don't get a strong spark there test the spark from the centre lead on the distributer -- if you get a strong spark (25mm) there but not
at the ends of the plug leads this points to a rotor arm and or distributer cap problem but this type of failure would show up first during cold
starts.
If you get a spark at the plug lead but not at the spark plugs then the plugs are just probably badly fouled, spark plugs can't really be
cleaned and eventually if repeatedly flouled they will not respond to first aid treatment.
The starting on a bump start but not the starter sugest perhaps the battery is approaching the end of it useful life -- the amp hours capcity of
batteries decreases with age and every discharge-charge cycle.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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r1_pete
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| posted on 25/7/16 at 08:41 AM |
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Also check the anti run on valve on the carb is energizing when your ignition is on, these can stick, open, closed, or midway and cause all dorts of
problems.
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David Jenkins
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| posted on 25/7/16 at 09:23 AM |
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I'd certainly check for dirty connections - maybe something is giving a good connection when cold, but not so good when hot.
Don't forget to check the earth lead from the engine to the chassis as well.
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novicebuilder
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| posted on 25/7/16 at 09:27 PM |
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Thanks to you all. Especially British Trident
I took all the plugs out and turned the engine over a few times with accelerator fully depressed. I cleaned all the plugs then replaced them and it
fired first time. So I presume the diagnosis of a float chamber problem is correct.
What should I do now, or is the problem now fixed?
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novicebuilder
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| posted on 25/7/16 at 09:29 PM |
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PS. I have the standard engine run fuel pump from the CVH, nothing added or changed.
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