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BMC 1.5: occasional misfire, some smoke, running fast on idle


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I have a BMC 1.5 that has always been very reliable. However a few months ago it started to occasionally misfire on idle and with each misfire a small puff of smoke (more white than any other colour) was seen at the exhaust. All fine under load.

 

All filters are new and oil changed etc. Next I took out the injectors to be checked. They were in poor shape had them all reconditioned.

 

The engine continues to run fine under load but still get an occasional misfire on idle (every 2 or 3 seconds, but not regular) and the smoke now is definitely bluer. The other change is that it is running much faster now in idle than it did before the injectors were reconditioned.

 

A local diesel injector company have suggested that I do two things:

 

1 - remove the top from the lifter pump and clean a mesh filter underneath

2 - remove the backplate on the fuel pump (where the inlet pipe joins the pump), and clean another mesh filter in there.

 

Any other tips before I start working my way through the fuel system?

 

On a seperate note (but possibly contributing to the issue) the air filter is one of these (foam filter inside). Is this standard? I have never been convinced it is what was meant to be on this engine.

 

 

airfilter.png.bbf73e10e7013acef50afcdc569149ef.png

Edited by rgriffiths
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I wonder how much backlash you have in the camshaft and injector pump drive. If only does it at idle I would suspect excess backlash. This could be a stretched timing chain and worn tensioner or, if you have not been cleaning the injector drive lubricator and strainer, worn pump drive and/or camshaft skew gears.

 

I don't know how confident you feel about taking the pump off and checking how much play there is in the drive or taking the timing cover off for a look-see.

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1 minute ago, rgriffiths said:

Thanks for the thoughts. Will check the tappets and do a compression test tomorrow.

 

Can you confirm that these mesh filters are worth taking a look at?

 

If dirty or if t has been fitted with closed cell foam it might explain the "blue" smoke that may be greyish black, but unlikely to cause a misfire as described. try it with no filter.

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32 minutes ago, rgriffiths said:

Sorry - I was meaning the mesh filters in the lifter and fuel pump as suggested by the injector company I contacted.

 

A blocked filter in the lift pump is, in my view, unlikely to cause a misfire but may cause a loss of power/speed,. An air leak into the lift pump from the large  O ring in the cap or the soft washer around the cap bolt just might cause a misfire but more likely the engine would rev up and stop.

 

The strainer in the injection pump rarely causes a problem in a half decently maintained engine but if it did partially block the engine would most likely rev itself up a bit.

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5 hours ago, Tracy D'arth said:

If any doubts, get a compression test done.

 

In my experience an engine with poor compression is a bitch to start, but once running its fine. 

 

Dear OP, does your BMC start easily or does it need a good caning?

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Just a quick update, along with thanks for all the tips.

 

It turned out that a combination of putting in a thermostat (I didn't realise it was missing), a glowplug not fully tightened, a couple bolts holding down the throtle cable in place loose causing the high revs on idle. etc etc. All these little things sorted and the engine runs much better with no misfiring.

 

So a bit of a false alarm but all advice above very useful for the future - thank you.

  • Greenie 2
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Pleased it is sorted but I can't see how any of them could cause an occasional misfire.  The glow plug may have caused a chuffing sound and worse cold starting and the loose cable may well have caused the idle to alter. I can't see how a missing thermostat would cause any easily noticeable problems apart from a low running temperature and  a very long warm up.

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My BMC 1.8 used to puff out sweet little white smoke rings, from cold and until it was warm. (But not always, and there was a period of about a year when it stopped doing it, then it began again one day.) It might be interpreted as a misfire, and may be what the OP was talking about.

I rather liked the smoke rings which were about 3 per second.

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45 minutes ago, Stilllearning said:

My BMC 1.8 used to puff out sweet little white smoke rings, from cold and until it was warm. (But not always, and there was a period of about a year when it stopped doing it, then it began again one day.) It might be interpreted as a misfire, and may be what the OP was talking about.

I rather liked the smoke rings which were about 3 per second.

 

I think you might well be correct in that it was a phenomenon that had misfire attached to it rather than give more of a description.

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