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Weird no-start behavior - Engine flinch


Paul7002
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I don't know how else to describe it.  So, my '02 won't start. Or at best it will run a few seconds - everything seems normal - then it stops.  Then it won't fire at all or maybe just a quick splutter.  I'm thinking fuel related.  But here's the weird part:  As I turn the ignition back to the off position, the engine flinches, or jumps, just a tad - The engine moves just a bit on its mounts and the fan moves The Other way, a few degrees.  I can change  a water pump and adjust the valves, so I'm not not completely inept (just mostly 🙂), but I have no idea what would be related to the ignition that would cause this. Perhaps starter related?

 

What do y'all think?

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That 'jump' makes me most suspicious of an ignition issue.  If the cylinder on the compression stroke has some air/fuel mixture in it when the engine stops turning, and then the action of turning the key off errantly triggers the coil, then it'll fire the plug for that cylinder.  And with the engine stationary, a single combustion would not be that powerful, it might turn a little forward, or a little backward!  I'd start at the coil. . .

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It sounds like the 12v resistor bypass relay, that temporarily provides direct 12v to the points when starting is getting wonky, it should be on the firewall right by the distributor, it sounds like it's not passing voltage when cranking then as the key turns to run position it fires one or two times as you turn the key to off.

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Running a Crane ignition system so no ponts or condensor.  But it's the same unit that's been in there for 18 years now so could be suspect.  Ignition switch has been fine.  In fact everything was good (well, except for the choke - that's never been right) right up until it wasn't.  Will check coil, etc. as suggested above.  Thanks all!

Edited by Paul7002
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Have you done a step-by-step ignition diagnosis?  Start with the plugs and see if you're getting a spark when you crank the engine...a nice fat blue spark.  If no spark there, go back to the dizzy--see if there's a spark there...then the coil...  You get the picture.

 

If I had to hazard a guess, I'd suspect the Crane system...electronics do fail...and with your system you can't revert to points/condenser without a lot of work (why I like my antediluvian Delta Mk 10B CD box).  So just keep testing and make sure you're getting consistent spark before you delve into your fuel system.

 

mike

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Coils hardly ever fail. Do you mean that the motor doesn't turn over when you say "the engine flinches, or jumps, just a tad" or will it crank over but not start when you turn your ignition switch to the start position? It is kind of hard to tell from your description what is happening.

 

The first thing to be concerned with if your motor isn't  turning over when attempting to start is your the condition of your starter and electrical system (must have enough juice to power the starter). Do you have a voltmeter? If you have a no crank situation, what is the voltage reading in your battery at rest (ignition switch off)?

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Starter is definitely getting power.  It turns/cranks, but generally doesn't fire. A couple of times (a couple of days apart) it did start and ran seemingly normally for a few seconds.  The little flinch happens as I turn the key back to the off position.  I was thinking fuel but somehow an ignition problem seems likley - perhaps the Crane XR700 system I've been running forever is bad - either the contol box on the firewall or the distributor pieces, or maybe its the coil or a relay as per comments above.  I have not had time to delve into it yet.  A friend who's  way more mechanically skilled is going to take a look with me Monday.

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Typically, ignition systems fail bad- the start and run for a few seconds seems a bit unusual, but who knows.

 

What kind of carb(s) are you running? A quick and dirty test for presence of fuel is to look down a carb throat with a flashlight and pump the throttle. If you have fuel you should see a squirt from the accelerator pump.

 

You haven't said what the situation was before this problem. Was the motor running normally and this suddenly started to happen? Was any work done on the motor recently?

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  • 4 weeks later...
  • Solution

Problem Solved!  Turns out the 18 year-old Crane XR700 ignition unit finaly went bad.  If found this Old post about a problem that sounded a lot like mine.  Replaced both the black box on the firewall and the trigger piece inside the distributer (a fiddly operation but not too bad).  And Presto!  At least so far.

 

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