Engine won't fire--how to tell if coil is bad

[rwaterbury]

I've got a chaparral 5.7L Volvo Penta I/O that won't fire. The starter turns the engine just fine but the engine never tries to fire. Since I've had problems with my kill switch I originally thought it had something to do with that but I checked and there is 12V going to both leads on the coil. If I disconnect the lead coming from the coil to the distributor cap and hold it ~1/2" from a ground (engine block) I get no spark when I crank the engine. Is there anything besides a bad coil that could explain this?

I'm puzzeled a little cause the engine was starting just fine. I replaced the AM/FM radio and now have this problem. My original guess was that some electrical connector under the dash came un connected. I check everything and can't find it. However I'm assuming that since I get 12V to the coil that the kil switch and all other connections are OK. Is this the case?

Thanks in advance.

 

[Don S]

Re: Engine won't fire--how to tell if coil is bad

5.7L Volvo Penta I/O

Volvo has been using 5.7's for a lot of years and all kinds of different setups. Got a full model number of your engine?

 

[Maclin]

Re: Engine won't fire--how to tell if coil is bad

This is just a shot in the dark, but is simple to eliminate as a problem. There are probably two wires on the negative terminal of the coil. One goes to the distributor and the other is probably gray and is the tach signal wire and goes to the tach in the dash. You may have grounded that wire accidentally somehow during the install of the radio. It is simple to check, just remove the grey wire from the coil and try starting. Tachs can also short out internally and cause the same problem. If the negative terminal on the coil is grounded all the time then it cannot generate spark.

 

[rwaterbury]

Re: Engine won't fire--how to tell if coil is bad

The full model # is 5.7GL/SX.

Also both terminals on the Coil are at 12V (gray & purple wires I think) when the ignition is on so I don't think they are shorted.

 

[Don S]

Re: Engine won't fire--how to tell if coil is bad

The full model # is 5.7GL/SX.

No, that's not the right answer.
Have a look at this Volvo ID bulletin.

Click here

 

[rwaterbury]

Re: Engine won't fire--how to tell if coil is bad

Sorry Volvo 5.7GS

 

[Maclin]

Re: Engine won't fire--how to tell if coil is bad

Point of clarification, on measuring the voltage at the coil to determine if something is shorted or not, using a voltmeter as described will not show that condition because they measure voltage potential. If you have your meter grounded at the battery or other suitable ground and check at the negative terminal of the coil with the ignition on you will see 12v potential (or thereabouts) even if the negative terminal is touching ground. The reading will be virtually the same grounded or not.

The tach may not be the problem, I just wanted to clarify that the reasoning you gave would not show it as the offender. If you remove the tach wire from the coil and use an ohmmeter to check it then you may be able to determine if it is grounded or not somewhere between the coil and the tach. Or just remove it and try the test for spark again to eliminate it as a possibility.

 

[legoman67]

Re: Engine won't fire--how to tell if coil is bad

i had a simular probelm the other day, on a mercruiser. Turns out one of the small leads on the postive coil terminal was loose and touching the block causing it to short. It wasnt anything obvious though, no hot wires, no smoking, nothing, just no spark at the plugs. follow all the leads comming off the positive end and make sure there is not a short. Or if you are comfortable with it you can remove all the leads except for the ones going to the dizzy and try to start it by hotwiring the coil. If it works then you know that you have a short somewhere. Read up on ground running a marine engine, that will tell you how to start it without having the dash hooked up