excel 225 no start

[1987suncat]

I have a 1987 excel 225 that will only start in the microprocessor bypass mode. I'v cleaned the crank position sensor and it has 720 ohms

Ive cheked the yellow wire in the main harness it has 9 volts or more during cranking.

Any ideas ??

[boats.net]

Test crank sensor with peak reading voltmeter to see if within specs.

[1987suncat]

Using a DVA while cranking ? What is peak volt spec. ?
On a side note as I'm cranking when I let the key off it sometimes backfires through the exhaust ??

[rodbolt17]

if it runs in bypass we can eliminate pulser coils,stator and ign coils.
now focus on inputs to the ign system modifier(micro processor).
voltage in,grounds such like that.

[1987suncat]

Got it I'll check them all real close. As a test could I run cables from the battery straight to the ground lead at the starter and the poss. lead at the rectifier ?

[rodbolt17]

if it cranks over and starts I doubt battery cables are your issue.

[1987suncat]

Gotcha.... it seems to have the same characteristics and a bad crank sensor on a auto I had. Other then an ohm test how could I test it ?

[rodbolt17]

voltage output, and much below about 10V on the yellow wire to the processor,the processor drops offline taking spark with it unless bypassed.

[1987suncat]

OK so I had 9.6-9.8 at the yellow wire just before entering the processor under cranking. So I used a jumper wire from the battery and supplied it with 12.6 and it started !! About 2 hours later I tried it without the jumper ...it started. I've had someone try it several times throughout the day without the jumper and it starts, then after about 12 hours it didn't start again.

When I get back to it tonight I'll try it again with a jumper ???

[rodbolt17]

now go find the bad splice or connection.

[1987suncat]

Even with a jumper wire supplying 12.6 to the yellow wire which goes to 10.2-10.6 under cranking it won't start. but will in bypass ??

Is my bad splice or connection on the yellow wire circut ??

[rodbolt17]

could be the ground path.
simple voltage drop testing can find out.

[1987suncat]

Voltage drop is .001 at the microprocessor .... i'll keep checking ???

[1987suncat]

Hello again, been out of town for a week and now back at it.
I'm going to start over with voltage inputs and ground path voltage drop tests.
Would the tp sensor, knox, thermo, and crank sensor prevent it from starting or just make it not run right ?

[rodbolt17]

if any of the sensors failed it would start just not run correctly.