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Merc 57 Ignition Problems

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shiftymagoo

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I have a 89 Merc 5.7 carbuerat

I have a 89 Merc 5.7 carbuerated. I had a problem the other day where it started and idled but when I wanted to give it throttle it stalled and had a hard time re-starting. I thought it was flooded but once I got it started again I had a look around and noticed a bit of a misfire and then it stalled all together.

I took it off the lake and put it on the earmuffs and started it and was looking for the problem. I could rev it up some times and other times it would stall. then it would stall on its own with a slow death. Shortly before it would do this it would mis more often. After this it would crank but not fire or start.

Today I wanted to check to see it the coil was sparking and I didnt see any spark (tough to check by myself from up front). SO I replaced the coil and tried to fire it up.

It cranked a few times and then it did nothing. I started to second guess that I hooked up the terminal wires correctly and may have blown the coil. So I hooked up the old coil and had the same result ( no fuel pump cycle and no engine response). I tried re-arranging the terminals on the side I wasnt sure about with no change then I tried jumping a wire from the + on the batt to the + terminal on the coil and the fuel pump cycles.

I see that there looks to be a thunderbolt ignition module bolted to the manifold. I thought that this may be the culprit.

Did I fry the coil the module both or what.

I bought this boat with the this engine but it was originally a 305. Done by a marine dealer.

Your help is appreciated. Thanks
 
Main question is did I blow a

Main question is did I blow a fuse somehwere or is it possible to blow the ICM by reversing 2 wires on the coil?
 
"Have you performed the basic

"Have you performed the basic tuneup? plugs, wires, cap, rotor, fuel filters? Under the rotor is the optic sensor that may be covered in rust which will stop her dead.

Perform the following:

Tests for Thunderbolt Ignition:
W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!

#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts is present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced."
 
Disconnect the tach which may

Disconnect the tach which may be fried; gray wire on neg. side of the coil. They are notorious for shorting out ignition when they go bad.
 
"Guy Thanks for your help. The

"Guy Thanks for your help. These will be very helpful once I get things back to where I was before I tried replacing the coil.

My problem now is that I think I may have reversed the connection on 2 wires while re-installing the coil. These would be the + and - terminals on the downstream side of the battery.

I had the fuel pump cycle and got a few cranks out of the new coil and then it stopped. Now I cannot crank or get the fuel pump to cylce with the key.

My thoughts are that I may have blown a fuse somewhere other than the main fuse panel. Or I damaged the ICM or some other circuit.

I know that the fuseable link is not blown as I get other electrical responses on blower, horn and such.

Any suggestions on where to start? Thanks again."
 
"...Disconnect the tach wh

"...Disconnect the tach which may be fried; gray wire on neg. side of the coil. They are notorious for shorting out ignition when they go bad."

Ok so if this was the case what component would be damaged?

There are 4 wires connected to the coil. they are 2 greyish and 2 purrple. I know the ones on the I'll call it the batt side were Purple on + grey on -. On the downstream side I had it at first Purple on + and gray on - then cranked and then nothing. Tried reversing those 2 and nothing. Tried old coil and nothing.
 
tach would be damaged before y

tach would be damaged before your wire flipping; now may be fried. Leave it disconnected for now.

Check your fuse block for blown fuse or if inline fuse at ignition switch. Reset main breaker. Check for 12 volts on coil purple wires.
 
OK so no power on the positive

OK so no power on the positive side of the coil. Non out of the harness to the ICM when I pull it off the ICM. Checked the main breaker by trying to press hard on it but it doesnt move more than a slight button wiggle. I do have 12V on the terminal on the breaker and on another terminal on the other component in that same location.
 
what about fuses under the das

what about fuses under the dash? Main 25 amp fuse attached to large red wire on key switch.
 
OK so after your last suggesti

OK so after your last suggestion I went back and double checked the fuses. There was a 20 amp on the red wire and it looked good but I took a closer look and tested it and it had blown. I replaced it and now I can turn over the engine.

I get 12V on the + of the coil. I tested the harness at the ICM and I get 9-10V on the middle purple and nothing on the white/red and the white/green. I get minimal response on the other 2.

After reading another post where you helped Thomas I decided to take off the ground on the ICM and clean it. I did not get the good result that he got.

I am having a hard time checking for spark as I have to turn the key from upfront. I am thinking about rigging a remote start or buying one of the tools to turn the ignition from the back so I can see if I get a spark. Can I use my multimeter to test for spark in the mean time. I can see the display from up front and it may save me some time.

Thanks again for you help so far.
 
"NO, I am going to do the test

"NO, I am going to do the tests that you mention now systematically, being that I now get ignition and starter response.

Now I have to rig something up so I can cue the ignition from the engine area to look for spark jump on the coil. As I am working on this by myself."
 
"OK so I tested for 12v on the

"OK so I tested for 12v on the Red/Wht on the dist and not 12v present. I took off of terminal and tested for 12V on nothng. I assume that they mean test with ignition on or cranking. Either way it failed and provided no 12V or any signal.

When it says "ignition amplifier is shot and must be replaced" Do they mean the (what I call the) ICM bolted to the manifold?


I took it off to have a better look and I noticed that it has 3 (what seemed to be) non metalic spacers on it, however one of the bolts is a ground so I am thinking that if this is true this could prevent grounding if the bolt is not completely clean. I will clean everything off and attemp to re-acquire 12V from red/wht."
 
"OK so I changed the ICM to a

"OK so I changed the ICM to a new one and I changed the sensor in the distributor. Now I get 12v on the red/wht wire and still no spark.

I have changed the coil,ICM,distributor pickup. I have checked the harness to the ICM>Dist for continuity and its good. I have cleaned all terminals and grounds and checked grounds.

I have determined that I have spark at the coil now but not from the coil to the dist. I am going to replace the coil wire and see if that fixes the problem. Not much else to change out if this doesnt work.

I will let you know how I fare."
 
Shiftymagoo:

You are on the


Shiftymagoo:

You are on the right track. Consider replacing all the wires if they have some years on them. Good work.
 
"Yup, changed coil wire and sh

"Yup, changed coil wire and she starts up no problem. I do think that it wasnt just the coil wire as I was not getting 12V on the red/wht. I am sure that changing the sensor on the dist will pay off anyway.

Thanks for your support you were in-valuable. I hope this post can help out someone else having the same problems. Thanks again."
 
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