Need help trouble shooting 2007 model 4.3 mercruiser ignition

[casey.d]

Hello all and thanks in advance for the input. I am trying to help a friend troubleshoot his mercruiser. The boat is a 2007 with a mercuiser 4.3L v6.
The engine is carbed, S/N 0W658073 "family" 6M9XM04.32VC D.O.M. JUL2006. This engine has an ignition module located on the port side exhaust with P/N 861251-1.

I know that this boat gets regular use and has ran like a top all summer, I have boated along side him several times this year. His complaint was that the engine would not run up to proper RPM and complained that the boat acted like it was trying to idle along and wouldn't plane. All of this occurred between usage, no work was performed.

I began with listening to the engine running on muffs and everything sounded good, it would start up instantly and idle seemingly fine. I placed a timing light on each plug wire and ensuring that all cylinders were firing, looked good.

I removed the dist cap and cleaned corrosion off the spark points and rotary piece and re-assembled in the same position. ( did not loosen or rotate distributor)
Afterward the engine still started great and idled smoother than before.

I then removed the anti-siphon valve and knocked out the ball and re-installed. Checked the fuel filter at the top of the carb and it looked perfectly clean. The fuel looked clean and smelled like good fuel.

I also checked the oil for water intrusion and it looks perfectly clean as well. We stopped here and decided to water test a few days later.

Go to water test and the boat will not start at all, not even a cough. I switched out the fuel line from tank to pump with a new rubber hose in case i made a hole in the original one, re-installed the now hollow anti siphon valve with some sealer on the threads only. No change.. Removed fuel line at the top of carb and verified fuel was pumping while cranking the engine over... fuel pump is moving plenty of fuel and the carb seemed to be moving plenty into the venturi as well.

I was able to get the boat started by advancing the throttle quite a bit in neutral. It now runs even worse and will not maintain idle, acts like it starts loading up and flooding out. I checked with the timing light again and it looks like cylinder number 2,4,6 are firing regularly but numbers 1,3,5 look really erratic. I tried to read up on timing this model (hard to do using smartphone) and found to ground the PUR/WHT wire to lock in base timing mode.

I then disconnected the normally open switch that is on the starboard side exahust (used for neutral shift safety) I checked continuity between the black wire that was previously on the shift switch to the NEG battery terminal... had continuity.... then took the PUR/WHT lead that was unused and connected to the grounded black lead to lock in base timing mode..

No change as far as the firing of 1,3,5 I would get a few hits here and there but nothing steady like 2,4,6. I loosened the distributor and tried to rotate it with to get 10deg while on number one lead. I saw what looked like inconsistent firing and wasnt able to get close to 10deg on the flywheel. The engine would only stall easier. I was trying to get to 10deg in between small revs with the engine because it would load up and stall if I let it idle more than 20 sec or so.

Sorry for the rant, trying to be detailed as possible so that I can get the best help possible. I am stumped as to why it ran in his drive way and wouldnt run at the ramp even out of the water without alot of throttle advance. All the plug boots where on and I am certain that I did not move the distributor and placed the cap back in the same position prior to the the water test. It started in his driveway no problem and idled smooth. Now its all jacked up. Ive moved the distributor and unable to get proper timing and maintain idle.

Where should I go from here? Thanks

 

[achris]

The switch on the stdb elbow is the shift interrupt switch, and it should be normally OPEN. (neutral safety switch is in the control box and will only stop the engine being cranked). HERE is a write up on the ignition system. That describes how the system works, and give a you a flowchart to diagnose problems, but with a consistent spark on even cylinders and nothing/intermittent on odd, I'd disconnect the shift interrupt and re-check...

Chris....

 

[alldodge]

Pull the distributor cap back off and have a look.

 

[casey.d]

Thanks for the feedback.
I hope to get back to troubleshooting within a few days. I will follow the guide posted above to the letter and make notes along the way. I hope to obtain a fix but if not I will report back with the results and keep bouncing ideas off the experts on here.

 

[casey.d]

I had some time to get back to troubleshooting today and wanted to post the results to gain some feedback.

I checked the ground for the distributor pickup base, WHT/RED and WHT/GRN leads to module, cleaned the denso box contact plugs, checked all plug wires, distributor cap, coil wire, oil pressure switch wire, and just a good all around spot check prior to following the trouble shooting guide posted above.

I removed the shift interrupt switch contacts, and removed GREY lead to ignition coil
I checked for 12V on the purple wire to ignition coil. had 12V
I checked for 12V on the WHT/RED wire from module to distributor pickup base.. had 11.4V
I removed the coil wire from distributor and installed a make shift gap tester, attached a jumper cable from batter neg terminal to exhaust manifold in order to have a good ground up top and then tapped the WHT/GRN lead from module to the grounded cable. No spark from ignition coil..

I was certain others said to remove the GREY lead from coil but re-installed after the no spark condition... Now have spark coming from coil with both GREY and PUR wires to coil. I reconnected coil hight tension lead wire to distributor, shorted PUR/WHT wire to ground for base timing and tried to start.
Engine now starts and maintains idle. I was able to set timing at what i think is 10 deg BTDC.

The engine started without hesitation or failure numerous times, maintained smooth idle, and revved crisp. In regards to the timing on the flywheel. There is a label marked 9.......0........10 from left to right on the flywheel. I placed timing in base mode just to the left of 9 where the label "begins". I could turn the distributor to obtain the 10deg mark to the right of 0 deg but it seemed to run best left of the 9 mark before 0... I assume this is 10deg BTDC but can anyone confirm?

Next I took a good look at the tach while running. For the most part idle seemed to be right around 1000rpm out of the water but..... the tach would jump all over the place without me touching the throttle so there is def and issue with the tach or the wiring to it. The tach needle would move from 1000-4000 and in between all while idling smoothly. I went back to the coil with the engine running and wiggled the GREY wire on the coil while watching the tach, couldnt see any change in the tach that seemed to correlate with my wire movement. Can anyone point me in the next direction for checking the GREY lead from coil to tach and does this have anything to do with the intermittent ignition troubles I saw, or my friends low power/RPM that we originally began troubleshooting?

Thanks

 

[achris]

...I was certain others said to remove the GREY lead from coil but re-installed after the no spark condition...

There are 2 grey wires, one is to the tacho, the other is the 'fire' wire which goes back to the ignition module. You need the 'fire' wire for it to spark... You just remove the grey TACHO wire.

There is no timing label on those engines, just a TDC 'notch' on the timing/front cover of the engine and a machined line in the crank pulley. You need an advance timing light (or 'timing tape', but I don't trust timing tape. And yes, I know a few 'graybeards' like it, I don't) to set the timing.

Tacho could be any of the three wires to it. Purple for power, gray for signal and black for ground. I would use a jumper wire (about a foot or so long) with alligator clips and 'bridge' each wire in turn to a known good point (another gauge on the panel for example). That should help narrow the search.

Chris..........

 

[casey.d]

Thanks for the help, a few things I am not clear on yet

There was only a single grey lead on the coil, the other side has a purple lead with 12V. I looked at the wiring schematic found in manual #25 pg 341. It shows a single grey lead as well and splices into grey from the module and tach. I need to find this splice and check the connections because it seems this may have been the point of failure. May also disconnect that grey lead to tach at the splice to help isolate.

I like your idea for jumping the ground and voltage at the tach, will give this a try.

For the timing, you are correct about the single notch and no tab on the engine. I have a white stripe on the notch for visual aid but the flywheel does indeed have a white label or decal adhered to it. starts a 9 on the left, goes to 0, then 10 to the right. My timing light has a dial on the back to "advance." I set that dial to 0 and matched the notch on the engine to just left of the 9 mark , its actually off the label. I can go right on the label and align with 10 but it sounds better at 10 before 0. Does the timing seem setup correctly?

Thanks

 

[achris]

That sounds like someone has previous;y put a timing tape marking on it. If you lift the label, you should be able to see the single groove in the balancer. If you 'advance' your light by 10 degress, does it bring that timing label back to 0?