Engine won't get boat on plane - ignition issue?
 

Tried to test run the boat today, and it did not go so well. Idles fine, revs fine in neutral, but when in gear under load acts like it's missing and coughing, not making any power. Acts like an ignition problem - fuel pressure is steady at 5-6 PSI (Holley 800), and no backfires or anything like that. I just can't understand this because this engine was dyno'ed several weeks ago with the same ignition system (Merc 24* module) and ran fine. Nothing was changed on the motor since then - did not tweak timing or carb. Only differences are marine headers with muffled tips, new Carter black fuel pump, and it's now running through the Merc harness. I also ran it through the Merc harness on my startup stand and it seemed to run fine, but there's no way to put a load on it like that.

Things I tried today:

Replaced distributor cap
Replaced ignition coil
Replaced pickup coil in distributor.

Don;t have another 24 module to try right now or I would have done that.

Checked all my grounds on the back of block and couldn't find any that are obviously loose. That is the only thing I can think of right now that makes sense.

I'm getting pretty desperate at this point. Heading to the lake on Thursday for a long weekend. Right now I'm so frustrated and disappointed with this thing that it was tempting to pull the plug when I was floating out on the river. :mad: Kids and wife are pretty disappointed too.

I would welcome any ideas you guys can come up with. Right now I'm so beaten down by this thing that I just want to go to bed.

Budman I have to say your posts make me want to beat my own head in but I have to commend you for putting it all out here and leaving info others may find helpful in future. I have a few merc modules, I can overnight one to you tomorrow if you email me your address. [email protected]

That fockin' thing is going to fight you right to the the bitter end isn't it . You should name the boat " Cursed Cubic Inches " Keep your head up bro you'll be out beatin on it in no time . :angry-smiley-038:

What is your voltage going to the coil while running? If it ran well on the dyno but not in the boat I would look at the variables first, namely making sure the wiring from the boat is in good condition and carrying proper voltage to the coil under load.

bud,can you give me some info,what prop and gear ratio in drive and how old is fuel in the tank?

I was just thinking the same thing as Mike. Could the fuel in the tank have phase separated?

Red, that's a very generous offer and much appreciated! I may take you up on it, but a buddy had a 20* HP500 module. Would that work to tell me if the ignition module is the issue? I know the total timing would be different, but it should show me if it is the issue since it happens almost right off idle.

Mike, I drained the tank and refilled it with fresh fuel today. Running 89 in it which is what it was dyno'ed on. I guess it's always possible that I got a bad tank since that grade isn't used as much, but it sure acts like ignition. You know a lot more than I do, though. Keep the ideas coming, we'll hit it eventually.

And yes, for the record, I am starting to think it's time to sacrifice a live chicken over the bow of this thing to break this damned voodoo curse that is afflicting it.

Should I expect to see a full 12-13 volts on the coil leads under load? It does run a wire off the positive side for the electric choke and as a trigger for the fuel pump relay. Hmmm, starting to wonder about that choke. Might call the dyno shop in the morning to see if they had it energized when they ran it.

Forgot to answer - 23 Mirage Plus with a 1.36 drive. 600 ft lbs should swing that easy.

with a 1.36 ratio that prop might be too much pitch.maybe you can borrow a smaller pitch prop to test.

i think donzi matt,s idea is a good one and pretty easy to do.

I'm definitely going to look at the wiring. I think the quickest way to eliminate wiring to the coil might be to run a hot wire straight to the battery. Before I do that I might just eliminate the circuit for the choke and fuel pump that run off the positive side of the coil. If that doesn't fix it, then the hot wire to the battery might tell me if it is a problem in the circuit coming back from the key that is getting me.

How much voltage should I expect to see across the coil leads with a DVM?

Jesus Christ .

Bud , I'd be willing to bet your boat wiring sucks azz. The purple wire from the ignition switch should provide more than 12v while running. Even though the alternator is prob putting out 13+ volts you rarely will see that at the coil because of the long run of wire from the 9 pin connector to the ign switch, then back to the coil.

I'd start with checking the voltage at the coil before replacing more parts

Also, I would lose the electric choke or at least NOT wiring it from the same wire as the coil.

Are you sure the choke flap is opening and staying open under throttle ? The symptoms you describe sounds like the engine is getting a gulp of fuel and no air upon acceleration . Look for the stupid little things that easily get overlooked first . Wire the choke open or better yet remove it , you don't need it anyway .

Right from the Holley Literature.

Connect the long wire from the kit to the posit
ive choke cap terminal marked (+). Connect the oth
er end of the wire to a
fused ignition activated 12V source. The choke cap
should only get voltage when the engine is running
. Check your
voltage source with a voltmeter.
WARNING: The distributor side of the coil is not a
12V source. Connecting the choke cap to the ignit
ion coil will
result in unacceptable choke operation and possible
engine misfiring resulting to possible engine
damage. Do not connect the choke wire to the coil!

Bud, if you have a stock 3 wire merc alternator, i am pretty sure you can power the coil from the purple wire coming from the alternator. It should only provide 12V when the engine is running. Verify that first with a meter though.

I would remove those and wire them to something else.

You cant measure across the coil leads for voltage as the ground side is pulsed by the ignition module. Ground to the engine block and measure the power side of the coil.

I certainly would not share the fuel pump and choke wiring with the coil. If anything, run a separate relay to power the fuel pump. Ideally it should be run through an oil pressure safety switch so the pump won't just run with the key on and engine off. It isn't really a difficult circuit to wire up correctly. Ditch the choke altogether, you don't need it, but if for some reason you decide you want it you can run that off of the relay for the fuel pump.

MT, it's the late Motorola/Prestolite style that Merc was using back in the 80's. It does have a purple wire attached that I believe is the ignition feed.

And you are correct - the wiring on this boat is pretty clustered up. They were pretty bad straight from the factory, and this thing is 27 years old and has been through several owners who had their hands on it. I have cleaned up some of the wiring at the helm. Guess I need to move the engine wiring harness up higher on that list. And yeah, total "duh" moment pulling the choke lead from the coil. That being said, it ran fine like this two years ago with the other engine. I hope this is it - it would be a much easier fix than poring through all the grounds and wiring. Thanks for the help.

Did you check to make sure it's not sucking water back through the exhaust?

I would lose the choke all together. It is common to mill the choke blade/flap housing right off as it is not even needed!

I had a similar issue once, running stock 330's w / Q-Jets. Port engine was coughing, sputtering, backfiring at anything close to 4000 RPM. I thought it felt like I was losing ignition, but after testing I was convinced that I had a fuel issue. So, I changed the fuel pump, water sep filter, in line filter, still the same results. At that point I was going to pull the carb and rebuild it. When I disconnected the fuel line at the carb, I found the filter in the carb was filthy and pretty well plugged. I replaced that filter instead of pulling the carb, and the engine ran fine, no more problems. Apparently, it was getting enough fuel through the plugged filter to run on the primaries, but not enough for the secondaries. Sure wish I'd have checked that first... my question for you is, while you have good fuel pressure, have you confirmed what kind of flow you have into the carb itself?

Baja, considering my earlier issues with the Lightnings, that is a valid question. Didn't pull a header because they are a b!tch to get on and off. However, oil remains totally clear, and I would think milkiness would be showing up by now if it was sucking back enough water to make it run that bad. Might revisit later if I rule out ignition.

Offshore, the Holley's don't have the little inlet filters like the Q-jets do. Had a friend looking down the throat of the carb while I was trying to get on plane, and he said it looked like a good, steady stream of fuel.

I'm thinking if the electric fuel pump is wired into the coil, you're losing voltage at the coil. I'd wire in a relay on the fuel pump, to eliminate voltage drop.

Jonesy, I have a relay for the fuel pump that is triggered off the coil. I just don't have one for the electric choke, and that is the most likely culprit at this point (I hope). :pray:

Get your buddy's module first. 242ls almost missed a poker run because of this issue. Module took a dump and scattered timing. Luckily I bring a bunch of parts with me everywhere I go :)

Red, will I need to reset the base timing to test this, in your opinion? Just planning to run it on the trailer to see if it changes. Damned thing didn't even have enough balls to get the boat all the way up on the trailer.

Budman, check the battery cable connections at the on/off switches. I had one come loose and it did the same thing to me at the lake. Good luck!

Last couple yrs I've had. 1 motor in my cruiser not up to par with other. Was not as responsive and lower RPMs as other. Mechanically it was perfect. A timing light showed it fine at idle, would go up with RPMs as should, but then timing immediately dropped off after a couple seconds when RPMs held up. Doing some troubleshooting last yr I found only getting 11.5 v to coil. Traced issue back to dash. The power wire from the 9 pin goes up to dash, key then back to coil. At the dash that wire supplied 12v for the nav lites and etc. by feeding the fuse block. From the fuse block, leads went off to the acc and also to ignition switch. All fused. Most all the fuses were fairly loose and the spade crimps where also poor. The fuses and wires were warm do to the loose connections at fuse block creating résistance. Ditched the cheap POS Baja fuse block and put in a Blue Seas block and redid all the wire connections. Surprising how much everything now works right. Gauges are all steady, volt gauge no longer drops with each accessory turned on and the motor runs like a champ with full voltage back to the motor. With the lower voltage it was screwing up the knock sensor thus keeping the timing retarded resulting in low power. 4 yrs ago that same motor tuliped a couple of valves and blew a head gasket. Looking back, I think the wire issue was the cause of the motor failure.

Check and make sure that your timing has about 34*-36* of advance at about 2200- 2500 rpm.

Get that f*kin choke wire off your coil.

LOL.

BTW: Real men don't use chokes. Double lol.

Choke? We don't need no stinking choke!

Bud, I would pull a couple plugs and see what they look like.

This is the same out drive and prop from the boat when it did run, right?

Does seemed propped a bit tall with the 1.36.

Heh, don't forget many people have run into tach's causing symptoms like this. #1 make sure it's hooked to the negative side of coil. #2, if it is, try unhooking tach and see if it clears out. #3, make sure ground from distributor is on and clean, ground from module, etc,etc,etc.

OK, went through the wiring - what a cluster! One thing I did was put wires back in that had the correct color codes so it is obvious what goes where. Had one green wire and one yellow going to the coil, which were supposed to be grey and purple but got spliced out at some point in the past. Then made sure coil was wired properly, and moved choke lead over to the relay for the fuel pump. Ran like a champ after that! Heading to the lake in the morning, and life is good again. Thanks to the guys at OSO! I owe you a beer if we ever cross paths. :)

Ummmmm.....you owe us way more than a beer ! But, that is a good start !

If you are still on the trailer, how do you know everything's fine ?