[Thunder Pumpkin]

Here's my problem ....I have a 632" BBC with 13.7:1 naturally aspirated (no start retards or motor reatrds). My boat worked fine when I put it on the trailer for the winter last year....move forward to May of this year and i decided to install a MSD Digital 7 programable #7531 so i could take advantage of a launch program and a diverter timer.
For the last 12 years I had been running a MSD Digital 7 Programmable Plus with a crank trigger that worked just fine (but you couldn't run a launch control out of my old MSD box). Swapping out the 2 boxes was easy and all the same wiring plugged right in......1st time out the boat would hardly run off idle finally diagnosed that the crank trigger went bad over winter (bad luck)...replaced the crank trigger boat worked good for 1 day, then the following weekend (at the CP Regatta) it wouldn't run over 7,000 rpms.....it runs hard up to 7k but almost acts like theres a Rev limit and the boat surges. I went to the lake last Monday and screwed around and still have issues.
I checked the the MSD program and had 2 other people that have been using the programs for a few years and all of my Rev Limits are set correctly (7,800 rpm) so its not that...I sent the box and coil (I run a HVC #8251 but I ordered a #8261 yesterday to try) back to MSD to get checked out and their fine....checked the float level and fuel pressure an everything is good there too....did a plug check and they look great (same jetting/set-up I had for the last 3 years)...I checked the timing, rotor phasing, ect. everything good there....when you put a timing light to the motor it doesn't jump around so I wouldn't think the pick-up polarity swicthed??...I run the shielded gray crank trigger pick-up so interference should be an issue....I replaced the spark plugs (gapped at .040), wires, checked ground at the box and the cyl. heads, ect.... Now I'm to the point of trying another coil, replacing the cap and rotor (they looked fine), and flipping the polarity of the crank trigger pick-up, after that there's nothing else to replace or check except trying another box.....the motor should pull around 7600rpm.....The only thing I changed from last year to this year was the MSD box....any help or ideas would be great...thanks guys

 

[Red Rocket]

Try another coil I have had several go bad.

 

[cs19]

Crank wheel also, heard a story about one going bad yesterday, the magnets die or get weak.

That thing will turn a tick less RPM that it did in the past based on what we did but not 600 rpmUnsure

 

[six-oh-nine]

I'd say the only logical ignition thing left is the coil... or the new box... even though MSD said it was cool... I've sent several things back to them that they said was "good" and still had issues.

I forgot to ask before... but is it popping at 7k or otherwise missing? Or is it just hitting a wall at 7k?

You know... just for shits and grins... did you ever check to see if you have a broken or weak valve spring? You can borrow my spring checker if you like.

 

[Thunder Pumpkin]

Chris..your right with the work done should turn 7300-7400 but it just flat out stops right at 6900-7000 and surges/pops. I'm hoping its the coil too since i had a couple fouled plugs......I heard the same thing yesterday on another forum about the crank wheel magnets getting weak. I'll put the new coil, cap, & rotor on next week and I'm going to bring a spare box and crank wheel to the lake and try it again. I'm going to regap the plugs at .030 too....right now I'll try anything. Hell by the time i'm all done I'll probably have replaced the whole damn iginition system

 

[Hass828]

To bad you dont know someone local that would have a good vertex mag that you could borrow just to be sure that it is the ignition system thats causing the problem.

 

[jockorace]

To bad you dont know someone local that would have a good vertex mag that you could borrow just to be sure that it is the ignition system thats causing the problem.

Then when that mag solves the problem, you can start negotiating a price to buy it! :grin: Jocko

 

[FARMER JOHN]

Wes, when your down here testing it and need parts, just give me a shout, that is one thing i do have, and thats plenty of parts,

The deal is with loaner parts means you can't kick my ass on the water:wink2:

 

[Sleeper CP]

Chris..your right with the work done should turn 7300-7400 but it just flat out stops right at 6900-7000 and surges/pops. I'm hoping its the coil too since i had a couple fouled plugs......I heard the same thing yesterday on another forum about the crank wheel magnets getting weak. I'll put the new coil, cap, & rotor on next week and I'm going to bring a spare box and crank wheel to the lake and try it again. I'm going to regap the plugs at .030 too....right now I'll try anything. Hell by the time i'm all done I'll probably have replaced the whole damn iginition system

Have you changed the coil wire ?

Coil to Dizzy ?

S CP

Jon

 

[Hass828]

Then when that mag solves the problem, you can start negotiating a price to buy it! :grin: Jocko

The usually the exact way it goes down :wink2:

 

[Thunder Pumpkin]

Wes, when your down here testing it and need parts, just give me a shout, that is one thing i do have, and thats plenty of parts,

The deal is with loaner parts means you can't kick my ass on the water:wink2:

Right now the only ass getting kicked is mine......damn thing ran fine, should have never touched it :wink2:

 

[Thunder Pumpkin]

Have you changed the coil wire ?

Coil to Dizzy ?

S CP

Jon

Yep
Changed all the plug wires too

 

[Sleeper CP]

Right now the only ass getting kicked is mine......damn thing ran fine, should have never touched it :wink2:

Here's a thought...if you still have the old MSD and it just plugs in ....swap it in and see what happens.

S CP bulb

P.S. Was it you or your dad that got the ride in the blown GN boat and left a spot in the seat when you got out ?

 

[motormonkey]

Sure its not a fuel problem or springs like mentioned above? Another thing, whats your plugs look like?

 

[Thunder Pumpkin]

Here's a thought...if you still have the old MSD and it just plugs in ....swap it in and see what happens.

I have it but I need to change the plugs on the old box to match the new box plugs......I know of a 19' Daytona w/ a similar set-up collecting dust that I can borrow parts off of

S CP bulb

P.S. Was it you or your dad that got the ride in the blown GN boat and left a spot in the seat when you got out ?

It was me.....when your passenger you might as well have a speedo that reads another 100mph because thats how it feels...

Sure its not a fuel problem or springs like mentioned above? Another thing, whats your plugs look like?

I dont think its fuel..I drained the tanks tried a new drum of fuel. I replaced all the valve springs at the beginning of this season (not to say I didn't get a bad spring) and I checked the valvetrain on sunday to make sure nothing was broke or loose....the plugs are a medium gray with a light brown tint. Heat ring down about 1-2 threads.

 

[SoldHondaBoughtHondo]

To bad you dont know someone local that would have a good vertex mag that you could borrow just to be sure that it is the ignition system thats causing the problem.

X2
The op seems like he has done a very serious attempt at a proper diagnosis..And being a retired GM service tech 'by the book' will usually solve the problem although shortcuts can save a lot of time.
Most GM electrical manuals begin with "Charge battery, load test, check charging system, check for draw" I guess them GM engineers
figured out that electrical parts work better with the correct voltage:hmmm:

And after stumbling through several pages of trouble trees, and check voltage here and resistance there, it usually says
"Replace with a known good part"
AKA "When in doubt,throw parts at it!".......

I guess them engineers figured out that a part can fail and there is no for sure way to actually bench check it.

 

[LOLYFE]

My past experience is that the grey shielded magnetic pickup wire should not be routed anywhere near other electrical wires in the car/boat. I replace my coil wire after 50 runs, that's with a hvc pro power 2 coil, its what works for me, T

 

[gn7]

My past experience is that the grey shielded magnetic pickup wire should not be routed anywhere near other electrical wires in the car/boat. I replace my coil wire after 50 runs, that's with a hvc pro power 2 coil, its what works for me, T

No pickup wire should be routed near other electrical wires, specially the alternator and its wiring. They idea behind the shielded wire is it is less susceptible to outside interferance, not more. Its used when it impossible to get the pickup wire isolated well enough, and if your using things like eletronic timers etc.

Every 50 runs? Damn, we would have to stop twice during the race to replace the coil wire. The Nascar boys would be in the pits for coil wires more often then tires and fuel.



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[motormonkey]

You know what else to try checking. I had a issue twice with alt regulators going out. One did close to what yours is doing. It would put out power up untill it got to higher rpm and die. When the rpm came back down it would charge again. The other one was similar when the regulator went out all together and over charged my MSD and it would shut off like it had a circut breaker and die. Would be fine on restart.
Msd is power sensitive, but lately they are hit and miss also.

 

[68 Hallet]

It really sounds similar to a problem we had with our comp eliminator car. Car wouldn't run past 7000rpm, not good when you dump the clutch at 6800. Anyways the msd box had a traction control lockout. Changed the box for a spare we had in the trailer and won the next round at Pomona.