Carver Owners Forum

Hi all. Hoping to confirm diagnosis.

New to us boat came with reman long block 5.7 thunderbolt 4v engine. On first cruise would not cross 3k rpm. Installing mechanic adjusted timing and idle. Now on acceleration @ 2500 + mild popping noises and still wont cross 3k. Mech says is control module mounted on top of motor.

Wondering if this rings true to experts here.

Thanks for any insight you can share,
Mark

Not sure what control module would be on an '89 vintage?
A couple ideas....
Verify that the firing order is correct. (plug wires from distributor to cylinders) also recheck timing and verify advance is working.

the 2557 should be a single engine I believe, just a thought, verify that the replacement engine is of the proper rotation. a counter rotating long block with standard rotating parts (distributor, starter etc) will give you some crazy issues.

tomschauer wrote:Source of the post Not sure what control module would be on an '89 vintage?
A couple ideas....
Verify that the firing order is correct. (plug wires from distributor to cylinders) also recheck timing and verify advance is working.

the 2557 should be a single engine I believe, just a thought, verify that the replacement engine is of the proper rotation. a counter rotating long block with standard rotating parts (distributor, starter etc) will give you some crazy issues.

Thanks for the reply. Wires from the distributor lead to a black sealed box. They tell me it controls the advance where as a traditional set up would have weights inside distributor to advance. Any idea what timing @ idle should be?

Hadnt thought about wires connected wrong. Will ask mech to dbl check.

Like Tom says, check wires, popping sounds like a misfire, bad wire... wrong order.....not enough fuel.....one thing though, dont rely on just the base timing at idle in gear but the curve needs to be right and the total timing also needs to be in spec on marine engines or you will hurt them very quickly ......

One engine? Alpha Sterndrive? Can you post a pic of the "black box," I'm trying to figure out which module you have. Does it have a "Denso" label on it or is it Mercruiser?

Is it original to the OEM setup or was this changed when you installed the long block? If original, do you have the original engine serial number that you can post? Did this boat come from factory with a 5.7L?

bud37 wrote:Like Tom says, check wires, popping sounds like a misfire, bad wire... wrong order.....not enough fuel.....one thing though, dont rely on just the base timing at idle in gear but the curve needs to be right and the total timing also needs to be in spec on marine engines or you will hurt them very quickly ......

The popping sound didn't start until he backed down the timing a little, and I feel like the motor ran decent enough before he messed with timing that I'm not sure wires are wrong - fuel tho' I'm not sure about. Timing in gear? New concept for me, in the old days we timed a car @ idle in park and @ like 15k rpm, still in park though (or neutral on a standard). As far as hurting quickly - what do I look for? When we first put in the water we ran down river trying to get on plane, no joy. Went WOT @ 2950 or so and then backed off and slow cruised to Slip @ Marina (Columbia Point to Clover Island.) It sat there for 2 days when the mech came down and we took out on the river to duplicate and that's when he messed with timing and idle speed which is when the popping started. He had timing light and such and adjusted @ distributor saying This motor (presumably all Merc 5.7L Thunderbolts) liked 10 degrees BTDC, but backed down a point or 2 he said. I think that's what created the popping. Pics to follow, see next post.

Viper wrote:Source of the post One engine? Alpha Sterndrive? Can you post a pic of the "black box," I'm trying to figure out which module you have. Does it have a "Denso" label on it or is it Mercruiser?

Is it original to the OEM setup or was this changed when you installed the long block? If original, do you have the original engine serial number that you can post? Did this boat come from factory with a 5.7L?

Single engine, Alpha 1, Gen 1 I believe. I'm pretty sure Original motor was same setup although may have been an earlier variant. This seems to be the 4th motor since new according to the (large) file folder of receipts I have. I have pics:

Close up of the module they say needs replacing and controls advance:

More pics of the engine bay:

Heh man....not sure of the procedure for timing adjust on thunderbolt 4.....I dont think him taking 2 degrees out should create any popping, just cut back power.The suggestion about the timing set in gear is really just to create a small load therefore taking any slack out of the timing chain....idle always set in gear. You still need to get the total timing in spec and that module if pooched could be your problem. The correct advance curve is critical to your engine making max power when you need it without creating detonation under load.

To add, since someone has been in there now, check all your connections and grounds, clean and reconnect if it were me.

bud37 wrote:Source of the post Heh man....not sure of the procedure for timing adjust on thunderbolt 4.....I dont think him taking 2 degrees out should create any popping, just cut back power.The suggestion about the timing set in gear is really just to create a small load therefore taking any slack out of the timing chain....idle always set in gear. You still need to get the total timing in spec and that module if pooched could be your problem. The correct advance curve is critical to your engine making max power when you need it without creating detonation under load.

To add, since someone has been in there now, check all your connections and grounds, clean and reconnect if it were me.

Thanks, very good suggestion - grounds and connections. I think at this point tho' since a "professional" shop installed and gave clean bill of health unaware that WOT was wonky, I'm going to insist they get it up to snuff. Only after they've given a verifiable okie dokie will I mess with running gear... crossing fingers at this point that they are correct on what the problem is!!

On that note... was told new impeller in outdrive, I physically observed gimbal and bellows were sound prior to outdrive being reinstalled (assuming outdrive is good to go since they did the impeller) what else should I wonder about in the running gear as possible weak points?