[Sman0624]

I wanted to get your oprions on this issue, it's driving me nuts.
Engine is a 5.7 L EFI with Delco HEI ignition.

Here's the issue. When I take the boat out it runs fine, strong starts and lots of power. Then after about 45 minutes of operation I would notice that when I give it anything over half throtle the engine surges, ocassional backfire through the throttle body (carb, the engine is fuel injected), just a total lack of power. When this happens the tach will jump all over the 4,000 to 5,000 range even though I know I'm only doing about 3,300 to 3,500 RPM. Note: When "cold" the engine runs fine and the tach does not jump.

After a pressure check to the electric fuel pump I found it was losing pressure and I was running lean (fuel starved which explains the backfire). After replacing the fuel pump the problem came back. I did the basics also, fuel seperator (fine, no contamination), new plugs, cap, rotor, wires, electronic control module in the distributor yet the problem still occurs.

I'm thinking a bad coil?? In the process of doing a compression check but I doubt that is the issue otherwide the engine would run bad all the time and not just after the first hour. It's not bad fuel either otherwise the problem would be there all the time. I'm thinking electrical since the problem is worse after things heat-up.

What are your thoughts? Has anyone ever had this problem and if so then what did you do.
Thanks, Dave

 

[Garry]

Bad coil, pick up, or did you get the fuel filter down low (long shot)? I know they are there on a Rinker, I would imagine it might be on yours as well. Small in-line filter, easy to miss.

 

[Sman0624]

QUOTE(garry454 @ Jul 24 2009, 02:48 PM) <{POST_SNAPBACK}>Bad coil, pick up, or did you get the fuel filter down low (long shot)? I know they are there on a Rinker, I would imagine it might be on yours as well. Small in-line filter, easy to miss.

Thanks garry for the reply...
I didn't see any additional in-line fuel filter but I will look again. However, if it was a fuel filter issue then the problem would be there all the time and not only after it warms up. In addition..I did check the anti-siphon valve also and it's fine.

Nothing worse then replacing parts and hoping you find the problem.

 

[SEMIJim]

QUOTE(Sman0624 @ Jul 24 2009, 08:52 PM) <{POST_SNAPBACK}>Nothing worse then replacing parts and hoping you find the problem.
True, but look at the bright side: It definitely sounds electrical (heat-related), and you've covered all the other electrical components. The coil is all that's left

.

Jim

 

[Away Point]

No expert here, but seems like the tach acting up could be a clue. Since it sounds like you already replaced where the tach is connected, what other things do they have in common? Intermittent loose ground?

What about the voltage when it happens? Perhaps something is going on with the alternator and whacking out the voltage to electronics.

Probably no help, but something else to ponder...

Good luck!

 

[Sman0624]

As far as I can tell all the grounds are clean and tight. I haven't measured the output from the alternator directly while this happens, but the dash gage reads steady at 13 to 14 volts. Problem typically happens under load and over at speeds over 27knots.

Since the tach gets it's signal from the primary windings of the coil I'm thinking that it's the coil going bad which would be good news since it's only $100 give or take a bit.

If I can determince the specifications for the coil then I'd check the resistance on the prinary and secondary side. It might be that simple...then again it could be something ugly.

 

[Sman0624]

Update....
Looks like all is well. The issue was a bad shift interuptor switch. By-passed the switch with a paper clip and the jumping tach as well as backfire stopped. When checking the switch while driving with an Ohm meter the meter was jumping all over the map..open, closed.

New switch installed and ran for 1 1/2 hours with no issues. Now... let summer begin!

 

[Garry]

Good to hear ya got it licked!!

have fun!!

 

[Formula Bob]

QUOTE(Sman0624 @ Aug 4 2009, 11:23 AM) <{POST_SNAPBACK}>Update....
Looks like all is well. The issue was a bad shift interuptor switch. By-passed the switch with a paper clip and the jumping tach as well as backfire stopped. When checking the switch while driving with an Ohm meter the meter was jumping all over the map..open, closed.

New switch installed and ran for 1 1/2 hours with no issues. Now... let summer begin!
Nice catch. Electrical problems can be a biotch to find.