loss of 800 RPM due to bad ground?

mlrman

mlrman

Petty Officer 3rd Class
Joined
Jun 3, 2010
Messages
82
Hello, I have a 1991 Sunbird 262 Corsair with 4.3 GM V6 OMC outdrive, and std. aluminum prop. The boat starts and runs great, however, there are times when the engine loses approximately 800 rpm at WOT. Normal WOT rpm is around 4400 (I believe, it's been a while since out on the water) and at that rpm the boat does around 45-47 mph. Sometimes the boat will only do 3800 rpm or so and 38-40 mph, and it slightly sputters/bobbles.

I believe this to be an electrical issue, maybe bad ground, because:
1) when this condition happens, I can usually turn off the ignition, restart the boat, and it runs fine.
2) a couple times when hitting large waves at speed, the condition has been triggered, and it has also stopped. Like the
wave jarred a loose connection.

Any other ideas why hitting a wave hard would trigger this engine to run badly, or trigger it to run great would be appreciated!

Thanks.
 
Bondo

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,525
Re: loss of 800 RPM due to bad ground?

mlrman said:
Hello, I have a 1991 Sunbird 262 Corsair with 4.3 GM V6 OMC outdrive, and std. aluminum prop. The boat starts and runs great, however, there are times when the engine loses approximately 800 rpm at WOT. Normal WOT rpm is around 4400 (I believe, it's been a while since out on the water) and at that rpm the boat does around 45-47 mph. Sometimes the boat will only do 3800 rpm or so and 38-40 mph, and it slightly sputters/bobbles.

I believe this to be an electrical issue, maybe bad ground, because:
1) when this condition happens, I can usually turn off the ignition, restart the boat, and it runs fine.
2) a couple times when hitting large waves at speed, the condition has been triggered, and it has also stopped. Like the
wave jarred a loose connection.

Any other ideas why hitting a wave hard would trigger this engine to run badly, or trigger it to run great would be appreciated!

Thanks.
Click to expand...

Ayuh,... It could very well be a bad ground,...
Crawl in there, 'n pull 'em all off, 'n clean 'em, shiny metal clean, 'n Try it...

Ya might check the contents of the fuel filter for water, 'n throw a new 1 on...
Just to rule out a Fuel issue....
 
P

perna00

Petty Officer 1st Class
Joined
Jun 28, 2009
Messages
249
Re: loss of 800 RPM due to bad ground?

This is an easy way to trouble shoot it to determin if it is a grounding issue. Run the engine with muffs on about 1500 rpm. Start moving wires, shaking harnesses, and other parts that may move under water pressure. Find out which parts make the engine stumble.
 
mlrman

mlrman

Petty Officer 3rd Class
Joined
Jun 3, 2010
Messages
82
Re: loss of 800 RPM due to bad ground?

I realize this is an old thread, but I wanted to give an update in case anyone else runs into this problem. Last summer, I finally solved the mystery. After having a couple shops charge me for diagnostics, changing fuel filter, etc., I finally did as suggested and found the culprit to be a loose connection under the dash on the wire coming from the battery. That is why the RPM's would drop when hitting a wave. Thanks for the suggestions.
 
You must log in or register to reply here.
Top