1988 4.3 LX intermittent power loss

[Another retired guy]

Well, I finally get to start a "what's going on with my engine" thread

4.3LX S/N OC 323999 - 4 bbl carb - alpha 1 - Thunderbolt IV

New problem, just showed up last two times out. Starts fine, and everything is normal until after 10 minutes or so at cruising speed (3,500 rpm ) then it suddenly starts to lose power. I can both feel and hear it struggling. If I apply more power it gets worse, so I back off for a couple minutes and then it picks up ok and keeps running for a while, then repeats the problem.
Plugs, rotor, cap new last season - now have about 30 hours running time.
Carb and pump filters changed 2 months ago - no signs of crud. No water separater filter.
Fuel is a mix of 70% 1 year old and 30 % fresh premium. Startron added every fill.
Went down to dock today to run the engine - 1 pump to set choke and she started right up, but ran rough for 10 seconds then cleared up.

I'm thinking either
1. Bad fuel
Or
2. Intermittent misfire on one cylinder

How many votes for 1. or 2 or 3 (other) ??

All opinions much appreciated

 

[Bondo]

Re: 1988 4.3 LX intermittent power loss

Well, I finally get to start a "what's going on with my engine" thread

4.3LX S/N OC 323999 - 4 bbl carb - alpha 1 - Thunderbolt IV

New problem, just showed up last two times out. Starts fine, and everything is normal until after 10 minutes or so at cruising speed (3,500 rpm ) then it suddenly starts to lose power. I can both feel and hear it struggling. If I apply more power it gets worse, so I back off for a couple minutes and then it picks up ok and keeps running for a while, then repeats the problem.
Plugs, rotor, cap new last season - now have about 30 hours running time.
Carb and pump filters changed 2 months ago - no signs of crud. No water separater filter.
Fuel is a mix of 70% 1 year old and 30 % fresh premium. Startron added every fill.
Went down to dock today to run the engine - 1 pump to set choke and she started right up, but ran rough for 10 seconds then cleared up.

I'm thinking either
1. Bad fuel
Or
2. Intermittent misfire on one cylinder

How many votes for 1. or 2 or 3 (other) ??

All opinions much appreciated

Ayuh,.... That was 2 months ago, Pull the filter, 'n check it's Contents,...

A New filter, 'n a remote tank will tell ya whether the fuel or tank are Ok,...

 

[Fun Times]

Re: 1988 4.3 LX intermittent power loss

Could be 1 or 2 so be sure to have a look at them both.

Also another possibility could be, if your exhaust manifolds or riser "gaskets" were to be leaking water intermittently, then water could be getting into the cylinder area making it run like that.

Have a look at the gasket area between the riser and manifold for signs of water leaking down the manifold while keeping in mind that it could be leaking on the inside of the manifold and not necessarily the outside.

Another rough running condition that could take several minutes of run time before showing up could be an intermittent issue with the ignition sensor assembly within the distributor housing.

Ensure that all the battery cables are clean and tight.

Good luck.

 

[slothman]

Re: 1988 4.3 LX intermittent power loss

hmm...how old is the coil ? maybe your getting weak spark.

 

[Another retired guy]

Re: 1988 4.3 LX intermittent power loss

Thanks guys. I'll confirm/eliminate fuel problems first - will check filters and see if I can borrow a remote tank. If fuel is ok then I'll look into the ignition/electrical stuff. No signs of water leaks anywhere. Coil looks really old, maybe original!

 

[slothman]

Re: 1988 4.3 LX intermittent power loss

Thanks guys. I'll confirm/eliminate fuel problems first - will check filters and see if I can borrow a remote tank. If fuel is ok then I'll look into the ignition/electrical stuff. No signs of water leaks anywhere. Coil looks really old, maybe original!

pull the coil wire and see if you can see a nice spark (at night time)

 

[Another retired guy]

Re: 1988 4.3 LX intermittent power loss

Update.
Changed fuel filters - looked clean.
Installed water separator filter - ran for 20 minutes at dock at 2000 rpm - then drained filter. I have dark yellow, cloudy gas with a clearly visible layer of water at the bottom. And this is after only 20 minutes Now I'm draining the tank - $100 of bad gas
No idea if this is an accumulation over the years, or ethanol related, or just gas going old after 9 months, or a combination of all three??
My advice to anyone experiencing a power loss at cruise or WOT - install a water separator filter and check the fuel. Don't trust modern fuels much past 6 months. Local Marina owner confirmed that fuel related problems are big business for them! ( including my $110 for filters !! )

 

[Fun Times]

Re: 1988 4.3 LX intermittent power loss

Now I'm draining the tank - $100 of bad gas

While that hurts to think about, it's much better than the $1000.00's you could of spent by ignoring it. Thanks for the update.