1990 Mercruiser 4.3 Stalls

[Red128]

Hey everyone! I have a 1990 Regal Sebring with a merceuiser 4.3.

My issue is that it rides great for maybe 10 minutes and than dies. It’ll start up after but won’t run as long maybe a few seconds before shutting off again. Tired of getting towed out. Sometimes it’ll run a little longer if I keep rpms low. WOT will shut it off after a few seconds.

I’ve been doing tons of reading but can’t figure out if it’s a vapor lock issue, a fuel pump issue or tank vent issue.

So far I’ve had the carburetor rebuilt, replaced fuel pump, replaced carburetor small filter, replaced valve with ball at the tank and replace the fuel/water separator.

Any steps I should take? The lake isn’t THAT close to me so driving out there alone to get stranded everytime is a buzzkill.

 

[Scott06]

Hey everyone! I have a 1990 Regal Sebring with a merceuiser 4.3.

My issue is that it rides great for maybe 10 minutes and than dies. It’ll start up after but won’t run as long maybe a few seconds before shutting off again. Tired of getting towed out. Sometimes it’ll run a little longer if I keep rpms low. WOT will shut it off after a few seconds.

I’ve been doing tons of reading but can’t figure out if it’s a vapor lock issue, a fuel pump issue or tank vent issue.

So far I’ve had the carburetor rebuilt, replaced fuel pump, replaced carburetor small filter, replaced valve with ball at the tank and replace the fuel/water separator.

Any steps I should take? The lake isn’t THAT close to me so driving out there alone to get stranded everytime is a buzzkill.

I would get a spark gap tester to see if you have spark when it dies ( or you are loosing spark/weak spark). Basically need to determine if this is fuel or spark related. Would also look to see if you have fuel coming out accelerator pump circuit when this happens. What di the contents of the fuel filter look like?

What is the condition of the ignition components?

try opening the gap cap when it happens if you have a clogged fuel tank vent it will create a vaccum and fuel may not come out of the tank. Common for insects to get in vent and clog.

 

[Red128]

Okay I’ll remove the spark plugs and test the gaps today. I don’t believe that’s the issue only because it fires right up cold and idles great with muffs and in water. I’ll check them anyways.

Ignition components are in good shape I believe since it starts without issue. Any specific parts I should check?

Is there a way to test the tank vent before heading to the lake? I removed the vent hose that goes to the screen on the outside rear and blew into it and when I release it blows fuel vapor back out like there’s pressure. When I remove the gas cap and blow into the tank vent it blows through.

 

[Scott06]

Okay I’ll remove the spark plugs and test the gaps today. I don’t believe that’s the issue only because it fires right up cold and idles great with muffs and in water. I’ll check them anyways.

Ignition components are in good shape I believe since it starts without issue. Any specific parts I should check?

Is there a way to test the tank vent before heading to the lake? I removed the vent hose that goes to the screen on the outside rear and blew into it and when I release it blows fuel vapor back out like there’s pressure. When I remove the gas cap and blow into the tank vent it blows through.

not test spark plug gaps with a feeler use a spark gap tester like this

https://www.amazon.com/Lisle-20700-Coil-Spark-Tester/dp/B00IXMA1RY/ref=asc_df_B00IXMA1RY/?tag=hyprod-20&linkCode=df0&hvadid=692875362841&hvpos=&hvnetw=g&hvrand=4364936092586588861&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9007369&hvtargid=pla-2281435178338&psc=1&mcid=75ff051bec563ca1af65573c0cc3b1a4&hvocijid=4364936092586588861-B00IXMA1RY-&hvexpln=73&gad_source=1

it is a good quick check of spark strength should jump at least a 3/8" gap and have a nice blue spark.

if you have cleared the vent you may want to pull the pick up screen and check this and the anitsiphon valve which will be in fuel line connection on top of fuel tank

ignition parts- look at cap and rotor for corrosion and arcing. Plug wires you can ohm test, same with coil to cap wire. Might be worth ohm testing the coil to see if it is on the edge of working well enough to get a hot spark

 

[Red128]

I appreciate the help. I just ordered the spark tester. I should be getting it tomorrow.

I haven’t cleared the tank vent. I’m not sure how. I wanted to test it before pulling the line but not sure how. I blow air through the line from the tank vent into the tank and it blows back out. Is that normal or clogged? When I do the same with the gas cap opened it blows air in fine without blow back.

 

[Scott06]

I appreciate the help. I just ordered the spark tester. I should be getting it tomorrow.

I haven’t cleared the tank vent. I’m not sure how. I wanted to test it before pulling the line but not sure how. I blow air through the line from the tank vent into the tank and it blows back out. Is that normal or clogged? When I do the same with the gas cap opened it blows air in fine without blow back.

yeah sounds like vent is clogged.

 

[Red128]

How do diagnose it?

 

[airshot]

Have you checked for water in your fuel ? If water is in the tank, they usually startup then stop or run rough after 15-30 minutes.

 

[Red128]

I also removed thermostat cover to check it out and looked like this

Have you checked for water in your fuel ? If water is in the tank, they usually startup then stop or run rough after 15-30 minutes.

Yes I have. There is no water in fuel. I removed the fuel/water separator as well and cranked the pump into a clear bottle. No water.

 

[Red128]

I can’t upload pictures for some reason. Something about the servers

 

[Red128]

Have you checked for water in your fuel ? If water is in the tank, they usually startup then stop or run rough after 15-30 minutes.

Yes I have. There is no water in fuel. I removed the fuel/water separator as well and cranked the pump into a clear bottle. No water.

 

[bbook83]

Try running from a remote tank.

 

[nola mike]

yeah sounds like vent is clogged.

Take your gas cap off if it does it again, see if you get a whoosh of air.

 

[Scott06]

How do diagnose it?

When it starts acting up open fuel tank fill.

the vent attaches to the tank via hose. Take hose off tank blow compressed air out it.

 

[Red128]

Take your gas cap off if it does it again, see if you get a whoosh of air.

Okay I’ll give this a try tomorrow. What does it mean if it has a whoosh or no whoosh?

 

[Red128]

Try running from a remote tank.

I’ll try this but what will this show?

 

[Scott06]

Okay I’ll give this a try tomorrow. What does it mean if it has a whoosh or no whoosh?

if there is a big vacuum into the tank then you know the vent is clogged

I’ll try this but what will this show?

if it runs ok on a remote tank you know your issue is with your in boat tank- vent, supply line, pick up tube, water contamination, or antisiphon valve. If it still runs like chit on remote tank you know the issue is carb or ignition not tank related. Easy way to narrow down where the issue is to avoid throwing parts cannon at it