95 Mercruiser 5.0lx stalls/stumbles after getting warm and sitting

Badfish95

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Please help! I have been trying to fix this issue myself and am getting awful frustrated. The last few times I thought I had solved the problem I got a little cocky and relayed it to the family... Only to get out on the lake and experience the same results. The last time my 5 year old daughter Lilly told me, "Daddy, maybe you should double fix it."


Help me double fix it!


Symptom: The boat starts and runs fine first thing in the morning. We typically cruise the lake for 45 min to an hour and then drop anchor or tie up in a cove. After a few hours we'll go for another cruise and it usually puts the kids right to sleep. Lately, when we are leaving the cove the boat doesn't want to fire right off like usual. Then when attempting to get on plane it'll stumble or even stall out. One time it refused to start and we had to take the tow of shame to the dock...


I'll attach photos of the parts I've replaced but here is a summary of the repair attempts thus far:


1. Replaced the ignition coil pickup sensor inside the distributor. No change in performance.
2. Replaced the ignition coil. I used an auto coil from Napa but the parts guy assured me a coil is a coil, no change in performance.
3. Replaced the fuel pickup tube, anti-siphon valve and rubber fuel line to the fuel pump. There was a bunch of junk in the tube and the valve was crazy corroded. No change in performance....
4. Replaced the electronic control module in the back of the distributor. Spent $400.00, Used the heat sink grease and still no change in performance......
5. Rebuilt the 4 bbl quadrajet. I took my time and even did the upgrades like install the plugs where these tend to leak..... No change in performance.........
6. Winterized it and sticking in the shed until now.

So, good folks of iboats, got any ideas?
 

Bondo

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3. Replaced the fuel pickup tube, anti-siphon valve and rubber fuel line to the fuel pump. There was a bunch of junk in the tube and the valve was crazy corroded. No change in performance....
4. Replaced the electronic control module in the back of the distributor. Spent $400.00, Used the heat sink grease and still no change in performance......
5. Rebuilt the 4 bbl quadrajet. I took my time and even did the upgrades like install the plugs where these tend to leak..... No change in performance.........
6. Winterized it and sticking in the shed until now.

Ayuh,..... I'm guessin', from yer story, yer fightin' a fuel delivery issue,....

A little diagnosis when it don't start would help,....
Nothin' crazy with the family on-board, but checkin' for spark mighta saved ya a ton of fuel money,....
Is fuel present in the carb,..??

Has this got an electric fuel pump,..??
No mention of the fuel filter,..??
or the debris found in it,....
 

Badfish95

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Thanks for having a look. Yes, I forgot to mention that I replaced the fuel separator/filter and the basket filter at the front of the carb inlet. Also, I poured the contents of the seperator in a clear mason jar and found no water in the fuel at all. The tank was fully rinsed out a few years ago too.

This is what I found in the small screen inside the pick up tube:



I thought for sure, this was the problem but nope!

It has a mechanical fuel pump and I can't remember if I checked for fuel by pumping the throttle and checking for streams of fuel or not. I keep bouncing back and forth, is it fuel? Or is it spark?
 
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Badfish95

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Here is a photo of the fuel pump. Can mechanical fuel pumps be affected by heat buildup in the engine compartment?

 

NHGuy

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What about putting your hand or a laser thermometer on the fuel pump after the heat soak? See if it's real warm.
Maybe your fuel is borderline vaporizing.
If it is too hot maybe take some steps to get the fuel temp down.
Is the fuel tank in the engine compartment? Does the engine run hot? If it does you could run the motor at a higher speed in neutral before shutdown to cool it down a bit.
You could also correct any cooling deficiencies if you have any..
If the idle is wrong, cooling inadequate or timing too advanced you could have the heat issue.
I also wonder if the wiring in the engine bay is having issues when warm.
It wouldn't hurt to just go over the contacts & clean them all up. Including the master plug, the grounds and battery leads. Just go through them all.
I don't know i that will solve your problem. But those are things I have done before and got nice results.
 
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Badfish95

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Thanks for the suggestions. I replied within your post below.

What about putting your hand or a laser thermometer on the fuel pump after the heat soak? See if it's real warm.
Maybe your fuel is borderline vaporizing.
If it is too hot maybe take some steps to get the fuel temp down.
Is the fuel tank in the engine compartment?
No, it is located under the deck in front of the engine compartment.

Does the engine run hot?

I don't think so. When I purchased the boat a few years ago I noticed the previous owner had pulled the thermostat out. It's had a little bog when going from idle to full throttle ever since I've owned it. I installed a 140 degree thermostat a few years back. I hoped it would let the engine run a little warmer and eliminate the bog/hesitation. It didn't, however the dash temp gauge never reads above 140 and I believe the correct thermostat for this engine is actually a 160?

If it does you could run the motor at a higher speed in neutral before shutdown to cool it down a bit.

This may be worth a try.

You could also correct any cooling deficiencies if you have any..
If the idle is wrong, cooling inadequate or timing too advanced you could have the heat issue.
I also wonder if the wiring in the engine bay is having issues when warm.
It wouldn't hurt to just go over the contacts & clean them all up. Including the master plug, the grounds and battery leads. Just go through them all.
I don't know i that will solve your problem. But those are things I have done before and got nice results.

I actually did clean the major terminals at the battery, starter and ground strap.
 

Fun Times

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This is what I found in the small screen inside the pick up tube:



I thought for sure, this was the problem but nope!
While this is sort of doubtful being a 1995 boat, That part in your hand almost looks like fiberglass particles which could either be debris that fell into the tank or hopefully your fuel tank isn't constructed out of fiberglass material due to with todays fuels, ethanol could start to dissolve the inners of the fuel tank clogging up the entire fuel system to the engine.
 

Badfish95

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While this is sort of doubtful being a 1995 boat, That part in your hand almost looks like fiberglass particles which could either be debris that fell into the tank or hopefully your fuel tank isn't constructed out of fiberglass material due to with todays fuels, ethanol could start to dissolve the inners of the fuel tank clogging up the entire fuel system to the engine.

I pulled the tank out in 2013 and thoroughly cleaned it inside and out. I'm guessing this ball of thread and debris was stuck up in the pickup tube even before I cleaned out the tank. Here is the installed tank after I cleaned it. I believe it's some kind of polymer.
 

Badfish95

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I'm looking for suggestions on how to diagnose the problem while on the lake. It is an intermittent problem that occurs after getting warm and sitting for a few hours.

Spark:
I thought about bringing an ST125 spark tool out, but it usually happens when going from idle to on plane. It also surges at the top end, so this would not work with a plug wire off...

Fuel:
Auxiliary tank?
What should I look for?

More parts:
Should I replace the distributor Cap and rotor(Replaced in 2013)? Wires? Remove 140 degree thermostat?

Any and all suggestions are welcome...
 

Badfish95

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I didn't mention this earlier but I'm also dealing with a starting issue. I turn the key and nothing happens two or three times and then on the fourth or fifth turn it cranks right over. I have the starter off and will take it in to get checked but that lead me to the slave solenoid and eventually to the Nuetral safety cutoff switch. Now I'm wondering if I'm possibly having intermittent spark issues due to a faulty Neutral safety cutoff switch. Any idea how to troubleshoot?
 
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Bondo

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Now I'm wondering if I'm possibly having intermittent spark issues due to a faulty Neutral safety cutoff switch.

Nope,... The switch controls the "Start" circuit,.... It has nothin' to do with the "Ignition" circuit,.....
 

alldodge

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I would suggest getting a vacuum fuel pump tester and check the fuel pressure at the carb, it should be 4 to 7 psi. You could pickup a Tee and some fuel line and barb fittings and replace the line from the pump to the carb, or just enough fuel line to go between the carb end and the carb.

http://www.harborfreight.com/fuel-pump-and-vacuum-tester-93547.html

Also how is you oil level, and do you smell anything like gas in it?
 

Badfish95

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Oil level always reads full to the full line. As far as the gas smell, I can't really say since Its in a fresh oil change. I always change the oil before I winterize it.
 

Badfish95

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I would suggest getting a vacuum fuel pump tester and check the fuel pressure at the carb, it should be 4 to 7 psi. You could pickup a Tee and some fuel line and barb fittings and replace the line from the pump to the carb, or just enough fuel line to go between the carb end and the carb.

http://www.harborfreight.com/fuel-pu...ter-93547.html

Also how is you oil level, and do you smell anything like gas in it?

Ok, so after replacing the spark plugs and a set of Premium plug wires.... the problem persists.

Good news: I bought a CTEK MUS 4.3 battery charger and was able to bring my dual purpose marine battery back to life! I highly recommend the ctek chargers. I also replaced the starter slave solenoid on top of the engine and no longer have starting issues.

Bad News: took the boat for the 1st time this year. Started and idles fine. We idled for about 5 minutes in the no wake zone. When I went to get on plane it bogged pretty bad when the secondaries opened but then regained power and away we went. 10 minutes at about 3,000 rpm to get it warmed up seemed to going fine. I started into a WOT run when it bogged/hesitated as I got into the secondaries. It struggled to get over 4,000 rpm and was surging when I heard a pop under the sun deck. It sounded like a high rpm backfire. I eased off it a bit and it ran fine under 3,000 rpm. It fealt like if I stayed in the primaries it would get us through the weekend...

We sat at the cove for an hour or so and then went for another cruise. It ran fine at 3,000 rpm to the end of the lake. We turned around and it started surging at 3,000 rpm. I slowed to 2,500 and it continued to miss/surge. Eventually it was so bad I had to come off plane. It ran fine at 1,000 rpm and below. Temperature gauge never climbed above 140.

I'm pretty sure I have a mechanical fuel pump going out. My only reason for thinking this is I have replaced everything else on this damn thing!

I attached photos of my fuel pump. It looks like the safety barb that is supposed to flood the carb if the diaphragm leaks is completely gummed up. Could this be my problem? BTW, I smelled the oil on my dipstick after today's run and it did have a hint of gasoline smell to it. I had just removed the fuel pump so it's hard to say for sure.

 
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alldodge

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The crud in the overflow tube means there is an issue with the pump. Only way to prove it out is with testing pressure. I would change it for any other reason then because of the stuff in the over flow tube
 

Badfish95

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Ordered a Sierra 18-7283 fuel pump from Amazon. Should be here Wednesday. I'm going to go ahead and change the oil after I swap it out. Thanks for the help and I'll post back after the next Lake test.
 
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