Engine Missing / Cutting Out after 45 min?

A

ajkolar

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
120
First of all my boat is an '88 VIP with an 350 small block, electronic (pertronics) ignition and distributer (new 2 years ago), quadrajet 4 barrel and an OMC Cobra drive. I just replaced spark plugs (MR43T), fuel filter / water separator and a new 160 degree thermostat. Plug wires are 3 or 4 years old (all test ok with ohm meter). Fresh oil and filter as well.

The boat starting acting up a little bit at the end of last season and has continued to do so for the 1st two times I have taken it out this year. It starts up GREAT, and runs FINE as soon as I get to the lake. However, it seems like after I am out on the water for about 45 min - 1 hr, especially after I have been sitting (with the boat off) for awhile it starts cutting out and missing. I can't tell if it is getting too much or too little fuel, or not running on all cylinders or what. Today it started doing it when I was just cruising along at about 2800 RPM. I took a short video of the engine when it was acting up and it can be seen at this link:

http://www.americaninspections.net/andy/video.htm
(just right click on the link and then click "Save Target As" and you can download and view the video) And, yes I know the flame arrestor is off, I wanted to make sure the choke was interferring, but it was wide open like it ought to be.

The carb has not been re-built since I have owned the boat ~4-5 years. But it seems like if it was the carb it would ALWAYS do it, and not be in consistent like this. Like I say, if I take it out tomorrow it will probably run start and run like a champ for the first half hour!

Any help or suggestions ARE REALLY appreciated. I want to get things running properly before the warmer weather gets here! Thanks!
Andy
 
C

Coors

Captain
Joined
Dec 8, 2006
Messages
3,367
Re: Engine Missing / Cutting Out after 45 min?

"save target as" makes some people not want to open it, y'know?
 
A

ajkolar

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
120
Re: Engine Missing / Cutting Out after 45 min?

Sorry... I didn't know the best way to do it as it is 38 megs... if I just post a link staight to th video your default media player ties to open it but as it is soo large most people would think it isn't working (while it is downloading) and just close it anyway... What is the best way to post such a large clip?
 
a70eliminator

a70eliminator

Captain
Joined
Sep 9, 2007
Messages
3,762
Re: Engine Missing / Cutting Out after 45 min?

Sure sounds like ignition cut out to make it miss like that, I would be looking at the shift interrupt switch, when you shift into reverse or from neutal to forward you notice the momentary engine cutout, is that what your miss sounds like? also there is an overstroke switch these micro switches look identical and are close to each other so they should be easy to spot, I believe you can bypass them just to see if you still get the symptoms, Don knows for sure about how to bypass them I think just a little jumper will do it. Also coils have been known for breaking down under under heat stress, then work fine again once cooled off.
 
S

slia67

Petty Officer 1st Class
Joined
Jul 11, 2007
Messages
272
Re: Engine Missing / Cutting Out after 45 min?

The first thought that came to my mind was a coil breaking down under heat.
 
N

neilmw

Petty Officer 1st Class
Joined
Jul 19, 2004
Messages
245
Re: Engine Missing / Cutting Out after 45 min?

....
 
Last edited:
A

ajkolar

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
120
Re: Engine Missing / Cutting Out after 45 min?

I have two coils and get the same problem with both (that wasss my first thought as well). I have a mechanical fuel pump that runs off a cam lobe (so I don't think the oil pressure sensor could cut off my fuel supply) or can it? If so, any way to test it?
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Engine Missing / Cutting Out after 45 min?

Have you done the fuel system tests I linked to a few days ago?
 
A

ajkolar

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
120
Re: Engine Missing / Cutting Out after 45 min?

Not yet Don, keeping really busy with work and probably won't get a chance for a week or two. I will need to pick up the vacuum / fuel pressure guage as well... Any recommendations what / where to get that? Thanks for the good info!
 
S

soler

Seaman Apprentice
Joined
Apr 29, 2008
Messages
32
Re: Engine Missing / Cutting Out after 45 min?



Sounds like some lazy workers I know. Showing up and then disappearing until quitting time. I'd fire it and hire another, more hardworking engine! :D

SOLER
 
A

ajkolar

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
120
Re: Engine Missing / Cutting Out after 45 min?

I may finally get some time to try an diagnose this problem as outlined by the post / artical referred to by Don. When it says in stall a piece of 8 in. vinly tube, I am assuming it means an piece of vinyl tubing with one end plugged and on a "t" type fitting right before the carb.... And this vinyl tubing is separate from the fuel pressure / vacuum gauge that also needs to be plumbed into the fuel line... Is this correct?
 
A

ajkolar

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
120
Re: Engine Missing / Cutting Out after 45 min?

Please don't miss my above post... but I had one more question... Should the fuel pressure gauge be plumbed into the fuel line between the fuel filter / water separator and the fuel pump, OR between the fuel pump and the carburetor to start with? Thanks!
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Engine Missing / Cutting Out after 45 min?

Here is a copy and paste of part of procedure.

1. Install Vacuum and Fuel Pressure Gauge such as Snap-on? Tools MT311JB or equivalent, and 8 in. (20,3 cm) of clear, fuel resistant vinyl hose into the fuel line at the filter fuel pump inlet fitting. (NOTE: On some engines there is a filter hard plumbed to the fuel pump, these engines should have the gauge attached to the fuel filter and not the pump itself. )
Click to expand...


Gaugehookup.png
 
A

ajkolar

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
120
Re: Engine Missing / Cutting Out after 45 min?

Ok, I finally made it out today to do the test that Don recommended and also hooked up the vacuum guage to the intake. The vacuum/pressure gauge was connected to a "t" fitting inbetween the gas tank and the fuel filter with 8" of clear line from the "t" to the fuel filter inlet fitting.

vacdiag1.JPG


While running at WOT the pressure/vacuum gauge read ~ 0 (under 1 for sure) and every once and awhile I would see a very very small air bubble go by (air bubble the size of the tip of a pencil lead).

vacdiag2.jpg


When I turned off the engine Large air bubbles formed in the clear plastic line (coming back from the fuel pump side). Is this normal when the engine is off for air to work back into this line?

vacdiag3.JPG


Also, I believe I could see a very very small amout of fluid (less than 1 teaspoon) in the clear plastic line that runs from the carb back to the fuel pump (I think that can indicate a broken diaphram in the fuel pump or something). But I drained the line and nothing seem to return.

Also.... I hooked the vacuum guage up to a port on the intake manifold (on the top of the manifold on the starboard side above like piston #6. The gauge read 18 at idle. As I accelerated and increased speed/rpm the vacuum guage dropped in pretty much a linear line until it was about 0 at WOT. Then when I got home I started it in the driveway (with muffs) and it read 19.5 at a couple hundred RPM over idle and as I bumped the throttle it dropped to below 10 and then to about 25 and then steadied out at 19.5. Should the vacuum decrease linearlly like that when running under load? The vacuum diagnostic sheet indicates restricted exhaust in this scenario I belive. I have straight through hull exaust and can see all the way up to the risers with no restrictions (unless restricted inside the manifold). Is it normal for the guage to act differently like this when not under load?

vacdiag4.JPG


I was out making 2-4 min WOT throttle runs and crusing around 3K RPM for about an hour and it never acted up. It usually doesn't act up until I let it sit for awhile (like floating in a cove or something, which I didn't have time to do today).

What are your guys' thoughts? What next? Thanks for the help!
 
A

ajkolar

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
120
Re: Engine Missing / Cutting Out after 45 min?

Bump, bump. (added some images).
 
A

ajkolar

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
120
Re: Engine Missing / Cutting Out after 45 min?

Please help! No further thoughts on the information I collected out on the water Sunday??
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Engine Missing / Cutting Out after 45 min?

It all depends on what the fuel vacuum gauge reads WHEN you have the problem, not when everything is working. The large air bubble when you shut it off is normal if you don't have an antisiphon valve, or it's stuck open. Which would also be the reason for the very low vacuum. Nothing there for the fuel pump to overcome.
I would check (replace) the antisiphon valve for sure, just because it's not working and could be a safety liabilty.
 
A

ajkolar

Petty Officer 2nd Class
Joined
Jan 17, 2006
Messages
120
Re: Engine Missing / Cutting Out after 45 min?

Thanks for the info... I just thought some of that stuff may have indicated what may be causing the problem. So am I mistaken that I should maintain a reading of ~18 all the way through the RPM range?

Where would I look for the antisyphon valve?
 
C

Coors

Captain
Joined
Dec 8, 2006
Messages
3,367
Re: Engine Missing / Cutting Out after 45 min?

Where the fuel line connects to the tank.
 
You must log in or register to reply here.
Top