Vacuum test - 3.0L Mercruiser

[Mile-High Mariner]

Okay, I've perused all of the other posts related to vacuum testing and still have a question: how many places are there to check vacuum on a 3.0L Mercruiser? I see folks checking engine vacuum and fuel line vacuum at various points, so I'm asking for all the points and the specifics on hooking up the gauge, please. Explanation of the significance of each would be helpful, thanks!

 

[Don S]

Re: Vacuum test - 3.0L Mercruiser

To test engine vacuume, you need to hook your gauge to the intake manifold. Should be a pipe plug on it somewhere. Remove the plug and put in a fitting with a hose barb for your gauge.<br />In the fuel line, it best to put a tee between the fuel pump and the line coming from the fuel tank. Use a piece of clear hose between the tee and the fuel pump so you can see air bubbles if there are any while the engine is running.

 

[Mile-High Mariner]

Re: Vacuum test - 3.0L Mercruiser

Sorry, Don, I didn't see your reply until today. I've looked on the manifold and I see four bolts facing the port side of the boat that I assume secure the manifold to the block. Is there some indication in Service Manual 13 or other source as to where the pipe plug is, exactly? The only pipe plug I know of is the manifold drain - would this be sufficient for vacuum testing?<br /><br />I have the tee fitting for the fuel line and other fittings, as well.<br /><br />Thanks again for your input!

 

[Mile-High Mariner]

Re: Vacuum test - 3.0L Mercruiser

Update:<br /><br />After perusing Bondo's 02 December post to crawdadric, I think I can use the other pipe plug (foreward of the manifold drain). I have the one-piece manifold with two pipe plug fittings on the bottom. Thanks again for your help!

 

[Bondo]

Re: Vacuum test - 3.0L Mercruiser

I Don't remember the Post,+ I Don't ever remember seeing a Vacuum Port on the Bottom of a Manifold,......

 

[Don S]

Re: Vacuum test - 3.0L Mercruiser

You may not have a plug for checking vacuum. If you do, it will go directly into the intake part of the manifold.

 

[Scaaty]

Re: Vacuum test - 3.0L Mercruiser

are we talking intake here?

 

[Scaaty]

Re: Vacuum test - 3.0L Mercruiser

." one-piece manifold with two pipe plug fittings on the bottom. <br /> Or exhaust?

 

[Don S]

Re: Vacuum test - 3.0L Mercruiser

Intake is Vacuum. <br />Exhaust is Pressure.

 

[Scaaty]

Re: Vacuum test - 3.0L Mercruiser

Seems I have not the faintest idea where this thread is going. Guys looks for vac plugs, seems like he referring to exhaust <br />...."use the other pipe plug (foreward of the manifold drain;"..<br />and some how it went to exhaust pressure...jeezz, Im going back to bed......

 

[Don S]

Re: Vacuum test - 3.0L Mercruiser

Sorry robby, but you are the only one that mentioned exhaust.<br />David is trying to find out where to hook up a vacuum gauge to his engine (Look at the first post)the he was under the impression it might be one of the plugs on the bottom of the manifold.

 

[Capt Ken]

Re: Vacuum test - 3.0L Mercruiser

Don't believe there is a vacuum plug on a 3.0. Least I don't remember ever seein one. Was one on the older 2.5

 

[Mile-High Mariner]

Re: Vacuum test - 3.0L Mercruiser

Okay - I forgot the 3.0 has a combination manifold - of course the bottom plugs drain the exhaust. Now, do any of you fellas have a good recommendation on where to retrofit a vacuum test plug or port for this application?<br /><br />(BTW - Bondo: I was looking at the diagrams you posted for crawdadric from the Service Manual and got all happy about the pipe plugs, completely forgetting that they are ported into the pressure side of the manifold.)

 

[John Hink]

Re: Vacuum test - 3.0L Mercruiser

The most likely place that I can think of would be an adapter plate between the carburetor and inake manifold.<br />My book does not mention doing a manifold vacumn check, but the automotive side of these engines have lots of vac ports for testing and the adapter is included.

 

[Don S]

Re: Vacuum test - 3.0L Mercruiser

The most likely place that I can think of would be an adapter plate between the carburetor and inake manifold.

No such thing on a marine 3.0L

 

[Scaaty]

Re: Vacuum test - 3.0L Mercruiser

Originally posted by Mile High Mariner:<br />[QB] Okay - I forgot the 3.0 has a combination manifold - of course the bottom plugs drain the exhaust. <br /><br />Thats why I mentioned exhaust...

 

[Mile-High Mariner]

Re: Vacuum test - 3.0L Mercruiser

How does one go about testing vacuum on the 3.0 if there is no means provided by which to access it? Has anyone ever successfully tapped a manifold for this purpose? Mercruiser provides vacuum troubleshooting details in the Service Manual, so there must be some means by which the authorized service centers accomplish it (Don?).

 

[Mile-High Mariner]

Re: Vacuum test - 3.0L Mercruiser

Okay - a reply from another source indicates that the only vacuum source he knows of on the 3.0 is the idle air screw on the carburetor. Anyone care to comment?

 

[Weirdwalt]

Re: Vacuum test - 3.0L Mercruiser

Drill a hole, tap it, test it, then plug it. That would be the fantasy way of testing it. The reality way is: Drill hole that ends up being all oblong. Proceed to break tap off in hole. Try to get broken tap out which by the way is the first thing a young mechanic learns is impossible. Finally shatter tap and all the pieces fall into the intake. Remove manifolds all the while swearing with new combinations unheard by human ears. Clean out manifold and set down on bench and stop to think how you're gonna fix that hole. Pop open a beer. <br /><br />8 beers later leave manifolds on bench and go inside. <br /><br />Next spring find manifold still sitting on bench under all the junk you piled on it over the winter. <br />Tell wife in your best "know what I'm doing" manner that you need some new parts for the boat and they're gonna be about 700 bucks. Use lots of mechanicy sounding words.<br /><br />Six weeks later with summer season in full swing the UPS guy brings your manifolds which cost 300 dollars extra for shipping and handling. <br /><br />Install on boat, and after two days of trying to get the boat started realize it is out of fuel. Use mechanicy sounding terms to the wife again to avoid embarrassment. <br /><br />When wife finds the old manifold on the bench and inquires about the big huge messy hole in it say "Oh it musta threw a rod" and explain that a mechanical malfunction caused a bigass backfire which made that hole and thank god no one was hurt and how lucky I found it before we took it out that way.<br /><br />Try to remember why you were doing a vacuum test in the first place.

 

[Bondo]

Re: Vacuum test - 3.0L Mercruiser

How does one go about testing vacuum on the 3.0 if there is no means provided by which to access it?

Well,...... I Guess a Vacuum Test is Out of the Question on a 3.0l............<br /><br />You Already Know that you have a Dead Hole in #2,.........<br /><br />Did you do the Leak-down Test,+ See where the compression is Gone too,..???....