View Full Version : Vacuum Port?

12-20-2004, 03:14 PM
Hi everyone,

I have recently purchased a 1990 Prostar 190 with the Ford 351 Indmar engine. It sat for a while which created some issues that I have figured out. It is now up and running well, I think. I like to use a vacuum guage as a diagnostic tool but I can't find anywhere on the intake to plug one into. Does anyone have any advice on where I can connect a guage? I realize I may have to undo a plug of some sort on the manifold and install a fitting and that's not a problem, I'm just wondering where a suitable plug may be located.

Any help will be appreciated. Hope everyone has a great Christmas!!


12-23-2004, 02:51 PM
No one uses a vacuum guage?

12-23-2004, 02:58 PM
I try to stay away from anything call vacuum!
Sorry no help!
Merry Christmas!

12-23-2004, 03:03 PM
No clue? :confused:

12-23-2004, 03:22 PM
Congrats on the 190

I cant answer your question either. Keep poking a stick at this thread and I’ll bet you get the info you need.


12-23-2004, 03:29 PM
If it is carburated, then you can run a spliced hose with a brass or high temp plastic barbed connector shaped like a "Y" or "T" from the intake spacer(little plate under the carb with a hose that connects to the valve cover and pcv valve). The spliced hose can now be accessed by a vacuum gauge. I would suggest either splicing the current hose and just cap of the open end when not in use.

12-23-2004, 03:34 PM
Martini is correct, there should be a vacuum port below the carb...however, when running a gauge make sure it is the only thing connected to that port, do not run it with the "T" or "Y" connector. Just as airflow, vacuum takes the least restrictive route. If it is connected to a gauge and to the PCV it will suck from the PCV since it is so easy, and you will have less vacuum for the gauge.

12-23-2004, 03:43 PM
See Hunter, I knew it!! Got a love this site

12-23-2004, 03:52 PM
but, what is a vacuum gauge gonna tell you?

I mean, you gotta have baseline established firstimages/smilies/confused.gif

12-23-2004, 10:59 PM
but, what is a vacuum gauge gonna tell you?I dont know:confused:

12-24-2004, 07:52 AM
I have an 87 with the same engine and can't help you on where to connect the vacuum guage. The only thing I have ever used a vacuum gauge for is verifying vacuum advance on the ignition but since these engines don't have vacuum advance there isn't a need. The only other thing that I can think of that you would use one for would be troubleshooting / verifying proper operation of the secondaries as they are vacuum actuated.

What else would a vacuum guage help with? I am curious as I am always trying to learn a little more about troublshooting / diagnostics tips and tricks.

Dan K
12-24-2004, 02:29 PM
I used to use a vacuum gauge to set my timing on older cars.
I would just rotate the distributor until I maxed out the vacuum. This would theoretically indicate optimum performance. Never did this on my boat, but it may be worth a shot.

12-29-2004, 03:59 PM
Hi everyone,

Thanks for the replies regarding the vacuum port. I believe it requires drilling into the manifold or the spacer and installing a fitting in order to be able to do it.

As for what you use a vacuum guage for, they are extremely valuable diagnostic tools. They can tell you a ton about the internal condition of your engine, particularly the valve train. I have found through many years of messing with car/truck motors that you can determine very accurately the condition of an engine with three tools;a mechanical oil pressure guage, a compression guage and a vacuum guage. The vacuum guage is generallly the easiest to hook up (except in the case of a marine manifold as I have found out) and, with a little practice, is easy to interpret.

Thanks again for the replies. Hopefully everyone had a great Christmas!


12-29-2004, 04:56 PM
Thanks to you for educating us!
Happy holidays!