Engine Diagram

Discussion in '1974 - 1978 Mustang II Talk & Tech' started by Dr Black, Nov 4, 2013.

  1. Does anyone have an engine diagram? Or some really awesome pictures that detail how the vaccuum pressure is supposed to work in the engine? The previous owner of my II rewired alot and not the engine sounds like trash, and idles really high. I cant feel any vaccuum pressure from the carb or anywhere else on the engine so I'm assuming thats the problem.
  2. Which engine?
  3. Sorry should have been more specific. 302 V8
  4. Saw your post last night-I did have wiring diagrams (which I can't find now), but no vaccuum diagrams. But I chewed on your problem for a while and reminds me of 2 different cars with what sounds like similar issues. The first was a V6 car which ran fine but idled pretty high. It turned out that the engine had a carb on it from a 302. We were never able to get the idle down on that car. The other one was my first 302 car. The intake bolts weren't torqued properly and it idled rough, but if memory serves the idle speed was somewhere around where it was supposed to be. Once I found the loose bolts and torqued them down, the engine idled smooth. Not knowing all the specifics about your engine, it is also possible that it may have a late model cam in it that requires the HO/351W firing order? That would definitely cause it to not run well if the firing order wasn't changed accordingly? Of course all of that is also assuming that the engine is in pretty good condition. Good luck and hope this post is a little more helpful than my posts about your brake equalizer... :)
  5. Thanks for the reply! I dont know much of the specifics of my engine either and I'm still a gear head in training, so I apologize in advance if I what I say is confusing. I don't have much history on the car and the only thing I did was have have the clutch replaced when it went. I'll see if I can find the number of the guy I bought it from and ask about the cam.

    It has a an eddlebrock carburetor and manifold. My dad and I are trying to figure out how the vacuum pressure works, because there's nothing attached to the distributor cap. There's not pressure from the front of the carb either so we're kinda at a loss. He's new to mustangs, but has over 20yrs exp as a mechanic so I'm helping to middleman us into getting the car up and running. So any info is greatly appreciated.
  6. The good news is that the engine must be pulling vacuum if it's starting and running at all which you mention that it is. If it wasn't you might have a bad cam, valves, or compression and need a full rebuild.

    So the problem is likely someplace at the intake manifold / carb or possibly between the two. I've never come across a carb that wasn't pulling any vacuum at all at any of its ports while still starting up and running at all. A wild cam could draw less vacuum, but there would still be some. Badly misadjusted valves would also still draw some vacuum, or as I mentioned the car wouldn't start at all. And even if it's idling super-high it should still be pulling some vacuum. You'll usually have two vacuum ports -- one which provides manifold vacuum (highest at idle and lowering as you rev up the engine) and one which is ported (doesn't draw vacuum at idle but does so when you rev up). One of them HAS to be drawing some vacuum unless the path to it is blocked. So I'm a little confused.

    Possibly an explanation which would require some pulling-apart on your part... is it possible that someone bolted a spread-bore carb onto the wrong square-bore manifold (or visa-versa)? Edelbrock makes both in manifolds and carbs. Depending on the arrangement it might be blocking off some of the vacuum ports, specifically those which are feeding the external passages which could go to your accessories. Another possibility is that some shadetree mechanic plugged the vacuum ports purposely (or by badly failing at a rebuild) but we'll hope that's not the case. Another off-the-wall possibility is that someone mounted a marine carb which doesn't have any vacuum ports.

    Are there any ports on the intake manifold you could check for vacuum? Do you have any other carbs lying around which you could test-fit after ensuring you have the right match to your intake manifold? Do you have vacuum elsewhere -- PCV port or a port for the vacuum brake booster?

    Once you re-establish vacuum at the carb ports, it's possible it's idling high because the vacuum circuit was blocked and someone adjusted the idle higher to get out of the idle circuit which might not be working at all at the moment -- also due to the vacuum issue.
    #6 jozsefsz, Nov 6, 2013
    Last edited: Nov 6, 2013