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New Ford 390 motor giving me fits


Bob Shafto
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Here’s a problem that ought to be solvable but no solution has been found after a great deal of effort by two different skilled mechanics.
 
I bought a professionally rebuilt 390 Ford V8 long block to replace the tired 390 motor in my ’66 Galaxie 500 from a rebuilder that has a good reputation for quality work.  After installation of the new motor, it won’t run correctly. It is drawing too much air and thus running too lean, leading to difficultly idling and general dysfunction at any speed. Control the auto choke by hand to reduce air flow, however, and the motor runs fine. 
 
Here’s what has been done in light of the problem:
 
  1. All vacuum lines into the carb & manifold are fine (connected correctly and not leaking).
  2. It’s getting fuel. Fuel filters have been replaced but the old ones showed no dirt or grit. 
  3. The carburetor has been torn down and no problems found (it worked fine on the replaced motor prior to the exchange). Mounting gaskets replaced.
  4. Cam timing has been checked; we have correct valve overlap in cyl. #1 at TDC.
  5. Distributor and ignition wires are correctly placed in accordance with the firing order; timing is adjusted and spot on; new plugs, points, etc. installed.
  6. Internal air leaks checked by blocking off the oil filler and PVC valve openings in the valve covers; no leaks were detected.

There is no computer in this car, and I don’t believe in evil spirits, so this has to be a mechanical problem that must have a solution. Unfortunately, I have no idea what that solution is. Any thoughts or suggestions would be much appreciated. What have we missed? Anyone ever had a similar problem?

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You could try blocking every vacuum port that goes to the engine or carburetor or PCV plate and see if you get any dramatic difference. Some device at the end of a vacuum hose could be leaking, a power brake booster for instance. Does this one have a plastic vacuum manifold up on the firewall? Sometimes they rot and break.

Edited by Bloo (see edit history)
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1 hour ago, Bloo said:

You could try blocking every vacuum port that goes to the engine or carburetor or PCV plate and see if you get any dramatic difference. Some device at the end of a vacuum hose could be leaking, a power brake booster for instance. Does this one have a plastic vacuum manifold up on the firewall? Sometimes they rot and break.

 

No power brakes or vacuum manifold. 

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First off.........did you put a five gas machine on it? Otherwise how do you know it’s lean? Did you try adding HC’s using propane? I’m still guessing it’s an intake manifold............but without putting the ignition on a scope, everything is conjecture. Should be a ten minute diagnosis. On a new engine, if it doesn’t get located quickly, pull the intake.........fast and easy. Not to be a smart ass........a running problem on a 390 should be figured out in fifteen minutes. Stoichometry isn’t rocket science..........

Edited by edinmass (see edit history)
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7 minutes ago, Bob Shafto said:

Thanks guys, looks like the next step is to take the intake manifold off and see what's what.

 

It would be a LOT EASIER if the intake were an Offy aluminum 2x4 with 2 genuine Carter AFB carbs ;)

 

Reinstalling that cast iron intake requires 5 individuals: 2 on each side to lower the intake onto the heads/block, and 1 to make sure everything is aligned.

 

Jon.

Edited by carbking (see edit history)
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2 hours ago, carbking said:

Reinstalling that cast iron intake requires 5 individuals: 2 on each side to lower the intake onto the heads/block, and 1 to make sure everything is aligned.

 

Jon.

 

No, it just takes one person and an engine hoist. Yes, I've done it that way. 😁

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Those FE intake manifolds are particularly challenging as the manifold actually includes the top of the valve cover gasket interface, which makes it bigger and heavier...  Really best with 2 people -or use the engine hoist suggestion above.

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Intake manifold relationship to head machining issue.....vacuum leakage. 

Take plenty of time to check manifold fit up to heads and block deck.

A lot of info to read about this problem online.

Use a engine hoist for easy controllable R&R of this boat anchor intake..

Edited by c49er (see edit history)
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On 8/21/2021 at 4:08 PM, nickelroadster said:

Spray the joints with starting fluid to find out for sure.  That manifold is easy to have a slight misalignment.

 Remember that the intake to head joint is UNDER the valve covers.

If you are going to spray something in there you must remove the valve covers. 

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