f150 rough idle

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Apr 6, 2013 | 02:35 AM

F-?rebuild90

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f150 rough idle

i have a 1990 f150 replaced long block 351 w efi w/ E40D auto 1356 tcase 9" rear have done tune up - plugs, wires, cap, rotor, tps sensor it was bad, new computer was burnt!, fuel filter, checked fuel pressure 45 at rail, checked timing its good, no check engine light and i seems to have a slight misfire or rough idle. runs good uses some gas of course but wonder if egr valve or something needs replaceing if you can help please do thank you.

Apr 6, 2013 | 10:11 AM

Conanski

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Joined: Jun 2006

Posts: 31,930

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From: Ottawa, Ontario

That truck should have an 8.8 rear, a 9" has no VSS sensor and that wouldn't work with an E4OD.

Does it have 45psi fuel pressure all the time or just with vacuum removed from the regulator? It should be more like 32-35psi with vacuum attached and jump up when throttle is blipped.

Any codes present?

Apr 7, 2013 | 01:18 AM

GoinBoarding

Cargo Master

Joined: Mar 2010

Posts: 3,330

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From: Laramie, WY

Every 351W I've been around has a little bit of a rough idle. I was told the day it idles really smooth is the day I need to check fuel pressure. In my own truck, two different motors, 200k between the two, both idled a bit rough compared to a 302. Just a thought, maybe you're already aware. If that engine rebuild included a different (not stock) cam, that'll make it lope a little more at idle than usual too.

45psi does sound high though.

You can check the pressure regulator pretty easily by slipping the vacuum hose off of the top of the regulator. No fuel should come out the nipple, if fuel is present, replace the regulator.