1993 f150 emissions problem - Arizona

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Humming
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1993 f150 emissions problem - Arizona

Post #1 by Humming » Mon Sep 10, 2018 9:53 pm

Hey all,

I'm picking up a 93 f150 with 4.9L.

It failed the pressure test for AZ emissions several months ago when the previous owner took it to be tested, but the only thing I've been able to locate is the breather line into the air box was loose on the air box end.
I've refitted that, but does anyone have an idea about anything else that might be my problem? I put propane on every vacuum fitting I could find but the idle stayed even.
Image
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Any ideas appreciated.

Humming
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Re: 1993 f150 emissions problem - Arizona

Post #2 by Humming » Mon Sep 10, 2018 10:07 pm

Image

Says tamper evap bad, but the evap on the slip says pass and the pressure test says bad.

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MechRick
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Location: Las Vegas, NV

Re: 1993 f150 emissions problem - Arizona

Post #3 by MechRick » Mon Sep 10, 2018 10:29 pm

Check the rubber lines going to the carbon canister underhood. Fuel vapor will make them soft and eventually, leak.

The '80-'96 trucks all use a simple evap system (even the '96 obdII trucks-always wondered how Ford got away with that). The vents at the top of the fuel tanks have lines that should be sealed all the way forward to the canister. The canister allows fresh air in (through the carbon substrate). Another tap on the canister feeds the canister purge valve (which hooks to intake vacuum). That's it.

When pressure testing, the vapor line at the canister is somehow sealed, and the fuel tanks are pressurized with low pressure gas (usually nitrogen).
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

Humming
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Joined: Sat Jul 15, 2017 11:52 am

Re: 1993 f150 emissions problem - Arizona

Post #4 by Humming » Tue Sep 11, 2018 1:42 am

Thanks! So basically just check the lines from the fuel tanks to the canister, and then the one line to the purge valve? That should be it? I'm assuming they clamp the lines just before the canister then. How likely would it be that the purge valve is bad? I'm assuming they can't test the charcoal canister itself?

MechRick wrote:Check the rubber lines going to the carbon canister underhood. Fuel vapor will make them soft and eventually, leak.

The '80-'96 trucks all use a simple evap system (even the '96 obdII trucks-always wondered how Ford got away with that). The vents at the top of the fuel tanks have lines that should be sealed all the way forward to the canister. The canister allows fresh air in (through the carbon substrate). Another tap on the canister feeds the canister purge valve (which hooks to intake vacuum). That's it.

When pressure testing, the vapor line at the canister is somehow sealed, and the fuel tanks are pressurized with low pressure gas (usually nitrogen).

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MechRick
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Posts: 761
Joined: Wed Jan 04, 2012 7:43 pm
Location: Las Vegas, NV

Re: 1993 f150 emissions problem - Arizona

Post #5 by MechRick » Tue Sep 11, 2018 2:56 pm

The purge valve and associated hoses should be a visual inspection. Pressure testing should be from the canister toward the tank(s).
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

Humming
Registered User
Posts: 22
Joined: Sat Jul 15, 2017 11:52 am

Re: 1993 f150 emissions problem - Arizona

Post #6 by Humming » Tue Sep 18, 2018 5:26 pm

I got under it and saw the vent line on the forward tank was cracked. Ipulled the bed and replaced all the vent lines and it passed! Thanks MechRick!

MechRick wrote:The purge valve and associated hoses should be a visual inspection. Pressure testing should be from the canister toward the tank(s).

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