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Discussion Starter #1
hey guys, ive been having this problem for the past few days with my a/c. basically, while driving the air will blow out of the vents and then randomly switch to the floor and the defroster area. it does it on both norm and max. i found this thread and checked the white line but it looks perfect.
http://fullsizebronco.com/forum/showthread.php?t=46338&highlight=a/c+blowing+floor

any other ideas? this is on a 96 if it makes a difference.
 

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Check the vac hoses. I am deaf when it comes to vac leaks unless its a real screamer so I use a vac gun to check with the engine off.
 

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yo,
The basics first;
The air handling system is designed to provide defrost when no vacuum is applied to any of the three air door vacuum motors. This is done to prevent a situation where defrost cannot be obtained due to a system vacuum leak. Instead, a leak in the vacuum control circuit will send all airflow to the defroster outlets. This condition may occur during acceleration (slow leak), may exist at all times (large leak) and may happen only when certain specific functions are selected, indicating a leak in that portion of the circuit.. from F-150, F-250, F-350, F-Super Duty and Bronco, F-Super Duty Motorhome Chassis Workshop Manual
Source: by Ford

Did you open up the plastic harness cover to ck all of the White Vac line yet?
Other sources of a vac leak in the HVAC sys are
Vacuum Control Valve , vacuum canister, and inside to doors.control panel
see:

Top 1/4th of diagram is in Engine area; see all above "Cowl Panel"
 

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also;
Vacuum Line/Hose;"...The vacuum hoses used in the passenger compartment control circuit are constructed from PVC plastic material. The vacuum hoses used in the engine compartment are constructed of Hytrel. Because of the materials used, the vacuum hoses should never be pinched off during diagnosis to locate a leak. Use Rotunda Vacuum Tester 014-R1054 or equivalent to locate vacuum leaks. A wood golf tee can be used as a plug when it is necessary to plug one end of a vacuum hose for leak test purposes..." from F-150, F-250, F-350, F-Super Duty and Bronco, F-Super Duty Motorhome Chassis Workshop Manual

Mini-Tube Vacuum Hose Service in Climate Control System in a 96; "...Measure the length of the damaged area of the mini-tube vacuum hose. Cut a piece of standard 3mm (1/8-inch) ID vacuum hose approximately 25mm (1 inch) longer than the damaged area of the mini-tube vacuum hose. Cut the mini-tube vacuum hose on each side of the damaged area and remove damaged portion of the mini-tube vacuum hose. Dip the mini-tube hose ends in Tetra Hydro Furan (THF) or Methyl Ethyl Ketone (MEK). Either of these solvents will act as a sealer for the repair of the mini-tube vacuum hose. Insert the ends of the mini-tube vacuum hose approximately 9mm (3/8 inch) into the ends of the standard 3 mm (1/8-inch) ID replacement vacuum hose. Shake the service joint after assembly to make sure solvent is dispersed and vacuum line is not blocked internally. Test system for a vacuum leak in area serviced..." from 1996 F-150, F-250, F-350, F-Super Duty and Bronco, F-Super Duty Motorhome Chassis Workshop Manual
 

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Discussion Starter #6
ok well i got around to checking some of this stuff out today. the white line was indeed very dry rotted. i havent replaced it yet but i took the controls out of the dash and i can hear a hissing sound from the selector. the lines in that portion of the system appear brand new un like the white one outside. should i be hearing anything from that area or does it have an internal leak? it only hisses on MAX AC and OFF.

also i had 2 codes pop up in the CEL, codes p0401 and p0402. both are EGR related and both say a possible cause is a vac leak.

i also have a surging off idle.

what are the chances all of these are related to the same problem?
 

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-90 xlt, 351w, e4od, man 1356, 3.55, sag, warn hubs, 35s. -73, 400, np435, d20j twin, 35s
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Yeah, surging at idle is another symptom of a vacuum leak, usually a big one. I wouldn't be surprised if they're all related. I don't think a/c your selector should be hissing in any position, at least once the doors have a chance to move, but that doesn't seem large enough alone to affect idle. You may have a big leak elsewhere, or several small leaks.

Use a hose up to your ear & listen thru it to possible leak locations. Follow all those vacuum hoses. The power brake booster & it's hose are common places for a leak, the pcv hose is another, & sometimes it can be at an intake manifold gasket.
 

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yo I

Fix that white line and ck for other vac leaks
DTC P0401 & P0402: EGR Flow Insufficient Detected, & EGR Flow Excessive Detected; "...possible causes are a bad DPFE sensor, a bad EGRVR solenoid or possibly a bad PCM (NOT LIKELY!).
The first thing to check is the wiring for breaks and be sure the connectors are clean and tight. Also check the vacuum lines for proper routing and that there are no breaks or cracks in them..."; MIESK5 NOTE: only 95 5.8L California models & all 96 have the DPFE Sensor instead of EGR Valve Position Sensor (EVP); Ford also calls the DPFE Sensor an EGR Pressure Valve; my 96's Ford pn is F4ZZ9J460-B; new Plastic replacement version is MOTORCRAFT Part #DPFE15
Source: by Matthew W

I have DPFE etc tests in my site in.. Emission section. Exhaust Gas Re-circulation (EGR) System Pressure Feedback Electronic (PFE) & Differential Pressure Feedback (DPFE) Sensor


Vacuum Leak Test; On an idling engine check for vacuum leaks using a mechanic's stethoscope with the probe removed, or a ~3' garden hose section. Don't spray flammables on a running engine. MIESK5 NOTE; Also check: vacuum hoses; intake manifold gasket & throttle body; PCV line; vacuum reservoirs: EGR Sys Vacuum Tank & 2ndry air (coffee can); AC, heater, defroster, vent control ckt & vacuum tank (plastic ball type), under dash & lines to heat/blend/etc. doors; power brake booster; cruise control ckt, etc.... where applicable; (combined w/ Steve83's info, thnx) BEWARE OF BELTS/PULLEYS, FAN AND HOT ENGINE
Source: by miesk5 & Steve83
Vacuum Leaks, Finding; "...Cracked or broken vacuum lines, leaking intake manifold or plenum gaskets, injector o-rings, broken emissions solenoids, open vacuum ports are just a few of the causes of vacuum leaks. Use the under-hood emissions diagram and check every single vacuum circuit with a vacuum tester such as the Mityvac tool. A faster technique for finding intake manifold vacuum leaks is to get a bottle of propane and attach a length of rubber hose to the gas valve. Start the engine, be careful not to come too close to the fan or fan belts. Open the propane tank valve so you have a steady flow of gas. Then hold the hose near suspected leak points while the engine is idling. If there is a leak, the propane will be drawn in through the leak. The propane should cause a noticeable change in idle speed and/or smoothness. Always know where the closest fire extinguisher is and how to use it!..."
Source: by Ryan M (Fireguy50) at http://fordfuelinjection.com/?p=93
"...The vacuum hoses used in the passenger compartment control circuit are constructed from PVC plastic material. The vacuum hoses used in the engine compartment are constructed of Hytrel. Because of the materials used, the vacuum hoses should never be pinched off during diagnosis to locate a leak. Use Rotunda Vacuum Tester 014-R1054 or equivalent to locate vacuum leaks. A wood golf tee can be used as a plug when it is necessary to plug one end of a vacuum hose for leak test purposes..." from F-150, F-250, F-350, F-Super Duty and Bronco, F-Super Duty Motorhome Chassis Workshop Manual
Source: by Ford via thedieselstop.com

Mini-Tube Vacuum Hose Service in Climate Control System in a 96; "...Measure the length of the damaged area of the mini-tube vacuum hose. Cut a piece of standard 3mm (1/8-inch) ID vacuum hose approximately 25mm (1 inch) longer than the damaged area of the mini-tube vacuum hose. Cut the mini-tube vacuum hose on each side of the damaged area and remove damaged portion of the mini-tube vacuum hose. Dip the mini-tube hose ends in Tetra Hydro Furan (THF) or Methyl Ethyl Ketone (MEK). Either of these solvents will act as a sealer for the repair of the mini-tube vacuum hose. Insert the ends of the mini-tube vacuum hose approximately 9mm (3/8 inch) into the ends of the standard 3 mm (1/8-inch) ID replacement vacuum hose. Shake the service joint after assembly to make sure solvent is dispersed and vacuum line is not blocked internally. Test system for a vacuum leak in area serviced..." from 1996 F-150, F-250, F-350, F-Super Duty and Bronco, F-Super Duty Motorhome Chassis Workshop Manual
Source: by Ford via thedieselstop.com
Mini-Tube Vacuum Hose Damage Repair in a 92
Source: by JohnMcD348 at FSB


GL!
 

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Discussion Starter #9
ok looks like i got some more digging to do. i shall report back! thanks!
 

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Discussion Starter #10
well i just replaced the white line as per miesk's post and it seems to have fixed the a/c problem. i also cant hear leak behind the knob any more. i cleared the 2 codes to see if they will come back as i didnt see any problems under the hood as far as vacuum leaks go. if they come back ill pull the components and see whats up.
 

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yo,
ok good! one prob down

If you get the the 2 codes back again;
DPFE Testing & Vacuum/Voltage Parameters & pics on both older Aluminum & Newer Plastic Version; MIESK5 NOTE: only 95 5.8L California models & all 96 have the DPFE Sensor instead of EGR Valve Position Sensor (EVP); Ford also calls the DPFE Sensor an EGR Pressure Valve; my 96's Ford pn is F4ZZ9J460-B; new Plastic replacement version is MOTORCRAFT Part #DPFE15
Source: by tomco-inc.com http://www.tomco-inc.com/Tech_Tips/ttt36.pdf

I had bad DPFE last year; got the 2 new silicne hose from a local dealer; but they are $10.00 a foot for each; they are diff ID's

They & 3 other dealers in area want $150.00 for the DPFE Sensor though and will not discount; so I bought the MOTORCRAFT DPFE15 from TROY Ford thru Amazon w/free S&H for $60.

DPFE HOSES; 1L3Z-9P761-AA - 1/4" for REF - Downstream hose (INTAKE)
DPFE HOSES; 1L3Z-9P761-BA - 5/16" for Upstream hose (EXHAUST)

The DPFE is a genuine Ford MC part and checked out A-OK
 

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Discussion Starter #12
miesk5, if they come back i will check them out. i assume if one is faulty, this could be the cause of my surging?
 

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Good job. I used to give out lengths of rubber hose to the tech's with this same problem. I have replaced some of the plastic lines with rubber ones by cutting out the entire plastic line, but leaving enough sticking out of the rubber fitting, straight or 90 deg elbow, and slipping the rubber hose onto it and sliding it right up to the rubber fitting so it won't leak. Easier to replace it later than trying to locate plastic line. Those codes (insufficient air flow) on my Bronco & recently on my 97 F150 were related to a bad E.G.R. so I replaced it and it smoothed out and the light didn't come back on! I tested it the way I was told by a tech and that was to take the hose off and if the idle jumped up it was fine and if it did nothing the E.G.R. was bad. Not saying this is fail proof but both my vehicles did nothing and replacing the E.G.R. fixed both of them so it might be worth checking? You can do what I've done too and get a couple of vacumn fittings, just straight coupler ones, and slip one into each end of a long piece of hose and use it to replace the plastic hose when checking for leaks on the other lines...:thumbup
 

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yo!
Good stuff DNBELOWBRONCO & EL!

The Tomco Test Links also includes the EVR & EGR tests; The OBDII system monitors continuosuly
the DPFE signal at idle. Since there should be no
EGR flow at idle, the DPFE signal should show a
no flow voltage signal. The system compares the
Key On Engine Off (KOEO) stored voltage to the
DPFE signal at idle. If the signal is not consistent
with this value, it may indicate a stuck open EGR
valve. The DTC for this condition is a P0402.
Also;
DTC P0401 EGR Flow Insufficient Detected Possible Causes
Source: by Gateway Clean Air Program @ http://www.dnr.mo.gov/gatewayvip/docs/may06-gar.pdf

DTC P0401 is for exhaust gas recirculation (EGR) insufficient flow detected. This most likely means one or more of the following has happened:
• The EGR valve may not be opening due to a lack of vacuum;
• There is a blockage in the EGR (most likely carbon buildup);
• The DPFE sensor is faulty and needs to be replaced;
• The EGR valve is faulty. In fixing this code, it is quite common for people to just replace the EGR valve only to
have the OBD code return.
However, just like many other DTCs, the problem is not always obvious and the EGR valve is not always the culprit
READ MUCH MORE
 

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Hopefully I can easily find the cause of this same issue on my 94. Started after I pul the headers on. So its possible I cracked a line from the coffee can on the fender. Good info here, thanks.
 

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Any suggestions if it is stuck on vent?? I see that the default location is defrost which is what mine used to be and then a friend of mine hooked the vacuum line up and everything worked for a while. Now I am just stuck on the vent setting and it wont switch into anything else. The vacuum hoses look good.
 

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Any suggestions if it is stuck on vent?? I see that the default location is defrost which is what mine used to be and then a friend of mine hooked the vacuum line up and everything worked for a while. Now I am just stuck on the vent setting and it wont switch into anything else. The vacuum hoses look good.
yo;
Yep! Vac Line is likely again;
Underdash Ventilation Duct '80-86

by Ford via Steve 83
Ck that vac line to Panel Door (left side in diagram back to control panel)
Here it something very similar; Vac Line harness pic by Steve

A vac gauge is a great tool and intr panel addition!
Steve has one in his 83;


I see that SuperMotors still has aproblem, so click Refresh a few times to see any pic or diagram Links.

Esp. as these Broncos become older than most FSB members here, except for me..lol
 

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Thank you again Meisk5, and Steve. I love the vacuum guage idea, I'll have to try that! I will check out my harness tonight!!
 

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yw,
I know that a few V gauges alos have the old "Good Mieage (MPG) indicators in Red, Greeen, Yellow I think. Others show just the Numbers... some are designed to mount on top of dash or against/ or in dash.

Vacuum Gauge Diagnosis - Normal engine; Steady gauge 18"-20" at all speeds..." READ MUCH MORE
Source: by Craig U at http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm

Vacuum Leak Test; On an idling engine check for vacuum leaks using a mechanic's stethoscope with the probe removed, or a ~3' garden hose section. Don't spray flammables on a running engine. MIESK5 NOTE; Also check: vacuum hoses; intake manifold gasket & throttle body; PCV line; vacuum reservoirs: EGR Sys Vacuum Tank & 2ndry air (coffee can); AC, heater, defroster, vent control ckt & vacuum tank (plastic ball type), under dash & lines to heat/blend/etc. doors; power brake booster; cruise control ckt, etc.... where applicable; (combined w/ Steve83's info, thnx) BEWARE OF BELTS/PULLEYS, FAN AND HOT ENGINE
by miesk5 & Steve83


Vacuum Leaks, Finding; "...Cracked or broken vacuum lines, leaking intake manifold or plenum gaskets, injector o-rings, broken emissions solenoids, open vacuum ports are just a few of the causes of vacuum leaks. Use the under-hood emissions diagram and check every single vacuum circuit with a vacuum tester such as the Mityvac tool. A faster technique for finding intake manifold vacuum leaks is to get a bottle of propane and attach a length of rubber hose to the gas valve. Start the engine, be careful not to come too close to the fan or fan belts. Open the propane tank valve so you have a steady flow of gas. Then hold the hose near suspected leak points while the engine is idling. If there is a leak, the propane will be drawn in through the leak. The propane should cause a noticeable change in idle speed and/or smoothness. Always know where the closest fire extinguisher is and how to use it!..."
Source: by Ryan M (Fireguy50) at http://fordfuelinjection.com/?p=93
 

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Discussion Starter #20
lil update

i swaped out the egr valve, no dice code came back. i just swapped in a new dpfe sensor so i hope this fixes the code.
 
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