95 eddie bauer 5.8l bronco "bucking" intermittedly

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dworth24

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problem started a few weeks ago. truck started bucking. also while sitting at traffic lights the rpms would go up and down from 500 to 2500 rpms.  my brother who is a mechanic first tried cleaning throttle body and changed rotor and distributor cap. also replaced what he called a "IOC" valve..... none of this helped.  next step was to changed the throttle positioning sensor.... ran truck over next few days and thought we had it. nope...yesterday on way home it started bucking hard. as i got off parkway and headed for a parking lot, the bucking got more consistent, losing power like she was going to die. had a 1/4 tank of gas.  shutdown truck for about 15 minutes. restarted and started driving home which was 3 miles away. ran good for first 2 miles but then it started bucking again and i barely made it home. brother now thinks fuel pump may be crapping out. (this same thing hppened years ago with my 04 ranger and it turned out to be the fuel pump failing intermittedly) today we put a fuel line pressure tester on it and we were between 30-32 at idle which is lowest acceptable point. ran it about 40 miles hoping she would start bucking but it never did. anything else we should check or am i looking at a fuel pump issue ????  tough fuel pump to find. where can i look ???  many thanks in advance   don

 

miesk5

96 Bronco 5.0
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Yo dworth24,

Welcome!

[SIZE=34.2507px]Have it checked for codes for free at local parts store.  Ensure engine is @ normal operating temperature when scanned.  Post any codes found here.  Hopefully battery hasn't been disconnected recently.[/SIZE]

Some no code usual suspects by Ford;

Vacuum leak, see below
Air filter, is it relatively clean?
Air inlet atop radiator support to filter box and to throttle body; look for damage such as ooening after MAF sensir, obstruction; damaged tubing.

Fuel quality; Oxidized fuel often turns darker over time and may even smell sour. You can check stored gasoline by pouring some into a clear glass container and comparing it side-by-side with known fresh gasoline. If your old sample looks noticeably darker than the fresh gas, you have strong evidence the gas has gone bad.
Electrical connectors; inspect at coil, ICM, PCM, etc. especially those with broken locking tabs.

■ The loping idle main perpetrator  is a vacuum leak(s).

See  my vacuum leak test in post #20 @ http://broncozone.com/topic/23994-90-58l-getting-continuous-code-33-and-running-code-44/?p=125535

Grab a vacuum gauge and check vacuum first.

 Normal Engine Vacuum at Idle is 15-22 in-Hg for 96 Broncos;

Borrow or purchase a vacuum gauge and read this Vacuum Gauge Diagnosis @ http://www.diesel-da...tj/stj30013.htm

● 96 Bronco Workshop Manual, partial @ http://www.diesel-dave.com/vehic/manual/stj/stjleft.htm

GL!

 

miesk5

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Yo,what year do you have?

It shows 96 in this title, but f9r your newer post on the tailgate key switch you state is a 95.

 

miesk5

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Yo,

Ok  I edited the title.

Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19
http://broncozone.co...7&mode=threaded
PCM stores the Self-Test program in permanent memory. When activated, Self-Test checks the EEC system by testing memory integrity and processing capability, and verifies that various sensors and actuators are connected and operating properly.
Inspect the air cleaner and inlet ducting.
Check all engine vacuum hoses for damage, leaks, cracks, blockage, proper routing, etc.
Check EEC system including the wiring harness for proper connections, bent or broken pins, corrosion, loose wires, proper routing, etc.
Check the Powertrain Control Module (PCM), sensors and actuators for physical damage. TPS, ICM, DISTRIBUTOR, etc.
Check the engine coolant for proper level and mixture.
Check the transmission fluid & engine oil level and quality.

Make all necessary repairs before continuing with SELF TEST.

The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.

Run it around to heat the engine up and shift thru all gears including Reverse.
Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.
Then turn off engine, all accessories/lights (close driver's door) , etc.

Do KOEO test First

Post Code(s) here according to:
KOEO
&
KOER

A helper can assist you by counting the codes. Some use their smart phones to record them.
BEWARE OF FAN, BELTS, PULLEYS, HOT HOSES, IGNITION HIGH TENSION WIRES, AND ENGINE COMPONENTS
GL! 

 
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87BRONCXLT302

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I had a similar problem in 87 EFI turned out to be a cracked vacuum line from the vac reservoir to the little 3 way valve next to  ignition coil I think it is the vac advance for distributor timing.

 

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