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Discussion Starter · #1 ·
It is HOT as hell in Texas right now, and during the day my bronco runs like its misfiring.

It is most common at idle, and it shakes the truck enough to make the doors squeak. But, its not every time, and it is only when the temp is over 100 deg. f.

when its not idling, it happens during accellaration, and it is on and off. What i mean is, it feels like it works fine, then is sluggish- good- sluggish- good then good at crusing speed.

I have a code reader, and checked 3 times, and got no codes. CEL is not on.

I suspect a misfire, but i have never delt with a misfire on a distrbuitor engine, only on a coil per plug ignition system.

Within the last year and a half, here is a list of the parts i have replaced that might have any relavance:

1. ECU- New computer
2.Rotor
3. Rotor Cap
4. Spark Plugs
5. Plug Wires
6. MSD ignition coil
7. Six ltre upgrade! (including re gapping plugs and bumping timing)


anyone have any idea what could be happening? It runs great at night and early morning.

Thanks in advance
 

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The Anti Yam!
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I have a code reader, and checked 3 times, and got no codes. CEL is not on.
Did you do a KOER or KOEO test?

Whats the fuel pressure?

Did this start before or after you did the plug wires?
 

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dont mean to steal the thread but i am having the same problem with my 94 bronco 5.0. just replaced the plugs wires cap and rotor the other day and it has started misfiring. not so much at idle but under a load and its not a consistent miss. i was thinking about getting all new plugs again and returning these just to be on the safe side.
 

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Roller rockers are gay
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19,191 Posts
you probably routed the wires wrong or crossed them.
 

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Lick my balls
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I vote firing order too
 

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wires are good. i have quadruple checked them just to be sure and its not a consistent misfire, and it only does it under a load
 

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yo Friend,

I know you answered a lot of Qs, so bear w/me & take this as my looney tune way of re-asking...so I can get to da pin-point testing for you... before it snows

As G Man asked, were both KOEO & KOER tests done w/engine @ normal op temp for KOER?
See below for my Notes on da self-test

And again, Are plug wire routed as shown on rad decal?
Misrouted spark plug wires can cause a misfire or buck and jerk under load.
Spark Plug Wire Routing & Firing Order TSB 94-04-10 for 87-93 5.0 & 94-96 5.0 & all 5.8 - engine miss, spark knock, buck/jerk, surge and other driveability concerns;
MIESK5 NOTE; The firing order for 1987-1993 5.0Ls is 1-5-4-2-6-3-7-8. If #7 and #8, or #2 and #4 spark plug wires are routed next to each other at the separation bracket, an induction crossfire condition can occur.

& The firing order for 1994 5.0Ls & all 5.8Ls is 1-3-7-2-6-5-4-8. On these vehicles the #1 and #3, or #5 and #6 spark plug wires must be separated to eliminate the possibility of an induction crossfire. To eliminate the possibility of the coil wire becoming disconnected, route the coil wire under the spark plug wires at the distributor cap.
Source: by Ford via Steve83 (Steve, That dirty old truck) at SuperMotors.net

Pull a few plugs and look for a lean condition = intake man, EGR Valve , throttle body gasket, Vac Leaks, bad Fuel Pressure Regulator (FPR) or weak fuel press from Pump.. Pull red vac line from FPR - any gas or gas smell = replace da FPR
Disconnect the vacuum line going to the fuel pressure regulator. Fuel pressure typically jumps to 40 PSI ± 3 PSI (4.9L typically is 15 PSI higher). can get into PSI testing later..

Rich plug = O2 sensor /conn/wiring etc prob (should have a Code in KOER), ECT Sensor prob (code too)

Spark Plug Firing End Analysis, General Source: by gnttype.org

Over-advanced ignition timing can cause a misfire or buck and jerk under load. Pull SPOUT Connector and time it
Adjustment in Ford EFI Engines
Source: by Ryan M (Fireguy50) at fordfuelinjection.com

"...There are two types of EEC Self-Tests, Key On Engine Off (KOEO) & Key On Engine Running (KOER).
While both of these will test for various "hard faults" that are present when the test is run, the processor continuously monitors various operating parameters whenever the engine is running. If the processor detects a problem, it will store a "Continuous Memory" code and light the MIL. These Continuous Memory codes are put out during KOEO Test after any codes associated with hard faults are output. Codes are displayed by flashing the MIL. They are also output as voltage pulses on the Self-Test Output (STO) circuit in the Self-Test connector. In either Self-Test mode, all codes are output twice and in KOEO, the hard fault codes are separated from the Continuous Memory codes by a "separator" pulse. A technician that is unfamiliar with the EEC Self-Test can mistakenly believe that continuous Memory codes are not present when they really are. He may run KOER Self-Test and get a pass code (111) and not realize that KOEO Self-Test must be run to receive any Continuous Memory codes. He may run KOEO Self-Test while counting MIL flashes and misinterpret the repeated hard fault pass code (111) to mean that Continuous Memory does not contain any codes...."

The self-test plugs were mounted on the passenger side fender on 1985-86 EFI trucks;
The self-test plugs are located along the driver's side fender behind the air filter box on 87-95 EFI trucks...";
miesk5 NOTE; Self-Test Input (STI) is the Pin in the Lt gray Connector and Signal Return Ground (STO/SIGRET) is Pin E in black Connector in 87-95;

The engine temperature must be greater than 50°F (10°C) to pass the KOEO Self-Test and greater than 180°F (82°C) to pass the KOER Self-Test.
Run it around to heat the engine up and shift thru all gears incl Reverse. Then turn off all accessories/lights, etc. Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch. Do Key On Engine Off (KOEO) portion first.
On all vehicles equipped with a 4.9L engine, the clutch must be depressed during the KOEO Test. On all vehicles equipped with a 7.3L diesel engine, the throttle must be depressed (WOT) during the entire Key On Engine Off Self-Test.

Engine ID codes are issued at the beginning of the KOER Test and are one-digit numbers represented by the number of pulses sent out. During KOER; For gasoline engines, the engine ID code is equal to one-half the number of engine cylinders (i.e. 2 pulses = 4 cylinders). For the 7.3L Diesel engine, the ID code = 5. These codes are used to verify the proper PCM is installed and that the Self-Test has been entered.

The Dynamic Response code is a single pulse that occurs 6-20 seconds after the engine identification code. When/if the Dynamic Response code occurs, perform a brief Wide-Open Throttle (WOT). The dynamic response check is used on some applications to verify operation of the TP,S MAF or MAP & KS sensors.

On vehicles equipped with the Power Steering Pressure (PSPS) switch, within 1 to 2 seconds after the ID code, the steering wheel must be turned at least one-half turn and released. The PSPS Switch signals the EEC Module when power steering pressure exceeds 350 psi ±50. The engine then increases idle speed to compensate for the additional load. It appears the PSPS switch was deleted from the 94 model year. The PSPS mounts in the pressure line near where the rubber hose is crimped to the hard-line at the steering gearbox inlet. If you have the 5.0 with E4OD, you won't have a PSPS.
Connector Location pic

2 wire plug, wire colors are red/yellow and grey/red. Ford included the connector even if the switch wasn't installed.

EEC IV Legend by Ryan M
Pin 24 is PSPS Input to EEC IV Module, Yellow/Light Green
Pin 26 is V-REF +5 volts DC, Brown/ White

On vehicles equipped with Brake On/Off (BOO) input (such as E4OD), the brake pedal MUST be depressed and released AFTER the ID Code has been displayed. This tests the ability of the EEC system to detect a change of state in the Brake Lamp Switch.

On vehicles equipped with Transmission Control Switch (TCS) such as da E4OD, the switch must be cycled after the ID code has been displayed. This tests the ability of the EEC system to detect a change of state in the TCS. TCS = Transmission Control Indicator Light (TCIL) on E4OD it is also ref to as the OD on/off LED/Switch @ end of tranny gear stalk.

Look Codes up in my broncolinks.com site using the new Search function.
 

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dont mean to steal the thread but i am having the same problem with my 94 bronco 5.0. just replaced the plugs wires cap and rotor the other day and it has started misfiring. not so much at idle but under a load and its not a consistent miss. i was thinking about getting all new plugs again and returning these just to be on the safe side.
Also check because the 302 has a anti-knock sensor could be causing the problem.

Knock Sensor - Center rear of engine, behind intake

Note: the 351 windsor does not have an anti-knock sensor.
 
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