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Discussion Starter · #1 ·
Sorry for the long post, but need some help diagnosing my Bronco.

Less than a year ago, I bought a 1993 Bronco Eddie Bauer that my oldest son nicknamed Hank. It has 240k miles on the dash, but here are a list of the improvements that have been done since July 2020 and I bought it end of 2020. Rebuilt motor has approximately 2500 miles on it to date and I did the 1st oil change at 500 miles after breaking it in properly.
Items that were replaced/upgraded by PO:

Motor/exhaust
'96 Roller 351w (Rebuilt in July 2020, donor motor had 90k miles)
True GT40 heads w/ Ferrea undercut valves
Heads were faced and valve job with new Viton seals
Coated speed pro flat top pistons Reconditioned Rods w/ ARP bolts
Crane Hydraulic Roller Cam
Bassani Headers with Bassani Y-pipe
Flowmaster cat and exhaust
EGR was deleted by PO so check engine light is always on
New water pump, belt, idler pulley, plugs, wires, cap and rotor, alternator, smog pump

Drivetrain/suspension
4" BDS suspension lift with all new springs, shocks, long trailing arms, add-a-leaf & steering stabilizer
New 4.10 gears front and rear
New rear driveshaft
Transfer case seal
PO told me the guy that owned it before him replaced the transmission and it shifts smooth as butter
New Brake pads/Calipers & brake master cylinder

Misc
AC upgrade from R12 to R134
Custom 4-point 4130 steel roll cage with shoulder seatbelt tabs in rear
New wiper motor
New rear tailgate seals

Now to the problem. It was running great, out of nowhere the other day it cut off at a stop sign a mile away from my house as I was leaving. Fired right back up no problem and ran without issue the rest of the day. About a week later, it did it again, but this time after I fired it back up, something was running funny. Very rough idle (from 500 up to 2000 and will just bounce around), but runs great through 1st and 2nd gear. But as soon as I hit 3rd gear, absolutely no power at all, feels like I’m holding the brakes down and trying to floor it. I replaced the fuel filter and fuel pressure regulator because it feels like a fuel issue but those didn't help. Below are the codes I got when I ran them, keeping in mind PO deleted the EGR:

KOEO:
121 – Closed throttle voltage higher or lower than expected
327 – EGR valve position circuit below minimum voltage
552 – Thermactor air bypass solenoid circuit fault
553 – Thermactor air diverter solenoid circuit fault
558 – EGR valve regulator solenoid circuit fault
565 – Canister purge solenoid circuit fault

KOER (let it sit and idle erratically for about 30 mins, it cut off once on it’s own):
116 – Engine coolant temperature higher or lower than expected
173 – HEGO (HO2S) sensor fault/rich
327 – EGR valve position circuit below minimum voltage

I’m not a mechanic and am used to working on my old ’78 F100 with a carbureted 302 and much less electronics. I bought the code reader specifically for this issues in the hopes someone could help me diagnose the problem and I could avoid having it sit at a shop and me paying them to go on a wild goose chase. I’m not super familiar with the EGR system, only what I’ve read so I’m not sure what all codes are tied to that being deleted by PO. Any help/guidance would be GREATLY appreciated because we want to get Hank out this fall with the top off before winter!!
Tire Wheel Car Vehicle Land vehicle
 

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Yo D,
Here are the Codes that could cause the issues, I'll be back tomorrow for the remainder;

KOEO:
121 – Closed throttle voltage higher or lower than expected
TSB 94-26-4 "...The following is a list of vehicle symptoms which have been associated with the TPS, but can also be related to other vehicle components. Check engine light, ➡Stalls, quits, hesitation/stumble, fast idle; To minimize the replacement of good components, be advised that the following non-EEC areas may be the issue: Excessive blow-by, PCV malfunction, Vacuum leaks, Fuel pressure, Throttle sticking or linkage binding. MANY VOLTMETERS WILL AUTOMATICALLY CHANGE RANGES WHEN MEASURING TPS OUTPUT FROM IDLE TO WOT. WHEN A VOLTMETER IS USED TO MEASURE TPS OUTPUT FROM IDLE TO WOT, THE METER SCALES OR CHANGES RANGES AUTOMATICALLY. THERE MAY BE AN ERRONEOUS METER DISPLAY UNTIL THE VOLTMETER HAS LOCKED TO THE APPROPRIATE VOLTAGE READING. THE ERRONEOUS METER DISPLAY DOES NOT REPRESENT A DEFECTIVE TPS. NOTE: IT IS RECOMMENDED THAT THE "RANGE LOCK" FEATURE ON MANY METERS BE SET FOR CHECKING TPS VOLTAGE..."

●SEE Throttle Position Sensor Testing & Management @ Bronco Forum - Full Size Ford Bronco Forum by by Seattle FSB

See See my Vacuum leak test in post #11 incl jowens126 's HVAC Control Panel info @ Help with dtc codes and idle

Fuel Pressure;
"Fuel Pump Circuit Operation
When the ignition is switched to the ON position, it turns the EEC Power Relay on. The EEC Power Relay provides power to the EEC-IV processor and the control side of the fuel pump relay. Power for the fuel pump is supplied through a fuse link or high current fuse attached to the starter solenoid (battery side). From the fuse link or high current fuse, current flow is through the fuel pump relay and Inertia Fuel Shutoff (IFS) switch to the fuel pump. The IFS switch is a safety device used to shut off the fuel pump in the event of a collision. If the IFS switch is "tripped," it must be reset by depressing the white or red button on the top of the switch. The fuel pump relay is controlled by the Powertrain Control Module (PCM).

When the ignition switch is turned to the ON position, the fuel pump will operate. If the ignition switch is not turned to the START position, the PCM will shut the fuel pump off after approximately one second. The PCM will operate the fuel pump when the ignition is in the START position to provide fuel while cranking.

After the engine starts, the PCM will continue to operate the fuel pump unless the engine stops, engine speed drops below 120 rpm, or the IFS switch is "tripped.

Note: Maximum fuel pressure is obtainable at WOT or the vacuum hose removed from the fuel pressure regulator.

If fuel lines/systems have been drained or evacuated, it may take up to 15 seconds to obtain the pressure specified.
KEY ON, ENGINE OFF 35-45 PSI
ENGINE RUNNING 28-45
System Diagnosis
Note:
Grounding the FP lead at the DLC will allow the pump to run continuously with the ignition switch on

327 – EGR valve position circuit below minimum voltage
CONTINUOUS MEMORY DIAGNOSTIC TROUBLE CODE (DTC) 328, 327 OR 337: CHECK FOR INTERMITTENT SENSOR

Continuous Memory DTC 328 or 327 indicates the EGR valve was closed further than normal or EVP sensor or circuit has failed with an intermittent low voltage sometime during vehicle operation.

Continuous Memory DTC 337 indicates the EVP signal to the Powertrain Control Module (PCM) was above the maximum Self-Test limit sometime during vehicle operation.
Possible causes:
-- Poor continuity in EVP harness or connectors.
-- Intermittent open or short in EVP sensor or harness.
-- Damaged EVP sensor.
l Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.

l Install breakout box, reconnect PCM.
l Connect DVOM between Test Pin 27 and Test Pin 46 at the breakout box.
Key on, engine off.
Lightly tap on EVP sensor and wiggle harness connector to simulate road shock.
NOTE:
EVP voltage with EGR valve closed is normally between .24 and .67 volt and steady. A sudden change in voltage indicates a fault.
Is a fault indicated?
Yes REMOVE and INSPECT EVP sensor connector. If OK, REPLACE EVP sensor. CLEAR Continuous Memory (REFER to Quick Test Appendix, «Section 5A»). RERUN «Quick Test».
No LEAVE DVOM connected, RECONNECT PCM and GO to «DN91».
DN91 CHECK EEC-IV VEHICLE HARNESS FOR INTERMITTENT OPENS OR SHORTS
Key on, engine off.
DVOM connected between Test Pin 27 and Test Pin 46 at breakout box.
-- Grasp the vehicle harness closest to the EVP sensor connector. Shake and bend a small section of the EEC-IV harness while working toward the dash panel. Also wiggle, shake and bend the EEC-IV harness from the dash panel to the PCM.
l Is a fault indicated?
Yes ISOLATE fault and SERVICE as necessary. CLEAR Continuous Memory (REFER to Quick Test Appendix, «Section 5A»). RERUN «Quick Test».
No LEAVE DVOM connected and GO to «DN92».
DN92 CHECK VOLTAGE WHILE EXERCISING EGR VALVE
Disconnect vacuum hose at EGR valve and connect a vacuum pump.
Key on, engine off.
Measure voltage between Test Pin 27 and Test Pin 46 at the breakout box while performing the following: Slowly apply 5-10 in-Hg (17-34 kPa) of vacuum to EGR valve, then slowly bleed vacuum.
Does the voltage increase and decrease steadily from no more than 4.81 volts to no less than .24 volt?
Yes Unable to duplicate and/or identify fault at this time. For further diagnosis using the EEC-IV monitor box or Scan Tool, REFER to «Section 7A».
No REPLACE EVP sensor. REMOVE breakout box. RECONNECT all components. RERUN «Quick Test».
==============
552 – Thermactor air bypass solenoid circuit fault
553 – Thermactor air diverter solenoid circuit fault

558 – EGR valve regulator solenoid circuit fault
A lot of Ford's PCED/EVTM pin-point testing revolves around the BO Box settings, such as;
"...DTC 558: indicates a failure in the EGR Vacuum Regulator (EVR) solenoid circuit/Damaged EVR solenoid; Open harness, Shorted harness, Damaged Powertrain Control Module (PCM). ;
Install breakout box, leave PCM disconnected. Measure resistance between Test Pin 33 at the breakout box and EVR circuit at the EVR solenoid vehicle harness connector. Is resistance less than 5.0 ohms?
No - SERVICE open circuit. REMOVE breakout box. RECONNECT all components.RERUN Quick Test.
Yes - GO to DN13.
DN13 CHECK EVR CIRCUIT FOR SHORT TO POWER OR GROUND. Key off. EVR solenoid disconnected.
Breakout box installed, PCM disconnected. Measure resistance between Test Pin 33 and Test Pins 37 and 57 at the breakout box. Measure resistance between Test Pin 33 and Test Pin 40, 46 and 60 at the breakout box.
Is each resistance greater than 10,000 ohms?
No - SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RERUN Quick Test. If DTC is repeated, REPLACE EVR solenoid.
Yes -REPLACE PCM. REMOVE breakout box. RECONNECT EVR solenoid. RERUN Quick Test.."
Source: by Ford via miesk5 at FSB
as I mentioned in another thread here; In place of the breakout box, go to the EEC pin instead; for instance - Measure resistance between Test Pin 33 and Test Pin 40, 46 and 60 at the breakout box. Substiture EEC for :breakout box"
EEC Connector Pin Diagram & Overview by Ryan M (Fireguy50) at Wayback Machine

EEC Connector Pin LEGEND, Bronco & Ford Truck & Van: 4.9, 460, 5.0, 5.8;
Source: by Ryan M (Fireguy50) at Ford Fuel Injection
****

In front of the TAB/ TAD Solenoids is the EGR Vacuum Regulator (EVR); also called EGR Vacuum Solenoid
It is a "normally closed" solenoid, which means that when it is de-energized, the position of the disc allows for maximum venting to the atmosphere (resulting in negligible vacuum flow to the EGR valve)

Location pic by SeattleFSB (Seattle FSB)
The most common problem with the EVR is for its vacuum line to crack. Simply slip rubber vacuum line over the breakey
Static Resistance Values:
TAB/TAD: 50-100 ohms
EVR: 30-70 ohms
...
DTC 565 "...The canister purge solenoid dangles in its vacuum line between the R side of the engine and the canister on the R frame rail, so its wiring could have hit the exhaust manifold..."
DTC 565 Pin-Point Testing & Possible Causes
Source: by Ford via miesk5 at FSB
From Ford;
Possible causes:
Open harness (VPWR or CANP).
Damaged CANP solenoid.
Shorted (power to ground) harness.
Damaged Powertrain Control Module (PCM) (LESS LIKELY!!!)
Key on, engine off.
Disconnect appropriate CANP solenoid.
Measure voltage between VPWR at the CANP solenoid vehicle harness connector and battery ground.
Is the voltage greater than 10.5 volts?
Yes - GO to KD7
No - SERVICE open VPWR circuit. RECONNECT CANP solenoid. RERUN Quick Test
KD7 CHECK CANP RESISTANCE
Key off.
Disconnect appropriate CANP solenoid.
Measure CANP solenoid resistance.
Is resistance between 30 and 90 ohms?
Yes - GO to KD8
No - REPLACE CANP solenoid. RERUN Quick Test.
KD8 CHECK CONTINUITY OF CANP CIRCUIT
Key off.
Appropriate CANP solenoid disconnected. (some Fords have two)
Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box (see Pin Outs below to check w/o this box), leave PCM disconnected.
Measure resistance between Test Pin 11, 15, 31 or 54 (refer to pinpoint test schematic ) at the breakout box and CANP circuit at the CANP solenoid vehicle harness connector.
Is resistance less than 5.0 ohms?
Yes - GO to KD9
No - SERVICE open circuit. REMOVE breakout box. RECONNECT all components. RERUN Quick Test
KD9 CHECK CANP CIRCUIT FOR SHORT TO GROUND
Key off.
Appropriate CANP solenoid disconnected.
Breakout box installed, PCM disconnected.
Disconnect Scan Tool from Data Link Connector (if applicable).
Measure resistance between Test Pin 11, 15, 31 or 54 (refer to pinpoint test schematic ) and Test Pins 40, 46 and 60 at the breakout box.
Is each resistance greater than 10,000 ohms?
Yes - GO to KD10
No - SERVICE short to ground. REMOVE breakout box. RECONNECT all components. RERUN Quick Test.
KD10 CHECK CANP CIRCUIT FOR SHORT TO POWER
CANP solenoid disconnected.
Breakout box installed, PCM disconnected.
Scan Tool disconnected from Data Link connector.
Measure resistance between Test Pin 11, 15, 31 or 54 (refer to pinpoint test schematic ) and Test Pins 37 and 57 at the breakout box.
Is each resistance greater than 10,000 ohms?
Yes - REPLACE PCM. REMOVE breakout box and Scan Tool. RECONNECT all components. RERUN Quick Test.
No - SERVICE short to power. REMOVE breakout box and Scan Tool. RECONNECT all components. RERUN Quick Test.

Overview, Failure Symptoms & Depiction, general; "...Vent fuel vapors from the fuel tank to the charcoal canister, and control the purging of these and other vapors from the fuel tank into the intake manifold when certain engine speed and temperature conditions are attained. Above idle, the mixture becomes very rich. Stumble on acceleration, poor fuel mileage, flooded charcoal canister and catalytic converter overheat can occur. Check for ruptured diaphragms inside the valve and misrouted or damaged hoses..."
Source: by tomco-inc.com


CanP Location pic by Bbronco311


Parts Diagram
Item Part Number Description
1 9C987 Fuel Vapor Return Hose and CanP Valve Assembly
2 9D653 Evaporative Emissions Canister
3 N-S2 Screw, M6.3 x 1.81 x 16.0
4 9A220 Fuel Vapor Return Hose Assembly
5 10A812 Battery Tray Support
6 9E926 Throttle Body
7 12A581 Wiring Assembly A - Tighten to 5-7 Nm (44-62 Lb-In)

565 – Canister purge solenoid circuit fault
KOER (let it sit and idle erratically for about 30 mins, it cut off once on it’s own)

116 – Engine coolant temperature higher or lower than expected

DTC 173 for HO2S Failure, in POSSIBLE LOCATIONS OF WIRING SHORTS TSB 95-02-11 for 92-95 Bronco & F Series; "the HO2S wires in the 12A690 (subassembly of the 14B060 battery cable) harness may be cut on the lower right engine mount causing improper signals to be sent to the PCM. Damage may be under the electrical tape..."

&
DTC 173 Oxygen sensor not switching - system is or was rich - Single, Right or Rear HO2S; "...I'd guess there's either an obstruction in the exhaust pipe directing the exhaust away from it, preventing it from detecting & operating normally (not likely), OR there may be a fault in the heating element circuit (more likely). It comes off the circuit (can't remember which fuse) which also feed A LOT of other things and runs around the front of the radiator to the R side near the battery where it drops down by the engine mount & goes to the sensor. Make sure you have good power & ground to the appropriate terminals in the connector, and test for a signal voltage. Then, using the old & the new sensors, trace the fault..."
Source: by Steve83

DTC 173 in 94 by Ford
Fuel Control
Excerpts...1994 PCED OBDI-A
SECTION 6A: EEC-IV Pinpoint Test
Procedures
H: Fuel Control
H: Introduction

H1 CHECK FOR FUEL DILUTED ENGINE OIL



Diagnostic Trouble Code (DTC) HO2S Orientation Fault Definition
172r
136r
176c right or rear
left or front
left or front system indicates lean
173r
137r
177c right or rear
left or front
left or front system indicates rich
144c
139c right or rear
left or front no HO2S switch
detected
171c
175c right or rear
left or front adaptive fuel limit
reached

Possible Causes:
Fuel injectors.
HO2S.
Secondary Air Injection (AIR) system.
PCV/Hose.
Vacuum.
CANP.
MAP sensor.
Electronic Ignition Coil Failure.
Key off.
Remove the PCV valve from the valve cover. Inspect both rocker cover hole and PCV for damage, sludge build up, blockage and movement of valve plunger. Service as necessary.
Run Key On Engine Off (KOEO) and Key On Engine Running (KOER) Self-Tests.
Address any continuous ignition DTCs before servicing KOER DTCs.
Note: For a No Start, GO directly to H2.
Are any of the above DTCs present in KOER Self-Test?
Yes No
REINSTALL PCV valve. GO to H2.

No For Continuous Memory DTCs 139, 144, 171, 176,177
GO to H2
All Others:
CHANGE engine oil and filter. REINSTALL PCV valve

... skipping to ..

H14 CHECK HO2S INTEGRITY
HO2S always lean, slow to switch or lack of switching. Fuel at adaptive limit could be caused by:
Moisture inside the HO2S harness connector resulting in a short to ground.
HO2S coated with contaminants.
HO2S circuit open.
HO2S circuit shorted to ground.
Key off.
Inspect the HO2S harness for chafing, burns or other indications of damage. Service as necessary.
Inspect HO2S and connector for indication of submerging in water, oil, coolant, etc. Service as necessary.
Run engine at 2000 rpm for two minutes.
Key off.
Run Engine Running Self-Test.

Skipping to...
Key off.
Verify MAP sensor output voltage (refer to procedure in Pinpoint Test Step DF3).
Disconnect appropriate HO2S from vehicle harness.
For 4 wire HO2S (refer to schematic):
Connect DVOM to HO2S circuit and HO2S GND or SIG RTN at the HO2S connector.


Skipping to

H24 CHECK HO2S SIGNAL FOR SHORT TO POWER

With dual HO2S, DTC 173 refers to right or rear HO2S; DTCs 137 and 177 refer to left or front HO2S.
HO2S always rich could be caused by:
Moisture inside HO2S harness connector resulting in a short to power.
HO2S circuit shorted to power.
Key off.
Disconnect the suspect HO2S from vehicle harness.
Inspect both ends of the connector for damaged or pushed out pins, moisture, corrosion, loose wires, etc. Service as necessary.
Key on, engine off.
Measure voltage between HO2S circuit and PWR GND at the HO2S vehicle harness connector (refer to schematic).
Is voltage less than 0.5 volt?
 

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I appreciate all the info, just feels overwhelming. Why did we have to get computers involved in vehicles??
YoD,
I understand, been there!
Try the friendly tests such as;
Inspect both ends of the connector for damaged or pushed out pins, moisture, corrosion, loose wires, etc. Service as necessary.
Moisture inside HO2S harness connector resulting in a short to power.
Remove the PCV valve from the valve cover. Inspect both rocker cover hole and PCV for damage, sludge build up, blockage and moisture...
Etc.
 

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Discussion Starter · #7 ·
Thanks miesk5. My oxygen sensor in the Ypipe looks like garbage, gonna replace that and see if it helps.

I've searched and can't find what codes are always going to pop up when the EGR has been deleted. Obviously I assume any with EGR in the code name, but are there others?
 
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