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19 Posts
Discussion Starter #1
1990 Bronco with the 302 and automatic. Was my dads but he let it sit for years, was trying to get rid of it and i offered to take it off his hands.

—Broken throttle cable replaced

filled tank with fresh gas and a fuel injector cleaner, nasty backfiring thru intake blowing off vacuum lines and cracked air filter box. Raw fuel smell/strong fumes

—new Motorcraft TPS, back probed @ .88 volts
—new Motorcraft fuel filter
—Set timing to 10*(was at 0*)
—new Ford racing 9mm wires

found leaking FPR

—new FPR from oriellys fixed the nasty backfiring
—vacuum lines replaced, holds at 20

fuel pressure holds between 32-38psi crusing around but shutting off the pressure drops slowly but noticeable

still getting a small backfire off idle to 2000 rpms. 1500 is where it really struggles. gets worse as it warms up. Changed plugs today, cleared up the raw fuel smell.

—New Motorcraft IAC
—New Oriellys EGR
—New Motorcraft EVP sensor
—New NGK plugs @ .055”(no more raw fuel smell, #1 cylinder plug looked pretty bad, rest look fine)
—ECT resistance checks out

been pulling codes and clearing them as i go. These are the stubborn ones

KOEO - 83
Mem - 11
KOER - 41, 34, 25

during the WOT test it chokes and stays at 1500 rpms.

heres a video of some general driving, the thumping noise is the backfiring. Near the end i try a steep hill at WOT and i go nowhere.


Super Moderator
24,962 Posts
Yo 86,
DTC 11 in KOEO, KOER & CM is System pass!
So, since scan shows other codes, suggect you pull the EEC and inspect for leaky capacitors, damaged resistors etc.

"...Remove driver's inside kick panel adjacent to pedals. It comes out through cabin." by Seattle FSB; "Should be one small metal screw holding it. Just slide it out, but be careful w/ gasket for firewall. Don't mess it up, you can reuse it." by Darth_ted_82 H "To remove it first disconnect battery & get use 10 mm socket to unbolt the wiring harness "connector from inside the engine bay. Then pull plastic kick panel from inside cab & remove the retainer clip Remove it by lifting rear slightly & wiggling it out of the "pocket" ... the firewall rubber gasket will have a pretty good grip on the connector so it will take some persuasion to free. " "You have to unplug it under the hood very low on the fire wall (10 mm socket)."

EEC IV PCM in 85-86 Bronco is right under the dash just above the hump off to the right just a bit.

See EEC IV Capacitor Replacement in a 90 by seedpress @ Fuel Delivery Problem


DTC 25
DTC 25 Knock Sensor not tested (KOER); ignore if not pinging

You may not need to replace the KS;
25 comes up bec. the highlighted stuff wasn't done (or done in time) while checking for codes (by BroncoJoe19);
"You preheat the engine and turn her off.
Shut off all electrical accessories or disconnect them (radio, CB's, lighting, etc.).
set your jumper wire and start her up.
After you get four flashes, or sweeps (three flashes or sweeps for a 6 cyl).
you depress and release the brake pedal, turn the steering wheel 1/2 turn, push the OD on off switch, THEN after a single flash... snap the throttle (push it all the way to the floor once) See Edit Below.
Then get ready to read your codes
EDIT... prior to doing the throttle test, one should wait for the signal to do so. The signal is a single quick flash. Apparently some trucks do not require it, and it should not be performed without being prompted to do so.

I would check ignition timing to be sure its set correctely at 10 degrees before TDC with the SPOUT connector removed."

TIMING Article by Ryan M @ Ford Fuel Injection » Setting the timing

Yo Ryan,
DTC 34 - EGR voltage above closed limit Key On Engine Off (KOEO) or Engine Running (KOER) Self-Tests; indicates that the EGR valve may not be fully seated in the closed position; or the EVP sensor voltage is greater than the closed limit voltage of 0.67 volt. Because of the preload on the installed EVP sensor, it is very difficult to determine whether the EGR valve is seated or the EVP sensor is in contact with the EGR valve stem.
•Faulty Vacuum system - See my Vacuum leak test in post #11 incl some jowens HVAC Control Panel pics/info @ Help with dtc codes and idle
One way to do a quick check is to grab a vacuum gauge. Some parts stores will loan you a gauge with refundable deposit.
The vacuum gauge should read between 15 and 22 in-Hg depending upon the engine condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
The reading should be quite steady. .
When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.

When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.

•Damaged EVP sensor
•Corroded or dirty connector
•Damaged EGR valve
•Broken wire in harness
•Grounded harness
•Damaged Computer

- Failed sensor, carbon between EGR pintle valve and seat holding the valve off its seat.
Remove the EGR valve and clean it with carbon remover and a brush if necessary

Prior to re-installing see if you can blow air through the flange side of the EGR by mouth.

EGR Valve Position (EVP) Sensor Testing @ Ford Fuel Injection » EGR Valve Position sensor (EVP)
by Ryan M

DTC 41
CM HEGO sensor circuit indicates system lean (right side).
KOERNo HEGO switching detected always lean (right side).
"A visual inpection of the harness connector should be sufficient to determine its condition. Check connector pins for corrosion or backed-out terminals.
What the definition of the code means is that the computer can't find the sensor so it is running the engine on default."
"The engine is seeing a lean condition being monitored by the HO2S, and is adding extra fuel. It's a common misconception that a rich or lean O2 code means that an O2 sensor is bad, when actually the O2 sensor is fine and there is either a wiring issue or a mechanical issue. With a lack of other codes I'm inclined to think its either a vacuum leak (if you say it started around the time you replaced injectors I'm really inclined to think this, get a can of starting fluid and spray round the base of the plenum, all the vacuum connections, ect, listen for rpm changes, a short/open in the HO2S wiring." by reese

"tested the O2 sensor to see what it was doing. I tested it right at the computer to make sure all the wiring was good. With the engine warm, I started it up, and the sensor was doing exactly what it was suppossed to do, bouncing between about .1 to .8 volts. But after about a minute or two, it went full rich. The reading stayed around .9 volts, and the idle went up a bit. And the exhaust started stinking, too. The only way to correct this was to pull a vacuum line, and the O2 readings would start varying as normal, and the exhaust would smell clean (of course the idle went high as well). I'm going to swap back in the old injectors to see what happens. Maybe there's something wrong with the new ones. FIND might be right about my injectors." by extreme exploder

TSB 91-12-11 Catalytic Converter Diagnosis
Publication Date: JUNE 12, 1991
1988-91 F SUPER DUTY, F47
ISSUE: Lack of power or a no start condition may be diagnosed as an exhaust restriction caused by a plugged catalytic converter. A plugged catalytic converter (internal deterioration) is usually caused by abnormal engine operation.

ACTION: Diagnose the catalytic converter to confirm internal failure. Refer to the Catalyst and Exhaust System Diagnostic Section, in the Engine/Emissions Diagnostic Shop Manual and the following procedures for service details.

1. Lack of proper HEGO operation may cause, or be the result of a rich or lean fuel condition, which could cause additional heat in the catalyst. Perform self test KOEO and KOER, service any codes.
If the HEGO ground is good, the following areas may be at fault:
  • Ignition Coil
  • Distributor Cap
  • Distributor Rotor
  • Fouled Spark Plug
  • Spark Plug Wires
  • Air Filter
  • Stuck Open Injector
  • Fuel Contamination Engine OIL
  • Manifold Leaks Intake/Exhaust
  • Fuel Pressure
  • Poor Power Ground
  • Engine Not At Normal Operating Temperature
  • HEGO Sensor
2. Spark timing that is retarded from specification may increase exhaust gas temperature and shorten catalyst life. Refer to the following procedure for service details.
a. Check spark timing. Check base timing with spout disconnected. Set base timing to the specification on the vehicle emission decal.
b. Check computed timing with spout connected.
3. Misfiring spark plugs may cause an unburned fuel air mixture to pass through the catalyst, which could cause higher than normal catalyst temperatures. Refer to the following procedure for service details. Check secondary ignition, hook the vehicle up to an engine analyzer and check for a secondary ignition misfire.
4. Fuel pressure that is too high may cause rich air fuel mixtures to pass through the catalyst which could cause higher than normal catalyst temperatures. Refer to the following procedure for service details.
a. Check fuel pressure, install fuel pressure gauge, start and run the engine at idle. Fuel pressures between 28 and 34 PSI are typical (4.9L typically is 15 PSI higher).
b. 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). Visually inspect vacuum line for raw fuel.
5. Throttle plates in the throttle body not returning to the proper closed position may cause excessive catalyst temperatures during downhill grades. Refer to the following procedure for service details. Visually inspect the throttle body and linkage for:
  • Binding or sticking throttle linkage.
  • Tight speed control linkage or cable.
  • Vacuum line interference.
  • Electrical harness interference.
6. It is extremely important that all systems related to the engine and emission systems operate properly.
a. Visually inspect the engine compartment to make sure all vacuum hoses and spark plug wires are properly routed and securely connected.
b. Inspect all wiring harnesses and connectors for insulation damage, burned, overheated, loose or broken conditions.
c. Verify proper operation of the thermactor system. Thermactor systems that fail to dump thermactor air to the atmosphere properly or at the correct time can cause high catalyst temperatures.
d. Visually inspect thermactor system for damaged or kinked hoses and perform a function test on following components: air control valve, check valve, silencer, filter and the air bypass solenoid.
e. Verify proper operation of the engine cooling system thermostat.

DTC 83


169 Posts
Hi 86,
These all sounds exhaust/vacuum related. Seems like a good deal has been replaced. Replacement doesn't always mean repair.
I would start with checking the voltages at the O2 sensor and EVP are within spec.

if it has been sitting for a long time, getting some seafoam thorough the vacuum system would help clean out the system too.

19 Posts
Discussion Starter #4
Thanks. 1 and a half cans of seafoam have been run thru the engine via air intake and a half can thru the fuel tank

Vacuum holds at 20 in-hg(i think thats the measurement)

EVR solenoid has 12v and resistance at 55ohm(20-70ohm) havent checked the ground.

EVP has 5v and resistance is within spec as well.

timing, firing order and wires have been checked multiple times. Timing jumps to the 20s with acceleration.

guess i should check o2 resistance and harness

Super Moderator
24,962 Posts
If still getting a Pass Code of 11 in Continuous Memory; these codes are retained in memory for 80 warm-up cycles. To clear the codes for the purposes of testing or confirming repair, perform the KOEO test. When the fault codes begin to be displayed, de-activate the test by either disconnecting the jumper wire (meter, MIL or message center) or releasing the test button on the hand scanner. Stopping the test during code transmission will erase the Continuous Memory. Do not disconnect the negative battery cable to clear these codes; the Keep Alive memory will be cleared and a new code, 19, will be stored for loss of PCM power..." by Ford

If Code 11 appears again, pull EEC and inspect for leaky capacitors, damaged resistors, water leak damage, etc.

Super Moderator
24,962 Posts
Yo 86,
Ok, since Code 11 appears, pull EEC.

Also inpect its connector for corrosion, pin damage, etc

95 Bronco, 351W, E4OD, 4.56 gears, 35x12.50x15 Patagonia MTs.
318 Posts
Have you checked compression? I see a couple of your plugs were BLACK, indicating an issue with those cylinders. it could be stuck/broken injectors or low compression causing that. Try checking compression. If it's low you can try spraying some atf or seafoam in each cylinder, then turn it over to see if that helps free up any stuck rings?

Edit: drop in fuel pressure indicates a possible leaking injector. Try a boatload of techron and or remove and clean/test them.

19 Posts
Discussion Starter #12
Wait a minute. E6 on the ecu means 86 right??

rockauto lists it under 86 bronco with california emissions

CARDONE 784439 {#E6TF12A650YA, E6TZ12A650YA}Remanufactured; Plug & Play - No Programming RequiredInfo
Automatic trans.; with California Emissions; I.D. #(s) E6TF-YA

looking at 90 ecus theres so many listed

19 Posts
Discussion Starter #14
Reman ecu is in!

Got rid of previous errors!

KOEO - 11
CM - 11
KOER - 45, 25, 52

45 is the one im focusing on now. Any ideas? No vacuum leaks

Super Moderator
24,962 Posts
Yo 86,
IN KEY ON ENGINE RUNNING, code 45 is Thermactor secondary air is misdirected
Pic by SeattleFSB

DTC 45/95 Thermactor air system inoperative-right side: "...The code 45/95 is an Air Management fault. These particular codes are used for the Thermactor Air Diverter (TAD)/Thermactor Air Bypass (TAB) valve system (Fig. 3).
In following the diagnostic tree we were to first check for vacuum lines that could possibly be broken or disconnected. One line was found disconnected. At this point the codes were cleared and the emissions were checked. The emissions were lower, but not good enough.
We continued with the diagnostic tree and determined that the diverter valve was not at fault. We entered the output state check and cycled both the TAB and TAD solenoids on/off. They both worked correctly. Finally, we supplied vacuum to the solenoid to make sure that the vacuum did not leak down. The TAD solenoid would not hold vacuum. It slowly bled off. We replaced the solenoid. We then performed a KOEO and KOER test. No codes were present and emissions looked excellent. HCs were averaging about 97 to 112 ppm, and the CO was down around .2%. We concluded that the emissions readings were being affected by the vacuum bleeding off of the TAD solenoid. This allowed vacuum to be applied to the diverter valve at the TAD portion continuously. This resulted in the air always being diverted to the manifold before the oxygen sensor. The oxygen sensor would read lean, because of the extra oxygen, and therefore the computer would enrich the mixture. This is why the vehicle failed emissions..."

Source: by tomco-inc

19 Posts
Discussion Starter #18
Small update, went ahead and replaced cap and rotor with a duralast gold(made in Mexico), and TFI module with a Standard Ignition(made in USA)

reset timing, at 0* it backfires at idle. Moving the timing to 14* moves the backfiring up to the 1500rpm range.

waiting on oem TAB/TAD solenoids from Tasca. Original solenoids measured 75ish ohms resistance
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