Backfire at highway speed

Rumbler tag

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This all started this summer on the way back home I was going to pass someone and when I stepped on the throttle it would **** back in forth for a bit then all of a sudden shoot up in rpm like it should backfire jump around a little and then go back down in rpm, I continued to try and make it home like that the problem became worse until finally I made it about a mile from my house and it died while I was trying to crawl it home at that point it was barely running. I let it sit for 30 minutes came back started right up then I thought I had the problem the TFI module, so I ordered a new one and replaced it(the original one was still in it after all those years) but after replacing it I found out that the new TFI didn’t change anything. I tried to drive around a bit for a couple days to maybe get an idea of what’s going on same thing I would start it up just fine and let it warm up and if I tried giving it a lot of throttle it would backfire and **** around, at that point I had given up for a bit and now I pulled codes on the thing and only got EGR codes and O2 codes, so I said hey why not replace all the sensors in the vehicle as they are all original I replaced MAP, EGR, EGR valve on the left passenger side fender, EGR pressure feedback sensor, O2 sensor, Intake charge temp sensor, coolant temp sensor, idle air control sensor, throttle position sensor. Before replacing all the sensors I decided to try and take it out to fill it up with some gas on. This is the first time I’ve fired it up in winter the thing started like normal but when I went to town it ran like a lot better in the cold it could just be a fluke. After replacing all the sensors I still have the dreaded O2 lean code and EGR stuck open or closed, I took the fusible link out of the O2 sensor wire and it got rid of the O2 code for a little bit I took it for a spin with all new sensors and the O2 sensor hot wired and it still does the same thing I’m at a loss right now hopefully someone can help, I’ve also checked all vacuum lines
 

Tiha

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What year?

There is a pickup module, or pip sensor in the distributor, they can be heat sensitive like you described.

Otherwise lean O2 sensor code would point to a vacuum leak, intake leak. Or a weak fuel pump? Maybe pressure regulator?
 

miesk5

96 Bronco 5.0
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Yo Rumbler tag,
Welcome to our site!

Which year and engine do you have?
See Table 11:
Screenshot_20221201-161004_Gallery.jpg
Quick Test is the Diagnostic Trouble Code Test.

"The positive crankcase ventilation (PCV) system cycles crankcase gases back through the engine (6007) where they are burned. The positive crankcase ventilation valve (PCV valve) (6A666) regulates the amount of ventilation air and blow-by fuel vapor to the intake manifold (9424) and prevents backfire from traveling into the crankcase. The positive crankcase ventilation valve is mounted in a vertical position.

CAUTION: Do not remove the PCV system from the engine. Operating engine without PCV system will reduce both fuel economy and engine ventilation. This will weaken engine performance and shorten life."

Typical PCV Air Flow Diagram

1669929682481.png
ItemPart NumberDescription
16582Valve Cover
2To Air Cleaner Outlet Tube (9B659)
36758Crankcase Ventilation Tube
49E926Throttle Body
59424Intake Manifold
66A666Positive Crankcase Ventilation Valve

..." by Ford


Spark Plug Wire Routing & Firing Orders by Tank92 @ 1992 Ford Bronco wires picture | SuperMotors.net

5.0; The firing order for 87-93 vehicles 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. Distributor rotation: Counterclockwise ----------

●See my See my Vacuum leak test in post #11; includes jowens1126 HVAC Control Panel info & Mikey350's High Idle Tests @ https://www.fullsizebronco.com/threads/help-with-dtc-codes-and-idle.206824/
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.





another is; The air supply from the SMOG pump is controlled by the air by-pass valve, sometimes called a dump valve. During engine deceleration, the air by-pass valve opens, momentarily diverting the air supply through a silencer and into the 6atmosphere, thus preventing backfires within the exhaust system when deceleration supplies larger-than-normal amounts of unburned fuel to the exhaust ports. check valve is incorporated in the air inlet side of the air manifolds. Its purpose is to prevent exhaust gases from backing up into the Thermactor system. This valve is especially important in the event of drive belt failure and also during deceleration, when the air by-pass valve is dumping the air supply. The air manifolds and air supply tubes channel the air from the Thermactor air pump into the exhaust ports of each cylinder, thus completing the cycle of the Thermactor system.
includes jowens1126 HVAC Control Panel info & Mikey350's High Idle Tests @
 

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Rumbler tag

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Joined
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Location
Missouri
What year?

There is a pickup module, or pip sensor in the distributor, they can be heat sensitive like you described.

Otherwise lean O2 sensor code would point to a vacuum leak, intake leak. Or a weak fuel pump? Maybe pressure regulator?
1987 bronco II 2.9l EFI automatic, a lot of people are saying fuel regulator which would make sense, It’s just strange I have the 41 code and yet it runs super rich and smells like gas occasionally when it backfires, I also have the code 33 and one for a knock sensor not tested during test. The 41 and 33 never go away but the knock sensor is intermittent
 
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Rumbler tag

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Yo Rumbler tag,
Welcome to our site!

Which year and engine do you have?
See Table 11:
View attachment 30698
Quick Test is the Diagnostic Trouble Code Test.

"The positive crankcase ventilation (PCV) system cycles crankcase gases back through the engine (6007) where they are burned. The positive crankcase ventilation valve (PCV valve) (6A666) regulates the amount of ventilation air and blow-by fuel vapor to the intake manifold (9424) and prevents backfire from traveling into the crankcase. The positive crankcase ventilation valve is mounted in a vertical position.

CAUTION: Do not remove the PCV system from the engine. Operating engine without PCV system will reduce both fuel economy and engine ventilation. This will weaken engine performance and shorten life."

Typical PCV Air Flow Diagram

View attachment 30700
ItemPart NumberDescription
16582Valve Cover
2To Air Cleaner Outlet Tube (9B659)
36758Crankcase Ventilation Tube
49E926Throttle Body
59424Intake Manifold
66A666Positive Crankcase Ventilation Valve

..." by Ford


Spark Plug Wire Routing & Firing Orders by Tank92 @ 1992 Ford Bronco wires picture | SuperMotors.net

5.0; The firing order for 87-93 vehicles 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. Distributor rotation: Counterclockwise ----------

●See my See my Vacuum leak test in post #11; includes jowens1126 HVAC Control Panel info & Mikey350's High Idle Tests @ https://www.fullsizebronco.com/threads/help-with-dtc-codes-and-idle.206824/
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.





another is; The air supply from the SMOG pump is controlled by the air by-pass valve, sometimes called a dump valve. During engine deceleration, the air by-pass valve opens, momentarily diverting the air supply through a silencer and into the 6atmosphere, thus preventing backfires within the exhaust system when deceleration supplies larger-than-normal amounts of unburned fuel to the exhaust ports. check valve is incorporated in the air inlet side of the air manifolds. Its purpose is to prevent exhaust gases from backing up into the Thermactor system. This valve is especially important in the event of drive belt failure and also during deceleration, when the air by-pass valve is dumping the air supply. The air manifolds and air supply tubes channel the air from the Thermactor air pump into the exhaust ports of each cylinder, thus completing the cycle of the Thermactor system.
includes jowens1126 HVAC Control Panel info & Mikey350's High Idle Tests @
I have a 1987 bronco II 2.9l EFI automatic trans
 

Motech

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@Tiha is right on about the PIP sensor inside the distributor.

To test, when your engine starts running badly, disconnect the SPOUT connector, also known as the timing connector. If it runs better, it's your PIP sensor, period. No other test needed, or even possible without a lab scope.

They are a real bear to replace, requiring specialized distributor shaft pressing tool. Easiest thing is just replace the distributor.
 

Motech

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And for what it's worth, Ford was too detail oriented in there trouble code descriptions back then. They couldn't just say engine running lean, they had to tell us the oxygen sensor indicates the engine is running lean. Way too many oxygen sensors were replaced over this code, when in reality the sensor is fine. Poor running increases oxygen levels, and Ford's system reports that.
 
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Rumbler tag

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@Tiha is right on about the PIP sensor inside the distributor.

To test, when your engine starts running badly, disconnect the SPOUT connector, also known as the timing connector. If it runs better, it's your PIP sensor, period. No other test needed, or even possible without a lab scope.

They are a real bear to replace, requiring specialized distributor shaft pressing tool. Easiest thing is just replace the distributor.
The engine ran the same when the pip was unplugged
 

L\Bronco

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This all started this summer on the way back home I was going to pass someone and when I stepped on the throttle it would **** back in forth for a bit then all of a sudden shoot up in rpm like it should backfire jump around a little and then go back down in rpm, I continued to try and make it home like that the problem became worse until finally I made it about a mile from my house and it died while I was trying to crawl it home at that point it was barely running. I let it sit for 30 minutes came back started right up then I thought I had the problem the TFI module, so I ordered a new one and replaced it(the original one was still in it after all those years) but after replacing it I found out that the new TFI didn’t change anything. I tried to drive around a bit for a couple days to maybe get an idea of what’s going on same thing I would start it up just fine and let it warm up and if I tried giving it a lot of throttle it would backfire and **** around, at that point I had given up for a bit and now I pulled codes on the thing and only got EGR codes and O2 codes, so I said hey why not replace all the sensors in the vehicle as they are all original I replaced MAP, EGR, EGR valve on the left passenger side fender, EGR pressure feedback sensor, O2 sensor, Intake charge temp sensor, coolant temp sensor, idle air control sensor, throttle position sensor. Before replacing all the sensors I decided to try and take it out to fill it up with some gas on. This is the first time I’ve fired it up in winter the thing started like normal but when I went to town it ran like a lot better in the cold it could just be a fluke. After replacing all the sensors I still have the dreaded O2 lean code and EGR stuck open or closed, I took the fusible link out of the O2 sensor wire and it got rid of the O2 code for a little bit I took it for a spin with all new sensors and the O2 sensor hot wired and it still does the same thing I’m at a loss right now hopefully someone can help, I’ve also checked all vacuum lines
Backfiring under load is usually caused by excessively lean mixture, so I would say your 41 code is likely a symptom, not a cause.
Get a fuel pressure gauge on it, tape it to the windshield and drive it till it stumbles again, under load the fuel pressure should be about 9 psi higher than idle. (Mid 30’s at idle and mid 40’s at full load or with the vac line off)
If you are losing pressure under accel, check filters, and last the pump(s)
If your press stays high, check the O2 sensor ground, it should be an orange wire on the back of the left head. (Pass side)
Hope that helps.
Cheers
 
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Backfiring under load is usually caused by excessively lean mixture, so I would say your 41 code is likely a symptom, not a cause.
Get a fuel pressure gauge on it, tape it to the windshield and drive it till it stumbles again, under load the fuel pressure should be about 9 psi higher than idle. (Mid 30’s at idle and mid 40’s at full load or with the vac line off)
If you are losing pressure under accel, check filters, and last the pump(s)
If your press stays high, check the O2 sensor ground, it should be an orange wire on the back of the left head. (Pass side)
Hope that helps.
Cheers
Does this orange wire have a little eye hook on it to bolt to something is so I’ve literally just left it there because I don’t know where it goes it’s kinda just hanging by the distributer on the left side of my engine, where should I ***** it to
 
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Rumbler tag

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Backfiring under load is usually caused by excessively lean mixture, so I would say your 41 code is likely a symptom, not a cause.
Get a fuel pressure gauge on it, tape it to the windshield and drive it till it stumbles again, under load the fuel pressure should be about 9 psi higher than idle. (Mid 30’s at idle and mid 40’s at full load or with the vac line off)
If you are losing pressure under accel, check filters, and last the pump(s)
If your press stays high, check the O2 sensor ground, it should be an orange wire on the back of the left head. (Pass side)
Hope that helps.
Cheers
Ok so I attached the orange wire to a good ground and it did remove my code 41 all that remains is a code 33 which is just EGR related, it still does the same thing this time it’s not as bad though it’s drivable but when I put my foot down too much going up a hill it still pacifiers and jumps back and forth, so it would be a good idea too look at fuel now would it?
 

L\Bronco

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Ok so I attached the orange wire to a good ground and it did remove my code 41 all that remains is a code 33 which is just EGR related, it still does the same thing this time it’s not as bad though it’s drivable but when I put my foot down too much going up a hill it still pacifiers and jumps back and forth, so it would be a good idea too look at fuel now would it?
Yes, for sure!
Try to get a gauge on it taped to the windshield so you can safely monitor the pressure while driving.
Cheers
 
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