88 5.0 backfiring and missing.

[suddenchance]

Hey everyone,

Update! Bronco is running rich! Fuel injectors are new and fuel pressure is at 33lbs and holds. Spark plugs are fouling.

I have a 1988 Bronco with a 5.0 engine that's experiencing some issues. It’s backfiring through the intake and missing, making it feel like it's only running on six cylinders. The engine is new and was tested before installation, showing positive results. The ECU is also new and has been tested.

The engine starts easily, but after 2-3 minutes of running, it starts to miss, and I hear backfiring at around 1200 RPM and above and the check engine light stays on. There are no vacuum leaks, and the fuel pressure at the rail is holding steady at 30-33 psi. I’ve replaced the O2 sensor and changed the throttle body, the idle air control (IAC) valve, and the manifold absolute pressure (MAP) sensor.

After running the diagnostic codes, I found that both the IAC and MAP sensors are out of range. I tested the voltage on the MAP sensor, and it read correctly. The engine is running rich, and I’ve also installed new injectors, spark plugs, and plug wires. In fact, every component on the truck has been replaced. The truck is displaying the same symptoms it had with the old engine, so I know the issue isn't due to the new one.

It's acting exactly like the timing is off but the timing is set perfect and the firing order is also correct.

Any ideas or suggestions would be greatly appreciated!

 

[L\Bronco]

Hey there sudden, welcome to the zone!
That sounds like exh restriction, (maybe one side?)
Does it still have cats?
Hook a vacuum gauge to a manifold source, read it at idle, then 2000 rpm.
It should be 18ish in hg at idle and 2” higher at 2000 rpm (in neutral)
If it drops, it usually means a plugged cat.
The other thing is get it to backfire and miss for a few seconds and feel the intake runners. Any warm/hot ones have an exh restriction. (The exhaust gas backs up into the intake and lights the fuel behind the intake valve.
It might help you narrow down which side. Ive even seen a plugged exh manifold port or 2. (But they misfire immediately)
Hope that helps!
Cheers!!

 

[Tiha]

That is a great idea. I was gonna say pop an O2 out and start it, or pull the EGR and start is. Let the exhaust leak and see if it runs any better.

 

[suddenchance]

Hey there sudden, welcome to the zone!
That sounds like exh restriction, (maybe one side?)
Does it still have cats?
Hook a vacuum gauge to a manifold source, read it at idle, then 2000 rpm.
It should be 18ish in hg at idle and 2” higher at 2000 rpm (in neutral)
If it drops, it usually means a plugged cat.
The other thing is get it to backfire and miss for a few seconds and feel the intake runners. Any warm/hot ones have an exh restriction. (The exhaust gas backs up into the intake and lights the fuel behind the intake valve.
It might help you narrow down which side. Ive even seen a plugged exh manifold port or 2. (But they misfire immediately)View attachment 32575
Hope that helps!
Cheers!!

Appreciate the info! I did check and the exhaust and it did fix the backfiring issue! The engine is still misfiring. I checked codes and it's pulling 31 O, 81 O and 82 O. Would Appreciate any info!

 

[L\Bronco]

Thats great!
Strange that the misfire is still there.
Did you clean or replace the plugs on the misfiring cylinders? They may be fouled.
Code 31 is an EGR code, not sure about 81 and 82 though. Ill do some digging tomorrow for you.
Cheers

 

[Tiha]

81 o-- Air Management 2 (AM2/TAD) circuit failure
82 o-- Air Management 1 (AM1/TAB) circuit failure

I will try to find troubleshooting when I get a chance.

 

[Jimbo26]

The plot thickens.........
Tune in next week, folks.

 

[johnnyreb]

81 o-- Air Management 2 (AM2/TAD) circuit failure
82 o-- Air Management 1 (AM1/TAB) circuit failure

I will try to find troubleshooting when I get a chance.

What happened to BRONCO ZONE? i DON,T GET ANT MORE E-MAIL FROM IT AND SEE VERY FEW PEOPLE ON HEAR NOW. Help Ti !

 

[Jimbo26]

What happened to BRONCO ZONE? i DON,T GET ANT MORE E-MAIL FROM IT AND SEE VERY FEW PEOPLE ON HEAR NOW. Help Ti !

Been wondering about that for a spell also. Is like it went almost dead in here.

 

[Superduty 66]

I've noticed it myself and I will say that I have not helped out like I should. I do have 2 Bronco's that I am slowly working on in between keeping the kids cars going and keeping the property up. However I hope to be doing more with the Broncos this fall and I will post some pics and updates. I have enjoyed this group and hope it keeps going.

 

[Tiha]

Same here, Just been busy, or when I read a post my head isn't in the right place to make a valid contribution.

 

[Jimbo26]

Same here, Just been busy, or when I read a post my head isn't in the right place to make a valid contribution.

Strong liquor can be a great motivator

 

[L\Bronco]

Got a crown on the go now!

 

[Tiha]

This is off topic, but interesting note.

Verticle scope stock has nose dived. If you are not familiar with them, they are the company that came around and bought up as many forums as possible in a wide variety of hobby areas.

One of the largest contributors to the decline of forums like this was groups like FB where a person can usually get a nearly instant response to their questions.

To make matters worse, now AI is generating answers instead of allowing search engines to point people to forums like this that contain the answers.

AI will **** these forums eventually. It is making life easier in some ways but it is killing the online community.

 

[johnnyreb]

Hey everyone,

Update! Bronco is running rich! Fuel injectors are new and fuel pressure is at 33lbs and holds. Spark plugs are fouling.

I have a 1988 Bronco with a 5.0 engine that's experiencing some issues. It’s backfiring through the intake and missing, making it feel like it's only running on six cylinders. The engine is new and was tested before installation, showing positive results. The ECU is also new and has been tested.

The engine starts easily, but after 2-3 minutes of running, it starts to miss, and I hear backfiring at around 1200 RPM and above and the check engine light stays on. There are no vacuum leaks, and the fuel pressure at the rail is holding steady at 30-33 psi. I’ve replaced the O2 sensor and changed the throttle body, the idle air control (IAC) valve, and the manifold absolute pressure (MAP) sensor.

After running the diagnostic codes, I found that both the IAC and MAP sensors are out of range. I tested the voltage on the MAP sensor, and it read correctly. The engine is running rich, and I’ve also installed new injectors, spark plugs, and plug wires. In fact, every component on the truck has been replaced. The truck is displaying the same symptoms it had with the old engine, so I know the issue isn't due to the new one.

It's acting exactly like the timing is off but the timing is set perfect and the firing order is also correct.

Any ideas or suggestions would be greatly appreciated!

I bought a NEW---MR GASKERT FUEL PRESSURE GAUGE AND ITS JUNK. This junk from CHINA will have wasteing your time and money---Welcome to the Bronco Zone good luck. Theirs alot of knowledge guys on hear that will help you out.

 

[johnnyreb]

Have you checked the gas you put in it? Is it ethanol or regular gas? Ethanol gas will start turning into a syrup--if it sit for a couple of weeks. Also it will eat metal up (the float arm) was eaten up in my 78 that had been sitting for awhile. They should OUTLAW ETHANOL GAS--ITS THE WORSE JUNK YOU CAN PUT IN ANY FUEL TANK.