1990 Bronco 2 2.9L V6, Fuel Issue?

My 90 Bronco 2 2.9L V6 "Stock Engine"
is being annoying posted some thing on other sites and nobody knows the answer.
My truck starts right up and idle's perfect in Park and Neutral.
But when I put it in R/D I can only rev it to 1.7k RPM before is looses fuel pressure?
It wants to stall but it doesn't stall just puts and grumbles real low.

Things I was told to replace and did are:
Fuel Pump
Fuel Filter
Fuel Pressure Regulator
Ignition Coil
Throttle Air Bypass Valve
O2 Sensor
Catalytic Converter
Muffler
Distributor Cap
Cap Ignition Rotor

What else can I change? This Truck is starting to annoy me

It does this while idling when it's in gear?

AnnoyedEasy3 said:

My 90 Bronco 2 2.9L V6 "Stock Engine"
is being annoying posted some thing on other sites and nobody knows the answer.
My truck starts right up and idle's perfect in Park and Neutral.
But when I put it in R/D I can only rev it to 1.7k RPM before is looses fuel pressure?
It wants to stall but it doesn't stall just puts and grumbles real low.

Things I was told to replace and did are:
Fuel Pump
Fuel Filter
Fuel Pressure Regulator
Ignition Coil
Throttle Air Bypass Valve
O2 Sensor
Catalytic Converter
Muffler
Distributor Cap
Cap Ignition Rotor

What else can I change? This Truck is starting to annoy me

Click to expand...

Have you actually CHANGED any of this stuff?

Its hard to give advise as to what else might need changing if we dont even know what has been changed yet...

My first step would be the fuel filter.

Does it actually begin to lose pressure as seen on a gauge, or does it just sputter?

As you found out at the other site the description could be caused by a few things.
You could even add the PCM to that list, lol.

You said it loses fuel pressure, is that tested at the schrader valve on the rail, if so what were the pressure readings, KOEO, KOER, under load?
Normal is between 30-40psi

Basically you are just spitting in the wind without a few tests, but that's what keeps the auto parts stores and on-line sellers in business

BroncoIIPower said:

It does this while idling when it's in gear?

Click to expand...

Yes, only in gear Reverse and Drive/Overdrive

Surrey said:

Have you actually CHANGED any of this stuff?

Its hard to give advise as to what else might need changing if we dont even know what has been changed yet...

My first step would be the fuel filter.

Click to expand...

Things I was told to replace and DID are: <--This means I CHANGED IT
Fuel Pump
Fuel Filter
Fuel Pressure Regulator
Ignition Coil
Throttle Air Bypass Valve
O2 Sensor
Catalytic Converter
Muffler
Distributor Cap
Cap Ignition Rotor

RonD said:

As you found out at the other site the description could be caused by a few things.
You could even add the PCM to that list, lol.

You said it loses fuel pressure, is that tested at the schrader valve on the rail, if so what were the pressure readings, KOEO, KOER, under load?
Normal is between 30-40psi

Basically you are just spitting in the wind without a few tests, but that's what keeps the auto parts stores and on-line sellers in business

Click to expand...

No, it is not tested every time I go to the store, auto-zone tells me to replace something else. And that testing is a waste of money, but like you said of course they don't want me to figure it out...

AnnoyedEasy3 said:

Yes, only in gear Reverse and Drive/Overdrive



Things I was told to replace and DID are: <--This means I CHANGED IT
Fuel Pump
Fuel Filter
Fuel Pressure Regulator
Ignition Coil
Throttle Air Bypass Valve
O2 Sensor
Catalytic Converter
Muffler
Distributor Cap
Cap Ignition Rotor



No, it is not tested every time I go to the store, auto-zone tells me to replace something else. And that testing is a waste of money, but like you said of course they don't want me to figure it out...

Click to expand...

Missed the part where you said you've changed all that stuff already. When you say only in gear, then it doesn't bog down in neutral?

Thats a big-ass list of things to replace when you dont even know the problem - probably coulda taken it into a shop and have them figure it out with the time/money spent on all that stuff....

Check for leaks in your fuel lines. Have you done anything to test or clean injectors?

Have you checked timing?

Surrey said:

Missed the part where you said you've changed all that stuff already. When you say only in gear, then it doesn't bog down in neutral?

Thats a big-ass list of things to replace when you dont even know the problem - probably coulda taken it into a shop and have them figure it out with the time/money spent on all that stuff....

Check for leaks in your fuel lines. Have you done anything to test or clean injectors?

Have you checked timing?

Click to expand...

No it does not bog down in neutral.
Ya, that is a big list but its still cheaper then taking it to the shop the people in NC are crooked
Yes, I checked for leaks and there are none
No, I have not tested the injectors just cleaned them which now I regret I should have just replaced them and got it over with

Just as a heads up, when you replace anything on a computer operated engine you must disconnect the Neg. battery terminal, yes it is for safety but..........it also will reset the computer, this is required for the computer to re-learn any new parameters from sensors or changes to sensors.
People often do a "quick swap" and nothing changes, so they figure that wasn't the problem, but the computer is running on the old incorrect parameters, it doesn't "know" you changed anything, by disconnecting the battery for 5 min. the computer will run a self test when power is available again and also re-learn sensor and engine operating conditions.
Some sensors will take up to 50 miles of driving to be re-learned completely.


1990 is around the time the B2 2.9l was switching from MAP sensor to MAF sensor.
I think in 1990 only Calif. B2s had MAF sensors, all others were still using MAP sensors.

The MAP(Manifold Absolute Pressure) sensor is one of the main sensors that tells the computer the engine's "load", based on the intake's vacuum pressure.
So plays a big part in setting the fuel/air mix.
It is a small sensor usually located on the firewall, often hidden by wiring harness.
It has an electrical connection and a vacuum line, tracing the vacuum line is the best way to find it.

When you put the engine in gear vacuum drops a bit from the "load" so MAP should respond and PCM(computer) should increase fuel in the mix.
When you open the throttle the vacuum drops a lot so a fast increase of fuel is needed, if the MAP is not telling the computer about this then you would have very sluggish performance.

I would remove the vacuum line and check it for leaks.
The MAP electrical signal to the computer is not a voltage, it is a frequency, so can really only be tested with a MAP tester and vacuum pump, but there are some cleaver ways to do some tests on a MAP sensor.
Google: Test Ford MAP sensor


If you have a MAF sensor and not a MAP then look here:
http://www.therangerstation.com/tech_library/CleanMAF.html

MAF(Mass Air Flow) sensor will be on the intake manifold air plenum(big air tube) either at the intake end or air filter end.

Update: Truck Still runs the same. But now after I replaced the distributor Cap
the truck backfires,When I step hard on the gas. The back fire does NOT come from the exhaust. The sound comes from the Engine. I will try to take a video and post on youtube maybe that will help explain the sound/action.

Two things come to mind.
Does it back fire only when engine is warmed up?
If so then I would check the MAP or MAF sensor.
If fuel mix is not being richened enough then the too lean mix is igniting when it hits the hot cylinder, intake valve is still partially open so pop is heard.
This popping would get worse as engine(cylinders) warmed up.

If it only pops when cold then I would check the ECT sensor, computer is running engine too lean when cold.
Look here:
http://oldfuelinjection.com/?p=28

The other thing it could be is that the TFI system is not advancing the timing with the throttle position and rpm.
Look here:
http://www.therangerstation.com/tech_library/TFI_Diagnostic.html

Just Replaced the MAP sensor still no change...

I wpuld pull the TFI and test it...they're known for causing problems on these trucks.