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[CypsBronco]

I have a 1990 Ford Bronco, 5.0 EFI, has automatic transmission. I have performed compression test on all cylinders and all are well within the specified specs. I have replaced plugs, and wires, O2 sensor, ensured all vacumm lines are correct and tested ok, replaced the upper intake gaskets and valve cover gaskets after suspected leak. not pulling any codes since doing these items, however it is still running ruff, and a bit ********. I am currious if any one has experience these problems and would like some insight, I would like to learn how to test the fuel injection system. Please let me know where to go from here.

Thanks

GC [-o<

 

[miesk5]

yo

from others that have has sim symptoms with NO DTCs;

a guess;

Manifold Absolute Pressure (MAP);

Testing, Symptoms & Overview; "...Surging, Rough idle, rich fuel condition, which may cause spark plug fouling,Detonation due to too much spark advance and a lean fuel ratio, loss of power and/or fuel economy due to ******** timing and an excessively rich fuel ratio, vacuum leak will reduce intake vacuum and cause the MAP sensor to indicate a higher than normal load on the engine. The computer will try to compensate by richening the fuel mixture and retarding timing -- which hurts fuel economy, performance and emissions..."

Source: by aa1car.com http://www.aa1car.com/library/map_sensors.htm

Operational Description, pic & Parameters; MAP sensors are only used in Speed Density systems

Source: by Ryan M (Fireguy50) at fordfuelinjection.com

http://fordfuelinjection.com/index.php?p=27

Testing w/DVOM & Overview :...The most accurate way to test this sensor is to measure output using a DVOM (digital volt-ohm meter). In this case the meter must have a frequency measuring ability..."

Source: by kemparts.com via web.archive.org http://web.archive.org/web/20070309172250/http://www.kemparts.com/TechTalk/tt11.asp

 

[2percent]

I had this same problem and it ended up being the ICM on the side of the distributor. But it is always best to inspect and test before replacing. The easiest way I have found to test fuel system is

1)simply listen for fuel pump to kick on when key is turned on

2)check for fuel at the fuel rail by depressing the ball in the service valve

3)if fuel is present use a fuel pressure gauge to determine correct pressure at the fuel rail.

4)if all has checked out good I use a noid tester to make sure each injector is getting power(not required but it is my usual routine.)

If step 1 is not met check your fuses, fuel pump relay and for power to the fuel pump.

If step 2 is not met check for leaks or clogs usually found in the fuel filter

If step 3 is not met either you fuel pump has failed to supply enough fuel or your fuel pressure regulator has failed (The easiest way to check for a blown fuel pressure regulator diaphragm is to simply pull the vacuum line and inspect for dampness as it should be dry, if found to be wet replace your FPR)

If step 4 has failed inspect the wiring going to each injector if power is evident the injector will need replaced

I hope I have covered everything any thing I left out Im sure Miesk or Joe have better instructions.

 

[biker3r]

When i first got my 91, it pretty much ran the same way, had me stumped, turned out being the MAP sensor, runs great now.

 

[CypsBronco]

Thank you for all your input, I have taken the truck in to an advance diagnosis shop, so I can hopefully get to the root of the cause. I am used to working on the Old Broncs and the vacuum system is new to me. I <img src='http://broncozone.com/public/style_emoticons/<#EMO_DIR#>/clap.gif' class='bbc_emoticon' alt='><img src='http://broncozone.com/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt=' /emoticons/[email protected] 2x" width="20" height="20" />' /><' /> replaced the MAP sensor, throttle control valve and tested the EGR Valve "tested OK". I will let you all now what happens tomorrow.

Thanks,

GC