96 Chassis F53 Check engine light. Need diagnosis help

[MarvinG]

Thanks Subford. Found mine to the left of the steering column, mounted 90 degrees to the one in your picture. Don’t know how I overlooked it last night. The code on mine is BOXO.

Skyking421: yeah, it’s easy and fun to spend someone else’s money! Before I retired, my last position was purchasing manager for a large HVAC wholesale house. Got to spend a lot of someone else’s money. The guy who replaced me says supply-side scarcity the last 12 months has made the job a whole lot less fun.

Brucenem: Fuel leaks. The scary thing is when I changed fuel pumps alongside the road, I left the adapter on the rail (unknowingly in my haste) and it had to be leaking some fuel all the way home. Because it sure did when I started the vehicle a couple of days later here at the house. On the same trip prior to the pump failure we saw an automobile fully engulfed in flame. It is a sobering thing. DW said she saw people standing outside so hopefully they all got out.

Brucenem: Testing the sensor, this helps, I should be able to eliminate it early on in my testing: so I momentarily ground the signal wire and release and see voltage move toward 0 then momentarily put 12 volts on it and release and see voltage move to 1 volt? Or where am I measuring computer response voltage? I have a good digital voltmeter.

[subford]

More Info:

/

[MarvinG]

So I ground or connect to 12+ the wiring harness signal wire and watch the output of the O2 sensor go from near ground to +1 prox as the system reacts to my hacking the system wire. Am I on track?

Once I get this straight I can eliminate this whole loop of the equation and move on to testing other things.

[subford]

I would not put more than 3Volts DC on the HEGO wire (Heated Oxygen Sensor input wire) # 74 going to pin #29 of the PCM.
A higher voltage than 3 volts may damage the PCM.


I have not seen the output to the PCM go above 1.0 Volts DC.

[MarvinG]

Originally Posted by subford

I would not put more than 3Volts DC on the HEGO wire (Heated Oxygen Sensor input wire) # 74 going to pin #29 of the PCM.
A higher voltage than 3 volts may damage the PCM.


I have not seen the output to the PCM go above 1.0 Volts DC.

Yeah, I was thinking 12 volt as I suggested might fry something. Thinking maybe put a 1-1/2 volt battery between it and ground. Does that sound feasible?

[subford]

A 1 1/2 battery would send a rich signal to the PCM.
As noted above the O2 sensor generates a voltage from 0 to 1.1 volt signal.

[brucenem]

DO NOT PUT 12 VOLTS on any sensor wire. IT WILL ruin your ecm. What I meant was hold one end of the jumper in one hand and touch battery positive with the other hand. Your body will provide enough resistance to take down the 12 volts to approximately one volt. A 1.5 volt battery will do the same thing, just another way of testing.
This only tests the circuit from the harness connector back to the ecm, and shows if it will respond to a good oxygen sensor.

[MarvinG]

OK makes sense now. Thanks to both of you for your patience and guidance.

[MarvinG]

Today I put a fuel pressure regulator on. I haven’t driven it yet, but peak pressure with the old regulator by turning the key on and off several times was 37 lbs. Pressure with engine idling was 32 and with vacuum line off the regulator was 41.

Peak pressure with new regulator with key on and off several times, never hit 37, it would build up to near that and then drop back quickly to something less, maybe 25 or so. Pressure with engine idling is 32 and with vacuum line off the regulator was 41.

Almost like I’m going backwards here!

[subford]

Turning the key on and off several times does not tell you anything pressure wise other than the pump runs and the check valve works.

[brucenem]

To check static fuel pressure, koeo, turn the key just once. If it does not hit at least 40 psi and then drop back to around 33 slowly and hold- this will cause a hard start. Leave the gauge hooked up- it should hold pressure for at least 20 minutes. any other reading indicates an internal leak, fuel pump check valve, fuel pressure regulator, or a bad injector.
AS I stated before, fuel pressure regulators usually work or not with no in between, although with the age of the vehicle anything is possible.
With the new pump, did it come with a new electrical connector, and did you use it? I seem to remember that connector had an extra ground that had to be installed at the tank.

[MarvinG]

OK. . . . I test drove it this morning. Check engine light came on way sooner than usual (codes had been reset before driving). The most I can get out of it today is a cat’s whisker over 38 lbs with petal to the metal climbing a hill. Would you all recommend moving on to other testing or should I take this regulator back? It seems it is pulling my pressure slightly lower than the old one did.

[MarvinG]

My wiring harness had already been modified to fit the latest pump so it was plug and run.

I never have hit full pressure with just one key on, I usually have to cycle maybe five times to get pressure. With the new fuel pump, though it does hold pressure more than 20 minutes. 24 hours later I still have at least 15 lbs.

With this new regulator, is it possible, or unlikely, I got it put in cock-eyed so it isn’t sealing well?

[subford]

As was stated above by mpaton the Fuel Pressure regulator has a 39.1 pound spring in it.
So with no vacuum pushing on the diaphragm the fuel pressure would be 39.1 psi on a standard day at sea level.
From you readings above I would say your FP gauge is reading about one pound high.
That would mean you only had 37psi going up the hill.


That would also mean you still had vacuum going to the FPR.
Why would that be?
Throttle plates not opening all the way?
Clogged air filter or restricted air to the throttle?


You might try going up that hill with the vacuum line plugged and off the FPR.



/