Fuel pressure question

toomanybikes · Jul 29, 2015

Trying to clear three emissions codes on my '97 Ranger 4.0. P0136, P1131 and P1151. Was told it could be fuel pressure causing the lean 02 codes.

Tested my fuel pressure last night and will try again tonight. Filled up with gas this morning. Have a borrowed tester from the auto store.

The pressure was around 30 psi when at idle and when giving it the gas.

The specs call for 35 to 45 psi. Is this low enough to give me these codes?

Fuel filter is new as of June.

TxGasRacer · Jul 29, 2015

http://troubleshootmyvehicle.com/ford/4.0L/how-to-test-the-fuel-pump-1

RonD · Jul 29, 2015

30 psi should be fine, but................it could be dropping lower when engine is under load, pressure and flow are two different things but pressure will drop as flow increase so..............
You also need to shut off engine and see if the pressure holds, it will drop a little maybe 25psi, and then hold there, for a few months, so give in a half hour.
35-42psi should be the spec on '97

1131 and 1151 describe slow switching of O2 sensors on both banks of a V6 or V8 engine.
Assuming both O2 sensors didn't fail at the same time, not much of an assumption since it would be million to one shot, lol, either MAF sensor is not reporting correct air flow or air is getting into engine without going thru the MAF sensor.

Vacuum leak is the popular choice, any air leak includes the long air tube from MAF to intake, crack or worn gasket on that tube pulls in "extra" air without going thru the MAF.
Leaking power brake booster, bad PCV Valve.

toomanybikes · Jul 31, 2015

Pretty certain, now, this is electrical and not vacuum or fuel. At least as far as my codes go and getting this thing through emissions by Friday, next.

I'm sure now there is a bad ground to the two front O2 sensors. Tested them at the connectors and both heaters are good but there is no ground at the 10:00 position (yes, I have the test procedure from the web). There is 12volts at the 2:00 position and the fuse #20 is good.

Therefore, measuring between 10:00 and 2:00 there is no voltage at all. The heater is not getting juice. I also get no reading on my "live data" scanner for O2's when I drive. Another indication those two sensors are not giving out the data they should be.

Testing the final sensor after the cat and it tests out OK as far as getting a good ground, heater, etc.

I have located a diagram of how they get to the PCM and what pins are which and will trace out tonight if I can. Hoping it is dirty contacts as changing out the PCM looks to be an expensive pain.

Question:

How often do these PCM/ECM units fail and when they do can they go only partially?

RonD · Jul 31, 2015

PCMs rarely fail, not never just not common.
Yes, partial failure of certain circuits is what happens, you can usually see circuit board damage if you remove the top, leaking capacitors are usual cause of failure.

Fuel pressure question

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