I've been going round and round chasing these engine codes on my well used and abused (not by me, I bought it not 2 years ago) 1997 4 liter Ford Ranger.

The first bunch were all cleared by cleaning the two large connection blocks inside the engine compartment. This, after working weeks on the EGR system that was giving the codes. It was all just dirty connections, in the end.

So since that fix I now have three new codes to clear. They came up immediately after the others went away.

First, on the code reader I get catalytic monitor incomplete.

This, to my mind at least, means connections, again. The computer is not (yet) getting the information from the sensors to even begin to compute the data.

I have: P0136, P1131 and P1151. Correct me if I'm wrong but are these not the three exhaust sensors sitting on the manifold and tail pipes?

Can it be that one day they worked and the next all three went bad?

Tracing the wires back these each have their own 4-pin connector, which I have since cleaned and sprayed with Deoxit5. They all lead to the large wire bundles and on to the connection block under the passenger side back lid, where the computer sits. Which, as I said, has been cleaned, twice.

Question: I need to get this inspected by next Monday (7/27) or I lose the registration on this truck. Rather than reset the computer and lose the road time on all the other systems can I assume that if this new problem is fixed it will clear by itself?

Help and some practical advice appreciated.

 

Found this video dealing with two of the same codes as I have. P1131 and P1151 lean condition banks 2, the pre-cat sensors on each side of the manifold exhaust. This fellow shows how to test for a vacuum leak around the PCV valve at back of intake manifold.

Will try this test tonight.

 

Be careful what kind of spray you use, most are flammable & some aren't O2 sensor, or plastic safe, some are plastic stress crack promoters, or aren't seal material friendly.
Or, consider rigging an O2 sensor friendly unlit propane torch sniffer, using a length of tubing with a sports needle on the end as a probe & pass it around suspected leak spots with the engine at idle & listen for engine idle speed to increase when it gets a whiff. The sports needle can concentrate the propane & find small leaks.
Maybe purchase a cigar of your choice & blow the smoke into a vacuum line connection & look for whiffs of escaping smoke at the leak point.
The PCV valve & its rubber tubing are good suspects, as are the upper & lower manifold gaskets on this year 4.0L. Let us know what you find.

 

Is fuel pressure ok?

 

Hey, thanks much for the help. Most appreciated.

Last night I located the PCV on my truck. Interestingly, it was just behind and to the right of one of those large connector blocks I had to clean. The hose was not fully on and slipped off easily. Only a short sort of S shaped section of hose that went just above and into the top of the intake manifold. I may have disturbed the vacuum connection when fiddling with that electrical connector block.

The hose looked good but the fitting to the valve somewhat tenuous. Bought a new metal version Perolator PCV valve this morning for $4 or so. Might as well replace it. Cheapest thing in there : )

Will install that after work and use a small hose clamp to secure it. Clear the codes and go for a ride. Usually get codes within 10 miles or less. Then I'll see where I am.

As to the fuel pressure. I have not tested it. I did replace the gas filter last month and that cleared up the first set of (other) lean codes immediately. It seemed to be almost totally clogged when I tried to blow through it.

I also bought a set of Motorcraft spark plugs today. Was told if the gap is too large (from old plugs) this can cause a lean condition, too. Again, at 200+K miles probably needs them anyway. No telling if and when they were ever done.

If they say Motorcraft on them.... probably never.

 

Installed new PCV valve with hose clamp. Went in way tighter than the old plastic one came out so the fit now good and strong.

At first start some rough running, mild pops from the exhaust. Drove over 30 miles getting on the highway, getting off and doing city and back on the highway. A good drive. No engine light. Great!

Started up today, got to the end of my street and engine light on. Same three codes as before.

The thing is the truck runs great. Smooth as can be with the new PCV. Good mileage at around 25/gallon. Plenty of power and pickup. If it was running way lean I think the motor would have blown up well before the 206,000 miles it has on it. I get a good varoom sound from the fuel pump in the morning so I assume the pressure is in there.

Codes are P0136, P1131 & P1151. So I need to clear P0136, the lowest #, first.

Have not installed the new plugs yet as I need to use the truck for a trip to Boston this Friday.

I did find this reply to a similar issue on this site "First, the code 136 is being mis-interpeted. It is not the OX sensor but the cabling/connector or possible exhaust leak allowing excess air to enter ahead of the sensor."

There is that connector word again. Damn.

Also found this "Not sure if I'm oversimplifying it but I get that (P0136) error code whenever I run my gas tank too low. After a few days it'll clear of its own accord"

Actually, I do not keep a full tank in this truck since I do not drive it that often. Not my daily driver. Only use it some weekends.

Can this possibly be because I only keep around 1/4 of a tank in there?

What about the fuel injectors or do they have they own code if they go bad?

 

While the parts were being replaced, did you disconnect the battery B- cable to erase the codes & wipe the corrupt KAM fuel trim tables, so the computer can begin to rebuild new tables with the new parts in place????
Get the KOEO & KOER fuel pressure tested & post the numbers. Low fuel pressure can cause the injectors to give a lean squirt.
If all is ok & you still have lean codes, look to/test other things that affect fuel trim, like a dirty MAF sensor, especially if your using an oiled foam, or cotton gauze type air filter. Intake manifold gasket leaks are common on this vintage & with the miles on it, should be tested, or maybe check/tighten the manifold fasters to the specified sequence & torque.
Also with the mileage on this puppy, look to lazy/slow, narrow voltage range switching, O2 sensors.
Air intake temp sensor also belongs on the suspect list for testing.

 

No, I did not. Only cleared them using the reader. So that means basically it was not taking into account the work I did prior to my ride last night?

How long do I need to have it disconnected? There is a cap that holds the memory as I recall.

Watched a video on testing fuel pressure and I know where that valve is on the manifold. AutoZone has one for loan. Will see about getting it tonight after work.

I removed and cleaned the MAF early on in this code quest so that should be fine.

Yes, lots to do. Let me get the pressure readings, first.

Thanks!!

 

Keep plugging away at it because with this many miles & as you've found, you could have more than one thing messing with fuel trim.

 

On the scanner it says "Catalyst Inc". All other I/M Monitors are showing "OK"

I pulled apart all three connectors to these sensors and cleaned them. Much green corrosion on each. Did this three times. Coated with Caig spray. I checked fuse #20 (power to the 02 sensors) under the hood. OK. Then checked the voltage to the P0136 sensor. OK. Then checked the resistance of the heater in that sensor and it was OK.

Another drive and still the codes came back.

I rented a fuel pressure tester. Got a steady 28 to 30 PSI at idle and when giving it the gas. Around 20 PSI just with key on.

I removed all the spark plugs. Gaps were wide and some electrodes short. Installed new Motorcraft SP-500 Finewire Platinums gapped at .044. Dielectric grease on the porcelain and anti seize on the threads. Took it for a ride last night and with in 10 miles the three codes were back.

This Actron CP9575 I have is both a code reader and a live data monitor but I'm not sure what I'm looking for. Can anyone advise how this unit can help me pin point my problem?

 

That KOEO fuel pressure reading is low, it should be 35-45 psi.

 

Will test again this afternoon as the gas in the tank last night when I did the check was below E but would 5 points make the truck run lean enough to cause these three codes?

Where do I check for low pressure? The fuel filter is new as of June.

 

Check fuel pressure at the fuel rail Schrader valve test port. it should be
KOEO = 35-45 psi
KOER with the fuel pressure regulator vacuum line Connected = 25-35 psi
KOER with the fpr vacuum line Disconnected = 35-45 psi
Let us know what you find.

 

Once you get the fuel pressure sorted out, have the scantool look at the long & short term fuel trim, MAF & AIT sensors & both upstream O2 sensor readings & post the numbers.
After you replaced the spark plugs & other things, did you ever do a battery disconnect to wipe the corrupt KAM fuel trim tables???
Which codes have been returning after a drive???

 

KOER with the fuel pressure regulator vacuum line Connected = 25-35 psi
KOER with the fpr vacuum line Disconnected = 35-45 psi

Where do I find this vacuum line?

The codes I get are P0136, P1131 and P1151

I use the erase button to clear the codes. Actron (the scanner maker) says this will erase the memory in the PCM. Are you saying it does not?