2006 Ranger 4.0 SOHC Lean problem - likely vacuum leak - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 10-18-2013
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2006 Ranger 4.0 SOHC Lean problem - likely vacuum leak

Hey everyone.. Its been a few years. I'm back in the Ranger game.

I'm posting this from FRF, I posted there first because I thought the 4.0 section looked to be more active, but haven't gotten a response yet.

I just bought a 2006 FX4 Level 2 with 83k miles. I got it cheap, because it is running rough and is down on power.


I cleaned the mass air sensor with CRC MAF cleaner.

I have had a few codes come out of it, P0171 and P0174. I've done plenty of research and reading, in order to check out the common issues. I've read this thread.
If you have an 01+ 4.0 with lean codes (PO171 and/or PO174) look here! - Ford Ranger Forum

The PCV hose and elbows are all good. I did replace the PCV which did make a big difference, but it still running lean.

I have AutoEnginuity and the Ford package, so I scanned the Ranger, looking at the LongFT1/2 fuel trim PID's, as mentioned here.
Adaptive Fuel DTCs Diagnostic Techniques (P0171/P0174) - Ford Ranger Forum
(Really great write up)

Here is a screenshot of the values



So next up, I checked fuel pressure. Fuel pressure is excellent.. it idles at 65PSI, and when I turned the truck off, fuel pressure had only dropped to 60PSI after 20 seconds. The fuel filter has been changed.

So next up, I monitored those same fuel trim PIDs, and drove the truck down the road. With any amount of throttle, the fuel trims go down, closer to 0.
I'm not sure how well this chart will show up, otherwise I can post up the excel sheet.


The truck had an intake on it off of an older Ranger or explorer, with the different style MAF sensor, and likely leaked around the MAF. I replaced that with a Volant intake, to eliminate any vacuum leak due to the MAF not being sealed in the intake. Truck runs a little better but is still nowhere near as peppy or powerful as my old 01 4.0 was. I also picked up a new Motorcraft MAF sensor for $20 off ebay, and installed it. No difference.

Does anyone have any ideas? I guess I'm going to go around it with a can of ether and see if I can locate a vacuum leak, but that's my only idea besides throwing all new top end gaskets at it.
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2006 Ranger 4.0 SOHC Lean problem - likely vacuum leak-10320149305_f915b55ba5_b.jpg   2006 Ranger 4.0 SOHC Lean problem - likely vacuum leak-10319888253_41451d8499_o.jpg   2006 Ranger 4.0 SOHC Lean problem - likely vacuum leak-10319705354_06280afb40_o.jpg   2006 Ranger 4.0 SOHC Lean problem - likely vacuum leak-10320066276_e04a9ac650_o.jpg  
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Old 10-18-2013
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You haven't mentioned anything about the O2 sensors. They may not be the problem but they should be the sensors that are sending information that results in the computer throwing a code of being too lean. There is a method of testing the O2 sensors but I don't recall off hand how to do it.

That is kind of low mileage for an O2 sensor to go out but stranger things happen. I would not go out an just replace them but testing them couldn't hurt.

A friend was having a hard time passing emissions with his vehicle because it was throwing codes. He was told the catalytic converter needed to be replaced. I went to Pep Boys with him to see if we could find an additive that I was told about to help pass emissions. We found a product that I think was made by Mr Gasket that is used to clean the catalytic converter and O2 sensors along with a few other items.

He followed the instructions on the product and took it in for the smog test. It passed so clean we could not believe it. He said the vehicle ran better too. I don't know what it did but it worked.
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Old 10-18-2013
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I was also thinking clogged cats.
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Old 10-20-2013
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Thanks guys. I cleared the memory after installing the intake. I drove it 20 miles round trip Friday night. After around 15 miles, I started to get a little rough on it, to see what kind of power it had. It popped a new CEL.

P0420 - Catalyst system inefficiency below threshold, Bank 1.

It does sound like it could be a converter, especially now that this code is added to the puzzle.

Would a bad converter make it have some white, very fumy smelling smoke?

I am going to change all fluids and then watch the oil and coolant to make sure that it isn't using any coolant.
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Old 10-21-2013
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White funny smelling smoke is a good indicator of coolant (anti-freeze) in the exhaust.
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Old 10-25-2013
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Yup. I haven't noticed the truck smoking above what an average vehicle smokes/steams on a 40* day. I changed the oil and marked the coolant res, and I will frequently check the levels of both. So far after 100 miles of driving, there has been no change.
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Old 11-13-2013
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I would say vac leak cause you had the lean on both banks and the longterm fuel trim is a +25 when it should be between -4 to 3 if you can you should log the short term fuel trim
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Old 11-25-2013
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I think it seems like a tired fuel pump to me somehow. I have a A/F gauge, and I had the same thing happen to me.

I changed the fuel pump to 255lph, it fixed it.

My guess is a tired fuel pump. I know it does hold 65psi at idle, but it did that on mine also. It just didn't flow enough at the top end as it was tired.
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Old 12-03-2013
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inside the fuel tank, there is a pre-filter attached to the fuel pump intake tube
ethanol and chemicals degrade that little plastic filter quickly , and it dis-integrates
sometimes partially clogging the fuel pump intake tube

also the newer style fuel pumps at gas stations no longer utilize fuel filters before the fuel reaches the fuel pump nozzle, allowing debris to be pumped into your truck`s fuel tank
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