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Correct o2 sensor? And fuel regulator release tool?


beerhunter

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Hi

I need to change the o2 sensor and fuel pressure regulator on my 1990 2.9.

As far as I'm aware, there is only one o2 sensor, and that screws in to the y section of the exhaust. Is the following the correct one? I ask because Rock Auto describes it as an upstream sensor, but by their own diagram, I need a downstream sensor.

https://www.rockauto.com/en/moreinfo.php?pk=279849&cc=1137697&jsn=20

Also, there appears to be 3-wire and 4-wire alternatives. My truck currently has a 4-wire one fitted, but I have no faith in the previous owner having fitted correct parts. How can I tell which is the one I should be using? Do they have very different connector (i.e. is it even possible for the wrong one be connected)? Or do I need to count the number of wires that go to the receiving side of the connector?

Lastly, it seems a special tool is needed to release the black plastic coupling on the pressure regulator. Do the red-handled ones look right? The seller claims it suits petrol Fords:

https://www.ebay.co.uk/itm/3pc-CAR-FUEL-LINE-DISCONNECTION-PLIER-SET-PETROL-DIESEL-PIPE-REMOVAL-TOOLS/361336355534?hash=item5421533ace:g:kyEAAOxyLNpSHKcc

Thanks for your help. As stated, the previous owner was somewhat reckless regarding maintainance, so I'm having to double-check anything they have or may have touched.
 


adsm08

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When only one sensor is used it is the upstream. The dividing line for that determination is the catalytic converter. If it is between the engine and the cat it is an upstream sensor, if it is after the car it is downstream. The 2.9 never had downstream O2s.

That connector is fairly universal, and a 3 or 4 wire sensor should work correctly, as long as it plugs in. The difference in the 3 or 4 wire sensors is where the circuit grounds. Two of the wires are the power and ground for a heater in the sensor, to get it up to an operational temperature as quickly as possible. Those two wires are constant on all 3 and 4 wire sensors.

The third wire is a signal hot line. The fourth, if used, is a signal ground. Oxygen sensors contain a piezoelectric crystal that creates low voltages in the absence of free molecular oxygen (O2). From the amount of voltage created the computer can make inferences about how to adjust the fuel mix (although since it looks at the results of a previous firing event it is kind of like trying to make corrections to your math homework after turning it in). But since you need two wires, a hot and ground, to look at voltage there has to be a ground. On a four wire sensor there is a dedicated wire running from the sensor back to the computer for that ground. On a three wire sensor that circuit will be grounded somewhere common, usually to the engine block or a cylinder head. On the 2.9 it would have been a ground strap on the back of the right hand head, an orange and black wire with a big eye on it.

If you put a 4-wire sensor where a 3 wire goes I believe it would still work correctly, as the sensor can still ground to the chassis through it's case, if no better path to ground is available, it just degrades the signal a bit. That was why most companies moved to 4-wire sensors, that dedicated ground gives a cleaner signal to the computer.


For fuel line disconnect tools, just get this set:
https://www.ebay.co.uk/itm/LISLE-OF-USA-Air-Conditioning-Fuel-line-Disconnect-Tool-Set-L3700-37000/172445315160?epid=1522857513&hash=item28268ab058:g:WIQAAOSw44BYUXFj

Your supply and return lines are different sizes, so don't trust just one tool to handle both.
 

beerhunter

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Many thanks. The level of knowledge on this forum is awesome! I'd been out to the truck to count the number of wires on the receiver side (4) before I saw your reply, but happy to know I'll be good to go either way.

And thanks for the pointer re the disconnectors.
 

adsm08

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Yeah, if you have a 4-pin plug on the harness it is important to get a 4-pin sensor. I believe that you can put a 4-pin in place of a 3-pin, but I know you can't do it the other way around.
 

beerhunter

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Thanks - got 'em both ordered.

My fuel pressure regulator is leaking all over the rocker cover, hence wanting a new one. I'm also getting fuel in the oil, as it (a) stinks of fuel, and (b) the oil level has risen slightly. I had read that a defective pressure regulator can allow fuel up the vacuum line, and then in to the manifold and down in to the sump.

I had therefore suspected my defective regulator was the cause, but just now I ran the truck and disconnected the vacuum hose, expecting to see fuel coming out. However, nothing did. Are there any other usual suspects for fuel getting in to the oil? Or will it only happen when the vacuum line is connected (which seems counter-intuitive)?

The truck is lacking power and running very rich, and again I thought a dodgy regulator starving the injectors and dumping excess fuel in to the manifold via the vacuum line would be a contributing factor/the cause.
 
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