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Too Lean ... Bad Regulator?


rangerpilot

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I have been getting a "too lean" MIL code on both banks and while I preemptively replaced the O2 sensors, that did not fix the issue. So, I dug into the problem and have eliminated a vacuum leak (checked with a pressure gauge ... stayed in green under all conditions except fast / high rev of throttle)

I check the fuel pressure and only get a constant 40 psi under all conditions. According to the Haynes manual for the 4.0 liter V6, the range should be between 56-72 psi.

Is the regulator the first step to investigate? I have a new fuel pump (less than two years old) however the regulator and sender unit (both in the tank) are original and are only sold as an assembly at AutoZone.

I really feel this is the problem but don't want to spend $200+ for a new assembly is there is something else I should try first.

Oh...replaced fuel filter ... no change in symptoms.

Thanks
 
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Rock Auto 5% Discount Code: F9A1A579ACFAD1: October 1st, 2021

rangerpilot

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I have researched this problem extensively for a week now and trust me I have gone through all the steps I just read via your link.

As mentioned ... Verified no vacuum leak and O2 sensors are new so next step is fuel delivery since the pressure reading is low.

What I am curious about is whether I have a bad pump or if the regulator may be the culprit. The pump is about $100 while the whole assembly (new pump regulator and sending unit) is $225

Just looking for others that may have had this experience before I buy a $225 (order only) part.


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TxGasRacer

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(39 - 40 PSI )(30 PSI @ idle OHV Engines) ( 64 - 75 PSI SOHC Engines) Also you do not have a fuel pressure regulator except for the one on the fuel pump assembly in your fuel tank,there is also a check valve on the fuel pump assembly,I think that you might be having a intake gasket problem even though you said there were No vacuum leaks I would go over everything again. The OHV v-6 has a lot of intake gaskets because of the fuel log they used in the design of the engine,there are gaskets on top of the lower intak and above the fuel log and then on top of the fuel log to upper intake and any one of these could be causing your problem.
 
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rangerpilot

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Oh. I didn't realize both type of engines were used during that time frame for the the 4.0 V6 but upon further research, I might have the OHV engine. I will have to look when I get home. If that is the case then my fuel pressure stays a solid 40psi would be in range ... However it never went down (not even at idle) ... It stayed a constant 40psi and even after shutting the truck off for 10 min it was still at 40psi

I was referencing a Haynes manual and it said all engines EXCEPT the 3.0 Flex were to have 56-72psi. It sounds as if this reference may be incorrect under the assumption they did not specify OHV vs SOHC.


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rangerpilot

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I used a vacuum gauge to verify leaks. Should I back this up with a smoke check? I have done the starter fluid check to see if I can get it to rev up with no success which would lead me to believe no leak (unless it is possible to have an internal vacuum leak?)


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rangerpilot

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What about the injectors?


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rangerpilot

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Ok...shop said it was in fact a vacuum leak from intake manifold. Can anyone tell me a spec on what the actual vacuum pressure should be?

I used a vacuum gauge I two different locations on the upper intake manifold and read a constant 25 in Hg off the brake booster line (+/- .5 in Hg).

I think it was a little lower when using a smaller plastic line from the intake (can't remember what it went two)

The shop is basing this off of electronic diagnostic and didn't even put a vacuum gauge to it. Sounds like they are basing it off it off of fuel trims only which we all know could be anything from fuel delivery to MAF to injectors, etc.

For the price they quoted me u can rent a car for a month and do the work myself and still come out ahead. The trick is only worth $2k ... No way am I letting a shop cost me $1700 to repair it.


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rangerpilot

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(39 - 40 PSI )(30 PSI @ idle OHV Engines) ( 64 - 75 PSI SOHC Engines)
As a closure to this thread. I have the OHV engine but it is a returnless system so the Haynes manual is correct that I should have between 56-72psi.

I swapped the whole assembly (pump, regulator, sending unit) for $250 and the emissions problem is gone. Fuel pressure went from 40psi to 59 and stayed there several minutes after shut off.

What a pain but I am glad I finally got it worked out and didn't pay a shop to do a repair that was not needed.
 

TxGasRacer

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Just so you know the info that I posted about the fuel pressure was taken straight from the Tech section of this website. Glad you got it fixed though.
 


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