[Ravy96]

My RAV4's long term fuel trim is running at -24.2%, until I start driving. When driving throttle fully depressed it will go about -2.7% no matter what speed. But doesn't move anywhere from these points. Short term fuel trim looks normal. Some instances it's between -15% to 15% but never extreme.

 

[Bigphil555]

LTFT is a learned value that has the purpose of keeping the STFT as close to zero as possible.

With that level of negative fuel trim, I would look at a defective fuel regulator diaphragm for example

Have a look at this article Gears Magazine | Put Fuel Trim to Work for You

It makes it a little clearer

Hope this helps

 

[Ravy96]

I feel like it's more likely my injectors leaking. I'm not experiencing any misfires or anything. But I'm gonna look into it all. Possibly get my injectors flow tested.

 

[Bigphil555]

Certainly worth checking, it just seems as if the amount of neg fuel trim is very high, even at WOT you are still rich - it feels, but it is just a guess, that it is more than just injectors leaking. They may be commanded on permanently if there is a fault somewhere

Just my thoughts

 

[Ravy96]

So I read the regulator is in the gas tank itself, is this true? Is it easy to get to?

 

[BMR]

It’s not too bad. Access is thru the floor, under the rear seat. Beats dropping the fuel tank!

YT video:

 

[Ravy96]

I pulled the harness on the jump from the rear to do a compression test in the past, so I know where it is. Just seeing if that regulator is easily accessible. Haha

 

[Elle_Rav4]

Ditto what BMR said.

For what it's worth, the in-tank fuel pressure regulator is circled in purple in the photo below:

Fuel Pressure Regulator part number is 23280-74160.

I do not think I have seen a report of the fuel pressure regulator failing on a Rav4.1. But I can certainly understand your suspicion that it could be the cause of the negative LTFT.

While you have the fuel pump "bracket" out, replace the two filters. Both are in the purple boxes in the photo above. Part numbers:

-- sock strainer at pump suction, p/n 23217-74021

-- as part of the recirc system for the fuel pressure regulator, OEM p/n 23300-79535. Aftermarket by Baldwin BF7625. Two o-rings should come with this fuel filter.

Purchase a set of copper gaskets for the fuel pump assembly's banjo bolt. You will need two copper gaskets, 16mm OD x 12mm ID (give or take). Required torque on the banjo bolt is 21 ft-lbs.

For the negative LTFT, also try cleaning the MAP sensor.

Sea foam the injectors?

 

[Bigphil555]

@Elle_Rav4, I have had a regulator go bad, but as you say, not on our Rav I am glad to say. Same symptoms with full negative LTFT, but cured after a new part was fitted.

I have never used sea foam at all, what is your view/experience with it to clean stuff out?

 

[Elle_Rav4]

-- Bigphil555, your 2010 Rav4 is quite a bit younger than what folks here in the first generation (1996-2000) Rav4 forum have. But I appreciate your report.

-- I have not used Sea Foam on any vehicle. All I have is hearsay: here in the first generation Rav4 forum, many recommend it.

-- Per the attachment, page 6, the fuel pressure at the engine bay's fuel filter outlet is supposed to be 44-50 psi. From some eBay rav4.1 fuel pump specs, it appears the fuel pump is supposed to put out a minimum pressure of about 130 psi and a max pressure of about 160 psi. If the in-tank regulator fails, then I think all here can imagine the problems with LTFT.

-- From another thread of Ravy96, I see new spark plugs, distributor, cap, rotor, wires, and coil were all recently replaced.

-- Ravy96, how old is your Rav's front oxygen sensor? Is it an aftermarket oxygen sensor? Is your Rav4 spec'd for California emissions? A bad oxygen sensor does not always throw a code.

-- I would be a little concerned about what this rich fuel mixture is doing to the catalytic converter. I am not expert in this. I am just aware that unburned fuel entering the cat is a leading cause of failed cats.

Edit:
I wish someone would dremel open a Rav4.1 fuel pressure regulator and report especially on the diaphragm. Is the diaphragm rubber or metal? Also, if the fuel filter that connects directly to the regulator is dirty and clogged, could this cause a high outlet pressure?

 

[Bigphil555]

@Elle_Rav4 , thank you for the reply on seafoam, certainly was interested to note.

With those internal pressures, it is easy to see why, even at WOT, it is running rich. Once the reg issue is sorted, I would also check the whole fuel route and injectors to see if there is any residual leaking due to over pressure.

Certainly plus 1 for your Cat comment, that amount of fuel could easily do for the Cat.

 

[Ravy96]

At WOT my ltft drops significantly. I'm sure the front O2 sensor is the original. Looks pretty white. Spark plugs look fine too. Idk how to test the fuel pressure since there's no Schrader valve. My hood says it's not for California emmisions.

 

[Ravy96]

Is this pointing to the regulator??

 

[Bigphil555]

The O2's are reacting, that is for certain - whether or not they are lazy or not is difficult to tell until the large neg trim is sorted.

The thought process is that at WOT you are effectively creating an enormous air leak by opening the throttle body - and I mean enormous, and yet you are still rich. bear in mind, going the other way, a small tear in say the intake boot, which is much smaller than the throttle body, can lean you out fully.

Please bear in mind, I could easily be wrong as it is difficult to diagnose remotely, but with that amount of neg trim even at WOT, something is over fuelling and being corrected by the ECM.

It is possible that this symptom could be masking other issues, so you will need to verify the repair after addressing this, and you need to be aware you may have to correct other issues as they show up (just a heads up for you) eg permanently commanded on injectors for example, O2 misreads maybe another.

Again, these are just my thoughts

 

[Ravy96]

How do I test the fuel pressure psi? Because I'm starting to think that the regulator has failed and the pump is just sending too much fuel to the injectors.

 

[Bigphil555]

I am sorry, I do not know the architecture of the fuel delivery system on your Rav. You would need to insert a fuel pressure gauge in the system, then prime the fuel pump. Maybe a shop could do that for you if you do not have the kit. However, basic kits cost around £16 from fleebay here in the UK, I am sure they are similar with you over the pond. If you are into car diag/maintenance, they are a useful tool to have.

@Elle_Rav4 would you know at all?

 

[Elle_Rav4]

-- Ravy96, did you take the three readings above after the engine reached normal operating temperature? Was each reading taken for at least 30 seconds?

-- In the service manual section 1996Rav4SFI.pdf, on pages 5 and 6, are instructions for where to mount a pressure gauge. In short, the manual says to install the gauge at the outlet of the engine bay fuel filter. But this is a lot of trouble for a lot of folks, and I would not do this just yet. Plus I might get myself to a salvage yard and buy a second-hand fuel pressure regulator there, then swap it with the one currently in my Rav. For me, this would be easier than hooking up a pressure gauge. And I would replace the in-tank return line filter, as indicated above.

-- Does your CEL in the instrument cluster light with the key in the "On" position but engine off?

-- The attached 1996Rav4diag.pdf says on page 48, when the sum of {LTFT and STFT} is outside +/- 25%, then the CEL should light. The readings above are -24.2, -22.6, and -5.5. Assuming Rav96 took the readings correctly, these readings show Ravy96's vehicle's WOT fuel trim is getting close to being out of spec.

-- I am reading the diagnostics manual on pages 48 and 49. I am going from experience with the named causes on these pages for out-of-spec fuel trim. Ravy96 recently changed the plugs and wires. I would do three things as follows:

-- Check the resistance of the ECT sensor, using the resistance information at "Starting and Running Problems" at Elle's 1996-00 Toyota Rav4 Site. This should take like three minutes at cold engine, and another three minutes at hot engine (engine off). Do inspect the wiring harness to the ECT sensor too. This forum has seen a few reports of a bad ECT sensor.

-- I would also replace the front oxygen sensor. Use only a Denso front oxygen sensor. Any other manufacturer is a bit (or a lot) of a roll of the dice. For anyone saying, "Don't just throw parts at the problem": I disagree to some extent. For vehicles this old, I support a reasonable shotgun approach. Because a lot of these parts are aged; are about due anyway for replacement; and I think there is a benefit to having some confidence that these parts are not interfering with diagnosing.

-- Clean the MAP sensor. Use only MAP sensor cleaner or Mass Air Flow sensor cleaner. Google and you will find youtube and other sites that explain how. Once you have the cleaner in hand, this is pretty easy to do.

 

[Ravy96]

I see that that Manual shows how to do test at the fuel filter. That's very helpful! Thanks!

-- Ravy96, did you take the three readings above after the engine reached normal operating temperature? Was each reading taken for at least 30 seconds?

-- In the service manual section 1996Rav4SFI.pdf, on pages 5 and 6, are instructions for where to mount a pressure gauge. In short, the manual says to install the gauge at the outlet of the engine bay fuel filter. But this is a lot of trouble for a lot of folks, and I would not do this just yet. Plus I might get myself to a salvage yard and buy a second-hand fuel pressure regulator there, then swap it with the one currently in my Rav. For me, this would be easier than hooking up a pressure gauge. And I would replace the in-tank return line filter, as indicated above.

-- Does your CEL in the instrument cluster light with the key in the "On" position but engine off?

-- The attached 1996Rav4diag.pdf says on page 48, when the sum of {LTFT and STFT} is outside +/- 25%, then the CEL should light. The readings above are -24.2, -22.6, and -5.5. Assuming Rav96 took the readings correctly, these readings show Ravy96's vehicle's WOT fuel trim is getting close to being out of spec.

-- I am reading the diagnostics manual on pages 48 and 49. I am going from experience with the named causes on these pages for out-of-spec fuel trim. Ravy96 recently changed the plugs and wires. I would do three things as follows:

-- Check the resistance of the ECT sensor, using the resistance information at "Starting and Running Problems" at Elle's 1996-00 Toyota Rav4 Site. This should take like three minutes at cold engine, and another three minutes at hot engine (engine off). Do inspect the wiring harness to the ECT sensor too. This forum has seen a few reports of a bad ECT sensor.

-- I would also replace the front oxygen sensor. Use only a Denso front oxygen sensor. Any other manufacturer is a bit (or a lot) of a roll of the dice. For anyone saying, "Don't just throw parts at the problem": I disagree to some extent. For vehicles this old, I support a reasonable shotgun approach. Because a lot of these parts are aged; are about due anyway for replacement; and I think there is a benefit to having some confidence that these parts are not interfering with diagnosing.

-- Clean the MAP sensor. Use only MAP sensor cleaner or Mass Air Flow sensor cleaner. Google and you will find youtube and other sites that explain how. Once you have the cleaner in hand, this is pretty easy to do.

So my ECT sensor is new. My check engine light does come on when the key is in the on position, but not when the engine is started. My readers say no codes and none are pending either. I feel like it would be easier to test the fuel pressure versus pulling out the fuel pump because testing the fuel pressure can also point to other causes of my problem as well, no? My oxygen sensor is pretty white, so I know it was running too lean or hot for awhile before this. I can clean my map sensor, however I did have a Check engine light for it awhile back and replaced it with a junkyard one.

 

[Elle_Rav4]

-- Ravy96: You're right. Measuring the fuel pressure will instantly tell you whether either the fuel pump, regulator, or filter needs checking, and this is the info you really want. Go for it.

-- I would test the ECT sensor's resistance anyway. Some aftermarket parts turn out to be bad even when brand new.

-- If the fuel pressure reading is fine, then to me, this leaves the upstream (that is, front) oxygen sensor. I do not like upstream oxygen sensors that are old. To me, the LTFT and STFT readings you are seeing may very well be a sign of an old oxygen sensor. I would replace it. Figure $50 for a new Denso one. Denso p/n 234-2058 (OEM identical) or Denso p/n 234-2050 (universal; will require wire splicing, which is not a big deal for the experienced do-it-yourselfer; costs about half the price of an OEM identically-wired sensor). If you buy from eBay, make sure the seller guarantees it is really a Denso. The net has lots of reports on O2 sensors in particular being advertised as Denso, and then the sensor turns out to be not a Denso. This happened to me once.

 

[Bigphil555]

Plus 1 for the comment by @Elle_Rav4 on the aftermarket parts - I have been caught out a couple of times, even tho I was looking out for it.

You are going down the right path - your Rav will be on top form soon