[BlakeCo]

2005 Toyota Rav4
2.4 L
Automatic
182k miles

Bought the car at 55k miles. Used to get great fuel economy, but it's been poor for several years. Last two tanks have been 20 and 21mpg. Mixed city highway driving.
I've been playing with a simply OBD II scanner. Here's what I understand.
The long term fuel trims are high indicating a lean condition

Notable maintenance:

• New denso plugs and coils around 160k miles
• Cleaned MAF sensor and Throttle body last week, though I did not remove the TB for a proper cleaning, but I did at 150k miles. Not sure if I've ever cleaned IACV properly.
• Ran Seafoam in gas tank two tanks ago
• Very regular oil changes, burns no oil
• Original Cats

Symptoms:

• I've seen Long term fuel trims as high at 25% while cruising at 40 MPH, but is usually around 15%. Short Term always seems pretty low.
• I noticed that under WOT the Throttle position only read 80% open and load only at like 66%. I was going about 15mpg when and then floored it.
• Poor fuel economy
• Also, I still occasionally encounter the low speed surge in stop and go traffic.
• Very smooth idle otherwise
• No check engine lights or codes

I have data at Idle and 2500 RPM, and a Wide open throttle road test below

WOT: 2005 Rav4 OBII scanner WOT

Any ideas what I should be testing to trying next?

IDLE

IDLE O2B1S1 and S2 (V) Graphs:

2500 RPM

2500 RPM O2B1S1 and S2 (v) Graphs

 

[Bigphil555]

At idle, you have almost perfect FT's - you most certainly do not have a vacuum leak. I think you may have a fuel delivery issue though, as the ECU is adding fuel in LT trim. Even with that the O2's are not maxing out at WOT

The FT's at WOT seem pretty good tho, so maybe it is the fuel pump on the way out - can you test fuel PSI at all?

 

[BlakeCo]

Thanks for the feedback! I don't have the equipment to do that, but have a good shop if I end up going that route. Given that info though, I may try to run some more fuel cleaner...

 

[Bigphil555]

it can not do any harm IMHO - let us know what happens after running the treatment through

 

[BlakeCo]

Just an update - I was grabbing some Redline at the auto parts store and thought it would prudent to check my battery and alternator. They said the voltage regulator was bad, so I'll be addressing that next to see if that helps!

Also, I noticed that in WOT it goes to Open Loop, which is probably why the fuel trims drop back down. Under any acceleration, long term fuel trim maxes out to 25%.

 

[Bigphil555]

Bad battery or alternator will play havoc with the electrical systems in our Ravs.

The update on the FT is good, and it is leaning towards a fuel delivery issue rather than an air flow issue - keep us updated

 

[BlakeCo]

Hey Phil, would you mind reviewing my voltage outputs before I replace the Alternator? Just want to make sure it's bad before I replace it...
My multimeter would only go to 12V for a "Battery Test"

Battery output, vehicle off: 12.5 volts
Turned car on: 13.5 volts at first. After a few minutes it was 12.5 steady.
I followed a guide to test for a leaking diode. Changed to AC, connected to negative battery terminal and alternator output. Car running: .450 volts to .550 volts. Always changing.

 

[Bigphil555]

12.5 is a good state of charge, but as you say what happens after it fires up.

13.5 after start seems to be low to me - anything above 14.1 should be good. Now this is where we need to be careful. On our Rav, we do not have an intelligent charging system, so it is always north of 14.1. Do you know what system yours has? If it is not the intelligent system, then 12.5 is low.

WRT the AC - I do not know the specs for it. I would suggest you take it to a shop and ask them to check the state of the battery, also how much CCA (cold cranking amps) it delivers, and then also, the state of the regulator (you are looking for ripple and/or noise). I use a TopDon device that does that for me, so I am sure a decent shop would have the same.

I can not give any more details than that, but I hope it helps you some how

 

[BlakeCo]

Thank you! I'm taking it to my shop tomorrow. I'm stepping too far out of my basic mechanical knowledge...
I spoke with the mechanic and he asked me what symptoms I was having with the alternator and I explained all the long term fuel trims. He was pretty surprised lol. Agreed it's usually fuel delivery but said you definitely have to get the electronics right before moving on to anything else.
That's the thing, it's been super reliable so I'm a bit skeptical it's the alternator. But who knows, I have no idea if a different shop used OEM when it was replaced like 6 years ago.

 

[Bigphil555]

Please let us know how you get one

 

[BlakeCo]

Looks like I'm in the market for a new battery. Shop says that it's weak. Alternator testing fine.
They drove it and did a smoke test for vacuum leaks, didn't find anything else wrong with it.
They also didn't even charge me. Maybe because I toldt the shop owner that he left his headlights on

I'll report back after more testing...

 

[BlakeCo]

Update: I'm no longer seeing any 25% LTFT's!

2500 RPM LTFT's have improved as well from 15% previously to 5.5% LTFT (plus 3.9 STFT).

But, I'm still seeing the same 15% LTFT while accelerating or under load. ECU is clearly still recalibrating though. And fuel cleaner still working its way through. I'll post a real update after a tank or two of gas.

 

[Bigphil555]

That is good news, if the ECU is relearning, you have made a good step forward - keep us posted.

Anything less that a combined 10% is good BTW