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Discussion Starter #1
Ok.

So I’m working on a 1998 Avalon XL California emissions car 141000 miles

Admittedly and embarrassing since August 2019

I purchased it requiring work. It was left torn apart by an unscrupulous mobile mechanic. So I got an ok deal. 🤦🏼‍♂️

I reassembled it. And Bought it. The car was neglected suspension wise and replaced all 4 loaded struts “lost considerable ride” (bummer) new plugs checked wires and all good new intake gasket and related to accomplish it.

Developed a P0171 that has been a persistent b. Replaced the throttle body gasket. “After smoking the intake” and it improved but didn’t stop the P0171. So there’s that.

The flex pipe was bad so I replaced the mid pipe and converters as well.

Had an EGR code “I do not remember exactly” but replaced the triangle shaped sensor on top of it and have had no further code for EGR.

Being i had a P0171 and didn’t have the correct adapter to check fuel pressure I replaced the fuel pump to be certain. Also replaced fuel filter same time. No change.

In the meantime it started sucking fuel as hard as my 1996 K1500 z71. >250 miles a tank.

Fuel trims crazy all over the place. 52% both bank 1&2 for long term on highway with engine at operating temp.

Replaced MAF with a known good used “took from good running car and tried it” no change. Swapped back. Also purchased one and installed “no change”

Today replaced both bank 1 and bank 2 A/F sensors. Bank 1 looked typical. Bank 2 was carboned or oil crap on it.

I believe the extra soot was my fault I purchased an oreilly pcv and drove home 225 miles and now know how finicky the pcv valves for these v6 are. It did use oil on the ride home and still does randomly and not at all consistent sometimes a week little or no loss other times seems tank and half a quart.

I am getting familiar with this Toyota v6 and relearned why I tried to avoid them in the past. But, hopeful I can figure it out and not lose my tail on this.

The P1153 and P1133 came on tonight during the initial drive. The car has declined. It is not idling as well. It is not accelerating as it was even prior to the new AF sensors.

At this point I’m hoping for a hint towards as solution.

I have over 25 years as a car builder “buy and fix others problems” and try to sell or drive a while.

The AF sensors I used are denso 234-9007 and 234-9009

I’ve been forum bouncing and read for hours and have seen similar issues and no real fixes mentioned.

If I am able to get this straightened out I will post the fix.
 

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Discussion Starter #2
I have to add that the fuel trim issue is also not consistent. Sometimes it is ok and then starts acting wonky slight misses and that seems to continue regardless of acceleration, constant speed, or deceleration.

The miss is able to be felt but it does not register in codes.

The gas cap has also been replaced. Two nights ago I installed a stant 10595 “I believe without double checking” from oreilly auto.

I had a P0136 code come up shortly after the AF sensors were replaced as well.

I do not know if the downstream is part of the issue and I have not had the P0420 at all so I hoped that sensor would clean off possibly.
 

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Glad to hear you used Denso sensors. I double checked for ya, and those are the correct p/n’s. Where did you buy them? There are counterfeits online, particularly on eBay and even Amazon. If they were substantially cheaper than $90, they likely are.
 

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Discussion Starter #4
I was suspicious about that being a possibility. But hopeful.

They did come from fleabay. And we’re priced reasonable.

So unfortunately it would appear that could certainly be an issue. But, I’m certain not the only one.

Any chance you or others have any experience with potentially a leaking lower intake gasket?
I’ve read that can contribute to the P0171?
 

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You said you replaced the pcv, which means you either removed the plenum, or just finagled your fingers back there. Did you check the hose from said PCV to plenum? It sits in what is basically a small oven, and will often cook and crack causing vacuum issues. Also, have you bothered cleaning the throttle body? These are notoriously filthy motors due to the poorly designed baffle system on the valve covers, which would clog very quickly and cause massive amounts of sludge buildup. It also managed to let lots of oil from the crank case breather hose into the intake, which would cake the entire intake system with a very thick layer of build up. There is also an ACIS which can become stuck, though somewhat less likely. Might be worth it to check the vacuum lines from the ACIS, and make sure the actuator is operating fine.

Sent from my SM-G950U using Tapatalk
 

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Discussion Starter #6
Yes I replaced the pcv. Now factory part. Line/hose also replaced. Went long to see if possibly dumping oil into the intake. Only residue so far.

Throttle body has been off two times and cleaned.

However my second time replacing the throttle body gasket I did have what looked like a bunch of something that was entering the throttle body “looked oily dark greasy stuff” thru the AIC. That gets its air supply from two lines that attach to the lower portion of the plenum and come together at a plastic box and attached to the aic valve.

Not familiar with ACIS at least the acronym. I will look it up and see what I come up with.

I am now “after updating my scanner” showing very high numbers on the bank 1 sensor two 99.xx%

I have however never had anything for a code on sensor 2. The downstream oxygen sensor. My understanding with the many hours of forum reading is that sensor is more or less to read if the catylatic system is functioning. No P0420 in my time owning.

If I’m incorrect on that please advise.

Thanks so far for the direction and ideas.

Bank 1 still shows acceptable numbers 3-8% “except I have a pending P0171” which doesn’t make sense. “Possibly lower intake gasket failing?”

Bank 2 still currently showing 19.49 give or take the decimal numbers as a typical trim for short term

Long term is pushing 53% which is problematic.

I wonder if the possibility of the intake gasket failing could allow the greasy gunk to be making it to the throttle body AIC area.?
 

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Discussion Starter #7
Ok. ACIS shouldn’t be the issue. After reading I can safely say I have never attempted WOT or even close. If there is something else that could activate that and then it could be an issue.

The engine did have a minimal amount of sludge when I acquired it. But it wasn’t much.

The valve covers were cleaned up and reinstalled.

I have only probably 2,000 miles since purchased and am not driving regularly due to ridiculous fuel sucking currently.

Avoiding highway completely until I get the trims under control.
 

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Discussion Starter #9
The oil pan was also removed and cleaned out. The pickup tube also removed cleaned and reinstalled to be certain sludge wouldn’t kill it.
 

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I have however never had anything for a code on sensor 2. The downstream oxygen sensor. My understanding with the many hours of forum reading is that sensor is more or less to read if the catylatic system is functioning. No P0420 in my time owning.

If I’m incorrect on that please advise.
You are correct about that. From what you’re saying about the fuel trims, I suspect counterfeit O2 sensors are the problem.
 

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To some degree, it’s normal for greasy gunk to be pushed thru those tubes. This is blowby gases passing by the rings and down into the crankcase. That gas then passes up into the valve train area and into the intake to burn. Ages ago, engines just vented this gas into the air. So it’s a pollution control thing. One downside is that this gas carries oil with it, which eventually gums up the intake. Some folks build a “catch can” with some steel wool in it, and route the gas thru it prior to dumping it into the intake.

Now, if your motor has excessive blowby because the rings and/or cylinders are worn out, that’s another story. The only way to fix that is an engine rebuild.
 

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Discussion Starter #13
The gasses your mentioning are the pcv and breather lines tho. Correct?

Blowby should be fed into the intake breather prior to the throttle body or AIC. “from the bank 2 valve cover” Or thru the PCV valve “bank 1 also located in the valve cover” line that attaches to the lower rear of the upper plenum.

The area on the bottom of the throttle body/plenum is where the oily gunk was deposited when it passed thru the aic. Nothing on or in the intake tube and there is carbon/oily residue inside the intake as most all have. Nothing too much tho. Residue only.

If it has continued I will add pics of what I’m seeing.

The lines appear to be going towards the injectors “inside the lower plenum” but looking at pics of the bottom of the intake I couldn’t see where it comes from other than that.

If it does also get its air from the upper part of this motor... it’s definitely a design flaw besides putting a 60 degree V6 in turned 30 degrees or so. With one set vertical and the other like a Subaru H engine.

Thanks so far for the suggestions. I was able to get my scanner updated so I’ll be able to actually view the live data and share if anything is looking bad. Will attempt to reinstall the old sensors tomorrow.
 

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The gasses your mentioning are the pcv and breather lines tho. Correct?
Correct. I'll take your word for where these gases are fed back into the intake. It's been a while since I looked at that on mine.

Just remembered... these hoses are for the "air assisted" injectors. Air should be going into the intake manifold thru these hoses, not out of them.
 

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Discussion Starter #15
Oh my. Sorry for the lack of vocabulary.

The only thing I know about this is that the box has a hose that attaches to the aic. So maybe wrong since before my ownership?

I purchased it torn apart so I guess anything is possible. I have service manuals and will have to start going over it hose by hose for the exposed to verify.

I have a fuel related question I haven’t seen but will recheck and post in the appropriate place.

Thanks again.

If I happen upon a fix or additional info I will post it.
 

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If you need any help figuring out where hoses go, to or from, just ask. I can look at my '96 and tell ya how mine is, or post pics if necessary.
 

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Discussion Starter #17
Well it seems my problems are potentially worse then I had hoped.

This below is what the computer claims it caught as freeze frame data.

To me it appears the circuit is somehow faulty.

Or possibly computer is contributing to my problem.

Fyi for replies this was captured when the check engine lit on a highway at 65 mph up to full operating temperature, the ambient temp was about 35-38 degrees.

You can see the manufacturer of my scanner and it was updated this past weekend.

The additional issue is the new surging. Feels like fuel or something. It’s more consistent now that it’s back to the old sensors. But the same A/F sensor codes showing up.

I am going out now to verify the fuel pressure, I installed a banjo bolt with the schrader valve so I’m able to check the pressure with simple tools similar to gm.

Thank you again for the time and replies

The data is all the info available from my scanner. Many different that’s why so many photos. The update caused some things to be doubled in the readout not sure what that means.
 

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Also. My understanding is that freeze drama data is the capture of data that was present at the time of the check engine light being illuminated.

Again if that presumption is incorrect please advise
 

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I see coolant temp and intake air temp are both at -40 degrees!!! Any idea what's up with that?

Makes me wonder if the ECU is kaput?
 
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