raptor510

Hey guys!

I'm back at square one with a code 25 issue I've been chasing down for 2 months now. Originally the check engine light came on one day then went out a few minutes later and stayed off for 2 weeks. When it came back on I pulled the code again to make sure it was still 25 and it was so I tackled the obvious things first: I replaced the O2 sensor with an OEM Denso one and it made no difference. I replaced the distributor to rule it out and it made no difference. I also replaced the spark plug wires, cap and rotor and nothing made a difference.I checked for 2 hours for vacuum leaks and could not find any at all. I pulled the wires with the engine running and did find I had no difference in the engine sound/performance when I pulled the center wire on the passenger side so the cylinder was dead. I pulled the spark plug and it was bone dry and had no gas smell so I concluded the injector was clogged or dead. I bought a set from TeamYota and replaced all 6, reset the ECU and the code was gone! Unrelated however, I had a coolant hose on the TB over the knock sensor connector crack and dump about a half gallon of coolant all over the connector and basically fill up the intake valley shorting out the sensor, and got a code 52. I paid dearly at a shop to have them replace the knock sensor and the pigtail connector and the code 52 is now gone. They also put on some new gaskets and replaced some shoddy vacuum lines and some crusty coolant lines. They checked the timing and set it to 10 degrees as the FSM states. However, 6 miles after I left the shop the check engine light came on again with a code 25!!! I just spoke with the lead tech at my shop and he was stumped. He suggested I change the fuel filter and the VAFM, and maybe bring it back in the have a fuel pressure test run. At this point I am very low on funds and need to put my money into a solution rather than throwing parts at it and paying for blind diagnostics. Please help me out guys! I love my 4Runner and she runs great aside from this issue. I should state that since this started I have been horrible gas mileage, but I was told that is to be expected with this gas, as the ECU is trying to dump more fuel to correct the A/F mix. Thanks ahead of time for anyone's help!

raptor510

So while my engine was running I was under the truck trying to find any leaks and when I passed my hand around the O2 sensor flange it is puffing and sucking really good. It appears the flange is no longer lever, it's concave in the center which is not making a seal around the sensor. Could this air being sucked in cause the O2 to report unmetered air and thus the ECU thinks it's seeing a lean condition? I hope this is the problem! Any thoughts?

raptor510

Anybody? Bueller? Bueller?

scope103

Absolutely.

You can make your inquiry a little easier by putting a voltmeter on VF1-E1, then ground TE1 to E1. That will read the "conditioned" Ox1 voltage, so it should flop back and forth from 0v to 5v about 8 times in 10seconds. I expect that you will find yours stuck on 0 or 5 (I don't know which is "lean"), which is what triggers the code. Then if blocking the air leak in your o2 sensor causes it to start flipping again, you've found the problem (you might have to run the engine at about 2,500 rpm; the sensor has to be hot enough to generate a signal).

http://personal.utulsa.edu/~nathan-b...01heatedox.pdf

raptor510

Thanks Scope for your info. I am going to be checking that today as well as getting that mounting flange replaced. I have a loose PAIR hose I noticed yesterday that I will be tightening up too. I will keep you posted.
p.s. I will be very happy if a new flange fixes my issue!

RJR

0V is lean, 5V is rich.

Theory if anyone cares:
Lean means excess O2 in the exhaust. The O2 sensor compares O2 in the exhaust against O2 in the atmosphere. If it exists both places, it generates no voltage.
Rich means no O2 in the exhaust. Thus, O2 in the atmosphere but no O2 in the exhaust generates a voltage (about 1V), which the ECU amplifies to 5V.

raptor510

Went to the shop and had them grind the living crap off the mounting flange for the o2 sensor. Apparently the original gasket from 21 years ago didn't want to be evicted and staged a strike. They sealed it up, reset the ECU to clear the code 25 and I made it a few miles home without a CEL coming back on. I have some more errands to run today so I am keeping my fingers crossed and hoping that is the fix. I will keep everyone posted. Still burns me that 4 shops didn't think to check that! Heck, if I hadn't been nosing around under the truck with it running I wouldn't have noticed it either but still...makes me mad.

raptor510

Update: The gasket is still not seating flush and puffing & sucking air into the tail pipe and thus my code came back on. It seems the shop needs to grind the edges where the mounting bolts are so the gasket can make better contact with the mount. The code 25 came back on around 20 miles later towards the end of the day yesterday. Back to the shop today. Is there some kind of high heat sealant I can use if they give up and send me on my way?
On a side note, while it was on the rack yesterday I was looking around for my phantom exhaust leak and on the passenger side crossover pipe at the 90 degree bend I saw a 1.5" to 2" crack. Would this contribute to my lean code? Is this something that can be welded? I know it is a huge PITA to R&R that crossover!

scope103

Just so you know, the cross-over is listed as "discontinued" by at least http://www.toyotapartsoverstock.com/...rimLevel=18292 The part is not really one to wear out, so a salvaged one should be fine.

Removing it is not for the weak of heart, but it is much easier if you know the "secret." (Use the right wrench!)

raptor510

Thanks Scope. I have done it before, and it was not fun. I was doing my head gaskets at the time and I believe I wound up using a 3ft extension, WD40, brute strength, and an unhealthy dose of sheer hatred before I got it off. I have the truck at the shop now and they will hopefully be able to weld the stupid crack up as well as fix the o2 flange. My goal here is to simply keep o2 from sneaking in and triggering that damn code 25. After 2 months I am over it!

raptor510

Got the truck back from the shop. They were able to completely fix the o2 issue by grinding it flush so there is no more leak there. As far as the crossover pipe they didn't find any crack so that's really good news because I didn't want to have to deal with that! They seem to believe that my passenger exhaust manifold gasket is the source of the leak. I find this really hard to believe. 3 years ago I did a HG job and replaced all gaskets and seals included in a HG upper engine rebuild kit from Rockauto. Since I got it back together she has run like a champ and has passed emissions with flying colors. This was the same time I bought my WRX and the 4runner is no longer my dd. I have run her at most around 6000-8000 miles in the past 3 years, and so cannot believe that an exhaust manifold gasket would go out that quickly. The only thing on the passenger side I have touched recently was the EGR tube when I did a valve cover gasket job on her about 2-3 months ago. I did not replace the lower gasket on the EGR tube. Could that be the source of the leak, and in turn allow enough o2 into the system to trip the CEL25 I've been getting? I was going to try tightening the 2 bolts up and see if that makes any difference before trying to replace the gasket. I cleared the code just now and will drive her more to see if that code comes back up. I really would hate it if it is the manifold gasket...that is a huge PITA to replace and the shop quoted me $425 to replace it!

raptor510

Bump! Any thoughts guys? This is really getting to me!

RJR

My admittedly limited experience with exhaust manifold gaskets is that they either blow out pretty quick, or last forever. If they have the slightest leak upon installation, either because of improper tightening, or slightly crooked seating, it will only take a short time before the hot exhaust gases blowing through the hole enlarge the leak and trash the gasket. A few thousand miles sounds about right.

raptor510

Thanks for your info, RJR. So would O2 entering a crack in the exhaust manifold or it's gasket trip the O2 and throw the code 25? Because just now when I was running errands it came right back on. So in less than 30 miles from getting it back from the shop it popped up again. I am at an utter loss and my gas mileage is taking the hit.

RJR

Yes, if O2 is entering the exhaust system somewhere between the exhaust valves and the O2 sensor, it will add extra oxygen in the stream and fool the O2 sensor into thinking you're running lean (more oxygen than fuel, so all the O2 doesn't get used up = lean). The ECU tries to compensate by adding more fuel to enrich the mixture, which means your engine is actually running over-rich and using excess fuel, because of the bad measurement by the O2 sensor.

If you go back up a few posts in this thread, where scope suggested measuring the VF1 terminal with TE1-E1 shorted, you should see it sitting at 0V after warmup and running 2000-2500 rpm. If it's at a different voltage than that, let us know because that means something else is wrong in the emissions feedback loop.

raptor510

So I've been busy with work and didn't have time to get a voltmeter on the O2 sensor. I did however get it to yet another shop who fiddled around and said that 2 of my spark plugs were cross threaded and that could be allowing air into the engine. $300 later they sent me on my way and lo and behold, 60 miles passed and the CEL 25 came right back on. I have a replacement Denso O2 sensor I am going to replace tomorrow (got it free since mine was still under warranty) and will see if that makes any difference. The shop didn't do what I had asked, which was to check the VAFM as I did hear that could cause bad date to the ECU. Is that a possibility? I am stumped as I have been since this ordeal started 3 months ago. Also, I have no cracks in the exhaust system - they did verify that for me.
3 shops & $1300 and I am still nowhere. Help!

scope103

Well, probably not. The rheostat in the VAF "works" in open-loop mode; before the O2 sensor gets hot enough to generate a signal (around one minute). After the O2 sensor starts signaling, the ECU sets the mixture from that.

If it can. Generally, Code 25 means "I've done everything that I can to adjust the mixture, but the O2 sensor is still pegged." That's what you're looking for with a voltmeter on the O2 sensor.

Terrys87

iTrader: (1)

A cheap mulitmeter can be used to check your VAFM. I have seen them bad and not throw codes. A Haynes Manual will work for that check if you dont have access to a Factory Service Manual. It is a quick and easy check. Make sure your connectors are in good shape and not dirty or damaged.

raptor510

Thanks Terrys87,
So I got the call back from the shop and it's the worse news possible: low compression across all cylinders possibly due to worn cam lobes or rings. The shop basically said without tearing down the engine they would't be able to tell me exactly what the problem is and that would more than likely lead to an engine rebuild which I certainly don't have the money for. Seems my only option is to sell her as is and hope to get $2000 out of her. Shame since she runs great and has no other issue. 11 great years of service and 305k miles. Total bummer. Time to start saving for a Tacoma I suppose. Thanks for everybody's help and info.