j_cd

This is a 4x4 Tacoma. It passed the California NOX gas test by 1 ppm 2 years ago. Now after a new catalytic converter and front O2 sensor it is no better and failed. This engine has no EGR. Mechanic said it's running a little lean, MAF only reading 70% when it should be reading 85%. Suspects carbon on piston rings.

So I guess I'll resistance test the MAF again. Mechanic suggested pouring water into one of the hoses that runs to the manifold. Apparently he's never heard of Seafoam. So I'm thinking I'll slowly pour some Seafoam in and see if that cleans it up any. Should I replace the rear O2 sensor? It does have 292,000 miles. I'm also considering selling the truck at this point.

Any suggestions? How about a good link for doing that induction cleaning. I know some guys use an IV drip so they don't get too much Seafoam in the engine.

martinfan30

Please, what engine? When you say the MAF sensor is reading 70%, what do you mean? If it s a 4 cyl, it should read around 4 to 5 GPM. 6 cyl, upt to 7.

Seafoam will do nothing. Is this a federal, or cali emissions truck?

Lean conditions do typically cause higher NoX readings, so look for vacuum leaks or a contaminated MAF hot wire. I am suspecting this is a 4 cyl? With a cold air intake(K&N)? Over oiled filters coat the MAF and cause a lean running condition.

rob17san

There was a recent thread on a "motorvac" service. Look that direction. They also have a similar setup using BG products thats more popular. Not just the do it yourself can either. I would go to a reputable shop that has a motorvac, or bg induction cleaning system, and let the liability rest on their shoulders if they mess something up. I have never heard of a failure after these services, but have heard of them with seafoam. Seafoam fouled my spark plugs on my 99 explorer. (and those are a PITA to change).

You may also try the CRC branded "mass air meter cleaner". I use it regularly. Especially necessary if you have a K+N Oiled filter.

rob17san

Correct me if I am wrong but isnt NOX combustion temp readings?

JBurt

Even if you decide to sell it, it is still your responsibility to get it smogged because you are the seller (don't you love California laws!) That is unless you want to sell it for parts. Anyways I have heard great things about the motorvac service mentioned above for cleaning out carbon deposits. I think it runs about $200. If you want to keep the truck I would say to just go with that. If not I might try seafoam first. It's only $9 at autozone.

j_cd

martinfan30 - I did say California emissions. Sorry I thought all 4x4 SR5 had 5VZ-FE engine. The MAF was reading 70% of what it should be with the throttle all the way open. I'm not sure what unit of measurement he was using, I'll ask.

I've pulled the MAF off before and it doesn't look like other MAFs that I've seen people cleaning on this site. There is a wire inside that has a piece of metal in the center of it, but it doesn't have the red or amber droplet like other MAFs. If it's bad it will just need to be replaced. I'll hook up an ohm meter and blow air into it, see what happens. I checked the resistance between two pins a while back and it might have been a little low, but I thought it was OK. Maybe I was wrong.

My cousin said just sell the truck to pick-a-part. He must have known that the seller is responsible for smog. Other than the nox gas problem, it's been losing some coolant too. I have to add coolant to the expansion tank every few days. I can't see it leaking anywhere. When I run the A/C for a while on a hot day the temperature gauge goes way up and the truck almost overheats. The A/C works great though.

Hopefully if I change the MAF + rear O2 sensor and get some carbon cleaned out it will pass smog. Thanks for the replies.

Oh by the way, it's never had a K&N air filter. It's also way overdue for a new timing belt, and timing could be part of the problem I suppose.

martinfan30

Yes, it's caused by high combustion chamber temps, lean conditions(and anything that can cause that, O2 sensor issues, etc), Restricted EGR passages, inop EGR valve...



Your timing belt wont cause a problem until it breaks. Has it had the head gasket update done? When we were doing so many head gaskets on these, there was about 3 gasket updates during the whole period. You probably have an early head gasket that may be leaking. Although the majority of these gaskets leaked externally, I have seen a few leak internally like on the older 3.0.

For your original question, the rear O2 sensor is there just to monitor the efficiency of the cat converter. If you have a rich biased, or slow responding front O2 sensor, this could be where your problem lies.

j_cd

It had two head gasket recalls done, but it's been quite a while. I was just reading another thread where head gasket leak was mentioned. Got me to thinking, since I'm losing coolant but can't see where it's going, maybe a leaky head gasket is allowing coolant into the engine. That would probably explain why the exhaust smokes a bit sometimes, though it doesn't have that blown head gasket smell and it's not blue. I should probably have that checked before bothering with any motorvac service or buying a bunch of parts.

The front O2 sensor is a brand new Denso. It was installed along with the new cat. I'll go ahead and replace the rear one, unless I end up selling the truck.

rob17san

I would avoid selling to pick a part. Where do you live?

TheDurk

Forgive the Cali.ignorance, but are you failing due to a CEL, a plug-in test, or tailpipe sniffer? (I assume all '96 had OBDII, didn't they?) If the first, we need the exact code. If there is no light on and you failed in one of the other ways, then don't bother with the rear sensor, it only sets codes and has no effect on the running of the engine.

Was it an after-market cat and did you pass with it installed? If the answers are yes,no then that could be your problem right there.

If indeed, you are getting oil smoke at your mileage, you may be looking at a ring job or other more major engine rebuild before you can pass. Be careful before you throw too much $$$ at this engine. I had to junk an otherwise beautiful 30-year old Mercedes for exactly this reason.

j_cd

I live in the Southern California Inland Empire/Los Angeles area.

There is no CEL, but I've had cylinder misfire codes on cylinders 3 & 5 in the past. New plug wires and TPS seemed to have cured that, but who knows? I haven't cleaned the IAC or throttle body yet, but I was planning on it.

The new cat was installed by a local custom muffler shop. As I said, with the original cat I also had high nox gas. It's just that the mechanic massaged it until it passed by 1ppm that time. Yesterday he didn't remember that it was my car so he didn't put it on the dyno first and didn't try as hard to pass it. Obviously the old cat wasn't the problem.

So basically it's a gross polluter for whatever reason. I wonder how much the state would offer me for it? When I start it cold it runs rough for a few seconds before it fully kicks in and the idle smooths out. It does this to a lesser degree on warm starts. It's like something's not all there. Feels like it could be a fuel or air flow issue, or something entirely different. But I do suspect a leaking head gasket for the coolant loss now.

rob17san

From what I understand, california does not allow the aftermarket high flow cat. They have to be original style, so thats likely what you got.

martinfan30

Coolant burning will be white in color and have a sweet smell. Blue smoke is oil burning.

martinfan30

Mid-late '95 was the switch over to ODB-II.

j_cd

Yeah when it smokes it's white. I'm either bringing it to an independent toyota mechanic on Monday or retiring it for the year.

The new cat is of the round enclosed variety, I'm not an expert. The original one was oval shaped and had holes in it.