weakyota91

My 91 toyota 3.0 has a brand new top end as of august (new head gasket, plugs, plug wires, heads remachined, new valve guides, 2 burnt valves replaced, cap and rotor and timing is correct) now its time to smog and wont pass. specs for my truck are between 130 and 185 somewhere in there. at idle it shows up on the smog computer that the pollutant numbers are 580 three times the pollutant if i hold rpms at 3 grand for ten seconds or so the pollutant reading drops down to like 30- 60 extremly low. confused me and the smog guy what could cause this? plugs and wires all good. I havent done a compression test, but dont really want to find out that to be the problem.
thanks

FastCat

How did you determine that it is running lean? Did the smog checker use a wideband O2 sensor to determine it's lean?

Another thing you can check is that you don't have a vaccum leak somewhere allowing air into the intake without it being accounted for by the MAF, causing the fueling to be off at idle, i.e. lean. I don't know about Toyotas, but other vehicles I've experience with don't use the O2 sensor readings to control fueling at idle, and that would explain why when you up the RPM's the pollutant levels drop at higher RPMs, because the ECU is adjusting the fueling for the O2 sensor reading there.

Was the engine running at normal operating temps or was it checked with it relatively cold?

midiwall

If the pollution numbers are HIGH, then I'd bet you're running rich. Which "numbers" were these (they test for 3 things)?

If you're running rich at idle, but okay elsehwere, then I'd start looking at the cold start injector - sounds like it could be stuck open. I'm speaking 3rd hand since I don't have your engine, but from what i understand, there's a separate injector on the 3.0's for stuffing more fuel into the engine during cold starts (like a choke on a N/A engine). If that's stuck open, you'll be running WAY rich and could produce the symtpom you're looking at.

weakyota91

the check engine light came on during the smog and scanner read code that exhaust is lean sorry for not mentioning that

midiwall

Okay, so... the sniffer station actually plugged into the diag port and read the code, or did you paperclip it and read it yourself, or???

Do you remember what the code was? Even on your engine there are a number of "lean" codes.

If the ECU is claiming lean, then let's start from there. Clean the air filter, clean the air flow sensor, clean/adjust the TPS, replace the fuel filter.

When's the last time the engine was tuned? How old are the plugs? How old is the O2 sensor?

FastCat

Running lean produces high numbers for NOX emissions (oxides of nitrogen).

I wouldn't trust the ECM completely for determining if the vehicle is running lean as most factory O2 sensors have a very narrow range of accuracy.

I would find someplace that has a wideband O2 sensor and use that to get an accurate reading of the AFR (air-fuel ratio). You will then know just how lean or rich your vehicle is running, which may help you figure out what to look for. You need as much information as possible when troubleshooting problems like this one.

weakyota91

midiwall -correct. station actually pluged scanner into DLC under hood and it read exhaust to lean. replaced o2 sensor last nite went back 2 day 1-11-06 and didnt change anything. hold the engine at 3-4 grand for ten seconds in neutral and thats the only time the check engine lite comes on. At idle the hydro carbon ( i think thats what the reading is called) reads 400-500 2 1/2 times the pass amount. run the rpm up to 3-4 grand and it droppes down to 30-40 and I think thats why the lite comes on cause it is almost pure oxygen running past the o2 sensor . Im trying to rule out a burnt valve, low commpression in a cylinder or another blown head gasket because all that would make it run way rich with it only seems to so at idle. Im just trying to eliminate everything myself before spending big bucks at toyota. Thanks guys.

tc

But even then, the cat shoul have scrubbed out all the NOX, especially running lean with higher EGT...

Of course, I would make sure the A/F is right, but don't leave the cat out of the investigation

snap-on

I thought the EGR valve pays a big roll hear. as its vacume actuated it usually only "comes on" when the engine is under load. (cruseing on the interstate at 3K)

FastCat

According to weakyota, the problem doesn't exist at 3K RPMs.

I get the feeling he's got a vacuum leak somewhere and it's affecting his idle AFR, and it's overwhelming his cats at idle.

4Crawler

iTrader: (3)

My 22RE did this last spring, was about 2X the NOX level. EGR was working but was not doing enough at full load (dyno smog test) to cut the NOX enough. I pulled it all off, spent a day cleaning out the EGR (gun cleaning kit and solvent) and also ported out the exhaust return ports in my header and cleaned out the ports in the head. After re-testing NOX dropped to about 40% of the first test. This was with a new cat and O2 sensor. Also retarded my timing about 3-4 degrees and ran premium gas for the test.

InternetRoadkill

Wild guess: maybe a leaky injector is at fault? It would cause the idel to be rich, but would have little effect at higher rpms.

A bad AFM would cause the same symptoms. Maybe the vane is sticking?

hodgepodge79

Any idea what the specs are for the O2 sensor for good middle ground (not too lean, not rich)? i.e the amp or volt reading the O2 sensor should be give at 3000-4000 rpm?

Mark

midiwall

On the 87? That'll be a narrowband A/FR and "stoich" (14.7:1) is 0.450vdc. This may help a bit:

http://www.gmtcny.com/WBO2S.htm


But remember, in closed loop a narrow band O2 will swing wild from one end to another with the ECU doing averaging and using that as the trigger to dumping fuel. It's not straightforward to read the A/FR voltage with a multimeter.

4Crawler

iTrader: (3)

Per the FSM, you'll see approx. 8 voltage swings in 10 seconds of operation in the range of ~0.2volts to ~0.8volts.