Here's a good one

[offthepoint]

Here goes:

I've got a 90 ST (4A-FE) that refuses to pass smog at 15 MPH, high NOx and HC. The EGR system components have all been replaced/rebuilt/cleaned out and the car runs beautifully with no CEL. A new catalytic converter would be the only thing left I can think of but I'm not sure that would do it.

After much weekend tinkering by myself and a friend we've located a problem with the vacuum ports on the throttle body. The service manual states the ports, labeled E, P & R, should have no vacuum at idle and that ports E & P should have vacuum off-idle. The problem is port E has vacuum at idle (rises off-idle) and port R has vacuum off-idle.

Needless to say, I'm at a complete loss about what to do about this . A close visual inspection of the TB revealed nothing out of the ordinary and the only solution I can think of would be to remove and strip the TB and toss it in a bucket of carb cleaner.

Any ideas?

[TrailDust]

I'd agree that replacing the cat might do nothing to lower the values. Have you replaced the EGR valve or did you clean it?

[offthepoint]

ALL EGR components have been replaced with OEM parts: valve, modulator, VSV. I even took a fistful of carbon out of the EGR passage in the intake manifold *gross*. (BTW, oven cleaner works great for breaking that crap up)

[TrailDust]

Hmmm. Let me think about this one...there's so many reasons why you're still showing those high emissions.

[TrailDust]

The only things I can come up with are these, and I don't know whether you've explored them or not. For the high NoX I'd look at your cooling system as running too hot which would account for those high levels, so checking the thermostat, etc., would be in order. For the high HC I'd look at the oxygen sensor. Those high HC levels aren't good for a cat, and it'll force you to replace your cat much sooner that later due to damage.

[offthepoint]

Afraid I've replaced the thermostat and O2 sensor as well. Something hit me earlier today though (I had an idea about the fix too). I believe the vacuum discrepancy at the TB is the culprit. The fix?

Here goes: vacuum in an engine is caused by a restriction right? That restriction usually being the throttle plate. So if I have vacuum before the throttle plate, stands to reason that there is a restriction before the throttle plate, i.e. in the intake piping, the air filter (though it looked OK), etc. When I worked for Toyota of Simi Valley I once found the entire front page of a Chinese newspaper in the airbox of a Tundra.

At this point, I can't explain why this would cause my smog failures (odd vacuum readings messing with the MAP sensor or FPR perhaps?) but as soon as I return from this business trip, you can bet I'm going to dive in and find out.

[TrailDust]

Originally Posted by offthepoint

When I worked for Toyota of Simi Valley I once found the entire front page of a Chinese newspaper in the airbox of a Tundra.

Wow, that's a first for me! When you dive back into it keep me updated on what you find out...I'm so curious now....

[offthepoint]

TD, your tips are much appreciated. I'll be sure to post the (eventual) fix. As a token of my thanks please allow me to offer you that newspaper page . You can claim your prize if you ever find yourself in the Oxnard/Ventura area.

[offthepoint]

So, I ripped off the intake piping, started the car and re-checked my vacuum readings at the TB after giving the beastie a thorough cleaning and new gasket. The readings are still wrong! Unless my service manual is wrong (entirely possible) I'm out of ideas and am contemplating enlisting professional help, though my regular mechanic actually uttered the phrase "I don't know". Anyone have an OEM manual for the 4A-FE? Or any ideas?

Or a large, blunt object to induce trauma-based amnesia?

[93celicaconv]

OK, let's get to details. You said the "readings" at still wrong on the throttle body. Exactly what readings are you talking about, and what are they? Are you taking vacuum level readings from within the throttle body when the engine is running? If so, what exactly are the throttle body readings, and at what engine speed/engine temperature are you taking them?

[Bitter]

if your timing were off (ignition or cam) that could cause high Nox and HC, so could carbon deposits.

[offthepoint]

Bitter-

The ignition timing is set to 10 BTDC (with diag connector jumped) per the label on the hood. The cam timing I'll be looking into. Thanks for that.

93celicaconv-

As stated earlier in the thread, the vacuum readings at ports E and R on the throttle body do match with those specified in my service manual. Vacuum was checked with engine idling @ 800 rpm under normal operating temperature and then again with engine off-idle (1500 rpm).

I just noticed the emission label says that this car employs a TWC (three-way catalyst). Those are supposed to scrub NOx too. I didn't know Toyota used those.

[93celicaconv]

I have a 91 Celica ST. My emissions label doesn't say anything about the catalytic converter, but my shop manual says all Celicas employed a 3-way catalytic converter. The 3-way merely means the catalyst takes 3 harmful exhaust gases (CO, HC, NOx) and converts them via oxidation and reduction to 3 safe gases (CO2, H2O, N2). So your catalytic converter is nothing special or out of the ordinary.

When you checked your ignition timing (engine warm and the diag connector terminals TE1 & E1 jumpered), what was your engine idle speed? Was it at 800 rpm? It needs to be when you have these two terminals jumpered. If it isn't, adjust the engine idle via the TB screw to get the engine to 800 RPM.

Sounds like you changed a lot of components. Let’s make sure the TB vacuum ports are connected properly. TB port R needs to be connected to the EGR Vacuum Modulator, port R. TB port E needs to be connected to the EGR Vacuum Modulator, port P. TB port P needs to be connected to a coolant vacuum switching valve (VSV), a sensor located in the coolant piping at the transaxle side of the head, which in turn is connected to your charcoal canister. Are the 3 TB ports properly connected?

Vacuum on any of the 3 TB ports is dependent upon the position of the throttle valve (or plate). Port E is would have vacuum prior to port R as the throttle plate is opened (engine speed is increasing). All these ports may have a slight vacuum, even if the throttle plate isn't positioned to expose them to vacuum, if the upstream air flow is restricted in any way (dirty air cleaner, a foreign object lodged in the air inlet duct - and this has happened, like a piece of newspaper getting lodged in there).

NOx emissions are reduced when exhaust gases are recirculated through the EGR valve and back into the intake manifold to lower the maximum combustion temperature. I don't know what speed the engine is at when you are driving at 15 MPH, but TB port E is not uncovered by the throttle plate until the engine reaches at least 1,100 RPM, possibly slightly higher. So what is your engine speed at 15 MPH?

Depending upon what you find above, the last thing to check is the seat of the EGR valve. If something in the past caused the EGR system to no operate properly, it is possible now, as you changed all your parts and have everything reconnected properly, a carbon deposit developed in the EGR pintel seat area that the port is clogged, so there is no exhaust gas recirculation even if the new EGR valve opens properly. You may need to remove the EGR valve again, and then make sure the pintel seat is clear of any carbon and is not clogged. Same would be true for the tube that goes to the EGR Vacuum Modulator - that tube needs to be open to the exhaust system, so make sure that tube is not clogged. Clean everything very thoroughly. I know you said previously that you cleaned everything out, so I don't suspect this to be a problem, but the EGR pintel seat must not be clogged, and the port feeding the tube going to the EGR Vacuum Modulator must also be open, for the system to work, and those are very hard areas to clean out if the system hadn't been working properly earlier for a long time.

One last note, the VSV with a vacuum port going to the EGR valve, did you replace that also? If not, make sure this works. Air should flow freely from port E of the VSV out to atmosphere when the VSV is not energized. Air should not flow from port E of the VSV when battery voltage is applied across the VSV terminals. A faulty VSV will not allow the EGR valve to open, and hence, would not pass a smog test.

Hope something here helps you at least a little.

[offthepoint]

Engine speed was 809 RPM (according to my photo tach) during timing adjustment. TB ports are connected per the diagram on the hood sticker with all new vacuum hose. Engine speed at 15 MPH in 2nd gear is ~1800 rpm, so says the smog reports. EGR valve, VSV and VM (all brand new) were checked again per the procedures found in the Celica BGB the other day, all squeaky clean and functioning properly.

The air intake piping was my last idea, but that is clear (no newspapers) and the air filter was removed for testing purposes.

I find it strange that the car passes at 25 MPH but not 15. I understand the engine is more heavily loaded at 15 MPH on the smog dyno. Once at 25 MPH, the gas readings drop drastically.

Also, the exhaust has a strange smell to it. It doesn't smell like gasoline, but it doesn't smell like the exhaust of a properly functioning engine. And the car runs and drives just fine, other than needing new axles.

On a side note, this is far more useful advice than I've ever received from an internet forum and I would like to thank all contributors.
My familiarity with electronic controls and fuel injection is limited and I appreciate all the help.

[woodsie]

I'm also high in Nox. just checking the VSV . no power with key off . power to VSV with key on. Valve was getting warm. brougth the rpm up to 3k and still power to the VSV. WHen powered the valve is closed and no vacuum to the egr to open. What should I check?
I checked for trouble codes and I only got code 24 " intake air temperature sensor "
So I have vacuum from TB to Modulator. Vacuum from Modulator to VSV and then the VSV is allways powered with the key on keeping the valve closed, so no vacuum from VSV to EGR valve.

What do you think?

Thanks
ED