‘94 won’t pass emissions but NO CEL (1 Viewer)

[109madrid]

I am having an issue passing emissions, and I’ve done the basics like vacuum lines, tune up, oil change, charcoal canister, etc. Very easy emissions testing in NM but at this point, I’m thinking it’s the Cats but don’t want to throw money at it if I don’t have to. The o2 sensors were replaced under the recall in 2008, and test fine, so I’m at a loss. I have NO CEL and after the all OEM tune up, it purrs and runs smoothly BUT still has a high idle (a vacuum line under the intake manifold was missing and i replaced it but it still did not resolve the high idle) and I’m planning to do the distributor O-ring for good measure, so I will definitely check the timing next to see if that helps the high idle. Bottom line, should I replace the cats? I was thinking a single magnaflow 2 in 1 out (2.5in) and do a Borla muffler? Any thoughts?

 

[109madrid]

My levels of HC’s actually went up after the tune up. Also, my low fuel light will not turn off after replacing fuel filter, don’t know if that matters but it’s the only light on my dash at the moment.

 

[Pin_Head]

It is hard to offer meaningful advice without knowing what the measurements are and why it is failing, but if it is failing HC at idle, this often comes from a lean mixture that is often due to unmetered air leaking into the intake. It can also come from clogged injectors that can’t deliver enough fuel.

 

[109madrid]

Here’s my test if that helps any, the tech said HC’s went up significantly after the tune up, but that was before the oil change and haven’t tested since the oil change...

 

[109madrid]

Got a new gas cap too, btw...

 

[ppc]

You stated O2 sensors are 11 years ago but how many miles? In the 93-94 ODB1 models specifically in my experience need replacements more frequently that the ODB2 models, 80k and its time to replace. High HC is not the result of bad cats. You failed at idle RPM but not at high RPM. I would start looking for vacuum leaks, proper timing etc. Was was addressed in the "tuneup"? The is a very vague term. New plugs, wires?

 

[109madrid]

The tune up was new plugs, wires, distributor cap, distributor rotor, and vacuum lines (so I’m pretty sure the vacuum leaks are fixed -but there’s so many vacuum lines!) and I also added a gas cap because the tech said the gas cap failed the test. The mileage I’m not sure but it’s probably right around 80-100k however it’s not throwing any codes/CEL after I replaced the TPS and rear knock sensors so no CEL for about a year now. Timing was my next route hoping to cure the high idle before replacing the cats because I have to do the distributor O-ring but just been putting it off because of the timing adjustments and I don’t have a timing light. I will look into timing because in order to get the low speed idle test going, the tech had to put the trans in gear due to the idle maintaining 1100-1200 RPM so when it’s in gear it drops it to 700 RPM’s where it’s able to run the test. The vacuum line replacement did nothing to change the idle btw.

 

[Rifleman]

109madrid, Just as an FYI, if your spark timing is advanced beyond the factory setting, THAT CAN cause a HIGH HC reading at idle. A retarded spark setting will not only reduce your CO at idle, but your NOx reading too.

An increased idle speed over the factory setting will help to slightly reduce your HC readings at idle, but that can cause an increase in your NOx output. But it would seem that you don't need to worry about NOx readings. That's due to the fact your state only requires you to pass a 4 gas emissions test, instead of a 5 gas.

So as you can see, all these systems are very closely interrelated, so a small change in one direction, or another, can, and will have an effect on your final test readings.

 

[109madrid]

Hey, who you calling retarded? J/K this exactly what I’m looking for, thank you so much Rifleman, now I can at least make an educated adjustment to things. Third world countries don’t always have timing lights, but they definitely still have running LC’s - also, j/k. BTW, I just called the local dealership to see about getting my distributor o-ring done by them so THEY can adjust the timing and the quote was $192 FOR LABOR! Ridiculous!

 

[use2bn83]

If the high idle started when you installed the new TPS, I’d double check that it is adjusted properly.

 

[Rifleman]

I just called the local dealership to see about getting my distributor o-ring done by them so THEY can adjust the timing and the quote was $192 FOR LABOR! Ridiculous!

If you were to ask the dealership for a break down of their fee, then you'd understand how they came up with that amount.

I'd be willing to bet that their labor rate per hour is somewhere around 130 to 150 bucks per hour, plus shop fees, and parts cost (O ring) will get you to 192 dollars.

With costs like these, this is just one more reason why you should download a free copy of your trucks service manual here on Mud, and learn how to do jobs like this yourself. Cheers

 

[RayRay27]

I would make sure your timing is set to 3º BTDC as stated per Toyota and make sure you drive the vehicle around at highway speeds to get the engine and cats nice and hot prior to testing. A lot of times if you don't get the engine and cats up to temp prior to testing you can easily fail too. Pretty simple fixes without having to dump any cash. You can try adding a bottle of red heat to a nearly empty tank of gas and then add a about a half a tank of premium prior to testing. Sounds like snake oil but here in Colorado many 80 series owners swear by it.

Side note, if you still have OEM cats on I would hang on to them as long as possible. If you are not going to replace OEM and decide to use after market, most likely you might be replacing cats every few years. There are a ton of 80 series on the road today that still have the original cats and have no issues whatsoever passing emissions.

 

[jmills]

I just went through this on my 94. I finally determined the EGR valve was not closing fully causing a vacuum leak at an idle. This was hard to find. Once I replaced my EGR valve it passed California smog with no problem.

 

[Heckraiser]

My guess is that your high idle and your high HC are related--extra air getting into the system somewhere when the throttle is closed. Problem goes away once you open the throttle and the engine is working with a lot more air. Hunt around for a vacuum leak (I'm sure you have, but try again).

 

[109madrid]

Jmills, was your issue the EGR itself or the egr modulator? Your issue sounds eerily familiar, and I will add that my EGR modulator is the green version and it looks like those were bad and replaced by the blue modulator. Keep the info coming!

 

[109madrid]

So an update now that I have time To work on things...
EGR valve tests good (diaphragm is still intact) so I pulled it to clean it now that I have the intake and TB removed. I replaced every hose under the intakes including the coolant bypasses and brake booster vacuum and the VSV’s are testing within spec electronically but will not allow air to pass through their ports at all. I tried to clean all VSV’s with a wire like I did for the intake ports but it seems like they are plugged. Anyone else go through this or know how to clean VSV’s? I used mass airflow sensor cleaner within the ports to no avail. BTW, I’m doing the valve cover gasket and PHH while the intake is off as well since they are within easy access -tried the reach around method prior and should have removed the intake from the start.

 

[Rifleman]

109madrid If you Do a search using VSV as the search term you'll get alot of info, i just did that search using VSV and got over 50 pages of results.

 

[109madrid]

I was looking more for cleaning specifics on a clogged VSV but thanks for the reply. I couldn’t find much (I just skimmed) so I cleaned mine with safety wire (dirt bike grip wire) and some CRC throttle body cleaner. All but one cleared out but it didn’t pass resistance testing so it was replaced. Good ol’ VSV 90910-12079, it was the original though. Every hose under there is new OEM now including the PHH and it’s neighbor since I had the intake off.
I also found port R on the throttle body was COMPLETELY clogged (used a twist tie to clear that) so in addition to the VSV, that’s all I could chase down under there. I figured my vacuum leaks were done... not so. Tested the EGR with vacuum while running and only get a very minor reaction now, prior there was absolutely no reaction. RPM’s did drop down from 1200 to 900 also so a slight win and code 26 is gone but code 25 just popped back up after a few days.
Does anyone think the pair valve would cause a vacuum leak? I cleaned out of the plenum and EGR valve, plus the EGR valve tested good and still holds vacuum, both however were filled with carbon. Thoughts?

 

[109madrid]

Pair valve sounds like a rattlesnake and S hose has a small crack under the clamp BTW...

 

[Rifleman]

Every hose under there is new OEM now including the PHH and it’s neighbor since I had the intake off.

Just a quick question, did you replace the vacuum hoses with OEM hose too, or did you just buy your replacement vacuum hose from your local auto parts store? The reason i ask, the original factory vacuum hose is 3.5 MM in size, most auto parts stores don't sell metric sized hose. They'll want to sell you 5/32 size vacuum hose, It'll fit loosely on all your hose fittings, thereby causing you lots of little vacuum leaks. All those little vacuum leaks will NOT HELP you pass an emission test.