Emissions Fail

[IoN6]

Not sure about premium. I was always under the impression it wasn't actually "cleaner" or "better" in any way other than a higher detonation point. I always put it in my motorcycles with higher compression engines, but I've heard there's no point in low compression engines. I can't think of any reason it would be bad - just more expensive and no benefit. But I'm certainly no expert and I'm sure others can elaborate.

As far as MAF cleaning, I don't know. I was only planning to spray it with the specialized MAF cleaner. That's what I did on my 4Runner - not sure if it helped, but figure it can't hurt as long as you use the right cleaner. Again, I'm sure others with more expertise can elaborate.

You do not have a Mass Air Flow (MAF) sensor on a '94, you have a Vane Air Flow meter (VAF). It is electro-mechanical, where the former is entirely electrical. They are pretty simple and fairly reliable devices, but they are 30 years old now. Any long long NLA from Toyota. It does not help that they can easily be opened up and monkied with either.

Should at least be a pic of a VAF in this thread. I spent years struggling with my '93 and was ready to light a match and watch it burn.

 

[IoN6]

I should add, I have a '93 FSM and EWD should you find a need.

 

[Norseman12]

You do not have a Mass Air Flow (MAF) sensor on a '94, you have a Vane Air Flow meter (VAF). It is electro-mechanical, where the former is entirely electrical. They are pretty simple and fairly reliable devices, but they are 30 years old now. Any long long NLA from Toyota. It does not help that they can easily be opened up and monkied with either.

Should at least be a pic of a VAF in this thread. I spent years struggling with my '93 and was ready to light a match and watch it burn.

Any way to test if it's working correctly?

 

[IoN6]

Mine tested good. I never verified for sure, but my hunch is that the temp sensor acted up when it was hot outside. I have my questionable VAF still if you’d like to try it. Should run fine this time of year.

From the FSM:

 

[Norseman12]

Mine tested good. I never verified for sure, but my hunch is that the temp sensor acted up when it was hot outside. I have my questionable VAF still if you’d like to try it. Should run fine this time of year.

From the FSM

Mine tested good. I never verified for sure, but my hunch is that the temp sensor acted up when it was hot outside. I have my questionable VAF still if you’d like to try it. Should run fine this time of year.

From the FSM:

What temp sensor are you referring to? Is that part of the VAF?

 

[IoN6]

There is a intake temp sensor in the VAF. Now that I think about it, I think there was a typo in the FSM and which pin is which. I would have to do some digging to be sure though.

 

[LARGEONE]

I have cleaned my MAF sensor with MAF cleaner spray without issue. Just spray no wipe.

 

[Jacket]

Have you looked here?

Oh joy, P0401 is back... (and how 80's fail emissions)

Great to meet you today Bruce! Glad we could get a few things done on your truck and thanks again for the sensor which I will be throwing into my truck tomorrow with crossed fingers. Likewise thanks for putting up with my rambunctious boys! They enjoyed 'helping'. :) Let me know when you're on...

risingsun4x4club.org

 

[Norseman12]

Have you looked here?

Oh joy, P0401 is back... (and how 80's fail emissions)

Great to meet you today Bruce! Glad we could get a few things done on your truck and thanks again for the sensor which I will be throwing into my truck tomorrow with crossed fingers. Likewise thanks for putting up with my rambunctious boys! They enjoyed 'helping'. :) Let me know when you're on...

risingsun4x4club.org

Thanks for the link. I had a 401 when I bought it, but cleaning the EGR port took care of that. Haven't had a CEL since. EGR seems to be functioning, but who knows...

 

[ry303]

I had a vehicle that didn't pass because of high NOX. I learned a lot from that experience.
High NOX can be caused by oxygen entering the system from an exhaust leak somewhere between the upstream sensor and the downstream sensor.
I used a shop vac outlet to blow air into the exhaust and then spray very soapy water all over the entire exhaust system - headers, cats, all the connectors etc until I found the leak(s). There were a few small leaks and once those were fixed/patched the vehicle did not have a problem with NOX.
Something to consider for the NOX issue.
HTH

 

[Inukshuk]

Any way to test if it's working correctly?

Yes per that FSM page. I recently tested two and fixed mine. Happy to discuss if yours tests bad.
Mostly the only part in there that goes bad are broken solder connections. In my case, they broke on their own.
Often people break theirs by not opening the unit properly. DO NOT remove the connector screws. Plenty of Mud info in the AFM including things I posted.

 

[Norseman12]

I had a vehicle that didn't pass because of high NOX. I learned a lot from that experience.
High NOX can be caused by oxygen entering the system from an exhaust leak somewhere between the upstream sensor and the downstream sensor.
I used a shop vac outlet to blow air into the exhaust and then spray very soapy water all over the entire exhaust system - headers, cats, all the connectors etc until I found the leak(s). There were a few small leaks and once those were fixed/patched the vehicle did not have a problem with NOX.
Something to consider for the NOX issue.
HTH

Thanks for the info. My 94 only has upstream sensors - would the same technique you used apply on mine if there was a leak between the engine and the sensors?

 

[IoN6]

If there is a leak at the manifolds or anywhere before the O2 sensors then yes. Now that I think about it, that may very well be why I passed on the second roll last year. Was pleasantly surprised, and did not give it much thought at the time.

There are some basic vacuum tests you can do to see if you have an intake leak somewhere. Let me find the page.

[edit]
Not finding the page, but this post shows my numbers.

Have you downloaded the '94 FSM from 'mud?
[/edit]

 

[J1000]

It's an oxygen/fresh air leak before the cat that makes the cat not function correctly which causes NOX. I think it's pretty common for the stock y-pipe to leak at the y junction.

 

[ry303]

Thanks for the info. My 94 only has upstream sensors - would the same technique you used apply on mine if there was a leak between the engine and the sensors?

I think the same technique would work for upstream sensors only. You're just looking for bubbles from the soapy water to identify any leaks where oxygen could get in.
It does look kinda funny duct-taping a shop vac hose to your muffler, but it worked and my neighbor got a good laugh too.

 

[Norseman12]

Great ideas - now to find a shop vac in my temporary apartment....

 

[Norseman12]

Does anyone have tips on getting a PCV valve out when the grommet is rock hard...without removing the valve cover or dropping bits of rubber into the head? I can't pull the valve cover right now, but I want to replace the likely decades-old PCV before my emissions test on Friday.

 

[LARGEONE]

You are welcome to borrow my shop vac if you’re on the north side.

 

[IoN6]

Does anyone have tips on getting a PCV valve out when the grommet is rock hard...without removing the valve cover or dropping bits of rubber into the head? I can't pull the valve cover right now, but I want to replace the likely decades-old PCV before my emissions test on Friday.

Very carefully. While not ideal by any means, if you drop a chunk I personally do not think it will be the end of the world. I am pretty sure I got 90% of mine out when I replaced it and easily have done 60+k since then. Now if it totally disintegrates that might be a case where I would debate on pulling the valve cover.

 

[Norseman12]

I got the PCV replaced, set timing to 3, replaced the FPR, plugs, wires, rotor, and cap. This time, my CO great, but my NOx was much worse, so I failed again.

I did a smoke test on my vacuum system and it does look like my egr modulator is leaking.