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1990 White NA/Blue Interior
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Discussion Starter · #1 ·
Are all vacuum modulators the same? Can we use one from Camry or Lexus? They are obsolete for our car and not available anywhere. I’ve had multiple orders get canceled and I haven’t been able to source one after 3 weeks. So I’m considering trying to pass smog with a different model.
 

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Toyota Supra Turbo 7M-GTE with R154 5-speed
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Are all vacuum modulators the same? Can we use one from Camry or Lexus? They are obsolete for our car and not available anywhere. I’ve had multiple orders get canceled and I haven’t been able to source one after 3 weeks. So I’m considering trying to pass smog with a different model.
this one was fine

263993
 

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I was going to suggest going to a pick n pull yard and look for toyota cars of the same era. All of the actuators are all pretty similar, so finding one with the same routing should do the trick. If you have a vacuum hand pump you can test it’s function as well.

Out of curiosity is yours not working/the diaphragm torn? And have you failed smog? Not an expert but usually EGR is important for a visual but probably shouldn’t impact the sniffer test.
 

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Discussion Starter · #5 ·
I was going to suggest going to a pick n pull yard and look for toyota cars of the same era. All of the actuators are all pretty similar, so finding one with the same routing should do the trick. If you have a vacuum hand pump you can test it’s function as well.

Out of curiosity is yours not working/the diaphragm torn? And have you failed smog? Not an expert but usually EGR is important for a visual but probably shouldn’t impact the sniffer test.
Unfortunately, the car runs great, but I failed nox. So I am going with colder plugs, flushing the radiator, replacing the fuel filter, and looking to replace or clean the egr valve. Since I was going to replace the egr, I figured it would be a good time to do the modulator, then I discovered it can't be purchased. I've had to replace a failed one before, so wanted a backup. I just got my vac tool this week so I still need to test the modulator (plan to do that this afternoon).

HC and CO were both low, nox failed by around 20%. The car sat for 5 years in storage. There was a lot of rust in the radiator, so I am doing a rust flush and replacing the radiator with a mishimoto. The plugs I installed were a stage hotter than stock, so I dropped to 2 stages colder than stock. The fuel filter is probably pretty nasty (stock). I am in the process of replacing most parts withanything I can find new from toyota, purely to get as many more years as I can. I love this car, have had it since 2005, and want it to last me until I can't drive anymore.
 

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Unfortunately, the car runs great, but I failed nox. So I am going with colder plugs, flushing the radiator, replacing the fuel filter, and looking to replace or clean the egr valve. Since I was going to replace the egr, I figured it would be a good time to do the modulator, then I discovered it can't be purchased. I've had to replace a failed one before, so wanted a backup. I just got my vac tool this week so I still need to test the modulator (plan to do that this afternoon).

HC and CO were both low, nox failed by around 20%. The car sat for 5 years in storage. There was a lot of rust in the radiator, so I am doing a rust flush and replacing the radiator with a mishimoto. The plugs I installed were a stage hotter than stock, so I dropped to 2 stages colder than stock. The fuel filter is probably pretty nasty (stock). I am in the process of replacing most parts withanything I can find new from toyota, purely to get as many more years as I can. I love this car, have had it since 2005, and want it to last me until I can't drive anymore.

I see. Yeah I'd give it a test before hand to rule it in/out. I think there's a way to test it also by hooking one of the source lines to a vacuum source (if you don't have the pump) but I'd have to look it over in the repair manual... I don't recall off hand. I prefer using the vacuum pump if you have it. It can come in handy for other things too.

Was the car sitting and you fired it up and took it in? This is probably a good time to refresh some of the ignition as you are doing, check for vacuum leaks etc. One other tip - make sure the car is nice and warmed up thoroughly when going to the sniffer, to make sure the cats are up to operating temperature. I've also heard that a splash of E85 can help with HC/CO but not nox (?)

For sure keep her running! It can be a little tricky keeping some of these older cars smog compliant, but it isn't as hard as you think if you have a relatively well maintained car and still have catalytic convertors. Good luck!
 

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High NOx means it's burning hot, which could be from running lean or EGR isn't working. I don't think colder plugs will help any. There's an easy way to check if the EGR is working if you have a hand pump. Activate the valve while idling and the engine will stumble or stall. The TSRM talks about this.

The EGR piping will get clogged with carbon over time. You have to take the intake all apart to clean it out, but it's not bad as long as the cooler at the back of the head isn't clogged.

If the EGR is working, look into why it's running lean: air flow meter operation, intake leaks letting in unmetered air, working O2 sensor, and so on. Check codes first (as always).
 

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1990 White NA/Blue Interior
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Discussion Starter · #9 ·
High NOx means it's burning hot, which could be from running lean or EGR isn't working. I don't think colder plugs will help any. There's an easy way to check if the EGR is working if you have a hand pump. Activate the valve while idling and the engine will stumble or stall. The TSRM talks about this.

The EGR piping will get clogged with carbon over time. You have to take the intake all apart to clean it out, but it's not bad as long as the cooler at the back of the head isn't clogged.

If the EGR is working, look into why it's running lean: air flow meter operation, intake leaks letting in unmetered air, working O2 sensor, and so on. Check codes first (as always).
New o2, new afm. I agree on checking the egr, I finally got the vacuum gun, (mityvac) so I am going to run that test tonight. I wasn't sure on the spark plugs, I have never had high nox before and the only difference between now and my last smog (a month before I parked it) was the change in plugs, rust in my radiator, and the old gas that I pumped out.
 

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I ran into this issue a while back. So the three port modulators are more common as used on the 7MGE. The 2 port one on the 7MGTE is harder to find as its not the one used on the Camry and so on. My solution was a modulator from a mk4 2JZGTE. I suspect they are calibrated for each engine, but when you cannot get the correct one you have to improvise.

I agree its most likely the EGR system. But did the modulator fail the test in the TSRM? Mine did, but there's alots of of other issues that can go wrong. Worth troubleshooting using the TSRM to narrow down the problem. Post up your smog check numbers and we can diagnose better. If the mixture is lean it can make the catalyst lousy at reducing NOx.
264029
 

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1990 White NA/Blue Interior
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Discussion Starter · #11 ·
264092

Ok, I pulled vacuum on the egr and the engine stumbled, but didn’t stall.
I have vacuum going to the modulator on both inputs when I rev the engine, and the vacuum spikes on the other side of the modulator when I rev the engine.

When I tested, it was a hot day, my radiator was low on coolant, the fluid was full of rust, and the car had only been run for 30 minutes after 5 years of sitting. And the spark plugs were replaced with a stage hotter than stock.

i just flushed the radiator for rust, drove it for an hour with some injector cleaner, and I’m upgrading the radiator to a mishimoto.

the only other thing I can think of is to replace the fuel filter, clean the injectors, and go back to stock spark plugs or a stage cooler. The low HC and O2 tell me the cat is probably fine.

Currently replaced: AFM, O2 sensor, oil + flush, air filter.

any thoughts? Thank you!
 

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90T
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I need your CO2 and O2 numbers too please.

Seems as though your EGR valve is working fine.
Check if the vac modulator passes this test. If it does then the remaining thing is the VSV that control vacuum to the modulator.


264095
 

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Discussion Starter · #13 ·
I need your CO2 and O2 numbers too please.

Seems as though your EGR valve is working fine.
Check if the vac modulator passes this test. If it does then the remaining thing is the VSV that control vacuum to the modulator.


View attachment 264095
I tested the modulator with the tsrm directions and it’s working properly. Here are the full smog details. Thank you for your help!
264107
 

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90T
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264108


You are in fuel control but a tich lean. That's unusual for the 7M and I only see it when people are failing NOx.
Good news that the vac modulator passes. I would focus on the vac piping and VSV under the intake manifold. Something is preventing that valve from being turned on when needed at cruise.
 

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Discussion Starter · #15 · (Edited)
View attachment 264108

You are in fuel control but a tich lean. That's unusual for the 7M and I only see it when people are failing NOx.
Good news that the vac modulator passes. I would focus on the vac piping and VSV under the intake manifold. Something is preventing that valve from being turned on when needed at cruise.
Thank you! Is it possibly just a dirty fuel filter? I’ll try and find a vsv, but I imagine it will be difficult. I’ll also check all the vacuum lines going to the vsv.
 

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Discussion Starter · #17 ·
You can test the VSV. Apply 12V and see if it opens. I don' think it is the fuel filter. I think the ECU is commanding EGR and not getting it. The lack of inert exhaust gases is pushing the mixture a tad lean.
Thank you! I found the vsv test process in the same section as the modulator, so I’m going to check that and check the vacuum lines/replace any I missed.
 

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Discussion Starter · #18 ·
You can test the VSV. Apply 12V and see if it opens. I don' think it is the fuel filter. I think the ECU is commanding EGR and not getting it. The lack of inert exhaust gases is pushing the mixture a tad lean.
When you say the lack of inert exhaust gasses, are you referring to my oxygen level? Is the expectation that the oxygen level should have been higher?
 

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The EGR pumps inert gas (exhaust gas) into the intake.
The ECU expects this and reduces fuel to still hit stoich with less fresh air being injested.

This can cause your lean condition resulting in high oxides of nitrogen.
 

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90T
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yup. Your EGR system appears to be mostly working it just needs to get vacuum to it when its cruising so the NOx can come down. Seems like its down to just some vac plumbing issues.
 
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