Hello,

I have a 91 Honda Crx HF (D15B6). It is completely stock. Since I live in CA, I was required to smog the vehicle. It failed the first time for high NO number (max 812, but measured 886). So the smog tech suggested to change the CAT and O2 sensor before resmogging it again. So I replaced it with a CA compliant one. I brought it back to smog and it failed again. It has the same issue. High NO number. He tested the egr control valve and he believes the solenoid that controls the egr is not vacuuming the egr to stay open. I don't want to keep replacing parts unless I know that's the real issue. Is it unusual for a EGR control valve to go bad? Or possibly maybe I hook up the vac wrong since I did replaced the engine with a rebuilt one? Thanks

 

most emissions techs don't know troubleshooting, their first reaction is cat and O2 no matter the actual cause.

EGR can cause high NOx, but it is easy to test. engine idling, pull vacuum on the diaphragm, if the car stalls, then EGR ports are clean enough. secondly, is the diaphragm holding vacuum? if not, then that's probably an issue. if it is, then no issue at the EGR. next test is the solenoid that controls vacuum going to the EGR. Standard electrical test - is there resistance across the terminals?

 

How do I test the egr solenoid? Which settings do I set the voltometer to? And what do I use to test the vacuum?

 

Car doesn't stall when I pulled the vacuum line from the EGR? It continues to run smooth. And yes egr is holding vacuum.

 

If the solenoid was bad, the lift sensor on the top of the EGR would send a code to the ECU and you would get a check engine light.

EGR ports might be clogged with carbon buildup.
remove EGR and clean them out on both the EGR and the intake manifold.
Dont spray anything into the vacuum port on the EGR and try not to get solvents on the diaphragm.

How long did you use the car for after the new cat was installed?
what octane gas are you testing with?
Are you testing with any additives that you added to the gas?

 

read my post again.

nowhere does it say to pull the line off. that tells you nothing

I said to pull vacuum on the EGR - the car should stall. if not, clean EGR passages

 

Geeez.
i didn't read very well. Though he actually followed you directions and came back with those results.
Now it looks like he may have only pulled the vaccum line.

 

Sorry, I actually tried both. I pulled the vacuum line and I use a vacuum pump to apply vacuum to the EGR. The engine does stumble a bit but it does not dies. I can see the diaphragm actually going up as I apply vacuum.

But I did connect the vaccum pump to the egr vac line while I rev the engine. The more I rev the engine the higher the number on the vacuum pump itself. Correct me if I am wrong, but is it normal to see a sudden drop of vac pressure after continuously revving the engine. The pressure would suddenly drop to 0. So that leads me to suspect that the EGR control solenoid valve or the constant vacuum control valve (CVC)

 

Could the constant vacuum control valve (CVC) be defective? I tested the pressure on the EGR vac line with the vacuum pressure gauge attached. Whenever I rev the engine, the number on the gauge of the vacuum pressure pump goes up. But all of a sudden, the number just drops to 0 as if there was no pressure. I thought the higher the speed or RPM, the more the EGR diaphragm opens up? But I could be mistaken.

I failed the first time so I replaced the CAT and O2 sensor. But the NOX continues to stay the same. So I would say I have less than 20 miles on the new CAT before I resmog it again. I use regular gas (87), no additves were added prior to smogging the vehicle. Also I am not sure where the EGR port is located?

 

The EGR gets removed by taking off two nuts. The ports leading to and from the engine are underneath the EGR.
I've had success cleaning them with brake cleaner (CRC red can specifically) and B-12 chem tool (a little harder to work with).
With the EGR removed, you can clean the ports on the EGR as well.
There is a rod that is connected to the diaphragm that often gets caked up with deposits.
The vacuum pulls and releases the diaphragm which in turn lifts and lowers the rod that is actually closing and opening a path for exhaust gases to pass through.
Clean the rod off well to keep it from sticking during operation.

The EGR does not need to stay open during engine operation.
The ECU controls when it is necessary so I do not find it odd that you get a 0 vacuum reading at times.
It is likely the ECU just doing it's thing.

At one end of the EGR, there is an electrical connector attached to the EGR lift sensor.
When the ECU tells the vacuum to be introduced to the EGR, the vacuum pulls on the diaphragm, the diaphragm lifts the rod, and the lift sensor detects that the rod inside the EGR has been pulled close to it.
If you aren't getting a check engine light for EGR, then the vacuum, EGR, and lift sensor are all operational.

The ECU can not detect an EGR fault if the ports are clogged.
The O2 sensor ends up getting funky readings and starts adjusting as if the EGR was working.

After you clean out the EGR, head out for a drive. You didn't post any of your other numbers, but a catalytic converter may have manufacturing coatings and contaminants that you need to burn off before it can heat up and work properly.
Catalytic converters need to be hot to operate properly. Drive for a while before the test to get the cat nice and toasty. Pull up to the smog shop and don't shut the engine off. Leave the car idling until they test so the cat doesn't cool down right away. If they are busy and take longer than 5~10 minutes, then go for a drive and come back. It's not good to leave an engine to idle for too long.

Testing on a higher octane (89) should help lower the internal combustion chamber temps a bit - lower Nox.

 

Wow. Thank you for a detailed post. I really appreciate it. I will take your advice to thoroughly clean the EGR and the ports as well. Possibly even replacing the EGR valve. Would you suggest running it with 91 octane to help lower the NOX? The other numbers on the smog test are lower than normal range. I will post the exact numbers later.

 

So here are the results from the first and second smog test.

1st smog check
15mph
2392 rpm
CO2(%) 14.83
O2(%) 0.40
HC(ppm) 100 max, 41 average, 88 measure
CO(%) 0.61 max, 0.16 average, 0.04 measure
NO(PPM) 873 max, 463 average, 764 measure
Test result - pass

25mph test
2119 rpm,
CO2(%) 14.90
O2(%) 0.40
HC (ppm) 82 max , 33 average, 43 measure
CO(%) 0.52 max, 0.13 average, 0.03 measure
NO(ppm) 812 max, 396 average, 917 measure
Test Result - fail



2nd smog check
Replaced CAT and O2 sensor
15mph test
2575 rpm
CO2(%) 14.83
O2(%) 0.55
HC(ppm) 100 max, Average 41, Measure 24
CO(%) 0.61 max, Average 0.16, Measure 0.02
NO(PPM) 873 max, Average 463, Measure 948
Results - Fail

25mph test
2069 rpm
CO2(%) 14.74
O2(%) 0.60
HC(PPM) 82 max, 33 average, 22 measure
CO(%) 0.52 max, 0.13 average, 0.02 measure
NO(%) 812 max, 396 average, 886 measure
Test Result - Fail


So it looks like with the replacement of the CAT and O2 sensor caused me to fail the 2nd time on both the 15mph and 25mph test. However, the NOX number did drop a bit. And yes timing was set to 14BTDC.

The test result from the 2nd smog test leads me to believe that the CAT is not properly broken in yet hence the higher number on the test results.

 

Looking at your numbers, the cat and o2 did make numbers go down, but I'm not convinced you needed to replace them just yet.

 

So what do you think it is? I cleaned the EGR thoroughly. Is it normal for the engine to not stall if I apply vacuum to it while the engine is running?

 

When you had the EGR off, what exactly did you do for cleaning?
sometimes the ports are clogged and you can run them through with a coat hanger.
engine should stumble or stall when you pull vacuum on the EGR.

NOx is from high internal temps.
EGR is very likely.
too low octane gas is likely.
a lot of carbon build up on the pistons maybe
overheating and timing can do it too, but I don't think you are having those problems.

 

When I had the EGR off, I sprayed the EGR with CARB cleaners and scrubbed it down with a metal pipe brush. I applied vacuum to the EGR and sprayed the EGR port down with CARB cleaner until there was no more carbon deposits on it. I also scrub down the port on the intake Manifold. However, I am not sure if the Intake Manifold itself is clogged with carbon. But the EGR shaft moves freely. The engine is a rebuilt motor with less than 100 miles on it. However, the intake manifold was the only part that requires me to swapped over from the previous engine.

 

quick question. on your HF you should have had a manifold mounted cat. did you replace it along with a new (or used) non cat mounted manifold? or did you just add an under body cat?

i ask this because i was a commercial manager for oreilly auto/kragen for almost 10yrs and from what i can remember there were no replacement cats that were manifold mounted. for the crx chasss anyway. there were however some available for the ek chassis.

if you dd not replace the manifold cat i would bet thats your problem.

 

I replaced the CAT under the vehicle next to the shift linkage. I never thought of that. But I never realized that there were a manifold CAT on the exhaust manifold by the headers. But judging by the numbers from smog, it may be due to a clogged intake manifold or egr.

 

yeah go after the EGR issue. bottom line is the car should stall when EGR opens at idle. not to mention, and EGR is used to control combustion temps, which is the primary cause of NOx emissions.

 

Thank you sir 😁

 

So after 4 hours of thoroughly cleaning the intake manifold with oven cleaner and using high pressure water. I couldn't get the port within each chamber to clear. Each port appears to be clogged with deposits. The intake manifold was taken from a previous engine which had 280k miles on it. So, I decided to drill out the top of each chamber where the port suppose to be. Just as I suspected, each port was clogged with deposits. So I used a screwdriver and a coat hanger to clear each port. I also drilled out the side of the IM so I can clean the internals with a wire bottle brush and carb cleaner. I have a feeling my NOx will be a lot lower now 😉. However, I am still debating how I should fill the hole back up. I was thinking either JB weld or just tap it and fit it with a hex bolt.

 

Oh man - that's nasty!
Pretty wild that you had to drill into it in order to clear a path.
Usually a coat hanger is all it takes to get in there and clear a path..

At this point, it seems you would have better luck with a different manifold.
Welding the holes closed might work, but any other method may leak in the future.
I'm not sure how a smog tech would feel about a glob of JB weld in those places.

 

damn yo that's pretty extreme! I would have gone with a torch first before resorting to violence LOL

Hope you did that from the back side, though it doesn't look like it.

but yes, tap with the closest NPT and use some nice looking pipe plugs (find aluminum ones on mcmaster carr website) with teflon tape.

 

Tapped it with helicoil and a plug. Then I JB weld it up to ensure that it doesn't leak. Then a quick shot of engine gloss black to cover the ugly JB weld gray. Doubt it looks like I ever opened it up. 😜