EHA current / emissions question

[spektorm]

Hello,
I have a 1990 300te with 185k miles. It just barely failed emissions recently (on hydrocarbons). Here are the current values:
THC (g/mi): 1.87 (max 1.20)
NOx (g/mi): 1.34 (max 3.00)
CO (g/mi): 3.7 (max 30.0)
CO2 (g/mi): 739.1

Here are the values from 2 years ago, when it passed:
THC (g/mi): 0.97 (max 1.20)
NOx (g/mi): 0.75 (max 3.00)
CO (g/mi): 4.4 (max 30.0)
CO2 (g/mi): 798.1

Notice how THC and NoX went up roughly 100%. I don't know if that says anything.

It wasn't throwing any check engine codes, and I proceeded to check the EHA current. This is where it gets interesting. At key on, engine off, the current is about +22mA. As I understand, it should be 20. When running it oscillates around +3-4mA, and the duty cycle on pin 3 of the X11 connector oscillates too, which tells me that it's running in closed loop. When I disconnect the oxygen sensor under the passenger side carpet, the EHA current does NOT go to zero, but rather stays around 3-4mA, but does not oscillate. If I give it some throttle it changes a bit. Duty cycle on pin 3 is at a steady 49.9 with the oxygen sensor disconnected.

On top of this, the EHA is wet with gas underneath, so it probably needs to be replaced. Could this explain the current discrepancies? Could this also be why my car didn't pass the emissions test? Are there any other signals that could cause the EHA to have current without the O2 sensor connected, or is it definitely because the unit is leaking?

Thank you very much.

Michael

[stevebfl]

My guess is your ammeter is off. Its off 2ma at KOEO and when it should be zero it is 3-4 different. Looks very similar to me.

The fact you are in closed loop means you really are set-up in a way that should be plenty clean enough for IM testing. I would guess the catalyst is either degraded or too cool in the recent test.

I'm not in a testing area so I'm not too knowledgable on testing technique but I have read of products that perk up cats for testing purposes. I also would recommend a decarbonizing treatment and a good hard highway drive before the next test. On the day of the test also drive the car hard 3rd gear all the way, maybe.

And fix the EHA, and put in a new set of plugs.

[Duke2.6]

What location and type of of test? Also, did the printout provide O2 levels in the exhaust? The O2 level is a key diagnostic tool. If there is any O2 left in the exhaust it means there is room for improvement if the converter oxidizes more effeciently, which will usually occur if the converter is hotter. The converters on these cars cool considerably if the engine idles for more than a few minutes.

HC on M103 engines is usually high, and it due to too cold a converter at the beginning of the test, which is caused by excess idle time prior to the test or shutting the engine down for a period of time prior to running the test.

Prior to the test thoroughly warm up the engine and run it as hard as you can. In CA we have drive through emission test stations. My advice to owners is to go to one with a short or no line prior to thoroughly warming the car up as above. Keep the engine at 2000 revs with the defroster on Max (which will engage the compressor) to put some load on the engine while you wait.

Another alternative is to go on a rainy day and ask the tech to run the "tire dry test". This involves running the car on the rollers at about 25 MPH with no load for about a minute, and this will heat up the converter enough to reduce the HC count about 20 percent on the first 15 MPH loaded test, which is typically were the HC is on the ragged edge if not above the limit.

Duke

[spektorm]

Thank you very much for your responses.
The multimeter is brand new. It's one of the Sears ones recommended in another thread. Today I verified the result with another multimeter by a different manufacturer. KOEO current was +22.5mA. Upon cold startup, current started out around +9mA and slowly decreased. I disconnected the oxygen sensor, and it didn't go to zero. It kept decreasing as the car warmed up, leveling out at around +2.6mA. After leveling out, throttle did not affect the current. Upon plugging the oxygen sensor back in, the reading fluctuated between around +1.7 and +2.2 (different from yesterday, interestingly enough). Disconnecting the oxygen sensor left the value at 1.7. It seems that when the sensor is disconnected, the EHA doesn't go to zero, but "sticks" at the value it last read from the oxygen sensor. Even more interestingly, I shut off the car, and KOEO current was +21.7mA!

Can the EHA be "sticking" like that? Or is something else going on? I am in Oregon and, unfortunately, my DEQ report doesn't include the O2 reading. The test was right after a highway drive, but it did idle for a few minutes before the actual test. As for decarbonization, I have some Seafoam I can run through it. Has anyone done that? If so, what vacuum line did you use to put the Seafoam in?

Thanks again

Michael

[ctaylor738]

Everything seems to be working, but you seem to be getting about 2 mA more than you should. So something is telling the brain to enrich. You should be fluctuating right around zero at hot idle.

What readings are you getting from the coolant sensor? The spec is 2.3 - 2.8 kO at 20 degrees coolant temp, and 280 - 370 O at 80.

If the EHA is leaking, I would replace it on principle.

You might also try richening the mix in small steps and see if that brings the EHA readings down to around 0.

Assume you have checked for vacuum leaks around the injectors, manifold, and other plumbing?

[stevebfl]

The EHA does not control current the controller does.

From your readings, looking at the 2ma is similar to trying to count the number of trees in a forest by measuring how tall the first one is. While it may be interesting, it plays no part in the diagnostics in my opinion.

The whole point of the KOEO position is calibrating yor mind and instrument. From your readings everything works as it should minus 2-3ma.

[MrCjames]

Try holding the engine RPM's to approximately 2000 and make an incremental adjustment to your CO while monitoring your meter. The adjustment should bring your EHA current within the desired control range of 0mA. This may help reduce some of your HC; however, it is unlikely to have any significant effect to your NoX.

The 1990 103 should be fitted with an EGR system, the purpose is too assist with a good portion of NoX reduction. Your tube may be partially restricted due to carbon build up at the intake manifold opening. A completely clear tube will help reduce the NoX to some degree (case by case basis), final reduction is addressed by the CAT.

CAT temp is critical, as well it needs to working to some level of efficiency and your's may be getting tired.

Just say no to "Carbecues," repair the fuel leak.

[spektorm]

I would like to thank everyone for helping. I will get around to replacing the EHA, but for the time being, I put it all back together, with a new air filter, PCV breather hose (from the crankcase to the air filter. The old one was cracked.), and ran Seafoam through it.
The DEQ results were astonishing:
THC 0.71/1.2
NOx 0.29/3.0
CO 8.5/30
Compared to the last test, it's like a brand new car.

So once again, thank you everyone for your help. This site is an excellent resource.

Michael

[Duke2.6]

What is "Seafoam"?

Duke

[MrCjames]

Magic in a can that apparently works to varying degrees for some vehicles to pass a state emissions test. I may need to consider it for my vehicle as I do not have an extra 1500 clams for a new cat, it barely passed the last test.

[spektorm]

It is not even primarily marketed as an emissions testing aid (like some products). It is supposed to remove carbon buildup, clean injectors, remove moisture from the fuel and oil, free sticky piston rings, and stop world hunger, among numerous other things. You can put it in your gas tank, crankcase, or feed it into your intake. I only fed it into the intake on the Mercedes.

My son heard about it on the Toyota MR2 message board, where at least one member had very good luck with it. His compression results before the treatment were 190 191 187 192, and after the treatment, 184, 185, 183, 185. The link to the thread is here:
http://mr2oc.com/showthread.php?s=&threadid=18533
But I believe registration may be required to view it.

One drawback of seafoam is that your car will emit a noxious billow of smoke during treatment, so you will definitely want to do this in a well ventilated area, preferably away from your neighbors.
To give you an idea, someone posted the following picture on the MR2 board:


Here is some more information:
http://www.seafoamsales.com/motorTuneUpTech.htm

Hope this helps

Michael