California Smog and OVP - PeachParts Mercedes-Benz Forum

mansnes · #1 09-06-2012, 03:08 PM

Hi there all,
Much appreciate all the extensive knowledge on the site. I have been sucking it up like a sponge.

I just recently came into the posession of a '92 300E (124.030) which I think is grey market (VIN: WDBEA30D6NB691603), which required that I take it to a smog shop, who proceeded to tell me it was a GROSS POLLUTER, entirely due to excessive hydrocarbon emissions, especially at idle (560 vs 120 max allowable).

It did have a few idiot lights: coolant level, washer fluid level, ABS, and SRS all lit. Thanks to this site, I was able to identify the cold start and ABS light as being OVP related. Yep, the fuse was burned out. Replaced. Starts really easily now - within 3 seconds - instead of 15. Also thanks to the site, the resultant fast idle (1300-1500) after replacing that fuse was identified as a vacuum leak, which I think I've fixed for the most part (though idle is still a little high right around 1000 - I'm still looking for more obvious hose problems).

Of further note, also thanks to this site, I built myself a code reader. Pin 3 has no codes to report, which if I understand it correctly, would be the one I should be concerned with for passing the smog certification. (Pin 6 reported 2 & 3, and pin 14 reported 4, 6, & 11, which I'll inquire about in a separate thread.)

My question is, could the blown OVP relay fuse cause the excessive hydrocarbon emissions recorded previously? Should I take it and get it tested again? I'd rather not throw money away if it wouldn't change the result. Though the car has about a quarter million miles clocked on it, it is running smooth as a baby's bottom.

PS: also thanks to this site: I identified coolant level being sensor/switch issue: fixed. Washer fluid, just unplugged the connector so now no light. I do try using the search engine first.

whunter · #2 09-06-2012, 08:30 PM

Fuel Injection

OVP relay, Over Voltage Protection Links

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MAVA · #3 09-06-2012, 09:21 PM

Michael,

I do understand your pain of not passing the test in the Union of California-"no pass-no registration-cannot operate the car on the streets?

I had a Ford Taurus wagon with 320Kmiles on it, and mine ran like a top, but the piston-blow-by killed my readings on the Emissions Machine. Basically the CAT's were clogging-up.

In your case, it is real simple:

A)No check engine light can be on! Automatic fail...Some test stations will get your money first, and then tell you you failed, but many will not let you take the test, and these.

B)No idle can ever be close to 1000rpm or over! Every engine out there idle's at half the RPM of yours.

mansnes · #4 09-11-2012, 06:44 AM

Thanks whunter for the links. I'd thought I'd read all the pertinent OVP pages, but there was one I'd missed and a re-read of them all again was worth the effort.

So with the OVP not working previously, there was no lamda adjustments being done and the system was stuck in open loop. Now that the OVP is again operational (must be as there was significant change when it had the fuse replaced), the system is trying to go to closed loop and respond the o2 sensor's feedback.

Since it was running really well (when warm) w/o the OVP, I figured that someone had messed with the A/F mixture manually to accommodate, but the security ball is still in place blocking off the tube, so that doesn't seem to be the case.

Right now, the Check Engine light is not lit, nor has it ever been for the two weeks I've had this car. I've looked, but haven't been able to identify any further vacuum leaks, but the idle is still way high.

What would cause an excessively high idle? I know it was dumping extra fuel into the cylinders (at least it was with no OVP) since the smog check indicated unburnt hydrocarbons. At idle, they were seriously excessive. I would figure the system would get flooded. I'm guessing the racing idle is because the system is leaning out the excessive fuel by way of feedback from the O2 sensor. Question is, why is it getting such excessive fuel?

I also know that one sure fire way to fry your catalytic converter is to dump unburnt fuel into it. I'm guessing a catalytic converter purchase is in my near future.

Jim B. · #5 09-11-2012, 07:35 AM

The dreaded high idle problem on this might be traced to the idle (air) control valve. Have you tried looking at that?

mansnes · #6 09-11-2012, 06:53 PM

I was trying to check the air flow sensor by way of the ratio. I connected up my duty-cycle reading DMM to ports 1 and 3 of the 9 pin connector on the left fender and with the key on, engine off, I was getting a solid 70%, as expected.

Then I manually deflected the air flow sensor plate roughly 10%, expecting to get a reading of 10% but it stuck to 70. Deflecting the plate all the way down, it still said 70%.

When I fully depressed the gas pedal, it went to 80%, not the expected 40%.

I then started it up and it was fluctuating between 49 and 51, sometimes as low as 47 and sometimes as high as 52, again as expected.

According to the air flow plate deflection values, WIS says to test the throttle valve switch. Assuming that is the rocker switch that's triggered with the throttle cable/actuator just rear of the fuel distributor, then it tests out fine - infinite resistance normally, <1 ohm with it tripped.

Clearly, I'm missing something here. Am I not going about this right or what? How should I really be doing this and what should I expect?

mansnes · #7 09-12-2012, 03:31 AM

that switch I tested was the decel switch. Still have to test the other switch.

mansnes · #8 09-13-2012, 02:11 PM

Well I found a couple vacuum hoses that go to nothing and a Y fitting that has one port plugged. Is there anywhere I can find a vacuum diagram for it? I have no idea where the hoses are supposed to go.

mansnes · #9 10-19-2012, 10:28 AM

So I now have no vacuum leaks. The vacuum hoses are not necessarily connected to their factory locations, but I went by the engine vacuum diagram and matched it up (it was quite different than what was under the hood. But the idle problem persisted. Increased as a matter of fact, ending up around 2000 RPM. So I then disconnected the throttle control valve which brought it right down where it was supposed to be. Makes it a bit rough at startup, however, until it warms up. Does this mean the throttle control valve is bad or is it more likely it's getting bad signals from the computer? It did bring up the CE light, which I obviously can't have. I don't want to just throw parts at it unless I know they are going to resolve the issue. Any help?

mansnes · #10 10-19-2012, 10:41 AM

Duh, er, Idle Control Valve...

JohnM. · #11 10-19-2012, 05:15 PM

If your HC is off the charts, check the following, if you haven't already.

-O2 sensor (check voltage under the passenger floor mat)
-Condition of Ignition components (plugs,wires,cap,rotor)
-Catalytic converter (does it rattle when you hit it with a mallet?)

OVP will have very little to do with high HC (mixture/ignition) problems. Yes, the Idle Control valve might be bad, but it might just be gummed up. Remove it and douse the insides with carb cleaner and put it back in.

Merkey · #12 10-19-2012, 11:19 PM

California spec Magnaflow Cat was $137 delivered from Summit... worked wonders on my ex-190 2.6!

mansnes · #13 10-20-2012, 03:58 PM

I was definitely thinking of doing the Cat. There's a new, nearby shop that's got a grand opening sale for a catalytic converter for $99. With 250,000+ miles on the vehicle, it's pretty much exceeded the expected the lifetime for the catalyst by about 2x (I'm pretty sure it is original equipment).

But right now, my problem is getting the idle to go down. With everything connected the way it is supposed to be, it'll idle at 2000 RPMs. It is only if I disconnect the Idle Control Valve that the idle goes to where it is supposed to be, but kicks off the CEL. There's no way I'm going to pass smog with a 2k RPM or CEL lit.

I'll be testing the O2 sensor in a few minutes, when I go out and pull the idle control valve and clean it out. I'd figured it was working correctly because it will go into lamda and alternate between 49-51 duty cycle. But I guess who's to say that that is where it needs to be.

Plugs were recently changed, cables tested OK, but didn't look at the cap/rotor yet. But still, those won't affect idle.