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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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Discussion Starter #1
Hey guys, read some of the smog pump delete stuff, but they say that it shouldn't throw a CEL. This is a 1995 with the M104.

Mine has a CEL after deleting the smog pump. The pump itself was physically removed, a shorter belt put on. The red vacuum hose that went to the smog pump from the square vacuum valve/box at the front of the motor is just capped off. . The hard metal line going to the block was also capped off with the factory smog pump delete cap.

I'm getting a CEL, and the LED error code blinks 4 times which is "air injection inoperative". Is it maybe the electrical connector that used to go to the smog pump is just going to nothing now?
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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I think you answered your own question. Deleting the smog pump = air injection inop.
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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1,326 Posts
Hey guys, read some of the smog pump delete stuff, but they say that it shouldn't throw a CEL. This is a 1995 with the M104.

Mine has a CEL after deleting the smog pump. The pump itself was physically removed, a shorter belt put on. The red vacuum hose that went to the smog pump from the square vacuum valve/box at the front of the motor is just capped off. . The hard metal line going to the block was also capped off with the factory smog pump delete cap.

I'm getting a CEL, and the LED error code blinks 4 times which is "air injection inoperative". Is it maybe the electrical connector that used to go to the smog pump is just going to nothing now?
I don't know where you got your information, but on a '95, the ECU absolutely checks the status of the air pump and will throw a check engine light every time if the pump is removed.

I'm not sure if the ECU checks the current draw on the air pump clutch solenoid or checks for an O2 sensor swing when the pump engages, but if it is the former, in theory, it should be possible to wire a load resistor in place of the solenoid to "fool" the ECU into thinking the pump is there. If it is the latter, your only option is to replace the pump.
 
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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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307 Posts
Discussion Starter #5
Does anyone know the part number for a no smog pump car ECU? Or what the load resistor rating should be if I go that route?
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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I believe the Canadian version of the M104 HFM ECU does not have a smog pump. I had one, but I sold it when I sold my Turbo Techniques setup. PM member joef (from whom I got it) and see if he has the P/N and/or a line on one.

As for the resistor, I don't know the resistance value off the top of my head, but you would need to measure the resistance of the old pump coil and then calculate what wattage would be required (W = 196/R for this application).
 

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1993 230 TE.1999 om 606 td. and 722.6 3.2L,clk w208 1987 Kit car with 260e running gear.
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759 Posts
I could have helped you with a part number last year before I scrapped my e320 coupe. 722.5, no smog pump, no egr, 1995 model.
Sorry, maybe someone will chime in for you.
 

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04 odyssey (265k) 1995 E320 wagon (295k)
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One less expensive part to replace when it fails. That's about it.
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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It seems to me that this falls into the category of "If it isn't broken, don't fix it." The pump only runs at startup so its effect on performance is negligible. When the bearing goes, you may want to consider it.
 
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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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307 Posts
Discussion Starter #13
I don't know where you got your information, but on a '95, the ECU absolutely checks the status of the air pump and will throw a check engine light every time if the pump is removed.

I'm not sure if the ECU checks the current draw on the air pump clutch solenoid or checks for an O2 sensor swing when the pump engages, but if it is the former, in theory, it should be possible to wire a load resistor in place of the solenoid to "fool" the ECU into thinking the pump is there. If it is the latter, your only option is to replace the pump.
How would I know what type and rating of resistor to put on the old electrical connector that is hanging there?
 

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1993 230 TE.1999 om 606 td. and 722.6 3.2L,clk w208 1987 Kit car with 260e running gear.
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759 Posts
You would need to measure the resistance of the pump windings to start with.
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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With a digital meter, measure the resistance of your old pump clutch at the two pins coming off of it. Round down to the nearest 5% resistor value (a chart of these values can be found here: https://ecee.colorado.edu/~mcclurel/resistorsandcaps.pdf). Then determine the power rating required using P = (V * V) / R, where V = 13.8 volts and R = the value you chose from above. Round up to the nearest standard resistor wattage rating (For power resistors, usually, 1-5, 10, 20, 25, 50 watts). Then go shopping for one. Interestingly, Amazon is often a good source.

I will interested in the outcome if you do this - I've always wanted to know what detection algorithm is used by the ECU.
 

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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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Discussion Starter #16 (Edited)
With a digital meter, measure the resistance of your old pump clutch at the two pins coming off of it. Round down to the nearest 5% resistor value (a chart of these values can be found here: https://ecee.colorado.edu/~mcclurel/resistorsandcaps.pdf). Then determine the power rating required using P = (V * V) / R, where V = 13.8 volts and R = the value you chose from above. Round up to the nearest standard resistor wattage rating (For power resistors, usually, 1-5, 10, 20, 25, 50 watts). Then go shopping for one. Interestingly, Amazon is often a good source.

I will interested in the outcome if you do this - I've always wanted to know what detection algorithm is used by the ECU.
I have two multimeters, I set one to 200 ohms and got 3.2 but probing both pins from the air pump (mind you, the air pump is removed and is on the bench). The other multimeter I get 4.2, go figure. I think one multimeter when I touch its probes together says .1 The other meter when I touch its own probes together is like .7. So I guess I take the reading, and either take off or add the difference in resistance of the probes themselves amongst both meters.

The meters have a 20k and 2000 ohm setting as well, as those give different values. Can you educate me?
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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I'm not surprised that the higher range settings don't give reliable readings as a typical A/C type magnetic clutch (which should be similar to the air pump clutch) resistance of 3.5 to 5 ohms is a very small percentage of their full scale reading. The difference in readings on the 200 ohm scale are a little more disconcerting, Check the reading with the leads directly shorted - does each meter read zero?

Just for fun, I measured my air pump clutch "in-circuit" and got 3.2 ohms also. My second meter is foobared, so I can't double check it.

If it were me, I would take and $8 gamble and try a 5 ohm resistor, 50 watt resistor (https://www.amazon.com/LM-YN-Wirewound-Electronic-Industrial/dp/B076W841R9/ref=sr_1_2?dchild=1&keywords=5+ohm,+50+watt&qid=1592259545&sr=8-2) A 5 ohm load is about as high as you can go with just one resistor (there are higher power rated resistors, but these are harder to find) and 5 ohms should provide enough current draw to "fool" the ECU if indeed that is how it is determining pump viability.

But that's just me.
 

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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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Discussion Starter #18
I'm not surprised that the higher range settings don't give reliable readings as a typical A/C type magnetic clutch (which should be similar to the air pump clutch) resistance of 3.5 to 5 ohms is a very small percentage of their full scale reading. The difference in readings on the 200 ohm scale are a little more disconcerting, Check the reading with the leads directly shorted - does each meter read zero?

Just for fun, I measured my air pump clutch "in-circuit" and got 3.2 ohms also. My second meter is foobared, so I can't double check it.

If it were me, I would take and $8 gamble and try a 5 ohm resistor, 50 watt resistor (https://www.amazon.com/LM-YN-Wirewound-Electronic-Industrial/dp/B076W841R9/ref=sr_1_2?dchild=1&keywords=5+ohm,+50+watt&qid=1592259545&sr=8-2) A 5 ohm load is about as high as you can go with just one resistor (there are higher power rated resistors, but these are harder to find) and 5 ohms should provide enough current draw to "fool" the ECU if indeed that is how it is determining pump viability.

But that's just me.
The one meter with leads shorted shows the .6 to .7, the other meter shows the .1
I have a 50w, 6 ohm resistor....is the 6ohm too much?
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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The one meter with leads shorted shows the .6 to .7, the other meter shows the .1
I have a 50w, 6 ohm resistor....is the 6ohm too much?
My guess is that the meter that reads 4.2 ohms is also the one that reads 0.6 to 0.7 shorted. General purpose meters (read, inexpensive) meters can be inconsistent with low resistance measurements because there is no "zero" function.

I'd give the 6 ohm resistor a try since you have it. The worst that could happen in that the test is inconclusive and the ECU still throws a code.
 

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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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Discussion Starter #20
I've installed it, which is fun since it's the front of the valve cover area, and the resistors are that type that get warm. I placed it on metal bracketry where it wouldn't rest against any rubber vacuum lines and melt them. I also had to do it so that the black plastic front cover that snaps on wasn't interfered with. I'll give it a few days and report back.
 
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