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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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Cool. I will be curious about the results. Remember, the resistor should only be energized for a few minutes during cold startups.
 

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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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Discussion Starter #23
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.
Cool. I will be curious about the results. Remember, the resistor should only be energized for a few minutes during cold startups.
Given that it is energized for only a few minutes, is that more of an FYI on your part or are you warning me of something?
 

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1990 Benz 300E 2.6 (mine) ; 1994 E320 Wagon (wife's) ; 1993 300CE Cabrio, needs some TLC
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Mostly, if the 6 ohm resistor will be dissipating 25 watts, then using a 50 watt resistor is very appropriate.
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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Given that it is energized for only a few minutes, is that more of an FYI on your part or are you warning me of something?
No, just an FYI. With a 50 watt resistor, a 24 watts dissipation, and the short duty cycle, things should be fine.
 

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'95 E320 Wagon & '98 BMW M3
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I was thinking about deleting it on the '95 E320 (160k) as the bearing had become noisey... I just went thru replacing the fan bearing bracket and idler pulley. I ended up taking it out, replacing the bearing in the pulley and cleaning the pump inside. It's been quiet ever since.

The last noise maker is the A/C pulley, which I haven't tackled and I'm not sure its the same setup or even doable.
 

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1995 E320, 1995 E420
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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).
Not all cars. I have a 95 e320 Canadian import and it has smog pump and I occasionally get code 4.
I thought all Canadian cars were same as California models with onboard Blink and had equipment for emissions compliance.
 

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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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Discussion Starter #28
No, just an FYI. With a 50 watt resistor, a 24 watts dissipation, and the short duty cycle, things should be fine.
Poo, it threw the same light again, same code. Any other ideas?
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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Bummer!! I was hoping for an easy hack. A couple of thoughts:

A 6 ohm load may not be sufficient to fool the ECU which is expecting a 3 -4 ohm load, although I would tend to doubt it because, unless there is a specific need for precise current measturements, these types of circuits tend to be somewhat non-specific (and therefore cheap to implement) about the load to satiate them.​
Do you have a loose connection to the load resistor? Did it take longer (more drive cycles) for the CEL to come on than without the resistor? I think the air pump code one of those that normally pops up fairly quickly so a delayed CEL could imply that the resistor was working until the connection came loose.​

Other than that, I can only conclude that the ECU is also checking the actual airflow from the pump via the O2 sensor or via some other algorithm. While difficult to implement, this would make sense from a "systems" perspective. This would be like the delayed up-shift error - the ECU checks both the solenoid load and the actual delay in up-shift when cold.

So maybe, its' back to replace the pump or replace the ECU with a non-air pump version. While you're at it, you might want to get a non-EGR version as well if you can and save on any future codes.
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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I just happened to be looking at the table of error codes and noted that code 35 for the air pump says, "Model 124,129 and 140 AIR pump switchover valve and/or electromagnetic AIR pump
clutch." There is no mention of airflow as part of this error code. Is this the code you have? If so, this makes me think that you may have an intermittent connection to the resistor or it's value is not low enough to fool the ECU.

Just a late thought. . . .
 

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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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Discussion Starter #31
I just happened to be looking at the table of error codes and noted that code 35 for the air pump says, "Model 124,129 and 140 AIR pump switchover valve and/or electromagnetic AIR pump
clutch." There is no mention of airflow as part of this error code. Is this the code you have? If so, this makes me think that you may have an intermittent connection to the resistor or it's value is not low enough to fool the ECU.

Just a late thought. . . .
Sorry for late reply, been out of town for a bit.

So, I have error code 4 (air pump inop). I verified the connections as the car warms up in its first two minutes, especially that the resistor gets hot to the touch.

I can try another resistor, maybe 4 ohm?
 

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1990 Benz 300E 2.6 (mine) ; 1994 E320 Wagon (wife's) ; 1993 300CE Cabrio, needs some TLC
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a 4 ohm resistor likely would get even hotter, lets see, 12^2/4 is 144/4 is 36 watts, so you probably should use a 100W resistor.

but it also could be the switchover valve, I think this is on the front end of the head, next to the cam advance and cam timing things
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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Sorry for late reply, been out of town for a bit.

So, I have error code 4 (air pump inop). I verified the connections as the car warms up in its first two minutes, especially that the resistor gets hot to the touch.

I can try another resistor, maybe 4 ohm?
Which diagnostic pin number are you reading the code from? Do you have a California car with the Diagnostic module and the push button and LED on the diagnostic connector?
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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Here's an idea. Why not just hook up the air pump like it was designed to be? Just sayin'
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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Here's an idea. Why not just hook up the air pump like it was designed to be? Just sayin'
Ah, what fun would that be . .
 
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Discussion Starter #36
Here's an idea. Why not just hook up the air pump like it was designed to be? Just sayin'
They're expensive, and when the seize i've read about all sorts of nightmares, that's why.
 

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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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Discussion Starter #37
Which diagnostic pin number are you reading the code from? Do you have a California car with the Diagnostic module and the push button and LED on the diagnostic connector?
I'm holding the button on the LED diagnostic connector and getting those 4 blinks.
 

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They're very easy to find 2nd hand in the very rare event they seize. More likely they just make noise during cold start warm up and then they shut up.

You're obsessing over nothing IMO
 
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