Hello everyone.

Figured I will register after countless hours of searching and reading old threads, I have not seemed to find the solution to my problem. I have a 1994 e320 wag. My air pump started making terrible noises and bearing on it almost seized.

So I figured I will do some reading and bypass it and use a shorter belt. Which I did. I put a vacuum cap on the line that goes from the vacuum block on the front of the head, and I took off a valve and capped of a big air/rubber line that went from the pump to the metal line to the head eventually. After I was done and started the car, i noticed hesitation and misfire in my idle and you can hear the misfire by the exhaust flow and engine sound. The misfire is even more n
noticeable in Drive or Reverse then in Park or Neutral.

My first guess is a vacuum leak and I went searching for it, did I plug all the lines that needed to be after the air pump bypass or am I missing something? I have checked all the other vacuum lines and everything seems to be fine. Within last year MAF, Plugs, Filters, were all replaced on the car and it ran with no issues taking it has 220k on it. Where else should I look or what can be the culprit of the problem? Any information or diag process tips would be appreciated.

Hi,
does the vehicle/engine run fine at Operating Temperature?

__________________
Mostly, I don't know notin, I just know where to look.
I am looking back, to over 30 years in Electronics Design.
Electrons don't care if they move in a car, computer or relay!

95 W124 E320 M104.992 - Because, I love to repair, naaaah!
Over 221,000 Miles
Cheers,
Norbert

The airpump is a device that helps to make your engine run richer at cold start and til a certain engine temperature is reached. After that the pump is switched off.

The idea is that the pump allows additional air at cold start, which shows up at the O2 sensor as lean. The computer adjust to this condition by lenghten the fuel injection time, which runs the engine richer. Once a certain temperature is reached the air pump is switched off and the computer again adjusts accordingly.

By removing the pump and capping the air injection port, this control loop does not exist anymore. The engine doesn't get any additional air and the engine runs too lean during warm up.

If the engine runs rough after operating temperature is reached, then I would guess, additional air is making it to the intake ports.
If it only runs rough during cold start and up to, I believe, somewhere around 65C and runs smooth afterwards, you'll have to live with that or install a functioning air pump.

__________________
Mostly, I don't know notin, I just know where to look.
I am looking back, to over 30 years in Electronics Design.
Electrons don't care if they move in a car, computer or relay!

95 W124 E320 M104.992 - Because, I love to repair, naaaah!
Over 221,000 Miles
Cheers,
Norbert

Oldtrucker

thanks for the info , makes total sense. But in my case car misfires during a cold start and after at operating temp. Therefore like you said the question is there has to be an air/vacuum leak somewhere. I do not know if i am under looking something but I seemed to check everything. I have read some people having purge valve issues after air pump removal but I have not tested that component yet. I am quite sure the mixture is wrong at at the moment as I was inspecting it with an air-box off and looking for vacuum leaks and as I revved it up rapidly couple times i popped through the intake. Any further advice would be helpful as I do not know where to look next for a vacuum leak.