Where can I buy a pop hand held tester for testing the fuel injectors for opening pressure etc?

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

last 1 i saw for sale was on ebay and went for about 150 usd. they weren't cheap when new, either. i had to buy a bowl for 1 in 99 or so and it was 50, i think. i gave up on cleaning kjet injectors. they've usually been in too long and are wore out as opposed to dirty. about 100k is the life. if yours are steel and not brass, replace them anyways. mb started using brass in the 90s because of the rust problems steel presents. good luck, chuck.