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Old 10-11-2004, 07:00 PM
Registered User
Join Date: Oct 2004
Location: Summit NJ
Posts: 3
Angry Hard Start

Hi All,

First time seeking help. I have a 1985 500SEL with 225K. Problem is a hard start when warm/hot after 15 minutes to a couple of hours. Starts fine cold and hot.

I decided to put new injectors in and replace the accumulator and check valve. Fuel pump meets volume test. I dont think the pressure regulator is leaking in the distributor because I removed the return hose and nothing came out.

I am a hack with no testing equipment. Spark looked fine at the cap.

I also have noticed recently that the ABS light is on. Dont know if this is related to the ovp or the sensors are bad,... (not sure this is related)

Thanks in advance.
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Old 10-12-2004, 02:57 PM
Super Moderator
Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
Can you borrow a set of gauges for testing Bosch injection? They connect to the warm-up regulator and line to it. Then you can verify that you are have system pressure and control pressure when starting.
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 10-12-2004, 03:44 PM
Registered User
Join Date: Oct 2004
Location: Summit NJ
Posts: 3

will try to borrow one or buy a cheapo...

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Old 10-12-2004, 04:33 PM
nglitz's Avatar
Registered User
Join Date: Aug 2004
Location: Hamilton Square NJ, near Trenton
Posts: 391

Not sure if this is even relevant to your car. A similar problem on my '87 260E (KE Jetronic fuel injection) was caused by the coolant temperature sensor. This is a little brass bodied, two pronged, sensor that sits on the back end of my 6 cyl's head. No idea if your car has a similar beastie, but if it does would be worth checking.

Typical test procedure says to check from terminal to terminal. You should get a resistance that varies with coolant temp. Off the top of my head, 3k at 20 C and 100 at 80C, but don't hold me to those numbers. There's a chart floating around. What I found by looking at wiring diagrams is that the sensor is actually two resistors, both with an end at ground and the other end at a terminal. IOW, check from ground to each terminal and look for 1/2 the resistance. One side is for the ignition & the other for the fuel injection. If one side is open, try switching leads as a temporary fix, the fuel is much more sensitive than ignition. a new sensor is about $40.

An open circuit tells the electronics that you're parked in the Arctic & need lots of fuel. You'd need to hold the pedal down to keep from flooding it.

As far as "no testing equipment" goes, Sears sells a meter for $40 that does the usual volts & ohms and also duty cycle for fuel injection. It helps.
Norm in NJ
Next oil change at 230,000miles
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