Testing Cold Start Valves on a Gen1 - Mercedes-Benz Forum
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post #1 of 15 (permalink) Old 04-12-2019, 03:35 PM Thread Starter
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Testing Cold Start Valves on a Gen1

Afternoon folks!

So my 85 500SEC has a bit of lethargic start. Had some time today, and suspecting the Cold Start Valve wasn't firing, I did some tests.

Fuel pressure is good, injectors are all new, accumulator is new. After starting, car runs and idles flawlessly.

There fuel pressure in the line to the injector so fuel distributor is good.

I pulled the injector, put it in a jar and turned the ignition on - no fire.

Tried 3 different cold start injectors I've collected from parts cars - no fire on any.

Removed the wires from all the temp sensors thinking that could be a problem - no fire

I'm running a Gen2 FPR so I can get the pre-prime function, so I swapped out to my original Gen1 FPR - no fire.

Voltage test - none that I can see. even a blip.

Now I'm stumped. Nothing I've tested is triggering the Cold Start Injector to fire. Anything I'm doing wrong?

1991 560 SEC Euro
1986 420 SEL
1985 500 SEC (US)
1983 500 SEC (Euro)
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post #2 of 15 (permalink) Old 04-12-2019, 03:45 PM
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Hi there CC,

How frustrating!

The Cold Start Valve will only receive an actuating signal & work if the vehicle is 'cold'.

As I understand it .. sitting overnight, or sitting unused for more than, say 6-8 hours.

Before those parameters are met.... It should not function at all.

This message from the sometimes frozen NorthEast US.

That's what I was taught about a hundred years ago in Fuel Injection school...

Good Luck, man.

MBL


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post #3 of 15 (permalink) Old 04-12-2019, 03:50 PM Thread Starter
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Thanks MBL.

There should be a way to fake it, yes? Seems from reading that a ground comes from the Thermo time switch. Perhaps a way I can ground that part of the harness out to test temporarily?

1991 560 SEC Euro
1986 420 SEL
1985 500 SEC (US)
1983 500 SEC (Euro)
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post #4 of 15 (permalink) Old 04-12-2019, 03:55 PM
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Forgive me if I’m missing something, but I don’t think the injector will receive voltage with just the ignition on. My understanding is that it was tied into the starter circuit and only fires during cranking. But maybe by “ignition” you were referring to the “start” position.
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post #5 of 15 (permalink) Old 04-12-2019, 03:57 PM
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What car is it? I'll have a look at home over the weekend to see if I have something. Your profile says 1991 560SEC.
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post #6 of 15 (permalink) Old 04-12-2019, 04:00 PM
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Quote:
Originally Posted by jackjtr View Post
Forgive me if I’m missing something, but I don’t think the injector will receive voltage with just the ignition on. My understanding is that it was tied into the starter circuit andonly fires during cranking. But maybe by “ignition” you were referring to the “start” position.
You are correct Jack.

M
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post #7 of 15 (permalink) Old 04-12-2019, 04:01 PM Thread Starter
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The car I'm working on is a Gen1 500 SEC (1985). My Gen2 in my profile is working fine.

I *thought* the injector fired when it was in the START not RUN position. I can check again in RUN.

1991 560 SEC Euro
1986 420 SEL
1985 500 SEC (US)
1983 500 SEC (Euro)
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post #8 of 15 (permalink) Old 04-12-2019, 04:04 PM
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Quote:
Originally Posted by corellian corvette View Post
The car I'm working on is a Gen1 500 SEC (1985). My Gen2 in my profile is working fine.

I *thought* the injector fired when it was in the START not RUN position. I can check again in RUN.
Hey CC,

You're correct.

Its function is to provide extra fuel into the inlet for enhanced cold start.

OOPS. NOT run, as you said.

M


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post #9 of 15 (permalink) Old 04-12-2019, 04:08 PM Thread Starter
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OK sorry - just to confirm MBL

Does it fire with the Ignition in START on only during cranking?

I have been testing by turning the ignition to START but NOT cranking the car. All my tests performed under this condition as i recalled that's how it was on my Gen2.

However, the problem persists even when cranking. Just tried 2 injectors and started cranking the car, to no avail.

So now the question is if I can ground the Thermo valve switch and "fake" a cold condition to test. One problem I see is there are two thinks that look like they could work - one on the rear passenger side of the car, and one on the front drivers side near the cold start injector. I did test continuity between 2 connections at the front sensor, but grounding out the wiring didn't do anything.

So still, cranking or START position I still have no cold start injector.

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1986 420 SEL
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post #10 of 15 (permalink) Old 04-12-2019, 06:48 PM
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The pictures should should provide you the info you need.

Roy
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