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  #1  
Old 03-03-2017, 09:19 PM
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Location: Oklahoma
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Testing a cold start injector - '91 300CE (M104)

I am stumped. I have had cold start problems for years, literally...Have finally got around to pulling the cold start injector and have no fuel coming from the injector while cranking...

Did some more tests this afternoon. With KOEO, I have 12 volts at the cold start valve connector and it does not drop below 10v while cranking. When I hook up 12v battery voltage directly to the cold start injector, it sprays fuel perfectly. But, I can not get it to spray while cranking. I have a spare coolant temp sensor (4 prong one) and I put it in a cup of ice water and hooked it up to the car's wiring to try and simulate cold weather. Ohms adjust appropriately - to 5+k ohms, so I think this worked, but it still won't spray any fuel.

Why is my CSV not working?

Any ideas?

Ryan
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #2  
Old 03-03-2017, 11:36 PM
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If you are getting a reading of 12v and the cold start valve is not actuating, it's likely you are getting a "ghost voltage " reading. The volts are there but the power is not. Check with a loading meter or try and plug in a brake light bulb and see if it lights up.

If it doesn't light, check your grounds first.
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  #3  
Old 03-04-2017, 12:01 PM
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No ghost voltage...unless ghost voltage can light a brake light!

Getting more confused - backprobed the CSV connector -with CSV connected - cranked car and had approximately 10v while cranking and still no fuel from the valve. Reconnected battery voltage again and the valve sprays great - nice mist and pattern.

Can't figure this out? Is 10v not enough to activate the valve while cranking??

I'm at a loss..

ryan
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #4  
Old 03-04-2017, 12:38 PM
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The + side of the CSV is always hot; the ECU grounds the other (-) side.
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  #5  
Old 03-04-2017, 02:29 PM
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Well, I was wrong. I think I am dealing with ghost voltage....initially - not thinking thru things well - I tested the current at the CSV connector by grounding to the battery - and the brake light lit up. But, I went back and used the ground wire from the CSV connection and no light! After checking the bulb again by hooking it up back to a good ground - and getting the bulb to light again - I am now not getting 12v through the connector anymore. KOEO I now have no volts...

Not sure what I did here...
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  #6  
Old 03-04-2017, 05:45 PM
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Just figured out why I had no longer had 12v at the connector - I blew one of the 10 Amp fuses in the OVP. Replaced it and I'm back to 12v...

But, I have no idea why I have this phantom voltage??? I know it was suggested to check the grounds - but I'm not sure how to go about that?

Any suggestions??

ryan
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #7  
Old 03-04-2017, 11:40 PM
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Join Date: Mar 2017
Location: Denver, Colorado
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It's NOT A TUMOR!! No such thing as ghost voltage -- remember that current actually flows from ground to the positive terminal.

You have a bad ECU my friend. Don't buy new -- the coupe unit is the same as the 4 door, but you must use the same year, and the part number should match exactly.

Bet you could get one for $25 at the pull and pay.
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  #8  
Old 03-04-2017, 11:45 PM
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Join Date: Mar 2017
Location: Denver, Colorado
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Also, these cold starts are notorious for locking closed or open, while the wiring is still good. Found a few rebuilds on Ebay for $40. Might be okay, but I'll bet further investigation might find that BMW, 3.2 or 3.5 vintage would work. Flow isn't super critical on these since they're only on for a short amount of time. We. Shall. See.
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  #9  
Old 03-05-2017, 08:50 AM
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I was actually coming to that conclusion - albeit very slowly. I was thinking though that I had a bad MAS sensor - not a bad ECU. This model car has the MAS relay that controls a lot of stuff in one box...but you're thinking its the ECU instead??

Thanks! I appreciate the Kindergarten Cop reference btw...ha!

Ryan
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #10  
Old 03-05-2017, 09:19 AM
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On the MY91 300CE, the cold start valve is controlled by the CIS-E control module at pin 20 (brown/pink wire). The module drives pin 20 low to activate the valve.
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  #11  
Old 03-05-2017, 11:40 AM
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Quote:
Originally Posted by Rick76 View Post
On the MY91 300CE, the cold start valve is controlled by the CIS-E control module at pin 20 (brown/pink wire). The module drives pin 20 low to activate the valve.
"prof":
See Post #4 (above).
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  #12  
Old 03-05-2017, 01:26 PM
300E Portline
 
Join Date: Mar 2017
Location: Denver, Colorado
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Cold start injector

Or CIS module. It controls pressure to the Fuel Distributor, depending on Oxy Sensor voltage, and trips the cold start valve. Located pass side, underhood, near the top of the cowl. Snatch them both.

Life is too short to chase down a bad diode in these things.
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  #13  
Old 03-13-2017, 06:52 PM
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Location: Oklahoma
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Well, I replaced the ECU and I'm still having problems. Checked the duty cycle at X11 with my meter and I'm getting 70% at KOEO, but none of the static tests follow specs from the online sources. After engine is warm, regeneration valve capped off, I'm getting a 20% NON-FLUCTUATING duty cycle.

From what I know, this is possibly O2 sensor related, but I have replaced it within the past several years.

Any thoughts? Why no duty cycle?
ryan
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1984 300D
1972 250
1986 560SL
1991 300CE
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