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Testing the Cold Start Valve

Repairs and Maintenance Blog

The DeLorean needs routine maintenance and the occasional, more significant refurbishing.  Beyond that there are also a number of customizations and upgrades to improve performance, reliability and functionality. 

Testing the Cold Start Valve

Joe Angell

On Tuesday morning I had taken the W pipe off the engine so that I could move the mixture unit to get a better look at the distributor.  Spittybug on DMCTalk asked me to check the mechanical advance, which would mean revving the engine with the vacuum disconnected from the distributor.

That sounded easy enough, so I put the W pipe back on, reconnected the idle motor (I'd moved it for better access), popped back in an injector I'd removed, and spent ten minutes trying to get the car started.  While it would crank fine and almost catch (like it would fire for three cylinders and then just crank), I started looking at the idle circuit.

I pulled the cold start valve by removing the two allen/hex screws holding it in place.  Once it was out, I used a PowerProbe to apply 12v to one pin and ground to the other.  This should have sprayed fuel, but I got nothing.  I tried again, reversing the pins, but still nothing.

Dave Swingle at DeLorean Motor Company Midwest suggested a few other things to try, which I'll include here in its entirety:

I’d like you to do one more cold start valve test. I have NEVER seen one fail so it pains me to see people throw that part at the engine. Actually the symptom you describe sounds like a good cold start valve and  a bad everything else (stuck fuel distributor for example).
1 – take the cold start valve off the engine.
2 – plug the grey plug from the warmup regulator onto the cold start valve. Put the cold start valve in a cup or jar.
3 – Pull the RPM relay. Jumper the brown wire on that socket to the Yellow-red wire AND the white-purple wire (the fan fail jumper is good for this if you have one). This will turn on the fuel pump AND hotwire the cold start valve at the same time.
4 – See if this makes the Cold Start valve spray. If so, it is not bad and you are chasing other problems. If it does not spray:
4A – Take the line off the cold start valve and turn the fuel pump on again. If no fuel comes out of that line, the pump isn’t running and you are chasing other issues. If fuel comes out of that line you probably do have a bad cold start valve.
ALSO  - disconnect the cold start valve and measure the contacts on the valve with an ohm meter. If you read just about anything but infinity it’s good. Should be under 200 ohms.
ALSO – see  if you can start and run the car on brake cleaner sprayed into the intake. If it will run on this, the entire ignition is good.
ALSO  - take off the air cleaner. Have an assistant try to start the car. While cranking press the air flap with your finger. This will put more gas in the engine. If it runs like this you probably have the CO set way too lean to run.

I had seen a few other posts about how the CSV rarely goes bad, so I was more than happy to do these tests.  This is what I found: 

  • Swapping the CSV's blue plug with the WUR's grey plug did not cause the CSV to fire.
  • Jumping the RPM relay by connecting Br, W/P and Y/R had no effect either.  Br is always live, W/P is the fuel pump, and Y/R is the CSV.
  • Removing the fuel line from the CSV sprayed fuel everywhere (what with this being a pressurized fuel system).
  • Jumping the RPM relay's Br and W/P wire with the fuel line disconnected sprayed fuel everywhere. 
  • I got a reading of ~5 ohms from the CSV.  While Dave said it should be under 200 ohm, Bitsyncmaster on DMCTalk.org reported that his was 5.1 ohms and suggested that I'd misread the meter when I'd originally reported 400 ohm (he was correct).  

I didn't get a chance to try the "ALSO" suggestions, but at this point it was clear that the CSV was either electrically bad or (more likely) clogged and inoperable. 

That was all I had time for on Thursday; further tests would have to wait until Sunday.