Instant starting

[Bitsyncmaster]

Something I have noticed with my car. I always had instant starting unless the car sat a week or more (which it then needs the cold start valve). Last time I adjusted my mixture (Dwell) I set it around 42 deg. My car is very sensitive to mixture setting which I assume is my FD may need a rebuild to fix that. But with that setting my car does not start instantly on a cold start (it does on a warm start). So I set the dwell to around 37 deg and it seems to have made the cold start instant.

Not sure if this is the normal. I know my sensitive dwell setting is not normal. If you're car does not start instantly you may want to try tweeking the dwell a little.

[David T]

Something I have noticed with my car. I always had instant starting unless the car sat a week or more (which it then needs the cold start valve). Last time I adjusted my mixture (Dwell) I set it around 42 deg. My car is very sensitive to mixture setting which I assume is my FD may need a rebuild to fix that. But with that setting my car does not start instantly on a cold start (it does on a warm start). So I set the dwell to around 37 deg and it seems to have made the cold start instant.

Not sure if this is the normal. I know my sensitive dwell setting is not normal. If you're car does not start instantly you may want to try tweeking the dwell a little.

By "tweaking" the dwell to improve cold starts, (which are a very short part of a driving cycle) you are not optimizing the closed loop portion of the driving cycle where the car spends most of it's time and where you want the most efficient operation. Instead of messing up the dwell I would investigate the systems that operate during the cold start to see what can be done to optimize them, they only operate during a cold start so anything you do to them won't mess up your closed loop. What you really want is some kind of delay before the starter works so the fuel pump has a chance to get some pressure up for the cold start valve. That way once it starts cranking the fuel system is "ready to go". Remember, the fuel pump has to pump up the accumulator at least a little bit before you get enough pressure to start the motor. The motor starts on the cold start valve and runs on that long enough for the fuel pump to get enough pressure to finish pumping up the accumulator and then enough pressure to operate the fuel injectors.

[mike123]

I hope I don't derail this, but coincidentally, I've been taking measurements of my cold starts for a few weeks now. I also noticed "instant" starting (e.g. no cold start valve) up through at least 4 or 5 days of sitting in the garage since the prior drive. I use your cold start valve (my Thermotime switch is dead and unplugged) and and I have been timing the starts and it's always less than 1 second (typically 0.75s to 0.95s). Does this mean the fuel accumulator is holding *some* pressure even after 5 days?

Oddly, the only time I've had a cold start take more than 1 second was a 1.07 second start where I used the 3-second RPM relay prime first. The car did not sound happy with that, and was shuddering a bit for about 20 seconds into running at idle. For these 4 or 5 days between starts, it starts much better if I just turn the key all the way to Start all at once.

I am going to try to wait 7+ days for my next starts and do an RPM Relay prime for one and not use it for another to see if at 7+ days the prime seems to become more helpful.

My car has a relatively new accumulator (~3 years old) and got tuned at a DeLorean-only shop around that time, so I am assuming my dwell and CO stuff is in a good place. I sure haven't touched it since that.

[Bitsyncmaster]

I have done minor adjustments to my warmup regulator. You can adjust both the hot and cold pressures which I did set them to book values. The hot is adjusted with the plug accessible on the top of the WUR. The cold is adjusted with an Allen screw under the bottom plate. I drilled the bottom plate to access that screw but you have to seal the hole afterwards with our WUR due to it using vacuum to the case.

To fully charge our fuel accumulator it takes 40 seconds of the fuel pump running. There is a very small orifice inside the accumulator. That permits full fuel pressure to the engine as soon as the fuel pump runs. It also lets the engine run with full pressure even when the bladder in the accumulator fails. So I would not think not waiting for the RPM relay prime would affect instant starting.

I'm always thinking of rebuilding my FD but other then that sensitive adjustment the engine runs great.