Bleeding off fuel pressure overnight
 

Hey guys.
So I've searched on a couple of forums and have tried everything they suggested and haven't resolved my issue.

So my miata is taking forever to crank on cold starts. I originally replaced injectors with brand new DW700cc and put in a new radium rail with new lines from the firewall forward. This includes a new pressure regulator. Also have a new dw 300 fuel pump.

I am inclined to say that it may be the fuel cap but I dont Know. Also the car has a charcoal canister delete and the line is just open. (Not bypassed to the frame)

Thanks in advance!

Tune your cold start...

Many aftermarket fuel pumps tend to bleed down, from what we’ve seen. What engine management are you using?

I have had a local tuner check through the map and he suggested it wasn't an issue with the map.

I have a custom built speeduino v4.

The issue, as I see it, is fuel starvation on cold crank because of loss of fuel pressure.

I had a walbro 255 originally before I replaced it with the Dw. I haven't found anything suggesting these pumps don't hold pressure (not to say they don't exist) which leads me to believe I may just have a faulty unit. Thank you guys for the quick replies!

My DW300 doesn't hold pressure.

Cycle key a few times to build pressure, it should fire right up after that.

Hmm... that's interesting to know. Aren't they supposed to have an antidrainback valve? Anyone know where I can buy one?

I know nothing about Speeduino. On my MS 3X, with 1.52 Proto 4, I have my priming delay set to 2.1 seconds. What really happens, is that, when key to Run, the pump runs about 5 seconds with the actual priming pulse seemingly at the end. This gives plenty of time to build pressure and squirt a healthy prime. After the pump stops, I move key to Start, and the car starts within 1 second. Gasoline. True down to 36F so far. Will be colder tomorrow, so we’ll see how it does a bit lower.

Does the same thing as multiple key On cycles, but is more predictable on priming quantity. And it is easier to explain to other drivers.

Ted said he tried after-market checks and still had issues. I talked with a fellow at work who used to be with Chrysler. He said that the Whalbro pumps were hit and miss with their plastic check valve ball seats.

If if you can make the Speed run the pump longer before you move to cranking pulses, or better yet, before your priming pulse, you will have a better time of it.

I'll look into figuring out priming delay and setting my pump priming time from 2.5s to 5s. Will report back tomorrow!

Anybody else agree that the best place to put it is right out of the tank?

Thanks again everyone for the help and advice!

So after playing around with it I found the my priming pulsewidth was at 3.0 which was not only hindering pressure buildup but was flooding the cylinders. Turned it way down to 1.0 and now it starts after one prime cycle.

I also found some anti drain back valves on amazon for about 15$ that seem like they might do what I'm looking for.

Thanks to all for the help I really appreciate it!