MSefi.com read only forum (Jan.15,2018)

While troubleshooting hard starting I noticed that my fuel pressure drops pretty fast after the initial fuel pump prime(before cranking)...from 40psi to 10 psi in 5 seconds. Is normal?
I have this pump...
http://www.summitracing.com/parts/SUM-G3138/

With this regulator (gauge installed on it)..
http://aeromotiveinc.com/products-page/ ... regulator/

I removed the throttle bodies to see if fuel was getting out of the injectors but they were dry....no leaks anywhere in the high pressure lines.
I added a check valve after the pump...http://aeromotiveinc.com/products-page/ ... ve-orb-06/

Still loses pressure...any ideas or is this standard?
Pressure holds at 40psi once car is running.

BTW this is on a 66 bug with dual 48 throttle bodies.

Thanks

Aeromotive regulators don't seem to hold pressure when the pump is shut down like some others do, so I suspect you're OK there.

I have the same problem too.. my Malpassi FPR doesn't hold the pressure after the priming pulse either, searching for a solution though...

Me too. Malpassi adjustable non rising rate type. I'm thinking about changing back to the original fixed Lucas regulator. Since being able to adjust the pressure isn't as important with MS. It could also be down to the quite low pressure my original Lucas injection runs at - 36 psi - which I stuck with. With much higher ones the Malpassi may work as a non return valve.

But it doesn't appear to matter much with a cold start. My engine requires a bit of spinning anyway. Could be down to EDIS? Needs a couple of complete revolutions to sort out where to spark? Dunno.

But it does matter on a hot start. It starts easily if you run the pump first up to pressure - which takes a few seconds. Otherwise a lot of spinning over. Probably due to fuel evaporation on my particular installation. Lots of heat soak.

I've modified the MS pump circuit so the pump relay coil also gets fed from the starter switch (via an extra relay and a couple of blocking diodes). My car's an auto, so in drive the starter doesn't operate, but the pump will when you turn the key. Wait till it is up to pressure, then flick it into neutral which then runs the starter.

I've asked if it's possible to alter the length of the priming signal from MS to the pump, but apparently not easily.

Hmm... Alter the length of the priming signal... Haven't thought of that.
Maby one can put a big condensator to hold the relay voltage for a little longer but it would have been much easier to just change the lenght in the software.
I have replaced an old K-Jet on my 280 SL and it had an fuel accumulator to maintain the pressure for at least 20 min, Isn't there anything like that to buy anywhere?
I dont like to spin the start motor longer then necassery...

peei wrote:Hmm... Alter the length of the priming signal... Haven't thought of that.
Maby one can put a big condensator to hold the relay voltage for a little longer but it would have been much easier to just change the lenght in the software.
I have replaced an old K-Jet on my 280 SL and it had an fuel accumulator to maintain the pressure for at least 20 min, Isn't there anything like that to buy anywhere?
I dont like to spin the start motor longer then necassery...

It would be pretty easy to fit an external 555 timer which was triggered off the priming pulse - to extend that pulse to anything you wanted. However, the pump stops after a short while to prevent excess fuel spillage if leaking or flooding if you have a weeping injector. And of course the fuel needs to be cut off in event of an accident where the engine is stopped.

With my original Lucas EFI, the pressure stayed up for days. Only part I've changed from standard is the reg - the injectors, pump and pipework are all original spec.

The correct solution is of course to mount something on the fuel return line which hold the pressure between the fuel pump's "one way Valve" and the return line, if anyone have any suggestion, please share it.
ps. maby the old fuel accumulator from the Bosch K-Jet system will work, maby worth a try...
//Peter