I have a 1978 C3 with a L48 engine and auto box. When I bought the car 6 years ago it came with an MSD Atomic EFI system fitted, along with an MSD Digital 6A Ignition Control system.

In all the time I’ve had the car it has never let me down, but just lately it’s become a pain to start, and occasionally the engine will cut out if I have to make a quick stop. Also, if I have to lift off the throttle momentarily and then put my foot down again, there is a marked hesitation in engine pick-up. I’ve done nothing that I'm aware of that would bring about this change.

I’ve since checked out all the ignition system (timing, plugs, leads, distributor, cap and rotor, electrical connections, etc.), and all seems fine.

When checking the fuel system, I noticed the MSD hand held controller shows that the fuel pressure sits at 35 to 37psi on tick-over (800rpm), and on normal running at around 2500rpm the pressure only gets up to around 53psi maximum. Is this correct, or too low for the MSD system? I have yet to find a definitive answer as to what the pressures should be.

I don’t know how long the MSD systems have been fitted to the car, but since owning it I have fitted new pre- and post-pump filters, both are still clean. The electric pump is an unbranded out-of-tank, in-line item, with no indication of fuel pressure output. I’m wondering if the pump is starting to fail, and that the output pressure is too low for the MSD system to function correctly.

Any info, ideas or comments would be gratefully received.

Regards,

Mark R.

 

According to the instruction manual, the required fuel pressure is 42 to 48 PSI, so it sounds like you are OK in that department. It is possible the injectors may need cleaning.

 

If the required fuel pressure is 42 PSI. Then the pressure should jump to 42 PSI on key on. No exceptions.
The system on my car, (FiTech) requires 60 PSI. much like Harley's. Turn the key to on and fuel pressure instantly jumps to 62 PSI. pump runs for approximately 10 seconds and if engine is not started, pump stops until the ECU receives a tach signal. Check valve in pump holds at approximately 55 PSI.
So, at idle, your pressure is low. Hard starting? Dies at idle. Yes.
Is your problem with pressure regulator or pump.
I am unfamiliar with your specific system. So to give you precise trouble shooting directions is difficult.
Can you test pressure before and after the regulator? Not relying on the systems gauge, but using a proper fuel pressure gauge.
also. Pressure should ALWAYS be consistent. Other than that little bit of bleed back when pump is not running. A regulator should hold perfect pressure at all times. If it's a 60 PSI system. The pressure holds right on 60 PSI whenever the engine and fuel pump are running. (
The fuel system never varies with engine speed. Never