I've been trying to find the cause of two problems :

1) The car is hard to start.

2) The car hesitates during midrange acceleration. When you reach 3.5 K rpm, it suddenly develops a lot more power, which is when I think the second fuel pump kicks in. This is what made me suspicious about the primary fuel pump.

I hooked up a fuel pressure gauge. When you turn on the ignition, but don't start the car, and the fuel pump runs for the normal 2s or so, the fuel pressure goes up to 40 PSI. But when the pump stops running after 2s, the pressure immediately and rapidly drops to zero.

I don't think the rapid drop is normal. Can anyone confirm?

In case it was a fault with the fuel pressure regulator, I blocked the return pipe to the tank by crimping it with brake hose pliers. No change.

So it seems that either there's a leak somewhere, or the primary pump is faulty.

Has anyone seen this problem before?

 

Check the relays in the trunk and isolate the pumps -- see of each are working.

 

Do you have an answer to my question about whether the rapid drop in pressure is normal?

 

Not normal.

There are really only three suspects:

a) leaking injector
b) fuel pressure regulator
c) fuel pump reverse flow limiting

 

Well, I for one am happy just to have found the problem. The poor driveability was driving me nuts.

So how does the reverse flow limiting work on the pumps? Is there a one-way valve?

I don't think I mentioned in my original post, but I had the pumps done a year ago. Sounds like I got unlucky and got a bad one.

 

There is also the fuel pulsation damper that could possibly
leak, but you will smell gas in that case.

The reverse flow in the fuel pumps just prevents fuel
from backflowing through the pumps when the pumps
turn off. That maintains the pressure in the line. Yes,
I would call it a integral one way valve. Don't know
much more.

You describe fuel pressure bleeding off when the ignition
is turned off, and the three listed items would be the
suspects.

I see you have already done the regulator test so I have
edited out that suggestion.

 

... umm are any of the plugs extra wet
if you do the key on/key off?

that cylinder would have the leaky injector,
or at least be a strong suspect.

 

Thanks for the replies.

I will check the plugs. I actually did another test where I blocked the fuel crossover pipe - no change, so that means that any bad injector has to be in the left cylinder bank.

I wonder if I could connect the gauge before the fuel rail? Like at the filter?

Where is the fuel pulsation damper?

I've got the car in the garage, and was testing the pressure inside, so I would suspect that any leak would be obvious by a strong fuel smell, which I don't get.

 

The damper is on the right side rail. See the massive
thread started by maxwdg who fixed his. You would
see wet fuel around it.

What brand of fuel pumps?

Maybe the in tank hose has popped off. Known
problem with certain brands because the nipple
is actually just a slip fit and held by the clamp.
Airtex was named as having this config.

Can you get a clear fuel filter that will hold 40psi
to temporarily insert into the supply side so you
can see if the reverse flow is towards the pump
at key off?

One way of testing the fuel injectors is to release the
rail leaving the injectors attached, then pressurise.
.... I think.

Not all that easy on a SC rail.

 

when you key off or key on, can you hear gurgling in
the tank?

i tend to use a jumper at the relay rather than the key
because i can stand right at the trunk while manipulating
the pumps.

is it better/worse when the tank is full?