Hot-Start Issue: Rich vs. Lean...

[rossiz]

Thanks all for the responses. At this point I believe I've replaced all sensors and connectors, including CSV and associates plumbing. I plan on just driving/observing for a while to assess the cumulative effect of all these changes and then assess if I still have a problem.

I'm particularly interested in understanding the symptoms diagnosis of leaky injectors, as this is the one component I have not touched (short of new plugs/connectors). Would a fuel pressure gauge allow me to monitor if pressure is falling off after shutoff and indicate fuel leaking into the cylinders? This would be a huge worry, as I don't want to contaminate my oil...

[FastWoman]

Rossiz, I permanently installed a hardware-store-variety pressure gauge between my fuel filter and fuel rail. It's a made-in-china water pressure gauge for a well pump system. The gauge is 1/8" MPT and is screwed into a brass "T" fitting with three 1/8" FPT inlets. I have two barbs threaded into the other two legs. It's worked great. I think I paid about $10-15 in parts.

[rossiz]

ok, i installed a fuel pressure gauge between the fuel filter and the rail and i'm not sure how to interpret what i'm seeing because i don't really know how it's SUPPOSED to function...

from key OFF, pressure = 0psi, turn key to RUN and i get a blip at the gauge, sometimes it jumps to 5 or 10psi, sometimes up to 20 - not consistent, but always a blip

from key RUN, pressure = whatever left from "blip" above, turn key to START and pressure jumps up to 30psi while cranking and remains there once engine starts/idles

engine running, pressure = 30psi at idle, goes up to ~35 when i rev the engine up above 3k rpm, returns to 30 when it drops back down to lower speeds

engine shutoff, pressure sometimes stays at 30psi for as long as i watch it (waited a few minutes), sometimes slowly releases, sometimes drops right to 0psi

if i click key back/forth from OFF to RUN repeatedly (playing with the "blip") to try and get a consistent result, the pressure hits different levels, sometimes drops back to 0psi when the key goes to OFF.

things that seem odd to me:

my readings on how the fuel relay system is supposed to work indicate that the fuel pump should receive NO power unless either the engine is being cranked or running with either the alternator or fuel pressure signals present. so why the "blip" at key in RUN?

pressure seems low, and should it vary w/engine speed? my gauge could be off, which might account for the low reading but not the variation... the car does run well and doesn't seem to show any signs of lean condition or stumbling.

the inconsistent/intermittent pressure drain-down seems to point to leaky injectors - is this gas going right into my cylinders and into my oil??

[FastWoman]

I wouldn't worry about the blip. I don't think it means anything -- likely a bit of current through a relay contact before the relay energizes.

Pressure readings: Your gauge could easily be inaccurate. It should read 36 psi when cranking, but if voltage is low, it might not. When the engine is running, there's a vacuum in the intake manifold. The pressure difference across the injector -- from the fuel rail to the interior of the intake manifold, is regulated at 36 psi. When you rev the engine, air rushes into the intake manifold, and the vacuum lessens. As a result, the fuel pressure WITH RESPECT TO ATMOSPHERIC PRESSURE rises by the same amount. The result is that the pressure difference across the injector remains constant. So yes, fuel pressure should fluctuate to track the intake vacuum. That's normal and good.

Pressure leak-down can be due to leaky injectors, but it's more likely due to a leaky check valve on the outlet of the fuel pump. This part is no longer available, but I believe someone on our list found a substitute for it. You can also order an aftermarket check valve that you can install just before the fuel rail. See here:

One Way Check Valve for Gas or Diesel Fuel 5 16" Bio | eBay

Your check valve should hold the pressure at least until your engine has cooled down. If you lose all your pressure in 30 min, that could be the cause of (or a contributing factor to) your hot restart problem. I'd say your system is leak-free enough if you maintain at least 20 psi for maybe a couple of hours.

In the event your injectors do leak fuel into the intake manifold, I suppose some of the gasoline could get into your oil. However, we're talking about so little gasoline. I really don't think it would cause a problem.

[rossiz]

i ordered a check valve - will install and see how it affects pressure readings.

will also purchase another pressure gauge to check accuracy of the first (hardware store variety)

thanks for the replies

[Captain Obvious]

Probably too late, but I wouldn't bother with that check valve from ebay. I bought one and it didn't last. Worked fine new when cold, but as soon as the engine compartment got hot, the hot fuel attacked the sealing disk inside the valve and potato chipped it. Didn't hold pressure after that.

I've got pics of some of my alternate fuel check valve installs on the camera, but it's gonna take me a little bit to get them to the web and write something up.

[rossiz]

i'd be happy to get some info on your valve captain-O

the one in FastW's link said it was only rated up to 20psi so i found another one that cracks at 1psi and is rated up to 115 psi (many options for inline fuel check valves)

it was a whopping $9 so no biggie if it isn't a forever solution...

[Captain Obvious]

Gotcha covered:

http://www.classiczcars.com/forums/fuel-injection-s30/51862-fuel-pump-check-valve-alternatives.html