How to test fuel system pressure?

[babzenuda]

ok, this problem is starting to drive me nuts. the car starts, idles, and revs ok, and I can pull her out onto the street and get going, but after about a mile or so she starts stalling under medium to heavy throttle, until finally dying altogether. after a while i can get her to idle again, then i have to limp home in 2nd going super light on the throttle.

it's totally that "running out of gas" feeling of starving out under load, and I suspect the fuel pumps are starting to go (I seem to have both the main fuel pump and the in-tank pump on my '79 2.0L ... go figure), but before I go and replace them I want to test the fuel system pressure. how is this done on these cars? I can't find a 'schrader valve' or any other place to hook up a fuel pressure guage anywhere on the fuel line. everything's all banjo bolt connectors, solid steel line, and pressure-fitted connectors on the rubber hose. where the heck are you supposed to hook in??

any suggestions are welcome, nay, desperately encouraged.

Robert.

btw, i've replaced plugs, wires, dist cap & rotor, points & condenser, fuel filter. no improvement.

ghead

[KC Ron Carter]

Here is the way and at the bottom I show what I will sell you, for $29.50.





BMW Fuel Pressure Indicator Mechanical

But an allen headed plug with every order so the gauge can be removed.

I built three for my cars and can make a few extras, for the only REAL way to find out what the fuel pressure is.



Also a good time to replace that hose if it is over 10 years since it was replaced.






Later,

[babzenuda]

so basically you've cut the rubber supply line (pressurized, post fuel pump/filter) and put a T-connector in-line which you connect your gauge to. i've heard that this isn't good to do because the pressures are too high to mess with the integrity of the plumbing. is this true, or is is alright to make cuts in the rubber line and re-seal with standard hose clamps? it would be great to permanently insert a T-valve in the fuel line for later re-testing...

robert.

[KC Ron Carter]

Find who told you not to cut into the fuel line and ask him how to test!

Just joking, of course you can replace and fix anything.

Later,

[babzenuda]

Well just to follow up, after poking around on the E21 maillist (not much traffic over there...), I decided to risk being stranded and go down the hill to fill up my gas tank. I had heard that if the in-tank pump is starting to go, then the car will exhibit symptoms like what I was experiencing when the tank is below 1/4 full. Sure enough, I filled 'er up and the starvation/hesitation problem was gone.

Interesting... so how did owners of the early single-pump 320s put up with that crap? Maybe this means that my main pump is starting to go too...

This makes me wonder if there is a good alternative to the stock fuel pump(s). Anybody know if there is a more modern and inexpensive replacement pump out there? Anyone been brave enough to experiment with VW or Domestic pumps? There's gotta be something out there that could be rigged up to last longer and/or be cheaper to replace than this flakey and expensive dual pump stock setup.

Rob.

ps, thanks kc ron for the input on fuel pressure guage access. i think i'm going to do some experimenting once i get some replacement fuel lines from a parts car. just in case i screw it all up... :wink

'79 320i