Autozone doesn't have a fuel pressure tester, so I am shopping for
one on eBay. This one is available (at a very good price),
it has an adapter which actually is made to fit GM, but it is
metric. F itting size: M16 x 1.5 I don't have a clue what the fuel
rail fitting size is on my 740, so can't tell whether this one will
work. Then I have the problem of extending the gauge hose, as 3 ft
isn't going to get the gauge located inside the car to be read while
driving. I think it is best to buy a guage rather than shotogun a new
fuel press regulator, as my brother has a 740 GL also, and I am
probably going to buy another one myself. I haven't had good
experiences with parts from salvage yards, so I would have to pay $52
for a new regulator, posibly only to find it wasn't needed.
I gather that since fuel consumption has gone way up, then the fuel
rail presure might be too high at low speed or idle, and then way too
low when punching the accelerator? I checked the oil for signs of gas
in it...it is okay. I pulled the vacuum line off of the fuel press.
regulalor while running (immediately closing off the open end of
hose), and there did seem to be a slight difference in the sound of
the engine (possibly indicationg a change in fuel rail pressure/fuel
delivery)....but it was very slight.
I checked the spark plugs, and they have a light coating of
blackish stuff, but not jet-black soot...and there is not any smoke
coming from the tailpipe. They all looked identical.
On Sat, 18 Jun 2005 21:29:27 -0700, "Michael Pardee"
>"Geronimo" <email@example.com> wrote in message
>> Well, I will go get a fuel pressure gauge. It doesn't sound easy to
>> tee into the fuel rail somewhere...and then I have to run the gauge
>> line through the firewall somewhere so I can watch the gauge while
>> driving. What a pain!
>> I don't quite understand why an extremely rich mixture isn't
>> turning the chk engine lite on, as it seems like the o2 sensor would
>> trip an "o2 level out of range situation" for the ECU.
>> BTW, I am not sure my Haynes gives the normal fuel rail pressure. Do
>> you know what it is? Is the regulator suposed to keep it the same
>> whether driving or in park?
>> thanks for the help.
>I cut the fuel supply hose about 1 1/2 inches from the fuel rail fitting and
>inserted the tee there, then removed the short piece and connected the hose
>back to the fitting when I was through. With the vacuum hose removed from
>the fuel pressure regulator (and the hose plugged) the corect reading is 36
>psi, or 42 psi for the turbo model. Reconnecting the hose should drop the
>reading by the amount of manifold "vacuum" - about 10 psi less fuel pressure
>at idle. What you are looking for is a big deviation, like double the fuel
>In the '89 I don't know if the check engine light would come on with the
>rich mixture, but it would make sense that it would. Just a wild thought -
>when the battery failed in my Nissan 300ZX the mixture went way rich (so the
>top speed was about 40 mph and there was a black cloud following me) because
>the ECU was constantly being reset by the noise from the alternator; no
>check engine light. Oddly, the engine still cranked okay but replacing the
>battery fixed the problem. If you have a DVM around a check for AC voltage
>across the battery terminals would ward off a few evil spirits - it should
>be below 0.1 VAC. In addition, there should be less than 0.1 volt DC between
>the engine block and the chassis - more than that means the engine ground
>strap is bad.