Checking fuel pressure

[efnfast]

What size threads on the fuel rail so I can check pressure? Correct me if I'm wrong, but pressure should be about 55 psi. TIA. - Steve

[scottfab]

48 -55 psi is the range however, in my experience a new pump should be at 52 or above. That is if it is a good design. All this assumes the filter is ok and the regulator is functioning properly.
Thread size? Don't know.
The pressure gauge that I bought came with the right size.

[efnfast]

Thanks Scott. Key on engine not running should give me this, no?

[scottfab]

Originally Posted by efnfast

Thanks Scott. Key on engine not running should give me this, no?

Kind of.
The problem is the the secondary pump only runs 2sec. then shuts off
as soon as you "key on, Eng off".
This is not a good check for the 2nd pump.

[efnfast]

So I should?

[Paul Workman]

I went to AutoZone where they'll let you borrow a pressure gauge with a deposit. You decide to keep the gauge, you keep it and they keep the deposit.

I was also able to buy and extension for the gauge from them so I could tape the gauge onto the windshield to monitor FP under driving and WOT conditions.

Doing a static test with the key on, the secondary pump runs, as Scott pointed out, for about 2 seconds - perhaps not long enough to evaluate the FP, especially if the rail is not fully charged. However, that can be easily addressed.

By turning the key off and running a jumper wire from the positive batt post to the fuel pump test connector, both pumps should come on and you should see 52 ± a pound or so. (Note: The pump test connector is black connector attached to a short red wire located in the harness next to the testing/analysis connector (The yellow alligator clip is seen attached to the pump test connectory. FYI, A few early 90s had that connector located behind the battery).



FWIW, if you have a VOM, you can configure it to read current, and determine the current draw. This too will indicate wheter both pumps are drawing the proper current (about 4-5 amperse each for a total of approx 8-10 amperes if both are running normally).

So, with a FP gauge, and a VOM, you can determine a lot about the fuel system's operation in short order!

P.

[efnfast]

Thanks Paul, I know where the test plug is, Gordon pointed it out to me in BG. So, when energized both pumps will run? Also, what do you wrap the amp meter around? I would ASSUME that when energized by the test plug, not all the power draw is across there. - Steve

[Paul Workman]

Originally Posted by efnfast

Thanks Paul, I know where the test plug is, Gordon pointed it out to me in BG. So, when energized both pumps will run? Also, what do you wrap the amp meter around? I would ASSUME that when energized by the test plug, not all the power draw is across there. - Steve

With the key off and the test plug energized, BOTH pumps run, and continue to run as long as there is power applied to the test connector.

As for the VOM to read the amps, first set the meter to the 10A setting (you may have to move the red wire to the 10a position connection on (most) VOMs).

Then you can connect the red lead to the (+) terminal and the black lead to the FP test connector. (I find a pair of wires with alligator clips on them comes in handy to make the connections between the VOM leads and their intended connections.)

Soon as you make the final connection from the battery to the meter to the fuel pump test connection, you'll hear the pumps come on. If both pumps are running, you should see about 52# (give or take).

You can note the current draw to see if it is in the normal range, and soon as you note that, you can open the circuit and the fuel pressure should hold at that level or perhaps come to rest a couple pounds less than what it was when the pumps were running (I think it may be due to some reversion of flow until the check valves in the pumps close.) After the check valves close, the pressure should normally hold to within a pound or two for 10 minutes or more. (My last test went 30 minutes and lost only 2# pressure; from 46 down to 44.)

P.

[efnfast]

Thanks guys, I'll check this weekend and post up results. When I dyno'ed, I only showed 311 RWHP, not horrible, but looking for gremlins that may come up. I've only had the car a year. I think the PO was unattentive, not neglectful but didn't love Bertha as she deserves. Me, had her up to buck and a quater this weekend. Wife was along for the ride and didn't beat me up. Betha takes care of me as long as i take care of her.

[Mystic ZR-1]

Bertha Budd, one of the Budd sisters...
Nice talkin' to Steve!
D