scruffy341

Having a no start problem, think its fuel pressure related. What thread of adapter do I need to fit on my '85 928s? Thanks for any help!

John Speake

M12x1.5

Speedtoys

doesnt have to be a special thing?

hacker-pschorr

Recently used this one to test fuel pressure on an 85/86:

https://www.harborfreight.com/master...kit-62788.html

dr bob

Didn't know that H-F carried those. Was in their store yesterday with a 25%-off holiday coupon that saved me big on a $2 bag of tie-wraps.

I have the $20 basic fuel pump tester version, adapted to the 928 fuel rail with a used fuel rail cap drilled and tapped to 1/4" to use the GM connector hose. My setup requires a 1/4" compression ferrule in place of the ball-bearing for the end seal. Other alternatives for adapting the original cap include fitting a fuel-proof Schraeder valve there, maybe permanently.

Speedtoys

so a non specific baa bearing sized fitting will seal...

Randy V

Welcome!

How about an intro with pics!?

dr bob

The original fitting seals with a concave surface in the end of the nut, and a bell at the end of the rail. A 10mm or so ball bearing does the job nicely. When I decided to adapt the nut to use a GM-standard 1/4" thread, I found that the 1/4" brass compression ferrules is close enough to original size, pilots nicely on the protruding end of the GM hose fitting inside the nut, and has a convenient hole through it so the hose fitting can see the fuel in the rail. The brass is soft enough that it can do its sealing with minimum pressure from the fitting, and no risk of damaging the inside sealing face of the nut.

There are straight-thread Schraeder valves as well as NPT parts. A straight-thread adapter (for Ford fuel rails IIRC) would be my choice for a more permanent fitting if I needed one. Generally I'm not a fan of leaving an adapter in place permanently, since it would require a little surgery on the rail cover. Plus there's that annoying risk of leakage; nothing bad could ever happen from that, right?

Speedtoys

in racing where everyone has a test port, they never fail.

dr bob

yahbut, my connection method moves the actual sealing duty from just the bell end of the rail to there plus the inside of the nut, plus the threads added to the nut, plus the fitting itself.

If I felt the need for a permanent test port, I think I'd follow the lead that Ford and GM (and likely others) take, with a dedicated tapped port in the fuel rail itself and a Schraeder valve. Then the test port fitting could get a nice crush washer and a metal cap with an o-ring seal..

Reality for me is that I tend to only look at fuel pressure when there's a problem. And on my car that's only happened once in the almost-30 years since its birth. (weak/failing fuel pump relay marooned (in both the real and Bugs Bunny contexts...) me at the bottom end of the driveway.) The rest of the duty that my gauge has seen has been distributed among clinic cars.