Welcome all 928 forum refugees!
User avatar
By Sazerac
Hi All

So, I need to diagnose a problem and need to get a new fuel pressure gauge.

It is not my intention to leave such a gauge on the car permanently like some people seem to have on the fuel rail. This will be used only for a diagnosis and then put in the tool box until needed again.

Any recommended choices or vendors? Otherwise, I'll just get one "some place" and report on what I find.

Thanks, John
User avatar
By Gregs04.5
I picked up a cheapo kit from ebay, it works well, but have since acquired a snap on kit, and truthfully, it's not that much better.
Get something like this, it has multiple fittings, which will come in handy, and won't break the bank.

https://www.ebay.com/itm/Fuel-Injection ... 3345965058
User avatar
By Shifted
Part of the problem with the 928 fuel rail pressure test port is that it's not a common fitting. It makes it difficult to find a suitable connector. I forget the exact spec, but it's something like a M12x1.5 with a ball seat. Supposedly the nicer and more complete fuel pressure test kits have the right connector.

For my self, what I've finally settled on is a M12x1.5 to 1/8" NPT adapter, with an O-ring inside of the M12x1.5 end to seal against the test port (the adapter doesn't come with the o-ring, you need to supply one):


This makes a nice leak free seal against the fuel rail test port. You can then connect whatever you want to the 1/8" NPT end. I attached a coupler:


And a 0-100 psi fuel pressure gauge:

I don't recommend leaving it on the car all of the time, but it works well for testing and troubleshooting. If you need to watch the pressure as the car runs, I strongly recommend jumping the fuel pump relay first and checking for leaks with the car off and the fuel pump running. You definitely want to catch any leaks or seeping when everything is cool and the motor's not running.

If you haven't already pulled the cap off and/or know about the ball in there, be careful not to loose that ball. It's what seals the test port by fitting into the ball socket. Make sure that yours is nice and smooth and bur free. The previous shop that had my car put in a regular steel ball that was badly corroded and the wrong size. The right size is 9mm if you need a replacement. I have a bag of them, so if you (or anyone else) needs one, I would be happy to mail you one in an envelope.
User avatar
By Sazerac
Greg, Shifted, thanks for those responses.

I agree it is not my plan to leave a gauge in place. Good idea about actually ordering an extra ball. Marshall looks like a good company.

I'll think all this through now.
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