Measuring Fuel Rail Presure?

[trak ratt]

Anyone know of a way to measure the fuel pressure at the fuel rail of a 3.2 Carrera will driving? The problem seems to be finding compatible adapters and connectors more than anything else.

[DRACO A5OG]

While Driving?

Whoa, that would be interesting. Well, I would imagine a long enough hose to reach the cab and gauge set up. Or a electronic gauge and wire it back to the the reader???

[rusnak]

Don't do it while driving. The 3.2 fuel rail has a simple straightforward fitting.

[big911fan]

What type of fitting connects to the fuel rail? It has a ball bearing inside the nut and whatever fitting you use needs to accommodate the taper on the inside. I've been looking all over trying to find a reasonable priced fuel pressure gauge that adapts to the Motronic fuel rail. What am I missing?

It sure would be nice to know if I can adapt a normal fuel pressure gauge to the fuel rail with the proper fittings. Does a CIS pressure gauge adapt to a Motronic?

[rusnak]

How far are you from Fresno?

Otherwise just get over to HF and pick up an El Cheapo. That way at least you have the fittings and hoses, and you can get a nice gauge any time.

[Quicksilver]

I used a cheapo HF gauge hooked to a long enough piece of fuel hose to go out the side of the decklid and in through the driver's window. Only took a few blocks to see what I wanted to know.
(Still had the 10lb extinguisher next to me in the car.)

[big911fan]

I'm probably three hours from Fresno but there's a HF store on Modesto.

I assume from your response that the HF fuel pressure gauge set will work on a Motronic FI system. I thought it was just for a CIS system. I'll stop by HF and pick gauge set. Thanks.

[rusnak]

HF has a little El Cheapo gauge that will work, but if you spend a tad more, you can get the Master Fuel Pressure gauge set, which has a double decker case full of fittings, hoses, and stuff. It is teh chiznet of El Cheapo fuel pressure gauges.

[Quicksilver]

The cheapo HF injector test set I worked from didn't have the correct thread for the fuel rail test port. I found a SAE brass pipe thread in my Box-O-Hose-Stuff® that was "close enough" for test purposes. It engaged about 4 threads and with a liberal wrapping with teflon tape it worked fine.

(Be careful with teflon tape. One little fragment in the port and you have a very clogged injector.)

[big911fan]

That's exactly what I was worried about. I had heard that the Motronic fuel rail port was somehow different from the CIS port. Even if the outside thread type works, there's an inner tapered port that needs to seal also. That's what the ball bearing does. It stops fuel from leaking out of the external threads.

Does anyone know definitively what type of threaded fittlng we need to use on the fuel rail of a Motronic system? I've been all over the Internet looking for the correct brass fittings and can't find the right one.

I'd rather not mess with Teflon tape and the potential leak issues if I can avoid it.

[rusnak]

The test fitting is brass, has a cone shaped piece that fits into the fuel rail fixture, and is held on with a threaded collar. No leaks, no mess. Light torque only needed to tighten.

[big911fan]

Sounds like the right piece. I'll give it a try.

If you watch what you buy, HF is like a candy store for car geeks....

[dshepp806]

Come on,..someone hand us the damned part number and source for the EXACT NEEDED adapter,..one that fits PERFECTLY (looks like it frikin' GREW there),...all threads used,...no hodgepodge teflon tape horror..........

Again, I'm talking a perfect adapter that accomodates the rail's port (pitch, yaw, roll, taper, depth, nose, eyes,...etc).

Let's have it!

BEST!

Doyle

[rusnak]

Doyle, I'm due back home tonight (on the road now). I'll snap a high-def pic. There is no part number for the part, but if anyone wants to get the same test kit that I have, I can find the Item #.

[big911fan]

I agree totally. It shouldn't be a mystery. I doubt Porsche invented that fitting just for the Motronic application. It must be shared with other manufacturers or applications. Someone must make a metric fitting that will allow us to fabricate a decent fuel pressure gauge. All we need to know is the fuel rail fitting spec.

There are several companies out there supplying brass fittings. They just aren't familiar with what Porsche used on the fuel rail.

[Kidasters]

Originally Posted by Quicksilver

It engaged about 4 threads and with a liberal wrapping with teflon tape it worked fine.

Please don't try this at home. This is how people, cars and houses get burnt to the ground.

Right fitting - right threads - do it right.

[mytoy]

This just seems like a big secret. I asked the same question about 3 weeks ago and got no definite answer. But I just can't keep a secret so I will tell you that the fitting is an M14x1.5 female fitting for the fuel pressure port. So you will need a M14x1.5 male adapter to what ever you wish to use for the fuel pressure guage fittings. Most fuel pressure guages are 1/8'' NPT. I would suggest the you get a M14x1.5 male to 6an adapter and then make up a section of 6an line with a female 6an on one end to thread onto the adapter and a 6an to pipe adapter on the other end for the guage.

Hope that helps and I hope that I did not break some secret handshake code in revealing this info. I guess I could get banned from the forum for this.

[aston@ultrasw.c]

Monitoring fuel press is very useful, just like voltage.

Although having a fuel line behind the dash is prob not a good idea.

I tried to use a pressure isolator with little success.

If I was to do it again I would just break down and spend the money for an electronic sensor and matching gauge.

[dshepp806]

Originally Posted by mytoy

This just seems like a big secret. I asked the same question about 3 weeks ago and got no definite answer. But I just can't keep a secret so I will tell you that the fitting is an M14x1.5 female fitting for the fuel pressure port. So you will need a M14x1.5 male adapter to what ever you wish to use for the fuel pressure guage fittings. Most fuel pressure guages are 1/8'' NPT. I would suggest the you get a M14x1.5 male to 6an adapter and then make up a section of 6an line with a female 6an on one end to thread onto the adapter and a 6an to pipe adapter on the other end for the guage.

Hope that helps and I hope that I did not break some secret handshake code in revealing this info. I guess I could get banned from the forum for this.

THAT"S what I'm talking about! THANK YOU SIRE!

Banned? Are you frckin' kidding? You just "upped" your status!!!!!!!!!!

What about the alledged "taper"? And how is "that" spec'd?

Thanks, again!~

BEST!

Doyle

[big911fan]

Yep. I agree again. I'm still not sure we have the whole picture. Being a high pressure fuel line fitting I assume it must have some type of flare or taper.

I wonder if a straight M14x1.5 thread will hold the pressure without leaking.

All this thread talk is beyond my knowledge base..... is an M14x1.5 straight thread the final answer?

Let's see a picture of the fitting with a shot of the internal and external threads!

Anyone have one?