Fuel pressure guage 1978 z

[argniest]

Here is what happened tonight on my 1978 z car

Well I finally got around to hooking up my new actron fuel pressure guage.

For better or wrose, I put it after the fuel filter. It was easier to put it there for my first time doing this.

Here it is http://www.actron.com/product_detail.php?pid=16173

And here is what happened. My wife turned on ignition but not start it.

Immediately it shot up to like 40 psi and stayed there. She turned it off. It stayed at 40.

Turned it back on again w/o starting it, and it stayed around 40

Then she started it...and at idle it stayed around 40.

I dont know how accurate this fuel pressure guage is though. That seems way too high.

Is it possible I hooked it up wrong and caused it to read incorrectly? hmmm anything is possible.

Ok soooo....we let the car idle for a few minutes, and then had her revvvvv it up a little bit and hold it there. At a higher idle, it was sitting at 36psi.

And as she let her foot off the gas it went back up to about 40.

Then we let it idle a little longer...and after it got a little warmer it seemed to

hover around 38psi.

Then she shut it off. And it slowly went up to 40 psi after a few minutes.

I thought that was kind of wierd.

Then I kept an eye on it for 30 minutes, and after 30 minutes, it was down to 36 psi. I will check it in the morning and see where its at.

If the car was operating properly should it hold the pressure all night long???

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A few other things....I tighten down the clamps pretty darn good.

I dont know if they can be too tight. I suppose if it cut into the hose that would be too tight. I seem to always want to give things an extra ooomph to make them a little tighter rather then leave them looser. I suppose with time and practice I might learn what is right. I dont know how to apply to correct torque according to the manual for those clamps? What kind of screwdriver has a torque meter on it basically? There must be something like that.... I just never seen one.

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1. Should I hook up the meter before the fuel filter too?

2. Should I or can I even, hook it up on the return line back to the fuel tank?

[cozye]

The gauge is off I suspect. Does the car have the stock fuel pressure regulator on?

A lot of people, including myself just install this gauge

http://www.summitracing.com/parts/SUM-800160/

[sblake01]

I made my own gauge from hardware store stuff. Much less costly than the over the counter gauge. I never saw a need to 'install' a fuel pressure gauge as I would only use it for testing purposes.

[FastWoman]

Might be a bad FPR.

Like Steve, I just made my fuel pressure gauge from hardware store parts. I think it cost me about $15. It's surprisingly versatile and accurate for something made in China. It probably reads within a psi of being correct, in comparison with some better gauges of mine.

I agree with Steve about gauge installation. You only use the thing for diagnosis, and pulling hoses isn't a problem in that case. A permanently installed gauge is just one more thing to go wrong. The only point in its favor might be that it looks cool, which is certainly a valid reason, if that's what you're after.

Edited January 30, 2011 by FastWoman

[argniest]

When I said I installed it, I just meant that I hooked it up in the engine area temporarily so I can run tests with it. Not a permanent install. I hooked it up, after the fuel filter, using rubber hose, in a "T" formation. And at the top of the T, is the fuel prssure guage, If you click the link above, you can see the metal "T" connector I used.

Would it really be off by that much? Its reading 38psi during idle. I mean I just clamped it down good, and hooked it up. I could buy another one and see if it gives the same readings. I mean the chances of two of them being bad is probably unlikely.

The chances of me somehow hooking them up improperly is higher risk. But i just followed directions in the actron manual, and its reading about 38 psi at idle. I tested it again today. And when you rev it up a little and hold it there, it seemed to stay right around 36psi.

PS

So you are saying ace hardware type store has a fuel pressure guage? What parts do I need to make my own? And are you saying I would hook it up using a T connector like the one listed above?

Edited January 30, 2011 by argniest

[FastWoman]

Argneist, I edited my post (#4) while you were in the process of typing a reply to it. I can see that you used the "T," thereby blowing that theory of mine.

It sounds like you hooked it up correctly. And no, you wouldn't want to hook it up anywhere else.

If you already have the fancy job, there's no point in cobbling together a lesser gauge. You can probably check your gauge against another accurate gauge, using compressed air.

It's hard to say what's inaccurate. Gauges are generally pretty accurate, and so are FPRs. I would think that an FPR would regulate lower with age, if anything, due to weakening and rusting of the internal spring. Dunno.

[FastWoman]

Oh, and yes, the pressure should hold for as long as possible after you shut off the engine. (All night is pretty good.) I've read others reporting that their fuel pressure rises slowly after shutoff, so I suppose it's normal. I suspect it's due to heat buildup and the vaporization of fuel in the fuel rail.

[argniest]

It was interesting, I watched it go up to about 40psi after shutoff, it held there for a while (15 to 30 minutes maybe) and then it started to go down. I think it was about 60 to 90 minutes later...and it was down to 25 psi. I have to go out there to do my next testing...so I will see where its at now. I would imagine its pretty low. It seems to me if it doesnt hold pressure all night long, then there is leaking fuel injectors involved (or cold start injector), Unless its just a natural phenomena for the fuel pressure in any car to drop over a 24 hour period.

Interesting idea about testing the guage with compressed air. This will seem dumb question, but are you saying to hook up the fuel pressure guage to an air compressor. And then have the air compressor go up to say 40 psi, and then check it against the reading on the fuel pressure guage?

If that is what you meant.....welllllllllllll I dont know if I have correct fittings to hook them together. And also, my current air compressor isnt exactly the greatest thing in the world. Had it for years, and its a smaller one that cost me like 100$. So Im thinking its not going to be very accurate either.....

Edited January 30, 2011 by argniest

[Zed Head]

The FPR on my 78 parts car read 40 psi. I picked up another used one, just to try to get the spare engine tuned up and it read 38 psi.

The FPR on my 76 driver read 36 psi cold, but the pressure crept up in to the 40s when it got hot, so the engine ran rich and the exhaust was real gassy. It took me quite a while to figure out, since I only put the test gauge on when the engine was cold. I now have an aftermarket FPR on it, set to 36 psi, and the difference in the way the engine runs and gas mileage is significant (an extra 2 mpg).

So, in my experience, the FPRs can go bad. I have had one that read right cold, but wasn't, and two used ones that read high cold.

argniest, your gauge setup is correct, between the filter and the rail. The fuel pressure will creep up as the fuel in the rail gets hot when the fuel pump shuts off. Gauge accuracy is always worth checking, even on a good brand name. I dropped my dial-faced tire pressure gauge (same mechanism probably as the fuel gauge) and it is now off by 4 psi.

2 psi might not make a difference (38 vs 36). The best way to check the FPR's performance is on a running engine. Take a reading with the vacuum hose hooked up and then disconnect the hose. It should read 36 (or close) without it, and down around 30 with it connected. When you blip the throttle, the pressure should rise up to 36, then drop back down. You can actually calculate your engine vacuum off of your fuel pressure if you want to.

Just adding some information, not recommending anything. Use at your discretion. There are so many parts that work together on these cars, it's hard to tell which one's to "fix."

Edited January 30, 2011 by Zed Head

[FastWoman]

Zed, interesting that your FPR regulated differently hot and cold! I'll have to check mine sometime to see if it does that.

Argneist, I meant to simultaneously hook up your fuel gauge and a gauge of known accuracy to the same compressed air source. They should both read the same. When comparing gauges, I look for consensus. If two read the same and a third reads differently, then the third one is probably off.

[argniest]

Here is some more information....that I just posted in another thread about my test results tonight. I am buying more guages, and starting to learn how and where to hook them up. Im a software programmer, and I like having facts to look at and study. Otherwise its all a guessing game for a noob like me

Take a look at the thred below. I installed fuel pressure guage, vaccum guage, and used a hand vacuum pump too

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http://www.classiczcars.com/forums/showthread.php?t=40938&page=2