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Posted by: 76-914 Apr 9 2010, 11:47 AM

When setting fuel pressure, is there a recommended elevation to place the gage. Obviously, the reading changes as the gage is raised or lowered??
Any Guru's willing to comment on this???

Posted by: Brando Apr 9 2010, 11:51 AM

If you are meaning that fuel pressure is changing on placement of the gauge (high or low) it should not change.

Ideally you tap in to the fuel rail with the removable bolt. It's fairly easy to see.

Posted by: SLITS Apr 9 2010, 11:51 AM

If you can get a pressurized gauge to change pressures by elevation then you have a very special gauge indeed.

Now, if you are measuring barometric pressure then ..................................

And Brando ... the specified fuel pressure on a D-Jet / L-Jet is about 29.4 - 30 lbs. At 36 psig, you may override the injector solenoid.

Posted by: realred914 Apr 9 2010, 11:53 AM

well the Fi pressure is set to about 28 psi, any head pressure from gage hieght vartiation would be minimal percentage of the total.

i hook up my gage with a rubber hose right off the fuel rail port when I need to adjust and just let it lay at the same level as the injecotors more or less. even a couple feet of head presure variation would be a fraction of one psi. dont worry about it

Posted by: 76-914 Apr 9 2010, 12:01 PM

OK, I'm going to take a video of it.Maybe I'll even be able to post it here. It is moving about 1-2 lbs as the rubber hose is raised and lowered. The pressure of water changes about.4 lbs per ft of elevation and it's specific weight is close to 8 lbs per gallon. Anyone know the weight of gasoline. I could extrapolate some kind of guess from that if I knew it. Thx

Posted by: Brando Apr 9 2010, 12:05 PM

Thanks SLITS. I forget things.

realred914, are you sure you're not just seeing the needle bounce as the injectors fire? IIRC there's no dampener on the fuel system.

Posted by: SLITS Apr 9 2010, 12:09 PM

6.25 lbs/gal at 72 degrees F.

Put the joint out!

Posted by: SLITS Apr 9 2010, 12:11 PM

You assdragger pilots forget a lot of things.

Posted by: kwales Apr 9 2010, 12:14 PM

Got bubbles????

I bought one of those el cheapo Harbor Freight gages and realized that there is no way to purge air from it. So I looked and sure enough, real pressure gages (as used by mechanics and tv stars playing mechanics) have a bleeder.

Without an air purge bleeder, you might have an incompressible fluid compressing a compressible fluid and depending on how you move it, you might have different readings.

Posted by: realred914 Apr 9 2010, 12:14 PM

I have not seen much if any fluctiation when i run the motor, if you got good flow in the loop, variations are minimixed. at any rate I would think the gage should be at the same hieght as the fuel rail/regualtor, if you get a big change when you riase teh gage up in the air, then dont raise it up in the air, keep it low at teh same level as the fuel rail

the haynes manual for the D-jet says 28.4 to 29.6 psi so there is a big window of pressure to hit. the same book says that the L jet should be set to 35 +/- 1.4 psi again a big range. keep our gage at fuel rail level and you shoudl be a.o.k.

Posted by: 76-914 Apr 9 2010, 01:52 PM

OK, here is what I found. When the gage was in a certain position it would barely leak at the barbed fitting connector. I hadn't noticed that earlier as I had a white shop towel beneath the gage. When I went to video this I noticed it; so you were right Ron. I did have a special gage. BTW I was testing with the ign on so the pump was not constantly running. This time I set it w/ the engine running. Guess what? ?Sabes que, miho? This is the first time I got it to idle at 950rpm. Go figure. I'm tempted to put those "new" injectors in, now.

Posted by: Brando Apr 9 2010, 03:19 PM

"New" injectors or some well rebuilt ones may help.

Check out the prices for http://www.witchhunter.com/.

He was able to rebuild the L-Jetronic injectors for my old BMW K75 for $50 per injector. He can also flow-match them so you know each cylinder is getting the same amount of fuel. From the factory they do not always flow the same and after time they can flow very different amounts.

And SLITS, I would probably, somehow maybe take offense to that comment, but I forgot already... Who are you again and what did you do with RON?

If ya come down this way sometime lemme know. Have a few on me.

Posted by: realred914 Apr 9 2010, 04:02 PM

whitch hunter done my and tradsrad injectors, nice charts they provide with each injecter they clean and calibrate before and after reslluts of flow rate are proof.
recommend them.they ahd faster turnaround than i expected too.

Posted by: 914Sixer Apr 10 2010, 06:03 AM

New 1.8 injectors from Bosch are $50 or less depending on where you get them(Autohausaz.com). You have to look up 74 VW 412 with 1.8 motor but it is the same injector. Best to change out the hose though.

Posted by: 76-914 Apr 10 2010, 10:12 AM

I wasn't smoking a joint that time!