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Testing FI Fuel Pressure FAQ
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Randy in Maine
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PostPosted: Wed May 31, 2006 9:54 am    Post subject: Testing FI Fuel Pressure FAQ Reply with quote

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"How to test your L-tronic fuel pressure"

First off you need a fuel pressure gauge that will measure between 0-60 psi. A good quality gauge looks like this one from German Supply. http://www.germansupply.com/home/customer/product.php?productid=16610&cat=300&page=1 It is a good price for a quality set up.

I like to have a hose about 3 feet long made of 7mm FI fuel line so that I can do some of the testing behind the bus where it is easier and safer to do. I would not leave the gauge on the rail (although some people do). I keep mine in the toolbox. You can sometimes find a good gauge at the FLAPS for about $50 but you might have to cut off the end of the 5/16" hose and clamp it on to the fuel rail. 0-60 psi is the preferred range.

If you are stuck in the middle of nowhere, you can make one out of a "0-100 psi water pressure tester gauge" from Home Depot and some fittings from the "air compressor isle" that will allow you to attach it to the 7mm fuel line for about $20. Take your fuel line in with you to make sure it will fit on the 1/4" barbed compressor fitting. It is a good idea to make it so that the gauge can be removed from the coupler. Use 2 good hose clamps, one for the end that goes on the fuel rail test port (between injector #4 and #3) and the other for the barbed fitting. Teflon tape will help seal the connections. These are not as accurate as a real gauge and are not designed for petroleum. For a little more money you can get one that is really designed to test fuel pressure and is more accurate. A real one will last a whole lot longer.

To test the fuel pressure generally, relieve the fuel pressure in the system by opening the gas cap to relieve pressure in the tank and applying a little suction on the vacuum line that goes to the fuel pressure regulaltor for a couple of seconds to drop the pressure in the fuel rail.

Now is the time to install the pressure gauge on the fuel rail. The fuel rail test port is a little bolt (with a 7mm head) in the fuel rail between #3 and #4 injectors. Mount it securely, but you do not have to reef on the clamp.

Start it up. With the engine idling the gauge should read about 2 bars or about 29 psi +/- 3 psi. With the engine still idling, remove the vacuum line to the fuel pressure regulator and the pressure should go to about 2.5 bars or about 36 psi +/- 3 psi. The injectors won't fire if it is <26 psi.

Reconnect that vacuum line to the regulator and see if you get a pressure drop of 0.5 bar or about 7 psi (back down to about 29 psi) as the vacuum signal opens up the regulator diaphram. If you do not get it to drop in fuel pressure, check out the vacuum line for leaks. If that is OK, your fuel pressure regulator is faulty.

Since you are still hooked up, rev the engine up to about 3000 RPMs or so a few times and see if the pressure changes a lot or hopefully stays about 36 psi. Getting "on" the accelerator drops the vacuum signal to the regulator and tells it that you want more power as you are about to pass a semi or climb a big hill and you want more fuel to the injectors to make more power.

A dying pump or clogged fuel delivery system, will run out of gas by allowing the system pressure to drop to low. It should never go below 26 psi. It will feel like you are running out of gas, because you are. Razz

If the pressure is low on both parts of the test, either:

1) the pressure regulator is returning too much fuel to the tank or
2) the fuel pump is not delivering properly (could be a bad pump, plugged fuel filter, rust in the tank or a plugged screen in the tank but most of us do not have a screen in the tank).

If you pinch shut the return fuel line SLOWLY FOR ONLY A FEW SECONDS(when you are by the starter), the pressure should climb to about 4 bars or 59 psi and that will show you that the fuel pump relief valve is indeed working correctly, but your regulator is "toast". If the pressure does not rise, there is a problem with the fuel delivery system.

If the fuel pressure is too high, you need to shuff off the engine and remove the fuel return line from the regulator and direct it into a gas can. Run the pressure test agin and if the pressure is OK, there is something blocking the return line. Low pressure compressed air or a non-sparking wire might help clean it out. The gas pumping around the fuel rail is also what keeps the fuel pump cool.

The pump should put out about about 1 L of fuel in about 30 seconds if it is getting the 12 volts it wants. Check your pump ground, double relay, and starter connections if you are not getting correct voltage. I make sure the engine will not spark or start and just unscrew the gauge from the fitting and use that long hose to direct the flow to the gas can for the test since I am already hooked up to the test port.

To test for residual pressure when your bus won't start when warm:

With the gauge installed on the rail test port, run the engine to get it all pressured up, then shut it off. After 20 minutes the pressure should not fall below 1 bar or about 14.5 psi.

If it falls below that check:

1) all fuel line connections for leaks
2) to make sure that none of the injectors are leaking including the cold start valve and don't forget the injector seals.

The fuel pump also has a check valve to allow for only one way traffic for the fuel. To test the fuel pump check valve, run the engine and shut it off and immediatedly clamp shut the supply line from the fuel pump to the fuel rail. I have a pair of needle nose vise grips with a short piece of fuel line on each jaw to prevent real damage. If the pressure drops below the specification after 20 minutes, the fuel pressure regulator is faulty.

Remove the clamp on the supply line, start it up again and repeat the test and if the pressure is now within the specification of 14.5 psi, then the fuel pump check valve is faulty. New pump time.

One more thing...change out the fuel lines when you first get your bus so you will know when they were last done and then inspect them every year. We suggest changing them out with the correct FI fuel line every 7 or 8 years on your birthday and do them all including the vent line connections. Hate to see a nice baywindow bus burn down.

Richard's website has the fuel lines you need to come up with and where they go. Thanks Ratwell again for doing that!

German Supply has a nice diagram and has a kit that actually fits and it is of excellent quality. Thank you Scott for your good work!

Image may have been reduced in size. Click image to view fullscreen.


If you guys have something to correct or add to this, we can get one of the moderators to add it.


Randy in Maine


Last edited by Randy in Maine on Thu Jun 01, 2006 4:12 am; edited 1 time in total
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VWBusrepairman
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PostPosted: Wed May 31, 2006 10:51 am    Post subject: Reply with quote

Randy- thank you for your good work as well, but isn't every 2 years a bit frequent? If the hose is good quality, I'd say go with it- though an inspection each year would probably be wise as well.
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DurocShark
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PostPosted: Wed May 31, 2006 11:03 am    Post subject: Reply with quote

Great write up!

I noticed this on the page for the pressure gauge:
Quote:
This gauge is designed to be fitted permanently on the the fuel rail pressure reading nipple of Bosch jetronic injection systems found in Volksagen and Porsche cars and trucks.


Permanently? Clamped on hose? WTF? Do I want something filled with pressurized gasoline dangling off a hose with no support? That gauge will be bobbing around like mad while driving.
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PostPosted: Wed May 31, 2006 11:19 am    Post subject: Reply with quote

DurocShark wrote:
Do I want something filled with pressurized gasoline dangling off a hose with no support? That gauge will be bobbing around like mad while driving.

1. he said "bobbing"
2. maybe it's fitted right to the fuel rail directly with no length...?
3. any photos of this?
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PostPosted: Wed May 31, 2006 11:26 am    Post subject: Reply with quote

VWBusrepairman wrote:
DurocShark wrote:
Do I want something filled with pressurized gasoline dangling off a hose with no support? That gauge will be bobbing around like mad while driving.

1. he said "bobbing"
2. maybe it's fitted right to the fuel rail directly with no length...?
3. any photos of this?


That link has a photo of it mounted to the fuel rail: Linkypoo
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flat4freak1978
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PostPosted: Wed May 31, 2006 11:28 am    Post subject: Reply with quote

you could easily make one of these for about 10 bucks worth of parts from home depot.
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PostPosted: Wed May 31, 2006 11:31 am    Post subject: Reply with quote

DurocShark wrote:
Clamped on hose?


I'd be even more leery in that the connector on the rail doesn't have a flared end (like the "normal" hose connection points) to help hold the hose on.
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PostPosted: Wed May 31, 2006 11:34 am    Post subject: Reply with quote

VWBusrepairman wrote:
2. maybe it's fitted right to the fuel rail directly with no length...?


yes.

the hose is about 60mm long. there is about 15mm of free hose once it is on the rail spud, so it doesn't move at all. if the hose was longer there might be an issue of the gauge bobbing around, but the way it is, no issue. it just sits there.
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PostPosted: Wed May 31, 2006 11:42 am    Post subject: Reply with quote

germansupplyscott wrote:
VWBusrepairman wrote:
2. maybe it's fitted right to the fuel rail directly with no length...?


yes.

the hose is about 60mm long. there is about 15mm of free hose once it is on the rail spud, so it doesn't move at all. if the hose was longer there might be an issue of the gauge bobbing around, but the way it is, no issue. it just sits there.

that said, do you recommend installing these and leaving them in place, Scott? Do you think they could lead to a fire hazzard and a roasted bus? Shocked
Looks like something handy to have in place if the connection is secure at the rail.
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PostPosted: Wed May 31, 2006 12:12 pm    Post subject: Reply with quote

i don't either recommend or not recommend leaving it place. as long as it is properly installed i do not see any issue with it being there all the time, any more than having the spud with a little screw in the end there all the time.

however, any time someone does something to a vehicle, there is a chance the something they do will cause harm rather than good. i have a friend who has a VW bus and he has been fixing his bus constantly since he got it, to the point where he has fixed everything so well that the bus has not moved for almost 2 years. the engine is in pieces in his garage, the interior is a storage shed for all the spare parts he has accumulated. he has never actually fixed a single thing on the bus, he has in fact broken everything he has attempted to fix. there is nothing i can do about this. if i were to supply him with a fuel gauge i would tell him to put it on his desk and admire it, that way it could do no harm.

also:

VWBusrepairman wrote:
isn't every 2 years a bit frequent?


in my work on buses i have done the fuel lines on at least 6 buses so far this season. every one of them had original fuel lines, meaning they were over 25 years old. none of them were leaking, but they all needed replacement. if done properly i would say every 8 years or so would be fine. someone posted the other day that they replace them every year, but that is really excessive.
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PostPosted: Wed May 31, 2006 5:06 pm    Post subject: Reply with quote

VWBusrepairman wrote:

3. any photos of this?


Here's mine: bought from German Supply and installed 3 years ago. No leaks or other problems.

However, I noticed about a month ago that it is not holding pressure after shut off like it used to. Time to check the fuel pressure regulator IAW Randy in Maine's instructions. I do have a spare, in any case.

Image may have been reduced in size. Click image to view fullscreen.

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Lastly, you just referred to US citizens as 'Americans'. Exactly what kind of Canadian are you? From what continent?
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PostPosted: Wed May 31, 2006 5:42 pm    Post subject: Reply with quote

germansupplyscott wrote:
...he has in fact broken everything he has attempted to fix. there is nothing i can do about this. if i were to supply him with a fuel gauge i would tell him to put it on his desk and admire it, that way it could do no harm.


LOL!! Laughing Still chuckling over this post, thanks Scott I needed that. Laughing
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Randy in Maine
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PostPosted: Wed May 31, 2006 5:47 pm    Post subject: Reply with quote

Ok we can make a change in the fuel line change out.

How about to "One more thing...change out the fuel lines when you first get your bus and then inspect them every year. We suggest changing them out with the correct FI fuel line every 7 or 8 years on your birthday. Hate to see a nice baywindow bus burn down."

Anything else? Something that could be worded perhaps a little more clearly?
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PostPosted: Wed May 31, 2006 7:20 pm    Post subject: Reply with quote

dwill49965 wrote:
VWBusrepairman wrote:

3. any photos of this?


Here's mine: bought from German Supply and installed 3 years ago. No leaks or other problems.

However, I noticed about a month ago that it is not holding pressure after shut off like it used to. Time to check the fuel pressure regulator IAW Randy in Maine's instructions. I do have a spare, in any case.

Image may have been reduced in size. Click image to view fullscreen.



you do a lot of dirt road or desert driving?
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PostPosted: Wed May 31, 2006 7:25 pm    Post subject: Reply with quote

flat4freak1978 wrote:


you do a lot of dirt road or desert driving?


Yes - camping and touring around Nova Scotia logging roads and other off the beaten track places. There's a few gaps I should really plug up ...
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PostPosted: Wed May 31, 2006 11:59 pm    Post subject: Reply with quote

Taking off the gas cap relieves pressure in the tank, but *not in the fuel rail if your check valve and pressure regulator are good*.
The neat trick to relieve fuel rail pressure is to pull the hose off the plenum or tee that leads to the regulator. Suck on the end of the vacuum hose to the regulator and it will relieve the fuel rail pressure in seconds.
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Randy in Maine
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PostPosted: Thu Jun 01, 2006 4:13 am    Post subject: Reply with quote

Changes made. Thanks!
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PostPosted: Thu Jun 01, 2006 6:25 am    Post subject: Reply with quote

there are some other additions i would like to make. there are actually 4 FI hose configurations for the years between 75-79. 75, 76 and 77 are all unique. i now have 4 kits. the 76 diagram and the 78-79 diagram are below, the other two diagrams are coming soon.

Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


the hoses are quite different across the years owing to several factors. the fuel pump is located in 3 different locations depending on the year, the left injector rail is different, and there are no steel lines in the fuel ring (except the short injector rails) on 75, 76 and 77.

the other addition that needs to be made to the diagrams is the provision for the BA6 gas heater line which tees into the large hose near the fuel pump.
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PostPosted: Thu Jun 01, 2006 6:55 am    Post subject: Reply with quote

germansupplyscott wrote:


Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


Scott- I'm running hose B & C as rubber hose only as seen in first pic, though in the latter pic the metal lines are in this place with rubber on the endpoints- which do you think is better?
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PostPosted: Thu Jun 01, 2006 6:57 am    Post subject: Reply with quote

I dunno about Scott, but I *like* metal lines.
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