[v12-engine] Leak testing injectors

V12-Engine
1

Since I had them out I leak tested my injectors. My technique
was to connect the injectors one at time to a rig that allowed
me to pressurize with air using a bicycle pump. I pumped
it up to 40 psig and then sprayed the injector tip with a
dish soap solution. Worked nicely.

Ten injectors showed no signs of leakage. Two showed slight bubbling,
but not enough to cause noticeable pressure decay while watching my
gauge for a few minutes. My guess is if fuel were present instead of
air, which would require a more sophisticated test setup, it would be
a very small dribble.

So, now to my question. How leak-tight do they have to be? Should I replace
the two injectors?

BTW, who’s got the best deal on injectors now in case I do decide to replace
them?

Ed Sowell
76 XJ-S

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

2

On 15/09/2003, Ed Sowell told us:

Since I had them out I leak tested my injectors. My technique
was to connect the injectors one at time to a rig that allowed
me to pressurize with air using a bicycle pump. I pumped
it up to 40 psig and then sprayed the injector tip with a
dish soap solution. Worked nicely.

Ten injectors showed no signs of leakage. Two showed slight bubbling,
but not enough to cause noticeable pressure decay while watching my
gauge for a few minutes. My guess is if fuel were present instead of
air, which would require a more sophisticated test setup, it would be
a very small dribble.

So, now to my question. How leak-tight do they have to be?

I think they should be leak tight. The fuel in the lines is not as
compressible as the air in your rig, so the pressure will leak down quickly
with a very small leak, not to mention the problems which may result from
the accumulation of fuel in the engine.

I thought there was a Jaguar spec on leakage of a couple of drips an hour,
but I can’t remember where I read that.

Should I replace
the two injectors?

I would say yes. You might repeat your test, priming the injector with a
few drops of fuel to see if there is a measurable drip rate.

BTW, who’s got the best deal on injectors now in case I do decide to replace
them?

If you can’t find any that suit, there are usually NOS D-jet injectors
available at the Stoneleigh spares day, which I will be attending on
October 19, let me know if you want me to pick up a couple (and your top
price).

regards,
Mike Morrin

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

3

Ed,

Bear in mind that if you’re testing pressure drop, use of compressed air
will give significantly different results than a (stationary) fluid.

Did you clean the injectors? If you didn’t try that first, it may solve the
leaking problem.

No idea where to get new ones best in the States, but I’ve never had
problems with putting used injectors in a car. Just test them first!

Cheers,

Jack Verschuur

Since I had them out I leak tested my injectors. My technique
was to connect the injectors one at time to a rig that allowed
me to pressurize with air using a bicycle pump. I pumped
it up to 40 psig and then sprayed the injector tip with a
dish soap solution. Worked nicely.

Ten injectors showed no signs of leakage. Two showed slight bubbling,
but not enough to cause noticeable pressure decay while watching my
gauge for a few minutes. My guess is if fuel were present instead of
air, which would require a more sophisticated test setup, it would be
a very small dribble.

So, now to my question. How leak-tight do they have to be? Should
I replace
the two injectors?

BTW, who’s got the best deal on injectors now in case I do decide
to replace
them?

Ed Sowell
76 XJ-S

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

4

Thanks, Mike. I tried to put a little fuel in one of them but it’s
not that easy. The problem is they have been on the bench for a couple weeks
now so they are full of air which, together with surface tension, blocks
fuel from flowing down to the tip. The only way I can see to do it is to
put some fuel into the tubing connected to the injector and energize
the injector until fuel flows. Sounds messy.

I hope to have it back on the road this week, but thanks for the offer.

BTW, when I got the hoses off I discovered yet another style of barb
on the injector nipple. That is, in addition to the Christmas tree and
the single barb with a clamp land, I have tow injectors with a very thin,
sharp barb and a flat land upstream! I’ll post a picture soon.

Something else I discovered while testing my modified HE rail for leakage
was that hoses put onto the Christmas tree barbs without the little
dished end caps can pop off at 60 psig. This has caused me to go back
to my original theory that the caps are necessary.

Ed Sowell
76 XJ-S

You might repeat your test, priming the injector with a
few drops of fuel to see if there is a measurable drip rate.

BTW, who’s got the best deal on injectors now in case I do
decide to replace
them?

If you can’t find any that suit, there are usually NOS D-jet injectors
available at the Stoneleigh spares day, which I will be attending on
October 19, let me know if you want me to pick up a couple (and your top
price).

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

5

Thanks, Jack. I’m not set up to measure pressure drop or flow rate.
Just wanted to be sure they weren’t leaking. Did not attempt to clean them
either.
Guess I’d need ultrasonic equipment. Or, maybe I could find a local shop
to do it.

Thanks.

Ed Sowell
76 XJ-S

Ed,

Bear in mind that if you’re testing pressure drop, use of compressed air
will give significantly different results than a (stationary) fluid.

Did you clean the injectors? If you didn’t try that first, it may
solve the
leaking problem.

No idea where to get new ones best in the States, but I’ve never had
problems with putting used injectors in a car. Just test them first!

Cheers,

Jack Verschuur

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !