sevenracer
sevenracer Reader
1/22/22 7:22 p.m.

I've been trying to do a boost leak test on my TII engine before first start.

I have the exhaust down pipe sealed off with a plate and some silicone clamped on the exit flange, and I made a plug for the intake manifold elbow. When I put about 15 psi in the intake and spray with soapy water, I am seeing bubbles around the two secondary injectors. I unbolted the fuel rail and pulled the injectors out and the grommets seem to be fine. I ordered new seals that I was supposed to get today, but I guess the weather here slowed the delivery til Monday.

An observation - it doesn't seem like there is much force "clamping" on the injectors between the rail and the manifold when the bracket is torqued down.

Is there any type of sealant to use on the grommets? Or other idea's to improve the seal? I saw someone post that you could stack orings around the injector tip above the grommet to add some pressure to it. Seems like none of this should be necessary, but the injectors seem to have a much looser fit than I would expect and not really any way to adjust that without maybe bending the bracket.

 

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
1/22/22 8:44 p.m.

Those are kind of a goofy setup with the square seal.  They seem to require 35psi (might be 43 on FCs?) of fuel rail pressure to hold the injectors sealed to the injector cup.

The square seal MIGHT be supposed to seal to the sides too, but I have not seen a replacement seal that did.

Oh! There are two O-rings in the injector cup.  Even if the square seal seals to the injector cup, if those O rings are shrunken then you will have a vacuum leak.  Be very careful with the cups as they tend to be brittle, and they are shockingly expensive.  Some people eliminate the injector aspirator hoses but I find that they help a lot with atomization.

sevenracer
sevenracer Reader
1/22/22 9:26 p.m.

So, are you saying expect them to leak during the intake leak test if the fuel system isn't pressurized?

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
1/22/22 9:28 p.m.

Yep.

 

I found through painful experience that if you DO add spacers to squoosh the seal down tight, it can damage the injectors.

 

Goofy setup all around, but I can sort of see why Mazda did it that way.  No simple way to have the injector spigot into the injector cup without relying on the cup not distorting and causing problems.

sevenracer
sevenracer Reader
1/22/22 9:41 p.m.

Interesting. Thanks for the info. Lots of stuff I've never had to worry about with a Nikki carb running 2psi!

imgon
imgon HalfDork
1/23/22 8:36 a.m.

A couple of years ago I installed new RX 8 injectors on my NA FC. They would occasionally leak at first start up after sitting, swapped them to another brand and it stopped. Hope the new seals fix it. Pete's explanation of needing pressure sounds feasible as well.

sevenracer
sevenracer Reader
1/23/22 2:23 p.m.

Welp, tested again today with the fuel pumps running and... still leaking at the two secondary injectors.

Was hoping they would seal up so that I could keep my first start that's scheduled tomorrow afternoon with my tuner.  New grommets/o-rings aren't getting here until tomorrow morning at the earliest.

sevenracer
sevenracer Reader
1/24/22 11:28 p.m.

Just a quick follow up, new lower grommets did the trick. Thanks all.

Leaky version on the left, new Mazda part on the right. It is thicker and has slightly larger OD and ID and no rounded corners. I think the old ones came from the company that cleaned and tested the injectors.

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