Steven Harper

Is there a trick to getting the fuel injectors to pop in? I got new ones and switched out the o-rings with the larger ones from Roger but they seem too big to sest them. I've lubed them up with oil and even tapped on the rail with no luck. I'm in the final stages of my intake refresh and was hoping to get finished today.

nirich

I installed the same injectors from Roger a couple of months ago. They fit well, with lube, into my '88.
Just took some measurements from a spare set of O rings (I broke a pintle assembling them and ordered a couple more sets from Roger).
Hope this helps.

Steven Harper

I just got the aftermarket ones that measure 17mm which should be correct, although I have seen reference to 16.5mm too. I did get the intake refinished in Cerakote by Tru-9 Design. My understanding is that Cerakote is actually thinner than powder coat so I wouldn't think that is the problem. Plus it looks like I'd need to remove more than just the coat of paint to make them fit as they barely fit into the recessed area at the beginning of the hole before they taper in.

Mrmerlin

NOTE Ideally you would use new Tan/Brown O rings from the Bosch kit for the S4 engine.
as these are a special size.

NOTE when doing an intake refresh, getting the manifold powder coated is part of how these O rings seal,
if you dont PC the intake but rather strip it then repaint it for example,
then the injector port may be too wide to seal thus a leak will result.

I suggest to use the DC111 on the O rings as this will let them slide easily into the port.

Steve try using one of the old Tan/Brown O rings as a test fit.

Steven Harper

Sadly I threw them away months ago with the old, non-working fuel injectors.

Mrmerlin

Well I would suggest that you get the Bosch injector O ring kit, X 8
and replace the spacer and the O ring and the pintle cap.

NOTE the spacer on your injector now might be too thick,
and it looks like the O ring is too big,
once you take it apart compare how the Bosch O ring fits on the injector,
and compare it to the Black one ,
and compare the spacers.

ROG100

Just for the record the Bosch O rings are nominal 16.8mm OD - 8mm x 4.4mm CS
Our O rings are identical 8mm x 4.4mm CS
O rings have a nominal tolerance of 0.1mm (0.004") on the CS (cross Section).
I doubt .004" would make any difference to the fit.
More than likely the build up of paint is the issue. Clean out the hole and fit again.
We have been selling these O rings for nearly 15 years with zero issues.
Our injectors are fitted with the correct O rings and spacers.

Mrmerlin

OK thanks Roger for the O ring size info.

Steve did you try using the DC111 on final assembly?
this will let the O ring slide into place.
try to get the DC111 on the sides of the O ring so it will slide on the spacer as well.

nirich

Do you have the four 'rubber buffers' installed on the intake?
If so, then the injectors will not be low enough to slip into their respective holes.

Steven Harper

Maybe it is the spacers on them as the o-rings "fattened out" when I put them on the injectors and the lack of space could force the o-rings to ride a little high. By themselves the o-rings measure 17mm but on the injectors they are closer to 17.5mm. The spacer is 1.8mm thick but I can't find the spec on the official 928 ones. I'll get the complete kits and try them before I go through the pain of removing the intake to take more agressive measures.

nirich

The spacer I have (as shown in post#2) is 1 mm thick.

Steven Harper

Thanks, definitely thinner that what is on mine. I suspect that is forcing the o-ring to "ride up" which is causing the problem. I'll get the proper sized ones and see.

Also, I don't have rubber buffers for the fuel rails. Mine is a 1989 which I understand never had them.

nirich

Have you tried a 'test' install of just an injector without the fuel rail attached?

worf928

@Steven Harper The proprietor of Tru-6 called me the other day about your issue and sent me your above picture. Tru-6 has done intakes for my clients’ for almost 10 years. I know how this works.

The factory coating is “slippery” while the Cerakote is not. So, even though lube is always a good idea, it is absolutely required in this case. I recommend a “rubber friendly” lube that is primarily glycerin-based. The rubber will absorb the glycerin after a day or three leaving an air-tight non-slip seal.

That written, in your picture, the plastic spacer/stand-off between the o-ring and injector body is too small an O.D for the larger-than-standard 928 lower o-ring. The part in the 928-specific bosch kit will be a bit larger and that will help keep the o-ring from rolling. Note “help” not “prevent.”

Regardless, since the Cerakote isn’t “slippery” you made need to use a plastic tool to help the lower o-ring seat in the bore even with a bit of lube.

Most importantly, you must always install the injectors in the fuel rails first and ensure that the retainer clips are secured and “clicked in.” Then install the assembly. It is only the rails that located the injectors on the vertical axis. If you attempt to install the injectors in the intake first and then the rails you will have one or more injectors not properly seated in the rails. And that… is a car fire.

Last, as soon as you have the fuel system “buttoned up” bypass the fuel pump relay to operate the pump and check for leaks.

Steven Harper

I was out of town for a week and just got back to this project and wanted to close this out in case anyone else runs into the same problem. It was the spacers that were causing me issues. The spacer in the Bosch kit is much thinner which helped keep the o-rings from "flattening out". With some lube and a little persuasion I was able to get the injectors to pop in. So if you buy the Mustang injectors like I did, you have to change the o-rings AND spacers. The blue one in the pic is the correct one to use. I had no gas leaks when I ran the fuel pump. I assume it would be more of an air leak situation if the bottom o-rings didn't seat in the intake properly but will find out today when I try to start it up. Thanks for everyone's help.