S4 1987 na chassis, s4/s5 t2 engine. No bac or emissions. Walbro 255lph fuel pump, stock injectors, aeromotive FPR.

I had a weird problem last weekend and so I'm wondering about what the yellow check connector on the passenger strut tower actually activates.

I made new hard fuel lines along the bottom of the car, without touching the flex hose at the front of the car. Last year I installed an aeromotive fpr, new injectors of the stock cc, new flex hose around the fuel rails and to the inline filter and to the return hard line. When I did all that i confirmed that the system wasn't leaking.

So I dropped the fuel tank and rear subframe and installed new fuel and brake hardlines. As I did before, I used the yellow check connector to inspect the system after. I left the intercooler and UIM in place which I had not done before, as I didn't expect any leaks in that area since I didn't touch the rails or injector area. The hard lines and flex hose connectors at the fuel tank and the ones leading to the engine didn't leak. After about 45 seconds I noticed fuel was pouring down the back of the engine coming off the top of the LIM.

I took the intercooler and UIM off and dried up the area. The flex fuel hoses at the rails all seemed dry, and fuel appeared to have puddled around the primary fuel injectors. In order to pin point the leak i jumped the yellow check connector again , now with the area in plain sight, and I couldn't get it to leak again. I left it on for a few mins (engine off of course) and tried wiggling the lines and injectors and it never sprayed. It never flooded visibly either and didn't sound like they were injecting.

As I said, the engine didn't have any fuel leaks before I started, and I didn't touch on the rail or injector area. The only difference between the tests was that the TPS and UIM were removed for the second set of tests.

Does having the TPS hooked up with the yellow check connector jumped cause the injectors to inject? And in my case, maybe flooding to the point that it started to pour over the top of the UIM? Whenever I messed with the fuel system In the past, I always had the UIM off during the fuel leak tests.

I can't figure it out. Any insight is appreciated.

 

well it could i guess all the yellow plug is used for is too test the fuel system for leaks by pressurizing the fuel system without having the car on but maybe it could open them up

 

maybe your walbro is too much pressure for your stock injectors that its leaking by...i could be wrong but you could try cleaning them and getting new orings and such

 

I have the fpr limiting the pressure to 40 psi at idle vacuum. Or at no vacuum? When this was all happening the gauge showed 40 psi without the engine turning. The seals on the injectors were new with the injectors, and I actually replaced the lower grommets on them in the fall because I think I had s4 manifold grommets on before, and the s5 grommets fit much more snug

 

hmm well the stock pressure is 30 psi idk if that would effect it but the TPS shouldnt effect that in anyway because the systems still getting pressure. i would take the injectors out if its leaking from them and plug them in and redo the pressure test with the plug and see if it squirts out and try to lower the pressure to 30 and see if it still does but im sure the injectors can handle around 43 psi if i recall

 

maybe clogged fuel return lines could be and issue never had that problem so i wouldnt know lol

 

Yeah I would expect that the pressure isn't too high for the injectors but I thought that stock pressure was 34.1-39.8 psi in the service manual, if that's the right number. I aimed for the high range when I was setting it up I guess. I know that some people recommend taking the rails out with the injectors still connected or zip tying them for extra hold and running it to see if they inject. To do that though, it'd be the same scenario where the UIM would be off. Also they didn't leak the second and third times that I tried it, just the first time where everything was still assembled. I will check the return fuel line though and make sure that it's not clogged up though should all be good since its new and I blew them out before installing.

 

no, the injectors will never turn on just because of the yellow connector. the yellow test connector simply turns on the fuel pump relay, never goes near the ECU.

 

I was hoping that wasn't the case. Thank you