RX80JOE

iTrader: (4)

Hello,
I "may" have a really weird issue, or easy fix going on with my newly built S4 turbo motor. This may be a long post, so you can understand my issue.

The engine is all new (S4 13B turbo half-bridge port), RA seals, new S4 housings from mazda, New BW S366/.91ar turbo, New injectors (1000,2000cc High Impedance) New microtech LT9-c unit, etc. Everything is basically new on the engine. It sits in a 1980 s1. When we first started it up it had very little gas in it. We cleared it out for 15 seconds and turned off. Ran and rev'ed great! Filled it up with 6 gallons of pre-mix. We tuned it and ran pretty decent, but fuel pressure ended up dropping on acceleration and was bogging down, but it was drivable. At the time we had a A/F ratio 12.8 at idle and around 13.2 when running a tad rough on accel. We thought fuel pump was going bad, (cheap, but new, speedmaster pump, but specs where good enough to run this engine). We put in a aeromotive a1000, and it seemed the fuel pressure went up and stopped at 38 psi, and to 40-42psi hitting throttle. THAN!! after a few minutes the pump pressure went down when throttling, and was running rough, breaking up. THIS IS THE WIERD PART.. we had little to no fuel. We swapped the pumps out (again) and added 12 gallons of pre-mix (knowing it was out of gas, thinking that was the issue). Car started up and ran like it did during the first day, when we street tuned. OK.. so yesterday we wanted to work on another street tune, drive the car to the shop and it's acting up again.. Runs decent at some points accelerating, than breaks up pretty bad. At the shop we check the return fuel line.. hard as a rock on prime and pressure goes up to 55 psi on the FPR, and we take the adjustment screw out (no difference, stays at 55psi needle shaking).. OK.. Return line seems to be clogged or kinked. So, we did a test at the FPR (took the line off and added one line to an external fuel tank) and the pressure went to 38psi in a second on prime. OK, return line issue. We take off the return line at the fuel tank and fuel is coming out.. odd, pressure in tank blowing it out? Vapor lock? We cleared the line and put wire down the return pipe in the tank.. it seems there was no obstruction. Put it all together and we get an issue where the car starts but has a slight miss. We check plugs and install good ones. Same thing, running rough.(btw, we are hooked to a laptop looking at the specs). So, we check the heat on the manifold with a laser thermometer.. Frt rotor housing is cooler than the rear.. OK.. Disconnect CAS and Check compression, sounds great. That's not the issue. Connect the CAS sensor back up and start car, and it runs GREAT (great A/F ratios and temps seem equal on housings)!! A quick little tune in the garage and it's amazing how good it sounds!! Great fuel pressure and everything seems ok, BUT what was the issue??? We know something will happen soon, we need to know what the issue was. So, I drive the car home and get 1/4 mile and the car goes from running great to really bad, and I can barely drive it, bogging down big time.. Got it home and popped the fuel cap and a lot pressure came out within 3-4 seconds.. (It has about 6 gallons left in the tank) We feel there may be more than one issue here. Tank venting issue? Clogging fuel filter, clogged injector on frt rotor? Any ideas, or help would be greatly appreciated!! Thanks in advance.

Sincerely,
RX80JOE

Aaron Cake

iTrader: (1)

Try running the car without the fuel cap in place and see how it behaves.

RX80JOE

iTrader: (4)

We did that and it relived most of the pressure on the return feed and lowered psi on the FPR. I just ordered a new fuel cell, as we inspected the original tank and it was rusted and the new fuel filter has flakes in it. That will cure the problem for good. Thanks for the input Aaron!