Published on May 5th, 2015 | by Jos Roder0
One Five: Fuel Pump Pain and Dyno Dilemma’s
One of my first purchases after buying the S15 was to install a new fuel pump. My rationale for this was a new fuel pump would cancel out that variable when diagnosing inevitable issues in the future. This theory has backfired for me in a way and I will explain more on that later.
I decided to purchase an Aeroflow fuel pump from the good guys over at Forced Motorworx. The pump is E85 safe and would absolutely meet my flow requirements. Best of all it’s an easy in tank install. In theory. (Isn’t this always the case!?)
With the car in the garage, I opened the boot (trunk) and quickly realised the S15 fuel tank is located over the rear subframe, which is probably safer as it sits further away from any potential rear impact. Unfortunately it certainly makes changing the fuel pump a more difficult exercise and your legs do get a good stretch.
The one thing that no one seems to realise, or at least inform others, is that the included plug that is ‘plug and play” is not so at all! (in hindsight positive and negative should have been checked before installation. Lesson learnt the hard way).
I was stoked when I found out that there was no wiring and I could just plug the new pump in to the existing fuel pump wiring. Click. Easy! I then reinstalled the pump into the in tank cradle holder before sealing the tank and re attaching the hoses. I then reconnected the battery and started the car. Nothing. It was cranking nicely, but nothing was happening. This is where the painful chase started. Fuses, checking spark and scratching our heads. The next test was disconnecting the positive pressure fuel line before the fuel filter and finding a coke bottle to see if fuel was flowing once the fuel pump primed. Ahhh ha! No fuel. So once more off comes the fuel tank cover and the fuel lines, before I pull the pump from its highly flammable bathtub. The pump had been spinning in reverse.
Using a multi meter we then confirmed the standard S15 wiring was wrong for the new pump despite the plug being correct. So the wires were reversed in the plug itself and the process of re installation repeated. Finally the car starts! Problem solved. Or so we thought. Which brings me to the Dyno dilemmas part of the post.
With the help of my friend Choonga, we trailered the S15 off to the local dyno guru’s at Chequered Tuning to check the car was healthy and safe to thrash at the then upcoming Phillip Island track day.
Casting my thoughts back to the night I purchased the car, I remember the crisp feeling of acceleration when I test drove it around the block, so was hopeful the SR20 would reflect that feeling on the dyno. BA BOW. As soon as Trent first started to ramp up the throttle on it’s first installation run at 6psi, the thing was pinging like an Ice addict on a fresh hit. Seriously. Why?!!! My mind started to race and I even at one stage wished I had just left the standard fuel pump in place!
Hoping to cancel out bad fuel as the culprit, we raced off to the local service station to add some more fresh 98 RON. BA BOW. No change. Some banging on the fuel pressure regulator didn’t change anything so knowing my track day was the following weekend, the only thing Trent could do was retard the timing by 5 degrees. He also quickly informed me the engine would have almost certainly detonated itself at Phillip Island if I had not come for the check up! Yikes!
With timing wound back, the S15 then punched out an unimpressive 156kw’s at the wheels. Which is IMO below what a JDM S15 should be doing with an exhaust, intercooler and some boost. However obviously the timing was now retarded to prevent the engine exploding, so that figure was indicative of the situation. Advancing the timing back to ‘0’ should have added in theory another 30 odd hp, so it is closer to where I thought it should be.
Looking at the graph, it looks like the S15 is not getting strong fuel delivery until 4,000rpm, and this was confirmed by Trent.
This brings me full circle. I now am left with the variable of the fuel pump still creating this detonation issue still, as there is potential that the pump was damaged by incorrect installation.
I have now purchased a fuel pressure test kit to help better diagnose the fuel delivery issue, before returning to the dyno where even a full tune may still not be able to fix an underlying problem.
So to do everything I can to eliminate the problem I have now gone through cleaning up a whole host of ‘little things’ that needed to be ruled out as potential issues and I will bring you all these in another post shortly.
Sometimes I really do question why I continue with all these pains. I just have to look past these times and toward that moment where you strap the belts tight and smile as you roll onto the track again!
To check out the beginning of the S15 project, head here.