Since installing my front mount intercooler, and getting the boost up etc.. there's been an itching suspicion that there's something not quite right! .. basically, with over more than 10psi, the car would hesitate a bit.. very obvious to me as the driver.. but not to passengers! But anyhow, it would seem that the car would pull and accelerate harder at half throttle (by keeping the boost under 10 psi) rather than with full throttle.. plus the engine has been pinging a wee bit at high rev's.. 

Soo.. after having my exhaust checked out, and to see that the catalytic converter isn't blocked.. all things seemed to point at the fuel pump and fuel pressure.. yes, I should have taken my car on a dyno and had this suspicion verified, but at around $120/hour on a dyno, plus a mechanic's time etc, it would cost almost the cost of a new pump just to have it checked out...

So the solution.. a bosch motorsport upgrade pump, would cost around $295 upwards.. and Nissan Australia quoted me for a genuine replacement, to be around $680+GST+SHIPPING FROM JAPAN.. that was certainly out of the question! I've heard of people using VL Commodore pumps, so I started investigating this.. the problem was, half the people I spoke to assured me that the VL pump that runs high pressure (what I'm in need of) is the external pump.. as the VL has both an internal and external pump.. so I ended up going down to Repco and talking to them.. they didn't have any form of high pressure internal VL pump.. only a low pressure one.. but the VN Commodore uses only one pump, and its internal, (and high pressure of course), just like the Nissan S13! So I bought a VN pump for $153. 

I went into this whole thing blind, never done it before, but have done plenty on my car (like replaced gaskets all over the place, removed turbo, redone oil lines, redone sump gasket, clutch, front mount intercooler, custom ecu chip etc.. ) so I figured I was capable of doing the job.. but because I've never seen an intank fuel pump before.. I didn't know what the hell.. when I got the VN pump from repco, I looked at it.. thought "gee its small" and carried on my merry way.. I expected some big pump since I've only ever seen the enclosure to the pump in the boot! So anyway, I started to pull things apart.. 

This is where the Fuel Pump is located, in the boot under the carpet, it was raining at the time and my girlfriend wondered why I parked the car half out of the garage with the bonnet exposed to the rain.. she was surprised to know that the pump was in the boot and in the fuel tank :-).



Here I've removed the top couple covers, damn is was dirty underneath! You might notice in the top right a black cable.. that feeds my amp for my stereo.. I wanted to listen to music while doing all this.. but quickly realised that it was best to leave the battery disconnected (removed the positive terminal from the battery) while dealing with a lot of petrol fumes!



I just had to clean it up a bit before continuing! I disconnected the fuel pump from the power supply and attempted to start the car.. you need to release the built up pressure in the fuel lines you see.. otherwise fuel sprays all over you when you disconnect the fuel lines! (Truth be had, the car still ran, and I should have kept it running until the car stopped, and turned it over a few times, I failed to do this step properly as my car seemed to just continue to run! When I removed the main fuel line it began to piss out fuel.. I quickly learnt my lesson.)

I removed the pipes and started to pull the pump out, and undid the bolts that hold the pump assembly in.. I found that the floater that detects the level of fuel in the tank was in the way.. and I couldn't pull the pump out.. it was hard to work out when I could only lift it up about 4 inches to try and see what was going on.. The trick is that the floater's wire that attached to the gauge bit on the fuel pump assembly clips out... and I had to be careful not to drop it into the tank.. I didn't feel like fishing something out of the fuel tank.. Once I discovered that, I pulled the floater out (you can see it to below the pump in the picture below) and continued to raise the pump out slowly. 

Here's a picture of the new pump being fitted, the VN Commodore in tank high pressure pump is perfect in length, its not as thick as the old one though, so I didn't have to use a longer peice of rubber hose at the top of it or anything like that..  Thankfully, because I bought the pump new it came with all the rubber bits and the fuel pickup sock filter etc, which made life easy.. (so I'm not *not* regretting getting a second hand pump for $50).. the new rubber piece and filter sock assembly fitted in reasonably well with the pump assembly, (it wasn't PERFECT, but it was still a good snug fit). I know of people getting.. well.. apparently high pressure VL pump's, and having a lot of fun trying to fit the stock filter/sock from the stock pump onto their replacement pump.. I had a brief look at how one would achieve such a thing.. and I have no idea how you could do it without a serious note of bodgyness.

Here you can see how thick the old one is comared with the new one in the pump assembly..  There is some form of return line from the stock pump.. maybe if the fuel line was blocked the pump could release pressure out of it.. that's the only reason I could think of its existance.. but there wasn't scope for this on the new pump.. 

Here's a picture of the new pump fitted (with a bit of rubber and a tie around it holding it together, ready to put in.. the reason for the rubber around the pump is to secure it.. its not as thick as the stock one so it needed to be supported somehow.. the stock one had the cable tie around it, so its not an unsafe idea as far as I'm concerned.. truth be told, while fitting the pump in, the damn rubber seal around the top fell into the fuel tank and I had to fish it out.. but anyhow.. once I had the pump half way in there, I attached the floater thing.. once thing that buggered me up was there's actually a hole to poke the right angle bend of the floaters support wire into, and then it secures and clips in.. without that, the floater would spin around all over the place.. I had originally just clipped it in without noticing that I could stick the support wire down that hole in the middle of the thing and thought that this couldn't be right.. and fiddled around until I worked out what was going on.. unfortunately I hadn't noticed this when I had unclipped originally because it was inside the tank at the time!

In summary, the new fuel pump seems to spin faster, at a much higher rpm... therefore it has a higher pitch whine to it.. I expect this to be normal, since its smaller than the stock one it would have to spin faster to be more efficient than the stock pump, which it is... the noise is not too obvious but I notice it for the moment because I'm not used to it.. and perhaps the pump needs to 'run in' a bit.. if you stand behind my car you can hear it whining :-) .. 

The hesitation under high boost has disappeared, although I think my timing is a bit screwed up too because it still pings a little bit in the high end.. although it has been a damn hot day today as well, so the air was pretty warm which wouldn't have helped.. but I'm quite sure the results of the replacement pump has been worthwhile achieving. I'll have to go back to the drawing board and fiddle with my fuel and timing maps in my ECU and see if I can sort things out.

Update - this pump supplied more than enough fuel to produce 170kw@wheels, which is around 300hp at the fly wheel. With this in mind, I am quite confident this pump will suffice most S13 owners that's for sure.. I did find fuel regulator problems at a later stage which is likely to be the reason why I replaced the fuel pump in the first place.. but annnnyway.. live and learn?
If you have any further questions, I might be able to help - [email protected]