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During last weekend's pre-first start checks I noticed that I could not hear the fuel pump when attempting to prime the system with the diagnostic jumper. I disconnected the fuel pump and tested voltage at the fuel pump plug, which showed a worrying 8.4v and is a separate issue on its own, so I know the pump is getting power. The pump also did not pass the continuity check on the bottom two prongs, as shown on F-101. I believe this indicates that the pump is bad, per the FSM testing. Seeing as how the car has been in various states of storage since ~2015 with only 2 gallons of fuel in the tank, I'm not terribly surprised that it has probably corroded.
I tried to find a source to replace just the fuel pump, however Mazda seems to only sell the whole assembly and it's fairly expensive. I am curious what the modern stock fuel pump replacement guidance is for FDs with no intent to add power beyond basic upgrades. Power mods installed by the previous owner are 99 spec twins, a Bonez turbo back exhaust, and a Greddy intake, which should all be supported on a stock sized pump. I also need to pass emissions so this is probably the most change the car will see and I want to avoid enriching the idle/cruise due to an oversized pump.
Does someone have a good source for a replacement pump or should I just install a Walbro/Stealth and call it a day?
Last edited by Revelc20b; Dec 19, 2020 at 12:17 PM.
an aftermarket pump doesnt do anything outside the parameters of a stock pump. it only gives you the capability to do so. if you choose not to explore those capabilities then it will never do what it was designed to do, it will instead only do what the stock pump was designed to do (if that makes sense). get whatever name brand aftermarket pump you want and do the 12v mod and think not of it ever again. ive been using the aem pumps in a bunch of cars and i really like them.
Exactly. As long as your fuel pressure regulator is working correctly, and that goes for OEM pump too, you’ll never notice the difference. Unless you get a noisy pump.
, which showed a worrying 8.4v and is a separate issue on its own
factory setup has a two speed pump, so 8.4v is fine. you need to remove the speed relay to get the full voltage (NC relay, it opens to lower the voltage, so if it fails, you get full power, FC was the reverse of this)
the fuel pump on its own is/was N390-13-350, its NLA in the USA, but available in Japan, although its crazy expensive
I have an 044 already that was for my 20b project, but I didn't want to deal with it on a car that's staying at stockish power levels. Most of the fuel pump threads are circa 2004-2015, so I wasn't sure if people had found a direct replacement that was about right for mildly modified cars, outside of the usuals suspects. Based on what I've been looking at today, I think I'm just going to order a Walbro 255 and be done with it.
Originally Posted by j9fd3s
factory setup has a two speed pump, so 8.4v is fine. you need to remove the speed relay to get the full voltage (NC relay, it opens to lower the voltage, so if it fails, you get full power, FC was the reverse of this)
Is this wrong in the FSM then? I thought you should see battery voltage when the diagnostic connection is jumped.
Last edited by Revelc20b; Dec 19, 2020 at 04:37 PM.
According to that, the answer is yes. Those conditions should yield battery voltage. The solution is to bypass it with the 12v mod and think not of it ever again
I bought one of these. Has a little increased capability from stock but was completely PnP with new hose, clamps and sock. That was a two or three years ago and absolutely no issues. Just use care to get it from a reputable source. Apparently alot of Chinese fake/knock-offs out there.
Might be a good time for a new filter too.
I bought one of these. Has a little increased capability from stock but was completely PnP with new hose, clamps and sock. That was a two or three years ago and absolutely no issues. Just use care to get it from a reputable source. Apparently alot of Chinese fake/knock-offs out there.
Might be a good time for a new filter too.
I've had one in my FC for about 6 years now. This may be old news, but if you're looking for OEM fuel pumps on Rockauto, and check the Denso part for the FD and cross-ref to a mid-'90s Supra TT, the same Denso part # 951004 comes up for both cars, for about $160. Based on the picture though, it looks like it comes with everything except the sock.
Either go with Denso or Walbro. Banzai Racing is a great source, they get the real deal pumps straight from the manufacturer so you don't have to worry about fakes.
The Bosch 044 pump is 90's technology. It's crazy loud and a chore to plumb in. I'd be hesitant to recommend that thing for a track car build.
The Walbro 255 is a bolt-in, it uses the stock O-ring setup to seal. You do have to cut/crimp connector the wiring to the plug but that's not a big deal. I've had a Walbro 255 in my car for 12 years or so with zero problems. Installed just like stock with the O-ring seal.
Big one is pulling the pump out and seeing the condition. If you have a rusty hunk you may be needing a fuel level sender, the hanger itself, maybe even a tank.
The Bosch 044 pump is 60's technology. It's crazy loud and a chore to plumb in. I'd be hesitant to recommend that thing for anything other than a track car build.
fixed!
Big one is pulling the pump out and seeing the condition. If you have a rusty hunk you may be needing a fuel level sender, the hanger itself, maybe even a tank.
Well, stock FPR cannot bypass enough fuel from the 450 so fuel pressure jumps up and car is now running too rich.
Yep, this was my concern with just slapping in my large pump. My 20b parts pile has a much larger Aeromotive FPR, but it didn't make sense to put both in for just the stock ish power levels.
I ended up ordering a Walbro from Banzai to make sure I didn't get a knock off. Thanks for all the input.
Well, I found the problem. I should have pulled the pump/basket before I went and ordered something else. I suppose I'll try cleaning this up and reinstalling once I get the tank cleaned out. I saw several threads about restoring the gas tanks with POR15 in the FB section, so I may give that a shot before I go searching for another tank.
Tank itself had quite a lot of sediment/rust in it, but I don't think it's actually leaking.
Yep this is becoming more common as the cars age and as the cars sit. Having fuel sit in the car (especially the new ethanol blends) for a long time is super bad on the tank and pump assembly.
couple things to your post. I had a radiator shop clean my rusty tank a couple weeks ago. They would not coat it because that coating will peel off the plastic baffles in the tank and then cause even more headaches for you. Try to save the fuel level sender. They are no longer available new and VERY hard to find used. Be gentle, use electronics cleaner on it, and i had to even pull the metal rod out and lube it up with some 2 stroke oil to get it to move freely again. It was very nerve wracking trying to mess with that thing. Take your time to examine it and make sure you wont break anything disassembling and be gentle with it. To the fuel pump i'll echo what others have said. The denso pump from supra is plug an play into the oring and everything.
