Hey guys, check it out -

http://www.clubrx.org/default.asp?id...ntent=71&mnu=5

Been meaning to do this for a while.

The stock fuel pump wiring has a pretty good voltage drop. But, you don't have to reinvent the wheel or even add a relay to the system - just giving the stock circuit opening relay more voltage to start with does the trick just fine.

Basically, with some wire and an in-line fuse, you can make this work. Took me about 30 minutes, tops.

Results? I went from 11.8 volts at full throttle with no electrical load to 13.8 volts at full throttle with no electrical load - that's a BIG improvement. The more voltage the fuel pump gets, the better it can maintain fuel pressure at high RPM/high load.

Let me know if you have any questions or comments.

Dale

 

I'll definitely be doing this...very helpful. Thanks Dale!

 

Might be a dumb question but, did you notice any drivability issues after the rewire? I thought I read somewhere that Chuck wound up taking some fuel out of his maps after he rewired his fuel pump. Not sure if he did it b/c it was running richer than desired or if he felt a difference.

Thanks.

 

Thats interesting. I was going to rewire the fuel pump from the trunk, but this looks alot easier and less hassle. I'll probably tap into my power cable that I have running back to the battery relocated in the bin behind the passenger. Just to make sure the fuse you are using is a 20 amp correct?

 

Excellent write up. Might just be something to do with 8 inches of snow on the ground like there is right now!

Thanks!

 

I'm confused. You're running a (fused) line directly from the battery postitive cable to the power input of the circuit opening relay. So the voltage drop in the stock system is caused entirely by the internal fusebox wiring?

Would it be possible to replace the stock relay wiring in the fusebox with thicker wire? It would be cleaner.

 

No the stock system powers the fuel pump off the ignition circuit, the ignition circuit for crying out loud! ... and that circuit is not capable of supplying full voltage to the pump. Nice thing about this rewire is that it retains the stock two speed system.

 

It's been common on the DSMs for years and years. Guess it makes sense anywhere! Any real statistics (other than the voltage increase) on how much more the pump flows with the modification?

 

OK, time to answer a few questions.

- This shouldn't affect how the car runs in general. If you have a really well-tuned PFC map, it would be quite likely that you'll run a bit richer at higher RPM. But, I think that's primarily when you're REALLY pushing the fuel pump (ie, lots of mods and boost).

- Yep, the stock fuel pump circuit runs through the ignition switch, which is typically a pretty good voltage drop. Well, it's obviously a substantial voltage drop by my tests!

- I've done a more hard-core re-wire on FC's back in the day (all new wiring front to back, keeping the 2-speed system, with larger wire and relays) and it was a BIG job. The FD has good sized wiring stock, and I just don't see the need for it, especially with the results I've had.

- Yep, 20 amp fuse - I think in my install it's actually a 30 amp, since it's also for the car stereo amp (which is WAY underutilized ).

This is a mod that really won't magically make your car better, but it corrects a deficiency in the stock system, and that's my whole goal with my car - find areas that Mazda made compromises in and correct them.

Dale

 

I did this a few years back, but did it a little differently.

Instead of running a new wire and fuse, there is a spare fuse holder in the relay box that is powered by a 10ga wire direct from the battery. Simply cut the solid blue wire powering the relay back far enough to reach the spare fuse holder and solder a spade connector to it.

I had the same voltage increase that Mr. Clark did and had the max fuel pump pressure go from 75psi on the stock wiring to 80psi.

To clarify what twokrx7 said, the power for the pump is run though the ignition switch, this is done in many cars and I supect for redundancy, and this mod bypass it.

 

Hmm....this looks really good Dale. I think this will make up for my pressure drop at high boost with the Denso pump...

 

niceeeeeeeeeeeee

 

wow, I just visited your website, and I just want to tell you that you have some awesome info! Thanks

 

Gadd - good stuff! That would make it even easier to wire in!

Dale

 

Looks good but i would solder all connections and use marine heat shrink. It has a glue that seals the connection once dry.

 

There's a lot of debate about it, but a crimped connection is best in an automotive environment. I also illustrated using crimped connections as it's easy for most anyone to do and get a solid, quality connection.

Dale

 

this really isn't anything new......when fuel pump manufactures give you the flow rates of their pumps its @ 12-13v and the fact is no car gives its fuel pump 12+volts. i thought this was a pretty well known in the performance community but maybe not.

one of the main reasons for this mod is to lower inj. duty cycles at high rpm, but it does also cause a low rpm change as well. keep in mind that the fd (much like many other factory turbocharged cars) has a greater voltage supply as load increases (ie boost/+rpm). so when you change the main source of power to the pump its not just at WOT but in all the rpm range. < and on that note i CAN say with all the fd's I've done this to i have seen a few that did NOT run right after this "mod" was done (needed some miner "tuning" to idle etc.). it is not uncommon to see as much as a 1-1.5 (most will see about 0.7) afr point increase in fuel across the board. also i don't just do the power supply "mod" i also give the pump an added 2 separate grounds to help (which is almost just as important imo) on the other end of things.

-J-

oh and P.S. their is more than one way to wire this "mod" than has been stated but if this one works for you than great. i have been doing it a little different but that's just me!

 

With the stock fuel pump, this mod will not change your AFRs in any way. With aftermarket pumps all bets are off, the increased voltage may cause an aftermarket pump that worked well before this mod to overwelm the stock pressure regulator and incease the pressure the injectors see. This would make the car impossible to tune properly unless the OEM regulator was replace with one that could handle the flow.

 

So what kind of pressures can the OEM regulator handle? Instead of making a broad statement without backing, bring some details.

 

It's not a matter of pressure but flow. The only personal experience I have with pumps in this car are the OEM, the Walbro 255 and the Supra pump. The stock regulator works well with both the OEM and Supra pump but is overwhelmed by the flow of the Walbro at low loads. But did use terms like "all bets are off" and a word like "may" for a reason.

Paul

 

i do not concur. i have seen no problems with this before.
-J-

 

Stock pump with the wiring mod:







Walbro pump with wiring mod, no other changes.

 

Agree 100% on giving the fuel-pump a GOOD ground, esp. with the same or thicker gauge wire.

In my amatuer radio hobby, we fuse both the POSITIVE and NEGATIVE/GROUND power supply.

:-) neil

 

Thanks for the write-up Dale, I will do this mod soon!

 

Dale you rock...i was just searching on how to do this..