Walbro vs. Stock Fuel Pump (testing)
 

A bit of background.

I got my second FD last year. It had an M2 ECU, M2 SMIC Med, M2 intake but, stock exhaust all the way. The very first day I took off the stock catback and replaced it with a straight 3" pipe. On the third acceleration attempt, the engine went, taking out 2 apex seals.

Forward 3 weeks;

Reman engine, rebuilt non-ported seq. turbos installed plus now with the following mods:

PFC with commander.
M2 Intake
M2 SMIC Med
Downpipe
Midpipe with metallic cat
Corksport straight though cat back
Supertrapp exhaust plates to tune-in some backpressure to stop boost creep.
AEM UEGO wide band.
Fuel pressure gauge at the entry to the engine block.
Stock primary and secondary fuel injectors.

Got a "supposedly safe" fuel map to start off with. My initial AFR reads were 12.6 - 12.8 in 3rd and 4th near the redlines. I had to adjust the fuel map with the commander to entirely max out the map (1.496) in rows P16, 17, 18 to get back down to 11.3 AFR at high RPMs at 11 lbs of boost. That was as lean as I was able to get it with the stock fuel pump. My injector duty cycles were in the low to high 90s. My knock sensor peak reads were 120-180.

Today, I installed the Walbro pump and here are the BIG changes that seem to indicate to me that the stock fuel pump is not sufficient for power around 300 RWHP (Guessing my power, no dyno tests on this car).

Variables between the two tests:

1) With the Walbro, my fuel pressure increased 3 lbs, still using the stock FPR. Went from 31 to 34 at idle with the vacuum line connected.

2) Ambient temperatures were mid 50s in the previous stock fuel pump runs. Today it was 68F.

Results:

On all my WOT runs under full boost (11lbs) my AEM wideband was stuck on the lowest possible read of 10 AFR, which means that I was running probably BELOW 10. Car felt sluggish.

Reset all my fuel map numbers to my original settings. The highest setting came back down for row 17, N20 from 1.496 to 1.414. The AFRs with the much lowered map settings are now low 11s during WOT, touching 10.9 in 4th gear at 7000 RPM.

My injector duty cycles today peaked at 87%. My knock sensor peak reads were 20-24.

Conslusion:

Unless my Stock Fuel pump was a weak unit, this tests proves that the stock unit is simply not providing enough fuel for my relatively modest modifications. I was and still runnning the resistor in the pump circuit.

Not surprising to me at all. I have always figured that the stock pump was good for maybe 100 more crank horsepower than stock, which is right around 300 rwhp. I recently started a thread (entitled 'fuel system ramblings') which compares the walbro to the supra tt to the apexi BNR32 pump. In even includes flow maps that I found on the net, you should check it out, I'd be curious to hear your thoughts.

Excellent info in your thread. I missed reading it but, it makes good sense now with my test results to back it up...

I employed the same methods before making my change; Used Max's calculator and the Walbro fuel delivery curves to make sure that my setup would see enough fuel with this pump.

http://www.vfaq.com/pump-Walbros.html

Also from your thread:

https://www.rx7club.com/showthread.p...stem+ramblings

The above makes perfect sense now. It very much looks to be a fuel pressure drop problem with the stock fuel pump. I was simply compensating for it with the PFC map injector cycle settings but, it really was not enough. Now I am all but certain that this stock fuel pump blew up my engine when used with the M2 ECU, which runs at 12-13 lbs of boost. What was very much pointing to the fuel pump was that up to lines 14 in the injector map, my AFRs were fine. From line 15, up in the high RPMs, suddenly and very abruptly the car went lean. Seemed to run out of fuel and, in reality, it actually DID!

I guess, there is a wide tolerance on the stock fuel pump peformance, as some people seem to get by with up to 400 RWHP while others, like me, lose an engine at near 300 RWHP because of that pump. I almost think that in light of what we learned, the stock pump should be a "no brainer" replacement for any sets of modifications that approach 300 wheel HP.

Albert
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excellent thread.

wow I read this and the brake booster thread tonight, along with Rich's fuel pump thread earlier today. I must say this is the first day in awhile that I've read some very informative posts.

good stuff!!!!!!

Great thread.

*Subscribed*

Albert, I'm guessing your fuel pump wiring is not 100% for the stock fuel pump to puke out that bad. The non-Denso pumps seem to have less current draw than the Denso pumps and, therefore, are more tolerant of inadequate wiring.

I strongly suspect that I have the same problem, given the injector duty cycles I'm seeing after Steve Kan tuned my car. Once I get my wideband installed, I'll have to do the fuel pump wiring upgrade and see what changes occur.

Thanks for this and your other recent contributions, Albert. I've gone over your notes on your old car with Rick and you are very meticulous with testing and generating data. This forum will be well served by your continued info posting!

Yes, you could very well be correct. Probably should have put a voltmeter on the stock pump and monitor it under all RMP and load conditions. That would be very simple. Indeed, if the stock one draws more current, the voltage to the pump would be lower than with an other pump that draws less current. (more voltage would drop across the resistance of the wiring) I can still do it with the Walbro and see what the voltage is at the pump. A wiring update is also a good idea that I will consider if I find the voltage too low at the pump.

Thanks for your compliments. This is a great forum, even if it has gone downhill (according to some posters), from a stage that I did not know. I'll be more than happy to throw my experiences into the mix.

As far as my records that I got back from Rick, I was shocked to see that it was missing a whole line of testing that I did. I have no idea what happened to those records and why the original booklet I gave Rick did not include them. Over the years, he was always trying to pry my brains, claiming that I HAD TO HAVE more mods and tricks in my car as it was just way too fast for what was recorded. Actually, I think, it was nothing singularly major but a steady series of proven smaller gains, adding up to big gains.