I have a wideband installed in my car, an SAFC, and a Greddy Profec B Spec II. With my boost at slightly over 20 psi to redline and the SAFC zeroed out, my A/F ratios are close to 10:1 all the way to redline with a Walbro fuel pump. So if you add the fuel pump, I am sure that your A/F ratios will not be too lean if you raise boost. Unfortunately I installed the fuel pump before my wideband, so I don't know how the system responds to the increased boost with the stock fuel pump.

 

fuel pump has absoloutly nothing to do with it. if you don't tell the computer to take fuel out, or add fuel....its gonna get what the ECU tells it to. and you are gonna kill that wideband o2 sensor if you don't get a leaner mixture.

 

Actually, the fuel pump does have something to do with it, as some tuners have seen the stock fuel pump start to give out after repeated runs at high boost. This can cause lean conditions at high RPMs.

Also, I'm not running my car that rich, that was just my baseline run before adjusting my SAFC. My point was that the ECU still keeps the A/F ratios very rich with the increased boost, which was asked about earlier in this thread.

 

stock fuel pump is fine with stock boost up to high rpms. you don't get any more fuel pressure at 7k rpms than you do at 4. fuel pressure goes up and down with boost pressure. has nothing to do with RPMs. thats what i was saying. if you are gonna be raising the boost, then yes, you need a better fuel pump as the stocker can't flow that good.

and i know you didn't say that it did have anything to do with RPMs but the originality of the thread was about boost drop at high rpms.

we are kind of talking semantics here, so ill just leave it alone. damn internet

 

Yeah well there are TWO pills. Mine holds steady boost until 5krpm where i then loose 3psi.. There is a big pill and a small pill. WHich one should i put back in?? BOTH i assume...

 

Um .. not quite. The difference at 7k rpms vs 4k rpms is that the fuel pump has to flow nearly double (ignoring any non-linerarities int he fuel maps) the volume of fuel at the same pressure.

That is why it matters. So with the stock taper it is entirely possible that the stock pump could do jsut fine flowing all the way to redline given that it doesn't have to hold the same pressure sinec boost is decreasing. The question is: can the stock pump flow enough fuel to handle 19psi all the way to redline.

I can tell you that the stock DSM pump had problems with it and it wasn't just pressure related cause that isn't how pumped are rated. it was pressure + flow rate. The stock pump (unrewired) could easily handle 20psi at 4000rpm but it couldn't keep flowing enough fuel up to redline at that pressure and the resul was you leaned out.

So ... can the stock pump flow the required fuel demand to maintain pressure at 19psi at redline???

CAuse if it can then the stock pump is not going to be a problem when the taper is removed.

As for running lean just because you upped boost that isn't true either since the fuel maps will account for it ... ie it sees more air so it increases the injector pulse to inject more fuel. At some point the ecu thinks you are pushing too much air and then you have fuel cut. Sort of mitsu's way of limiting the table size they need not to mention protect the motor.

If you are leaning out as you increase boost, and only increasing boost, then you have a fuel pressure problem likley caused by a weak fuel pump and/or injectors that simply can not spray enough fuel even at 100% duty cycle.

But it was incorrectly implied that you needed fuel management to increase boost. That is not true. Fuel management does help make more power since the ecu likes to run richer and richer as it sees more air. But the only thing you NEED when you increase boost is the ability to supply enough fuel and that means enough pump.

Obvioulsy with enough air flow you will need larger injectors and then the fuel management to control it but that is not the case with just eliminating the taper to see 19psi straight to redline.

 

Man, if you increase boost(more than a couple psi) there is a reason you are supposed to safetly adjust the fuel maps or dump some 110 octane in the tank. even with a hi flow fuel pump, you can't just crank the boost. even if you put bigger injectors in there....you can't just crank the boost without computer upgrades.

 

True and I didn't say that either. What I said was fuel management is not required to raise boost without leaning out. The ecu does all the fuel addiiton you need. You aren't going to run lean just removing the taper, nor will you do it just upping it a few more UNLESS the fuel pump can't hold pressure to redline and/or if you injectors are max'ed out.

the reason for fuel management as you increase boost is to deal with the fact that the ecu is going to not only add more fuel as you would like, but add an ever increasing amount of fuel making it richer. Not to mention how mitsu likes to go to less agressive timing maps as it sees more air flow.

It is a whole other issue if you are just crnaking boost up to the point where the fuel mpump can't take it, the injectors are max'ed and you know damn well that when you get those worked out you will need fuel management to deal with it all.

The point I was making is that you don't just blindly need fuel management just because you are increasing boost and that if you are running lean after increasing boost no amount of fuel management will solve the problem because your problem is NOT in the fuel tuning but in the fuel supply.

 

That isn't correct. going by what you are saying, i could put a bigger fuel pump on the car and run 26psi on pump gas. Thats just wrong.

 

NO! thaT is not what I said. what I said is that you can put a fuel pump on and run higher boost without running out of fuel.

I NEVER said anything about doing it on pump gas because obviously that would cause detonation. Of course you can't run 26 psi on pump gas.

But even if you run 116 race gas you likely can't run 26 psi with a stock pump because it can not supply enough fuel at the pressure required.

I say likely because I admitted, above, that I don't know what boost the stock fuel pump is able to handle as far as supplying fuel at redline. I was assuming 19psi was fine; ie getting rid of the taper. But I'm willing to bet that you can't run 26psi with the stock pump no matter what fuel and what fuel management you have because it just won't flow enough fuel at pressure.

THAT is what I said ... don't read beyond my words ;-)

 

What causes detonation? too much air, not enough fuel so the pre-ignition(detonation) sets in. The reason you have to have engine management is because the stock ECU doesn't retard the timing to combat the high boost levels....it doesn't necesserilly add more fuel that the stock maps do. That is why you can't just upgrade your fuel pump and injectors without engine management.....everything isn't about fuel.

 

Well first off detonation is not pre-ignition. two totally different events though one, detonation, can quickly lead to pre-ignition.

As for everything else ... the ecu does retard timing as it sees more air (aka more boost) and it does add more fuel as it sees more air and infact it tends to add more fuel than just the extra needed meaning the fuel ratio gets richer. It is all about fuel as far as the discusion that was at hand. Fuel management is very important and don't think I don't know it. But you don't need it when upping hte boost a few pounds in order to stay safe and it will do you NO GOOD AT ALL if you can't even supply enough fuel in the first place because you have really started flowing a LOT of air by improving the volumetric efficiency and/or increased boost levels.

Oh and too much air and not enough fuel is ONE way to get detonation. so is too much effective compression ratio for the octane being used, a very hot intake charge (as compared to similar conditions but with a cooler charge) just to name two.