12V Mod issues.

[mensrea]

1J here, running Walbro 400. Used to have 255 which ran fine with the mod. Once upgraded to 400, It's running pig rich. Stalls on idle at times. I tried lowering base FP, but I can only lower it so much before going lean under boost. Tried adjusting TB set screw. -40 to -45 on SAFC doesn't help much either.
Here's the question.. If I plug back fuel pump resistor/relay, wouldn't that fix the "pig rich" problem on low RPMs/idle ? Would I need to rewire the pump, back to the original wiring, or just plugging back relay/resistor will put it in "dual voltage" mode ?

Thank's for any help.

 

[Supracentral]

What are your power goals that you need such a ludicrously large fuel pump?

What is your base fuel pressure set to @ idle with the reference hose disconnected?

What led you to believe you needed a bigger pump?

 

[mensrea]

~650whp. It's smaller than 2 walbro 255's. I was running out of fuel on single 255.

 

[Supracentral]

~650whp. It's smaller than 2 walbro 255's. I was running out of fuel on single 255.

Ok, just checking. We've had some people do silly things around here. What about the other 2 questions I added above?

 

[mensrea]

like I said, I was running out of fuel with the old pump. Currently have it set at ~ 28-30 PSI (BFP).

 

[Supracentral]

Base FP is right on the money. Running an S-AFC in that power range is pushing the limits of piggyback tuning.. What size injectors are you running?

 

[mensrea]

Oh, no, that is my power goal. I'm waiting till I get EMS, and drop in 680's for that.. 550's is what I have in ATM, running ~20PSI through 62mm.

 

[Supracentral]

Oh, no, that is my power goal. I'm waiting till I get EMS, and drop in 680's for that.. 550's is what I have in ATM, running ~20PSI through 62mm.

Hrm... Ok, an AFC should be able to manage 550's. (I've seen them mange 750's successfully with a few compromises). Normally I'd suspect a return line restriction, however you wouldn't be able to reduce your base FP if that were the case. I'll PM a few people and ask them to take a look at this thread - I'm drawing a blank.

 

[IJ.]

Crushed return line?

 

[CyFi6]

Are you saying you have the same fuel pressure as before but are running rich? Doesn't make sense, only way you would be flowing more fuel through the injectors is if A your injector size changed, B your pulse width / tune changed or C your fuel pressure changed. If you are tying to lower your pressure and it wont go down, that's another story.

 

[Supracentral]

Crushed return line?

I thought about that, but he wouldn't be able to lower the base FP if that were the case, no?

 

[mensrea]

I'll try checking it in the morning. It hasn't really been places where I could crush it. I'm gonna turn BFP down to somewhere around 22-26 and see what it does. I hate going over -30 on SAFC..
Could cams (264) make a difference as far as idle mixture ? I have 6 degree retard on exhaust.

@CyFi6
I'm pulling less vacuum (idle) with the cams.

 

[Supracentral]

Maybe we should take a step back here and understand your full mod list...

Yea, big cams will make your idle quality drop considerably. Depending on how much overlap you're running, you can get really pig rich under those circumstances. Driveability always suffers in exchange for high end flow.

What's the full list of mods?
What was changed since the car ran well?
Just the FP, or have you changed other components?

 

[IJ.]

I thought about that, but he wouldn't be able to lower the base FP if that were the case, no?

Guess it would depend on how restricted it is, it's the only thing that makes sense to me if the pump is the only change.

 

[mensrea]

@Supracentral, I'm running 264's from what I understand, they are not that much different from stock 1j cams.
I had the pump in for about a week, and driven it, may be 25-30 miles. Than put in the cams, which messed up the idle a little bit more (had 6 degree on stock cams as well). Now it just seems like I'm not pulling enough vacuum to lean out the mixture. Going from 35mph + to a quick stop, mixture goes all the way to something like 10.1. Than slowly raises up to 13.5-14.7. If it's a hot day, than about 30% of the time it stalls. Now actually, thinking about it, it does make sense, fuel return line could be too small, 'hence the excessive amount of fuel in the rail = rich mixture than eventually leans out. I have a DM return line, it does not go all the way to the tank thu.

 

[GrimJack]

What are you using for a wideband? I've had mine drop well below 10 without any stalling issues...

 

[Nick M]

Could cams (264) make a difference as far as idle mixture ? I have 6 degree retard on exhaust.

No. Low vacuum just means the valve is open and the piston is moving air faster. There isn't as much resistance to the piston's downward travel.

Define pig rich. You can run very rich before a car stalls.

 

[ifyouaint1sturlast]

I feel as though something else is going on here. I don't understand why you didn't put all of these details in your original post? So, fuel pump and cams were changed at around the same time? I believe SupraCentral to be right, I don't think you'd be able to lower your fuel pressure if your return line was the problem.

Could it be possible that it's heating up the fuel too much being such a big pump running at 12v all time?

 

[Nick M]

a big pump running at 12v all time?

Yes. I don't know about the heating part but... His pump isn't running at 12v, it is running at whatever the alternator can give it, within the capability of the wiring. 13.5-14.0 volts. And the injectors are big, but not 255 big, let alone 400 big.

 

[Supracentral]

The vaccum issue is likely the cams. If your exhaust valve is open at the same time the piston is in downward motion, it's going to draw some of the exhaust back into the cylinder at low RPM rather than air from the intake.

That "lumpy idle" that cars with big cams have?

Like this:

[video=youtube;JrS3YrsCG_Y]http://www.youtube.com/watch?v=JrS3YrsCG_Y[/video]

Is really the car running like shit. It works like this:

At the top end of the rpm range, the intake valve must open before TDC in order to make sure that the valve is open far enough to allow the incoming air/fuel charge in with the least amount of restriction once the piston begins to move downward. Likewise, exhausted gases that leave the combustion chamber create a vacuum behind them that is used to assist the flow of the intake charge into the combustion chamber, hence the need for a certain amount of overlap (ie: when both the intake and exhaust valves are open between the end of the exhaust stroke and the beginning of the intake stroke). This technique is called "scavenging" and is present it properly designed exhaust manifolds as well (which time each exhaust pulse so that each one helps draw the next ordered pulse out of the engine).

But there's a downside to this. Without a system like VVTI or BMW's double Vanos, you can only design a cam to perform well in a certain RPM range. Performance cams are tuned for the high end of the range and idle quality and emissions suffer greatly.

I suspect the degreed 264 cams have a lot to do with the way the car is running in the low end of the range.