Fuel Pressure and Boost

[klmnla]

Im getting close to getting this thing to run decent, but still getting a stumble at WOT after the boost gets to about 10-12 lbs. I have the actuator turned way out, and the boost controller turned way out to the lowest setting. The fuel pressure rises to about 50psi at wot, and never really goes any higher than that. Should I be getting more fuel pressure at WOT. I have a new TT chip set for mostly stock, new waste gate actuator, rebuilt turbo, new casper cam sensor cap, new R43 plugs, new plug wires. I set the FP regulator at 43psi with the vac line off, and have bypassed the waste gate solenoid. KR is minimal, but did show about 1.9 on my last test run. Do my O2 reading seem high? Could be the crappy NTK O2 sensor i put in recently?

At warm idle:
MV 900 about 850 at WOT
CC 165
ATS 125
IAC 22
AF 07 about 120 at WOT
L8 56
bat 12.9
Int 128
bl 117
tps .42 4.6 at wot (engine off)
no MAL codes
engine temp 185

 

[TurboBob]

the fuel pressure needs to rise 1:1 with boost. Your base fuel pressure is the reading with the line off, so 43. at 12psi of boost you should have 55psi of fuel pressure.

You need to fix this first, fuel supply is critical to preventing engine damage as you turn up the wick.

I see the hotwire kit in your sig, what fuel pump and fuel pressure regulator do you have? Make sure the vacuum block on top of the throttle body is
not loose and you don't have any issues with the vacuum line going to the regulator. Its the pressure in this line that makes the regulator raise the fuel pressure.

Bob

 

[87-WE2]

I certainly do not want to hijack, but i must ask. If we set our FP to 43 line off, then hook up the vac line again, it falls right? Doesn't it fall by about 3psi? If that's the case, aren't we asking our fuel pumps and regulators to increase MORE THAN 1:1 ratio??? I've wondered this since the first time i set my fuel pressure, but am just now getting around to asking. I'm not disagreeing, just wondering why.

 

[Fast4Ward]

your af (maf reading) should be 255 at wot.
4-6 is a good maf at idle.

 

[TurboDave]

aren't we asking our fuel pumps and regulators to increase MORE THAN 1:1 ratio??? I've wondered this since the first time i set my fuel pressure, but am just now getting around to asking. I'm not disagreeing, just wondering why.

No we're not..... If you watch your fuel pressure while driving (if you had that capability like many of us do) you would see that at zero manifold pressure your fuel pressure would be reading what it does at idle with the vacuum line off(same as zero manifold pressure). So, from zero boost on up, we're asking it to rise 1:1

 

[TurboDave]

BTW, klmnla..... if your MAF is only reading 120 with 12# of boost you have a serous problem right there too!!

 

[TR Custom Parts]

No we're not..... If you watch your fuel pressure while driving (if you had that capability like many of us do) you would see that at zero manifold pressure your fuel pressure would be reading what it does at idle with the vacuum line off(same as zero manifold pressure). So, from zero boost on up, we're asking it to rise 1:1

------------------------------------


And some of us fully understand this and still can't get the 1 to 1 ratio.

 

[87-WE2]

No we're not..... If you watch your fuel pressure while driving (if you had that capability like many of us do) you would see that at zero manifold pressure your fuel pressure would be reading what it does at idle with the vacuum line off(same as zero manifold pressure). So, from zero boost on up, we're asking it to rise 1:1

Well explained. It's crystal clear now - with line off we are fooling the regulator into a zero pressure or vacuum scenario. Thanks for the explanation. I hope soon to have mine running right again so can get that new gauge installed! Back to the OP's original issue.

 

[klmnla]

Im getting close to getting this thing to run decent, but still getting a stumble at WOT after the boost gets to about 10-12 lbs. I have the actuator turned way out, and the boost controller turned way out to the lowest setting. The fuel pressure rises to about 50psi at wot, and never really goes any higher than that. Should I be getting more fuel pressure at WOT. I have a new TT chip set for mostly stock, new waste gate actuator, rebuilt turbo, new casper cam sensor cap, new R43 plugs, new plug wires. I set the FP regulator at 43psi with the vac line off, and have bypassed the waste gate solenoid. KR is minimal, but did show about 1.9 on my last test run. Do my O2 reading seem high? Could be the crappy NTK O2 sensor i put in recently?

At warm idle:
MV 900 about 850 at WOT
CC 165
ATS 125
IAC 22
AF 07 about 120 at WOT
L8 56
bat 12.9
Int 128
bl 117
tps .42 4.6 at wot (engine off)
no MAL codes
engine temp 185

I have a hood mounted FP gauge. It actually does rise 1:1 with the boost, but never gets over 50-51 PSI, and the boost goes up to about 12-15. By the way, how do you increase the MAF reading at WOT? I have a K&N filter on the end of the air inlet tube.

 

[TurboBob]

remove the bad MAF, install a good one.....

Bob

 

[klmnla]

I might try a different MAF sensor. My current one is tied in with the translator plus, and I dont know what model MAF it is? Also, with my above average O2 readings, would the stalling problem at WOT not be a fuel delivery problem? I figure since my boost is at about 12, the max FP at a little over 50psi is okay?