Afr acting crazy...any ideas welcome
Mar 28, 2018, 05:27 PM
#1
Afr acting crazy...any ideas welcome
Hey guys, I have an 04 evo with evo 9 turbo and bolt ons. I recently did a headgasket, arp headstuds, gsc springs and retainers, and gsc s2 cams. Car is idling 11.5 - 12 afr and cruising and everything is rich. I’ve tried everything from taking the injectors (stock injectors) to get tested and cleaned, another stock fpr, rechecked timing, etc. Tuner says he doesn’t know what’s going on. I keep trying to think what I could’ve done wrong but everything checks out. Tuner had to scale injectors to bigger ones for it to lean out but that’s not right. I even started thinking about maybe I got defective cams or something where it’s not opening the valve enough at idle to let enough air in? Idk. I’m out of ideas guys please if someone can think of something it would really help me out. I’m on sd and iat is reading right. I’m about to swap out the Omni 4 bar with another one just for the hell of it. I have stock cam gears. I’m thinking maybe I need aftermarket cam gears to degree the cams? I would really appreciate your help...
Mar 28, 2018, 07:02 PM
#2
Hey guys, I have an 04 evo with evo 9 turbo and bolt ons. I recently did a headgasket, arp headstuds, gsc springs and retainers, and gsc s2 cams. Car is idling 11.5 - 12 afr and cruising and everything is rich. I’ve tried everything from taking the injectors (stock injectors) to get tested and cleaned, another stock fpr, rechecked timing, etc. Tuner says he doesn’t know what’s going on. I keep trying to think what I could’ve done wrong but everything checks out. Tuner had to scale injectors to bigger ones for it to lean out but that’s not right. I even started thinking about maybe I got defective cams or something where it’s not opening the valve enough at idle to let enough air in? Idk. I’m out of ideas guys please if someone can think of something it would really help me out. I’m on sd and iat is reading right. I’m about to swap out the Omni 4 bar with another one just for the hell of it. I have stock cam gears. I’m thinking maybe I need aftermarket cam gears to degree the cams? I would really appreciate your help...
Mar 28, 2018, 07:46 PM
#3
Fuel pressure at idle is around 45. I have stock injectors, stock fpr, aem fuel rail with gauge on it, 255 walbro. It was running fine before the headgasket, headstuds, spring and retainer and cam change. I went over everything I could think of. Tuner said maybe degreeing cams. I got pissed of and went wot and it was fine but idle and cruising is super rich. I’m so disgusted. I was excited man. Now got a kid otw and have to spend more money on this. I just don’t know what it could be. I even changed the o2 sensor
Mar 28, 2018, 09:08 PM
#5
hmm...fuel pump relay #3? doesnt this run off a resistor? i thought that people rewire the pumps because no matter what with the stock setup the pump doesnt get enough voltage...after the rewire is when its possible the fpr gets overrun because of higher voltage...if this is the case that somehow the pump is getting too high a voltage, what can be causing this? a faulty relay? i will try it tomorrow either way and see...first i have to figure out which one is #3...
* also, this always confuses me when people say fpr being overrun. If its being overrun, shouldnt i be able to see a higher fuel pressure on the gauge i have on the fuel rail? for example, at idle the gauge shows around 45 psi which is about right. if its being overrun, shouldnt the fuel pressure show higher?
* also, this always confuses me when people say fpr being overrun. If its being overrun, shouldnt i be able to see a higher fuel pressure on the gauge i have on the fuel rail? for example, at idle the gauge shows around 45 psi which is about right. if its being overrun, shouldnt the fuel pressure show higher?
Last edited by nor11384; Mar 28, 2018 at 09:19 PM.
Mar 28, 2018, 09:54 PM
#6
Account Disabled
Fuel pressure at idle is 33 PSI on the gauge as it always should be and always IS before you break it with mods done wrong.
A Walbro 255 pump wired correctly normally bumps it up to 38 or so PSI.
A walbro pump at full voltage normally bumps it up to 43 or so PSI.
Any pressure other than 33 PSI is wrong and the car won't run right.
A Walbro 255 pump wired correctly normally bumps it up to 38 or so PSI.
A walbro pump at full voltage normally bumps it up to 43 or so PSI.
Any pressure other than 33 PSI is wrong and the car won't run right.
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2winscroll (Mar 29, 2018)
Mar 28, 2018, 10:03 PM
#7
hmm...fuel pump relay #3? doesnt this run off a resistor? i thought that people rewire the pumps because no matter what with the stock setup the pump doesnt get enough voltage...after the rewire is when its possible the fpr gets overrun because of higher voltage...if this is the case that somehow the pump is getting too high a voltage, what can be causing this? a faulty relay? i will try it tomorrow either way and see...first i have to figure out which one is #3...
* also, this always confuses me when people say fpr being overrun. If its being overrun, shouldnt i be able to see a higher fuel pressure on the gauge i have on the fuel rail? for example, at idle the gauge shows around 45 psi which is about right. if its being overrun, shouldnt the fuel pressure show higher?
* also, this always confuses me when people say fpr being overrun. If its being overrun, shouldnt i be able to see a higher fuel pressure on the gauge i have on the fuel rail? for example, at idle the gauge shows around 45 psi which is about right. if its being overrun, shouldnt the fuel pressure show higher?
OEM, relay #3 connects pump to battery. When ECU sends ground signal, relay opens and breaks the battery connection to pump. Once connection is broken, pump only gets power from resisters, which give pump 8V. STM rewire does connect to battery when ever relay #2 is on (whether 8V or 12V). I rewired mine like how MrFred and Biggiesacks did their and kept the 8V/14V dual stage.
So if you disconnect Relay #3, you force power through resisters (8V). If this fixes your problem, then your Relay #3 is either broken where it doesn't switch or your ECU isn't grounding the wire to switch the relay.
Last edited by 2006EvoIXer; Mar 28, 2018 at 10:22 PM.
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Mar 29, 2018, 04:46 AM
#10
Account Disabled
There's a diagram on line from a 3kGT site which works properly.
It been tried and tested over 14 years.
It's pretty much the same but better.
http://www.3si.org/forum/f35/fuel-pu...method-199326/
Somewhere in there.
The 8 v you read at low load, that's actually wrong too.
With a stock setup it's closer to 9 volts.
When you fit a bigger pump it draws more current so drops more volts across the resistor resulting in less volts at the pump.
The downside is that under the worst conditions the pump can stall due to not enough volts. Not with a 255 pump but probably with a 400 where the volts will be even less due to the extra current consumption.
The fix is to change the pump resistor which also messes with the pressure when at low load / low volts.
Just to give you more to think about ...lol
It's called "tuning".
Like if you add a bit of maths.
45 PSI on the gauge is 12 PSI too high.
So instead of a base pressure of 43 PSI at idle (base pressure is the pressure across the injector) there's 55 PSI at idle or an extra 27%
That's maybe an extra 12% in fuel flow so a 14.5 to 1 AFR programmed into the ecu will come out at about 12.9 AFR.(no, it's not just some random number as some claim?)......then the fuel trims will kick it to try to shift it to 14.5 and it'll run lean under load when the base pressure gets back to normal.
It been tried and tested over 14 years.
It's pretty much the same but better.
http://www.3si.org/forum/f35/fuel-pu...method-199326/
Somewhere in there.
The 8 v you read at low load, that's actually wrong too.
With a stock setup it's closer to 9 volts.
When you fit a bigger pump it draws more current so drops more volts across the resistor resulting in less volts at the pump.
The downside is that under the worst conditions the pump can stall due to not enough volts. Not with a 255 pump but probably with a 400 where the volts will be even less due to the extra current consumption.
The fix is to change the pump resistor which also messes with the pressure when at low load / low volts.
Just to give you more to think about ...lol
It's called "tuning".
Like if you add a bit of maths.
45 PSI on the gauge is 12 PSI too high.
So instead of a base pressure of 43 PSI at idle (base pressure is the pressure across the injector) there's 55 PSI at idle or an extra 27%
That's maybe an extra 12% in fuel flow so a 14.5 to 1 AFR programmed into the ecu will come out at about 12.9 AFR.(no, it's not just some random number as some claim?)......then the fuel trims will kick it to try to shift it to 14.5 and it'll run lean under load when the base pressure gets back to normal.
Last edited by RightSaid fred; Mar 29, 2018 at 05:19 AM.
Mar 29, 2018, 06:47 AM
#11
Yes and almost yes.
I tested with engine off (pump was not running) at Relay #3 and got 8.1V and 12.1V. With engine running, I get 14.1V average at battery. So yes, it will be higher voltages with engine running (didn't measure). If you replace with Wally 255 pump, it draws very close to factory pump (probably the most efficient aftermarket pump).
The low flow power through resisters works fine. Resister is designed to limit current to pump when demand isn't there. You forgot about the ~20 feet of 12-14 awg pump wiring (barely sufficient for stock pump). Under high flow is the problem. Pump needs full power from battery. If the voltage isn't there, current increases to supply power (power=voltage × current). With more current, wiring heats up, causing more power demand. Rewire is necessary to reduce load on pump (higher current, which translate into more heat) and heating up the wires.
Definitely a lot to think about!
I tested with engine off (pump was not running) at Relay #3 and got 8.1V and 12.1V. With engine running, I get 14.1V average at battery. So yes, it will be higher voltages with engine running (didn't measure). If you replace with Wally 255 pump, it draws very close to factory pump (probably the most efficient aftermarket pump).
The low flow power through resisters works fine. Resister is designed to limit current to pump when demand isn't there. You forgot about the ~20 feet of 12-14 awg pump wiring (barely sufficient for stock pump). Under high flow is the problem. Pump needs full power from battery. If the voltage isn't there, current increases to supply power (power=voltage × current). With more current, wiring heats up, causing more power demand. Rewire is necessary to reduce load on pump (higher current, which translate into more heat) and heating up the wires.
Definitely a lot to think about!
There's a diagram on line from a 3kGT site which works properly.
It been tried and tested over 14 years.
It's pretty much the same but better.
http://www.3si.org/forum/f35/fuel-pu...method-199326/
Somewhere in there.
The 8 v you read at low load, that's actually wrong too.
With a stock setup it's closer to 9 volts.
When you fit a bigger pump it draws more current so drops more volts across the resistor resulting in less volts at the pump.
The downside is that under the worst conditions the pump can stall due to not enough volts. Not with a 255 pump but probably with a 400 where the volts will be even less due to the extra current consumption.
The fix is to change the pump resistor which also messes with the pressure when at low load / low volts.
Just to give you more to think about ...lol
It's called "tuning".
Like if you add a bit of maths.
45 PSI on the gauge is 12 PSI too high.
So instead of a base pressure of 43 PSI at idle (base pressure is the pressure across the injector) there's 55 PSI at idle or an extra 27%
That's maybe an extra 12% in fuel flow so a 14.5 to 1 AFR programmed into the ecu will come out at about 12.9 AFR.(no, it's not just some random number as some claim?)......then the fuel trims will kick it to try to shift it to 14.5 and it'll run lean under load when the base pressure gets back to normal.
It been tried and tested over 14 years.
It's pretty much the same but better.
http://www.3si.org/forum/f35/fuel-pu...method-199326/
Somewhere in there.
The 8 v you read at low load, that's actually wrong too.
With a stock setup it's closer to 9 volts.
When you fit a bigger pump it draws more current so drops more volts across the resistor resulting in less volts at the pump.
The downside is that under the worst conditions the pump can stall due to not enough volts. Not with a 255 pump but probably with a 400 where the volts will be even less due to the extra current consumption.
The fix is to change the pump resistor which also messes with the pressure when at low load / low volts.
Just to give you more to think about ...lol
It's called "tuning".
Like if you add a bit of maths.
45 PSI on the gauge is 12 PSI too high.
So instead of a base pressure of 43 PSI at idle (base pressure is the pressure across the injector) there's 55 PSI at idle or an extra 27%
That's maybe an extra 12% in fuel flow so a 14.5 to 1 AFR programmed into the ecu will come out at about 12.9 AFR.(no, it's not just some random number as some claim?)......then the fuel trims will kick it to try to shift it to 14.5 and it'll run lean under load when the base pressure gets back to normal.
Last edited by 2006EvoIXer; Mar 29, 2018 at 08:02 AM.
Mar 29, 2018, 07:22 AM
#12
Well I was looking back through older threads when I had other issues and in one thread I posted that fuel pressure was reading 50 psi but car was idling in the 13s. Now it’s in the 11s. I don’t understand how bigger cams would do it. I figure if anything it should go leaner since it’s letting more air in. I’m going to check the relay now.
Mar 29, 2018, 07:36 AM
#13
Disconnected the relay and same thing. Drops right down to the 11s. Even in cold start. One thing I noticed is the fuel pressure gauge reads 0 in the morning. I used to be able to let the car sit for a couple of weeks and when I go to start the car pressure would still be around 30 psi.
Mar 29, 2018, 07:46 AM
#14
Evolved Member
You may want to disconnect your FPR solenoid and make sure it’s not leaking to atmosphere, I have seen this cause inconsistent fuel pressure in the past. Just run the vacuum line straight to the manifold from the FPR.