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ΜΟΛΩΝ ΛΑΒ&
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Discussion Starter #1 (Edited)
EDIT: I've replaced/tested all of the following: Fuel pump, fuel lines, fuel rail, fuel injectors, spark plugs, ignition coils, TPS sensor, ECU, tune, o2 sensor, timing, throttle cable, vacuum leaks, boost leaks, and exhaust leaks. All have not fixed the problem.

I'll start with my main fuel mods:

EMUSA Turbo Kit at 9.5psi
Gates Submersible Fuel Line
Walbro 255
BDL Fuel Rail (Returnless)
Precision 525cc Injectors
AEM UEGO


The other day my car was running perfect. Then one day it got really cold (30* F) and I went to start my car. I always prime the system before I start it but that day I didn't for some reason. It took a bit to start and struggled to stay at idle. It was running a 17:1 AFR for a solid minute before it finally leveled out. I went to drive it and now every time I accelerate it's very lean (15:1-16:1) and I have no power obviously. Almost like the fuel pump isn't responding quick enough. I tested it again when it was warm the next day with no change. WOT is perfectly fine. It's just everything other than WOT that's really lean.

We hooked a Snap-On fuel pressure gauge to the car and took it for a drive. At idle it sits at 56psi. Acceleration doesn't change the fuel pressure, it stays at 56psi. At WOT it drops to 49psi. Then when we turn the car off the pressure immediately starts dropping until there's no pressure left.

I've checked all lines for leaks and everything is tight, no leaks. I ordered a new Walbro pump but the post office lost the package so now I'm dealing with that... :face:

Is there anything else I can check in the mean time? Do you even think it's the pump? If you have Kmanager you can see the attached datalog to see what I'm talking about with the crazy AFR's...
 

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ΜΟΛΩΝ ΛΑΒ&
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4,506 Posts
Discussion Starter #4
O2 sensor stuck on 0 volts and -37ma, is that normal when using AEM UEGO?
Not too sure. I'm using the AEM sensor and the ELD wire for tuning which is a 0-5V reference if I remember correctly. I have that selected in Kpro so it shouldn't be reading the 02 sensor
 

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ΜΟΛΩΝ ΛΑΒ&
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Discussion Starter #5
Another idea I'm having is my TPS sensor. Lately I've been having blips at WOT where it goes from 100% down to 0% for a split second. If under light acceleration I'm at 50% throttle but the sensor is only reading 30% then the ECU would be only sending enough fuel for 30% hence why it's lean and then going rich because the ECU is trying to compensate...
 

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Retired OG
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147,491,197 Posts
your TPS issue is another problem try recalibrating it through K-pro. If it doesn't fix the issue buy a replacement and see if that helps. If you say you're at 50% and you see the sensor is only at 30% how do you know your giving it 50% throttle?

how fast does your fuel pressure drop after shutting off the car? it is normal for it to do that but depending on fast the rate of drop can determine even a slight leak in the fuel line, my guess would be the gates hose (it might be able to stand sitting in fuel forever but i find the line itself isn't very durable) usually the culprit is from the clamps you've used to tighten the hose to the pump and fittings etc.
 

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ΜΟΛΩΝ ΛΑΒ&
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Discussion Starter #7
your TPS issue is another problem try recalibrating it through K-pro. If it doesn't fix the issue buy a replacement and see if that helps. If you say you're at 50% and you see the sensor is only at 30% how do you know your giving it 50% throttle?

how fast does your fuel pressure drop after shutting off the car? it is normal for it to do that but depending on fast the rate of drop can determine even a slight leak in the fuel line, my guess would be the gates hose (it might be able to stand sitting in fuel forever but i find the line itself isn't very durable) usually the culprit is from the clamps you've used to tighten the hose to the pump and fittings etc.
The 50% throttle thing was more of just a hypothetical statement as to why it might be lean under light to medium acceleration.

I actually did have a small cut in my fuel line from the clamps so I cut the affected piece off and bolted it all back up not too long ago.

The fuel pressure immediately starts dropping once the car is off. Maybe 3-5 psi every second IIRC. Pretty quick from what I saw...

I'll probably buy a new hose anyway since I had to cut it. I'm going to throw my stock fuel pump in today and drive around normally and see if anything changes. If not, then it might not be my fuel pump after all.
 

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Retired OG
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The 50% throttle thing was more of just a hypothetical statement as to why it might be lean under light to medium acceleration.

I actually did have a small cut in my fuel line from the clamps so I cut the affected piece off and bolted it all back up not too long ago.

The fuel pressure immediately starts dropping once the car is off. Maybe 3-5 psi every second IIRC. Pretty quick from what I saw...

I'll probably buy a new hose anyway since I had to cut it. I'm going to throw my stock fuel pump in today and drive around normally and see if anything changes. If not, then it might not be my fuel pump after all.
im going to bet that the fuel line is going to be your issue with the start up and hesitation. cold weather can and will affect your tune so you might need to make a few adjustments accordingly.
 

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ΜΟΛΩΝ ΛΑΒ&
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Discussion Starter #9 (Edited)
im going to bet that the fuel line is going to be your issue with the start up and hesitation. cold weather can and will affect your tune so you might need to make a few adjustments accordingly.
I'll replace the fuel line just to be safe but it has been pretty warm lately and the car still acts the same.

This happened this morning actually. I was driving to work on the freeway maintaining a constant speed and constant throttle. It was a level road, not going uphill or downhill. AFR was at 14.7:1 and then I felt the car vibrate a bit and I lost power for a split second. The AFR was "blipping" to 16:1 and then would drop back down to 14.7:1. It did this about 5-6 times before it went very rich to 11:1 and then back up to 14.7:1. This all happened while keeping the same amount of throttle and speed on the level stretch of road...:confused:

Fuel level at 3/4 btw.

Also, something I forgot to add. Sometimes it idles at 16.5:1 and sometimes at 14.7:1. Same tank of gas, same day, didn't turn the car off either. Just driving around town running errands.
 

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Try swapping to stock map sensor and edit in kpro after changing
 

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ΜΟΛΩΝ ΛΑΒ&
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Discussion Starter #14
I'm already running a stock map sensor. Should I try a new map sensor? It seems to be reading fine and consistent in kpro. One thing I am noticing though is my boost is taking less than a second to go from vacuum to 10psi at WOT and it goes lean real quick. Before this problem it would take at least 2 seconds or so to start working it's way up to 10psi
 

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:)
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prolly not, i had an issue with a hondata map sensor and swapped it back to oem and it was fine. I had random lean spikes too. Entire time, I thought it was my walboro 255 fuel pump/inj/tune/etc...
 

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Hey guys, did we ever figure out what was causing the lean spikes? I’m having the exact same problem as described 7 posts up. While cruising at a steady highway speed my AFR jumps up to 16-17 and the car sputters or hesitates, misfires whatever, for a second then AFR drops to 10-11 then goes back to normal. Also at idle or while comming to a stop my idle will be around 2000 till I come to a complete stop then it’ll drop down to 900. I’ve replaced everything this guy has along with new IM and TB gaskets, IACV and there’s only two vac lines, I replaced the little one to the left of my RBC and the one on top by the TB going to the break booster and FPR is new. All this and still no fix. I even replaced my wideband sensor. What could be going on? Before all this I did accidentally swap the tps and map sensor and ended up having to replace the map and TPS to get it to run half way decent so IDK if that could have done something somewhere.... I just hate reading all these forums only for them to dead end with no fix or solution. Any help would be greatly appreciated.
 
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