HELP! A/F jumping up and down
Sep 10, 2005, 06:25 AM
#1
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HELP! A/F jumping up and down
Help, I recently full throttle my car racing for a short period of time then all of a sudden I feel that the car is lacking power. Then I took the car to my friend's shop to check out what's wrong. We hooked up a HKS A/F gauge and found out that it reads anywhere from rich to lean. Sometimes the reading even jump to 20+ at idle. First we guessed it was the fuel system, and checked out the fuel pressure. Fuel pump and fuel pressure are checked and no problems there. But we don't have the tools to check the injectors. We also guessed the ignition system so we replaced both plug wires. We also checked out the computer, the Power FC and found the tuning is fine. The air flow meter is fine too. I have never encountered this type of problem before with any of my cars. Basically the A/F jumps up and down at idle and car sometimes runs super rich, sometimes perfect, sometimes super lean and is unsmooth. Can EVO specialist here help me figure out the possible problem? Thanks
Sep 11, 2005, 08:41 PM
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If what you're saying is that during idle your a/f jumps from like 13.0-16.0:1a/f that is perfectly normal. It's under full throttle and above a certain gm/sec (2.31gm/sec on 2G DSMs) where the timing and fuel maps are set to "perform". Under those circumstances it shouldn't really flutter that fast but it all depends on your set of tune.
If your a/f's are flickering as fast as they are at idle during WOT, check the fuel pressure regulator. Sometimes the mechanism goes bad and it doesn't allow 1:1 fuel:boost.
If your a/f's are flickering as fast as they are at idle during WOT, check the fuel pressure regulator. Sometimes the mechanism goes bad and it doesn't allow 1:1 fuel:boost.
Sep 13, 2005, 07:25 AM
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I'm not on D-Jetro... the A/F jumps up and down during idle and even when I'm driving. It sometimes even goes up to 20+ :1. Very weird situation here. The fuel pressure regulator is working properly. I connected a fuel pressure gauge in cockpit to check that. What else can possibily be the problem besides the injectors? I have new injectors coming in within 2 days... hoping that will sove the problem. Anyone else with other guesses? 
Sep 13, 2005, 07:33 AM
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It can be a number of things. Have you checked to see if you're receiving 12v at the fuel pump? Leaky injectors o-rings could let in unmetered air throwing off the a/f. Try measuring how much fuel is being injected into the injectors by pulling the fuel feed line off and priming the pump to see if you fuel pump might have a flow issue. See how many cc's of fuel it is spraying per minute. If I were in your situation I'd try out another wideband. Sometimes a faulty o2 sensor makes the wideband pick up goofy readings.. HTH.
Sep 13, 2005, 07:36 AM
#7
Sounds like your a/f guage is narrowband correct? If that's true then you will see the a/f varying. During cold start-up does your rpm fluctuate as your a/f changes? Did you ever get a p0100 CEL? I suggest doing a boost leak test to make sure there's no leak.
I have an apexi TT and somtimes at idle the a/f on the gauge goes up to 17-18 and down to 13. Crusing I'm seeing around 14.3-14.5. During cold start-up my rpm fluctuates which I think there's a boost leak but check twice and found nothing.
I have an apexi TT and somtimes at idle the a/f on the gauge goes up to 17-18 and down to 13. Crusing I'm seeing around 14.3-14.5. During cold start-up my rpm fluctuates which I think there's a boost leak but check twice and found nothing.
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Sep 13, 2005, 07:38 AM
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Since i'm too lazy to research...The HKS A/F gauge doesn't use a wideband sensor does it? If it doesn't, the gauge is only good for some movng lights.
Best bet is to hook up a true wideband lambda meter, and see what's going on. That and check for vacuum leaks...
Best bet is to hook up a true wideband lambda meter, and see what's going on. That and check for vacuum leaks...
Sep 14, 2005, 03:12 AM
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The A/F meter from HKS works fine in another EVO 8 we plugged in.... so it's not the A/F meter.... any other guesses? I'm still waiting for the injectors to check if that's the problem....
Sep 14, 2005, 05:04 AM
#11
Originally Posted by hybrids14
The A/F meter from HKS works fine in another EVO 8 we plugged in.... so it's not the A/F meter.... any other guesses? I'm still waiting for the injectors to check if that's the problem....
DOn't know what you mean by work fine. ALso you didn't confirm whether this was a WB or not.
Sep 14, 2005, 06:02 AM
#13
Wait.. your saying your AFR swings back and forth at idle, and cruising around.. Correct?? Your idle and cruise are CLOSED LOOP, this means the O2 sensor is feeding back to the ECU and allowing the AFR to hover around 14.7:1 HOWEVER since our stock O2 sensors are not very fast or responsive, it will swing back and forth. Since I don't know about the powerFC and if it replaces the ECU completely, or piggybacks to it.. I can't really tell you more other than to check the closed loop fuel control settings, and fuel trims. On the factory ECU, if your trims are out of whack where they go over +/-20% at idle the trim will periodically reset and it will swing either really rich, or really lean depending on which direction your trims are "Out of scale"
If the PowerFC functions like a piggyback and allows the ECU to do idle and cruise, you need to look at the ECU's fuel trims with an OBD-II Scanner, I'll guess you'll have to adjust the trims to be within +/-10% and the huge swings will go away. But swinging from 13:1 to 18:1 on a modified car is actually pretty common with the stock O2 sensor and closed loop feedback.
If the PowerFC functions like a piggyback and allows the ECU to do idle and cruise, you need to look at the ECU's fuel trims with an OBD-II Scanner, I'll guess you'll have to adjust the trims to be within +/-10% and the huge swings will go away. But swinging from 13:1 to 18:1 on a modified car is actually pretty common with the stock O2 sensor and closed loop feedback.
Sep 14, 2005, 06:06 AM
#14
Ahh nevermind, I just caught the kinda car your running the engine in.. However the closed loop fueling still stands, big injectors and cams can cause the AFR's at idle to swing a bit.. Are you running a MAF on this car? Usually when airflow drops and engine vacuum is inconsistent it can also be the source of your issue, if thats the case you may have to raise idle speed. Also check for silly things like a vacuum leak, or your DV/BOV open at idle (from high engine vacuum) or a leak near the MAF.. Try a different MAF too if possible..
BTW, Can you send me some info on how you went about doing the swap and what year/model mirage? I was considering getting a late model DX 2 door and doing an AWD swap with a spare drivetrain from a wrecked 8... At the moment my plans are to do this to my Honda Civic. Offtopic I know, but you can PM me if you like.
BTW, Can you send me some info on how you went about doing the swap and what year/model mirage? I was considering getting a late model DX 2 door and doing an AWD swap with a spare drivetrain from a wrecked 8... At the moment my plans are to do this to my Honda Civic. Offtopic I know, but you can PM me if you like.
Last edited by MalibuJack; Sep 14, 2005 at 06:11 AM.
Sep 14, 2005, 06:38 AM
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Originally Posted by MalibuJack
Ahh nevermind, I just caught the kinda car your running the engine in.. However the closed loop fueling still stands, big injectors and cams can cause the AFR's at idle to swing a bit.. Are you running a MAF on this car? Usually when airflow drops and engine vacuum is inconsistent it can also be the source of your issue, if thats the case you may have to raise idle speed. Also check for silly things like a vacuum leak, or your DV/BOV open at idle (from high engine vacuum) or a leak near the MAF.. Try a different MAF too if possible..
BTW, Can you send me some info on how you went about doing the swap and what year/model mirage? I was considering getting a late model DX 2 door and doing an AWD swap with a spare drivetrain from a wrecked 8... At the moment my plans are to do this to my Honda Civic. Offtopic I know, but you can PM me if you like.
BTW, Can you send me some info on how you went about doing the swap and what year/model mirage? I was considering getting a late model DX 2 door and doing an AWD swap with a spare drivetrain from a wrecked 8... At the moment my plans are to do this to my Honda Civic. Offtopic I know, but you can PM me if you like.
My car was running fine before, even with big injectors, I have stock cams, stock MAF. Vacuum might be an possible issue, but I haven't found the vacuum leak yet. I will try to make a home job vacuum tester
I have the cheap POS tomei BOV, so that might leak too. If you're interested in a mirage AWD... it's a lot of trouble... I believe I have one of only 2 Mirage AWD with EVO motor in the world, here's some photos of my car at this link:https://www.evolutionm.net/forums/sh...d.php?t=148856
Honda Civic AWD swap is an easy job, they offer AWD drivetrain for that car in northern part of Japan, all stock... bolts right on, just gotta find the drivetrain.
my aim is purplec320, shoot me an IM anytime... Let me know if you want more photos of what we did...