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    VWVortex


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    Thread: Suddenly started running lean

    1. Member
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      07-09-2014 09:19 AM #1
      Hey guys, hate to post this but I'm kind of stumped. I have an VR6 Stage 1 OBD2 Corrado that the other day was running great, 12.6-12.9 range on boost, 14.6-14.9 while cruising. Nearing the end of my cruising I was in need of some gas and stopped to fill up. Started heading back home and decided to get on it for a second and once I did it went no where, no power AT ALL! Looking at the boost gauge at around 3200 I was @ 5PSI but only pulled like I was at 0. By the time I realized I was probably running lean about 5-10 seconds had passed. So I opened the glove box (where my wide band is stored) and even at cruising throttle It'd fluctuate around getting 14.6-15.6 on the gauge, MUCH to lean of course for just cruising. The oment I'd get on it it would occasionally run very well, richen to 11.6 but then peg out around 12.6-13. Not exactly as good as before but acceptable.

      I figured at this point, given the MAF is a used component that maybe it was starting to go out as well as maybe bad fuel (place I stopped at didn't look to be used as much as some other places). So a few days go by, I drained the fuel out entirely, put in fresh and tried to start the car. For some reason it wouldn't start, long story short I unplugged my MAF and the car fires up and runs fine (albeit a check engine light on now). I figured I'd see how it ran with the MAF unplugged because I figured it's in safety mode and would run the system richer than usual which would point me to the MAF being the issue...Nope, no such luck. At idle I run well, 12.6-12.9, but under boost it goes to 11.6-12.6 for a few seconds and then walks itself out to 13-14-15, by the time it is hitting 14, I've usually let up but it's what the scale is showing so I figured I'd let you know.

      So, with the MAF unplugged I run just as lean when (at least with stock VR's) I should be pegged fairly rich in all parts. What would just up and suddenly make the car run like crap now? I have a known good 4bar fpr from a OBD1 car, could I run that and see if things improve or would that be to much?

      My setup:
      Stock VR6 head & block
      OEM G60 fuel pump (unsure of age/mileage)
      Fresh fuel filter (just installed in Feb)
      30# injectors (truthfully need cleaned but ran fine on the previous car)
      3bar FPR
      Intake - 3" K&N to 4" MAF housing back to 3" all the way to 3" turbo inlet
      All Vac lines checked and good (only have I think 3 due to all emission being taken out)
      Rule for posting in Corrado Forum- BEFORE clicking 'Submit Post' button, go ahead and have someone kick you in the nuts. Only then can you click the button.....it'll hurt less when you get your response.

    2. 07-09-2014 03:53 PM #2
      I would start with the fuel pump and maf. It sounds like your on the right track already. New maf + new fuel pump = cheaper than a new engine. Be sure to check the relay and wiring to the pump aswell.

    3. 07-09-2014 10:38 PM #3
      Connect a vag com to it and see that you are actually hitting the WOT switch. You can do that with the car running by looking at the tb in vag com. 14-15 while cruising is normal depending on your chip.

    4. Member
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      07-10-2014 12:45 PM #4
      So I'm thinking that when I order the fuel pump I may want to go with a Bosch or Walbro in-tank instead of a new pump and Bosch or Walbro in-line (I don't really care to bolt extra items under the car if it can be avoided, plus in-tank should be quieter and much more concealed setup). I figure I won't go over 300hp with the car but I'd rather have to strong of a pump than not enough. However, is there a DIY for modifying the stock basket to fit and securely hold the in-tank pump for a Corrado/MK3 fuel pump? I seen the setup Schimmel brought out but at 475 + shipping I can't seem to bring myself to pull the trigger given the pump is ~220, so more than 250 some bux for the adapters seems to steep to me IMO.

      As for the WOT switch, is it possible to do that without the car on? Even if I have to test with a volt/ohm meter? Reason being that the car doesn't seem to like any sudden punches or high revs before she leans out.

      Oh, forgot to mention I'm running C2's stage 1 chip.
      Rule for posting in Corrado Forum- BEFORE clicking 'Submit Post' button, go ahead and have someone kick you in the nuts. Only then can you click the button.....it'll hurt less when you get your response.

    5. Member waabaah's Avatar
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      07-10-2014 01:33 PM #5
      Curious for the throttle body info too. I believe I have issues with my TB. What percentage will I be looking for while WOT and static?

    6. 07-11-2014 09:49 AM #6
      It's also possible that you have miss fires, which will showup as a lean mixture also, check the plugs and coil(s).

    7. Member waabaah's Avatar
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      07-13-2014 03:17 AM #7
      Misfires would show up on afr as rich. (No spark, fuel injectors dumping in unburnt fuel)
      Last edited by waabaah; 07-14-2014 at 05:54 PM.

    8. 07-14-2014 09:20 AM #8
      Quote Originally Posted by waabaah View Post
      Misfires would show up on afr as rich. (No spark, fuel injectors dumping in burnt fuel)
      What he said. I would check that all of your t clamps are tight and that you have no rips in any silicone anywhere. I had a floor mat that was buncked up under the accelerator pedal which drove me nuts. Was just on the edge of the WOT position. Sometimes it would hit it, sometimes I would have to stand on the pedal.

    9. 07-14-2014 10:53 AM #9
      I'm with Marco on this one. An o2 sensor doesn't measure unburnt fuel. Based on it's name, I would guess it measures oxygen content. When you run lean you have excess o2 (meaning not all o2 is reacted into combustion products). When you don't have a combustion event, all the o2 that would otherwise have been converted to Co2, h2o or Nox is left as o2, so it looks like you have excess o2 and the sensor reads lean. Maybe I'm wrong, but this is also what I have experience in my car

    10. Member waabaah's Avatar
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      07-14-2014 06:09 PM #10
      You got somewhat the right thinking. But let me change the words around to grasp what's going on.

      Yes it's called an "oxygen" sensor, but there is no control for oxygen. This means the computer can't give more oxygen or less oxygen. The computers only control is injector duty cycle.

      The "oxygen" sensor reads the air to fuel mixture.

      According to the computer parameters, Oxygen is always the constant. Fuel is the variable.

      So a lean reading is x amount of oxygen. Little fuel.
      A rich reading is x amount of oxygen, more fuel.

    11. 07-15-2014 08:53 AM #11
      Quote Originally Posted by waabaah View Post
      You got somewhat the right thinking. But let me change the words around to grasp what's going on.

      Yes it's called an "oxygen" sensor, but there is no control for oxygen. This means the computer can't give more oxygen or less oxygen. The computers only control is injector duty cycle.
      So what? What does that have to do with the ‘oxygen’ sensor? The sensor is only giving feedback, it’s not controlling anything.
      Quote Originally Posted by waabaah View Post
      According to the computer parameters, Oxygen is always the constant. Fuel is the variable.
      No it is not a constant, changing RPM or TPS will alter the amount of air trapped in the cylinders, more air will need more fuel and vice versa.

      The ‘oxygen’ sensor does read the amount of air trapped in the exhaust, albeit it ‘reads’ the difference between the air in the exhaust stream and the outside air(there’s a little hole in the sensor for reference).

      So when you have misfires, you’ll have more unburnt fuel but also more unused air, which will read as a lean mixture.

    12. Member waabaah's Avatar
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      07-15-2014 12:37 PM #12
      Quote Originally Posted by MarcoVR6SC View Post
      So what? What does that have to do with the ‘oxygen’ sensor? The sensor is only giving feedback, it’s not controlling anything.

      No it is not a constant, changing RPM or TPS will alter the amount of air trapped in the cylinders, more air will need more fuel and vice versa.
      Ecu controls fuel duty cycle. Ecu does not control air. Ecu can not dump in 10percebt more air or take out 10 percent less air. So this means that air will ALWAYS be the constant and fuel is the variable here. Sure at 2k rpm you have less air then 4k rpm. There are already set parameters and the ecu is always looking for the same predetermined values, run after run

    13. 07-15-2014 01:07 PM #13
      I think we all know that the ecu does not control the air, it doesn’t dump or add more air yes, but when the mixture is not ignited, the air is still there and is pumped through the exhaust.

      Also at 2K or 4K rpm, you’ll almost have the same amount of air per cycle for the same throttle opening, although at 4K rpm the engine(modern petrol non turbo) will probably have a better volumetric efficiency than at 2K, where max torque is the highest volumetric efficiency as long it’s not limited by detonation.

    14. Member
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      07-15-2014 02:16 PM #14
      Hey fellas, sorry for not responding but thanks for the ideas! I went ahead and ordered an intank Bosch 040, should be here tomorrow. I talked to a few guys on the Corrado forum about how they setup their intank setups and it seems pretty straight forward. So hopefully this weekend I'll get a chance to install that. I'm also going to the junkyard this week to pull a few MAF sensors to make sure it's a problem with the MAF and not wiring (still seems weird it goes from running to dead, can't start, so I want to verify before buying new). I also got new plugs, the ones I have in it are OEM and only have 500 miles on them but that's 500 of break in so I'm going to get the NGK BKR7E plugs. I'm also going to go ahead and order a new FPR as well.

      I figure after doing all this my fuel system and part of my spark system should be good to go for a little while (specially since most of the parts on there are getting old from the previous car they were in). I figure if it still leans out then my injectors might need to be cleaned but I'm hoping to hold off and do that this winter when I break her down again. Oh, also forgot to mention, my O2 sensor is brand new, maybe only ~200 miles on it. So I think that sensor should be fine.

      Thanks again!
      Rule for posting in Corrado Forum- BEFORE clicking 'Submit Post' button, go ahead and have someone kick you in the nuts. Only then can you click the button.....it'll hurt less when you get your response.

    15. Member waabaah's Avatar
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      07-15-2014 02:36 PM #15
      Quote Originally Posted by MarcoVR6SC View Post
      I think we all know that the ecu does not control the air, it doesn’t dump or add more air yes, but when the mixture is not ignited, the air is still there and is pumped through the exhaust.
      That makes air the "constant" variable. It is always there. Fuel is the variable.

      It is a tricky and confusing subject only because the ecu does just the opposite. If the motor is truly rich, the ecu would attempt to lean out the mixture. And vice versa.

    16. 07-15-2014 03:03 PM #16
      I think that you’re the one that is confusing things up.

      The only constant here is the O2 percentage in the air, the air trapped in the cylinder(per cycle) is not constant(it’s not a diesel), otherwise the ecu would always inject the same amount of fuel for a given AFR ratio at any load and/or rpm cell... It’s a dynamic thing not a constant one.

      To the TO, you should not replace things like that, analyze and check things first, then replace if needed.

    17. 07-15-2014 03:09 PM #17
      Quote Originally Posted by waabaah View Post
      Misfires would show up on afr as rich. (No spark, fuel injectors dumping in unburnt fuel)
      So how will it show up then, as too rich or too lean?

    18. 07-15-2014 03:51 PM #18
      Quote Originally Posted by waabaah View Post
      That makes air the "constant" variable. It is always there. Fuel is the variable.

      It is a tricky and confusing subject only because the ecu does just the opposite. If the motor is truly rich, the ecu would attempt to lean out the mixture. And vice versa.
      Let's take this out of the context of an engine with an ecu, and instead use a long winded example .

      Imagine that you have two identical pipes with a mixture of gasoline and air flowing through them. You have 14.7 lbm/second of compressed air and 1.0 lbm/second of fuel, therefore a 14.7:1 mass based air/fuel ratio (stoichometric, for gasoline). These mixtures are not changing, so the actual air/fuel ratio is constant. At the end of each pipe is an oxygen sensor.

      In one pipe you have a spark plug which causes combustion. Since the air/fuel ratio is stoichometric, all of the o2 molecules in the compressed air are converted to water, co2 and likely some co and nox. There is no excess o2. The o2 sensor sees this lack of o2 relative to the ambient air and decides that lambda = 1.0, then reports out an air/fuel ratio of 14.7:1.

      In the other pipe, there is no spark plug (analogous to a misfire), so there is plenty of excess, unreacted o2. The o2 sensor sees this as a similar o2 content to ambient air and decides that lambda is much higher than one, so it reports out an air/fuel ratio of say ~19:1. The ACTUAL fuel/air ratio has not changed, but since the oxygen sensor is calibrated to look for combustion products it will give a false lean reading because it confuses oxygen rich pre-combustion air as exhaust products.

      Science aside, here is a log of my car misfiring. Jitters in the RPM signal (white wire) are small misfires. These correspond to the lean peaks in the yellow signal (AFR).



      Then some comments from a couple guys that know more than most about tuning...

      Quote Originally Posted by sdezego View Post
      Misfires usually show as Lean spikes (since you have unburned Fuel and Oxy), but that may not be saying that Dwell is not wreaking havoc in that range. In my experience, that is an area of high load and when IGN problem will be evident. What is EGO Corr doing there?
      ...
      Quote Originally Posted by need_a_VR6 View Post
      ...
      If you look at the AFR in the log it looks to spike lean a bit and changes in the fuel table wouldn't explain the behavior (look at gammave in this area to verify). It's likely misfires, and could be simple as a bad plug wire, etc.

    19. Member xtremevdub's Avatar
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      07-22-2014 11:11 PM #19
      Did you try to do a TB adaptation since you are OBD2?
      If the TB goes bad it will screw up all your fuel trims. Do that before you spend money on parts.. You can even try to watch it move while adapting it. It may be stuck (bad) and it will do all sorts of weird thing while driving.

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