I have an Evo 9 with a freshly built motor maybe 5,000 miles on it and 4,000 on the tune. 5,000 miles on a walbro and spark plugs. My

So I'm driving home from work today when randomly my car starts having large fluctuations in afr on the gauge. 13-18 while cruising and car won't idle when coming to a stop. It idles at like 18-20 afr which can't be safe and when I hit boost ( just a little to test afr) it goes to like 9.3!

Super rich at boost and super lean at idle.... Tell take sign of a boost leak. I checked all my intercooler piping, intake, very vacuum even rear egr and all are secure. Although I didn't perform a boost leak test since I have no tester I feel the afr at these extremes would need a massive boost leak to cause this. My fuel pump sounds kind of louder than before if that means anything.

It's cold as all hell in Chicago right now so tomorrow I will reluctantly pull the plugs and compression test my motor to make sure it's healthy and inspect plugs for fouling. Any other ideas, questions, or concerns? I want to log with evoscan but I'm worried to run my motor with 20 afr at idle. Can I do that safely?

Thanks,
Ryan

 

are you tuned on speed density? if so, it could very well be your map sensor going out, specially if you're running an omni 4 bar, they like to fail for no reason. let us know!

 

I'm having similar issues, although my idle is not that lean. My AFR at idle is around 15.5-16.8 with the occasional 17. Everytime it nears 17 my idle dips a little. The part that irritates me the most however is when my AFRs go below 10 (10 is the lowest my crappy AEM UEGO reads). At this point, there is so much fuel being dumped into the motor that the motor either comes close to or even stalls. This happens when I'm cruising on the freeway, driving through residential areas, or even at idle. I too am on SD and running an omni 4 bar MAP sensor. Could anyone recommend a MAP sensor that works? I'm at my wits end with this weird rich condition that I was ready to switch to a full standalone ECU.

 

I'm tuned on maf. I still have a 4 bar map sensor though because I was going to go speed density but didn't yet and misplaced stock map sensor.

 

Car won't start due to whatever caused this issue last night and having a poorly tuned cold start. It would barely start when it was working properly. Did a cold compression test anyways and got 60 psi at all 4 cylinders. Should see 120 with gsc s2. Think motors good. Thinking sensor, exhaust leak, or boost leak I guess. Suggestions, ideas?

 

Map sensor.

 

Would you be able to recommend a good map sensor to use?

 

there's a few vacuum lines behind and under the IM, did you check those? i assume so, just putting it out there because sometimes i miss easy stuff too.

as for the MAP sensor, i use OMNI and haven't had any problems with it. other than that, i'd go with another OEM one, if you don't due ECU boost.

 

I got another omni 4 bar. Problem solved. Another member said to install an oil catch can as the oil kills the sensor??? I didn't do that and not planing to anytime soon.

 

If you're blowing that much oil, at that power level, you may have another problem to fix. 😢
It should take a lot of psi to move enough oil to require a catch can.

 

Ok I got my car to start finally my unplugging the map sensor and giving it some gas. It idled at 14.7 until it reached operating temperature and then went lean to like 18-20 again. plugged map sensor back in same scenario. Logged with evoscan was reading 5.1-5.8 on the map sensor idling at operating temperature. My o2 sensor voltage was stuck at .0359 or something like that and would move to .01359 or something like that randomly. My fuel trims all read 0% and wont cycle. The o2 feedback for fuel trims was staying at 24.xxxx and if I gave it gas it would go to 15.xxxx. Are all of these readings normal? Essentially Once I reached operating temperature everything went leak again.

 

the car will start without some sensors until it goes to closed loop, so you are correct there.

EvoScan is reading -5.1 to -5.8, correct? it should be in the negative during idle.

if i'm not mistaken, your TPS should be reading around 13-14. mine is always at 13.33333

 

Seems like it ran at 14.7/1 until it went into closed loop then went lean. Then with the fuel trims not cycling or attempting to compensate by adding more fuel it points to the o2 sensor, but since that isn't used until closed loop it wouldn't explain the hard start.

I still think I have some kind of leak somewhere. I wish I had a boost leak tester. I feel like this issue screams unmetered air, and it sounds like the motor is choking.

 

a boost/vacuum leak was my first guess, too. it took me a year to find mine: it was a hose with a very small crack in it that i NEVER would have found without pressurizing the system.

good luck, man. this type of situation is frustrating.

 

It was weird for me as well. But I was also not able to restart my car when it happened. I got lucky a few time and I would rev it fast enough to get into gear and that was enough to roll my car home. It wouldn't even hold idle. Now I am able to drive my car with the new map sensor. Goodluck.