Instantly lean as can be???

[na_turbotalon]

I was driving my car around one night, then after my last stop on my way home it backfired like it hadn't since before it was tuned. My AFR was around 18:1. On the highway I could sometimes get it down to 16:1 but up to 19:1 isn't out of the norm. The backfiring leads me to believe that there actually is a problem, so I'll look past a faulty Wideband sensor for now. It's all over the RPM range, idles at 18:1, used to idle at 13:1, my fuel pressure hasn't changed. For what it's worth, the "tone" of my fuel pump hasn't changed.

What are your thoughts?

 

[DirtyBirdRacing]

Check your fuel system over again, make sure everything is working correctly. Do you have a log of this happening? You also might have a huge exhaust leak that is letting outside air in and letting the o2 sensor read really high, but for you to get readings like that at idle that is probably not the case at all.

Bill

 

[selmerguy]

First let me get this out of they way..... Your car rocks. Very nice mod list. Just to check bases, has your vac changed at idle? If it has changed then your wideband is probably telling the truth. Cars normally backfire when rich not lean but a lean back fire can happen. Other than the AFR changes what else is going on. Any other major differences? Surge, smoke, ect... Any more info would help narrow things dowm alot.

 

[GVR4592]

Have you done a boost leak test?

 

[na_turbotalon]

I haven't done a boost leak test yet, have to see if I can find the 4" tester, it's been a while. I'll give the test a shot but would a leak throw off a speed density car this much?The only smoke from the car is the little bit of oil burn off that there has always been. I reloaded my AEM cal, just in case. Didn't change anything, and it still all looks good on that end.

Since my Vac readings haven't changed at idle, and the pressure is the same at the rail, would it be safe to assume that the overall volume of fuel in the system is still the same as before up to the injectors? I have a friend who's sourcing me some others to test, but I'm gonna be pissed if there's something wrong that can't be fixed with a cleaning.

Could 1 injector not operating at full capacity throw off the AFR that much at such a small load?

 

[GVR4592]

I didn't realize it was speed density, but yes it can throw it off a lot depending on where the leak is. I had a bad injector o-ring and my wideband was reading 2 points leaner at idle, fixed the leak and it's back to normal.

I would make sure all of your sensor are functioning correctly, and if possible reload your current map onto the AEM. Sometimes the AEM unit freaks out and needs a little kick in the ass.

 

[selmerguy]

Yes, if the injector is not functioning right the AFR will be way off. Why do you think that injector 1 might be bad? Have you pulled plugs? Do they all look the same? That would be a good way to test this theory.

 

[na_turbotalon]

Tried a new set of injectors, that didn't help anything. So I'll look for boost and exhaust leaks when I get a chance. Then on to the MAP sensor I guess.

 

[DirtyBirdRacing]

Tried a new set of injectors, that didn't help anything. So I'll look for boost and exhaust leaks when I get a chance. Then on to the MAP sensor I guess.

A boost leak test is a good idea in general, but I doubt it will help you fix your problem since you run speed density you know. I would probably check the MAP sensor before you dealt with checking the exhaust and for a boost leak.

Bill

 

[GVR4592]

Can you post your AEM cal file or email it to me.

 

[na_turbotalon]

I'll try Emailing it or posting it on the AEM forum when I get a chance, but from past experience Tuners won't let you attach the .cal files.

Anybody know if you can check a MAP properly with a multimeter, instructions perhaps?