Thread: Fluctuating AFRs

Hey everyone, I've been trying to figure out an issue for a while, and figured I'd just ask around here to see if anybody has any ideas.

According to my UEGO, my AFR's are constantly fluctuating and changing sometimes while at idle, sometimes at cruise, sometimes not at all. I can go out and start my car, after it warms up and settles on a AFR, it will suddenly decide to go from around 15.4AFR (where I like to idle at) to around 11.8-13.0 range. And my idle will raise a few hundred RPM until it randomly decides to go back to ~15.4 where it should, then it behaves fine. It does the same thing while driving too! Usually I cruise around the same point actually but on my 20min commute everyday, for a good portion of it, it will decide to just run pig rich. What is normally 15.4 cruise will become 13.0 cruise and boost will be in the 11's or 10's, instead of 12.0 (which is usually spot on).

I've looked for vacuum leaks, I've done multiple pressure tests to search for leaks, found nothing. Now, when I replaced my fuel pump I went with an off brand Walbro alternative (I know, I know). Is it possible that the stock wiring to the fuel pump is just crappy and somehow fluctuating voltage going to it causing it to pump different amounts? A few weeks ago I was having issues with it not even priming when I turn the key on, that week, it ran super lean all week - it did not do any of this weird AFR fluctuating, just lean all the time. After a few days of that it seemed to correct itself and went back to being the way it always has been. I finally (after a year and half) purchased all of the -6AN adapters to install my Aeromotive AFPR with gauge, and am going to put it in this weekend so I can monitor my fuel pressure to see if it is changing strangely. I think I am also going to wire in a relay with a direct 12v feed from the battery as well to the fuel pump.

Does this sound reasonable to anybody, or do you think my problem lies elsewhere?

Sorry for the long/scattered post. I'm at work and just trying to type this up quickly. Let me know if you have any questions, I'd love to get this straightened out.

No ideas? I haven't had the time to get my Aeromotive in yet, but I'm still experiencing random changes in my AFR. Even at constant throttle on a relatively flat highway it'll just stray away from where it should be and run really rich for a while, then work it's way back to normal after a while.

The fuel pump itself hasn't given me anymore issues, but I find it hard to believe that it is randomly pumping drastically different amounts of fuel at random times. The only other things I can really think of are injector issues, or something MAF related perhaps? I need to get my laptop out and do some data logging... I'm considering sending my injectors off to be cleaned and flowed, and thinking of trying out a blow-through setup out of curiosity. I don't know if either of those will help my problem, but I don't really have any idea what else could cause something random like this.

Any ideas would be appreciated.

If the fuel pump is behaving well while you're getting the good readings, and then the fuel pump starts flowing more for some reason, the FPR should counteract that and still give you the same fuel pressure, and the same fueling. I'm thinking it is not a fuel pump issue. Check the FPR for good operation, and check the little vacuum line going to it for cracks and such.

The fuel filter also might be in rough shape, but just like the pump, it shouldn't cause these problems. Wouldn't hurt to check though.

I think injectors would be next, but it could be the injectors, or the ECU, or like you said it could be the MAF... =/

I know... there are so many variables, that's why I was looking for what someone else may think. I'm going to get the Aeromotive put in this weekend for sure to replace the stock FPR in case that is the issue. If it makes no difference, then I guess I'll move on to the injectors.

ECU did cross my mind, I hope it's not that though - it runs fine otherwise? Fuel filter is about a year old, but is already on my shopping list for this week when I go to get supplies for an oil change

any more info on this? i have/had the same problem, just recently found my soldering aron and redid all the connections and it's a lot better. now i think i just need to get a better tune.