408 car. Bought the car about 6 weeks ago. Ran great on the 400+ mile trip home. No surging, power was fantastic etc. Was tuned in Texas for 93 octane. 91 is premium in Oklahoma City, so after a tank or two of 91 I decide to play it safe and throw a couple of gallons of 110 in the mix. It was about then I noticed the car would start surging really bad at idle after warming up. Car also seems to break up under light acceleration (1st and 2nd is where I feel it the most) and WOT feels just okay. Definitely not where it was on power a few weeks ago. I have replaced plugs and wires but really don't think they are the culprit. Also don't really think it's rings. I think (and am hoping) that the race gas torched the front 02 sensors and that is making the car run like it is. The car needs to be retuned eventually because it would hang up around 2000rpms for a couple of seconds when coming to a stop. But other than that, it ran great. So, where do I need to look first? I have almost a full tank of 91 and 110 mix in her so I'm gonna start burning it off and fill to the top with 91 only. Then I'm gonna replace the o2's. What do you guys think?

 

Oh and the rear O2's are sims, and I haven't thrown any codes.

 

If the 110 was leaded, it's safe to assume the o2's are contaminated and shot. You need to flush the fuel system before putting new o2's in. Sometimes running the tank down close to E and adding in unleaded will help, otherwise you may need to flush the system. Check the plugs as well and look for an orangish brown color on the them.

 

I just did a plug change. Like 30 miles ago. The car was doing this BEFORE I did the change, but the car had TR55's in it so I went with a TR6. I'm hoping that a fresh batch of unleaded and 2 new o2 sensors will fix the problem. I really don't want to spend $140 on sensors if that isn't the issue.

 

Or maybe say "F- it" and tune the car in Open Loop and run all the race gas I want?

 

Any other thoughts?

 

OK then.

 

Do you have a scan tool you can use to see if the 02's are switching correctly? That would help alot. I would also check to see if the 02 switching codes are disabled in the tune. Some turn them off because they are nuisance with LT's.

 

I'm trying to find someone around OKC with HPTuners so I can data log some stuff and email the file to my tuner back home in Baltimore. No luck so far!

 

copy your high octane timing map into your low just for testing purposes. i say this only because i got a batch of bad gas, some water got to it or something, car ran like dog poop, on the low octane table.

 

This has been 3 or 4 tanks.

 

well, try it anyways. reset the battery cable while your at it

 

Anyone know the part number for the front o2's? I just picked up some bosch 13444 but they are obviously the rears. Thanks

 

Well, 2 new Bosch 13111's later and she's running like a dream again!

 

Excellent. Just stay away from the 110 leaded.

 

Too late! LOL. Well theres only a little over half a tank left in her of a 2 to 1 91/110 mix. Torco for the win! Oh and it's getting seafoamed this weekend. The motor only has 6 or 7k miles on it, but I'm interested to see how much **** actually comes out.