Fuel Stablizers and tuning.....

[Redline Motorsports]

Got a 00' C5 on the dyno for tuning that we just installed a mild head cam setup on. 222/226 on a 114 with ported heads, LT, 30 # injectors, blah, blah, blah...

The car is pulled 6.9 degrees on KR at 3800 rpms and its just killing the torque curve, as to be expected. The timing is very light as it starts out at 16 degrees at 2300 and is set to provide around 23 degrees at full advance. Just before the knock retard occurs, the timing is 18.5 degrees, hardly enough to cause detonation I feel. We (black02) thought it might have been burst knock in which we eliminated that as an issue.

I then made a pull with 15 degrees on timing across the board and no knock.....and no power!:bawl:

This concludes that it is most likely not a false knock situation. I called the customer to confirm the gas in the car. He claims it is 91+ but also indicated that before he put the car away that he put a fuel stabilizer in the tank. Does any have any thoughts on what the effect of stabilizer has on the octane rating of the fuel? I don't want to chase a ghost if a clean tank of gas solves the problem.

We also richened up the AFR to 12.5:1 to make sure it wasn't a WOT lean situation as well. I typically see these make best power at 13.0:1.

Howard

[SinisterSS]

With fuel stabilizer in the tank, the first thing that popped into my head is how old is the fuel? Drain it and put some fresh fuel in the tank. Eliminate the easy things first.

[Redline Motorsports]

The gas has to be at least 5 months old if I had to guess. The guy filled the tank before he put it away and it had to at least be by November.

Maybe being that old and the stabilizer knocked the goodness out of the fuel. Just can't see this thing knocking with such a conservative timing table....

[EfiOz]

Is is actually knocking? I mean, is it audibly detonating or is it just what the KR reads?

[Redline Motorsports]

We'll; the car is a head/cam/header car with a Borla Stinger exhaust. It is kind of tough to hear anything on the dyno. If I should hear it through all that then no I can't real hear it. Besides, it makes it tough to hear detonation when the PCM is taking timing away to stop it! As soon as knock is detected, the PCM pulls timing and knock goes away but alao pulls a ton more timing then needed!

The dyno graph shows it plain as day.

I think I am going to let my customer take the car and cruise it to empty the tank. Fill it up fresh with high test and start again. I would hate to spend all this brain power to find out its bad gas!