og556

Hey guys I'm lookin at a 91 fox body w/ a stock 5.0 and was told by the owner that it only likes to run well w/ 91-93 octane fuel. He told me that it pings and what not with 87 octane. Any ideas of why this would happen on a bone stock 91 w/ 5.0 motor ? Thanks.

samseed101

My first guess would be that he raised the timing to get more HP / TQ out of it. Pull the spout connector and use a timing gun to see what the base timing is set at. If it's anything above 10 degrees then he advanced the timing and that would be the reason. If that's the case, then that is a good thing as most of us here do that anyway for the free power

If that's not the case, then carbon buildup could be causing a higher compression ratio in the cylinders. Or there could be a small vacuum leak allowing unmetered air into the system thus causing it to run lean.

Those are a few things to check.

og556

What tool should I use to check the timing ?

samseed101

It's called a "timing light" or a "timing gun." You can either borrow one or buy one for like $30 at a shop. basically, youclip it to the spark plug wire of the #1 cylinder. Then you hook it up to the car batteryto power it up (unless it has it's own power source.) After pulling the spout connector you aim the light at the balancer and when it flashes, read what number it is at. it should be at 10. if its above ten, then someone adanced the timing and that is the problem. Although it's really not a problem.. it;'s a good thing because it gives you more HP and TQ.

For instructions on where the spout connector is and to learn how to reset the timing, check out this link.

Go Roush

I have mine advanced a little more and it also pings if you dont use premium fuel, but a little more money is O.K. for more horses.

og556

Thanks for the advice. The only problem now is if this isnt the case how do I clear all that crap built up in the engine ? I will be doing spark plugs/wires/ possibly msd ?, etc... Any suggestions ?

mattdel

http://www.seafoamsales.com/motorTuneUp.htm
available at your local autozone