Ok... We now know the deal on my brother's 3.1. I thought it was time to work on my tach for awhile. I used the variable pot and read the thread on how to fix it and FINALLY got it done. I was using an Autoxray scanner to do the tuning of the tach while on the road. I noticed as I was scrolling down the info on the scanner, my spark advance was showing 37* to 40* while doing 50 mph. Is'nt that kinda high? I can't remember what it is at idle. I was going to throw in an extra fuel rail/injectors that I got lying around. The injectors on that one ohm(ed) at around 12.7 on each injector. I'm going to replace the FPR while I'm at it. Any ideas on the high spark advance?

Ken

 

I don't have any specs in front of me but from what I know about engines, the spark timing should be advanced with higher RPM. It takes a certain length of time for the mixture to get lit after the spark flashes, so when that piston is coming back up at a higher speed at higher RPM, if it sparks the same time it did at idle the ignition in the cylinder will "miss the boat" so to speak and will be trying to force the piston down after its passed its optimal position in the cylinder to receive its power stroke resulting in a shorter power stroke under less compression which as I'm sure you know equals a much weaker bang.

Its kind of like trying to double bounce someone while jumping on a trampoline... spark timing works in a similar way. If you time it too early, your bounces will "collide" and stop them from bouncing back up at all. If you're too late, they'll already be airborne by the time your extra bounce arrives rendering it a waste of energy.

Just a thought... but if you can get a hold of the actual specs I'd check them out. Is the motor acting up on you at all?

 

Yep... it seems to have a pretty noticable miss when idling. The scanner shows the O2 sensor going from 100-700 then back to 500 or so, that might br normal. It also is showing 3 or 4 knock sensor signals. The one thing that did catch my eye was the scanner show a startup temp. of 200*. That sounds WAY OFF! The car had sat all day when I was at work so I know that can't be right. Car has no power either. Could be a stopped cat or low compression or any number of things. Problem did'nt go away after tuneup either.

Ken