Loop320

So, after rebuilding the top end to fix a dead cylinder I fine tuned the ignition timing to factory spec (10 degrees). The truck idled and ran great at this setting, however, no power, the thing flat out wouldn’t climb a hill here in Salt Lake City. After adjusting to 15 degrees of advance it did a lot better. Now have it set at about 21 and it’s better still. I’m tempted to keep advancing but know I’m probably close to the point of diminishing returns. My question is why? If toyota says 10 degrees why is it such a dog at that setting? Doesn’t make any sense. Also, any long term consequences running so advanced? Not noticing any pinging, Thanks....It’s a 944runner.

scope103

Just to eliminate confounding variables, you might want to check if your harmonic balancer has slipped. It has an annular rubber ring between the part that's keyed onto the crankshaft and the part with the pulley grooves and timing marks. I'd remove the #1 plug, put in a plastic straw (don't use a screwdriver; if you slip you could scar the top of the piston), and rock the crank to find TDC. Does the timing mark match? If not, you may need a replacement Harmonic Balancer.

There is also the small possibility that you "stabbed" the distributor off one tooth. One tooth off is about 28°. (That means it's running well at 7° ATDC, which doesn't seem likely, but something to consider.)

Loop320

Thanks for the response, I checked the mark on the balancer against the #1 piston with the heads off, it’s spot on. I’ll double check the distributor but I think that’s correct as well. There is an older thread on this where others reported better power with advanced timing, it just doesn’t seem quite right to me. Seems like something might be amiss. Runs awesome though, pulled a fairly decent grade at 70mph in 5th gear (manual) with the air on, up here at altitude.

QuiGonJon

I've heard the same and have had the same results. I heard one guy say toyota engines or at least the 3vze is tuned rich so a combination of leaning out the AFM, advancing the timing, and running 89 or 91 octane gas results in a lot more power output. I can't say I understand why exactly but I can say that it's true. My truck had much more mmph off the line, better acceleration, and more uphill power

scope103

The problem with changing the "timing" to affect power is the Toyota engine (and all modern engines) is the one controlling the timing (and the mixture), not you. No matter where you set the base timing, the ECM is constantly advancing the timing until (by means of the knock sensor) it detects pinging. Then, it backs off, and repeats this hundreds of times a second. If you change the base timing, you're just changing how far the ECM goes on the first step, and then it doesn't matter.

Same with playing with the "mixture" in the VAF. You have an Oxygen Sensor, and that's what the ECM uses ultimately to set the relationship between throttle position and injector open-time (which is how mixture is controlled). If you play with the VAF setting, the ECM quickly compensates that out with Learned Fuel Trim.

This ECM fine-tuning applies less at WOT, but how often do you drive with WOT?

Of course, I might be talking through my hat. If I was more interested in "tuning," I'd try re-setting my VAF and watch if Learned Fuel Trim changes. Or change base timing, and see if ultimate on-the-road timing changed by much. I haven't done that (and probably won't), so if you don't believe me, que sera, sera.

Loop320

I’m really starting to think I popped the distributor in wrong. Going to reinstall it now.

Loop320

Just to close the loop, it was the TPS. After reinstalling the distributor the timing was so far advanced I ran out of travel trying to correct it. Swapped out the TPS (lots of fun with the TB still installed). Fired it up, adjusted by ear, put the light on it and it was right at 10 btdc, steady as a rock. It idled well before but it really purrs now. I suspect those who are having good results with timing out of spec may have this issue as well.