Base timing change with timing belt replacement?
 

Gents,

Shortest story possible... I had to replace the transmission. I noticed the cam cover gasket and that dumbass plug at the rear of the exhaust cam leaking. When I pulled the cam cover, I found a split in the timing belt. I also noticed, and fixed, a few valve clearances that were out of spec. I had removed all the intake plumbing to do all the work.

With everything back together, I started her up and had a long start, some starter kickback, and some backfiring. That was not normal, but I thought it might be because it hadn't run in a while. It happened again on a second try. I checked the base timing and it was off. It needed to be reset from 5.9 degrees, to 8. I also needed to add some fuel to the 100 kPa startup box in the VE table. She purrs like a kitten now at idle.

Is resetting the base timing something that needs to happen when replacing the timing belt? I admit it's been a long time since I set it, but what else would make it change?

More importantly, is there anything I need to worry about with the spark table after resetting the base timing?

Thanks,

The base timing is derived from the crank, and can't possibly change due to cam timing changes. Changing from 5.9 to 8 removes 2.1 degrees from your spark table. There's no logical explanation as to why it might have happened. Are you running the stock trigger wheel? If so, the starter kickback is very common unless you run negative cranking timing.

Rev,

Thanks for chiming in.

There are only a few possibilities then... I checked the lower cover with the timing marks a few minutes ago. It's installed correctly. I removed and replaced the crank position sensor when I did the timing belt, but there's only one way for it to be installed. Either I set the base timing wrong years ago, which is certainly a possibility, or I set it wrong yesterday, which is also a possibility. I'll check it again when I get home from work.

Removing and reinstalling the CPS could affect the timing.

Gentlemen,

I believe I have a bad O2 sensor, but I've been wrong about shit before...

Whilst I'm waiting for the car to cool down, I thought I'd ask for second opinions.

I have the car all put back together, and pulled her out of the garage for the first time after the transmission and timing belt installs. The car had a really long start with lots of bucking and some backfiring. I believe I saw the battery light come on slightly a couple of times. When it started, it was running reasonably well, so I took it for a ride to check out the transmission install. When battling traffic at speed on I64, the AFRs were all over the place, but when I was off the highway and holding a constant speed/throttle position, the AFR looked normal. The really weird thing was 111% EGO correction at idle when I pulled into the driveway, and that's after increasing ReqFuel from 3.9 to 4.0.

The reason I believe it's the O2 sensor, is when I ran it in the garage after resetting the base timing, she ran beautifully, probably idling the smoothest I've ever seen from her (which I attribute to re-shimming some out-of-spec valve clearances). The next time, not so much, with no changes to anything.

The attached log doesn't include the start.

I'm heading to VIR tomorrow. I'm going irregardfull of whether or not I get this fixed, so any words of wit would be greatly appreciated.

Thanks much,

Okay, I'm a big dumbhead... the TPS connector plug was not completely clicked into place. Jeez...

https://cimg1.ibsrv.net/gimg/www.mia...4b414ab47e.png


Chinese aftermarket TPS sensor ? Some have a receptacle which isn't even compatible with the plug in the mazda wiring loom and blocks the mfrom being seated.