spark advance

**mutant5776** · 11-08-2009, 02:57 AM

What should the timing be on a 96 Suburban 350. Have my computer hooked up to the obd-2 port and the pid loop shows spark advance is -23 to -28. This does not seem right. Been try to figure out why milage is down and hp seams to be down. 228hp and 368 flb. est. with program.
Had new heads put on about 9000 miles ago. When first picked it up. Could smoke the tires for half a block. Had been getting around 19-21mpg. mostly highway driving. Now have to put in 4 low to back a small trailer up the barn hill. Milage is also down to 9-13. Long trips goes up to around 15.
The engine was rebuilt about 100,000 miles ago and punch out .060.
On my 4th tranny. L460 Keep burning up second gear and band. last replaced about a month before heads.
Keep thinking that most of my problems are from low horse power and that timeing is off.

One other thing that happened this spring.
Going down high way, truck deid with a load boom. Took it in and was found to be 180 degrees out and split the muffler and pipe 2 ft in both directions. Seams to run fine both before and after, and machanic could not find anything or explain what happened. any thought?

**MrShorty** · 11-08-2009, 11:58 PM

-23--28 sounds about right. The correct parameter for checking timing, though, is to get one of the more expensive scanners that can read the cam retard parameter. This parameter is supposed to be at 0 +/- 2 degrees.

**mutant5776** · 11-11-2009, 01:52 PM

Mr Shorty.
Thanks for the info.
How much effect will an cam retard of 4.8 degree have. Did a test last night on way home from work. Found that timing is reading min -38.5 degrees with a max of -8. Idle is around -27.5. Worked on older engines when a lot younger. This is the first computer controlled engine that I have attempted to trouble shoot.
Any suggestions on where to look for what the pid's should read so that i have a base line. to work with?
With the program I am using. I am finding that the long and short term fuel trim is in the red a lot.
This is a program Ii am still learning. (Palmer Performance Engineering Scan XL pro with enhanced ).

**MrShorty** · 11-11-2009, 11:48 PM

I'm not sure how bad it will run with a cam retard near 5. It shouldn't be hard to get it right though. My impression has been that it is basically the same as the old distributors -- loosen the distributor hold down bolt and rotate the distributor until cam retard is in that +/-2 window.

Timing advance still looks normal to me.

Long and short term fuel trims that are excessively high or low indicate trouble with mixture control: fuel pressure/fuel delivery isn't keeping up with the engine or there's a vacuum leak or an exhaust leak or a slow O2 sensor or anything else that can adversely effect mixture.