1995 K1500 LO5 tuning- Autoprom

[dave w]

I ran the tank of 87 octane very low and topped it off with Chevron 92. I don't have any WOT knock retard in first or third gears now, but still have up to 5 degrees in second gear. I've read where a worn tranny can cause this. I'm running the original 4L60E with 160K. Here's a datalog if anyone cares to look.

I looked at the data log for knock retard, nothing alarming. A few cells above 80 Kpa had an average knock retard of about 2 degrees. I can often eliminate knock by retarding spark advance by 0.50 degree increments in the cells that have knock.

dave w

[Roadknee]

Thought I'd provide an update of my efforts the last few weeks. Got to say I really enjoy this Autoprom. I have it installed in the glovebox. It is so easy to access with the laptop when I want to tune, or disconnect and close the glovebox for daily driver operation.

I'm on the third tank of 92 octane fuel now. Also pulled some timing (0.5-1 degree) in the 95 and 100KPA area of the spark map. The knock sensor is still pulling timing in the upper rev ranges at WOT; around 4 degrees above 2,800 rpm. Seems it only wants to tolerate 10-11 degrees of WOT ignition lead. I posted earlier that this was only occurring in second gear. However, in recent WOT runs I've seen KR in 1st gear too. It's interesting that KR is about the same with 92 octane as it was with 87. The 92 has eliminated the part throttle KR though. I suppose next step is to pull that 4 degrees out of the high kpa areas of the spark map and see if I can eliminate knock sensor activity in entirety.

I made another almost 400 mile loop over three mountain passes, datalogging, and massaging the VE tables. I had them in pretty good shape already, so adjustments were pretty minor. After I've been on the highway for a while and the engine is fully warmed, BLM's are consistently in the 125-129 range, and mostly 127-128. It feels very smooth. I did notice something interesting driving back worth mentioning. I was coming down the east slope of Stevens Pass, spending a lot of time decelerating. Outside temp was 20F or so. As I continued to down the hill the BLM's on decel rose to the mid 140's. Coolant temp was down to 177 from 183 where it normally cruises. Once the pass flattened out some and I got some heat back in the engine, BLM's returned to 127-128.

I've also fiddled some with the open loop AFR table to help with warm-up. In the stock bin, the engine enters closed loop at -1.8C and starts block learning at 20C. At colder temps, some of the BLM's would get into the low 100's. As the motor warmed up and I accelerated through these cells the INT could not move the BLM's fast enough to prevent some minor lean surge. I'd have to drive around for 1/2 hour before the BLM's would return to normal. I enabled use of the open loop AFR table in closed loop. To my surprise, the stock table with target AFR's of 16:1 in many of the cells was reasonably close. The engine goes into closed loop and the INT makes minor adjustments as needed to target the switching point of the O2 sensor. BLM adjustments are not made unless the values in the open loop table are equal to the Stoich AFR. I set all values in the table 80C and above to 14.7, which is what I have Stoich AFR set to. I later reduced the Maximum Temp for AFR lookup in Closed Loop to 80C to achieve the same outcome. I could have obtained a similar result by simply running open loop until 80C. I personally like running closed loop during warm-up because the engine will tolerate it, and uses less fuel in the process.

I'll admit tuning is addicting. As we move into spring though I'll need to burn a chip and remove the Autoprom to temporarily eliminate the temptation. It'll be time to move on to other things till winter.

[dave w]

Tuning can be addictive!

dave w

[HaulnA$$]

Sounds to me like your knock issues are mechanical rather than in the tune. L05's are infamous for false knock. You should be easily be able to run at least 25 deg. total advance at WOT with 92 octane and real knock counts diminish with the benefits of gearing, i.e they will increase as you go from 1st to 2nd and 2nd to 3rd as the load on the engine increases.

Several things can cause false knock. Valve train noise, especially from flat tappet cams can do it. Timing chain slap is a big cause. Lastly but least likely in your case is in my view bad valve stem seals. Oil entering the combustion process can cause knock.

Try running some straight 30W oil on your next change and test the chain by loosening all the rocker arms relieving spring tension. Remove the cap and try to move the distributor shaft. If it moves back and forth excessively, the chain is loose. There are ways to de-sensitize the knock sensor but I would only recommend that if you had a lot of tuning experience and eliminated all the mechanical issues. Hope this helps.

climbing BLM's on decell is normal and actually desirable for fuel economy.

[billygraves]

.............

[Roadknee]

Good points Billy. I have taken pretty good care of the truck, and addressed most of what you posted above. I verified the balancer with a piston stop last month. I replaced intake, TBI and EGR gaskets a few years ago. Copper terminal cap, rotor and wires are fairly new (good 8mm silicone wires). Motor bay is kept clean and doesn't leak a drop of oil. A few weeks ago I decarbed the top end using seafoam followed by a shock treatment of ringfree in the fuel tank. O2 is newer heated Delphi and switches very well in the datalog.

Although it runs well for a 1995 truck, I have to accept this is the stock 160K motor and trans and very well could have some mechanical problems. Oil consumption has increased over the last few years. It doesn't smoke, but I am adding a quart between changes. It's also consuming some coolant, and not from on external leak.

[billygraves]

.....

[Roadknee]

Next time you change our Oil and filter, I would add the pre-filled filter and the rest of the 5 or 6 quarts. Start it up and run for a min. Shut off. Then check the oil level. I have seen a number of dipsticks that are 1/2 inch long. I use a small tubing cutter and cut off the amount. Now the level is true and you won't be adding another quart.
Maybe the seafoam is better now but a few years ago the only way to de-carbon the chambers, pistons tops, and intake valves was to use the GM stuff. We tried a number of these at the GM Tech Center using a bore scope to check before and after. That is why I suggest you let it sit OVER night and not the hour. If you get the engine as hot as possible, pour the TOP ENg Clnr in and stall the engine the last 1/3 can it really works the best. If ya run Valvoline I have had the engine consume a quart every 500 miles. To fix it, change to Castrol if your using conventional oil. With 3 yrs on the intake and TB gaskets, check them again. Don't run the dexcool either.

I've run Chevron conventional 10W/30 oil for 100,000 miles. I've owned the truck since about 50,000. When newer it would use less than 1/2 qt in 3,000 miles. Now it's a quart every 1,200 or so. 4-3/4 quarts with a filter puts the oil level at the full mark on the dipstick after its been run. I run Chevron 5W/30 oil in our '06 Yukon and it doesn't use a drop in 6,000 mile oil change intervals.

No dexcool here. And it's used coolant for a long time; even before the intake gasket change. I've kinda been looking for a reason to overhaul it, port the heads, install a bigger cam...