1995 K1500 LO5 tuning- Autoprom

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.

Tuning can be addictive!:rockon:

dave w

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.

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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.

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Originally Posted by billygraves

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.

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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...

Can I talk someone into looking at the WOT runs in the attached datalog and tell me if you see anything out of the ordinary? Is the noise in the 02 trace normal? WOT runs start at about 13:30. Thanks.

It's not noise, it's cross counts you see moving O2 signal above and below Stoich.

Right at you WOT you can see it go flat. This is because the PCM goes into Open Loop during PE. See your O2 numbers around .930v? This is a very rich reading and good to see at WOT.

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Originally Posted by billygraves

If you LEAN the calibration out @ WOT, just keep in mind that in SOME engine combos it is FAT because of Mal-distribution problems that lie within the intake/TBI. Some cyls run Lean at certain RPM and are on the opposite side of the O2 measuring. So a A/F Ratio meter (on the other side) would be a good check. (And not to miss this point, some fuel is FAT to actually COOL the top and ring pack IF pulling a load up a long hill ect ect ect......)
(I was coached on a 5.7L TBI and with the intake sometimes cyl 5 runs lean and 7 runs FAT. This is because of the fuel is being robbed from one and pulled into the other. This was the intake release person I had discussions with in the early 90's about intake gasket leaks and how to help seal them.)
The TBI steers the fuel toward the rear of the engine where it is a bit rich or Fat. TBI was used by the companies because PFI was 900 additional an engine. This was back in the early 90's.

For those of you who are considering TBI use in High RPM ranges, I would you look at some other approach and go PFI. If you look @ the Holley 4 BBL TBI you will see them use a small tab that rests against the injectors. It is for this reason.
As the fuel is blown into the air stream at hi rates the fuel stream is moved toward the center of the air stream and this ends up with the outer 4 cyl very lean and the inner 4 very rich. Another way to see this is hold a hose with a stream of water up in the air and as the wind picks up it moves the liquid or bends it. The same thing occurs at 5,500 to 6,000 RPM or at an air flow rate, inside the engine. Just be careful.
The reason I know this is I ran one of Holley's first 4bbl TBI on my 9 second Vega. With 2 fuel pumps and about 6 passes with a best time at 10.80 from 9.40 with a 1050 dominator, I pulled it and reinstalled the dominator. The engine headers were coated and had turned blue from being so lean.

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On a factory TBI setup there is no possible way for 5 and 7 to draw from each other. They get fuel from opposite sides of the intake.

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Originally Posted by Fast355

On a factory TBI setup there is no possible way for 5 and 7 to draw from each other. They get fuel from opposite sides of the intake.

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He might have meant 5 and 8. I've been told more than once 8 will run rich and 5 lean on a SBC running a dual plane intake. These cylinders share the same runner out of the plenum (passenger side rear). When I recently changed the plugs on my LO5 they all looked good except 8 which was noticeably rich. 5 had slightly less color (lean) then the others.

5 and 7 are the two that get cross fire in ignition in a little tidbit billygraves gave us a few days ago. So he probably switched them up.

Took the truck on a one-day business trip and decided to check fuel economy. I topped off at the Chevron station in Quincy, WA and drove I-90 to Spokane and back. The tunerpro display bounced around 16-17 mpg with the cruise control set at 75 mph. Coming back I got into an awful headwind; one of the worst I've experienced on this stretch of highway. MAP spent a lot of time in the 80-90 kpa range with PE active The display bounced around 10-11 mpg. At one point on just a slight grade the trans actually downshifted. Anyway gassed up at the same Chevron station in Quincy and averaged 13.0 for the trip. Worst highway mileage ever for this truck.

I also noticed it bouncing in and out of DFCO. When it left DFCO at 1,200 rpm the added fuel would increase rpm to around 1450 and after the delay it would reenter DFCO. I was on a pretty long grade and it did this several times. I can't think of anything in the tune I would have changed to cause this, or perhaps I just never noticed it. There is a DFCO rpm hysteresis set to 200 rpm in the stock tune. I might try increasing it to 300-350 and see if makes a difference. It will probably be a while before I can repeat those conditions though.

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Originally Posted by Roadknee

Took the truck on a one-day business trip and decided to check fuel economy. I topped off at the Chevron station in Quincy, WA and drove I-90 to Spokane and back. The tunerpro display bounced around 16-17 mpg with the cruise control set at 75 mph. Coming back I got into an awful headwind; one of the worst I've experienced on this stretch of highway. MAP spent a lot of time in the 80-90 kpa range with PE active The display bounced around 10-11 mpg. At one point on just a slight grade the trans actually downshifted. Anyway gassed up at the same Chevron station in Quincy and averaged 13.0 for the trip. Worst highway mileage ever for this truck.

I also noticed it bouncing in and out of DFCO. When it left DFCO at 1,200 rpm the added fuel would increase rpm to around 1450 and after the delay it would reenter DFCO. I was on a pretty long grade and it did this several times. I can't think of anything in the tune I would have changed to cause this, or perhaps I just never noticed it. There is a DFCO rpm hysteresis set to 200 rpm in the stock tune. I might try increasing it to 300-350 and see if makes a difference. It will probably be a while before I can repeat those conditions though.

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I have hit those kind of headwinds before and for future reference you would have done better in 3rd gear with the engine rpm higher and out of PE.