Help me understand spark timing

[gpr]

I am trying to tune a 5.3L 2002 pickup. I logged it for the first time last night. For some reason it is getting KR once in a while at part throttle while cruising down the road. I'm not sure if it is false knock or not. Anyway i high light the part in the log where the KR is occurring and going into the tune tool to see where it is in the spark table. The cells selected show a value of -.5 and -.7 however the actual spark timing is much higher. It is showing an average of 28 degree's advanced. How is the high octane spark table showing such a low number yet the actual timing that is being scanned so much higher?

I understand that other influences such as coolant temp, IAT etc.. affect the spark but under normal operating conditions shouldn't the spark timing follow the spark table pretty close? Also I believe there is a PID that shows which table it is pulling spark off of, what is that PID for the LS1 pcm?

[gpr]

Oh i have one more random question. On this pickup the tow/haul button does not work anymore. I don't use it for a lot of towing but when driving in the mountains in regular mode it does a lot of searching for gears and the constant shifting is annoying. Is there a way to get the tow/haul transmission tables to see how they are setup, so i can make it search for gears less in regular mode?

[bobbycollier]

If you could post a log file and your tune file, that would help!

thanks, bc

[gpr]

Okay here is my log. The tune is basically stock, and i haven't messed with any spark timing values. I know i need a wb to see what the actual a/f is, but i haven't had the time to install it. plus at part throttle it should be in the 14.7 range anyway.

I have since installed the stock tune and the knock retard has almost completely gone away at part throttle, but I'm still unsure how the ecm is getting the value for spark advanced as it seems it is all over the place.

thanks for any help you can give to straighten me out a bit.

I was wondering if i was getting KR at part throttle because i was shutting off the EGR and air pump to hopefully increases mpg.

[nathans1987]

your only doign 1500 rpm the map is high 80+ and afr commanded is 14.7?? it would probbaly be real not ideal conditions i dont think. thats my opinion but i dont know much still new to this.

[WeathermanShawn]

GPR:

I am not sure you are logging the corresponding GM.DYNCLAIR.DMA PID to match up what spark value you are 'commanding' in the High-Octane Spark (or did I just miss it?)

I am curious what gear are you in with that 'part-throttle'. I would imagine some overdrive gear, as you have a really high MAP for such a low throttle opening.

If you are punching it in an overdrive gear you are more likely to experience a lot of stress on those pistons..probably is real knock. Especially at such a low Rpm..it is evident you are not in PE Mode, so you are not getting the benefit of additional fueling.

Seems like lot of spark for that low of an Rpm and high MAP.

[LS1_Dragster]

If it were me I would richen it up some at the MAP values and the commanded AFR just to see if it goes away. I took your tun file and made some changes, I'm not saying it's correct or even the correct way to fix the problem but if the knock goes away it will give you a direction to fix it.

Lee

[gpr]

Thank everyone for the help. I'm a newbie at this as well and still learning how everything is working. That was a log file of my drive into work and i was cruising down the interstate, then i get off the interstate and pull on a highway cruising at ~55 mph. I was very surprised to see that much KR just cruising along, and that is why the a/f is at 14.7 as i was not in PE mode yet.

I was thinking the same that, as sometimes it hits very high spark timings. However I haven't messed with the stock spark tables at all. I will try another log and add in the commanded spark PID. I think my main problem was i took the stock tune and changed a bunch of stuff then went and logged it, so i have no idea what is causing the excessive KR. Put the stock tune in and a lot goes away. I'll have to start changing one thing at a time from now on. It was weird cause with that tune i also got really poor gas mileage, when i was taking things off like cat protect mode, air pump, and egr to hopefully get better mpg's.

Do you guys have any other suggestions on PID's to log?

[LS1_Dragster]

I don't believe it's spark, I thinks it's too lean. With a WB and autoVE you would quickly find the problem.

BTW, keep the EGR. By disabling that it would definitely induce knock and reduce mileage. A lot of people love to disable it and I'm not sure why!

I would go back to stock and start over and richen it up a little in the areas it knocks.

[gpr]

I agree, I think my biggest problem is that it is lean from a few mods i made and i need to get my WB hooked up to see what is really going on.

I like disabling EGR because it will costs you power at WOT, but at part throttle i will leave it alone.

The more i think about it, how would I be lean at these part throttle cruising conditions? The engine should be in close looped mode and the a/f should be around 14.7:1, unless my o2's are going bad, correct?

[LS1_Dragster]

EGR doesnt work at WOT, at least none of the 3 cars I have....

Here's a little info:

Early (1970s) EGR systems were unsophisticated, utilizing manifold vacuum as the only input to an on/off EGR valve; reduced performance and/or drivability were common side effects. Slightly later (mid 1970s to carbureted 1980s) systems included a coolant temperature sensor which didn't enable the EGR system until the engine had achieved normal operating temperature (presumably off the choke valve and therefore less likely to block the EGR passages with carbon buildups, and a lot less likely to stall due to a cold engine). Many added systems like "EGR timers" to disable EGR for a few seconds after a full-throttle acceleration. Vacuum reservoirs and "vacuum amplifiers" were sometimes used, adding to the maze of vacuum hoses under the hood. All vacuum-operated systems, especially the EGR due to vacuum lines necessarily in close proximity to the hot exhaust manifold, were highly prone to vacuum leaks caused by cracked hoses; a condition that plagued early 1970s EGR-equipped cars with bizarre reliability problems (stalling when warm, stalling when cold, stalling or misfiring under partial throttle, etc.). Hoses in these vehicles should be checked by passing an unlit blowtorch over them: when the engine speeds up, the vacuum leak has been found.

Modern systems utilizing electronic engine control computers, multiple control inputs, and servo-driven EGR valves typically improve performance/efficiency with no impact on drivability.

In the past, a fair number of car owners disconnected their EGR systems in an attempt for better performance and some still do. The belief is either EGR reduces power output, causes a build-up in the intake manifold, or believe that the environmental impact of EGR outweighs the NOx emission reductions. Disconnecting an EGR system is usually as simple as unplugging an electrically operated valve or inserting a ball bearing into the vacuum line in a vacuum-operated EGR valve. In most modern engines, disabling the EGR system will cause the computer to display a check engine light. In almost all cases, a disabled EGR system will cause the car to fail an emissions test, and may cause the EGR passages in the cylinder head and intake manifold to become blocked with carbon deposits, necessitating extensive engine disassembly for cleaning.

[gpr]

Okay, while we are on the topic, what about the air pump? My understanding is that this blows fresh air into the exhaust to help out the emissions in the tail pipe and when going threw the cats. If i turn this off does it have much of an affect on anything?

[LS1_Dragster]

As far I as I know, the air pump pumps oxygen into the cat to help burn unburned fuel, a good thing. Of course there may be a few HP lost driving the pump but other then that It's a good thing to have.

Clip:

Since no internal combustion engine is 100% efficient, there will always be some unburned fuel in the exhaust. This increases hydrocarbon emissions. To eliminate this source of emissions an air injection system was created. Combustion requires fuel, oxygen and heat. Without any one of the three, combustion cannot occur. Inside the exhaust manifold there is sufficient heat to support combustion, if we introduce some oxygen than any unburned fuel will ignite. This combustion will not produce any power, but it will reduce excessive hydrocarbon emissions. Unlike in the combustion chamber, this combustion is uncontrolled, so if the fuel content of the exhaust is excessive, explosions, that sound like popping, will occur. There are times when under normal conditions, such as deceleration, when the fuel content is excessive. Under these conditions we would want to shut off the air injection system. This is accomplished through the use of a diverter valve, which instead of shutting the air pump off, diverts the air away from the exhaust manifold. Since all of this is done after the combustion process is complete, this is one emission control that has no effect on engine performance. The only maintenance that is required is a careful inspection of the air pump drive belt.

[WeathermanShawn]

Dragster, I think he is running closed-loop off the MAF. Since he is not in PE Mode, he would not be referencing the Commanded Fuel in Open-Loop Table anyway. Am I right about that? (though that table is way off!)

I will not get in the EGR debate..the 2002 LS1's are all disabled, so whether that is really this guys issue I do not know. As far as AIR..I took it all out. Made the engine compartment a little tidier and I just put the AIR Pump enable temperature to max..so it is no issue. But, check with your State's Emission Testing. If they do a visual, you may fail.

As long as everything mechanically is sound (plugs, wires, PCV system, O2 sensors, etc) I would just suggesting reloading a completely fresh stock tune file. Then do a log. Then go find some real high octane fuel (Sunoco, etc.) and run another log. Then you will know if that knock is real.

I respectfully disagree that it is necessarily a lean condition. Look at how low those rpm's and throttle opening are. He should be at 14.7 AFR. But OP, you are going to need a wideband. You can not just go by the narrowband O2's.

[LS1_Dragster]

If his EGR was enabled at the factory then they may have increased timing to take that into account.

Also, on my 3 cars I'm working on now all have 35+ timing at cruise with no issues. Plus I always think GM knows what they're doing for the most part, our jobs are to modify the tunes to match our upgrades and our immediate environments. GM's not going to let thousands of trucks/cars loose that ping with normal driving.

By richening up the areas that are pinging would let him know if it's real or false knock either because of his mods or his O2's are going bad. As I stated earlier this may not be the correct way to fix it but it will help decide what direction to go.

I absolutely do not know enough about tuning with the different OS's but usually simple deductions will lead you the right direction. I didn't know that the table B3605 was not used when using a MAF, I figured it was referenced to...Thanks for teaching me.

[gpr]

When you are running in closed loop how does that work? i would assume that you are using the MAF and then the o2's are used for fine tuning the a/f?

Also if that is the case the readings from the MAF and then your VE table is referenced for the correct amount of fuel to be injects, is this correct on how GM does it?

The tune i was running had the EGR disabled, the air pump turned off, and cat protection disabled. I do not have emissions testing where i live. Some how a few components have fallen off of this truck, its was weird. :) I disabled EGR from some intakes i have seen in the past that were gummed up and black. I will leave it enabled until i get more comfortable with tuning and then try turning it off to see what its affects are.

Anyway I am a newbie at tuning newer GM gas engines, but have tuned tons of other stuff so i know the basics very well. I'm trying to get familiar with how GM controls everything for when my new camaro gets here i can tune it.

The more i think about it, it could very well be from running lean. This is my uncles old farm truck. I serviced it up put new plugs wires etc... but it is an 02 with 95,000 miles so i bet the o2 sensors could be bad. I simply need to get my butt in gear and get my LC 1 hooked up, as i truly won't know what is going on until i do that.

thanks for all the help guys!

[WeathermanShawn]

Dragster, anybody that can go 148 mph knows what they are doing!

I have the same difficulty bouncing around with different OS's also.

Do you agree perhaps the OP should start over with a fresh stock tune? I think he even admitted he may have mixed and matched some tables.

I think once he gets a wideband it will clear a few things up. While his Trims look decent, you never know how the narrowbands are switching..we really do not know his true AFR.

[LS1_Dragster]

Shawn, I did mention it back a few responses ago that he should go back to stock and start over. With 95K I bet the O2's are shot!

I've been using fuel injection on every car I've built or raced the past 8 years but it was with the Holley Commander 950. The Holley is a thousand times easier to tune. The dragster was my first with GM's computer and it has been a real task figuring out what GM was doing. Now throw in a bunch of different computers and OS's and open loop vs closed loop vs speed density etc. and it gets real challenging trying to be part of this site!

BTW, I'm too smart (read chicken) to go 148MPH, that's my wife doing that! Her previous car was a '90 vette that did 8.65@165MPH, she's crazy if you ask me!

Lee

http://www.horsepowerracing.com/90_corvette/drag_racing/burnout.jpg

http://www.horsepowerracing.com/90_corvette/corvette_10.jpg

[LS1_Dragster]

I also did 2 mid 90's computers/programming with TunerCat and Datamaster - talk about easy! Everything was simple and straight foreward.

[WeathermanShawn]

Sweet ride!

That is quite a wife you have there!

I might hit that speed falling downward off a mountain pass..otherwise I have probably lost my nerve to even try it.

Was that run at SLC?

OP (sorry for the hijack..not being rude..)

[LS1_Dragster]

Yes here in SLC, we also ran it in Boise but I backed the throttle down to 35%, here in SLC we ran it at 40% throttle. It didn't like slippery tracks! So we sold it and I built the dragster. I think it would of dipped into the 7's all out. On the dyno it made 1100 torque and 800HP, so depending on who you talk to that's 900-950 at the crank.

Sorry for sending your thread sideways....I think the thread is done now that he should replace his O2's.

[gpr]

You ran 8's with only 40% throttle? that is amazing! what is the elevation out there at salt lake?

yeah this thread is dead, there is work i need to do and get it all lined out. Hopefully this weekend I can get some time to work on it. BTW, if the o2's are bad, shouldn't they set some sort of code indicating it is trying to adjust the fuel out of the normal operating range? (or something to that affect)

BTW, what does OP stand for? original poster????

[LS1_Dragster]

Our elevation here is 4400 feet but our corrected altitude in the summer is 7000-7500 feet! The motor was supposed to be a mild 632cu with 11:1 compression but it made 200HP more then I wanted. In fact when I built the car I wanted her run 9.90's. Once I got the tune right and suspension worked out 40% was all I'd give here, the secondaries never even opened!

I figure the O2's aren't dead just lazy or off. 100% of the people in that situation would never know the computer was pulling a few degrees out and they go about their daily lives, but since you have the reader you were made aware of it.

[chevy052500hd]

The tow mode trans tables will be labeled performance. If you would like to add a manual switch you could by changing D0409 from data buss to one switch.

[WeathermanShawn]

Yes, OP means Original Poster. It is a nice way to say it (I guess). Sometimes with all our ID's etc., you do not always know somebody's name. And some people have legitimate privacy issues, so while it may sound impersonal..OP is it.

And to reiterate, a set of fresh O2's can do wonders.

[gpr]

The tow mode trans tables will be labeled performance. If you would like to add a manual switch you could by changing D0409 from data buss to one switch.

sweet, so it looks like if you install a simple open/closed switch with one end going to a good ground and the other end going to Pin 71 on the ECM then this switch will replaced the tow/haul button on the gear shifter? Am i interpreting that correctly?

What does D3601 Performance Mode Pressure Adjust do? as it is disabled but sounds intriguing like it will change pressure in performance mode based on how you drive?

[chevy052500hd]

There are seperate pressure tables, I am assuming that this would enable or disable that table.

edit: That is how I inturperted that also, I haven't tried it, but knew it was in there.