Been having some good success in setting up the VE table on the Accel system. It is now running well all the way up to about 4100 rpm with minimal correction to the Fuel Air Ratio in closed loop.

Now I turn to the timing and advance table and need to start working on that. I have the stock knock sensor / electronic spark control hooked up (but not enabled) on the ECM. I could just start advancing the spark and monitor for knock.

Thought I would at least ask for input first. How much advance will a stock L98 tolerate? Right now I am at about 20 around idle and up to 45 at WOT over 3000 rpm.

 

mine is at 20 and i would go down lower as rpm go up not the other way around to avoid prefire at higher rpms

 

Red 87, Im afraid you misunderstand the purpose of ignition advance. It is to keep up with the increasing speed of the engine since the time required to produce a flame front after initial spark is a fixed value. The amount of ideal advance for a given engine combination to acheive maximum usable cylinder pressure is a fixed value for a given RPM. Once we know what this value is, we then increase ignition advance in pace with engine speed. Atleast this is how it works in a perfect world. In reality we make adjustments around changes in combustion to achieve maximum output without detonation.

Black 85 vette, I use an ACCEL DFI gen 6. You dont say what model youre running but generally, I would suggest you enable electronic spark control in the utilities menu and start out with about 15 degrees at idle to 40 at 4,000. Adjust your ignition map while watching the knock retard window. Increase timing until you see the knock retard begin to take it away, then back it off 2 degrees at the point you see knock retard. The basic rule which I mentioned above applies. Advance should increase with rpm. Play with it to get the most advance you can without knock retard.

 

I should make this note on what I said about using knock retard to tune ignition timing: ESC or knock retard will take more timing away than what is really needed to arrest knock. Its meant to run on the safe side. Another way of putting it is that you can run more advance, and make more power by staying out of knock retard. Some think that its okay to run the timing up and just let the ESC handle the knock. This actually robs power because the ESC will pull out more timing arresting knock than you could run if you stay out of knock retard with your base adjustment. I hope this information helps.

 

ASE doc; I have the Accel Thruster which is like the Gen 7 but less options. I can do it like you say plus use the logging function to capture knock retard with map and rpm to see where it is occuring on each test run.

I am with you on staying out of the knock retard and not let the ECM control it. That was part of what I am trying to figure out about setting the timing without letting the knock retard take over.

Thanks.

 

I recognize that my explanaition is a little over simplified. That's why I said we adjust for changes in combustion to acheive maximum performance without detonation. A more thorough explanation would include accounting for mixture density. Denser mixture, such as under load with high acceleration enrichment and low AFR, requires less advance. The higher density of fuel molecules speeds the propagation of the flame front.

That's why the ignition map uses MAP as well as RPM to create the advance curve. In conventional ignitions, the vacuum advance/centrifical advance serve this purpose. Lower manifold absolute pressure(higher vacuum) will want more advance, while higher MAP will want less advance. If you use the ignition map calculator in CALMAP to create an ignition map as a starting point, which I suggest, you'll see this general rule reflected.

 

ASE doc; Thanks for the good info. I was not clear on the relationship of the MAP to the advance. I will check the software and see what it says.

 

Hey, I try to help where I can. Sounds like you're putting the Thruster on a stock TPI. Is there a specific reason for that?

 

Yes. Owned this car for 8 years and I got tired of trying to troubleshoot a 25 year old ECM that was only made for one year, had very limited support, very limited scan tools, was prom based, and used a single year MAF/burnoff relay combo that cost about $500. I have worked to make this a very reliable car mechanically and the ECM was the last "old" piece left. Everything else has been replaced or rebuilt. Now I have a fairly new engine with a new harness and new ECM. It is running better than ever and "if" I decide to do some engine mods, I am ready for them.

I went with the Thruster because it has more options than the self-tuning systems but not as many as the Gen 7 and the price was in my ball park. I am very satified with the choice. I can monitor every sensor input to the engine in real time and do data logging to help in setting up the tables and troubleshooting. Huge difference from stock.

BTW; just went and looked but do not see an ignition map calculator in the software. I used a base config from the Accel web site that had most of the stuff pretty close. It started and ran first try after install and just had to tweek the TPS / idle / and timing to get it running OK. It has a quick set up in the menu and I selected "1 Bar MAP preset".

Here is my current spark table. See what you think.

 

It looks pretty good. I would go a little higher on the bottom row(high MAP). Perhaps try 40deg from 4200 and drop back to 34 at 3400. Just a thought. It looks like the the tuning software for the Thruster is alot more up to date than Gen 6. CALMAP for Gen 6 is DOS based and funky. But it works and like you say, reprogramming for engine upgrades is easy.

I forgot all about the 85 and the joy of dealing with its weirdness. No wonder you switched. No more $500 MAF module. The Thruster is wide band too. Very cool.

 

why do stock .bins show the timing drop at higher RPMs and higher MAP? Seems they are highest at moderate rpms at low load.

 

Timing will drop in most timing maps as the engine passes out its power band.

High "MAP" equals low manifold vacuum or high load. As I said earlier, dense AF mixtures require less advance because the higher density of fuel molecules causes faster propegation of the flame front.

 

Here is some useful info on tuning tips straight from the manufacturer.

 

Thanks for the tuning tips. You would think they would have made that part of the manual.

 

I agree it should be in the regular manual for everyone to read. To be honest i thought it was included with the software package. What i posted is just a small part of a manual that apparently was intended for the guys who got into selling accell fi systems but weren't familiar with EFI. The manual was available on the website for anyone to download, but disappeared about 4 or 5 years ago. It's about 6 or 7 mb in total and has a lot of good info. In fact i use it to tune factory systems since alot of the info applies to all efi systems. Holley also has a similar manual that disappeared from their website about the same time. It has even more useful info. PM your email addy and ill shoot you a copy of both manuals.

 

OK. This is starting to make sense. I read through the file and looked at the graphs and it seemed somewhat familiar. I have the Gen 6 book by Ray Bohacz and it has the same graphs. Since he wrote the course material for the dealer training I can see where the similarities come from. I will send a PM. Thanks a bunch!

 

ASEdoc:

Do the OEMs develop the timing tables on a dyno using SA that develops most TQ at a specific RPM/MAP? I presume other factors apply such as emmishions concerns?

 

Emissions compliance plays a big part in OE tuning. The vehicle's exhaust emissions have to remain below set levels throughout most of its operating range. In the time these cars were new, this meant that fuel and timing maps had to be kept fairly conservative. It also meant higher operating temperatures, great for reducing HC emissions, not so good for overall engine health or performance.

Today's engines, including the new LS series engines, are much more efficient, making more power from less fuel. OBDII self diagnostics and enhanced emissions systems are also much more effective at reducing emissions without significantly affecting performance.

In most states today, emissions testing of OBDI vehicles is limited to idle emissions, making older performance vehicles much easier to tune for compliance.

 

Most of your question about timing has been answered but I would suggest looking at a stock timing table bin file and maybe starting with that, but not the ARAP one. I think 45 deg at WOT is 10 deg way to excessive. I saw some timing retard on the factory ecm at 36 deg timing on my L98 over 4000 rpm. Not sure how you are getting away with 45 at WOT unless you mean free revving off idle to max rpm. There is no load there so you can get away with more timing.

 

Post #9. Looks like he dropped the SA at WOT to 34d

 

yeah cant see the pic at work. But now I can, and i'd smooth that table out alittle bit in the areas where it goes from 45 deg to 34 all of a sudden over a 400 rpm window.

Like 72 kpa, in the 3400-3800 rpm range, you go from 34 to 45... thats a steep rise and really isnt needed. I'd probably lower the 45 down to 40 max for the values between 72kpa and 42kpa.

WOT looks fine except in last cell theres a 0 at 5700 rpm...make that 34. 34 is a good place to start on a stock car but may find it will take 35-36 on 93 oct and make power.

And at 77.8 and 83.x kpa, you can add 2 deg entire row if you want

 

Orr89RocZ; thanks for the tips. I am going to be trying to get my timing pretty close before a trip to the dyno. Hope to get there in the next couple of weeks.

Appreciate all the helpful posts guys.

 

Well ain't this the pits. Went out to do some testing. Input all the initial changes to the timing and went for a drive. It started running rough then A/F went lean. Closed loop was showing 25% correction. Eased back to the house and put the fuel pressure guage on it. Showed it at about 20 lbs. Fuel pressure reg diaphram is new so I am thinking the fuel pump has an issue. I have a spare in the shop but it was not how I wanted to spend my shop time. Had to put front wheel bearings in my pickup this morning. Guess getting the timing done on the Vette today was not meant to be.

 

That sucks. Be sure to check fuel filter for restriction, and if you end up replacing the pump, replace the filter with it.

 

hey guys i'm kind of interested in the accel ECM can i run that on TBI and does anyone have a link or website where i can take a look at this set up?

 

Yes it will do TBI. Settings under injection type are: sequential, staggered batch, tbi and tbi dual quad. It can handle just about any model of ignition system also.

Here is a link to the product info. for the Thruster which is what I am using. The Gen 7 is the pro version.

http://go.mrgasket.com/newproducts/flyers/74342G.pdf

Here is the main site.

http://www.accel-dfi.com/

I will have to admit that their product support is pretty poor. Just trying to find information can be tough. Product is good quality and it works great.

As you are looking around I would say also have a look at Holley. They have better documentation and support.

 

Ill throw in my two cents here. The discontinued Gen 6 DFI, which I run in my IROC project, uses an early style Motorolla ECM, alot like the ECMs used in the 3rd gen f-bodies. It's a very durable unit. Their wiring harnesses are very well made. Aside from this and their Billetech Distributor, I have not had good luck with Accel products. The 300+ ignition system that I originally installed with the DFI, quit on me and alot of the parts Ive installed for customers have ended up failing. As a result, I no longer sell Accel parts.

I will continue to run the Gen 6 DFI in the IROC, as long as it continues to perform without issues. However, and it makes me very sad to say, I cannot in good conscience recommend Accel products.

 

Back on the road and working on the timing. Only had a little more than an hour but I did get to make a couple of runs and verify that the knock sensor was working properly and I was able to log the ECM data. In the picture below the red is RPM, the blue is MAP, the purple is total advance and the green is the knock retard in degrees. You can see at about 3,000 rpm and 77 MAP that the knock sensor fired and the total advance was pulled down 2 degrees. So I went into the table and reduced the advance about 4 degrees and made another run which was clean. Need to keep working on adding advance in different areas until knock is detected and then pull it out. It is great being able to capture the data and see exactly what happened and when.

 

Finally got some time and a nice day to do some more work on the timing. The VE table is looking pretty stable at this point. I made a number of runs up to about 65 mph and backed out any knock retard that happened. Most of it was in the 3200 - 4200 RPM with MAP at 85 to 95. Here is the timing as of right now;

http://www.flickr.com/photos/17576549@N05/5384969762/

Here it is in 3D graph form;

http://www.flickr.com/photos/17576549@N05/5384969800/
Trying to schedule some dyno time this week to work the higher RPMs

Any comments on the timing as it is now?

 

Generally, we want to try and smooth out any dips or peaks in the graph. It should make a smooth transition from lower rpms/high MAP to high revs/low map. As you test you may feel those dips and uneven areas in the engine's acceleration.

 

[QUOTE]I think 45 deg at WOT is 10 deg way to excessive. I saw some timing retard on the factory ecm at 36 deg timing on my L98 over 4000 rpm. Not sure how you are getting away with 45 at WOT unless you mean free revving off idle to max rpm. [QUOTE]

These quoes are from Orr.

You still have 40d SA at WOT. Seems like a lot of SA for WOT.

 

Does seem excessive. i cant view the pics right now. Not sure if there are any other timing functions in the ECM that pull timing via air intake temps, coolant temps, misc adders, etc...not just knock control.

But as said a few posts above, avoid peaks/dips in the graph and smooth out once you find a good base map to work with. Drive around in various loading situations and make timing changes like you are doing now. Then in the areas of engine operation where you didnt hit yet, smooth the transitions out. 3D mapping of the table helps this alot. Its very hard to hit ALL the areas of the timing table in normal driving situations so work the areas you can hit and fill in the gaps later.

 

I just reread your post. I had somehow missed your point that you had to pull out timing in a certain rpm/MAP range. The fact that you experienced ping at those particular points in the map is interesting. It might be worth looking at your Base Fuel Map for a possible lean condition in that range.

In response to Orr89RocZ, in the Accel DFI system, aside from knock retard, the ignition map is absolute. There are no outside factors affecting timing.

 

So it experienced abit of timing retard in those areas? Your map there has lower timing than the WOT column and the lower map ranges...you can see the dip in the 3D graph.
Is it going lean there? How does the motor run in those rpm ranges and say 70-80 kpa?

In the graph, you can see map goes up while rpm seems to hold constant and timing was pretty constant until knock was detected... more load needs abit less timing so it makes sense to pull some out...unless you did go lean like above said. I'd check that area. 30-32 deg in that area should be ok and you probably could get away with abit more timing there. You pulled 4 deg there and it now runs ok with 30-32. Check the fueling at that spot and see if it will take that timing back.

 

ASE doc & Orr89RocZ;

Thanks for all the help! I saved all the data logging that I did when checking the knock. Looking at the data I see knock at about 3000 rpm / 80.5 map. ECM pulled 5 degrees out at that point. With 5 degrees removed total advance was 30.5. I also was logging 02 correction. A:F was set to 13.73 at that same point and O2 correction shows -2.16 so it was actually running a little rich (if I understand this correctly). I was not running it hard and throttle was just 47%.

Calibrated SOP (seat of the pants) sensor does not detect any issues. Runs clean and pulls pretty good. No obvious dips, lagging or other indications. In fact, if I did not have the data logging I would have said the engine is running fine. Right now I am tuning to the data not a "performance" issue.

I will go back and monitor my fuel pressure, duty cycle of the injectors, and actual O2 reading. Then see what it is looking like at that same spot. Anything else I should be looking at? Should I go richer than 13.7?

 

Sounds good then, leave it around 30 in that area. I used to make max advance of 34 deg and have it all in by 3200 so i'm kinda surprised it only wants 30 at 80 kpa and 3000 rpm but give the motor what it wants.

I like getting abit richer by 80kpa if possible. I'll do the 14-15 to 1 air fuel between idle and 70kpa but taper off to 13's to 1 by 80 and 12.5-13.0 depending on where max power is at WOT. Engine seems to run smoother through that transition from half throttle to full throttle when the fueling gets progressively richer. I mean most factory systems have PE (Power Enrichment) mode enabled in the heavy part throttle ranges. Closed loop will drop out and it will get richer. More load like that needs the extra fuel to make power and keep cylinder temps down.

 

OK. Things are starting to come together. Had to get my brain on the right track thinking about rich / lean. I was thinking of it as the ECM and VE table worked to keep the A:F at the target value. Since it was not having to add any fuel I was thinking "not lean". But after you guys posted about the fuel in that range I went back to the map and moved it from 13.7 to 12.0 in the area that was knocking.

Then I started moving the spark back up. Ended up around 34 degrees in the area that had been having problems. So thanks to you guys I think I am on the right track. It feels better and the data is looking much better.

Now I will work on smoothing out the tables.

Thanks!

 

Out for some more testing today. Starting to go for more RPM and speed. It is now pretty good up to 75 mph under all load conditions.

I do have another question for you. This car has always, even with the old ECM working well, had the temperature creep up a few degrees when doing stop and go driving in town. About 2 degrees per stop sign.

Radiator is fairly new.
Debris cleaned out between condenser and radiatior.
Replaced water pump with a high flow pump.
No underdrive pulley.
Cooling fan is on the entire time.

So I don't think it is the cooling system. It will run on the highway around 186 degrees all day long. But in town it will creep up to 200 or so. I tried the AFR around 13:1 and reduced the advance in the areas of slight load and low rpm. Seemed to help some but not totally.

Am I even thinking right here?

 

usually you want abit more advance in those low rpm low load situations and you should see a cooler motor but I've also heard too much advance will show the same thing.

It could be that the fan is not powerful enough to pull enough air thru the rad at low speeds. What t-stat do you have?

 

It is the stock fan and seems to move air OK. No problems keeping temp down when stopped at idle even with the AC on. Thermostat is a 180.

Have not tried increasing advance.

 

Im going to differ with Orr89RocZ here. Increased advance will generally always increase operating temperature. However, your rise in temp when driving in town is not really abnormal. We should expect to see a slight rise in temp lugging around in stop and go traffic. Consider the fact that your water pump is turning much more slowly on average. This will cause more heat to collect, especially in the upper portion of the motor, where the temp sending unit is located. Also, while your fans do a sufficient job of cooling the radiator, they do not match the cooling effect of air pushed through the core at highway speed.

When you say your fan is constantly on, you dont mean you have it wired to run constant do you? I trust you have it running via the Accel's fan control. It would be normal for it to run steady in stop and go traffic.

 

ASE doc; the fan is controlled by the ECM. Right now I have it set low so I can eliminate the fan as part of the temperature change.

Is it even worth the effort to change fuel / timing to address this?

 

If you believe the engine is suffering, it's your call whether to address it. I'm meerly saying that some rise in temp is normal in crowd conditions. If you were to address the issue, i would start by reducing ignition lead and richening AFR. Your fuel efficiency will suffer for the changes. Also, beware of the factory temp gauge. They are notoriously inaccurate.