We'll I'm trying to work out my cam surge problem. I've tried removing and advancing timing as much as 12 degrees in the affected cells with no improvement. The cam surge does get noticeably worse as the car goes into closed loop. BLMS are alittle high on the right side but it looks like both O2 sensors are acting normal. Is it normal for cam surge to get worse as a car goes into closed loop? Is there anything else I should try besides playing with timing to remove cam surge?

 

leaner = more cam surge with a big cam

So when you step into closed loop the A/F goes leaner compared to the regular open loop A/F table, you will see this on your 02's, you are mostly likely running in the 8-900mv range when in open loop under normal driving condititions, you hit closed loop and thats it.

I've tuned my car to only lean out so much and then tell the BLM's to stop leaning out past a certain point where I notice cam surge, by adding fuel with my 24X/25X cam on a 109 lsa in 6th gear with 3.73 I can pull from 1500 rpm and the car is smooth, let the o2's lean out where they think its 14.7 even though its not, it's prolly still rich, and you have shaking under loan / cam surge.

I have done all learning on my own and tons of experiments to try new things, the theory is this, with more fuel you actually bring up the dynamic compression, the fuel burns for a longer period of time and basically is a band aid method to boost DCR at low RPM, bad part about it is you run rich, you go too crazy and you get SES light "left/right o2 rich" and car goes to open loop until you get off the pedal and 3 seconds later you're back into closed loop, so its ok, other bad part is even if you let the o2's do their job in closed loop and they think its 14.7, chances are you are still running rich, but not so much as you are at idle because with a cc306 or even my cam anything about 2k rpm the o2's are pretty accurate I have to say, but below that and you run even richer, so say you add more fuel, you are prolly gonna run around at 13:1 or 12.5:1 A/F but the car will run real smooth because all that extra fuel is giving you more burn time and thus adding to the cylinder pressure.


Here is one example why it works, but make sure you have good plugs and check them, make sure you don't run too rich, but by that time you get the ses light too soon, so you got to get it where it just stops surging like crazy and where you feel that the car is smooth enough, don't try to make it like a stock cam, but hell once you do it, you'll fee like it is, I know I did lol.

Anyways, here is an example, you get an old car that burnt it's valves prolly overheated and the valves don't seat for sh*t, you do compression test and the thing has like 40 psi on one and 200 on another cyclinder, well good luck having her run stoich, it aint happening, she'll die or whatever, you add fuel, lots more fuel, heck add propane cuz it burns super rich, the engine smooths out, because the extra fuel is like a band aid to add to cylinder pressure at low rpm where valve seat sealing is key.

Big cam is more less the same, it has no pressure at low rpm so it surges, it has no pressure so it shakes the car under load and low rpm, add fuel and see what happens, its a messy way to do it but you knows whats funny, when I did, my gas milage didn't change at all, at lower rpms the car actually drives fine and has tons of pick up instead of being a slug, plugs prolly won't last as long, and if you have a cat, well get rid of it LOL.

Also with big cam, add more timing down low, it won't hurt it cuz you aint making the cylinder pressure, with more fuel you also may want to add timing to start burning faster since there is more fuel so it will burn longer, so the sooner the spark the better.

But long time ago I was just like you, playing with timng, lol all it did is make the car either weaker or stronger but still ran like a bag of $hit, I figured I'd rather sacrifice my plugs and get my valves a little dirty then shake my drive train into hell. But at idle, the less fuel the better, smooth isn't always mean better that i the key, at idle you have no load, too little fuel will also kill a cammed car, but at idle I say the less the better is because that is all you can see, at idle your o2's can read 0 but you will probably be great at the engine if not rich, depends on the overlap/cam size, so I figure I'll make her richer after idle to around 2200 rpm but leaner at idle and the valves should lean themselves at idle LOL, no but its hard to explain, take out fuel at idle cuz normal = too rich at idle, and add a little at cruise because normal = just a bit rich and you can make her richer to smooth her out.

 

I have seen much of the same things that Bunker has lived through. The CC306 is tuff to get a good lean idle (no stinkies) and eliminate cam surge in the 1200 to 1800 range. Adding fuel at these low rpms can help surge. I elected to live with the surge and just drop down a cog (M6) to stay out of that range. Cleaning up idle is a different challange all together. I forced my car so lean (via PE idle with locked BLM & MAF recalibrations) that It would barely run and the exhaust still never really cleaned up. There's just too much overlap and fresh Air fuel charge that heads out the pipes. No good way to clean it up totally IMO. Good post Bunker!

Steve

 

Great Post Guys! Lots of Help

 

No probs, always feels good to share my experience and help others.

 

So guys whats the best way to richen the car up in the 30-60kpa and 1200-2200rpm range? Should I just increase the most affected cells by about 20 or so and the less affected cells by about 10? Is there anything else I have to do to richen it up? Thanks for the help guys!

 

Well what I did to richen her up is see where she surges or shakes under load and read the AFGs from the MAF at that area, drive around and make sure you get them so if its like 20 afgs then take like 17-25 and richen that section by say 10%, then go driving, you will notice in those areas if your short term blms were (not long term) say they were 118 blm, well they will now be say for example 113blm, well what you can do granted no other areas cruise around 113blm is limit the MINMUM integrator to 128 BLM, I know I know, something is wrong in Tuner car, so it 128 means 118 or so give or take 2 points can't remember now, so now the PCM will never have the short terms go down below 118blm, but the PCM needs to go to 113 to get what it thinks is stoich, cuz when she's at 113 that means she's pulling fuel, but she will only be able to pull down to 118 so youwill be running 5 BLM richer, notice the difference now.

It takes some time to play with. Also limit the Long term to 118blm, long term isn't screwed up if you put 118 it means 118, short term 118 means more like 108 or 110.

 

Sorry Bunker one last question. I'm using tuner cat and I found BLM max and min under the constant tables but I don't see anything about separate adjustments for the short term and long term. Thanks for the in-depth explanations. I'm sure this information is useful to alot of people.

 

Short temrs is called Integrator, if you do not see it, you need a newer DEF file.

 

Sorry to dig up an oldie but I am having the same problem, Just installed an 847 in a full bolt on Lt1. I under stand the adjustments of the maf tables but if I limit the short tems and long terms will that affect all ranges of driving? Also my car stumbles really bad when I take of slowly if it idles for longer than 30sec at a stop light. How do I fix that. I tried to raised the min temp to enable closed loop to 74c hoping that it would ignore the O2s alittle while longer but to no avail.

Edit: what is the newer def file? I don't have long term,short term, just blm

 

So, with the big cam, to improve the idle, you are adding fuel. The PCM identifies it as a false RICH signal, and wants to lean out the A/F mixture? I ask cuz, primarily, I hear of a need to REMOVE fuel from the mixture, due to a false lean signal. The PCM gets this false lean from the O2 sensor input, due to the raw fuel that goes out the exhaust, during the overlap of a big cam. The O2 being a sensor that recognizes air, and not fuel, sees the unused oxygen that accompanies the raw unburned fuel, and identifies this unburned oxygen as extra oxygen. The PCM then, based on O2 sensor input, adds more fuel to an already rich condition.
Static CR, as well as dynamic CR is a mechanically derived ratio, established with selection of given hard parts. Not a flow calc such as VE.
Cylinder pressure has no bearing on this. An engine so 'tired' that it has too little compression left to keep a parked (engine off) vehicle (in gear of course) from moving on a slight hill, without the aid of the emergency/parking brake, will still idle very well. The key being an effective AFR, that allows a satisfactory idle, and equal power production from all cylinders.
The fastest flame propagation is at the AFR that develops the most power. This ratio is in the area of 12.5 to 1. Moving away from that ratio, IN EITHER DIRECTION, will slow down the burn rate. IOW, at an AFR of 16.0 to 1, the rate of burn will be slower than at the fastest rate of 12.5 to 1. Same comparo using 10.0 to 1 ratio. So in summary, I'll state it may/can use more timing at idle. However, unless it is pig rich (10.0 to 1 or appr.), where you smell it to the point of being obnoxious, it is not due to a richer mixture.
After reading first part of your post, you are confusing me here.

 

You're reading my post wrong, no load you lean out mixture such as idle to keep the car running great, although you have the best mixture at 14.7:1 under load on big cam you are not looking to have the best mixture but rather have the fuel burn longer, by making the fuel burn longer you actually increase DCR its not just mechnical, you have to think real life not what you think is best, thats how I used to think thus why my car ran like crap and I dind't get why, have you ever heard the term richer = smoother?

At idle no load you can not utilize more fuel thus richer runs like crap at idle, leaner usually is nicer, under load its a different world, trust me I must have done atleast 200 tunes, I've been there done that, and now I have a 24X/25X cam in a 350 on a 109 LSA that pulls on the highway from 1400rpm without stumbling.

There are a few things you have to keep in mind here, with big cam you loose DCR, with big cam you can add more timing because you loose cylinder pressure, now you can utilize that timing by adding fuel, = more then enough time for the engine to burn it, although not fully burnt as the rich mixture suggests, you are essentialy bandading the overlap affect.

Try this, run your car lean on a big cam and try to drive her under load at low RPM and the thing will shake your teeth loose, make her rich and she'll drive smooth, of coarse at idle the world changes, richer = worse leaner = nicer, those are my findings and I've tuned almost every f-body around here, mine being the most extensive.

Then I've talked to a good friend of mine who is been a mechanic for years and does a lot of high performance work, this is when he explained to me that richer would normally slow a car down driving around under load, while something that can't seal and has a ton of overlap can actaully use that fuel to it's advantage, the longer that fuel burns and the more of it, the more pressure you can create inside the cylinders.

Sure I though well 14.7:1 is the best burn so why don't I get the most power, aparently it's because when you have a big cam it's not the best burn you are looking for, but how longer that burn can stay ie. increase fuel/increasing octane level/increase timing because you can get away with it as you are not looking for a quick peak but a more consitent longer flame.

 

Bunker,

I think your first phrase should read " Try this, run your car LEAN on a big cam and try to drive her under load at low RPM and the thing will shake your teeth loose"

BTW, Your thinking on cylinder pressure, timing advance and slower fuel burn rate make sense on a practical level.


Steve

 

Yeah sorry it was late when I was typing, I saw a few mistakes after I was done the post but was too lazy to correct, didn't see that one lol

 

You posted you saw a few mistakes. This apparently, is in addition to the rich/lean error noted above. You obviously have not gone back and corrected (what you consider) mistakes as of this time. I'd like to digest (and maybe respond) to what you posted, but would appreciate if you'd take the opportunity, when available, to go back and correct those mistakes, as I don't know what they are, or if they could change the meaning of what you've posted.