FAST startup surging

[callmeebryan]

Yeh that log doesn't do me any good bud... that was with the old tune.

I read your readme and went ahead and tweaked your CPP map, including all the changes i made to the "working-on-start" map.

USE THIS MAP for the logs!!! otherwise its a waste of time

Same logging procedure.

 

[Dusty Bradford]

Too much timing at idle IMO.... run no more than 30.

Bad advice.......what's your reasoning here?

It sounds like the cams more aggressive because less than 30 at idle is not enough lead. 30 is even low unless you have a very efficient chamber design which the buick does not have. The car will be responsive at 30 but it needs at least another 4-6 degrees.

Also, what works on a Buick may not work for all other motors. His V8 may love 40 degrees at idle...my Chevy V8 did before I swapped heads. Now it needs much less.

I have seen Buicks that can idle at 14.0, some need 13.0....again each car is different or else we'd all have the same gct. Depending on cam size, one car may idle at 850, the other may need 1000.

The IAC is good advice.

Tuning over the internet is not easy and you can not make changes to someone's map just because it doesn't look like yours....not saying this is what you're doing but just making sure. Nothing beats being able to make a change and hear and see what difference it makes with the car.

Scott, the IAC vs coolant will have little to do with the start hunt. The IAC valve is too slow anyway to change the idle that quickly. The fix will be in getting your a/f ratio where it's happy by adjusting the VE table. You also need to look the timing to see what it's doing at idle. If it's moving from 30-38 due to the timing trim, it needs some adjustments.

 

[callmeebryan]

Bad advice.......what's your reasoning here?

It sounds like the cams more aggressive because less than 30 at idle is not enough lead. 30 is even low unless you have a very efficient chamber design which the buick does not have. The car will be responsive at 30 but it needs at least another 4-6 degrees.

Also, what works on a Buick may not work for all other motors. His V8 may love 40 degrees at idle...my Chevy V8 did before I swapped heads. Now it needs much less.

I have seen Buicks that can idle at 14.0, some need 13.0....again each car is different or else we'd all have the same gct. Depending on cam size, one car may idle at 850, the other may need 1000.

The IAC is good advice.

Tuning over the internet is not easy and you can not make changes to someone's map just because it doesn't look like yours....not saying this is what you're doing but just making sure. Nothing beats being able to make a change and hear and see what difference it makes with the car.

Scott, the IAC vs coolant will have little to do with the start hunt. The IAC valve is too slow anyway to change the idle that quickly. The fix will be in getting your a/f ratio where it's happy by adjusting the VE table. You also need to look the timing to see what it's doing at idle. If it's moving from 30-38 due to the timing trim, it needs some adjustments.

From my tuning a few different cars, 30* timing at idle seems like a good average number, or atleast a good place to start. My buick likes right around 30, but my previous project (supercharged 3.0 v6) liked 25. You are right that every motor is different which is why im having him do a bunch of logs so i can see what is going on.

I did notice that at 30* his car was hunting. However, timing trim only reacts with the value you put in the table, and its based off RPM deflection. Ideally you dont want to use any timing trim, but thats the perfect scenario and never really is the case. I changed his idle timing to 36* and changed his timing trim linear from 0 to 3* across the map (car shouldnt need more than 3* to recover).

His RPM fluctuation does seem to relate to the A/F.... it starts up and runs mid 15's, then starts dipping into the 12's and rpms plummit. Then it recovers and A/F raises again.

The weird thing that ive been trying to fix is the fact that his current VE tables make for a perfect A/F at idle when the car is warmed up, yet on a cold idle the AFRs are all over the place... which could be because of the IAC going crazy or just not enough fuel for cold operation. I went in and added some cold start enrichment to see if it would help smooth out those afr's. Well see on this next log.

If the car is relying too much on IAC to idle, and the IAC isnt responsive, the car will hunt. Thats why i like to avoid relying on the IAC and have the throttle plate set so it idles with minimal IAC. That way, the car will ALWAYS have enough air to idle at the set idle speed.....

 

[Dusty Bradford]

Sounds like you are doing a nice job.

One thing that makes tuning out the VE table during the "hunting" by watching the a/f ratio is the delay from the time the ecm enters the cell to the a/f reading. You can log it but there's a good bit of lead time invloved so the cell your operating in during the hunting does not necessarily reflect the a/f ratio. Everyone tries to keep the cells at idle very close numerically to avoid the hunting but I have seen a couple cars that need quite a jump in VE#'s to avoid the hunt.

I don't like a lot of timing trim either.

Do you have the idle at the colder temps a little higher?

 

[MSDGN]

Sounds like you are doing a nice job.

One thing that makes tuning out the VE table during the "hunting" by watching the a/f ratio is the delay from the time the ecm enters the cell to the a/f reading. You can log it but there's a good bit of lead time invloved so the cell your operating in during the hunting does not necessarily reflect the a/f ratio.

Dusty...can you elaborate on this more...exactly what would I look at during the hunting...

 

[Dusty Bradford]

Dusty...can you elaborate on this more...exactly what would I look at during the hunting...

First thing to check would be the timing in the dashboard. If it's moving around a good bit you need to set up the timing trim or make some adjustments to the timing map to get the timing steady. If the timing changes much, so does the a/f ratio.

Next, if you log the engine while it's hunting and then overlay the log on your VE table you have to keep in mind that the a/f ratio you are seeing displayed on the dashboard does not necessarily relate to that exact spot on the VE table where your bubble is at. If it's moving around at a steady pace the VE table is changing the fueling and it takes a bit for that change to make it's way to the oxygen sensor. If you have a lean spot it's a good chance you need to go back a few tenths on the log and see where the bubble was at. If it's in a different spot I'd make the necessary adjustments there. Don't be afraid to change a large area of the VE table to numbers that are somewhat close to make the car hunt less. You can then go back and fine tune. Fatten it up a bit and see if it affects the hunt. Usually to lean of an a/f ratio or large timing fluctuations make the car hunt.

 

[BigBird R/T]

Yeh that log doesn't do me any good bud... that was with the old tune.

I read your readme and went ahead and tweaked your CPP map, including all the changes i made to the "working-on-start" map.

USE THIS MAP for the logs!!! otherwise its a waste of time

Same logging procedure.

Sorry about the worthless logs (I learn). Here's two from this evening and when I started the cold start it didn't die, almost but didn't. Seems to idle great hot.:smile:

 

[callmeebryan]

Sorry about the worthless logs (I learn). Here's two from this evening and when I started the cold start it didn't die, almost but didn't. Seems to idle great hot.:smile:

Alright, the problem has to be the car is not getting enough fuel during a cold start up. Right after your RPMS are done going crazy, watch how your AFR's go from 15's (@ 80*F temp) almost linearly down to 13.0 (@ 130*F temp).

The thing that seems weird to me is between CTS enrichment and After Start enrichment, the current tune is adding like 15% fuel to your idle ve's right after start up. That means your car needs more than 15% more fuel at cold start up. However, you can see that the AFT enrichment is fixing the problem if you look a couple seconds after the car starts up...it was idling good for a 2-3 seconds.... the AFT enrichment was set to decay out way too fast and the car went way lean again and started hunting after that.

Its like a loop. Your cold start condition is lean. The car starts to drop rpm's, the IAC simultaneously tries to open WAY up to try to save the dieing engine, and your spark trim maxes out trying to save it.... it gets to the point where your IAC is pretty much all the way open and the car finally has the correct AFR at a real LOW rpm to recover.... so at like 400rpm its at the correct AFR, it starts making power again, but your IAC is too slow to close and motor ramps back up.

I went in and added more CTS correction as well as after start enrichment.... you are at about 25% max now (equal to VE's of about 63!). I have the AFT decaying out at about .4%/sec. This means after the car starts, your AFT enrichment will go from 18% to 0% in about 45 seconds, at which point your CTS correction will take over and the car should be idling real nicely. Im pretty sure thats going to fix the problem. Try this out and let me know how it works out for you.

Dont change your VE's any more!! Its perfect right where its at!

 

[MSDGN]

First thing to check would be the timing in the dashboard. If it's moving around a good bit you need to set up the timing trim or make some adjustments to the timing map to get the timing steady. If the timing changes much, so does the a/f ratio.

Next, if you log the engine while it's hunting and then overlay the log on your VE table you have to keep in mind that the a/f ratio you are seeing displayed on the dashboard does not necessarily relate to that exact spot on the VE table where your bubble is at. If it's moving around at a steady pace the VE table is changing the fueling and it takes a bit for that change to make it's way to the oxygen sensor. If you have a lean spot it's a good chance you need to go back a few tenths on the log and see where the bubble was at. If it's in a different spot I'd make the necessary adjustments there. Don't be afraid to change a large area of the VE table to numbers that are somewhat close to make the car hunt less. You can then go back and fine tune. Fatten it up a bit and see if it affects the hunt. Usually to lean of an a/f ratio or large timing fluctuations make the car hunt.

I agree that too lean A/F makes the car hunt but why does it smell so rich...here's the weird thing...I start the car(cold)...it runs at a higher RPM nice and smooth for about 10-15 seconds...then the RPM's drop and it starts to hunt...all this time I can smell the exhaust...smells rich...makes my eyes water a little...no black exhaust or anything like that...even when the car warms up and idles smooth it still smells rich...I had to put the 2 lower left cells of the VE table into the teen's...(like 14 and 15) just to get close to the target A/F at idle...which is set at 13.0-13.3 for those cells...even then the actual A/F is 12.5...should I lower the VE numbers more?...or is this causing my hunt?...if so how do stop the hunting and get close to the target A/F at idle?...

 

[Dusty Bradford]

I agree that too lean A/F makes the car hunt but why does it smell so rich...here's the weird thing...I start the car(cold)...it runs at a higher RPM nice and smooth for about 10-15 seconds...then the RPM's drop and it starts to hunt...all this time I can smell the exhaust...smells rich...makes my eyes water a little...no black exhaust or anything like that...even when the car warms up and idles smooth it still smells rich...I had to put the 2 lower left cells of the VE table into the teen's...(like 14 and 15) just to get close to the target A/F at idle...which is set at 13.0-13.3 for those cells...even then the actual A/F is 12.5...should I lower the VE numbers more?...or is this causing my hunt?...if so how do stop the hunting and get close to the target A/F at idle?...

I agree and it is wierd and I see it on my own car as well. It idles fine but smells rich. There's no problem going to 14.0-14.5 to see if the car likes it. I know your on the low end of the VE #'s already.

You can go up on the injector opening time a bit to see if it helps. If it's 1.0, try 1.2 and see what the effect is. The VE #'s are just a calculated number and depend on a couple other settings in the system. Injector opening time will effect it, target a/f ratio will effect it. Try to make all VE #'s around your idle the same or within 2-3 of each other. Don't worry about it being fat, you can walk it back down once you have the idle stable.

What do you have the idle set at? It may want to idle a little higher. You may have to set the IAC up so it doesn't operate while your trying to sort it out. Set the TPS value so that IAC will not function at idle, do not just unplug the IAC, it has been known to fry the driver.

 

[MSDGN]

I have the inj opening time set .8...it was originally .9 but I reset it to try and get idle closer to the target A/F...idle is set at 1000 RPM...not sure I'd want to bump that any higher...like I said when the hunting stops...after about 20-30 seconds it idles very smooth...I'll try messing with the VE's numbers around the idle cells...it doesn't really bother me that much with the hunting...the car runs great other than that...heck it ran 130 MPH the 3rd run after installing XFI...and I've just started dialing it in...would be nice to get rid of the hunting but it's something I can easily live with...

 

[callmeebryan]

I have the inj opening time set .8...it was originally .9 but I reset it to try and get idle closer to the target A/F...idle is set at 1000 RPM...not sure I'd want to bump that any higher...like I said when the hunting stops...after about 20-30 seconds it idles very smooth...I'll try messing with the VE's numbers around the idle cells...it doesn't really bother me that much with the hunting...the car runs great other than that...heck it ran 130 MPH the 3rd run after installing XFI...and I've just started dialing it in...would be nice to get rid of the hunting but it's something I can easily live with...

Do a log just like bigbird has done, that will tell us what is going on.

 

[MSDGN]

Going racing tonight so will create a log as soon as the car starts hunting after I fire it up...

 

[BigBird R/T]

Try this out and let me know how it works out for you.
Dont change your VE's any more!! Its perfect right where its at!

Loaded your .gct, started the engine, no throttle and it fired right up with NO surging as far as I could tell. Idles great and when the electric fans come on it doesn't bog like it use to. I am one happy camper, Will try to do some crusing this weekend and see how multiple starts and stop work. Here's the log file from this afternoon.

 

[callmeebryan]

Loaded your .gct, started the engine, no throttle and it fired right up with NO surging as far as I could tell. Idles great and when the electric fans come on it doesn't bog like it use to. I am one happy camper, Will try to do some crusing this weekend and see how multiple starts and stop work. Here's the log file from this afternoon.

AWESOME! Looks PERFECT. When i told you the AFT% would phase out about 45 seconds, i actually decreased the decay after i typed that.... it turns out that slower decay is just perfect. Everything is how it should be. When the air temps start to drop there may have to be some adjustment made, but we can address that later.... keep the current tune on your car and let it be for about a week or so. Just to make sure everything is working as planned.