Searched all night and couldnt find the answer. So, here goes. I'm working on a 383 HSR combo with a 230 cam 544/555 lift. I have approx 30 miles on it and I'm working on my lower VE tables using Tunerpro to read my 1990, 730 SD. The problem I have right now is a slow speed surge. Looking at the datalog the problem appears when going from BLM cell 8 to cell 9. Now, when I look at a BLM Cell layout for the P4 it shows cell 8 and 9 to be 1600RPM and 60/70 KPA. Comparing that to my datalog doesnt match up, my surging happens when I'm driving slow approx below 1200. I have to drive it two footed when coming to a stop to keep it above 1,000 RPM or it will die. When I put it in park I can safely take my foot off the gas and the surging goes away.

Cells 8 and 9 (datalog) both appear to be slightly rich (cell 8 114, cell 9 122). Could this cause the low speed surge? If so, how do I determine what RPM/MAP need to be leaned in the VE table by reading the BLM cells?

I'm pretty sure this problem is self induced cause I dont remember it surging when I started on Monday it was all just pegged at 96 BLM's. I have the surging area saved in an excel file if someone would like to take a look at it I can e-mail it.

Oh, and yes this is my first attempt at tuning so the learning curve is steep but I am learning! Thanks.

 

I'm pretty sure cell 8 is a low RPM cell, and cell 9 is the RPM cell above it, in the same MAP region. So, if the low boundary is 900, then the surge will be below and above 900. Maybe it's set to something different in yours.

A boundary surge is a tricky thing to figure out, because fuel from one cell can lie to the other cell for just long enough to make that cell learn one point wrong, and then come back to the other cell, and learn just long enough to make that one wrong, and they can diverge after a lot of surging. The cause is usually the VE table, since that's what the BLM is fixing anyway. Sometimes some DMAP AE will get thrown in if the surge is enough. Sometimes excessive timing will cause problems like that. There's a bajillion possible combinations. My best advice would be to two foot it to one of the cells, and calibrate the fuel, using less timing. Then use that VE as a reference in the lower RPM but subtract some as the RPMS go down. In general, blend in that VE to the rest, and try to calibrate as many points as possible down low using the two foot method. Don't do it for minutes at a time, or you'll toast your tranny fluid. Just hit an RPM and MAP point, look at BLM, and change the VE accordingly and blend into the map. It'll take several iterations, of course.
How does your lower RPM VE look right now in that MAP region?

 

How does your lower RPM VE look right now in that MAP region?

It doesnt look good!

Looking at it by RPM to MAP and BLM cell, points out a problem. It appears I am dipping into an area of the VE table I havent adjusted yet when my surge is occuring. Its easy to see now what I need to do, but before I was just looking at BLM's and not getting the big picture. The cells with the VE in the upper 20's are what I have already adjusted, the higher ones I havent. Cool, I'll go smooth out my VE table a little better and test run.

800 RPM @55KPA, VE is 25.79 and in cell 8.
800 RPM @65KPA, VE is 55.39 and in cell 8.
600 RPM @60KPA, VE is 46.09 and in cell 8.
1000 RPM at 50KPA, VE is 27.34 and in cell 9.
1100 RPM at 45KPA, VE is 28.13 and in cell 9.

 

Oi! Yeah, that could do it. Hope that fixes your problem.

 

Tuned my .bin all weekend and have concluded the following.
1. Desired RPM is stuck at 900, no matter what I do it will not change.
2. When I tune to 128 at idle, BLM cell 9, my low speed drivability richens to the 106 BLM range and causes the surge.
3. Tuning for 128 during the low speed area leans my idle to the 154 BLM range.
4. I have since learned that the idle in S_AUJP is hardcoded to 800. That would be fine for me but I simply cant get there.

I retarded intial timing from 10 deg to 6, adjusted the Throttle blades, reset the IAC and TPS. The only sigh of relief was when I reset the IAC, the car would actually idle down to 650-700 with IAC disconnected. As soon as I hook up the IAC, the idle shoots back to 900.

I have also changed idle RPM vs coolant temp to 800 (and 700), lowered IAC counts to 60 max and removed 50 RPM from RPM added in park. Is there somethinig else I am missing? My next step is to change the hardcode which I dont know how to do, yet.
Any ideas where to go next? Thanks

 

AUJP has the hard code for 800rpm. Not sure, but think that is in drive.
S_AUJP has it moved to 1200 rpm or so.

 

When I tune to 128 at idle, BLM cell 9, my low speed drivability richens to the 106 BLM range and causes the surge.
3. Tuning for 128 during the low speed area leans my idle to the 154 BLM range.


Hello,
When you make the above statement, do you vary your rpm at idle? What is low speed driving (this will cover a large part of the VE tables)? Is it rich everywhere? You need to tune each individual value in the VE table. You're going to have to be very exact while taking data, evaluating it and making your modifications. SD is very touchy. Count on hundreds of tunes...it's called trial and error...but don't get frustrated. Get a 'lab' book and write everything down, put your VE table printouts in it and stay organized.

In general, you'll need to reduce the fuel at low MAP and idle. You don't need to read 128 all the time, that's what a fuel trim is for. Good luck.

 

No, I am not varying my RPM at idle (car in park). When I stated low speed driving I am referring to under 15mph and zero throttle. At this point, the engine operates in the same BLM cell 9, at the same rpm/kpa as it does in idle. So, tuning it for 128 at idle makes it excessively rich when it enters the same area while driving (low speed) and causes a surge. I am fairly certain my car should not be idling at the same rpm/kpa it sees in drive, anyone disagree? What I believe I need to do is figure out how to lower the idle. With idle being controlled by the computer through the IAC I am limited to what I can do. The car is undriveable right now because of this.

The only way I know of to fix this is to modify the code to make the car idle lower. Tunerpro shows my desired idle at 900, which is exactly what my car is doing. I just need to figure out how to modify the code and idle it lower. Could someone explain where it's located and how to do this?

 

You probably understand this but just in case you don't:

Fuel cells are blocks in the VE table that contain subcells. For example fuel cell 9 includes all the 'subcells from 60 to 80 kpa on one axis and 900 to 1600 rpm on the other axis. You can be rich in one area of cell 9 and lean in another area of cell 9.

When I've heard guys on these message boards complaining of surging it has been an IAC problem. You might want to do a search on IAC if you already haven't. An idle of 900 rpm doesn't seem too high. If you have to hold your foot on the gas at a light to keep it from stalling then reducing the idle isn't going to help.

If you're idling in cell 9 what kpa is that? ...above 60 kpa? How much overlap do you have in that cam?

 

When idling at 900 RPM, in park, it fluctuates between 45-50 KPA.
The cam is a Comp Cams 230/236 dur, .544/.555 lift on a 112deg centerline, 10.82 compression with AFR L-98 Al heads. The cam shouldnt be too agressive for this motor, maybe a step above the 276HR.

It is only stalling because of the surge. It surges from 650-1375 RPM as I witness it going through BLM cell 8 and 9. If I dont drive two footed, it will die at the low end of the surge. Exactly the reason I'm not driving it. Driving two footed I can keep the rpm's up and it will never see cell 9 and it wont surge, just stays revved!

Keep it coming.

 

Could this be one of those cases where the IAC is wired or operating backwards?
You said the only time it tamed down was when it was disconnected.
might want to look into that if the IAC was replaced or the harness was modified.
If you adjust the thottle blades to close while logging, do the counts increase on the IAC? They should if the idle is being controlled by the ECM & IAC.
Did the RPM drop when you adjusted?
Are the temp sensors reading normally? Cold indications will raise the idle as well.
Just throwing some stuff out there.
The park/Neutral idle is something I'll be playing with this weekend (don't have a good understanding as to how to lower mine either)
The "in gear" idle WILL drop by changing the idle Vs Temp table. I've confirmed that does the trick.

 

Might be all wet on this but have wondered what the effect of a higher comp will do to the reaction time of the o2 output signal.
With the higher CR, could the o2 be behind the times or just missing the adjustment period because of the induced lag from this table.

 

Judd, that table is very interesting. Take a look at the paper RBod did years ago regarding the PID code in the 7747, it's very similar.
If your chip was done "properly" the air flow would be pretty accurate since VE, displacement, and MAP are used to calc air flow... a larger motor will have a higher MAP but at that MAP will be a lower VE at idle (where closed loop usually has the hardest time adjusting). So your "air flow" will be okay, now look at the position of the o2 sensor in the exhaust stream, might want to increase the delays if it's further away from stock. It doesn't have to go very far to change the "swing" of the rich/lean. What's cool about adjusting the closed loop PID tables is that you can effectively make a closed loop tune run (on average) richer or leaner than stoich. I've played around with this and found it to be very useful when trying to get through the sniffer .

 

As I understand it (from my offline talks with Magman), the surge is most prevalent when coasting to a stop in drive. I had him change both the idle RPM vs coolant table and the hard-coded idle (in drive) in AUJP (both locations) and it didn't seem to affect the idle (according to Magman).

The IAC seems to be functioning properly under all circumstances except for the surge under these conditions.

Magman - I'd be curious to know what would happen if you start your car and get it to where it idles smoothely at 900 RPM or so, then disconnect the IAC and go for a drive. I wonder if it will still surge. I doubt it would help, as the surge appears to be a problem with the cell 8 to 9 transition because of the difference between cell 9 during coast vs cell 9 at idle.

I had thought you mentioned that the surge goes away once you're stopped and as soon as you put it in park. Is this correct?

 

It's John . Anyway if adjusting the table and the others and the idle did not change leads me to a vac leak somewhere.
I surly don't know what else could be holding the idle that high.
Jon, I'd like to go into what you said deeper but that's for another thread.

 

JP86SS, the IAC/ECM is commanding it to run at 900 in park as seen reading Tunerpro.

Mangus, you are correct I have a lower idle in gear (zero mph), when placed to park, idle goes up to 900 as commanded. Since we talked last I was informed the coolant temp vs RPM table controls the idle while in drive, not park. I did not road test after we changed the idle in drive, hmmm...