I'm trying to tune my 89 C2500 350/700R4 truck and need a couple things cleared up. I'm using a 7747 (formerly 8747 ECm when it had TH400) ECM and flash chips,winaldl for logging, and tunerpro for editing. I got the 7747-mine xdf from Moates and started from a stock AMUR bin that I copied from the stocker. The stickies here and on fullsize chevy have been very helpful so far. My first question is I've noticed the truck doesn't idle in closed loop, I'm pretty sure with the old ECM that it would. Shouldn't it idle in closed loop (when warm)? Next I have a stumble just off idle that I'm not sure where to start. According to the wideband it goes pretty rich just off idle when ever slowly taking off from a stop. If I give it just a little more throttle it's almost not noticeable, but if I don't do that it will sometimes surge enough to die. I'm not sure if its a closed to open loop transition problem or what. Any ideas? I did start tuning the VE tables today a little and so far that is going ok. Thanks, Dave

 

Are you running headers??? If so the o2 may be cooling of and causing the ecm to go into open loop. You shouldnt have a hesitation just off idle, but have you done any mods to the engine?? Cam/intake/fuel pressure etc??? Im running the same ecm and xdf file in a 1500 chev. I have a cam/headers/intake/ignition/fuel pressure/ and old style performance heads. Let me know what you get for blm readings once the engine is fully warmed up. That is the best way to change your ve tables. Warm engine,Consistant throttle staying out of it and gathering info that has more than 10 samples etc. You may have richend up or leaned out that part of your ve table that will cause the bog and or Your cooled down o2. Hope that this helps some and let me know how your datalogging goes.

 

Bone stock motor. It did this as soon as I switched ECM's. I even have another 7747 ECM and it did it with that one too. So are you saying it should idle in closed loop? Does yours?

 

The HD 350 TBI that was run in front of the TH400 and used the 8747 is a DIFFERENT engine than the LD 350 TBI that used the 7747. The Timing and VE tables have BIG differences in them.

 

Quote: Shouldn't it idle in closed loop (when warm)?

I dont see that as a negative. What is the WB reporting for OL idle? I believe there is a table to change the A/F. I believe it is coolant temp based OL table.

As far as tip in I would work with the AE TPS table. If WB shows it going significantly rich pull 10% from that table at all %(0-25) and see how that responds.

If engine is stock you should have an easy time.

 

The open loop idle varies from ~13-low 14's. I was aware the engines are different, do you think I could read the chip from the 8747? Would the xdf for the 7747 work with it? I guess I'll just try it in a little bit.

 

I must be having a brain fart, the only table I see like that is PE enable vs %TPS. That table sounds like it will only change when it enters PE mode. Could you look at my bin and point out which table it is?

 

I cant open it. i think my company blocks it. After the car comes off choke it runs on the OL-A/F vs coolant tables I believe until it hits the 160F to allow CL. I believe it also uses that table for a couple secs until the 02 starts giving feedback . Look in the TP "tables" and I am certain you will find it. i run EBL now so I am certain my table looks different. 14.00/1 seems fine to me for OL idle.

 

Ok, I tried making changes to the Delta TPS Acelpmp uSec table and it didn't seem to make much difference. I went as far as taking out 30% when I noticed some of the values would change back to what looks like a default minimum value? Are there minimum values for this table, or others?

 

The constant "RPM Threshold for PE" in my bin is set at 2000, does this mean that it won't allow PE until 2000 rpms or more like I think it does?

 

i believe you are correct.

 

I changed the threshold and that didn't really seem to do much either. After looking over the timing table today I added a few degrees in and around the area right off idle and it fixed the problem. Does anybody know of or have a stock bin for an 89 C2500 so that I can compare my timing table to it? Or what xdf to use to read the bin from the 8747 ECM?

 

I happen to have both a XDF to read it and a stock P-series Step Van bin.

 

You have a PM.