First off, sorry this post is so long.

Hey guys, I hope someone can/will help. Another shop brough us a 1991 C10 with a summit 383 installed. Edelbrock manifold with port injection. The cam is way to big in my opinion. Don't remember exact specs but LSA is 109-107. This was our first attemp at TBI tuning so i spent alot of time on this site. We have done TPI's before so i figured i would give it a shot. Needless to say the truck runs great.

Truck is back now with a slight surge after coming to a stop and the idle seems to stay high after putting it back in park. I have done multiple min. idle sets and have read the IAC sticky 20 times.

What i have noticed from my datalogs is the IAC counts will not drop below 39 no matter what i do or change. I have to turn the idle screw down for it to idle correctly which i think is causing my idle problems. I think i have gone over everything in the sticky and the code but can't figure it out.

Hopefully one of you TBI guru's can shine some light on this subject.

Thanks in advance for all your help.

 

Can you post your idle logs? Since you have such tight LSA your idle vacuum might be low, which will cause MAP to report higher than normal load to ECM. ECM will compensate by adjusting idle higher as if there is additional load (i.e lower than normal vacuum) which is not really there. This can be dealt with. Also, I presume your C10 is using 1227747 (or later equivalent) ECM.

Measure you idle vacuum with a gauge and post your idle logs.

//RF

 

Thank you for your reply.

Yes it is a 7747 pcm.

When manually turning the idle down to get it to idle correctly, it idles around 65kpa at 950rpm, not consistently though with the cam. After doing a min. idle set with the IAC disconnected, setting it at 850-875, then plugging it back in, it stays at 1200rpm with 50-55kpa. Either way I do it the IAC count will not go bellow 39.

If you would like I can hang an actual gauge on it, and get a few longs using WinALDL. The truck has good cold start and drivability so i think the VE is pretty good, but i could be wrong. If the .bin would help I could post that too.

I set idle around 950 only cause any lower it doesn't seem to like. They put a 3000 stall converter in it so at least I don't get any harsh engagement when going into gear.

Thanks agian for such a quick response and i will get those items you asked for as soon as possible.

 

There are couple of tables (tunerpro with 7747.xdf loaded) that you'll have to play with

1) Desired C/L Idle Speed
2) IAC Position vs. Temp


In a stock ASDZ calibration min IAC @80C is 24 steps with desired C/L idle of 525 RPM which your cam can not do. Try dropping min IAC steps from 24 to about 10 and increase C/L idle speed to about 700 to 750 RPM. Can you burn your own EPROM's?

//RF

 

We have the AutoProm from moates. We did a custom tune on this truck a few months ago. This is the only problem he has come back with since then.

I already tried putting the desired IAC Position vs Temp to 5 above 56C, but that didn't help either. Desired idle speed at operating temp is set to 925rpm.

I might go to the shop today and if i do I'll get a few logs and also post up my .bin for you to take a look at.

Thanks again for your help on this. With the cam installed there might be a chance he will just be stuck with a poor idle.

 

So here is a datalog from the truck. It is a start-up hot, running in park for around 30 seconds. Then in gear for about 30, then back to park for another 30. This is just after doing a min. ilde set to 875-900 rpm. As you can see the IAC counts never drop below 39 and then when going back into park they stay at 61 which puts the idle around 1350-1400. i know the BLM's are a little lean in the 1200/50kpa area but while driving they are just fine, and while idling in gear the BLM's are in the 125 area. Im kinda stuck at this point so hopefully someone can help me on this one. I also loaded the BIN for you too.

I just read somewhere that you are able to prgram in open loop idle. Would that be something of benifit for this application? Just a thought. Not sure how to do that either.

Thanks again to all that can help us out.

 

I took a quick look at your bin file - I do not know who did your SA tables but amount of timing is excessive. Even for a wild cam having 31 deg of timing at idle is a bit much. Try bringing SA tables in idle area 400 to 1000 RPM by 30 to 55 MAP from 30+ down to 21 deg. This should 'tame' idle speed a bit. Second observation is that someone simply increased timing in all cells - advancing timing beyond 45 deg will result in ark over to subsequent post in the distributor (360/8 = 45 deg). Typical SBC does not need more than 36-38 degrees of total timing at maximum torque point in the power range. Pull a copy of ASDU bin and use it as an example. 48.87 deg and above is a no-no. I am assuming that you have 0 deg base timing set (EST disconnected).

 

I recall the 7747 also has a PE "adder" table for SA. Might the timing be in excess of the main SA table?

Does the 7747 have an OL idle option? I recall it did not. I used 7747 locking OL by setting CL coolant temp to max. Might want to try that temporaritly to see how idle behaves in OL. Fast355 posed his heavy truck timing tables many times.

 

I think there might be something wrong with the file you downloaded or your XDF file. I downloaded the file and it matches the origianal file i attached. In the area that you highlighted i have 21-23* of timing at ilde. The table you posted looks nothing like the one im looking at. I can try to reloading it if you want. For some reason it looks as if the table you posted has 10* added to the whole thing.

Or there is something wrong with my XDF file. Im not getting any knock counts though which i think i would with that SD table.

 

I went back and loaded a known stock ASDU.bin and a copy of your bin file using 7747-mine.XDF from Moates into TunerPro-RT. From what I can see there is a problem with SA tables. I did not look any deeper except that initial SA set for 0 degree in your bin. Do the same comparison on your computer just to get some degree of certainty.

//RF

 

Well i might see where we are having our problem. We are using 2 different XDF files. you are using 7747-mine.XDF and im using 42.XDF from tunerpro's website. Im wondering which one is correct?

My XDF is set for 10* base timing also. Don't know if that changes anything.

 

XDF file does not set base timing. XDF provides a digital to human instruction set i.e how to interpret bin file contents. Let me try your BIN again with 42.XDF.

You can also get a timing light and see what the actual timing is at idle. If you have one of adjustable or dial-in timing lights it is an easy check.

//RF

 

I already checked timing. Was one of the first things i checked when it came back. I just wasn't sure if my XDF had taken out the base timing from the SD table. It doesn't make sense that it would do it but i've seen wierder things.

Thank you RF for all the help you have given so far. Greatly appreciated.

 

I did a side by side compare of timing definitions used in 7747-mine and 42.XDF files:
7747-mine.XDF............................................. 42.XDF
Initial Spark Advance .....................................Initial Spark Advance
Address (Hex): 0x009 ....................................0x014
Size: (8 bit) ................................................(8 Bit)
Eq: 0.351560 * X + 0.000000 .........................0.351563 * X + 0.000000

Main Spark Advance .....................................Main Spark Advance
Address (Hex): 0x035 ...................................: 0x035
Conversion: 0.351560 * X + 0.000000 ............ (0.351563 * (X - Y)) + 0.000000
Argument 0................................................. Argument 0
.................................................................Argument 1

I went back to old notes and white papers (1227747) on diy-efi and initial spark advance is stored at address 0x09. Main SA table begins at address 0x035. It appears that 42.XDF performs base SA offset calculation on the MAIN SA table - which results in strange values! It looks like base spark offset in 42.XDF is incorrect.

http://www.diy-efi.org/gmecm/papers/747spark.txt

//RF

 

I dont know if you got this fixed, but my experience with the IAC motor lasted almost a year. I used a romulator, so I was able to change a lot of stuff and experiment without much trouble. I tried everything, but it turned out the be the VSS. Not saying this is the magic bullet, but I will describe my condition on the hope that it can help others.

Fire up engine - no problem (iac count was 90 (my max as I run 2 IACs)
in drive engine about 100 -150 RPM about desired, but still OK (max IAC)
after about 3 min on road and temp gets about 150-160, stop in gear and the IAC would drop from 90 to 39 counts and no setting would change that except setting max lower than 39.
Could reload computer (resend bin to romulator) which reset the computer, it would then lower the counts below and then behave.
If I shut the car down and restarted after temp dropped below approx 150, same problem.
Set my voltage jitter to 0 and then connected my VSS, It holds max IAC until you stop in gear and then IAC drops below 39 and controls idle without a problem.
After a year of being side tracked, I can now concentrate on tuning other parts.

Ted

 

Key on engine off, does the CE light flash on off once, then stay on?

Does thaat XDF allow a set # of IAC counts just for idle? Is that XDF for IAC counts showing a table for RPM vs coolant? If so I would set it at 5 steps for 155-200F and check that out.

No vac leaks right.