I have a 6395 pcm with a BHDF bin in a 94 7.4 suburban. In the scalers there is a box for initial advance. Does the pcm use that number in advance calculations or is it just there for reference.
I have a 6395 pcm with a BHDF bin in a 94 7.4 suburban. In the scalers there is a box for initial advance. Does the pcm use that number in advance calculations or is it just there for reference.
It will be used. It's the timing advance the distributor should be set to. for example, if the initial is 10* then the ECM takes 10* off of it's timing advance calculations.
I thought that also but had some indicators that made me think differently. So today I plugged a bunch of different numbers in and it does use that in the calculation but it seems if you stray very far from the intended number it gets unhappy.
The initial advance parameter is where you enter in what your distributor base timing is set at. Most all I have seen has been 0*, but I think I have seen some 7.4L bins have around 4*.
You want that parameter to match your distributor. It does effect timing. If you set your base timing to say, 5*, and you set the parameter in the bin to match, then the ecm knows there is already 5* and subtracts that from the timing tables/calculations to account for it. That way it doesn't go over what is programmed.
However, if you have your distributor set to 5* but have the parameter in the bin set to 0*, then the ecm thinks its zero and will make no changes, while in the meantime, your getting 5* added to all your timing.
So long story short, make sure your distributor base timing and the initial timing parameter in the bin match.
79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy
93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver
99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.
JeepsAndGuns: I have a 350 Vortec with 7427 ECU and the ignition timing varies between 0 to 10 degrees advanced as read by a timing light on the balancer. The ignition advance table values are something totally different. Trying to make some sense of what is going on. According to your post you have knowledge of the 7427 and small HEI distributor operation. Please expand on knowledge of this ignition system workings. Please advise. Thanks.Originally Posted by JeepsAndGuns
rsicard, you seem to be chasing two problems. 1) perceived lack of timing activity for an engine that is running outside a vehicle, and 2) the need to know *everything* about the ecm, ignition system, code, etc to diagnose and repair #1). Keep in mind that very few technicians have an in-depth understanding about how the timing control works, and that most tuners don't know how all the variables work together, and yet both groups are able to successfully diagnose and repair many problems related to the ignition system. As a technician, and as someone with in-depth knowledge about how the ignition system works, I don't believe your problem #1 warrants the time or effort required to successfully satisfy the conditions for #2. If you are simply chasing knowledge for curiousity's sake, that's fine. If you wish to determine whether or not your ignition timing is working as it should be, folks here could certainly help. I believe there are some unanswered questions in your original thread?
Don't need to KNOW EVERYTHING. Just want reasonable idea about ANY correlation between TunerPro Ign Timing and that read from the balancer. Don't know how to be clearer about this.
Just trying to understand if there is ANY correlation from what is read of timing advance from TunerPro and that read using a timing light on the balancer. Not sure what things to modify in the binary to get some type of relationship between the two. Hope this is not too hard to understand. I think I understand how the ECU generates timing advance in subtracting milliseconds, in correlation with binary timing table, after sampling timing several DRPs. This may be errant thinking, but it is the best I have come with. As to what other factors, KNK, MAP, RPM etc. have an effect on ignition timing, have little knowledge of same. There are SEVERAL items under SCALERS that affect ignition timing. Have disconnected the wire from distributor ign module to ECU and set timing with light on balancer to zero degrees. Also replaced the ign module. Did not change a damn thing. Igntion timing ran DAMN good with HEI distributor and 4 barrel carb. Trying to figure out a calculated path on which to proceed. Ign timing on TunerPro varies greatly, yet timing light on balancer varies 0-10 degrees. DON"T UNDERSTAND what I am missing. Still somewhat of a Noobie to this EFI tuning. Someone has helped greatly with fuel tables. Have looked all throughout gearhead-efi and found LITTLE about ignition timing. Came to you as it SEEMS you have greater knowledge, and maybe practical experience, of this ignition timing. Trying to get more knowledge to form ideas as to a direction to proceed to with ignition timing.
Sorry about being verbose about this. Have been in Aviation Electronics (Avionics) for 38+ years from repairing all the way to systems certification. Have been retired and likely losing out on innovative thinking.
Experience comes with exposure. Have limited exposure to TunerPro and EFI tuning. Yet, understand electronics as have been in the business the greater portion of my life. Rebuilt several engine including my own aircraft. Not a Noobie to things mechanical. Not a Noobie to electronics. Once adequate exposure is gained to EFI tuning, TunerPro etc., will become much better at it. Much knowledge of this EFI system is likely in the brains of retired GM engineers. Do not have access to that knowledge.
Just a thought but could it be that your ecm is not actually connected to the ign module or is effectively in limp home mode. With a base setting of 0 you would see about 10 or so degrees on the balancer at 1600-1800 rpm.
I have check the continuity of the wiring between the ignition module in the distributor and the ECU. Ignition module replaced. Same results after these two checks. Fuel table altered and the change in Wide Band AFR was good. Therefore, must assume it is NOT in limp home mode.
One last thought, are you sure you are getting proper voltage on the set wire?
Don't understand the terminology "set wire". Please explain in more common terms. Thanks.
I am assuming you are using a hei 7 or 8 pin module and was referring to the wire you disconnect to set the base timing. It is usually tan with black stripe in gm harnesses and I have heard it called a bypass wire.
The timing displayed in TP should match what's measured. You should have nearly 100% correlation. If there is an error it should be restricted to a fixed amount consistent at any commanded timing. You should not have to alter the calibration to make the displayed timing match measured timing. What you are describing is atypical.Don't need to KNOW EVERYTHING. Just want reasonable idea about ANY correlation between TunerPro Ign Timing and that read from the balancer. Don't know how to be clearer about this.
It is possible that TP is not displaying the right value. The datastream definition must match the mask ID of your calibration. You should be able to command a fixed spark advance by using the max advance and max retard values. Set them for a specific value, such as 12 degrees. The timing light and the value displayed by TP should match your limits. Disconnect KS as some calibrations apply Knock reductions after max retard limit is checked. Watch TP to see what is displayed. Setting limits should eliminate all ECM based variables. Seeing 10 degree changes after changing limits implies problem is faulty ECM or in TP definition file.
It is an 8 pin module. Thanks for the clarification.
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