I have updated my prom from mask $32 to $6E and have been logging data with TunerPro RT to see if I like it. (so far, I do)

I've noticed that my actual speed is lower than the ALDL logged speed.

Is there something in the bin that I have to modify to tell it the gears that I have or do I adjust the value in TunerPro software with the factor and offset?

 

Hi “wwnf”
Let’s see if I can help you.
I have an 87 LB9 and I did the change to the $6E mask. I am very happy with the setup and in particular when I change to the APYP bin (350 manual bins). I use a 3:31 gears.

The bin don’t have a particular point where you can change the final transmission (gears)
The VSS is the sensor should be calibrated to get the correct speed for your ECM and for your speedometer. Check in the net to find the best driven gear for your speedometer cable. You need to check also your tires size.

But be aware that the settings on the bin file have taking in account the corresponded gears. Let’s say that the bin is based on the rpm band for that particular engine.

You can check this site to see what is the original gear setup of your selected bin.
http://www.efitune.com/broadcast_codes/

I hope this will help you.
Regards,
Cobra289

 

I have a mechanical cable, so I don't even know how it can report a speed other than calculating it based on rpm, gears, and tire size.

Everything works fine as long as nothing is messed up in the code with the incorrect speed. Like if the MPH is used in any calculations.

 

If you haven’t change nothing to the final gear and tire size than it should work properly and it should be report the correct speed.
If you change the tire size of the final gears than you should change the driven gear at the transmission output for the cable. (Plastic gear)
Check this link you can see pictures of the gear that I mean (Purple one)
https://www.thirdgen.org/techbb2/sho...hreadid=243617

The ECM uses the speed to drive the CCP and the TCC.
Regards,
Cobra289

 

I think I might have confused everyone, my speedo is fine it's the speed that is logged by TunerPro that is off, it's a good bit higher. I was just wondering how TunerPro can log my speed when I have a mechanical cable.

Is the ECM reporting it somehow or is TunerPro calculating it with defaults based on engine speed?

I have 3.23 gears (stock, never changed) and the log files look like they are calculated using 2.73 gears.

 

OK I will tray to explain this speed input to the ECM.
You have a cable connected to the transmission and this cable is also connected to your speedometer. Here is the place where your ECM takes the speed information.

At the back of your speedometer is a mechanical / electronic device that converts every turns of the cable into a signal for the ECM.

How it works?
Well the cable drives a polished steel plate; on top of that there is a Photocell emitter diode and a Photocell receiver diode, the emitter send a light beam and is reflected by the steel plate when the cable rotate ½ turn, so every turn of the cable you have two reflections and this reflections are catch by the photocell receiver.

So here you are from a mechanical device (Cable) to an electronic signal.
This signal is translated to ECM via and buffer and it is located at ECM pin “A10”.

TunerPro use the information received by the ECM and make and output during data logging, I have never check the speed with TunerPro, but I don’t think that the speed output is incorrect.

GM has changed thru the years the way of obtain this information for the ECM; late models have at the transmission an electronic sensor that send a signal to the ECM.
Here you can see on the picture what I mean.
Regards,
Cobra289

 

So there is a sensor on the mechanical cable!

I was the one confused, =). I have to replace the o-ring on my speedo sleeve so while I'm down there I'm going to get the colors/count teeth on those guys.

But wait, when my speedo says ~70 MPH the ecm reports 80. Shouldn't these two read close no matter what I'm running?


I will be investigating this further before I get a ticket.

 

I know the OEM maf bins have something for rear gearing. Nobody has found it though. Go to the GM dealer and ask for a MAF prom. The PN can only be located after you give the rear gear ratio. I had two different proms, one for a vette/3.73(i think that's the ratio) and one formula 350 prom/3.43's. Each prom made the ecm display a different MPH. The speedo didn't change and I used that as a reference. FYI, I have an electronic speedometer. The only time to change the speedo gear(in trans) is if the speedometer is off. If the ecm doesn't display the same mph as the speedo then you'll not be able to match them by a simple speedo gear change. So you need to make sure the speedometer is correct and ignore the ecm's speed error. All 165's have the mph slightly off. Untill somebody finds the location of the table/constant to correct for rear gear ratio.


Unless the vss buffer (yellow box) can be "adjusted". That thing sends the vss signal to ecm (and electronic speedo).

 

I'm going to follow my wife at 70 mph tonight on the freeway to check my gauge. If it's correct I'll be looking for that bin location. =)

 

I follow my wife every night without success. (Joke)

Sorry I don’t think that you will find something in the code referring to the gears.
I have used several BIN files (ABUT, APYS, ANZA, APYP) in the same ECM and the speed was equivalent. It was and observation and not a real check.

Like I say before “The bin is based on the RPM band for that particular engine.” The RPM of the engine is determined by the final gears and the transmission. That is the reason that GM makes different type of Bin’s for different type of gears, emissions and the same engine.
The ECM has conditions that use the speed. Like “Minimum MPH for ESC enable”

GM has a calibration of 1 mile correspond to 1000 revolutions of the tire.

That means that we have in your case a 2000 pulse per mile frequency (At the buffer) that is used by the engine control module for various emission and torque converter lockup functions.

I think that your speedometer is giving you a low speed. Because the speed at the ECM should be the same as the cable.

If you look to the TunerPro you can see at the data stream that there is no calculation
(factor is 1)

Here you can find more information about VSS.
http://www.jagsthatrun.com/V8-chapte...ed-Sensors.pdf

Regards,
Cobra289

 

Check the ads file just to be sure the calculation basis is entered correctly.
Maybe you edited something and changed it by accident.
In the "general" screen for the connection you can push the button to edit the parameters.
See what's in there.

Duh , now the picture comes up on my screen.
(Good job Cobra )

 

so lets say at

120 mph * 2000 ppm = 240000 pph

so

240000 pph * 1 h /3600 sec = 66.666666 pulses per second

so

120 / 66.666666 = 1.8

so to get current speed you find your current pulses per second and multiply by 1.8?

So something like this is being done in the ECM?

I guess I could have came to the same number via

1p/sec * 1mile/2000p * 3600sec/1hour = 1.8mph

 

Well I followed my wife on the free way and she signaled when she was at 70. I looked at my speedo and it was around 62mph !?!?

Doh, so my ecm is correct and there's something wrong with my speedo. I guess I need to search on this now since I know what's going on.

I'm guessing something is worn out in my speedo.

This sucks, I'm surprised I didn't get a ticket yet, =).

Thanks guys

 

Congratulations, you found the source.
Now you have a different type of problem, the speedometer! You can try at second hand speedometer internals.
Good luck with your car and watch the cops.
Regards,
Cobra289

 

I just wanted to give an update on my speedo. After finding out that my speedo was reading slow I made sure the ECM was reporting the correct speed and I came to a conclusion that my speedo was 12.5% slow. I called some speedometer shops and was given some prices of $100 - $150 to fix it. For that much I decided to try to fix it myself.

I first bought an extra 145mph gauge cluster for backup. I next did some research on how these things work and found out that the iron magnet that spins inside the cake pan can become weak over time. They are not permanent, DOH!

So you have this cake pan turned upside down that's connected to the needle and spring. The cake pan sits on top of the magnet and the magnet is connected to something that looks like football goal posts that spin on the outside of the cake pan. This somehow transfers torque to the cake pan when it spins.

So to increase the amount of torque that is transfered to the cake pan I had to bend these goal post evenly closer to the cake pan. Too close and it'll grab the pan and snap your needle, =). I always tested with my fingers first before I tested with my cordless drill.

Before I started changing these posts I got a baseline using my cordless drill at low and high speed settings. I got something like 18mph at low and 61mph on high speed. After playing with the posts and a drop of wd40 on the tail of the needle shaft that goes into the magnet I got it to go to 69mph at high speed on my drill. That's a tad more than a 12.5% increase but when I did my test drive and compared it to my ECM it was dead on or within 1mph. Woohoo! Took me 3 nights but it worked.

I'll probably keep the extra cluster for backup since I have no room left to increase the speed. This magnet won't last forever.

later

 

Congrats!

 

Ok this is totally off topic, but when did the BCC lookup come back? Is it related to the original one (that I never found out about until it got shut down. )