Enable F0501 Fuel Gauge PWM Table on 98-99 Vortec Blackbox?

[JR96CK]

Hello, everyone... this is my first post here although I've been a long-time lurker.

I've been active on the PPE GM Truck forum for many years, and we've been working on a solution to the 98-99 GMT400 vibrating fuel gauge issue. We've managed to come up with a permanent solution to this problem, but it does require re-scaling the PWM fuel gauge table in the calibration. Having only recently purchased EFILive, I am now looking to do exactly this, and get the fuel gauge repaired on a 99 Tahoe once and for all. But, I've hit a snag.

The OS loaded into the blackbox PCM on this 99 Tahoe I'm working on is #09365085 with a fuel system calibration #9351032, and it does NOT show the field required to re-scale the commanded PWM signal for the gauge. It only shows fuel tank capacity. However, when I open up an Express Van (411 PCM for L31) tune with an OS #12212156 and fuel system calibration #16264666, there is a table (F0501) wherein the commanded PWM can be adjusted. I am using V2 with the latest software and hardware updates, but I cannot find table F0501 in the blackbox calibration.

Another member on the PPE forum has already done this with success on his Tahoe (so I know the table is there in the blackbox calibration) , but he is using HPTuners (screenshots are posted in the thread). Is there any way I can get EFILive to display this table? I'm really close to getting this problem solved if I can just get this table re-scaled.

I don't know if forum etiquette here frowns on linking to other forums, but (if permissable) I can provide a link to the thread where all this is thoroughly discussed if anyone wants to see what I'm talking about.

[EagleMark]

Links are OK and I'd like to see what your working on? I did the 0411 swap and still have the shakey gauge, also not correct anymore.

But as far as getting anything added to 98-00 Vortec, it ain't going to happen. I tried and tried, did tons of work on it and handed everything needed on a silver platter, they are just not interested.

[JR96CK]

Hi, Mark... thanks for the reply.

If you want to see the entire 17-page thread about this issue (an issue which eventually shows up on ALL 98-99 GMT400 trucks & SUVs), here is the link. My involvement starts on page 2. My user name is JR96CK over there as well. The pics I had posted are no longer hosted, so they are not visible, but the several YouTube videos I posted are still viewable via the links throughout the thread:

http://www.pacificp.com/forum/viewto...er=asc&start=0

As to what's going on with all this, this vibration issue is not the same as a sending unit issue, which is the usual misdiagnosis. On the 98 and 99 GMT400 (CK-Series) GM trucks & SUVs, they changed the way the fuel gauge is controlled. The in-tank sending unit sends an analog signal to the PCM, not to the gauge itself as in previous year models. This is why you don't see the issue on 96, 97, etc. year models, as they are wired directly to the sending unit and thus receive a relatively steady analog signal, not a pulse. The problem is, GM did NOT change the gauge cluster at all when thye made this change, so you have the exact same gauge being driven in 98 & 99 by a PWM signal from the PCM. This is not a problem at first (for maybe the first 100,000 miles if you're lucky) because the gauge itself is filled with silicone damping fluid from the factory. However, over time this fluid dissipates from inside the plastic gauge motor (driver) housing and migrates out of the gauge. You can usually feel the sticky residue on the copper windings on the exterior of the gauge driver. When this happens, the gauge can no longer damp the PWM pulse it is receiving from the PCM, so we start to see the high-frequency vibration (it has been referred to as the "hummingbird" effect due to the rapid motion of the needle) manifested in the needle. It should be noted that the gauge will still read the proper fuel level and will still work fine, provided that there is not also a problem with the in-tank sending unit. If the gauge is jumping around to vastly different fuel levels or is reading completely incorrectly, then one is advised to correct the sending unit problem, and then if the vibration (hummingbord effect) still exists, then that can be resolved separately (what we are attempting to do here). This same migration of the silicone fluid will happen in the non-PWM controlled (96 & 97 model) gauges as well, but in this instance, it won't matter, as the gauge is not having to damp a vibrating signal like the 98 & 99 PWM units are, so no vibratory behavior is ever seen in those trucks.

One solution is to send the cluster off and have the driver replaced, but this will eventually result in the problem coming back down the road. GM does not offer replacement drivers, and all attempts to source replacements via other means have been dead ends thus far. Successful attempts have been made by others in this thread on the PPE Forum to refill the silicone fluid inside the driver, but my issue with this is that this will eventually result in the problem coming back down the road too.

The solution I eventually came up with is seen in the YouTube video below. My goal was to flatten out the PWM signal from the PCM before it gets to the gauge, essentially electronically damping the pulse instead of relying on the silicone fluid inside the driver. This would provide for a permanent solution to the problem and it would not matter if the driver is old or new (how much or how little silicone is left in it), as the gauge itself will no longer have to damp anything. As the gauge ages and the fluid runs out, the vibration will not return since the signal has now been "conditioned" into a much smoother one.

Resistor/Capacitor Solution:

http://www.youtube.com/watch?v=jiu_5y2mKW8

The problem with my solution was that the addition of the capacitor to damp the signal skewed the reading of the gauge drastically. In order to "pull" the gauge back into its range, I had to employ a resistor on the signal line to alter that signal. The gauge works on the principle of two competing magnetic fields induced by external copper windings acting on a small disc (immersed in the silicone fluid) inside the driver. This disc is attached to the shaft and thus the needle. I had to essentially equalize these competing "pulls" after the capacitor was installed, thus throwing off the relationship of the two fields.

At that point, the problem was mostly solved, but the needle would not go as far towards "Empty" or "Full" as it really should. It was suggested that the fuel gauge scaling could be changed in the PCM, and another member of the forum did exactly this (with his HPTuners software) later in the PPE thread, and the issue was then fully resolved. I did not have any tuning software with which to do this until recently, and I opted to go with EFILive. The fuel gauge re-scaling was the last remaining thing I needed to do to get the problem permenantly solved.

If you're using EFILive, then you can already do this re-scaling of the gauge IF you are using the 411 PCM. However, it seems at this point that EFILive does not support this table in the original 98-99 blackbox Vortec PCM. Unless this is added in to EFILive, then it appears the only option to employ the resisitor/capacitor solution on the 98-99 Vortec blackbox PCM is to use HPTuners since the other member on the PPE Forum did this successfully (screenshots can be seen in the PPE thread).

[turbo_bu]

The only other thing that EFILive can do for you is IF you know the address to the table that you want to fix, you could create a CAX to edit this. This is pretty much reserved for expert users (I know of what they do ... not how to get the addresses / variables needed), but would allow you to use EFILive to make the changes necessary. Don't think that HPTuners has the same function built in .... either it's in there, or it's not.

I know this doesn't help you directly, but could be useful if you could determine where in the code the table is. Others might be able to do a file compare if you could get a read of the HPT with the same OS.

[JR96CK]

The only other thing that EFILive can do for you is IF you know the address to the table that you want to fix, you could create a CAX to edit this. This is pretty much reserved for expert users (I know of what they do ... not how to get the addresses / variables needed), but would allow you to use EFILive to make the changes necessary. Don't think that HPTuners has the same function built in .... either it's in there, or it's not.

I know this doesn't help you directly, but could be useful if you could determine where in the code the table is. Others might be able to do a file compare if you could get a read of the HPT with the same OS.

I will have to educate myself on how to find the address and the whole procedure for creating a CAX, but thank you for mentioning it. I hadn't yet considered that option. Good to know all the options I have at my disposal here.

[Lextech]

The Black Box PCMs for 98-2000 also have the PWM Hertz set to 59.5 The 2002 Express Van with the 0411 PCM has the setting at 60.1 Wouldn't the slightly higher Hz setting make for a smoother gauge?

Jeff

[hog]

I will have to educate myself on how to find the address and the whole procedure for creating a CAX, but thank you for mentioning it. I hadn't yet considered that option. Good to know all the options I have at my disposal here.

JET and TC2 have this stuff. Download the Jet DST program from teh Jet site, grab some calibrations, you can look and tune the calibrations, you just cant flash, with Jet that is.

peace
Hog

[Charles]

I will have to educate myself on how to find the address and the whole procedure for creating a CAX, but thank you for mentioning it. I hadn't yet considered that option. Good to know all the options I have at my disposal here.

Very cool fix, nice job! Did you make any headway on a CAX using EFIlive?