Speedo correction, Abbott box and ABS: PROGRESS

[fest3er]

Sorry it's taking me so long to do this. I had to buy an oscilloscope to continue.



In a nutshell, the Abbott box can be modified to correct the speedo/odo signal between the CAB and the PCM. This is good news for folks with four-wheel antilock brakes, as they won't need to buy three Abbott boxes: one will do the trick. Also, since the correction is after the CAB, there will be nothing to interfere with antilock brake operation.



I have a bit more work to do to ensure a robust solution. With luck, I'll have more news in a week.



Following are technical details for those geeks who like them.



I've finally gotten the Abbott box to correct the speedometer/odometer after the CAB. There is a trivial solution that simply makes it work (adding a single resistor), but it leaves open the possibility of damaging the Abbott box or the PCM. We don't want that!



The correct solution requires four resistors, a capacitor, some wiring, cutting a single trace on the Abbott circuit board, and removing several unneeded components. This solution employs an unused comparator in the Abbott box.



Thus modified, the Abbott box will provide a safe signal to the PCM and provide static protection to the Abbott's output. Installation will involve tapping into the CAB-PCM VSS wire (instead of the RWSS-CAB wire).



Look for an update next week.



Fest3er

 

[Pete Peterson]

Thanks for the update Neil, will be looking forward to the next installment... ... ... . Pete

 

[fest3er]

Well, it's been a week.



First, Matt told me Rickson are using a new box that corrects the message sent to the dashboard over the CCD bus. Thinking about it, there *may* be a problem with this method if the correction takes place *after* the PCM: the PCM stores what it thinks is the latest correct mileage, and if the dash loses its memory, the PCM *could* restore an uncorrected odo reading. But if this is not a problem, then Rickson have a viable solution and the Abbott box can join all those cats and air boxes lying in the dust bin.



Now, having thought about my findings re: the Abbott box, I believe the trivial solution is probably the best and easiest. I remembered that the PCM was originally designed to take a signal from the transmission sender directly. It would cost DC a lot to issue a new PCM, so they probably left the PCM the way it was, and had the CAB send a suitable signal to it. Which is why the trivial solution worked.



"So what *is* the trivial solution?" you ask. It is a simple matter of soldering in a 4. 7K resistor between +5VDC and the white input lead. In electronics terms, the CAB needs the other end to supply a pull-up resistor so it can pull the signal to ground for each pulse. I believe the standard output is strong enough to drive the PCM.



Oh, and the Abbott box would then be inserted into a different wire (the one between the CAB and the PCM).



The +5VDC can be gotten from anywhere on the board, but it is probably easiest to get it from the output of the voltage regulator. If you are good with a small soldering iron, you could attach the resistor to any +5VDC VCC pin on one of the ICs.



I haven't got a digital camera (yet), so I'll have to draw up a diagram for those brave enough to perform this mod.



If you are interested in this mod, let me know, and I'll do up a diagram and send it to you.



Fest3er

 

[work2muchplay2little]

fest3er, thanks for putting your brain power behind this. This comes just in time as I'm on the verge of installing taller tires. Would you be able to post the diagram to the TDR website, or prefer to email? One other question: would you, for a reasonable fee, make the mod on an Abbott box that a member would send to you, return postage paid?



TIA

 

[Rambling]

Nice going!

fest3er,



Thanks for sharing your efforts with the rest of us. I don't have a need the info now but I'm filing it away just in case. You just never know when you need you'll need something like this.

 

[RADdodge]

I just received the new box from Rickson. Haven't had a chance to install it yet, will be a few weeks. However the instructions have the unit installed between the CAB and the PCM, so it shouldn't affect the ABS. It cuts and splices into the Wt/OR wire coming out of pin 12-C1 on the CAB to pin 27-C2 on the PCM. The adjustment is by a screw (variable resistor I assume). It has provision for two settings selected by a switch (summer/winter tires). It's called "Superlift TruSpeed Speed Sensor Calibrator. " It's a little pricey Imo, but if it does the job, great. I'm tired of trying to get it done the way it should have been done all along - with the DBR tool at the dealer.

 

[DieselDoghouse]

Abbott box upgrade

Ditto on the info filed away. I too was hoping to reset the PCM with a DRB tool on my '98 (see my post DRB & PCM) but after an hour of foiled attempts, found the current version 5051 of DRB software cannot get the PCM there, so its sounds like an Abbott or equiv will be in my future. Since the PCM is an EPROM someone suggest writing correction software on a PC. Anybody out there a 'Code Warrior'???

 

[fest3er]

Originally posted by work2muchplay2little

fest3er, thanks for putting your brain power behind this. This comes just in time as I'm on the verge of installing taller tires. Would you be able to post the diagram to the TDR website, or prefer to email? One other question: would you, for a reasonable fee, make the mod on an Abbott box that a member would send to you, return postage paid?



TIA

Download the Abbott Box modification drawing. A couple parts, a couple tools, a bit of skill, and you can modify your box.



Anyone want to volunteer to be a guinea pig and try the mod to be sure it works? Field results rarely match lab results!



As to me doing it, what's a reasonable fee? Cost of parts plus a pittance for my trouble? Of course, we're probably treading on thin ice now re: TDR website rules. I'd have to check part prices (oh, like how much can a resistor and 6" of wire cost anyway?). $10 would be in the ball park.



Darn. I knew I forgot something. I forgot to indicate which pin on the CAB connector this gets patched into. Print a copy of Bruce's post. Though a drawing of *exactly* which pin it is could be helpful.



Fest3er