HDJ81 Cruise control top speed

[diesel junkie]

Res 2012 chip 6k8 1/4w 2mmx1.25x0.5mm surface mount.
Dick Smith Electronics - New Zealand is where i got mine, should be able to source locally at any electronics store.

 

[CruiserGord]

Oh! so it is a bigger resistor than a 1206... damn I just got my 1206's in and they are really small. D Junkie could you post a pic of where the circuit board is? I have a RHD 1HDT but I couldn't see anything underneith the kickboard other than a white square shaped thing on the side.

 

[diesel junkie]

I assume its in the same place as my 1hdft, alloy box just above the steering shaft before it goes through the firewall.Sits on a bracket screwed to the firewall.
ABS and airbag modules to the right & kick panel.

 

[Adam B]

It seems the 2012 is the same physical size as the 0805.

They can be sourced locally in the Digi-Key catalog or online.

Here's as much info as I can get off the packing list....

RL12S6.8FCT-ND
RES 6.8 OHM 1/4W 1% 0805 SMD

Only available as a 10 pack but even that is only $3.71CAD. I ordered with other items so I don't know how much the S&H would be on just the little pack of resistors. They're in stock, usually ships out the same day if ordered online. I ordered one afternoon and received them the next morning.

Now I just have to find that cruise control ECU and get out the magnifying glass. These things are TINY!!

 

[CruiserGord]

That is great Adam! Can you post picks of where that Cruise ECU is when you start working on it. I haven't had any time to actually start looking for it because of work and also this damn weather hasn't gone above -20 in the past 3 weeks. I have to order some of those resistors hopefully this Monday while I still have the chance before I head off to work again.

 

[Adam B]

I found the cruise control ECU quite easily. It's the only thing right beside the steering shaft under my dash. On mine it is a black plastic box about 5x4x1" with SPEED CONTROL printed on it (you won't be able to read this until you remove it, of course). It can be removed by disconnecting the 21 pin electrical connector and removing two M6x10mm hex bolts (10mm head). Take the metal bracket off, pop off the end cover, and the curcuit board slides right out.

And then you find the problem...

On my 1991 1HD-T powered truck the cruise control circuit board is totally different than what the guys with 1HD-FTs describe. There is no position R507 (they go up to about R432 I think) and there are no surface-mount resistors. There ARE 3 empty resistor spots, each of which takes a different (physical) size of resistor, ranging from about 1/2 - 3/4" hole spacing. I have no idea which one, if any, would do anything useful here. Trying to follow where they go, 2 of the 3 would be connected to transistors that are not on the board (empty spots) and the third is connected inline with one of the other 2. It doesn't look like adding a resistor to any of the 3 available spots would actually do anything besides make a funny smell...although it is pretty hard to see, let alone follow, the board layout.

Oh well...so close...

 

[CruiserGord]

Ah dang thats a real s***ty deal hehe. Oh well it was worth the try thanks for the input Adam.

 

[kenavt]

This thread has been dead for a long time, but figure other folks have seen this thread while doing research... in the past fourteen years, has anyone tried replacing/stuffing R507 on the cruise control ECU circuit board? If so, what resistance, a 6.8k?

I think the latest discussion in the intervening years has been around switching the ECU with a different market's one ('95 HDJ81 Cruise Control Question - https://forum.ih8mud.com/threads/95-hdj81-cruise-control-question.922441/page-3).

Regardless of the answer, I'll probably end up trying it. Would really like to go above 115km/h on my upcoming roadtrip (109 km/h + 5% with 33" tires), and it would be trivial for me to just stuff a resistor on the ECU board.

 

[Dusten]

This thread has been dead for a long time, but figure other folks have seen this thread while doing research... in the past fourteen years, has anyone tried replacing/stuffing R507 on the cruise control ECU circuit board? If so, what resistance, a 6.8k?

I think the latest discussion in the intervening years has been around switching the ECU with a different market's one ('95 HDJ81 Cruise Control Question - https://forum.ih8mud.com/threads/95-hdj81-cruise-control-question.922441/page-3).

Regardless of the answer, I'll probably end up trying it. Would really like to go above 115km/h on my upcoming roadtrip (109 km/h + 5% with 33" tires), and it would be trivial for me to just stuff a resistor on the ECU board.

A us ecu fixes the problem.

So if you're dead set in fixing it, swap it out.

 

[kenavt]

I went ahead and decided to try stuffing this resistor as a break from other work I was doing on the truck. After a 3-minute session on the local interstate it does seem to work! I was able to hold 115 km/h and 120 km/h as indicated by the cluster, whereas before I topped out at 112km/h.

I really, really wonder how this was discovered. Maybe this is the one difference between an US or Aussie ECU versus a JDM one.

I used an 0603 6.8k resistor from Adafruit's 0603 passives book. I think 0603 is the right size, but an 0805 or even better would fit okay. I really doubt wattage matters - for reference, if this is a 12V signal (which I doubt it is as it appears to be going into a chip of some sort, which I tried Googling but got nowhere) then the max power consumed by the resistor would be 21mW (I^2*R). Every 0603 6.8k resistor I see available on Digikey is rated for much more then that - minimum 63mW but 100mW seems much more common.

Gratuitous photo dump if it helps anyone:

 

[Dusten]

Looks like in have a new project