HDJ81 Starting Issue (SOLVED!!!) (1 Viewer)

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Nov 20, 2018
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Salmon ID
Hello all. Haven't been on Mud for awhile since I last owned my 3x'd 40th about 12 years ago.

Jumped back into the obsession with both feet with a 3x'd 1991 HDJ81.

I was mid upgrade and had just finished installing a winch in the ARB bumper when my troubles began. I killed the battery winding the cable back in, I threw a charger on it while I went to work on something else. When I came back I think I started the truck up and reeled in the remainder of the cable. A few starts later, my starter stuck. I ran around banging on it and trying to pull the battery cables to get it to stop grinding away. Finally got cables pulled and got it shut down. A starter contactor build was in my future..........after a steep learning curve on 24VDC starting systems!!! The starter contacts were indeed fused together and the rebuild was simple. I slapped in the starter and went to fire up "Turbo." Nothing.......nada......well not nothing, the 24 combo relay seems to be the only thing clicking under the hood when keyed to start.


I have the FSM and am fairly good with electrical circuits, so I figured I'd be able to located the issue w/an afternoon and my DMM. So far I have tested or changed the following:
  1. New batteries.
  2. All fuses are good.
  3. Bypassed the AM1 fusible links and problem remains, are there fusible links elsewhere. The only ones I see are on the DS battery 1 for the glow plugs and double pin plug.
  4. Checked (what I think was the) neutral safety switch, and it was fine.
  5. Followed FSM troubleshooting for 24 combo relay and starter relay both were functional.
  6. I pulled the key switch and it tested good.
  7. I actually pinned out the voltage converter timer (That's an absolute biatch!) and it tested ok, voltages were in the 5-7VDC range and not 12VDC but manual did not state what voltage you would have at the pins, just said VOLTAGE YES/NO for the tests.
Now I can start the vehicle (but not consistently) by applying 12VDC voltage to the starter relay, and I did get the starter to turn by jumping the key switch pins, but that doesn't always work either. Yesterday after replacing the batteries and needing to get Turbo running I jumped the starter relay and it started right up, however once I got it back home I tried to restart it to move it and I could hear the starter plunger pulling in, but the starter wouldn't spin. Now as I understand the circuit the starter always has 12VDC to it from the driver side battery. I didn't have time to crawl underneath to verify, but technically the starter should spin if the solenoid is closing the contacts because it has a constant 12VDC. So that would just leave me with the ground.

This evening I'll verify voltage at the starter and inspect the block ground. This may address the issue w/jump starting from the starter relay, but doesn't address the non-key start issue. Any ideas, experiences, or something I've missed?

Thanks.
 
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K keep in mind i know nothing but here's what i would try in your shoes. Disconnect the + post clamp of the low side battery, then disconnect both the + and - post clamps of the high side battery. Use some quality booster cables and connect one red booster cable clamp to the the low side + post and the other red booster clamp to the high side - post. Your batteries are now in series and your high side battery + should now be 24v.
Now connect one black booster clamp to that 24v high side + post and the other black booster clamp to your starter relay input power bolt. Now run power to the starter relay switch or whatever to let the 24v flow.
This should tell u if the problem is the starter itself or the relay running temporary 24v power to the starter no?
 
Joined
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K keep in mind i know nothing but here's what i would try in your shoes. Disconnect the + post clamp of the low side battery, then disconnect both the + and - post clamps of the high side battery. Use some quality booster cables and connect one red booster cable clamp to the the low side + post and the other red booster clamp to the high side - post. Your batteries are now in series and your high side battery + should now be 24v.
Now connect one black booster clamp to that 24v high side + post and the other black booster clamp to your starter relay input power bolt. Now run power to the starter relay switch or whatever to let the 24v flow.
This should tell u if the problem is the starter itself or the relay running temporary 24v power to the starter no?

When I first started my troubleshooting I did measure voltage directly at the starter and w/the key in start position there was 24VDC at the starter + contact. The solenoid however was not pulling in to make the contacts to turn the starter motor.
 
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Is it possible you damaged the starter when the solenoid stuck? If it’s able to start when jumped only intermittently, it may need some attention...
 
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Haven’t been able to do anymore troubleshooting since it’s been freezing and windy every day since I posted. This weekend we’re expecting warmer temps so planning on doing some additional troubleshooting. Right now I’m planning on;
  1. Checking voltages coming into the starter relay. I really don’t understand the voltage converter timer, but the starter relay ground is provided by this mystery device.
  2. Check voltage at starter both keyed (24VDC) and not keyed (12VDC.)
  3. Check ground at starter and try and jump start with booster cable to starter body.
  4. Inspect motor ground.
 
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Joined
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Is it possible you damaged the starter when the solenoid stuck? If it’s able to start when jumped only intermittently, it may need some attention...
I might be inclined to think that if the starter solenoid would engage every time with the key, but I don’t think I’ve got it to engage with the key since this problem arose. If my voltages look good at the starter w/out engaging the starter solenoid but it won’t start when I do I may look deeper into the starter. Right now I feel that something in the circuit is preventing the starter relay to pull in w/the key.
 

brownbear

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I feel when your starter stuck on the long duration of it being on could have comprised a single wire somewhere. I've had wires become open, meaning they fail or melt from heat.
If you have the wiring diagrams in the FSM you may want to ring out individual wires from the relays to there other end. I'd start with specific wires involved in the ignition and starter relay. When the key goes to start you have to see where it is going to energize what.. The lighter wires are the ones that tend to get damaged when relays or things go wrong.
 

mudgudgeon

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When I first started my troubleshooting I did measure voltage directly at the starter and w/the key in start position there was 24VDC at the starter + contact. The solenoid however was not pulling in to make the contacts to turn the starter motor.

Have you verified both batteries a good under load?
Test each battery while you have a decent load on it (high beams, or winch running).
You should see voltage stay above 12volt for each battery
If you have one battery with a bad cell, you may not have enough current to fire the starter motor relay.

Also, high side - low side was mentioned above. Not sure this term applies to the hdj81 system?

Hdj81 uses both batteries together in parallel for lights, accessories etc.
When you turn the key to start, there is a change over solenoid that breaks the parallel link, and links both batteries in series for 24volt start only.

Because both batteries are in use all the time, if one is bad, it can destroy the other as the good battery tries to pick up the slack.

One bad cell can bring the hdj81 to its knees
 
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Ok, well I got some quality time w/the DMM & Turbo today. Here’s what I think I’ve narrowed down;
  1. There is 10.something VDC at the the back side of ST1 with the key in the “on” position. Voltage increases to 11.something in the “start” position.
  2. There was one instance when the voltage was 0 at ST1 w/the key in the “on” position and it went to 12+VDC when I cycled the key to start. I also had 12 VDC at the plug that goes through the Neutral Start Switch (NSS.)
  3. I jumped a wire from the plug that comes from the key switch to the NSS directly to the starter solenoid (ST pin) and had the ground (E) connected to the ground. Started perfectly with the key......once. Then I was back to having 10.something voltage at ST1 in the “on” position and LC wouldn't start.
  4. Tested NSS and it appears to be fine.
  5. I think I have a short to ground between the NSS plug and the starter solenoid plug pin “ST” as I have 12VDC from that pin to the positive post on the battery.
I think I may need a new key contact block, but I’m tired of throwing money on parts that aren’t bad and I’m still in the same situation.

Planning on unplugging the key switch plug and the NSS plug. If I can provide 12VDC to the bypass that I had wired up earlier and get the starter to consistently turn over. I’ll run a new wire from the plug output (after going through the NSS) to the starter relay. Then I’ll order a key switch contact and try that.

1970621
 
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Joined
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Have you verified both batteries a good under load?
Test each battery while you have a decent load on it (high beams, or winch running).
You should see voltage stay above 12volt for each battery
If you have one battery with a bad cell, you may not have enough current to fire the starter motor relay.

Also, high side - low side was mentioned above. Not sure this term applies to the hdj81 system?

Hdj81 uses both batteries together in parallel for lights, accessories etc.
When you turn the key to start, there is a change over solenoid that breaks the parallel link, and links both batteries in series for 24volt start only.

Because both batteries are in use all the time, if one is bad, it can destroy the other as the good battery tries to pick up the slack.

One bad cell can bring the hdj81 to its knees
Batteries were both replaced.
 
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So I got some more time under the hood and dash today to troubleshoot. I chased wires and relays all over the truck. The wiring itself seems sound as all everything seemed to wring out correctly when I disconnected and tested individual components. Still getting random low VDC at the key switch plug. Then I dug into the “magical” voltage converter timer box. Once I opened it up I was hoping to find some relays etc to test out, but it was nothing but IC boards, transistors, resistors, etc. I did find one diode that is bad.

I hoping someone out there on Mud that’s converted their starting circuit to a 12 VDC or has a HDJ that they’re parting out has one of these that their willing to part with. If anything I could at least swap out the bad diode from a donor box.

Tomorrow I’ll try and disconnect the “magical” timer and see if that gets rid of the weird voltages at the key switch.
 

brownbear

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How I check for shorts to ground is by putting my meter in ohms and then putting the back lead to chassis ground. Then you can check a wire that would go to ground to see if it's shorted. You can also ring out a wire. Go to one end and then the other. See if you have resistance.

SO 0 ohms is perfect circuit. Most meters have a little resistance when they measure. like .03 ohms or so.

When you ring out a wire to see if it has continuity it will let you know if its. But you have to actually disconnect each end. The wire you suspect is a good one to check to ground and ring out. You should have no continuity until you depress the clutch switch.

If they clutch switch has failed it might be showing as low voltage like you mentioned. As it would have resistance and some voltage is dropping crossing it.
 
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I started using the schematic that’s in the HDJ80 chassis manual rather than the simplified schematic in the engine manual since it gives pin out numbers and wire colors.

While scrolling through the manual I randomly saw that the cruise control ECU had some tie in into the starting circuit. On a whim I disconnect the CC ECU and now am no longer getting an under voltage reading at the starter switch ST1 when the key is in the run position.

Checking the circuit all the way through I’m getting +12VDC to the starter relay coil plug. The only thing that I’m not getting is a ground signal from the voltage converter timer (VCT) when keyed to start. The wire is good since I grounded the plug pin to ground and had + & - VDC at the starter relay plug. So hopefully the VCT ECU is indeed faulty as I found the bad diode in it. It is operating the 24 VDC combining relay just fine though.

Still looking for a VCT and if anyone has a troubleshooting shooting procedure for the VCT that be helpful as well since I can’t seem to find one.
 

brownbear

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Are you able to change the diode? Can you see the direction the diode sits? They have a bar marking on one side, which shows the flow (block) of current. If it's totally melted it may be hard to see the direction it must be soldered in.

I would certainly replace that diode and give it a try. It's possible that reverse polarity of some sort fried the diode.

Change the diode and give it a try.
 
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Are you able to change the diode? Can you see the direction the diode sits? They have a bar marking on one side, which shows the flow (block) of current. If it's totally melted it may be hard to see the direction it must be soldered in.

I would certainly replace that diode and give it a try. It's possible that reverse polarity of some sort fried the diode.

Change the diode and give it a try.

Resistors are easy enough to identify and swap out but other than knowing that diodes should only flow current one way is about the extent of my knowledge base, otherwise I would have taken a soldering iron to it already. When I tested against the other like diodes on the board the functioning ones had 550ish Ohms (maybe that was .5ish voltage drop) the one at the bottom left of this pic had half the resistance (or voltage drop) and flowed current in both directions.

IMG_4252.jpg
 
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I don't have much to add to help your troubleshooting but I'd do away with at the 24v switching and install a 12v starter and be done with it. It's Gunna cost a bit, but will save you headache later. I used a bosche unit from ebay and it has been flawless.



Good luck!
 
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I don't have much to add to help your troubleshooting but I'd do away with at the 24v switching and install a 12v starter and be done with it. It's Gunna cost a bit, but will save you headache later. I used a bosche unit from ebay and it has been flawless.

I've definitely considered it more than once during this process. The stopping point has been that the wiring that I've seen still utilizes the VCT as the signal to pull in the starter relay. Of course I could rewire it, but that's still an option w/the system that I have. Once I get the system operational, I'll probably convert over to a 12 volt starter system to simplify it when there a component in the system fails and requires replacement.

I seriously never would have thought this would have taken me down the rabbit hole as far as it has.
 
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Hi,

Last year I had some intermittent no crank issues with my 1991 hdj81. I was convinced it was the Voltage Converter Relay at first as i was see excessive voltage drop across it after startup when the batteries where charging back up. In my case it turned out to be the NSS (if I jiggled it or put it in neutral it would start); a under the truck disassembly, clean, sand contacts and grease fixed it. Before doing that i spent some time trouble shooting the starting circuit and will give my 2 cents.

First of all, regarding your diode on the pcb. In some circuits you most remove at least one leg of the diode in order to test if it is good or not (other components in parrallel with the diode can give you a false reading with the DMM).

The VCT operation is rather simple:
Key in On Position:
---- 12V across pins 2&7
---- 0V across 5&6, 1&3, and 4&7
---- VCR state
1+ connected to 2+ (LH/RH batteries in parallel, by connecting positive terminals together)
E connected to 1- (LH starting battery neg post connected to engine ground)
Key in Start Position:
---- +12V across 1&7
---- VCT applies +12V across 5&6
---- VCR actuated
1+ & E No Connection
2+ connected to 1- (LH battery in series with RH although only the starter (and alternator charge cable if connected to LH battery) see 24V)
---- VCT Circuits waits for +12V across 4&7, then
---- VCT connects pin 7&3 grounding the E pin of the starter relay (cranking the engine if everything else is functional)

A) I would suggest first manually running the starter to make sure the VCR and starter are working properly.
1. Disconnect the VCT and VCR harness plugs
2. Apply +12V from the RH battery (drivers side of hdj81) across e and g of the VCR
3. Check for +24V at terminal 30 of starter, check voltage across 2+ and 1+ on VCR (leave DMM connected for next step)
4. Apply +24V from the 1+ terminal of the LH battery (drivers side of hdj81) to terminal 50 of starter
5. Engine should crank, during note voltage drop across 2+ and 1+. If excessive could indicate failing VCR contacts.

B) If the above process works repeat, but this time for step 4 do this (checking the wiring between starter relay and starter):
4b. Jumper across the B & MG terminals of the starter relay plug.

C) If the above process works repeat, but this time for step 4 do this (checking the starter relay itself):
4c. Apply +12V from the RH battery (drivers side of hdj81) across E and ST of the starter relay itself (while the plug with B&MG pins is left connected).

D) If the above process works repeat, but this time for step 4 do this (checking the ignition switch and wiring to/from the VCT):
4d. Jumper across pins 7 & 3. Then turn the ignition switch to start position

E) If the above process works repeat, confirm that the only issue present is the VCT not applying ground to terminal 3:
1. Reconnect the VCR and VCT plugs. Disconnect the starter relay harness plug containing the ST/E pins
2. Turn the key to/and hold in the start position
3. Check for operation of the VCR confirming +24V at terminal 30 of starter
4. Connect E pin of starter relay to ground, then jumper from harness plug ST to ST pin on the starter relay
5. Engine should crank, during which note voltage drop across 2+ and 1+

If all of the above checkout then the VCT is likely faulty, although a low voltage or bad ground to the VCT itself may cause the circuit to misbehave as well. If so, you could probe the voltages the VCT pins while performing step E. An oscilloscope and circuit model would make this much easier and definitive. If you are comfortable soldering a pcb, you can use a soldering iron to free up one leg and then test it properly (preferably with the diode test function of your DMM, rather than resistance mode). If it is bad, finding a replacement should not be too hard, but there is no guarantee that will be the only bad component (there are other solid state components present... transistors/mosfets).

Pay particular attention to the VCR making sure that it maintains 24V operation under load. The VCR takes alot of abuse in the case of having one battery low and the other fully charged.



BTW, there was recall in Japan related to the issue that you experienced to start this whole mess. Below is the info from toyota.jp when i ran a recall check for my chassis #.
1. Vehicle phenomenon
  1. (1) Repeated running such as off-road or large step ride may cause excessive force to be applied to the steering and suspension relationships, so the knuckle arm mounting part may slacken or the cross shaft of the gear box may deform. Therefore, if proper use and maintenance are not performed and the product is used for a long time as it is, the part may be damaged.
  2. (2) When starting the engine with the performance degraded of the battery, the operation of the starter circuit control computer becomes unstable due to the voltage drop, and the contacts of the electromagnetic switch repeat ON / OFF in a short time and the wear of the contact may be accelerated. As a result, it takes time to start the engine or noise is generated. If the contact of the electromagnetic switch of the starter is used as it is and the contact point of the electromagnetic switch of the starter exceeds the wear limit, the contact generates heat locally and welds and the starter May continue to spin and smoke.
2. Content of improvement
(1) In addition to informing about the use and handling of cars and the necessity of maintenance and maintenance, we will inspect the steering relationship (free) and if there is any abnormality, I will ask for maintenance.
(2) In addition to informing the maintenance of the battery and precautions at the start, inspect the electromagnetic switch of the starter (free) and replace the one with large contact wear with new one.



S-HDJ 81V KC-HDJ 81V





Toyota
Land Cruiser





HDJ 81-0000017 to HDJ 81-0078271





From January 22, 1990 to December 22, 1997





(1) (2)


 
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E) If the above process works repeat, confirm that the only issue present is the VCT not applying ground to terminal 3:
1. Reconnect the VCR and VCT plugs. Disconnect the starter relay harness plug containing the ST/E pins
2. Turn the key to/and hold in the start position
3. Check for operation of the VCR confirming +24V at terminal 30 of starter
4. Connect E pin of starter relay to ground, then jumper from harness plug ST to ST pin on the starter relay
5. Engine should crank, during which note voltage drop across 2+ and 1+

Awesome help, thank you.

I’ve gotten to this step in your troubleshooting process, and wanted to confirm that #4 was ST1 from the key switch harness, not elsewhere.

I purchased another VCT online, and I have the same results. Vehicle is starting perfectly by jumpering pins 3 & 7 of the VCT harness. With both VCT’s.
 
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