HDJ81 strange intermittent starting problem with 12-24 switchover relay (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Joined
Dec 4, 2015
Threads
81
Messages
2,031
Location
Dubai, UAE
So I'm driving around a bit (finally) in the RHD to LHD converted HDJ81 and it has an intermittent starting problem. A good fraction of the time when I turn the key I get a buzz but no crank. Batteries are fully charged and in the green.

Originally we thought it was the switchover relay:
1643979549320.png

1643979564389.png

And we replaced it with the above. But it behaved even worse. So we put the old one back in:
1643979612454.png

Now it is back to the intermittent behavior. The technician showed me a trick--one person cranks the key while the other just taps the big terminal on the left with the end of a screwdriver. It seems to work pretty consistently. I have no idea what is going on.

This is my first 12-24 diesel and from reading here some have suggested that the fusible link under the windshield washer might be the culprit. Here's the wiring diagram:
1643979973872.png

When you tap the switchover relay it is not like you are knocking it loose, it is more like you've made an electrical connection. The only thing I can think of is bad grounding. I note those two triangles at the bottom showing that the two batteries have two different grounding points.

Anyone have wise words for this newbie?
 
If physically contacting the relay is causing it to switchover I'd think the contacts in the relay are sticking.

Looking at the drawing it shows the rh batter going to ground.

The lh battery goes to the relay. When the relay cycles it's sending the Lh battery to ground and this giving you 24v.
 
If physically contacting the relay is causing it to switchover I'd think the contacts in the relay are sticking.
It really did not feel like that--it wasn't that I hit it and jarred it loose, but rather the moment I touched it with the blade of a screwdriver--making electrical contact with my hand on the shaft of the screwdriver, the relay flipped. I may be mistaken in all this. (And thank you for your other observations about the diagram.)
 
It really did not feel like that--it wasn't that I hit it and jarred it loose, but rather the moment I touched it with the blade of a screwdriver--making electrical contact with my hand on the shaft of the screwdriver, the relay flipped. I may be mistaken in all this. (And thank you for your other observations about the diagram.)

A relay is a small contactor. The click is light and it often doesn't take much contact for the arm to flip.
 
Make certain that your battery connections are clean and tight. Double check tight.
Then fusible link from passenger side battery, next wire under wiper fluid container. You can always bypass that wire by connecting at or near the starter relay.
 
Make certain that your battery connections are clean and tight. Double check tight.
Then fusible link from passenger side battery, next wire under wiper fluid container. You can always bypass that wire by connecting at or near the starter relay.
Thank you Squash. We've replaced the two of the four battery clamps and I cleaned up the ground on the passenger side battery that goes to the passenger side fender. I have not gone through the fusible link yet. I need to read up on those. I've seen guys making up their own.

BTW, today I happened to go up to Sharjah to look for several items and I found a 'half-cut' 80 with a turbo diesel (RHD) and was able to get a couple of items off of it. I asked about the 12-24 switching relay while I was showing the salvage guys something on my truck and both of them immediately said that they get a lot of guys looking for them.
 
Had a similar issue once with an HDJ81 I had recently acquired. All battery posts appeared to be clean, appeared to be tight, upon physically removing connections to have a look I found that one battery post was badly worn and grooved for some reason, would no longer make consistent contact even with clamp bolt bottomed out. Weird, but it happened.
 
Have you tested battery voltage under load?

The 24 volt start systems are voltage sensitive. If one of your batteries is weak, it won't pull in contactors in the change over relay, or in the starter.
The 24 volt starters also burn through contacts faster than in a 12 volt starter. It's common for the copper contacts to be eroded away through arcing.

A buzz, or rapid clicking can indicate a problem with battery voltage, or eroded contactors
 
Have you tested battery voltage under load?

The 24 volt start systems are voltage sensitive. If one of your batteries is weak, it won't pull in contactors in the change over relay, or in the starter.
The 24 volt starters also burn through contacts faster than in a 12 volt starter. It's common for the copper contacts to be eroded away through arcing.

A buzz, or rapid clicking can indicate a problem with battery voltage, or eroded contactors
Interesting. Helpful. When it fails to start there is a buzz. Both batteries are almost new, but I should check their capacity. They are identical, bought at the same time, Group 27 I think.

I will check the voltages. Lately it seems to just buzz about 1/3 of the time. The truck was off the road fore 18 months, BTW. Not sure if that is relevant.

I'm making an effort to drive it every day to get a feel for the truck. I have to say that it has plenty of pep, especially when I compare it to my 1HD 80.
1644161500085.png
 
More strangeness....

My parts guy was able to source a new relay. I put it in and it did not even buzz. Just nothing. I also tried cleaning the connector on the pigtail coming off the relay.

Put the old one back in and it was back to sort of intermittent but started usually on a few tries.

I then pulled up the washer bottle but at least in my truck there is no ground cable running under it. In the process I did move the wire loom around a fair amount because the washer bottle is a little hard to get out.

After all this it seems to more reliably start on the old relay. Could be my imagination. Could be that something is marginal in the loom. Either way, this is a bit of a pain. Mulling over next steps. Suggestions?
 
The problem is almost certainly not in the relay then.

My problem ended up being a slowly dying alternator which led to really weak batteries that had big voltage drops under load (i.e., while starting). Running thru the FSM tests with a ohmmeter was more confusing than helpful, I recall the relay not behaving correctly AT ALL and just adding to the confusion. The problem with a mechanical relay like that is if it gets right near it's lower operating voltage it will intermittently function. I'd recommend, in order of difficulty:
Recharging your batteries with an external charger (NOT the alternator because maybe it's bad like in my case!) and see if it goes away
Measuring the voltage during starting and see what's happening, and check while grounded to the frame vs. battery terminals (and across terminals vs. across the relay) and see if there's any big differences. I think a big drop could mean weak batteries, a big difference between points indicates a bad ground or bad wires.

I also noticed doing other maintenance later that my ground point on that side (straight off that relay on the bottom of the engine block, IIRC) was nearly all the way broken off thru vibrations/rubbing/movement over the years so I crimped a new connection on it. Come to think of it, I think I accidentally discovered the same thing on the right-hand side after I first got the rig and fixed that as well....it's a real bear to get to without removing stuff, I think it's down there near the turbo so it's not even easy to inspect if I remember right.
 
I kind of peered down to that ground lead to the engine block on the drivers' side and then shied away... it is dark and really hard to get to.

You are right. I need to take some systematic voltage measurements and really understand that diagram much better.
 
The truck seems to be starting every time now. I do notice just a fraction of a second delay between turning the key and the starter engaging. Is that the normal behavior?
 

Users who are viewing this thread

Back
Top Bottom