Another Glow system mystery

Trinker · Post by **Trinker** » Sun Feb 25, 2018 11:22 am

Here's what I have going on now,

92 Chamonix, with the super fast (2 relay) glow system. Glow plugs new in the fall, glow ECU rebuilt start of November. New battery last month.

After my ECU was rebuilt in the fall, the van was cold starting as good as it ever has. Glow plugs were functioning almost perfect. The only issue I had was when the engine was warm, the ecu was still flashing the glow plugs for about 7 seconds.

My first thought is temperature sender, but I neglected to fix it with and upcoming six week trip to South America.
Upon returning home, the issue continued, but only recently became worse. When the engine was cold, the ecu was working perfectly, but when it was warm, it started turning the plugs on for longer and longer, and when the plugs were on, not allowing me to crank the engine (likely due to the power draw?) And therefore over using the plugs. Now I'm at the point, when the engine is warm, the the glow relay turns on, and stays on, therefore I can't start it when's it's warm.

This is where it gets interesting.. as a simple fix to get me back on the road and down to the island, I decided to go back to a manual switch I installed previous to getting my ecu fixed. Much to my dismay, now my manual override only intermittently works. And with no apparent cause. I've since removed the switch from the system and have been troubleshooting without it (just manually operating the relays) and sometimes they work for a time and then next thing you know they both simultaneously stop working. Yesterday it seemed to be working normally and I had time to put it all back together, checking for normal operation at every step. It worked all the way up to when I went to check the amount of juice I was receiving at the plugs, and then sure enough, nothing..

Insights? I'm going to potentially replace the wiring for the manual switch today, might even pop the relays out (if I can get them off their home on the wall) and see how they're looking...

helibrian · Post by **helibrian** » Sun Feb 25, 2018 1:37 pm

I had the same problem but I don’t have a manual switch. I had 2 wires chaffed together in the harness above the fuel pump. Check it out the engine vibrates so insulation will wear down.

Trinker · Post by **Trinker** » Sun Feb 25, 2018 1:59 pm

How did you go about finding the chafe? Ripping open harnesses at random and checking each wire?

Trinker · Post by **Trinker** » Sun Feb 25, 2018 4:57 pm

Update, now I have check for continuity on all of my.manual glow switch wiring, passed with flying colours. Next I pulled the relays out and cracked them open to inspect. They were shiny and clean on the inside with nothing visibly wrong. Next I opened up the wiring harness that comes off of the injector pump, and no wires show any signs of significant wear. Next thing I did is brought my new battery in to get load tested (running out of things to try) and it passed the test no problem. Gotta love electrical, it's like looking for leprechauns under the hood..

john clem · Post by **john clem** » Mon Feb 26, 2018 3:27 am

spent $100 to get glow circuit brain box rebuilt, but still had similar problems as yours so unplugged the ECU, i ran a wire from an ignition switched on source, fused it and then to the solenoid relay for the glow plugs with a 2 terminal push button start type switch. have to hold for about 2 minutes.Then she purrs. warmer weather i push button for 20-30 seconds for the pre-heat. cost for repair $4.00 For really cold weather or if you wanted faster preheat one would need 2 switch setup to activate the double voltage initial cycle they program in there. was just a temporary fix if all else fails (2 yrs ago)

Trinker · Post by **Trinker** » Mon Feb 26, 2018 11:49 am

Hey John, I have a similar back up system to you. I draw power from one of the hot side of the relays, running to an On-Off-On momentary switch. Then two wires run back to the relays to operate them on and off. I've have good continuity with all my wires, a constant 12v flow. However the relays are still only operating intermittently. When they arn't operating, as soon as you open the circuit to the relay the entire thing goes dead.. 0V

Post by **Growlerbearnz** » Mon Feb 26, 2018 3:14 pm

Trinker wrote: My first thought is temperature sender, but I neglected to fix it with and upcoming six week trip to South America... ...it started turning the plugs on for longer and longer, and when the plugs were on, not allowing me to crank the engine (likely due to the power draw?)

Maybe I need to add a line to the ECU FAQ that says "if you're replacing the ECU also replace the temperature sender". That little thing can cause *so* much trouble.

I'm thinking maybe a failed temperature sender has caused the ECU to burn out your new glow plugs. I would pull the glow plugs out and bench test them (check resistance, and then apply power to make sure they're still glowing) just to make sure they're actually still working, and work backwards from there.

(Were these genuine Mitsubishi plugs?)

Trinker wrote: It worked all the way up to when I went to check the amount of juice I was receiving at the plugs, and then sure enough, nothing..

Well that's not right. I would turn on the manual bypass and then test for voltage at the glow plug rail, glow relay output(s), dropping resistor (if you're using the 6V/super-quick relay) and then glow relay input(s). Something has to be the weak link.

Still bench test the glow plugs though.

Trinker · Post by **Trinker** » Tue Feb 27, 2018 6:14 pm

Checked the glow plugs (pulled them out and hooked them up to the battery one at a time, they lit up perfectly

) so at least I didn't fry those.

What I did find with further digging is a rather melted wire coming off the battery terminal and running into one of the harnesses.

: wire.jpg (17.98 KiB) Viewed 7613 times

I unplugged the wire and checked for power at my relays getting a reading of 0.4 ghost volts...
Reconnected the wire and checked for power at the relays getting 12V once again.

I'm going to replace the wire feeling that it's part of the problem, failing to transfer enough juice for normal relay/glow system operation.

Additionally I took a reading of the resistance between the two terminals on my temp sender. I realize that it might not be the most useful information, but I got a crazy high resistance reading (in the 1000's of ohms range). I'll have to drain a little coolant, pull it out and give it a proper check here soon, but first step is restoring my manual switch function and getting back on the road.

Trinker · Post by **Trinker** » Thu Mar 01, 2018 12:49 am

The wire was the woe of my manual relays malfunctioning after all. It is in fact a fusible link for the harness that runs from your battery to your glow relays. I'm just guessing here but I assume that my ecu partially cooked the fusible link when it was over glowing the glow plugs. When I hooked up the manual switch it was intermittent due to the restriction of power flowing through the (*almost* completely destroyed) fusible link. (see #70 in image below..)

: fusible link.png (287.78 KiB) Viewed 7592 times

For the time being I have simply replaced the fusible link with slightly smaller spades and some regular wire. But that is hardly ideal because if I were to experience a short I could melt the harness or do significant damage to something that would be much harder to replace. Alas my next immediate mission is now to either find a scrap van to pull the fusible link from, or create a new one myself..

Trinker · Post by **Trinker** » Thu Mar 01, 2018 12:52 am

It may actually be #54 or #55 that is the exact fusible link in the photo above, but you guys get the idea..

sk66 · Post by **sk66** » Thu Mar 01, 2018 7:57 am

I would replace it with an in-line fuse holder available at any auto parts supply.

Trinker · Post by **Trinker** » Thu Mar 01, 2018 9:47 am

sk66 wrote:I would replace it with an in-line fuse holder available at any auto parts supply.

That's my plan, the only tricky part is figuring out which size fuse would be appropriate...

Post by **Growlerbearnz** » Thu Mar 01, 2018 1:52 pm

It's not a great idea to replace a battery compartment fusible link with a fuse. Fusible links are used in battery compartments partly because a large overload causes the wire to melt and separate without sparking. (Much. And any sparks are isolated inside the silicone insulation, I guess). Fusible links can also withstand occasional power spikes which would blow a regular fuse. A slow-blow fuse might do the job, but getting the value right might be tricky.

A regular fuse in a high-current overload situation can blow very quickly, spraying metal particles all over the inside of the fuse housing, which might form a path for continued current or create sparks and arcing- which isn't ideal in a battery compartment, what with the possibility of hydrogen being present.

You can buy fusible link wire, and it's colour coded, but I don't know if the colour codes are consistent between NA and japan.

sk66 · Post by **sk66** » Thu Mar 01, 2018 3:38 pm

Looks like they go by wire gauge and not amperage.

: Screen-Shot-2018-03-01-at-5.32.48-PM.jpg (262.22 KiB) Viewed 7574 times

The main 80amp FL *looks* more like a regular fuse.

Post by **Growlerbearnz** » Thu Mar 01, 2018 3:50 pm

sk66 wrote:The main 80amp FL *looks* more like a regular fuse.

Yeah, the 80A alternator fuse is just a fuse, though it's in a large housing and is quite well insulated. I'm not sure why they went with a fuse there, maybe to protect the alternator's electronics from power spikes? (whereas a fusible link's job is to protect the wiring, so it will withstand power spikes).