To glow or not to glow.

[Green1]

In about Feb of this year, it started doing:
*When the engine is stone cold, glow plug circuit works completely normal
*when not fully warmed up, circuit works normal, either 2 clicks a few seconds apart, or 2 clicks very close together
*when fully warm, and it has sat for 5-10 minutes, no clicks at all. Given it is hot, it starts just fine.

Any theories?

I *think* that's the way it's supposed to work... when fully warm the temperature sensor sees that there is no need for the plugs, and tells the glow controller not to use them.

[mararmeisto]

@Erebus - what's you've described is a properly functioning glow circuit. When the engine is warm there's no waiting for the glow circuit because it's already turned off by the ECU via the glow controller.

[drrod]

So all this talk about glow plug function has got me wondering. Here is what ours does:
- first cycle takes abou 5 secs.
- second cycle (turning the key off and on) is almost instant between the 2 clicks. This is regardless of how cold it is.
- the control unit continues to click several times even after the engine starts.
- even with the engine warm, the first cycle is about the 5 sec range.
- The van starts as soon as you hit the starter, regardless of how cold it is if we cycle the plugs once or twice (and it has been plugged in when really cold).
- We never cycle the plugs more than twice regardless of how cold. I didn't think it necessary because the second cycle was so short.

Since it has always started so good, I have not really thought much about it.
Should I be concerned about the conrol unit? The multiple clicks after startup has me a bit worried now.
Probably overthinking this but any thoughts would be appreciated.
Thanks
Rod

[Erebus]

So all this talk about glow plug function has got me wondering. Here is what ours does:
{snip}
Since it has always started so good, I have not really thought much about it.
Should I be concerned about the conrol unit? The multiple clicks after startup has me a bit worried now.

What you describe is how mine used to work. Multiple clicks after startup is normal.

Further to the description of how mine is acting. The other day, when engine fully warmed up, the 2 clicks came about 1 second apart. That's how it always used to be. Then the next time I started, about 20 minutes later, no clicks at all. It's the no clicks that is relatively new. Before I ALWAYS got clicks.

[drrod]

Ours will always have a noticeable (ie. seconds) gap between clicks on the first cycle. This happens even if the engine is fully warmed up. I usually wait for the cycle to complete before starting the van, not because it is easier to start, but I am thinking that there something, somewhere, in the system, that would be damaged if I didn't. I know that is probably not true but it starts and runs so good that I don't want to screw anything up.
From reading, it sounds like a faulty temp sensor. The only thing going against that is how well the van starts, even at 40 below after one 5 sec cycle and one very short cycle. I am a big fan of "if it ain't broke, don't fix it" club so I haven't done anything about it for almost 2 years.
Rod

[Blackberry]

My '92 L300 had been starting fine/immediately after 2nd click (say 7 seconds after 1st when temp 5c) but seemed to belch too much whitish/greyish/blueish smoke for a minute or so upon cold start. It looked like it was coming out of the tail-pipe in irregular bursts, so I thought, hmm, maybe one or 2 GPs are going/not heating uniformly. So I was travelling in SE Asia and I bought some aftermarket glow plugs. The GPs in the van were OEM Mitsu green-tops with 6.2v stamped on them. I've scoured the i-net high & low to figure out exactly which glow system my van has and all info eventually led to: OEM part number MD092392 for the dual-voltage glow system found in 02/91-06/93 4D56T engines. I believe this system uses 2 relays as well (there's a ton more detailed info about this on the mdocuk site than on ours, BTW...and, apparantly, this "super quick start" dual-voltage glow system is problematic - which might explain why it was so short-lived). So anyway these aftermarket (HKT knock-off's, part# CP-06) had 6.2v stamped on them and even had MD092392 stamped on the box so I figured they had to be the correct ones. I put them in and nada... no initial clicky/no current/no starty. I'd bought a box of 10 so I put another set of 4 in, just in case...same non-result. So I checked the resistance on them and it was slightly over 1 ohm. I checked the resistance on the OEMs and it was below 1 ohm - can't remember exactly what but .25-.8 ohn range rings a bell. So I think there must be some kind of feedback to the ECU that doesn't happen if the resistance is too high. According to the mdocuk site there's many aftermarket GPs that are supposed to be MD092392-compatible but that don't work. They've had success with one brand, so I've bought a set from them but have yet to try them. Before I do I'll pull the ECU to have a close look/sniff to see if anything is cooked...which could even possibly be why it didn't like the aftermarket GPs with such a slightly higher resistance. I also changed my temp sensor but that had no effect on the blue smoke (and when I got the old one out and tested it, the resistance was within spec).