Won't Cold Start

Does your Mitsubishi L300 make a strange noise? Need wheel alignment specs?
Trinker
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Won't Cold Start

Postby Trinker » Tue Oct 03, 2017 8:10 pm

Here's another mystery for the forum, 92 Chamonix L300 4D56 285000kms:

Brand new glow plugs, manual glow plug relay (that works, tested today),
New top end recently (head replaced)
Re-built injector pump two years ago and replaced injectors two years ago as well
Fuel filter changed last year, battery works well, starter cranks well

Won't cold start, just cranks and cranks until battery dies or you plug in the block heater to warm it up and try again later. Temperature around freezing at night recently, warming up during the days, should still fire without the block heater. It's always been a smoky starter but still always started...

Ideas???
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Growlerbearnz
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Won't Cold Start

Postby Growlerbearnz » Tue Oct 03, 2017 9:27 pm

When it's cranking, is it trying to start at all? Any little coughs or smoke out the exhaust? That it doesn't start unless the block heater is connected really does suggest a lack of heat in the engine, which usually means cold glow plugs, could you have missed something?

A quick test is turn on the headlamps, then turn on the glow plugs. If the headlamps dim, the glow plugs are probably working- they're at least drawing a lot of power, which they should. If not, did you reinstall the engine earth strap? The definitive test is to pull the glow plugs and power them with jump leads, and watch for the glow.

The only other reason for a lack of heat would be low compression. Too-tight valve clearances would do that.
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Trinker
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Won't Cold Start

Postby Trinker » Tue Oct 03, 2017 9:57 pm

100percent sure my glow plugs are working, brand new good quality glow plugs getting 12v when I hot flash and something like 8-9 volts when I use the warm flash (on my manual relay system). Its barely trying to start when its cold but a little bit of sputtering occasionally.

Once it's warmed up and fired up it runs well, valve clearances were tuned to factory spec when the new head went on last week.

I'm curious to check cylinder compression here on it, but the bottom end shouldn't be so worn as to not make enough compression to start with glow plugs around freezing, plus like I said before, always started when cold (even if poorly) before all of the recent work..
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Won't Cold Start

Postby Growlerbearnz » Tue Oct 03, 2017 11:18 pm

Thinking of things that might have changed since you replaced the head:

Maybe timing one tooth out? I would think you’d notice once it was running, but if it was retarded (rather than advanced like when the belt skips) it might be subtle.

Was your new head a protruding valve head to match your (presumably) protruding valve pistons? (viewtopic.php?f=94&t=17332)
A flush valve head would lower the compression. Might be a good idea to do a compression test, just to eliminate compression as a source of trouble. A new engine should be 440psi, lower limit is 320psi, no more than 45psi difference between any two cylinders.

Another thing that helps when starting from cold is to push the accelerator about halfway while cranking. You're probably doing that already, but if not, give it a try. (but yes, I appreciate that it used to start just fine before the new head. Something's changed.)
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Won't Cold Start

Postby Trinker » Wed Oct 04, 2017 7:15 am

Replaced with the matching (protruding valve) head.
Accelerator being held halfway down when cranking
And I don't think it's a tooth off because it only seems to be a cold weather issue, runs really well when once running, and starts no problem when warm.

I guess I'll check the compression here next and see if that's the culprit, and re-adjust valve clearances while I'm at it
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Won't Cold Start

Postby Growlerbearnz » Wed Oct 04, 2017 12:54 pm

It's a puzzle for sure. I can't really think of anything that makes starting harder when cold, apart from compression and glow plugs. You're not going to get fuel gelling at 0C, and anything else that causes poor starting isn't usually temperature sensitive.

Air leak at a rubber fuel line junction that only shows up when it's cold?

Anecdote unrelated, but similarly mysterious: I had one car that would stop with an ignition-sounding misfire every time it got slightly hotter than usual (idling in traffic, driving uphill). Replaced the spark plugs, leads, distributor cap. Bypassed all the wiring (hotwired it, basically). Replaced the entire distributor. Eventually, in frustration, I paid to put it on a dyno and ran it hard until it stopped again, which revealed that a tiny pinhole in the radiator hose was opening up under pressure and squirting water directly at the distributor, but only when the engine was super hot. The moment the engine stopped, the squirting stopped, and the water on the distributor dried up almost instantly. I'd noticed the coolant was disappearing and the radiator hoses were a bit old, but I was determined to fix the cutting out problem first.
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Won't Cold Start

Postby Trinker » Fri Oct 06, 2017 11:41 pm

That's quite the anecdote, and not too re-assuring. I'm starting to convince myself here I'm missing something, been digging through electrical sections in the manual looking for the meaning of every plug in the engine bay. My current theory is something to do with my temp sensor (which controls the glow plug relay) may be up to something nefarious, but as of now I can't seem to find any electrical control on the IP, still looking for the diagram that will show me everything that connects to temp sensors. The other thing that happened after the head replacement is where as before I could flash the glow plugs multiple times by turning on and off the key multiple times, but after the engine work it will only flash once for me when i first turn the key but always too short and then won't flash for any subsequent key turns. Hence the installation of my manual relay. Hmmmmmm, is there anything that might run off the temperature sensor that could control how much fuel the engine is getting when cold starting? I'm going to work on eliminating that theory here first, back to the manual for me...
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Won't Cold Start

Postby Growlerbearnz » Sat Oct 07, 2017 3:59 am

Fuel delivery is entirely mechanical (apart from the fuel cut solenoid, which shuts off the flow of fuel when you want the engine to stop). There's nothing electrical that alters how much fuel gets injected.

The temperature sensor is two sensors in one package, one side controls the glow plug timer, the other side runs the temperature gauge on the dashboard. It's not uncommon for the glow plug sensor side to fail. It's a cheap part, so might be worth replacing just to see.

Though all that shouldn't make any difference if you're using the manual switch. I forget if I asked this- the manual switch is connected to the 12V relay, not the 6V relay, right? And the manual switch is wired in parallel with the relay, so the glow controller can still turn the relay on?

The throttle position sensor on the IP is used by the glow controller to alter how long it pulses the 6V side once the engine's running, and also to control exhaust gas recirculation (the glow controller manages that too).
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Won't Cold Start

Postby Trinker » Sat Oct 07, 2017 9:42 am

Hmmm, interesting. I hooked up my switch in line with the 12v relay, aaaand the 6v relay with a on-off-on momentary switch. I have it set up so the 12v relay side is hooked up to the glow controller and my switch but the 6v relay side is only hooked to my switch. I could switch it around pretty easily though and try again
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Won't Cold Start

Postby Growlerbearnz » Sat Oct 07, 2017 3:04 pm

The on-off-on momentary switch is a clever idea!

It probably doesn't matter that the ECU no longer controls the 6V relay, that shouldn't change how easily it starts. It'll just run a touch more roughly for the first 30 seconds or so where the ECU would normally be using the 6V relay to assist combustion until the cylinders warm up.

Now I'm thinking about those relays. Burnt contacts might test ok but not allow enough current when under load. I wonder how well the engine would start if you powered the glow plug bus bar directly with a jumper cable- eliminating all the relays, switches, and ECU.

...being careful not to weld the jumper cable to the rocker cover, of course. Ouch.
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Trinker
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Won't Cold Start

Postby Trinker » Tue Oct 10, 2017 1:25 pm

Ok, Valve Clearance re-adjusted, Re-Checked power wasn't fading under load at the glow plugs, still no cold start.

What I really need now is a wiring diagram for the injector pump, or an entire engine wiring diagram (or harness diagram). I've checked all the shop manuals listed on this forum and Delicaclub and they are all missing that vital piece of information. My gut feeling is that there is a cold start timing advance or something along those lines that I'm missing on the IP itself causing my grief...

Any body have leads on something like that?
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Won't Cold Start

Postby Growlerbearnz » Wed Oct 11, 2017 10:19 pm

Cold start advance device: I've never seen one on an L300, though they do exist on some VE pumps. They're pretty primitive though:
dsc05348.jpg
dsc05348.jpg (501.14 KiB) Viewed 86 times
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Trinker
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Won't Cold Start

Postby Trinker » Thu Oct 12, 2017 1:17 pm

Not equipped with a cold start advance, still curious as to the other wiring running to the IP, going to check the timing again here next and also make sure it didn't magically jump a tooth somehow...
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Trinker
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Won't Cold Start

Postby Trinker » Thu Oct 12, 2017 11:48 pm

Replaced the Injector Pump wiring harness now (found the old one had a wire almost worn through) along with the temp sensor. Cleaned the starter leads and double checked the Timing Belt hasn't skipped a tooth (it didn't). Didn't appear to start any better after all the work. Probably check compression here next and then possibly get the IP timing tuned by a pro here. So annoying...
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Won't Cold Start

Postby helibrian » Fri Oct 13, 2017 11:39 am

Maybe take some pictures of the engine and post them. You might have missed something with the glow plugs or earth strap when putting the head back together.


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