HZJ73 runs rough on cold mornings

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Mountainjnky75

Mountainjnky75

Joined
Jun 16, 2022
Threads
5
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Location
WA
There's gotta be a thread about this somewhere on here, lol. My '95 HZJ73 (with the 1HZ) runs rough and blows out a bunch of blue smoke when it's warming up on cold mornings. Once it's warmed up, it runs great with no issues. I've heard about a cold start circuit and how that may to blame, but I'm not sure where to start looking around in the engine bay to fix this. Any help would be greatly appreciated!
 
I haven't checked the glow plugs- it seems to fire up ok, just runs rough until it hits normal operating temp. Would that be a glow plug issue?
 
not familiar with the HZ, but the old 2H had a "smart" glow system. It would glow full voltage for a few seconds and then go to like have voltage for a longer time. If I remember it had a water temp sensor as part of the system. I would imagine that the HZ would have something similar. I would still check the glow plugs just to make sure they are all good.
 
Blue smoke means a little oil and rough cold start I’d start looking at injectors. Could be valves/rings but if it smooths out and smoke goes away, that valves/rings aren’t an issue (not much at least). Could also need a valve adjustment, but it would need to be pretty out of adjustment.

If it only has issues cold, glow check for all cylinders also clear hose for fuel inlet lines to check for air in fuel is a good place to start also.
 
I would start with the glow plugs system.
Make sure that you have power to the busbar when the key is turned on, and as the system powers down.
If yes to the busbar, then test the glow plugs. If one is bad change them all.
Sensors:
Toyota uses one coolant sensor for the gauge, and one for the glow system/ecu depending on models.
I daily drive a HZJ75 with over 500,000, and she loves two glow cycles...just runs so smooth on start up.
You can also try unplugging the water temp sensor (glow system) this should fool the unit into believing that it is actually cold outside.
Had a 13bt in a 74 series, damn thing never liked starting in mediocre weather, unplugged the temp sensor, and now she had a great glow cycles.
 
coldtaco said:
not familiar with the HZ, but the old 2H had a "smart" glow system. It would glow full voltage for a few seconds and then go to like have voltage for a longer time. If I remember it had a water temp sensor as part of the system. I would imagine that the HZ would have something similar. I would still check the glow plugs just to make sure they are all good.
Click to expand...

coldtaco said:
I have to do the same thing- glow it for a couple seconds then do it another time before it starts then it fires right up... I'll check out the glow plugs and make sure they're looking good.
Click to expand...
 
Tennessee Jed said:
How cold are your mornings in July? What is your glow routine? On actual cold winter mornings I will double glow mine and it starts perfectly.
Click to expand...
Not too cold in July, lol, but for 8 months of the year it's pretty chilly here. I do the same thing and double glow it in the morning and she fires up each time.
 
mattressking said:
Blue smoke means a little oil and rough cold start I’d start looking at injectors. Could be valves/rings but if it smooths out and smoke goes away, that valves/rings aren’t an issue (not much at least). Could also need a valve adjustment, but it would need to be pretty out of adjustment.

If it only has issues cold, glow check for all cylinders also clear hose for fuel inlet lines to check for air in fuel is a good place to start also.
Click to expand...
It's more of a bluish white smoke and smells like BBQ lighter fluid- I think it's just a ton of unburned diesel pouring out the back... I'll check the glow plugs and be sure they're looking good. Maybe even just replace them all since I don't think they're too expensive. How would you check for air in the fuel line?
 
Squash said:
I would start with the glow plugs system.
Make sure that you have power to the busbar when the key is turned on, and as the system powers down.
If yes to the busbar, then test the glow plugs. If one is bad change them all.
Sensors:
Toyota uses one coolant sensor for the gauge, and one for the glow system/ecu depending on models.
I daily drive a HZJ75 with over 500,000, and she loves two glow cycles...just runs so smooth on start up.
You can also try unplugging the water temp sensor (glow system) this should fool the unit into believing that it is actually cold outside.
Had a 13bt in a 74 series, damn thing never liked starting in mediocre weather, unplugged the temp sensor, and now she had a great glow cycles.
Click to expand...
That's a good idea about testing the busbar and glow plugs. That's everyone is pointing to, so I think that's where I'll start... Where is the coolant sensor on the 1HZ?
I usually do two glow plug cycles on cold mornings as well because she usually won't start unless I do.
 
This is actually very common on 1HZ's , when I fire up in cold temps I immediately either turn on the hand trottle or push the accelerator in a bit to raise the idle and get trough those first 20 seconds . It's just the nature of the beast
 
After testing the glow plugs and busbar... give the resistor a test. Had similar symptoms with all new IP, injectors, glow plugs, bus bar, 1HZ after a rebuild. Hadn't replaced the resistor because NLA and that was it for me. The glow resistor for the 2H works in the 1HZ

Credit to @JDM Journeys. Hey jumped through ALL the hoops testing his. I just copy/paste. See > Builds - OL'BETSY ZX: 1991 HZJ77 - https://forum.ih8mud.com/threads/olbetsy-zx-1991-hzj77.1232170/post-14120373

The 2H part number is 28621-64011
 
Guyute said:
After testing the glow plugs and busbar... give the resistor a test. Had similar symptoms with all new IP, injectors, glow plugs, bus bar, 1HZ after a rebuild. Hadn't replaced the resistor because NLA and that was it for me. The glow resistor for the 2H works in the 1HZ

Credit to @JDM Journeys. Hey jumped through ALL the hoops testing his. I just copy/paste. See > Builds - OL'BETSY ZX: 1991 HZJ77 - https://forum.ih8mud.com/threads/olbetsy-zx-1991-hzj77.1232170/post-14120373

The 2H part number is 28621-64011
Click to expand...
Those are some great ideas, I'll have run through the system and test all those parts to make sure everything is working right. I'll check out JDM Journeys write up. Thanks for the tips!
 
joekatana said:
This is actually very common on 1HZ's , when I fire up in cold temps I immediately either turn on the hand trottle or push the accelerator in a bit to raise the idle and get trough those first 20 seconds . It's just the nature of the beast
Click to expand...
It's more than just a rough start, it's 15-20 minutes of running rough until the engine is up to temp, then it smooths out and runs great.
 
Mountainjnky75 said:
It's more than just a rough start, it's 15-20 minutes of running rough until the engine is up to temp, then it smooths out and runs great.
Click to expand...
Yup. Where you at in Washington? I'm across the border in Portland and have a new spare 28621-64011 if it helps in your to troubleshooting.
 
Guyute said:
Yup. Where you at in Washington? I'm across the border in Portland and have a new spare 28621-64011 if it helps in your to troubleshooting.
Click to expand...
I'm in Prosser- kinda south central WA. Funny you mentioned about having a resistor, I just ordered one from Amayama! Fortunately they had one in stock will ship out in a couple days. I figured I'd start with that because symptoms sound just like what JDM Journeys was describing with his. I appreciate the offer and the words of wisdom, hopefully this get the ole beast ready colder weather again!
 
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