• Advertisement

4JG1T Troubleshooting/Timing/Knock/Rough Running

Get help fixing your Isuzu from other club members

4JG1T Troubleshooting/Timing/Knock/Rough Running

Postby jimpad » Thu Feb 02, 2017 11:42 pm

New user here with a couple questions.

I've got a skidsteer loader with a Isuzu 4Jg1T engine and I cannot find much info on the web to service it. The engine developed a knock on the number 4 cylinder and I thought it was a bad valve so I pulled the head and found no valve problem. The engine is also low on power runs rough. I've sent the injectors off and they've got some slight issues but nothing that should've caused a knock. So, now I'm thinking injection pump and have the following questions. I should add, the reason i'm suspecting fuel is because the #4 head area has significantly less soot on the combustion/valve surface whereas the other 3 cylinders have a fairly uniform layer of soot across the combustion surface. The #4 head combustion surface is almost shiny metal with no oil and very little soot.

I'm no mechanic so I'd appreciate any troubleshooting/repair guidance

Questions:

1. Can the head gasket be reused?
2. Does the valve cover gasket require sealant or is it meant to be used dry?
3. How is the injection pump timed?
jimpad
Isuzu Baby
 
Posts: 13
Joined: Thu Feb 02, 2017 11:29 pm
Age: 100
Country: usa
City: ny
Vehicle: 4JG1T

Re: 4JG1T Troubleshooting/Timing/Knock/Rough Running

Postby geeves » Fri Feb 03, 2017 4:41 am

Cant reuse head gasket
I prefer to use gaskets dry unless the handbook says not to
Question Did you do a compression test before taking the head off?
Sanding your knuckles before starting work can help. That way you cant skin them
User avatar
geeves
Site Admin
 
Posts: 8962
Joined: Sun May 10, 2009 1:36 pm
Location: Rangiora
Age: 63
Country: NZ
City: Rangiora
Vehicle: 94 bighorn 4jg2
2013 Subaru XV

Re: 4JG1T Troubleshooting/Timing/Knock/Rough Running

Postby jimpad » Fri Feb 03, 2017 8:46 am

Did not do a compression test, based on where the noise seemed to be coming from I was convinced it was a valve problem. If it makes a difference, the problem did come on suddenly. Thanks for replying.
jimpad
Isuzu Baby
 
Posts: 13
Joined: Thu Feb 02, 2017 11:29 pm
Age: 100
Country: usa
City: ny
Vehicle: 4JG1T

Re: 4JG1T Troubleshooting/Timing/Knock/Rough Running

Postby geeves » Fri Feb 03, 2017 4:21 pm

valves would be more of a tapping noise. They are conventional rockers.
Posibilities are cracked piston loose gudgeon pin bent rod bent crank bad big end bearing. Being no 4 a loose flywheel cant be ignored as a posibility.
Im a bit worryed about the clean piston top. That indicates no combustion. Reasons would be no fuel or poor compression
Sanding your knuckles before starting work can help. That way you cant skin them
User avatar
geeves
Site Admin
 
Posts: 8962
Joined: Sun May 10, 2009 1:36 pm
Location: Rangiora
Age: 63
Country: NZ
City: Rangiora
Vehicle: 94 bighorn 4jg2
2013 Subaru XV

Re: 4JG1T Troubleshooting/Timing/Knock/Rough Running

Postby jimpad » Fri Feb 03, 2017 7:56 pm

Yes, I think the clean combustion area is the key. If it was low compression problem and the injector was working wouldn't there be either a lot of soot or unburned oil in the cylinder?
jimpad
Isuzu Baby
 
Posts: 13
Joined: Thu Feb 02, 2017 11:29 pm
Age: 100
Country: usa
City: ny
Vehicle: 4JG1T

Re: 4JG1T Troubleshooting/Timing/Knock/Rough Running

Postby Roderunner » Sat Feb 04, 2017 12:08 pm

No. 4 cylinder might have been steam cleaned by a slow water/coolant leak into the cylinder, hence the knocking sound from the delayed combustion due to the presence of moisture in the cylinder. - I'd be looking at the head gasket for telltale leak marks, and I would also get the head crack /pressure tested. The injection pump might benefit from a can of diesel fuel system cleaner too.
Roderunner
Isuzu Senior
 
Posts: 219
Joined: Sun Feb 26, 2012 2:58 pm
Location: Central highlands
Age: 48
Country: Australia
City: Melbourne
Vehicle: 93 Jackaroo

Re: 4JG1T Troubleshooting/Timing/Knock/Rough Running

Postby jimpad » Sat Feb 04, 2017 12:27 pm

Wow, that's a good line of thinking. Seems I remember hearing water acted like bb's when exposed to the high pressure of diesel combustion. Do you think there would be signs (like peening) if water in the combustion area. Also, this happened on the coldest day of the year... 10 degf, although i'm pretty sure the antifreeze is -20degf. Also, while it was warming up I remember an abnormal exhaust smell... maybe burnt antifreeze but I thought it had the smell of hydraulic oil. But at that point I wasn't really aware of a problem so I barely gave it a thought.
jimpad
Isuzu Baby
 
Posts: 13
Joined: Thu Feb 02, 2017 11:29 pm
Age: 100
Country: usa
City: ny
Vehicle: 4JG1T

Re: 4JG1T Troubleshooting/Timing/Knock/Rough Running

Postby geeves » Sat Feb 04, 2017 2:50 pm

4jg2s are known to crack heads but 4jb1s rarely have this problem. As far as I know the 4jb1 and 4jg1 share the same head but head gaskets can blow on any engine. Did it have any tell tale signs of a head leak?
Sanding your knuckles before starting work can help. That way you cant skin them
User avatar
geeves
Site Admin
 
Posts: 8962
Joined: Sun May 10, 2009 1:36 pm
Location: Rangiora
Age: 63
Country: NZ
City: Rangiora
Vehicle: 94 bighorn 4jg2
2013 Subaru XV

Re: 4JG1T Troubleshooting/Timing/Knock/Rough Running

Postby jimpad » Sat Feb 04, 2017 11:23 pm

I'll be giving it a good look today. What are the telltale signs of a leak? If I can't see anything should I dye penetrant test it or should I take it to a shop at that point? Should I remove the valves for a more thorough inspection?
jimpad
Isuzu Baby
 
Posts: 13
Joined: Thu Feb 02, 2017 11:29 pm
Age: 100
Country: usa
City: ny
Vehicle: 4JG1T

Re: 4JG1T Troubleshooting/Timing/Knock/Rough Running

Postby jimpad » Sun Feb 05, 2017 9:17 am

Well I took a close look at it today and see no signs of a crack, or water migration through or around the head gasket. This was just with the naked eye though. The coolant tested at -10degf. Additionally, the problem developed after about 45 minutes of running so it was certainly warm by then, if it had cracked from freezing i'd expect an immediate problem. If I wanted to get a rough idea of the injector pump I'd assume I could set it at full throttle, roll it over by hand and collect the amount from each fuel line to get a relative comparison. Is there any issue with rolling the injector pump without the injectors installed?
jimpad
Isuzu Baby
 
Posts: 13
Joined: Thu Feb 02, 2017 11:29 pm
Age: 100
Country: usa
City: ny
Vehicle: 4JG1T


Return to Engine

Who is online

Users browsing this forum: No registered users and 13 guests