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Help 4JB1T running rough when cold
Posted: Sat Apr 30, 2016 7:37 am
by Rolledeo
Hey all,
this seems to be a common issue and ive read a few posts about it with the 4JB1 running a little rough when its first started on a cold morning and mine seems to be doing just that, even if I let the glow light go out twice or three times even, when i first fire it up it runs like shit for the first few minutes unless i hold the revs around 750 or higher to smooth it out a little, I have just replaced the glow plugs and the old ones were a little wet when I pulled them out did too, is that normal? Ive also had the injectors replaced for new ones too (just to eliminate possibilities) the motor has 171k on it so its not exactly over worked, is this likely to be any major issue or is it just a standard thing for these motors and if it is what is the fix? When its warm it doesnt seem to smoke at all and seems to run smooth enough.
Another question is that im planning to upgrade my turbo and injector pump, now before I go ahead with any performance mods and start upping fuel and boost should i get a compression test done and also have the valve clearances done too? I just want to make sure when I start winding things up its not gonna shit itself after i throw a heap of money at it

Re: Help 4JB1T running rough when cold
Posted: Sat Apr 30, 2016 7:01 pm
by isuzurob
the plastic water trap can leak air causing the ruff running, does it smoke and miss when you start it up? if so the injector pump will need a rebuild
As for the performance upgrades, every engine is differnt and needs to be tuned, if you dont want to pay for a tune at least fit a exhaust temp gauge, tappets are pretty good on these engines
Re: Help 4JB1T running rough when cold
Posted: Sat Apr 30, 2016 7:29 pm
by geeves
how cold is cold? I dont know where bunbury is or what weather it gets.
The glow plug system on the 4jb1 is pretty crude but it does work. Because its direct injection it will start without a glow and until its quite cold the timer only gives about half a second of glow. The trade off is that it does start rough if the temp is between 5 and 10C.
For performance before doing anything fit a good air cleaner and 2.5 inch exhaust. On paper it doesnt give more horsepower but you will be surprised how much better it runs. Re turbo fit a boost gauge As long as you are getting 10 to 15psi at full throttle between 1800 and 3500 a new turbo isnt going to help much unless you are building a fire breather which might be only happy at certain revs I suspect your not after a race car just a little bit more on the highway.
Compression test might tell you things you dont want to know. If the engine isnt burning oil and takeing the oil filler cap off with the engine running doesnt show lots of crankcase fumes the engine is probably ok. A compression test may show cylinders out of spec but if it runs right does it matter. Tappets are easy enough to adjust and should be done every 40000km They are no different to an old pushrod petrol engine of 40 years ago. I did mine at 200000 and only one was out by a tiny amount. there were no scratches on the locknuts to suggest they had ever been done before. I certainly hadnt touched them in 110000km
Re: Help 4JB1T running rough when cold
Posted: Sun May 01, 2016 4:53 am
by Rolledeo
At the moment temperatures on the mornings are starting to drop under 10C, probably around 5 or 6 and it will get a little colder through winter but the rest of the time in the warmer months its fine. Is bypassing the timer and wiring it to glow for longer a good way to get it to run better first thing? Also the fact that the old glow plugs were slightly wet with oil when I removed them is that normal or excessive blow by?
Ive aready replaced the air filter for a K&N one, made a full 2.5" exhaust but im still running the stock dump pipe fornow until I make a new one, as for the turbo and injector pump, im having a IHI VI95 built by turbo care in NZ to suit the 2.8 and a rebuilt injector pump with a 12mm head to keep up with it, I have a boost and EGT gauge already but havent mounted them just yet, and a intercooler setup from a 3.1 jackaroo, when its all done ill be taking it in to the local injection place to get it tuned, I just want to make sure that the motor is healthy before I go ahead with all this and that the running rough when its cold isnt a serious underlying issue that could bite me later.
By the sounds of it I probably wont even need to touch the tappets from what you have said there and it doesnt seem to be making any excessive noise to warrant doing them either, ive checked it running without the oil filler cap and there doesnt seem to be any crank case fumes or smoke too. I know its running slightly over filled with oil at the moment, would this cause excessive blow by?
isuzurob wrote:the plastic water trap can leak air causing the ruff running, does it smoke and miss when you start it up? if so the injector pump will need a rebuild
As for the performance upgrades, every engine is differnt and needs to be tuned, if you dont want to pay for a tune at least fit a exhaust temp gauge, tappets are pretty good on these engines
It does chuck a bit of white/grey smoke out first thing when its cold, and it does run like shit so im guessing its possibly miss firing also, so its the injector pump?
Re: Help 4JB1T running rough when cold
Posted: Sun May 01, 2016 5:11 am
by geeves
Mine ran like that untill the temp droped below 5C then it started and ran fine unless I did something very naughty. I was in the habit of just starting it the same as a petrol car ie climb in turn key reverse out of driveway and drive off. One morning it was cold but here I was no wait for glow plug light reverse out drive off knocking something terrible then notice glow plug light still on knocking stoped 100 meters down the road and the light went out. I miss my 2.8 My 3.1s will not start unless you wait for the glow plugs even on a 15C morning.
Re: Help 4JB1T running rough when cold
Posted: Sun May 01, 2016 1:26 pm
by Rolledeo
geeves wrote:Mine ran like that untill the temp droped below 5C then it started and ran fine unless I did something very naughty. I was in the habit of just starting it the same as a petrol car ie climb in turn key reverse out of driveway and drive off. One morning it was cold but here I was no wait for glow plug light reverse out drive off knocking something terrible then notice glow plug light still on knocking stoped 100 meters down the road and the light went out. I miss my 2.8 My 3.1s will not start unless you wait for the glow plugs even on a 15C morning.
So do you reckon that its just pretty normal for the 4JB1's to do this when cold and its nothing really to worry about?
Re: Help 4JB1T running rough when cold
Posted: Sun May 01, 2016 7:37 pm
by isuzurob
seems to be all the 4jb1 rodeos had this issue, all my 2.8 bighorns start mint no smoke, my rodeo smokes on start up and has a miss, have done new injectors, compression test, and the injector pump fixed it
Re: Help 4JB1T running rough when cold
Posted: Sun May 01, 2016 9:21 pm
by Rolledeo
Thanks for the help fellas, if its a case of a new injection pump I may aswell wait until my new comes when its done with the turbo and ill switch it all out together,
Regarding the glow plugs being wet when I took them out, is that a sign of excessive blow by or that normal too?
Re: Help 4JB1T running rough when cold
Posted: Sun May 01, 2016 11:35 pm
by isuzurob
wet glowplugs is pretty normal just diesel, oil and carbon on them
Re: Help 4JB1T running rough when cold
Posted: Mon May 02, 2016 4:04 am
by geeves
It really is a case of is it annoying enough to fix. My 2.8 bighorn did it for 19 years before tinworm sent it to the wrecker but we might be talking different things. The 2.8 was just rough when started and when really cold wanted to idle at 500. Often when cold it would start then stall almost straight away . If the wire was taken off the thermostat housing that controlled the cold start the glow plugs would glow 10 seconds and it would start like it was fully warmed up. There might be fuel and timing tweaks that could make it better
My Wizard had symptoms more like Robs description but its a 3.1 Start fine then after a few seconds start to miss until the first time you got it over 1500 revs. New injectors and turbo improved it but not fixed. Pump rebuild for a leak made it run like new. I put up with it for 5 years and if the pump hadnt leaked it would still be faulty. Pump rebuild by the professionals wont leave change from 1200