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Daewoo/Doosan G30E.. Mis-fires after running hard and temporarily loses compression

centerline

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Jul 11, 2016
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Location
Salem Oregon
we Have a Daewoo G30E dual fuel, conventional forklift that starts and runs great, UNTIL it gets ran hard/travels at higher speed for a couple minutes, then it begins to slowly start misfiring.
if we stop and let it return to an idle, it misfires and sometimes dies, and sometimes stays running... when it dies, when we attempt to restart it, it seems as if there is no compression except on one cylinder.... but within a couple minutes it will restart with a miss, and then pick up all 4 cylinders again and run fine, until it gets ran hard again.

when the engine remains running but badly misfiring, it will begin firing on all 4 cylinders within about 30 seconds and run fine again.... until it gets ran hard again.


I have thought it may be a tight valve train that is heating up and holding the valves open too far, but this seems like kind of a stretch of the imagination, considering it has hydraulic lifters and it runs so good when the rpms are at the lower end of the tach...

the the machine does not have to be moving for the engine to act up, as it will do the same thing while setting in neutral and pegging the throttle against the governor..... it does NOT over rev, but will run fine for a little bit and then start misfiring, and yet still run great after having a chance to cool down for a few seconds...

the mis-fire/fault is dependable and reproducable everytime....

we have replaced the oil and filter, fuel filter, engine computer, O2 sensor, crank position sensor and the distributor pick up coil, spark plugs and plug wires but without any change in performance...... where should I look next?.... thanks
 
Last edited:

TD24

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Which fuel is it on when this occurs, gas or LP?

Does it occur on one fuel more so than the other?
 

centerline

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Messages
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Location
Salem Oregon
Which fuel is it on when this occurs, gas or LP?

Does it occur on one fuel more so than the other?

it makes no difference which fuel it is running on.... we currently have it on gas, but we thought it may be something to do with the carburetor or fuel pump, so we switched it to propane without any difference whatsoever....
 

TD24

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Which engine do you have ?
Yellow Cat 1404 or overhead cam with shiny valve cover?
 

TD24

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Watch your e-mail. Follow up on it's instructions.
 

Akmc5

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May 30, 2010
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SW WA
I know this is old.....but I have a G30e doing the exact same thing.....did you ever get this fixed? TD24, What was your recommended solution? It has the doosan engine.
 

centerline

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Jul 11, 2016
Messages
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Location
Salem Oregon
yes.... i found that the valve stems were carboned up and the valves wouldnt snap back closed all the way, causing a loss of compression....

try running some seafoam in the crankcase at about twice the concentration that is shown on the seafoam bottle.... run for about an hour and let it sit at least over night..... then run it for about an hour again..... and then change only the oil filter.... DONT continue to run it for over about 4 hours total without changing the filter because it WILL loosen all the carbon and sludge that may be in the engine and it will plug up the oil filter..... after 4-5 hours of run time, change the oil and filter. you should see an improvement within an hour of run time after adding the seafoam
.

the alternative is to remove the head and disassemble the valves and remove the carbon manually.... i found the problem because i was out of options to try, and so i removed the valve cover to see if the valves were too tight, and found that some of them were extremely LOOSE, because they werent coming up and closing fully.... I thought they may have been bent and it was a heat related issue holding them open when the engine got warm, so I removed the problem valves and found the carbon deposits....

I feel this problem may be due to someone using sub-standard oil in the crankcase as some point in the former life of the engine..
 
Last edited:

Scottlift

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Jun 19, 2022
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Nj
I know this is an older thread but just wanted to comment on the reason this happened the truck was run on propane at some time the propane gummed up the valve stems and the springs can't bring the valves back fast enough to close the valves.the propane has an oil base that caused this .it happens when the truck gets hi hours on it .the real fix is to pull the head and pull the valves out and clean the carbon off the steams .l have tried trans fluid down the carb when the truck was running with some success the problem is you must take it outside because it will smoke badly untill all the trans fluid burned off keep the gas petal at hi speed when doing this
 

centerline

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Joined
Jul 11, 2016
Messages
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Location
Salem Oregon
I know this is an older thread but just wanted to comment on the reason this happened the truck was run on propane at some time the propane gummed up the valve stems and the springs can't bring the valves back fast enough to close the valves.the propane has an oil base that caused this .it happens when the truck gets hi hours on it .the real fix is to pull the head and pull the valves out and clean the carbon off the steams .l have tried trans fluid down the carb when the truck was running with some success the problem is you must take it outside because it will smoke badly untill all the trans fluid burned off keep the gas petal at hi speed when doing this

because we DID have to take it apart, we pulled the valves and cleand them and checked the valve guides for buildup, and did our best to clean them... after reassembling it and getting it going properly, we added seafoam additive to the gas and to the crankcase... which all the efforts have cured the problem....
BUT, as for the propane being the culprit, I would have to question that... because I work on a huge amount of propane fueled equipment and have never encountered this before...
but have seen this issue twice since.... once in another forklift, and also in a generator that runs on gas only....

luckily, my previous experience helped solve both issues... just adding seafoam additive to the crankcase cured the problems, except for the additional problems of the generator, which the stuck valve caused the pushrod to bend.... we disassembled it to unstick the valve manually and found the pushrod bent..... we sprayed some seafoam down the ports and worked the valve til it was free, straightened the bent pushrod, and reassembled it... it started up immediately and has not given a hiccup since.....

my theory is that the many many short run times without ever really warming up to be the cause of this issue... but with knowing "why the engine looses compression", its an easy fix.... and a bit of seafoam every couple oil changes is good preventive maintenance...
 

TD24

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MS
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because we DID have to take it apart, we pulled the valves and cleand them and checked the valve guides for buildup, and did our best to clean them... after reassembling it and getting it going properly, we added seafoam additive to the gas and to the crankcase... which all the efforts have cured the problem....
BUT, as for the propane being the culprit, I would have to question that... because I work on a huge amount of propane fueled equipment and have never encountered this before...
but have seen this issue twice since.... once in another forklift, and also in a generator that runs on gas only....

luckily, my previous experience helped solve both issues... just adding seafoam additive to the crankcase cured the problems, except for the additional problems of the generator, which the stuck valve caused the pushrod to bend.... we disassembled it to unstick the valve manually and found the pushrod bent..... we sprayed some seafoam down the ports and worked the valve til it was free, straightened the bent pushrod, and reassembled it... it started up immediately and has not given a hiccup since.....

my theory is that the many many short run times without ever really warming up to be the cause of this issue... but with knowing "why the engine looses compression", its an easy fix.... and a bit of seafoam every couple oil changes is good preventive maintenance...

Agree. Have owned and had to repair forklifts with all brands of engines, some conversions from gas to LP and hundreds of out of the factory on LP. Never had this occur. Believe as above, or may be a certain oil and its viscosity might be the culprit.
 
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