# 1989 chevy k1500 Rough Running



## EPS (Sep 17, 2007)

I have a question. I have a 1989 Chevy K1500 which when first started runs and drives excellent! However when it warms up the check engine light comes on and runs rough what could this be? Also it will go into 4wd fine when cold but when the truck warms up if I take it out of 4wd and then try to put it back into 4wd it will not go. :realmad:


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## REAPER (Nov 23, 2004)

Sounds like a vacuum leak some where.

The actuator I believe is vacuum operated for the 4x4.

Maybe when is cold the line is stiff enough to keep it sealed. 

As it warms the hose may be soft enough to open up the small leak.


A good way to check this is by taking a propane torch turn the gas on but do not light it and run it along all your vacuum lines while the truck is running.

If you notice a increase in idle RPM's that is the propane being sucked in the hose. 
Via the leak. 

If it is a vacuum hose leak I would go ahead and replace all the vacuum line on the truck because the other lines are just as old.


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## EPS (Sep 17, 2007)

*vacuum leak*

Thanks for the tip reaper I will check into that. Sounds like that could be my problem.


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## B&B (Nov 4, 2006)

EPS;411154 said:


> Thanks for the tip reaper I will check into that. Sounds like that could be my problem.


It definitely could be a vacuum leak causing you rough running when hot but it's isn't what is wrong with your 4WD as it's electric, not vacuum. On the TBI Chevy's, the most common cause of a vacuum leak is either the gasket between the throttle body or the intake gaskets themselves. Use the propane method like Reaper mentioned to help pinpoint it. Your 4WD problem is more than likely the front axle actuator since they are notorious for failing, especially on the 88-94 truck's. When they're failing they can do exactly what your experiencing..very slow or erratic engagement.


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## EPS (Sep 17, 2007)

Thanks I am going to try the propane thing and will get a new actuator as it is slow to engage. Also it goes into 4 Lo real hard I'm afraid of breaking the damn thing I have to push so hard.


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## B&B (Nov 4, 2006)

EPS;411294 said:


> it goes into 4 Lo real hard I'm afraid of breaking the damn thing I have to push so hard.


A "hard" 4 low engagement is usually caused by rust and corrosion on the shifter mechanism under the plastic console. You'd be surprised at how rusty and corroded they get under there..


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## cwags73 (Sep 3, 2007)

Those transfer cases will shift hard if the oil has moisture in it as well. I have no clue how it gets there but I've changed the oil in several of them and it helped a lot.


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## B&B (Nov 4, 2006)

cwags73;413270 said:


> Those transfer cases will shift hard if the oil has moisture in it as well. I have no clue how it gets there but I've changed the oil in several of them and it helped a lot.


They'll also shift hard if they're low on oil too..


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## Jgrub75 (Feb 16, 2006)

If the check engine light is on there should be a code set, That will tell you what is wrong. I believe auto zone checks them for free. Let us know what they say. Sounds like it might be a coolant temp sensor.


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