[Louie4]

So some of you may be aware of my saga to fix my overheating and ultimately found my original 4.0L engine was tired and corroded with build up in the cooling passages. I bought a 4.0L from a ‘99 TJ that was very clean and had maybe 80k miles.

When I got it home I put a new set of main and rod bearings, oil pump, timing chain, valve seal, etc. The only thing I did not take off was the cylinder head. I did pull the distributor and reinstalled to what I thought was TDC. At first it would not crank so I pulled the distributor to make sure it was, re-oriented and it fired up...but the engine was racing at 2500-3000 rpm's. I cranked it a few times that way to see if it would back down but only went to 2k. I finally got the radiator on and filled it with coolant. I let it run and it began to overheat and I just thought the system needed to be burped but after a few times it would puke coolant back out. Another thing I noticed was pushing on the gas pedal didn’t do much difference and even seemed to bog down some.

At this point I’m back to square 1. My next thought is to make sure the timing is correct.

Any way, I’m looking at what next steps are. I’m 99% sure the timing gears were correct when I installed them. Dots were lined up and everything. The firing order is correct too.

 

[Jason B]

So some of you may be aware of my saga to fix my overheating and ultimately found my original 4.0L engine was tired and corroded with build up in the cooling passages. I bought a 4.0L from a ‘99 TJ that was very clean and had maybe 80k miles.

When I got it home I put a new set of main and rod bearings, oil pump, timing chain, valve seal, etc. The only thing I did not take off was the cylinder head. I did pull the distributor and reinstalled to what I thought was TDC. At first it would not crank so I pulled the distributor to make sure it was, re-oriented and it fired up...but the engine was racing at 2500-3000 rpm's. I cranked it a few times that way to see if it would back down but only went to 2k. I finally got the radiator on and filled it with coolant. I let it run and it began to overheat and I just thought the system needed to be burped but after a few times it would puke coolant back out. Another thing I noticed was pushing on the gas pedal didn’t do much difference and even seemed to bog down some.

At this point I’m back to square 1. My next thought is to make sure the timing is correct.

Any way, I’m looking at what next steps are. I’m 99% sure the timing gears were correct when I installed them. Dots were lined up and everything. The firing order is correct too.

Just throwing things out there did you check the idle air motor to see if its stuck wide open

 

[Louie4]

Just throwing things out there did you check the idle air motor to see if its stuck wide open

I did not. It was last night so I just gave up after my successive failures. I can check it

 

[93YJ4FUN]

Is the throttle position sensor working correctly? Or is it old school without?

 

[Boojo35]

Try undoing something up high as possible, like a heater hose connection, remove the t-stat, etc. so you can fill the engine as full as possible without air in it. Close it back up and top of with coolant. I always use a spill proof funnel from there and run until all the air comes out. This can take a long time.

Do you have a heater core installed? If not, do you have the engine connections blocked of or did you run a loop of hose from one to the other. That loop can be important in some vehicles regarding correct flow.

As far as the high idle. The TPS and IAC have already been mentioned. Is the throttle really shutting all the way? Vacuum leaks can cause this also.

Does the check engine light function? Does it have any codes in it?

 

[Louie4]

I bought a spill proof funnel just for this moment. It did not hold up to its name and coolant spilled out of the funnel when I shut the engine off and it was hot. It filled itself up and boiled out I guess. After my first couple overheats I pulled the heater hose off the t-stat housing and no coolant came out so I filled it up until it started to come out. The upper radiator hose did get hot which tells me thermostat finally opened.

When the rpm’s are high, the throttle plate is closed as much as it can be.

 

[Boojo35]

Maybe these will help you.

 

[Louie4]

Thanks Boojo. I I’ll pull that distributor and start over. My next question is, would the engine still run like it does if it was off like I think it is?

 

[Boojo35]

The distributor of course has to do with timing but the cam sensor in it is more of a fuel control rather than timing. I really do not have a better answer for you. The way that the 4.0L uses the distributor for fuel synch is kind of unique. I cannot say that I have ever dealt with one that was off maybe a tooth or two. Sorry to not have a better answer if it will make it run like that.

You have an issue that I am trying to wrap my head around. Why does opening the throttle not make much of a difference? That could be a bad TPS or wiring. That kind of ties hand in hand with the high idle. I will try to explain it. When an engine is off idle, or the throttle is depressed, the IAC moves outward and allows more airflow. The ECM knows that the throttle is depressed by reading the TPS. When you let off the gas to return to idle, the ECM sees that the engine should be idling and starts to control the IAC. It should have to close down and allow less air flow if everything is correct. This way of operation allows the engine to settle into idle speed without stalling or spikes in emissions.

I still stick with checking for vacuum leaks. That is a very common cause of a high idle.

 

[93YJ4FUN]

@Boojo35 , would a vacuum leak also contribute to the overheating?

 

[Boojo35]

@Boojo35 , would a vacuum leak also contribute to the overheating?

Great question. If it is severe enough then yes. Really lean conditions are hot.

This is contrary to popular belief.

Too much fuel in an engine is rich. It will run cooler.

Not enough fuel, or too much air which creates lean will make it run hot. ( too much air or not enough fuel are the same)

We are speaking gasoline engines here. Diesel stuff breaks some rules.

EDIT: I do want to reiterate though that what Louie described as far as spitting coolant and stuff is a classic example of air in the cooling system.

He likely has two different issues.

 

[93YJ4FUN]

To be honest, I just want Louie to have a Jeep with no overheating issues. I think he deserves that.

 

[Boojo35]

To be honest, I just want Louie to have a Jeep with no overheating issues. I think he deserves that.

So do I. I try to post and help Louie at every turn in the road. He is a dude that I will roll up my sleeves for in a heartbeat to try to find a resource that may help him.

 

[Louie4]

Thanks guys. I do appreciate that. So I pulled the codes and got 24 which is the TPS and make sense. It’s the original from 1993 so I plan to just replace it.

As for the overheating,I’m hoping it’s air. The entire engine was dry before I put coolant in it.

So tomorrow I’ll get a new TPS and some starter fluid to look for a leak in the intake.

 

[93YJ4FUN]

Check the connections? Might seem simple, but you've moved an entire new engine in there. Things got moved.

 

[Louie4]

Check the connections? Might seem simple, but you've moved an entire new engine in there. Things got moved.

I unplugged and plugged in both the TPS and IAC but alas, no change.

Something else to mention is that the throttle plate is barely open and it’s still running that high. I put new intake/exhaust manifold gasket on but who knows?

 

[Jason B]

I unplugged and plugged in both the TPS and IAC but alas, no change.

Something else to mention is that the throttle plate is barely open and it’s still running that high. I put new intake/exhaust manifold gasket on but who knows?
[/QUOTE
Remove the IAC motor and clean and make sure its not stuck unplugging it I don't think will do anything

 

[EABiker]

If you have a high RPM situation with the throttle plate nearly closed, you have another source of air intake, such as a large vacuum leak. Spray some carb cleaner all around the intake area with the engine running and listen for an RPM change.

 

[Louie4]

Update time. So I put the new TPS in and it had no effect…which I’m not surprised TBH. But, I unplugged the MAP sensor and the idle finally dropped to a reasonable level. Normally I would think it would nearly kill the motor but no. I then put my hand over the throttle body to choke it out but it kept running! I then sprayed some carb cleaner around the intake gasket and the RPM went up. So…bingo. At least I hope.

I bought a cheap gasket kit versus a Felpro and here I am. I plan to buy a hood gasket and install. It all makes sense now.

More to come.

 

[Awesome]

Dang Louie, you have rotten Jeep luck.