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1993 Wrangler YJ 4.0

3K views 33 replies 6 participants last post by  MudMagnetYJ 
#1 ·
Hello, My name is Chuck and I'm new to the forum, I've recently had a freeze plug blow out completely while driving, I hade to pull over and get a tow home, after replacing the freeze plug I did a complete fluid change, anti freeze (obviously) and oil change, no sign of anti freeze in the oil, when I was finished the Jeep would not start, it wanted to but just couldn't, so I tested everything from the coil to spark and replaced the crank sensor @ $78, finally the jeep started but only when I had the gas peddle to the floor for a period of time, rough idle, rough start and shaky, now the temp guage is way hot but the water is bubbling out of the over flow tank ice cold, can also hear the water in the radiator bubbling and moving, no heat at all but again the jeep is hot according to the temp guage, I fear it's a head gasket but wanted to see some other opinions and maybe theirs something else I can do to confirm it's what I think it is, thanks in advance for your time! Chuck.
 
#2 ·
Welcome to the forum!

This is a long shot, but is your water pump rotating in the right direction? From the way you describe the water bubbling out of the overflow tank it sounds like a possibility.
 
#3 ·
I'm not sure if the water pumps are interchangeable as far as bolt pattern and passage pattern between the 4.0 and the older 4.2/258, but the older water pumps that are driven by V belts might rotate the opposite direction than the ones for use with serpentine belts depending on how the serp belt is routed.
 
#4 ·
Well, it's a serpentine belt so it only really goes one way, diagram on the top of frame, unfortunately I've checked the dip stick and seen that the oil is milky and white, so looks like I'll be changing the head gasket after all, strong running Jeep so I want to fix this, she's got 250,000+ miles on the straight 6, 5 speed and my kids love it during the summer time, what seems to be happening is the thermostat isn't opening, but when I took it out and boiled it it works fine, then I noticed the lower spring loaded hose at the bottom of the radiator that comes from the water pump is rock hard, along with the top hose that goes to the thermostat was also hard, it's so puzzling to me and it's not something I understand b/c I've never seen anything like this before, Jeep is hot but the coolant is ice cold. I also had to change the spark plugs b/c the jeep got so hot it chard the plugs so bad they were unrecognizable and was probably the main reason for why it wouldn't start and not b/c of the crank sensor which was replaced, the jeep fires right up with no problems, until the weather breaks and I can find the time to fix this what is your take on buying one of those pricy head gasket sealer additives? Do they really work and is it worth it? I don't think my head gasket is that bad but any leak is bad and with this motor having so many miles I don't wanna harm it anymore then I have too. Thanks again for your time.
 
#6 ·
Remove the throttle body completely and give it a good cleaning. Make sure you clean the idle air control valve.
 
#8 ·
Make sure you burp the cooling system. High pressure at low temperature indicates air bubbles. You could test for a blown head gasket but it really just sounds like an air bubble and a sticking idle air control valve (IACV) at this point.
 
#9 ·
Any medication that claims to fix a problem is a waste of money (in my opinion).

For instance, a product that claims to stop leaks in automatic transmissions contains a solvent that swells the seals. It works temporarily until the solvent evaporates. Then the seals are hardened and leak even worse. You can do the same thing by pouring lacquer thinner in a transmission.

To cure a head gasket leak requires at least a new head gasket.

From what you describe, I would try a cooling system flush. Of course, change your oil & filter. Have you done a compression test and a leak down test?

Good Luck, L.M.
 
#10 ·
Yeah... Just noticed the part about the sealer...

Stopleak just blocks fluid flow from the wrong parts... Get's tied up in water pump, radiator cores, water jackets, thermostat, etc. Yet it still leaves a leak 9/10 times. There's a reason it's on the front counter at the auto parts store but you don't see many shops advertising it as a service.
 
#11 ·
Ok well, turns out it was my head gasket, I noticed chocolate milk like oil on my dip and when I took the oil cap off you can clearly see water in the oil, so I have already replaced the head gasket last weekend, nice easy job that I did with my 9 yr old but now we have a new issue, Hard start, almost with the gas peddle to the floor for a good while just to get her to turn over, low RPM, between 1-0 its driveable but only when she's cold, once warm it'll stall and be tough to get running again, I've already replaced the crank sensor, cleaned the throttle body and idling control, checked that all cylinders are firing correctly, replaced spark plugs and checked all vac lines but no luck on why she is running like this, while idling it runs but the engine is shaky and like I said very low RPM's it's very rough, all gauges are normal I just don't know what else it could be or what to do next, it can run in idle all day, like right now it's been running for the past 30min just trying to see if anything changes with the gauges but nothing yet, any advice is greatly appreciated, thank you in advance for your time. Chuck.
 
#12 ·
Just changed the Throttle position sensor but still the same, I guess now I try the air control valve sensor??? This is costing me a fortune but I need to get to work until my Dodge is done, then this will be my weekend fun. Still it's giving me issues.
 
#13 ·
My post isn't very nice. Your head may be warped from heat which is what could have killed your last head gasket. Knowing you had a bad head gasket, would be good to check your spark plugs as they may have had some exposure to coolant. If you did have coolant in the combustion chamber, lots of things can go real bad real quick. Water not compressing very well, things have to give, like rings and rods and push rods, etc. I would run a compression test while you have the plugs out. I really hope none of this is the case.
 
#14 ·
Well lucky for me it's not, when I did the head gasket everything looked clean, did a compression test, checked the spark, coils, all of the above that would render a hard start and stall, spark plugs and wires were all changed when I did the head gasket along with the cleaning of the valves and rods, after changing the throttle position sensor, crank sensor and finally the air control (which seems to have fixed my issue) but only for a few days, now when I did the head gasket obviously a lot of things need to come off the top end of the motor and while taking off the exhaust manifold I noticed they were not tight at all, I mean not even close, I could of pulled them off by hand if it wasn't so difficult to get too, I always thought I had a hole, now that it's tight with a new gasket she's so quiet and runs beautifully then just today it started to stall and run low RPM's again, only after a good hour long ride home, could this now be because of my catalytic converter? I'm thinking now because these bolts were so loose before the engine was able to breath enough to drive, now that it's tight and correct maybe it's starting to fail? Everything else is 100% all my gauges read normal and it sits at 6-750 RPM at idle, it wasn't until I was almost home that it started to read a low rpm then stall, starts right back up with no issue but I don't know of anyway to be able to tell if this is the problem as theirs no check engine light to tell me, as the weather gets warmer I'll be doing a complete top end refinish with new rings, rods and valves and purchasing the whole thing but I still have this issue, I'm going to take a ride in a few and see how it runs cold, if it runs fine then it only stalls when warm and I don't have a clue where to go from here when I replaced every possible sensor that could be causing this issue. Thanks for all your help I appreciate everything!! Chuck.
 
#15 ·
I'm slightly lost in the information here. You had a bad head gasket and replaced it. Did you take the head to a machine shop? Replace the bolts?

Head gaskets usually don't just go bad. Most of the time, the head will actually warp. This requires machining. Every time the head comes off, it needs to be taken to a machine shop to check the tolerances.

Also, the head bolts are torque-to-yield which means they are tightened beyond their physical capacity, and stretch out. They must be replaced every time.
 
#16 ·
Freeze plug blew out, a couple weeks ago, then after I replaced that I noticed antifreeze in the oil, my 93 has 250,000 miles + so I replaced the head gasket, new bolts all torced to the proper setting, now when I did the freeze plug I also had anti freeze bubbling out of the over flow ice cold, couldn't understand why but it was something new to me, the only thing I could think of was the gasket was bad, the jeep runs perfectly fine and for the past 2 day I've drove 80 miles each day with no issues after these sensors were replaced, until today, its back to stalling when coming to a stop and the clutch is in, if it's in gear it rides perfectly quiet, I didn't take it to a machine shop as I'm not exactly financially able to do so, after replacing the head gasket I haven't had a coolant issue, now I have a issue with it stalling when coming to a stop, it'll sit in idle all day long, RPM's read 6-750 but the engine does have a bit of distortion but I don't think it's anything out of the ordinary or abnormal as it always did this b/c it has so many miles, I really hope this clears anything up, I'm really not trying to be difficult I'm just trying to get to the bottom of what could be causing this stalling issue while driving, and as long as I have the clutch in and keep my foot on the gas high enough so it won't stall it'll be fine, then I can sit in idle until a green light and move on, obviously this isn't how I want to drive it but it's the only way until I can come up with a fix. What I don't understand is how the past 2 days it drove and idled completely fine, no stall, now abnormal RPM, then today it stalled after a hour long ride home.
 
#17 ·
Remove your throttle body and clean it up, you probably have crud in there and the idle air control valve is probably sticking. You have to remove the throttle body completely to clean it properly.
 
#19 ·
Now I would suggest testing the vacuum of your engine with a vacuum gauge (cheap at Harbor Freight). Your symptoms indicate low vacuum. Low vacuum can be caused by:

1. Vacuum leak
2. Slacked/jumped timing chain
3. Valvetrain issue

There may be others I am missing but those three are the most likely. They are in order of probability, with vacuum leak being the most likely. Check your MAP sensor vacuum line first.
 
#20 ·
Vacuum seem to be all ok, its all working correctly, what I don't understand is how it could start up one day perfectly fine then sometimes I have to lay on the gas just to get it to turn over, I'm now thinking I may have a wiring issue, maybe a bad ground or something's not right, after poking around and tugging on wires to see if anything was loose it fired right up and idled perfectly at 750-800 RPM I'm now letting it idle until warm to see if it jumps down a little it's roughly 44 degrees in Pa so it's a bit chilly so once it warms up if I have a problem with it stalling then I know it's only when its warm. This is tough, b/c when it ran for those 2 days with no problems it ran great! I can't thank you all enough for your help and input on everything without this forum I would be lost! So TY all.
 
#21 ·
Vacuum seem to be all ok, its all working correctly.
You should measure your vacuum, that one number will tell you lots. When I had trouble with a random misfire on my Jeep, and also an intermittent stumble/misfire, I hooked up a vacuum gauge. When it would stumble/misfire, the vacuum dropped. That's how I knew I had an issue with my valve timing, which happened to be a timing chain.

With vehicle diagnostics, guesses and assumptions are the reasons you struggle to find the real issue.
 
#22 ·
Chuck,
In MudMagnetYJs signature there is a link to several Factory Service Manuals. Click on MMs link and find the manual closest to your year Jeep. Look through the FSM for a diagnostic flow chart for rough running or stalling.

Following the flow chart will be the least expensive way to locate and repair your problem.
The flow charts may not describe your exact issue so you may have to work through a couple charts to discover the cause.

Simply guessing what the cause and cure may be is a costly way to repair a vehicle. Experts wrote the FSM and I use mine regularly.

Good Luck, L.M.
 
#24 ·
I don't know if this will help with anything but I noticed when I first start it up 9 out of 10 times it'll crank right over, idle forever, with no issue, then when I rev the engine to around 3,000 RPM's it'll drop all the way down and stall, then I have to lay on the gas just to get it to turn over, then again once started it'll idle all day long at 6-750 RPM. I am on a mission today to check all vac lines, some could use replacement but I don't think they are losing air, when I take them off the engine will bog down and the vac feels real strong when I put my finger over it, the closest harbor freight is 40 miles away so I'm still in search for the proper tools to check everything correctly. Thanks to you all for your input, I'm determined to get to the bottom of this and I will continue to post everything I've checked and came up with. Thanks again.
 
#26 ·
Yes, you're looking for the sensor on the thermostat housing. The factory service manual in my signature has a chart of the ranges for the resistance of the sensor.
 
#27 ·
So I did the ignition key (check engine light trick) where you turn the key on and off 3 times leaving it on on the 3rd and then the check engine light blinks, giving you codes, while doing this I got codes 13: No change in Manifold Absolute Pressure sensor (MAP) from start to run
14: MAP sensor circuit open or shorted; voltage too low
Does this mean I need a new MAP sensor? These are the only 2 that came up other then the code for the battery being disconnected in the past 50 miles or something, which I did have disconnected when I put the other sensors in. Thanks again.
 
#28 ·
Not necessarily... These codes aren't always helpful. This can mean a few things.

1. Low vacuum
2. Bad MAP sensor
3. Another sensor is bad but the MAP sensor is the first thing the PCM can't read
4. Wiring issue
 
#29 ·
Just when I thought I had a fix, well considering I already replaced both sensors in the throttle body and the crank sensor I guess I narrowed it down to the temp sensor and MAP, I'm looking to check the vacuum of the jeep today so hopefully I'll be crossing that off the list. Thanks.
 
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