94 Ranger Coolant in Intake Manifold?

94 4.0 Ranger. I used to own this truck but I gave it to my uncle a few years ago. He's 67 years old and doesn't beat on the truck at all. It never had this problem when I owned it.

The ranger ran great for a long time, but developed a misfire on cylinder 3. Upon pulling the plug I could see that it was all fouled up with black gunky stuff. It just smelled like oil, but it was hard (not soft and mushy). I wasn't sure what it was. All the other plugs looked great. I did a compression test, and the results were good.

Cyl 1: 183 psi
Cyl 2: 168 psi
Cyl 3: 183 psi
Cyl 4: 180 psi
Cyl 5: 181 psi
Cyl 6: 172 psi

I replaced the plug, but it began fouling up quickly (within 100 miles). The plug doesn't smell like gas, so I thought maybe there was a bad fuel injector. I put a long screwdriver on the injectors and I could hear them all clicking, but I suppose it's possible the number 3 injector is clogged. All cylinders ARE getting spark. I confirmed that with an inline spark tester. Cyl 3 isn't firing at all, even with the new plug (I pulled the wires off the coil pack while it was running and cyl 3 is the only one that doesn't change the idle). I don't know how long my uncle was driving the truck with this dead miss on cyl 3, so I'm wondering what kind of damage driving with that misfire could cause? I don't see any oil in the coolant, or coolant in the oil. Both look, smell, and feel normal.

So I pulled off the upper intake manifold with the intention of changing the fuel injector and I see what I believe to be coolant in the upper intake manifold port. See attached files for pictures. The other intake ports look black and 21 years old, but normal. Then I pulled off the fuel rail and lower intake manifold. You can see coolant in the lower intake manifold in the cylinder 3 port. Most of the gasket came off the lower manifold and onto the top of the motor. The gasket around ALL of the coolant ports looks kinda crappy to me, but the gasket around all of the intake ports themselves looks to be ok.

I also took picture of the bottom of the lower intake manifold. You can see how the bottom of the manifold looks different around the cyl 3 port. It looks as if some of the coolant is stuck to the bottom of the manifold as well. But that's only around the cyl 3 port. The bottom of the manifold looks normal around all the other ports. So perhaps the lower intake manifold gasket was simply leaking around cyl 3, and the coolant made its way in there?

Are these 4.0 intake manifolds known for cracking? I haven't found any cracks yet. I'm hoping the lower intake manifold gasket was simply leaking around those coolant ports. I realize I could also have a cracked head or head gasket. It puzzles me as to how this coolant would have gone UP the intake manifold instead of just down into the oil. Could my uncle have done severe damage by driving with this misfire? He hasn't reported any overheating.

Thanks for any help guys. I'm debating as to whether or not I want to take off the heads and keep investigating, or just try throwing a new gasket on the manifold here and putting it back together. I'm interested in all input!

It looks like a simple gasket failure to me. From the compression test results and if was mine, I would not pull heads. I'd clean all the mating surfaces like crazy and put it back together. Of course my opinion is worth what you paid for it!!!

But, it is your truck, your time and your money!

It looks like a simple gasket failure to me. From the compression test results and if was mine, I would not pull heads. I'd clean all the mating surfaces like crazy and put it back together. Of course my opinion is worth what you paid for it!!!

But, it is your truck, your time and your money!

That's probably what I'm gonna do.

So what would cause the misfire when I replaced the fouled plug with a new one? Clogged injector?

Maybe you could check the condition of the plug to the injector too..If you change one injector on a high mileage motor maybe think about changing all six.

Do you think you could have a vacuum leak in the runner of no.3 leaning it out?Maybe putting a ohm meter on the no.3 plug wire?

The way coolant flows through the lower intake of the 4.0 a failed gasket could conceivable let coolant into a cylinder through the intake valve, enough to cause a misfire. It's not likely, but if you have evidence of coolant in an intake runner I think that is where I would start.

Are intake runners what I've been calling "ports?" (picture 7, first post) I've attached a picture of the port leading down to cylinder 3. You can see how gross it looks in there. A normal cylinder is shown in the last picture of my first post.

trail B2 - The engine has about 125K on it. It's an old truck but I don't know that I'd call that very high miles. If you mean put an ohm meter on the injector connector wire, I could do that. What would a normal reading be?

I'm going to wash that intake down really good and check it for cracks. Carb cleaner and then hot pressure washer. Someone was in this intake before. The gaskets on the top and bottom of the fuel rail are both in REALLY good shape, and they're Fel-Pro. I guess they just didn't take off the lower manifold.

It's possible that this coolant has been leaking into the cylinder for quite a while. I'm starting to worry about rust on the cylinder walls.

Rust, don't think so. You did a compression test. So, the piston and rings are doing their thing.

enjr44 said:

Rust, don't think so. You did a compression test. So, the piston and rings are doing their thing.

Click to expand...

Maybe I should spray some B12 or something on that intake valve to help clean it up a little? It looks pretty bad in there.

I hear this is a common problem on early 4.0 ohv motors. The bolts on the intake manifold work looseand the gasket material degrades. I believe Ford did something about this around '96 or so, but not sure. Also unsure about your misfire.

I think that intake runner was just sucking so much coolant with every stroke it was drowning out the fuel/air mixture, causing the misfire. I think I had spark and fuel, but there was too much coolant in the cylinder for it to fire. The injector from that cylinder seems to work well.

I completed the repair a few weeks ago. I thought I'd post the results to keep the forum search function valuable.

The intake manifold gasket was very brittle when I removed it. It was leaking coolant into the oil, and into the cylinder 3 intake runner. I replaced it, the cylinder 3 fuel injector (not sure it needed the injector, but I had one on hand already so I put it in), the thermostat (because why not), and I did an engine flush (motor medic) and changed the oil twice after the repair.

There was coolant in the oil, though I couldn't see it initially. I left the oil drain plug out while I had the lifter valley open and dumped a few quarts of oil down there to "rinse" out the engine. That's when I saw the coolant in the drain pain. The coolant in the oil must have been the cause of the clacking sound I had. After the repair, engine flush, and oil change, the clacking sound has disappeared completely, there is no more misfire, and the vehicle is running like a dream. I checked the cyl 3 spark plug after the repair and it was initially very white (probably from burning off all the coolant that was in that cylinder). I changed it and checked it again after a few hundred miles and it looks normal. I have a feeling the catalytic converter might be clogged because it was burning coolant for so long, so I'll have to get my hands on a gauge and check that sometime soon.

The only odd thing remaining after the repair is the temperature gauge on the dash. The truck never used to run hot, the temp needle would often sit between 1/4 and 1/2 the way up the temp gauge when the truck was warm. Now the needle doesn't even reach 1/4 of the way up the gauge. It's just barely in the [normal] range on the gauge. The upper radiator hose is getting plenty hot when the truck is warmed up, so I'm thinking the coolant temperature sensor may be faulty. I did remove it when I took the intake manifold off and cleaned it. I'll buy a sensor on my next purchase from rockauto and see what replacing it does.

Thanks to everyone for their help and guidance!