QUESTION: 1996 4.6L Intake Manifold

The cracking was at the thermostat mounting on the composite manifolds. It's at the front, #8 is at the back. Any other puddles of coolant on top? Since you said the plug hole was full of coolant before you pulled the plug, I'd wonder what coolant lines run above the manifold so coolant would dribble down in the hole. Look for a leaking hose, first. Even a pin hole can spray enough under pressure to fill the plug hole, maybe from somewhere off to the side. Once coolant gets there, the plug misfires. I hope this is helpful.

PoD

By the way, I'm a shade-tree hobbyist. The pros that hang out here will likely have better answers.

PoD

Be sure and post if Paul is correct. I am about to change manifolds as you did. The coolant can come from several locations. I currently have Marine silicone sealer around my plug wire holes. What brand manifold did you buy?

Frank

Frank:

I will be sure to post and let you know what happens. The new intake will be here tomorrow and I will install it at that time.

I got the first replacement intake from a parts dealer on eBay. I don't think the part had a brand name. The only reason I bought the part is because it was under $200 and had a money back guarantee if it didn't fit. It fit perfectly and worked well for 2 years. Only recently did I ever have any problem with it at all. (I am STILL hoping that the fault is with the intake and not with my block or cylinder head!!!)

The intake that I am getting tomorrow is made by Dorman and has a lifetime guarantee. I ordered it from a local auto parts chain store (Advance Auto Parts).

I am seriously tempted to Permatex the whole thing when I install it. I really, REALLY do not want to go through this again. >:-(

from my experience your right on. Any fluid from any where on top can end up in any plug hole. I have only seen them leak around the t-stat area but I don't know off hand where all the places it COULD leak....A pressure tester would help you find it though :)

OK, I have just finished installing the new intake manifold, and there are still problems.

When I took the old intake off, a small amount of coolant did splash into the spark plug holes that are closest to the rear of the engine on either side.

No my car WILL NOT stop misfiring, despite the fact that I have mopped and vacuumed up every drop of coolant I could find. The misfires are mainly in cylinder 8, but one time I did get a misfire code for cylinder 4. There is a tiny amount of coolant still lingering around those two spark plugs, but I didn't think that the misfires would still be here after I have been cleaning those two spark plugs so much. I keep pulling the plugs and drying them off, and the last time I pulled them they were almost completely dry, which leads me to believe that the vast majority of coolant has been mopped up or burned off.

My car runs VERY rough when you accelerate, but it idles very well.

I'm starting to suspect a vacuum leak, but I have NO CLUE where it is or how I find it.

I also have no clue how to correct a vacuum leak.

Let's face it -- I HAVE NO CLUE WHAT IS WRONG AND I'M ABOUT TO GIVE UP.

Coolant is hard to clean away. If you haven't done it, you might think of new plug wires (do the plugs while you're at it, too).

Before that, there is one very common vacuum leak I found the hard way. The hose from the PCV valve runs to a metal pipe. At the other end is a short hose that connects to the intake under the throttle body. That short hose often bends and gets a hole in it that throws the whole system off. Have a very close look at it. I missed it twice before I actually saw the hole.

You might also have an air bubble in the fuel rail but it's not very common.

My 4.6L got rough, especially on acceleration, it was the wires.

PoD

Have you tried compressed air to remove the moisture from the plug holes? If you do not have a compressor, you can get canned air used to clean off keyboards and other small jobs at many places like Office Depot, Sam's Club, Costco, etc. Just swabbing them out isn't going to do it. Also, if the plug hole had coolant in it, the end of the wire and boot may be badly corroded.

How did the car run before? Did it misfire, run rough or what. Have you run a compression check to be sure coolant did not damage the cylinder before going to the trouble of replacing the intake? Have you done a compression test since. Coolant getting into cylinders is hell on valves, pistons and rods. You may not addressed all the potential problems by replacing the intake. BTW, you should never remove a plug in a recess w/o blowing it out with compressed air to remove debris and contamination that may enter the cylinder as the plug is removed. As an apprentice in the '60, the shop forman damn near broke all my knuckles for that. Except for emergencies, I haven't done that since.

Lugnut

sounds like its time for plug wires. Use compressed air to blow the holes out.

In my experience, gotta be bone dry.

Hi, Lugnut:

I have an air compressor, and I have used it a couple of times to try to blow out the impurities from cylinders 4 and 8, which are the ones that have registered misfire codes.

It was misfiring and running rough for about 2 weeks before I discovered the massive coolant leak on the intake in the area around cylinder 8.

It would idle fine, and it would seem to run OK when you were up to speed, but during acceleration it would jerk and misfire.

I have replaced the intake with a new one, and the problem is still there.

The car idles just fine, and it actually runs AND accelerates fine UNTIL the engine warms up. Then the engine runs VERY rough whenever you accelerate. Once you get up to speed, it smooths out again. The only cylinder that is showing a misfire code is cylinder 8. I have checked the spark plug on cylinders 4 and 8 and they are now bone dry.

QUESTION: If the car had a vacuum leak (something I'm starting to suspect), would it still idle OK?

Here's an interesting observation: Sometimes when I am accelerating and the car is running rough, there will be brief split-second moments when the engine runs smoothly. It's as if the engine is TRYING to run right, but it just can't...for whatever reason.

switched coils # 4& 8 with to other cylinders. if the missfire codes move to the switched cylinders, you have bad coils

What you describe sounds like a misfire under load. These are usually traceable to electrical problems including the injector system. More often than not, it is the ignition. If you have replaced the wires, try swapping the coils as suggested by another poster to see if the misfire follows the coils. Have you cleaned the MAF sensor? If you have had coolant getting into the intake, it could very easily have contaminated the MAF sensor. Also, if you have lost coolant into the engine, the HEGO sensor(s) almost always becomes contaminated and can cause mixture problems that may result in misfire under load. They are not in the circuit for the first 90 secs or so of engine operation. The ECT sensor tells the ECM the engine temperature which has great bearing on fuel mix. I would not suspect this until you have cleared every other option. Vacuum leaks are almost always more critical at idle/low engine speeds. Vacuu, leaks become a lower precentage of total air intake as the engine speed/load increases therefore making them less influential on engine operation. Most vacuum leaks are constant resulting in a consistent operating condition.

Lugnut

You're talking about replacing the spark plug wires, right? I replaced them once about 5 years ago. They seem to be in good condition just looking at them, but is it possible that they are already wearing out? How long do spark plug wires usually last?

I have bought new spark plugs (Autolite Platinum) and I plan to put them in and see if they help.

I have not checked any of the sensors you mentioned. I guess I was just hoping that any malfunction that might have happened as a result of the coolant leak would be temporary.

Would you go ahead and replace the spark plug wires if you were in this situation? After paying over 200 bucks for that new intake, I hate to put even more money into this thing, especially if there is a possibility that it is not necessary. But if it will fix the problem, I will be more than willing to do it.

The potential problem with the wires is corrosion inside the wire cores if it has been exposed to moisture for any lenght of time. The wires use a suppression carbon core that does not like being wet. I mention this because you talked about water in the plug hole. With the engine hot, the plug and wire end are taking a sauna in there. No guarantee new wires will help. A wire with high resistance may overload a coil leading to failure.

It may not be temporary if the sensors are contaminated.

Unfortunately, there are no guarantees in auto repair. You can improve your odds of success with a great deal of knowledge, experience and diagnostic tools. Whatever the problem, you need you work the basics first.

Some parts stores have individual replacement wires in appropriate lengths. I would ask around before buying a set if you are kinda tight. 5 year old wires in a hot climate are likely in an iffy condition at this point. The right thing to do is replace them and know that this is no longer the problem. You may also want to check the resistance in each wire with a DVOM. Resistance will vary according to the length of the wire. Check several and do the math with a handydandy calculator to compare the misfiring cylinders to some of the others. You are looking for ohms/foot resistance. You can see when one is higher than the others and maybe get a clue as to whether or not one is bad. Keep in mind that the ECM leans out the fuel mix as it gets warmer. This requires a hotter spark as the engine is loaded. A spark plug can have the same problem. More engine load with leaner fuel offer more resistance to spark which means the whole system has to be up to par. You may want to consider new plugs if you haven't already. I have an old '94 CV with this engine and it is happy as can be with regular old-fasioned copper plugs. I replaced the last set after 50K miles and it never had any symptom of a misfire. The more expensive platinum plugs are primarily for longevity and reduced maintenance. Plug wires are a different ball game with the 4.6L - it needs good ones.

Lugnut

4.6 Fords eat plug wires for lunch. Gap the plugs for sure. If the wires don't come with dielectric grease get some and use it on every wire end. I have found that light acceleration at high speed will show a bad plug and/or wire quickly. I have had good luck with motorcraft wires and AC/delco wires but you will probably be ok with any good set like the "lifetime" ones from parts stores.

Did you find cracks in the intake or was it a gasket situation?