Intake Manifold Gasket or Head Gasket?

[phil.o]

I've been trying to diagnose this problem for a little bit now and I want to see if anyone has an opinion out there. I'm pretty new to car repair. I'm going to get in there this weekend I just want to have it kind of nailed down before I get there.

I know I have a misfire on cylinders 5 and 6. I have a slight coolant leak coming from the engine(the exact location I'm not sure). My oil is not milky. The spark plug from cylinder 5 is coming out completely black. I have just a touch of white smoke coming out of the back, but it's cold in Jersey and it goes away pretty quickly.

The computer reading came up with lean gas mixture and misfire on cylinder 5 and 6. The it said were intake manifold gasket,mass air flow sensor, plugs, wires, coils. I replaced everything and cleaned the MAS by myself last weekend. The intake manifold gasket is the last thing on the list.

I haven't done a compression test but I'm almost positive that it will come up with at least cylinder 5 being bad. If that is the case could it be intake manifold gaskets? Or would it have to be farther down?

If anyone can point me in the right direction I would be very grateful. I have no choice but to do the work myself because these problems are going to cost more than I have in my bank account if I pay a mechanic(If you are a mechanic out there: you're work is very valuable and appreciated but I'm a bit lean funds wise). So I'm either doing the intake manifold gaskets or going deeper to do head gaskets and doing the head gaskets(which I've never attempted) makes me a bit nervous.

 

[blenton]

I would definitely do a compression check on those two cylinders before you do anything else. If they are both low (like, REALLY low) that usually means your head gasket is toast. Of course, there are always exceptions to the rule, but you can be fairly confident that it's the head gasket as long as all the other cylinders are in good working order. There are several posts on how to do a compression check and determine if rings are worn, valves are bad, or other problems exist.

Unfortunately, I'm told the intake gaskets are also a likely culprit on these engines as well. Of course, you can always take a it to a shop to have them diagnose the problem. It will probably cost you $50 - $100, but sometimes that's better than throwing parts and your time at it, then finding out that you didn't fix the correct problem. It could also be a cracked in the head between the two cylinders (hate to throw more dark on a dreary situation).

I haven't done head gaskets on this motor, but have done several others. They aren't too difficult - you just need some decent organization skills and a lot of patience. Though I may end up doing mine on my exploder soon and I'll end up eating my own words...

I'm usually in the same situation as you (as far as funds go) so I befriended a mechanic way back when I was in high school and drove a '79 bronco. Now I bench race with him on occasion. Anyways, DIY is usually the way it goes around here, so no worries!

 

[phil.o]

Thanks Blenton that was helpful, I will definitely do a compression test. Though I might just have a shop diagnose it because, you're right, that would be really frustrating to not fix the problem after spending a whole weekend working on it.

When I found the coolant leak it was dripping down the opposite side of the motor. Cylinders 5 and 6 are on the passenger side and I found the drip on the drivers side.

By the way its a 1998 4.0l OHV 2WD.

 

[2000StreetRod]

V6 cylinder numbering

Thanks Blenton that was helpful, I will definitely do a compression test. Though I might just have a shop diagnose it because, you're right, that would be really frustrating to not fix the problem after spending a whole weekend working on it.

When I found the coolant leak it was dripping down the opposite side of the motor. Cylinders 5 and 6 are on the passenger side and I found the drip on the drivers side.

By the way its a 1998 4.0l OHV 2WD.

cylinders
Rear
3 6
2 5
1 4
Front

coil pack
Rear
3 4
2 6
1 5
Front

I suggest you check your ignition wires for correct connection.

 

[phil.o]

Are you sure that's correct? I labeled them when I took them off. I rechecked the wires today but I would have them lined up differently according to your diagram. And wouldn't that make cylinders 4,5, and 6 misfire?

 

[swetrid]

He is right! Everybody always switches # 5 and 6 at the coil and causes misfires. 4-5-6 are driver side cylinders.

 

[phil.o]

4-5-6 are not drivers side coils. There's just no way. My car would have been undrivable probably unstartable if I had gotten the coils that mixed up. I was very careful when I replaced the coil, though I will double check when I get home.

 

[2000StreetRod]

embossed numbers on coil

If you check your coil pack closely you should notice the matching cylinder numbers embossed on it. Ford used a waste spark system with paired cylinders firing simultaneously - one cylinder in compression and another in exhaust. There are actually three high voltage coils in the V6 coil pack. The unusual numbering scheme on the coil pack accommodates the paired cylinders. Ford claims firing the spark plug on the exhaust stroke reduces emissions but I think it was done simply to reduce complexity and cost.

 

[bobflood]

4-5-6 are not drivers side coils. There's just no way. My car would have been undrivable probably unstartable if I had gotten the coils that mixed up. I was very careful when I replaced the coil, though I will double check when I get home.

You do NOT want to argue with these guys when it comes to Explorers - they are experts!! And Ford numbers their cylinders as they said - in a V6 1,2 and 3 are on the passenger side and 4,5 and 6 are on the drivers side. For V8's like mine 1 thru 4 are passenger side and 5-8 are drivers side.

 

[phil.o]

My apologies. You guys were in fact correct.

I'm still not sure how that happened, I was very careful when I took off the wires and replaced the coil. Thank you all for your help, I really do appreciate it. I'm pretty sure my head gasket is starting to go bad though as I am leaking coolant so I'm glad I took this time to look over my car really well.

I gotta tell you I had gotten myself kind of psyched up to do my first sizable repair replacing the intake manifold gasket. Now, I have a whole weekend with nothing to do.