Is it really the intake manifold gaskets?

[Frederick Walker]

Okay, first let me say that I am an Expedition man. I love my Expy. What brings me here is my significant others 1998 Ford Explorer EB 4x4. I guess the only engine put in those was the 4.0 at the time? Anyway, one day she went out to crank it and it would not start. A friend changed the coil pack with no luck, the coil pack didn't seem to be working. After much research, I discovered that it could be the Crankshaft Position Sensor and after cleaning the leads it started right up. After listening to it run rough and trying to figure out the problem as to where it could be, I discovered that someone had swapped the number 3 and number 4 plug wires on the head (how I didn't check that first is beyond me). So after going through all of that, here is the problem that I am now faced with (there are actually two). The engine will start but idle rough for about two minutes before it smooths out. There is no hesitation when the gas is stepped on, even under a load. It will run great until you turn it off and restart it, then it idles rough again for a few minutes before smoothing out. I have read some forums that say it could be the intake manifold gaskets are causing a vacuum leak? I am thinking that this could be an issue since when I spray starter fluid in one area (to the best of my ability since there are so many obstructions) the engine rpms will change ever so slightly. I am thoroughly confused by this. I have cleaned all the sensors that I can think of but that didn't make any difference. I don't want to go blindly throwing money at something and that not be the problem. Once I get this figured out I will be throwing Seafoam at it to clean it out. Any suggestions would be much appreciated. (I will elaborate on my second problem in another thread since it is unrelated to this one).

 

[BrooklynBay]

Welcome to this forum! Are there any trouble codes with a check engine light? It probably has bad gaskets since you said that the idle changes when you spray starter fluid on the gaskets.

 

[Frederick Walker]

No, I can't get it to throw any codes. That's what is making this so difficult to diagnose.

 

[koda2000]

The problem with saying it's a 4.0L engine is that there were two 4.0L V6 engines offered for 1998. An OHV and a SOHC (plus a 5.0L V8). The SOHC is typically the one that suffers from intake manifold air leaks because it uses two sets of skinny O-ring gaskets on the intake manifold which dry out and stiffen with age, then they leak. As the weather turns colder they leak more air longer and then throw codes (P0171/174). The OHV engine can also leak air and water at the intake manifold gaskets.

From you description of what's happening, I'm going to assume the truck has the SOHC V6 engine. Running rough until the engine warms up a bit are typical indications of intake manifold O-ring leaks. In that case the issue sounds very much like the upper/lower intake manifold O-rings probably need to be replaced. The O-ring set is inexpensive, and the replacement will typically take a DIY'er around 3-4 hours to change them. The '98 intake has one set of O-ring gaskets between the upper and lower intake and a second set between the lower intake and the cylinder heads. In later versions of this engine Ford used a 1-piece intake and fatter O-rings against the heads, allowing them to eliminate 2 of the 6 bolts which old the intake on.

On the SOHC engine, trying to spray starting fluid around the intake is difficult because of the way the intake mounts to the heads (vertically). The fact that you've noticed a slight increase in RPM when spraying is a further indication of air leaks.

 

[MAS Tequila]

Let me start by saying that I have 0 experience with either 6 in the Explorer, my Mountie is an 8.

I had a couple of F150's with the 4.2 V6 that experienced the same intake o-ring leaks.

What makes me curious is that you say the idle smooth's out after a couple of minutes.

My Mountie recently had a similar issue, upon start up it would run rough but after reaching operating temperature it would smooth out and be good until it was shut off.

It ended up being one of the O2 sensor heating circuits was bad.

A new O2 sensor and all is better.

If you have access to a scanner check the fuel trims and see if 1 bank or the other is way out at start up and comes back to normal after warming up.

I'm not saying that is your problem, but checking never hurts.

 

[koda2000]

Let me start by saying that I have 0 experience with either 6 in the Explorer, my Mountie is an 8.

I had a couple of F150's with the 4.2 V6 that experienced the same intake o-ring leaks.

What makes me curious is that you say the idle smooth's out after a couple of minutes.

My Mountie recently had a similar issue, upon start up it would run rough but after reaching operating temperature it would smooth out and be good until it was shut off.

It ended up being one of the O2 sensor heating circuits was bad.

A new O2 sensor and all is better.

If you have access to a scanner check the fuel trims and see if 1 bank or the other is way out at start up and comes back to normal after warming up.

I'm not saying that is your problem, but checking never hurts.

They smooth out because as the engine heats up the aluminum heads expand (and to a lesser extent the plastic intake manifold does also). This expansion closes the leaks so no/less un-monitored air is getting into the engine. This is a common problem with the Job 1 SOHC 4.0L V6 engine. My old '97 Sport SOHC ran perfectly during the summer months, but ran like crap when first started during the winter months (and would throw lean codes P0171/P0174) until the engine ran for a few minutes. Then it idled fine. I never did get around to replacing the O-rings (still have a brand new set in my garage) and I sold the truck this past spring.

 

[Frederick Walker]

When I start the engine and spray the starting fluid at the intake manifold, the rpms will increase more drastically than when it's warm. That's why I am leaning towards the gaskets. I have had O2 sensor issues on my Expy and it has always thrown codes, so wouldn't it do the same thing on the explorer? Could it have something to do with the Crankshaft Position Sensor since all I did was cleaning that when the coil pack wasn't firing? I'm going to change the gaskets but I'm just trying to look a head to see if anyone else has had an issue like this. I will keep everyone posted when I get the gaskets changed.

 

[koda2000]

It has nothing to do with the crank shaft position sensor. It either works or it doesn't and when it doesn't you get no spark to the spark plugs and the engine doesn't run.

If you own a Job 1 SOHC 4.0L V6 you will have this issue at some point. Replace the intake manifold O-rings/gaskets.

Example:
http://www.autozone.com/external-en...lpro-intake-manifold-gasket/579209_46006_5297

 

[MAS Tequila]

I wasn't saying Koda isn't right, he likely is.

On mine the heater on the sensor was out, and it was enough to make the short term fuel trim FUBAR without throwing a code.

On my F's with the 4.2 the o-rings were the culprit just like on the 4.0.

If I'm not mistaken the 4.6 suffers from the same design 'improvement'.

I'll stick with the 5.0 that uses 60 year old basic design tech.

 

[koda2000]

I wasn't saying Koda isn't right, he likely is.

On mine the heater on the sensor was out, and it was enough to make the short term fuel trim FUBAR without throwing a code.

On my F's with the 4.2 the o-rings were the culprit just like on the 4.0.

If I'm not mistaken the 4.6 suffers from the same design 'improvement'.

I'll stick with the 5.0 that uses 60 year old basic design tech.

I couldn't agree more re the 5.0L V8. I hate the 4.0L SOHC engine and wouldn't take another Gen II Ford with that engine if you gave it to me for free.

 

[Frederick Walker]

I'm not saying that he's wrong either. Just taking the cheaper of the two evils. I appreciate all of the input on this, I really do. If it's not the gaskets then I will move to the O2's. It would just be so much easier with a code, these gremlins are killing me. I am also chasing down a headlight issue where they come on when the vehicle is started (headlights/tail lights/ dash lights). After about three minutes they will go off. It does have daytime running light switch but even with it off they still come on intermittently. There was a short but I found that one and that's just a story that I don't want to get into, let's just call it redneck wiring. Not so much worried about that anymore since it's not draining the battery. Like I said this thing has gremlins. LOL
.

 

[lobo411]

I'm guessing that replacing the SOHC O-rings is similar in difficulty to replacing them on the OHV. In that case, it's 2-4 hours *the first time you have to do it, because you don't know what stuff needs to be take off.* Every time after that, you can do it in an hour and still have 15 mins for a beer.

 

[koda2000]

I'm guessing that replacing the SOHC O-rings is similar in difficulty to replacing them on the OHV. In that case, it's 2-4 hours *the first time you have to do it, because you don't know what stuff needs to be take off.* Every time after that, you can do it in an hour and still have 15 mins for a beer.

Yeah, it's not a particularly hard job. Just a lot of stuff in the way. I like to coat the new O-rings with some Vaseline (always do this with rubber gaskets/O-rings) so that they don't bind during installation/reassembly. I figured in the extra time for a first-time DIY'er in my time estimate too.

 

[Frederick Walker]

Okay, first of all, I want to say thank you for all of the input. I haven't been working on this thing for a few days but I did find the vacuum leak. There is a "T" fitting towards the front of the engine that connects to two ports on each side of the intake. One had been cracked. It was hard to hear the leak due to engine noise. Unfortunately, I couldn't find a replacement, so I put a band-aid on it until I can find one. I had to go to Home Depot and get a hose splicer. A little tapping and about 6 inches of vacuum line later the vacuum leak is now gone. Now if I could just find the cause of the rough idle and the headlights coming on when starting the truck and going off a minute or two after you shut it off I would be doing something.

On the plus side, I now have a CEL on so that I can get some codes off of it.

 

[Spuddy]

The rough idle is probably still the intake manifold gaskets.

Auto lamps on your mirror is what controls your automatic headlights. The switch gets wonky over he years. I ended up just unplugging mine at the mirror.

 

[Spuddy]

Oh... you have a 98 just like mine. You probably also want to do the chain tensioner that is included in 00M12 service notice/kit and while you have your manifold off you can look for your slow coolant leak at the top of and around where your sensors are located.

Ask me how I know...

Do some research and you can get a 3 for the price of 1 bonus in here.

Got my 00M12 kit NOS on eBay for $25

 

[fast_dave]

Fredrick Walker; help us help you ;-)

Please confirm which 4.0 V-6 you have: the OHV or the SOHC.

Heck - you might as well put it in your vehicle profile, below your screen name

They're two completely different engines, and knowing which one you have will make helping you a lot easier!