On my '98, it threw me a 400 code, EGR leak... So I went to change the gasket and make sure the exhaust tube connection was clean and sealed...I ended up dropping a bolt underneath the intake. As I stuck my hand under there to find the bolt, the plastic was all dry rotted and so brittle it was literally cracking apart in my hands... Is this common, as the Autozone guy would have me believe? I thought that plastic was really just a heat shield... Is it part of the intake plenum, and could that be causing the rough running and misfires? Please help me on this one fellows, I don'r want to spend $350 and a day changing it if I don't have to.

 

And I also have a '96 5.4 motor that's destined to go in eventually, but for now, would that intake work on this 4.6?

 

In 96 , there was a 5.8, not a 5.4, - not until 97 anyway. So it won't work.

And yes, the Autozone dude is absolutely correct. That's surprising lol.

That your sound insulator falling apart. It's like a jacket of sorts, - completely normal, won't hurt anything.

 

Musta been a 97', then... It was given to me with the truck when I bought it, the guy I got it from was going to do the swap, but never got around to it. Believe he told me it came out of a wrecked Navigator...

And now I'm confused...

You said it sounds like the Autozone guy was correct... He told me that the plastice down there was part of the intake plenum, and with it cracking in pieces, it's sucking in un-metered air...thus all my problems...

Then you said it was normal and won't hurt anything...

If the time were financially right, I'd start the 5.4 swap now, but it's just not a good time...

But soon

 

That year engine will say on the heads what it is. It will say 5.4L right around the EGR pipe area, but on the head.

What your referring to , that rotted, is the noise insulator (induction noise), here, right under the manny-



Yours may be a little different than mine. But No, it has nothing to do with heat, - I don't recall you saying that before, -nor do I recall you mentioning unmetered air and rough running. That's another problem all together.

You have an upper and lower intake, - in the picture I posted. The Plenum is bolted to the top of that set up (mine isn't installed in this pic).

Your PCV valve line connects just below that into your upper intake, -OR, some connect @ the bottom of the plenum (throttle body elbow, = same thing). Yes, this line does rot out and needs replacing. That's common and usually will force 171-174 DTC's. AND rough running.

What PO 400 code did you get?

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Here's a better pick of the insulator -




Here a pic of what's letting unmetered air in -



Here's a pic of the Plenum (throttle body elbow)

 

Jbrew, thank you for taking the time to respond to me... You have no idea how much I appreciate any help right now... Actually I've been absent from this site for a while, but if you want, you could go back 4-5 years and I've been trying to figure out this problem... It's been running rough and misfiring and hesitating for that long

I got a 400 and a 401 code this morning, along with a 301 and 308... The misfires are random, and switch cylinders monthly. I've changed plugs and wires twice, checked every hose and tube that I can, swapped the coil packs to see if the problem followed (it didn't)... I'm just at a loss.

I replaced the EGR gasket and Tefloned the exhaust tube connection, and it did get better... But it still bumps at idle, hesitates under acceleration, and has little power. Above 3k RPM, it makes good, but not quite normal, power. The misfire seems to almost go away. And it's burning fuel like crazy. I've read in other places on here that there are vacuum 'resevoirs' on the passenger side fenderwall... I'll look for those in the morning...

I've worked on cars all my life, but for some reason this one is just kicking my a$$.

 

Look @ your wiring harness in relation to your AC accumulator. What can happen over time is either the harness drops to close the AC accumulator causing a mag field ignition disturbance. Or , the harness drops on the accumulator itself ( from age or possibly re-routing incorrectly) which can rub wear thru the insulation and aluminum sheathing that should be protecting the harness from Mag field disturbances. If both main harness plugs are switched on the firewall bracket, it is routed wrong, resulting in ignition conflict and/or premature failure of components.

Check were the harness loops just up from the accumulator. If know wire/harness chaffing is apparent, tie the harness further away regardless. You can also move the harness around if the problem is @ idle and listen for any change taking place while doing so. Any deflection in idle will confirm.

Good Luck

 

Will do first thing in the morning, as long as Bonnie allows us some dry weather...

 

Here's what I've found:

Visually inspected the harness above the accumulator. Found nothing that looks cut, burned, abraded, or torn. I did still zip tie them up above the accumulator to rule out interference. No change.

Changing out the EGR gasket and Tefloning the pipe made a WORLD of difference. It runs 50x better...

However, it still does have a misfire and hesitation and surge. It has not set any codes since I last cleared them. But definitely much more drivable.

My next option will be to replace the PVC valve, plugs and wires. For the longest time I thought the leaky valve cover gaskets were dripping oil into the plug wells, and causing problems that way. But the wire boot to plug connection is clean as a whistle, along with the plugs. Now, I am using Autozone plugs, along with MSD coil packs and wires. I will be going back to Motorcraft plugs, or maybe Denso's, I've heard the Denso's work really well in these motors. May bite the bullet and replace the MSD plug wires also.


Here's the current symptoms: At idle, it's real smooth, but perhaps once a minute I can feel it stumble. At 1/4 to 1/2 throttle, it takes off smooth and feels like it has good power. Any more throttle than that, it shakes, hesitates, and accelerates even slower. But once it gets up to 3k, it pulls hard, but still surges.

A small test I use (very bad for the truck, I know) is to power brake in the gravel driveway. Before fixing the EGR, it would break the tires loose a WOT. After, it breaks them loose at less than 1/4 throttle. Only reason I do it is because the misfire or whatever only shows itself under load, and that's a lot easier than going down the road.


JBrew, or anyone, any other suggestions?

 

Have you pulled the throttle body and cleaned it - especially the EGR ports? How do the vacuum hoses look coming off the DPFE?

 

Vacuum hoses are in good shape all under the hood... can't find one that looks like it would leaking. A couple of years ago I did remove and clean the TB, had to get the carbon out of the EGR ports with a drill bit, it was in there so solid... Ran better, but still enough of a random misfire to set a code, and keep it from getting inspected...

 

I i remember correct when I pulled my intake, I think there was some insulation on that plastic lower intake, and that was falling off mine down in to the opening under the intake.I have a friend who owns a repair show and they replace alot of these plastic lower intake pieces.They do so many off them, that their wholesale parts store carries them instock at all this now.

 

I believe you're right... When I was feeling around under there, in addition to the plastic pieces, there was some soft stuff that felt like fiberglass insulation... I was just under the impression that it was actually part of the intake plenum, where air travels through before entering the manifold... If that has holes in it, that would definitley explain my problems....

 

My motor exploded internally @ about 29,000 miles in 2000. I purchased the truck new, - fall of 98. Anyway, Ford put a new one back in it for me, no problem. That all took place in 2000.

In 2005 I was replacing intake gaskets and I found about 1/3 of a piston in my lower intake , - No S H I T It had been in their for almost 5 years lol.

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98Lariet4x4, - If I haven't mentioned it yet, your going to have to do a compression check. Let me know when/if your going to do it. You need to do this just right to be accurate. Testing to see if your still within tolerance works on a percentage and with your problem, you need to dig right into it right after shutdown and relatively quick. You need to quick test all 8 w/oil @ same temp. Not cold/ not @ room temp. Closest to operating temp as you can get it. It can be done, I'll help yuh.

We'll figure it out lol.