Well, after ten years of trouble free service, my check engine light came on. I ran the codes and found that the intake manifold gaskets were apparently sucking air and causing a lean condition. The truck ran fine, but the problem was enough to trip the light. After doing some research, I learned that this is a common problem with the 4.2L engine. Alldata had a technical service bulletin on it. Fortunately, the problem is not the lower manifold gaskets between the manifold and the heads. However, it’s the upper manifold gaskets and the two-piece plenum gaskets along with the isolator bolts. In and of itself, that’s not too bad to fix, but the engine is partially under the firewall of the cab which makes access to the upper manifold very limited.
I was able to use a series of universal joints and a range of extensions and remove the upper plenum half without too much hassle, but it wasn’t easy getting to the rear bolts. Once removed, I saw no sign of leaks…yet.
So then I ventured lower. Once the upper half is off it gets pretty easy. I removed the isolator bolts and the bottom half comes off easy enough.
BINGO! You can see where the old gaskets were leaking. Also, the rubber (or what once was rubber) seals on the isolator bolts were as hard as concrete. No one had the isolator seals in stock, but Ford had the entire bolts which were expensive, but I was able to get them the day of the repair so I went with it. In the photo below you can see the difference in material in the seals on the bolts.
Now it’s just a matter of cleaning up the manifold parts and installing the new o-ring gaskets. Then it goes back together the same way it came apart.
Now is also a good time to clean the throttle body and idle air control assembly, and if it needs it, it would be easy to route plug wires at this time. However, I’ve only got about 20K miles on this set of wires, so I’ll let ’em ride. And back together it goes…
That’s pretty much it. It was challenging to start the engine, mainly due to all the carburetor cleaner I had sprayed into the ports had partially fouled the plugs I think, but once it cranked she cleared up and ran great. Now it’s ready to go…and no more check engine light!
Until next time…
Nicholas Fluhart 
I have an 03 that has done the same thing, I had a shop do it for right under $500. it fixed the problem for about a year now it is back doing the same thing. have you had any issues since you made the repair?
Comment by Matt — February 7, 2014 @ 12:16 pm |
I have had no problems with mine since the repair. I think I’ve put about 15k miles on it since then. Does your computer show the exact same codes? There are other things that can cause similar symptoms but are unrelated to the intake gaskets. If the codes are the same as last time, do you know exactly which parts they replaced? To fully solve the intake gasket problem, you must replace the isolator bolts/seals with the updated seal material along with replacing the upper plenum o-ring gasket (large o-ring that seals the two plenum halves) and the six lower plenum o-rings gaskets.
Comment by nfluhart — February 13, 2014 @ 10:17 am |
Down to my last options on my 03 F150 4.2. All new o2 sensors. Idle air control valve cleaning. MAF sensor clean. Throttle position sensor, which was bought new. Cleared codes, and drove the drive cycle FORD recommends after a reset. Codes still come back 171 and 174. Next option is the gaskets on the intake.
Comment by Tmbrwulf — October 4, 2015 @ 5:51 pm |
Replacing the gaskets was an easier task than I originally thought. If you’ve got moderate mechanical experience, you should be fine.
Comment by nfluhart — October 25, 2015 @ 5:31 pm |
This job is probably in my near future. I have been ignoring my CEL for several years now. It was diagnosed as a vacuum leak / PCV elbow / manifold gasket. I’ll probably do the manifold gasket and isolator bolts pretty soon. Thanks for putting this together. Really very helpful. Thanks!
Comment by Chris Hackett — February 11, 2016 @ 12:46 pm |
How much did the isolater bolt costs? Thanks
Comment by Sam — September 19, 2017 @ 7:08 pm |
It was a few years back when I bought them. I want to say they were about $90 from Ford w/the bolts. I’m sure there are aftermarkets cheaper.
Comment by Nicholas Fluhart — September 20, 2017 @ 3:41 pm |
Very helpful information buddy! That helped me a lot. Thanks
Comment by Richard — May 8, 2018 @ 1:22 am |
Old thread ..But just started this today ,,back bolts were a nightmare ,Though able to remove the rear center with a 1/4 drive ratchet and 10mm deep socket .Question how did the isolater bolts come out ? What size are they ? My socket just spins off Tried 8-7 mm
Comment by Jeffrey mcintyre — March 29, 2019 @ 9:35 pm |
It’s been a long time, but I think I used a 5/16. I don’t recall having any issues with them.
Comment by Nicholas Fluhart — March 30, 2019 @ 11:12 am |