plmbst
Member
- Joined
- March 3, 2002
- Messages
- 10
- Reaction score
- 0
- City, State
- Northport,NY
- Year, Model & Trim Level
- '97 XLT SOHC
It was early December when I first noticed that the idle on my '97 XLT (4.0 SOHC) with 235k miles was seriously uneven. After cleaning the IAC valve there was no improvement so I purchased a new valve and gasket ($150 or so) from the local dealership. A little better, but I knew it could be better.
I had read about the Seafoam treatment and decided to give it a try, after 235,000 miles what could go wrong? I should have known better.
Not wanting to "favor" one side of the manifold I decide to apply it through the IAC intake, which is a plastic tube off the rubber intake boot right after the MAF sensor. The entire bottle gets drawn in, I wait the 20 minutes or so and fire it up. Lots of smoke, but the idle is still rough and it runs worse than before. At light load, between 30-40 mph, the vehicle feels like it's "bucking".
I connect my 9 year old Auto XRay scanner and get multiple misfires and lean bank codes. After browsing multiple threads I conclude that the misfires are due to the lean conditions, and that the Seafoam has loosened crud on or near the intake gaskets causing them to fail.
Diagnose BEFORE you repair, right? I find instuctions for a home-made smoke machine on the net (it involves a metal 1qt. paint container and a smoldering rag) and it reveals a leak at the lower manifold.
Back to the dealer for upper & lower gaskets + an EGR tube gasket, just in case.( If they try to sell you the black ribbed gasket instead of the green O-ring, don't bite. It may fit with persuasion, but I wasn't about to try when it's18 degrees and the plastic manifold may crack)
The green O-rng was good enough to reuse and all went back together well enough. (Remember the vacuum tank BEFORE you install the upper manifold)
Starts and runs well for about 3 miles then i get the same "bucking" I'd had since the Seafoam treatment, but no codes and it is running better, though not smooth.
On my '97 there is a variable intake right behind the IAC and that's where the Seafoam passed on its way to the intake manifold. Maybe THAT gasket is damaged, so I remove that and the gasket is barely protruding above the surface. It's Sunday so out comes the high temp silicone gasket maker (sensor safe). A test drive now throws a code for misfire on number 6. Now this is the cylinder directly below the point that I used to feed the damp (water vapor being a product of combustion, and incomplete combustion at that) smoke into the intake system (I used the brake booster connection).
I swap #5 and #6 plugs, and the code reads #5. Hot damn.
It's getting late and colder, I put in new plugs on 4,5, and 6 and it's idling and running smooth.
My conclusions...
the IAC needed replacement. Cleaning the original made it "hum"
the intake gaskets were failing and driven over the edge by the Seafoam
some plugs were fouled by the Seafoam. I should have checked them earlier.
BTW, the threads and posts by 2000 Street Rod are informative and well written.
My thanks to all who contribute.
P
I had read about the Seafoam treatment and decided to give it a try, after 235,000 miles what could go wrong? I should have known better.
Not wanting to "favor" one side of the manifold I decide to apply it through the IAC intake, which is a plastic tube off the rubber intake boot right after the MAF sensor. The entire bottle gets drawn in, I wait the 20 minutes or so and fire it up. Lots of smoke, but the idle is still rough and it runs worse than before. At light load, between 30-40 mph, the vehicle feels like it's "bucking".
I connect my 9 year old Auto XRay scanner and get multiple misfires and lean bank codes. After browsing multiple threads I conclude that the misfires are due to the lean conditions, and that the Seafoam has loosened crud on or near the intake gaskets causing them to fail.
Diagnose BEFORE you repair, right? I find instuctions for a home-made smoke machine on the net (it involves a metal 1qt. paint container and a smoldering rag) and it reveals a leak at the lower manifold.
Back to the dealer for upper & lower gaskets + an EGR tube gasket, just in case.( If they try to sell you the black ribbed gasket instead of the green O-ring, don't bite. It may fit with persuasion, but I wasn't about to try when it's18 degrees and the plastic manifold may crack)
The green O-rng was good enough to reuse and all went back together well enough. (Remember the vacuum tank BEFORE you install the upper manifold)
Starts and runs well for about 3 miles then i get the same "bucking" I'd had since the Seafoam treatment, but no codes and it is running better, though not smooth.
On my '97 there is a variable intake right behind the IAC and that's where the Seafoam passed on its way to the intake manifold. Maybe THAT gasket is damaged, so I remove that and the gasket is barely protruding above the surface. It's Sunday so out comes the high temp silicone gasket maker (sensor safe). A test drive now throws a code for misfire on number 6. Now this is the cylinder directly below the point that I used to feed the damp (water vapor being a product of combustion, and incomplete combustion at that) smoke into the intake system (I used the brake booster connection).
I swap #5 and #6 plugs, and the code reads #5. Hot damn.
It's getting late and colder, I put in new plugs on 4,5, and 6 and it's idling and running smooth.
My conclusions...
the IAC needed replacement. Cleaning the original made it "hum"
the intake gaskets were failing and driven over the edge by the Seafoam
some plugs were fouled by the Seafoam. I should have checked them earlier.
BTW, the threads and posts by 2000 Street Rod are informative and well written.
My thanks to all who contribute.
P
sounds like one step forward, one step back but at least you got it solved. High Five
