Dreaded system bank 1 and 2 lean | Ford Explorer Forums - Serious Explorations

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Dreaded system bank 1 and 2 lean

RedRider125

New Member
Joined
February 18, 2015
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City, State
SoMD
Year, Model & Trim Level
1998 Explorer Sport
Hey everybody,

I have searched throughout the forums with a ton of confusion- a lot of people with the same issue have been replacing parts that don't equate with vacuum leaks. Anyways, so a little background on the Expo. It's a 1997, 5 speed, 4wd, 4.0 ohv. I know these things have a ton of problems with vacuum lines all over. I've noticed this problem for a while, mainly noticeable in the colder months. In the summer, code goes away and starts fine in the morning. My reasoning is that the intake manifold gaskets seal and expand in the summer and don't seal and contract in the winter. Now in the winter, when the temperature really starts to drop, it'll run rough at idle until it warms up.

In attempting to fix the issue, I've replaced the following (related to any vacuum issues)
Both pre-cat o2 sensors
upper intake manifold gasket
EGR green seal

When i tackled the upper intake manifold gasket, they seemed pretty hard and flush with the sealing surface. The code went away for about 3-4 days, and idled better upon colder start up. I read the codes today and under the freezeframe data where the code went off, it was under light load like idle.

My guess is the lower intake manifold gasket needs to be replaced, but I know it's going to be a major PITA. Anyone's thoughts and suggestions would be appreciated!
 



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You are probably right, the lowers likely need replacing. I was putting some of those in and discovered someone previously did just the uppers.
 






Intake manifold O-rings are very likely the reason for you lean codes. Another thing that may cause this is a badly clogged fuel filter or a fuel pump that's not putting out 100%. Check your fuel pressure at the fuel rail with a fuel pressure gauge. The '97 still had the return-type fuel system. Your fuel pressure at the rail should be around 35-37 PSI.
 






Correct me if I'm wrong, (as I may have picked up the wrong gasket set) but doesn't the upper have the o-ring style gaskets that go into the upper manifold, and the lower gasket set is a typical style flat gasket for the lower? I'll have to check the pressure next time I get a chance.

Intake manifold O-rings are very likely the reason for you lean codes. Another thing that may cause this is a badly clogged fuel filter or a fuel pump that's not putting out 100%. Check your fuel pressure at the fuel rail with a fuel pressure gauge. The '97 still had the return-type fuel system. Your fuel pressure at the rail should be around 35-37 PSI.
 






Correct me if I'm wrong, (as I may have picked up the wrong gasket set) but doesn't the upper have the o-ring style gaskets that go into the upper manifold, and the lower gasket set is a typical style flat gasket for the lower? I'll have to check the pressure next time I get a chance.

On the '97 both the upper and lower manifold seals are more of the O-ring persuasion. Not a flat gasket.
 






You need to do your lowers, my 01 came with just the uppers done, I don't get why really, people go that far, and in the case of the SOHC, ten minutes more will do the lowers if you're good with your hands and tools.
 






OHV has a flat gasket under fuel rail/spacer plate, and than the oddly shaped o ring sort of gaskets in the bottom of the upper intake that is usually plastic,, they sometimes get so compressed they are very difficult to remove, , i used a dental pic type tool top get them out,,

i have it down to about a 25 minute process to get to the bottom of the rail now,,, make sure you're very careful with the injector top seals/o-rings,, they can be brittle and crack and leak if they have not aged well,, use vaseline on them to let them slide into the rail holes easily,, ford sells them separately,,
 






On the '97 both the upper and lower manifold seals are more of the O-ring persuasion. Not a flat gasket.
Great, thanks. Yeah the gasket kit I got had the flat gasket for the bottom, so good thing.
 






You need to do your lowers, my 01 came with just the uppers done, I don't get why really, people go that far, and in the case of the SOHC, ten minutes more will do the lowers if you're good with your hands and tools.
Yeah, I get you. At the time I had the wrong gasket, so that's why. Plus I didn't know i'd have to pop the valve covers off and the fuel rail. At that point i'd like to have new gaskets for that.
 






OHV has a flat gasket under fuel rail/spacer plate, and than the oddly shaped o ring sort of gaskets in the bottom of the upper intake that is usually plastic,, they sometimes get so compressed they are very difficult to remove, , i used a dental pic type tool top get them out,,

i have it down to about a 25 minute process to get to the bottom of the rail now,,, make sure you're very careful with the injector top seals/o-rings,, they can be brittle and crack and leak if they have not aged well,, use vaseline on them to let them slide into the rail holes easily,, ford sells them separately,,

I'll have to tackle the lower at some point when I'm back from school. I had no problems with the upper, except for getting the tricky EGR tube to seat properly. Any other old indian tricks you've found for tackling the bottom like in the valve covers, popping the rails off? Is it possible to leave the upper plenum on since I've already done that, or would that have to come off too?
 






OP, Sorry I thought you were asking about a SOHC. I missed where you said it was an OHV. Please disregard what I said about O-ring gaskets.
 












for the lower , it all has to come off cause the bolts are under one side of the upper and can't see them,,

the way i do the valve covers is with a small air ratchet, , i put on a medium length extension and a swivel than the socket,, no ratcheting required, just push the button on the tool,,
quick and easy,,
 






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