4.0 SOHC Running Problems
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Senior User
Joined: Feb 2004
Posts: 220
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From: Castalia, Ohio
4.0 SOHC Running Problems
My 98 Eddie Bauer Explorer is having a "low power" problem with the 4.0 SOHC engine. Any suggestions would be greatly appreciated.
Symtoms: 1. I have a lot less power off the start from a dead stop
2. Idle is rough. Similar to an ignition miss but is not as consistant (hunting)
3. Engine surges/bucks while holding accelerator steady at speeds under 55 MPH. Runs decent at highway speeds.
4. My vacuum gauge (mounted on my A-pillar) shows only 10 inches of vacuum at idle in park (used to be 17-21 inches)
5. Check engine light is not on and I have no trouble codes (DTC's) stored.
I have replaced the fuel filter (which was pretty clogged), spark plugs, fuel pressure regulator, PCV valve. I cleaned my K and N air filter and ran a fuel injector cleaner through the system and had no changes in the problem. I have done a compression check (105-115psi between all 6 cylinders cold) and I have spark at every cylinder. I pulled off the upper and lower intake manifolds and checked all the O-rings, and checked all vacuum lines coming off of the upper intake and found no leaks. Fuel pressure is @38 psi at idle which I thought seemed a little low but it is EXACTLY the same as my friend's 98 Explorer. I pulled the EGR valve off, cleaned the carbon off the pintle and checked it's operation, looks fine.
My Haynes manual states there is no way to check base timing so I haven't done anything with timing. She' got 126,000 miles on her and I have NEVER had any engine problems with her. It's a great truck and I really need to get her back in shape because I'm driving my 78 F-350 meantime and getting about 6 MPG out of the 460!
ANY help or information anyone has would be greatly appreciated! I posted this in the Explorer forum two days ago with no responses. Thanks!
Symtoms: 1. I have a lot less power off the start from a dead stop
2. Idle is rough. Similar to an ignition miss but is not as consistant (hunting)
3. Engine surges/bucks while holding accelerator steady at speeds under 55 MPH. Runs decent at highway speeds.
4. My vacuum gauge (mounted on my A-pillar) shows only 10 inches of vacuum at idle in park (used to be 17-21 inches)
5. Check engine light is not on and I have no trouble codes (DTC's) stored.
I have replaced the fuel filter (which was pretty clogged), spark plugs, fuel pressure regulator, PCV valve. I cleaned my K and N air filter and ran a fuel injector cleaner through the system and had no changes in the problem. I have done a compression check (105-115psi between all 6 cylinders cold) and I have spark at every cylinder. I pulled off the upper and lower intake manifolds and checked all the O-rings, and checked all vacuum lines coming off of the upper intake and found no leaks. Fuel pressure is @38 psi at idle which I thought seemed a little low but it is EXACTLY the same as my friend's 98 Explorer. I pulled the EGR valve off, cleaned the carbon off the pintle and checked it's operation, looks fine.
My Haynes manual states there is no way to check base timing so I haven't done anything with timing. She' got 126,000 miles on her and I have NEVER had any engine problems with her. It's a great truck and I really need to get her back in shape because I'm driving my 78 F-350 meantime and getting about 6 MPG out of the 460!
ANY help or information anyone has would be greatly appreciated! I posted this in the Explorer forum two days ago with no responses. Thanks!
New User
Joined: Nov 2004
Posts: 4
Likes: 0
Have your cat converter checked for a restriction low vac sounds like low output, as long as the vac gauge is not jumping your valves should be fine. other than that there is not many things unless your check engine light does not work 96 and above will pick up most problems, restricted cats are iffy
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