thedave360 Posted November 5, 2010 Share Posted November 5, 2010 Ok guys, I would like some advice on what to do. My 92 4.0 HO is having some problems. I have no idea how many miles it has on it, all I know is it is A LOT. Its always had low oil pressure (20psi at hwy speed, 55-60 and 1800ish RPMs), and its always ran a little rough since I bought it in march of 09. About a year ago, I changed the main bearings and the rod bearings. Along with the timing chain, water pump, and oil pump. All that did little to nothing for the oil pressure and performance. (not that I would expect the water pump to inprove oil pressure though) Last week I went on a trail run with some buddies and it did fine, until the ride home. Any time I was accelerating and got near 2500rpm it would start sputtering and hesitating and generally sounding like crap. A guy I know has a 91HO and I drove it the other day, it was SOO much more powerful than mine. Right now I'm running 2quarts of Lucas Oil Treatment and 4 quarts of 40w oil, and I'm still only getting 20psi above 1000rpm when its at operating temp. When its cold, its close to 60psi. From what I've seen on the forums, 20psi isn't considered "optimal". I'm running out of Ideas here. I'd rather not spend gobs of money on a new crate motor. I just don't know what to do anymore with this thing. Please help me out with some leads on what I can do to fix this thing. Link to comment Share on other sites More sharing options...
veritas4156 Posted November 5, 2010 Share Posted November 5, 2010 Did you try replacing the oil pressure sending unit? Also check your engine ground straps. Both can cause false readings on the pressure. Did the spitting and sputtering go away after that ride home? Could have been caused by a bunch of things. I've knocked rust loose in my tank while on a low tank and nearly immediately clogged my fuel filter. Ended up having to drop the tank to clean it out. And damn man, what's your fuel economy like running that thick of oil? Link to comment Share on other sites More sharing options...
jimoshel Posted November 5, 2010 Share Posted November 5, 2010 What clearance do you have on the bearings? Did you mike the journals or just replace with standard? Link to comment Share on other sites More sharing options...
thedave360 Posted November 5, 2010 Author Share Posted November 5, 2010 Did you try replacing the oil pressure sending unit? Also check your engine ground straps. Both can cause false readings on the pressure. Did the spitting and sputtering go away after that ride home? Could have been caused by a bunch of things. I've knocked rust loose in my tank while on a low tank and nearly immediately clogged my fuel filter. Ended up having to drop the tank to clean it out. And damn man, what's your fuel economy like running that thick of oil? -Sending unit is brand new. Where would these "Engine Ground Straps" be?? -I haven't driven it at all since the ride home. I will check out the fuel filter though. I went damn near vertical on the trail a few times...that could have stirred up the tank a bit. -Fuel economy is... nonexistent lol. I get 13ish just driving around. What clearance do you have on the bearings? Did you mike the journals or just replace with standard? I don't recall off hand what the clearance is on the bearings. I replaced with stock bearings. Man, I'd really hate to have to change those bearings again :headpop: Link to comment Share on other sites More sharing options...
Eagle Posted November 5, 2010 Share Posted November 5, 2010 The factory sometimes cut the rod and/or main bearings .010 smaller than spec and installed bearings to match. There are codes stamped into the passenger side of the engine block to indicate what size bearings should be used. Link to comment Share on other sites More sharing options...
veritas4156 Posted November 9, 2010 Share Posted November 9, 2010 Ground strap from the factory is in the back of the engine connected to one of the back two head bolts. Should go to the firewall. Link to comment Share on other sites More sharing options...
Comanche County Posted November 9, 2010 Share Posted November 9, 2010 Mine was only pushing 20 psi or so until I had the head rebuilt....new valve stem seals and a new head gasket seem to have done the trick. Its got over 200K and pushes between 30-50 psi depending on the engine temp. Link to comment Share on other sites More sharing options...
dasbulliwagen Posted November 9, 2010 Share Posted November 9, 2010 A general rule of thumb for oil pressure is 10 psi per thousand RPM, and 20 psi at 1800 rpm is within that spec.... especially for hot oil at driving speed. What type of oil filter are you using too. That has been known to cause issues with the 4.0L's especially if its a Fram oil filter. Some filters just restrict pressure too much. Get a WIX or K+N, or just something other than what youve been using and see what happens. Link to comment Share on other sites More sharing options...
carnuck Posted November 10, 2010 Share Posted November 10, 2010 Could be you have an orange oil filter? I routinely hear of low oil pressure due to them collapsing internally. Link to comment Share on other sites More sharing options...
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