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Years of working on my 87 Renix Wagoneer XJ and nursing it along as I approach 300,000 miles on the beast has taught me a lot. Most of the history is in my old threads here already. Had it for about 8 years now. Put about 60,000 miles on it.
Today's update is about old cooling system problems, low power during acceleration, spark plugs and low oil pressure, etc.
My jeep had many problems, not just one of two. I fixed all the cooling problems, transmission problems, electronic and wiring and sensor problems and so on. I fixed many of the low power and low oil pressure problems. I replaced the valve stem seals and got the oil valve seal leak and #1 and #2 spark plug fouling problem under manageable control with NGK copper core ... spark plugs on those two cylinders only. I was having to change or clean plugs every 200 miles before the seals and every 500-600 after new seals. The NGK spark plugs have added to time interval needed to clean the plugs.
Now for the interesting part. I recently had the usual low oil pressure during the summer days with the AC on, getting down to about 21 PSI at idle.
I had the oil changed only, kept the old filter. And now the oil pressure is holding about 29-31 psi minimum and 7-8 psi higher when cold.
I also have not cleaned the spark plugs in 500-1000 miles. The oil had 3000 to 6000 miles on it (not sure exactly) and was about 2 years old (I was ill and not driving for nearly a year last year).
So here is my conclusion based on 8 years of alternating low oil pressure with this rig.
As the spark plugs in the 2 weak cylinders (about 115 to 125 psi compression) with the worn valve guides, Cyl #1 ans #2 slowlu leak oil and foul the plugs, the number of missfires increases (but is not noticeable to me). That leads to unburned fuel and oil dilution and thinning of the oil!!!! Add to that oil break down over time, and it explains why just changing the oil brought the running oil pressure up about 8 psi!!!!
I have already been planning to rebuild the head when I get help and time this year.
But the story here is that a slow long term fouling of the plugs over time from slow valve stem oil leaks can foul the plugs and cause oil dilution from unburned fuel thinning out the oil, over time and lead to low oil pressure!!! Misfires of any kind, from any cause can do this!!!!
According to my research the NGK spark plugs for the 4.0 are wee-bit hotter plug than the platinum plugs I have been using....and takes a lot longer for them to foul. I have an older thread here about the spark plugs I was testing for this problem, that I put up here about 2- to 2.5 years ago. I bought about 7 different plugs to see if I could avoid the head job for a while by running those cylinders a little hotter since the compression is a little low on them. I also run Restore in this engine. Great stuff!!!!
Today's update is about old cooling system problems, low power during acceleration, spark plugs and low oil pressure, etc.
My jeep had many problems, not just one of two. I fixed all the cooling problems, transmission problems, electronic and wiring and sensor problems and so on. I fixed many of the low power and low oil pressure problems. I replaced the valve stem seals and got the oil valve seal leak and #1 and #2 spark plug fouling problem under manageable control with NGK copper core ... spark plugs on those two cylinders only. I was having to change or clean plugs every 200 miles before the seals and every 500-600 after new seals. The NGK spark plugs have added to time interval needed to clean the plugs.
Now for the interesting part. I recently had the usual low oil pressure during the summer days with the AC on, getting down to about 21 PSI at idle.
I had the oil changed only, kept the old filter. And now the oil pressure is holding about 29-31 psi minimum and 7-8 psi higher when cold.
I also have not cleaned the spark plugs in 500-1000 miles. The oil had 3000 to 6000 miles on it (not sure exactly) and was about 2 years old (I was ill and not driving for nearly a year last year).
So here is my conclusion based on 8 years of alternating low oil pressure with this rig.
As the spark plugs in the 2 weak cylinders (about 115 to 125 psi compression) with the worn valve guides, Cyl #1 ans #2 slowlu leak oil and foul the plugs, the number of missfires increases (but is not noticeable to me). That leads to unburned fuel and oil dilution and thinning of the oil!!!! Add to that oil break down over time, and it explains why just changing the oil brought the running oil pressure up about 8 psi!!!!
I have already been planning to rebuild the head when I get help and time this year.
But the story here is that a slow long term fouling of the plugs over time from slow valve stem oil leaks can foul the plugs and cause oil dilution from unburned fuel thinning out the oil, over time and lead to low oil pressure!!! Misfires of any kind, from any cause can do this!!!!
According to my research the NGK spark plugs for the 4.0 are wee-bit hotter plug than the platinum plugs I have been using....and takes a lot longer for them to foul. I have an older thread here about the spark plugs I was testing for this problem, that I put up here about 2- to 2.5 years ago. I bought about 7 different plugs to see if I could avoid the head job for a while by running those cylinders a little hotter since the compression is a little low on them. I also run Restore in this engine. Great stuff!!!!
EcoMike..!