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davehop, Ford Technician
Category: Ford
Satisfied Customers: 1395
Experience:  Fully certified in all phases of automotive repair as recognized and certified by Ford Motor Company
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i have a 1997 f150 4.2 liter V-6 with low compression in #1

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i have a 1997 f150 4.2 liter V-6 with low compression in #1 and #3 cylinder and black oil build up in the intake spark plugs are a mess except for #1 its normal compression is 185 on #1 and 175 on #3 the rest are around 220
Hello and welcome to JA, I wouldn't exactly consider 175 psi low compression, but compared to the others, it is a tad off, does it missfire on those 2 cylinders? Was there any reason you were checking the compression?
Customer: replied 8 years ago.
engine would only run up to 40 mph major power loss, did smoke (blue)
used oil last 3 weeks of running, odd growling noise when winmilling engine, heads rebuilt 6 months ago alot of carbon on valves now, heads are off intake full of black oil gunk also driver side intake butterfly(not sure what it is for) does not move. oil pressure low but not enough to over heat the engine. have not winmilled the engine with the heads off to see if noise is still here. no oil in cooling system or coolent in oil,not sure why oil gunk gets into intake that only has air going throught it
The oil gunk is actually carbon, a byproduct of the fuel air mixture, that is being sucked back into the engine by way of the egr valve. Before we continue, can you tell me what winmilled means?
Customer: replied 8 years ago.
turnning over of the engine without spark plugs to check compression one at a time
ok, never heard that one before. the butterfly is the intake runner, which is used for fine tuning the air/fuel mixture at higher rpms, when they get stuck, they will cause the engine to run lean on the bank that is stuck, which will accelerate the build up of carbon, and cause the excessive gunk build up. this will cause a low or no power condition, inspect the actuator at the rear of the intake manifold and see if the rods from the actuator to the butterfly flappers are connected and not seized.
Customer: replied 8 years ago.
is the compression to low in #1 and #3 compaired to the rest to just clean and replace gasgets fix intake runner and run the engine should i replace oil pump or should i rip down the rest of the motor? i was allways told that to much pressure difference between the high and low cylinders wasnt good
at this point I would clean it up, make sure the runners are free and working properly, and reassemble.
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Customer: replied 8 years ago.
but what about the odd growling noise its not the starter
when does this noise happen? Only when checking compression?
Customer: replied 8 years ago.
while i am turning over the motor at any time one other thing i found the dipstick out of its tube about an inch after the last time it was running
you may have some blow by, does smoke come out of the breather or pcv when you last had it running?
Customer: replied 8 years ago.
then you have blow by, which means the rings are shot.
Customer: replied 8 years ago.
ok well i will tear the motor down check all parts and specks and go from there thanks for your help and if i run into anymore problems i will be back
i will be here