Help 4.9L/300 compression test results.
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Tuned
Joined: Feb 2004
Posts: 339
Likes: 3
From: Saudia Arabia
Help 4.9L/300 compression test results.
Hi all:
This is the first time in my 13 years of driving my 66 F100 with the 4.9/300 erratic or rough idle. At higher speed seems OK. All wiring and plugs, coil, fuel system works fine. The rough idle does sound strange not like when the engine misses from a fouled plug. My exhaust is cracked and leaks with sound.
So I figure my engine is not healthy, I done my compression test this morning and got the following results:
#1 - 130 PSI
#2 - 135 PSI
#3 - 130 PSI
#4 - 135 PSI
#5 - 130 PSI
#6 - 135 PSI
After adding a table spoon of heavy oil ( gear oil grade 90) the results:
#1 - 165 PSI
#2 - 165 PSI
#3 - 145 PSI
#4 - 160 PSI
#5 - 160 PSI
#6 - 150 PSI
What does that indicate, any relation to the rough idle?.
I am attaching some photos as it might help. Thanks for your sharing.
This is the first time in my 13 years of driving my 66 F100 with the 4.9/300 erratic or rough idle. At higher speed seems OK. All wiring and plugs, coil, fuel system works fine. The rough idle does sound strange not like when the engine misses from a fouled plug. My exhaust is cracked and leaks with sound.
So I figure my engine is not healthy, I done my compression test this morning and got the following results:
#1 - 130 PSI
#2 - 135 PSI
#3 - 130 PSI
#4 - 135 PSI
#5 - 130 PSI
#6 - 135 PSI
After adding a table spoon of heavy oil ( gear oil grade 90) the results:
#1 - 165 PSI
#2 - 165 PSI
#3 - 145 PSI
#4 - 160 PSI
#5 - 160 PSI
#6 - 150 PSI
What does that indicate, any relation to the rough idle?.
I am attaching some photos as it might help. Thanks for your sharing.
Last edited by ftrk66; Dec 6, 2016 at 03:10 PM. Reason: grammer
Fleet Mechanic
Joined: Nov 2002
Posts: 1,643
Likes: 69
That engine looks good for 13 years of driving on it. It is possible that the cracked exhaust manifold is contributing to the misfire. On my V8 motorhome I'v cracked two manifolds and both times the engine had an erratic idle, probably due to sucking cold air back into the cylinder through the crack in the overlap cycle. I would clean up the head and do a valve job and re-gasket it. You will likely find coked up intake valves. Its too bad you did not do a leakdown test on it as that is more definitive than a compression test
Thread Starter
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Tuned
Joined: Feb 2004
Posts: 339
Likes: 3
From: Saudia Arabia
I should have done the troubleshooting before tearing down the engine.
Anyhow I am planning to re ring the pistons, put a new main bearing rear seal and re install the head and do the leak down test. Hope it will be OK.
Anyhow I am planning to re ring the pistons, put a new main bearing rear seal and re install the head and do the leak down test. Hope it will be OK.
Fleet Mechanic
Joined: Nov 2002
Posts: 1,643
Likes: 69
Check the piston skirts for cracks - a very common problem on hi-mileage engines. If you find you need new pistons go with the late model hypereutectics.
Reassemble w/ a FelPro #1024 premium head gasket.
Great truck, BTW.
Reassemble w/ a FelPro #1024 premium head gasket.
Great truck, BTW.
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
For those who are following this thread, the name of the OP is Hamid and the truck was originally used at an airport in Saudi Ababia, at which Hamid's father worked. Later, Hamid worked there as well and was able to purchase the truck. I had the pleasure of meeting and having a meal with Hamid and his son when they visited the US about 2 years ago. Hamid attended school here in the states. Please assist him any way you can!
Hamid, The Frenchtown Flyer is a retired Ford Engine Development Engineer. The engine he worked with was the 302 V8, but his understanding of the 300 in vast and he is very successful drag racing with the inline six. Thanks for assisting Hamid, Sir.
Hamid, The Frenchtown Flyer is a retired Ford Engine Development Engineer. The engine he worked with was the 302 V8, but his understanding of the 300 in vast and he is very successful drag racing with the inline six. Thanks for assisting Hamid, Sir.
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Fleet Mechanic
Joined: Nov 2002
Posts: 1,643
Likes: 69
You're welcome. It looks like a nice project and doesn't look all that bad to me considering the sandy, windy operating conditions it must have been exposed to. Getting the right parts over there must not be easy. Good luck with your project.
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