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Old 12-28-2010, 04:14 PM
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compression problem w/ Ford

this is not a hot rod question , but i thought it would be easy for you guys. Please dont be insulted. I have a 1996 f350 with a 351w. It over heated because of a freeze plug and i sent it to a engine lab for rebuild. I had to tow the truck home from the shop , never run right. Smells rich. Checked compression after getting truck home and all cylinders had around 150 , but run rough. Took it to two ford dealers with no help. Maybe 75 miles on engine and tried another compression test and none fo the cylinders would hold compression long enough to read it. Would pump up to 150 but leak down fast. Pulled off plugs and saw cylinder 8 made no differance. Had spark to plug but plug and was white and all others were brown. Did a home made leak test to cylinder 8 with piston at top and 80 lbs. of pressure. Air came out throttle body. what is wroung with this rebuilt engine

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Old 12-28-2010, 08:08 PM
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I'll bu mp u back tttop
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Old 12-28-2010, 08:20 PM
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Old 12-28-2010, 10:02 PM
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Quote:
Originally Posted by mrtyc
this is not a hot rod question , but i thought it would be easy for you guys. Please dont be insulted. I have a 1996 f350 with a 351w. It over heated because of a freeze plug and i sent it to a engine lab for rebuild. I had to tow the truck home from the shop , never run right. Smells rich. Checked compression after getting truck home and all cylinders had around 150 , but run rough. Took it to two ford dealers with no help. Maybe 75 miles on engine and tried another compression test and none fo the cylinders would hold compression long enough to read it. Would pump up to 150 but leak down fast. Pulled off plugs and saw cylinder 8 made no differance. Had spark to plug but plug and was white and all others were brown. Did a home made leak test to cylinder 8 with piston at top and 80 lbs. of pressure. Air came out throttle body. what is wroung with this rebuilt engine
Intake valve not closing would be a good guess
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Old 12-29-2010, 01:17 AM
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Your first problem with this thread is the title, I have edited this for you, maybe now we can get some answers. Please Help is so very unclear most folks won't take the time to read it. Good luck, let's hope for an answer. Dan
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Old 12-29-2010, 04:54 PM
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Quote:
tried another compression test and none fo the cylinders would hold compression long enough to read it.
Ayuh,... For starters,.. Compression Testers hold the pressure, Not the cylinders...
Quote:
Pulled off plugs and saw cylinder 8 made no differance. Had spark to plug but plug and was white and all others were brown.
ALL of the sparkplugs should be pulled Before the compression test, Not after...

A Very Clean, new looking plug can be an indication of Water in the cylinder,...
It steam cleans the plug...

If you're homemade hook-up is pushing air out the intake, the intake Valve is leaking...
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Old 12-29-2010, 04:58 PM
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I agree with an intake valve leak.
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Old 12-29-2010, 05:17 PM
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351w

pull allthe plugs,and both vave covers.remove dist cap,turn over by hand direction of rotation when rotor points to #1 check the rockers,use a feeler gauge and a long screwdriver,pry the rockers away from valves,you should get clearanc.you are colapsing the lifter.do both valves. if they are ok go to next in fireing order(351w should be #3) when roter is pointing where #3 plug wire would be if cap wher on.check all cylenders.the rebuilder could have refaced the seats and valves and not taken any off valve tips,as rockers are not adjustable this could be the problem.or fireing order not corect.this would show if during previous checks rotor pointed to #5 next after 1, this is a easey check for bothe possible isues.if you cant get valve clearanc at cylender you can back off rocker nut,but be aware these are a temp check as nuts must stay bottemed.some have corected by useing self lockers frome older 260 289 good luck
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Old 12-30-2010, 11:18 AM
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compression test

if the gauge holds compression and not the cylinder , I must have two testers that are bad. When i first tested the compression and it leaked down I bought a new tester from sears and it did the same thing , But if that is how they work I will exchange my tester.Not that i don't believe you but the test was the same with a old and new compression tester.Are there any exceptions to what you say?
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Old 12-30-2010, 11:25 AM
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My Sears bought compression gauge holds the pressure until you release it. But it is old enough that it was bought when the name "Sears" actually meant it had some quality.
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Old 12-30-2010, 11:59 AM
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bondo stated maybe a water leak , how would i check for this. The cylinder 8 plug looks brand new and has no smell of gas. How can i prove that the fuel injector is not working.I did test for voltage and a ohm test. Plus it worked before the rebuild. Not that it means anything. I took the truck to 2 different ford dealers.Three hundred dollars later it is still not running correctly.At first it seemed to run better after it warmed up and then all of a sudden it started running bad all the time. A Strong fuel smell. I thought it was an electrical issue but their are no codes and the truck runs the same without the # 8 plug wire on. Yes there is good spark to the plug.
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Old 12-30-2010, 12:27 PM
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A quick and dirty way to check fuel injectors is this. Put your finger on the body of the injector, and feel the vibration. Do that to another injector. They should feel the same.
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Old 12-30-2010, 12:42 PM
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thanks , i all ready did that. The plug just looks so clean and there is no smell of gas. Can the intake valve not closing do this , or does there need to be a water leak also. Thanks in advance for your responce.
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Old 12-30-2010, 12:50 PM
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Quote:
Originally Posted by mrtyc
if the gauge holds compression and not the cylinder , I must have two testers that are bad. When i first tested the compression and it leaked down I bought a new tester from sears and it did the same thing , But if that is how they work I will exchange my tester.Not that i don't believe you but the test was the same with a old and new compression tester.Are there any exceptions to what you say?
You must have a bad one. I have never seen one with out a check valve. Even the 35 year old cheap one I have has a check valve
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