Compression Readings
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Tuned
Joined: Feb 2013
Posts: 258
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From: Peterstown
Compression Readings
Is there a thread on compression readings? I have a 1995 F150, 5.0L. I installed a new rebuilt engine in it last Fall. A lot of you may remember. I got a lot of help from ya'll. Now I have a pretty serious problem. First of all, through trial and error, when I first put the engine in the truck, I found out that the block was older than 1994. So it has the older firing order. Now, back to my current problem. It had been idling erradically, the last couple of days. So, I pulled spark plug wires, with engine running. Number 1 and number 2 are not firing. I then removed the fuel pump relay, pulled the spark plugs and checked for spark. Both plugs are firing. Then I checked compression on just those 2 cylinders. Both cylinders got up to 35 psi, dry. Tested wet, they both went up to 45 psi. Looking for someone that may know the cause of this condition, or can point me in the direction to look it up for myself.
Senior User
Joined: May 2015
Posts: 466
Likes: 2
From: Dallas, TX
Well you need to run the compression test on all cylinders to get your base line....
If I remember right the PSI can vary depending on what position the throttle body or something? So test all cylinders and compare. If 1 and 2 test at 35 dry and 45 wet then the rest should too as long as nothing else has changed.
Also I am not sure but it sounds like you went from a roller motor to a non-roller motor so I am not sure if it will ever run right since the roller motor had more stroke or something then the non.....
Again I may just be giving a bunch of misinformation. Someone will come along and help.
Good luck.....
If I remember right the PSI can vary depending on what position the throttle body or something? So test all cylinders and compare. If 1 and 2 test at 35 dry and 45 wet then the rest should too as long as nothing else has changed.
Also I am not sure but it sounds like you went from a roller motor to a non-roller motor so I am not sure if it will ever run right since the roller motor had more stroke or something then the non.....
Again I may just be giving a bunch of misinformation. Someone will come along and help.
Good luck.....
Senior User
Joined: Aug 2006
Posts: 377
Likes: 6
Well you need to run the compression test on all cylinders to get your base line....
If I remember right the PSI can vary depending on what position the throttle body or something? So test all cylinders and compare. If 1 and 2 test at 35 dry and 45 wet then the rest should too as long as nothing else has changed.
Also I am not sure but it sounds like you went from a roller motor to a non-roller motor so I am not sure if it will ever run right since the roller motor had more stroke or something then the non.....
Again I may just be giving a bunch of misinformation. Someone will come along and help.
Good luck.....
If I remember right the PSI can vary depending on what position the throttle body or something? So test all cylinders and compare. If 1 and 2 test at 35 dry and 45 wet then the rest should too as long as nothing else has changed.
Also I am not sure but it sounds like you went from a roller motor to a non-roller motor so I am not sure if it will ever run right since the roller motor had more stroke or something then the non.....
Again I may just be giving a bunch of misinformation. Someone will come along and help.
Good luck.....
Anyways, if you only have 35-45 psi in 2 cylinders, and the rest are normal (120ish generally, the actual number isn't too exact, I would definitely test the rest. If nothing else it'll tell you if your gauge is working properly or not) ), then you have some form of hard parts problem. Since it's 2 cylinders right next to each other, there is a good chance it is either a bad head gasket, or a cracked head/block between those 2.
Also, if you swapped your 1995 that was originally the HO firing order out to the old firing order, your fuel injectors no longer fire in the correct order. I'm not real good with these trucks, but AFAIK if you have a MAF then you'll run HO and sequential injectors (the injectors fire 1 at a time and in the same order as the firing order) , if you do not have a MAF you'd have the old firing order and bank fire (4 injectors at a time).
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Tuned
Joined: Feb 2013
Posts: 258
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From: Peterstown
My truck does have the MAF system. I purchased this engine from a engine rebuilding machine shop, up in Maine. I ordered a 1995 engine, which is what mine was. I have no idea, what actual year this engine is, but, I found out through trial and error, when I first installed it, that it had the earlier cam. Because when I connected the spark plug wires in the 95 model year firing order, which was on a label under the hood, it had a bad miss. I found out from the good folks on here, that I had the wrong firing order. So I looked in the book and found out that I had to use the 94 and earlier firing order. The block didn't even have threads to screw my knock sensor in. The hole was there. I just had to tap it. Now, I have completed a compression test, both wet and dry, and I have also completed a leakdown test. Number 1 cyl. was 43 PSI, Number 2 cyl. was 45 PSI. 3- 147, 4-147, 5-143, 6-144, 7-137, 8-146. On the wet test, 1-45, 2-49, 3-156, 4-154, 5-150, 6-151, 7-141, 8-155. The leakdown test revealed head gasket leak between 1 and 2. And either 1 and 2, or 1 or 2, has air leaking into the crankcase, and 5 and 7, even thought they have good compression, has air leaking into the crankcase.
Cargo Master
Joined: Mar 2010
Posts: 3,339
Likes: 293
From: Laramie, WY
Its worth a shot. If they warranty work long enough or give a partial refund he'd be wise to try. I think I'd be finding a new machine shop for any future work though. Unless they really take care of the broken 5.0L.
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Tuned
Joined: Feb 2013
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From: Peterstown
I bought it about a year ago. It supposedly has a 4 year/40,000 mile warranty. It currently has 10,497 miles on the engine. I bought it as a long block, and all I wanted to do to it was diagnostic testing. I contacted the man last evening, and told him of the problem and the test results. He asked me if I had pulled the head to look at it, and I told him no. I didn't want to do anything until I contacted him. So, now, he has asked me to pull the head and look at it. And I will probably take it to my local machine shop to have it checked. What is weird about the whole thing, is that the blown head gasket is so bad, that, when I put the cylinder (1 or 2, either one) on TDC and do the leak down test, the air leaks by the gasket (or crack) and leaks through the open valve in the adjacent cylinder. Also, on 3 or 4 of the cylinders (1 or 2 or possibly both, and 5 and 7), on the leak down test, I hear air leaking through the crankcase. Yet, on the compression test, 5 and 7 test good. And I left the compression on the gauge for a 2 or 3 minutes, and it did not leak off. Quite puzzling!
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Logistics Pro
Joined: Aug 2010
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From: Chillicothe
I contacted the man last evening, and told him of the problem and the test results. He asked me if I had pulled the head to look at it, and I told him no. I didn't want to do anything until I contacted him. So, now, he has asked me to pull the head and look at it. And I will probably take it to my local machine shop to have it checked.
Tuned
Joined: Sep 2005
Posts: 437
Likes: 4
From: SE Missouri
I agree I wouldn't touch that thing without something in writing with his company name at the top of it. Besides that I would take it to him to see for himself and also bitch about it being the wrong cam cause your injectors and spark plugs are not working together.
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