Engine Compression levels?
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New User
Joined: Dec 2006
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From: Round Rock, TX
Engine Compression levels?
Greetings, It has been a very long time since I have posted and from what I have been reading many others are having the same problems I am right now with my truck. 1991 F150 302 auto, 165K on first engine trans and I have recently replaced both due to a knocking rod and slipping A4OD(?) auto trans.
Here are my issues, After break in I have had very low power and almost no power at higher speeds. Idle has slowly gotten worse, my check engine light has gone from flashing to solid on and my gas mileage had dropped dramatically.
My friend and I pulled codes and they red like a who's who of EGR, MAP, IAC and even some 40, 20 and 30 codes popped up. Slowly I have found a leaking vaccume lnie from the EGR Solenoid to the EGR and fixed it. ( light went back to flashing) Cleaned the EGR and tested it to hold vaccum. Replaced the Map sensor as it was showing to be reading out of range. Changed out the tem sensor as it was out of range also? Pulled and cleaned the throttle body and the IAC. Put it all back together replaced the plugs wires, cap and Rotor again and where I now have more power I am getting horrible gas mileage and Check engine codes are flashing.
So today ( back to my title ) my frinds brother( a 20+ year mechanic) said to check compression in the engine.
1) 165
2) 175
3) 150
4) 180
5) 190
6) 175
7) 175
8) 190
I think we have a problem with #3. Put a few CC'S of oil in it and tried it again, 175... Bad Rings or rings have not set? Going on 5500 miles since new engine. I would say it is broken in quite well... Is this the source of my problem? Or just one of my many probems?
Other notes:
Cat temp: 404 north of cat 540 south of cat and cat ran a bout 600+ Deg.
Replaced intake plenum gasket as we thought we had a leak in it and it looked like the #2 and #6( I think) did have a small alignment issue on the gasket.
I pulled the fuel pressure regulator and replaced it: Pressure drops off pretty quickly once the engien shuts off, Is that bad?
Timing was off a bit at one time but we have set it twice since inital install one time was to replace the module on the dist. and a second today after we did more work, just to double check ourselves again.
Sorry for so many questons, That is what happens when you sit back and wait in the wings. Please ask, suggest and anyone tell me what I may have missed...
thanks,
Thomas
Here are my issues, After break in I have had very low power and almost no power at higher speeds. Idle has slowly gotten worse, my check engine light has gone from flashing to solid on and my gas mileage had dropped dramatically.
My friend and I pulled codes and they red like a who's who of EGR, MAP, IAC and even some 40, 20 and 30 codes popped up. Slowly I have found a leaking vaccume lnie from the EGR Solenoid to the EGR and fixed it. ( light went back to flashing) Cleaned the EGR and tested it to hold vaccum. Replaced the Map sensor as it was showing to be reading out of range. Changed out the tem sensor as it was out of range also? Pulled and cleaned the throttle body and the IAC. Put it all back together replaced the plugs wires, cap and Rotor again and where I now have more power I am getting horrible gas mileage and Check engine codes are flashing.
So today ( back to my title ) my frinds brother( a 20+ year mechanic) said to check compression in the engine.
1) 165
2) 175
3) 150
4) 180
5) 190
6) 175
7) 175
8) 190
I think we have a problem with #3. Put a few CC'S of oil in it and tried it again, 175... Bad Rings or rings have not set? Going on 5500 miles since new engine. I would say it is broken in quite well... Is this the source of my problem? Or just one of my many probems?
Other notes:
Cat temp: 404 north of cat 540 south of cat and cat ran a bout 600+ Deg.
Replaced intake plenum gasket as we thought we had a leak in it and it looked like the #2 and #6( I think) did have a small alignment issue on the gasket.
I pulled the fuel pressure regulator and replaced it: Pressure drops off pretty quickly once the engien shuts off, Is that bad?
Timing was off a bit at one time but we have set it twice since inital install one time was to replace the module on the dist. and a second today after we did more work, just to double check ourselves again.
Sorry for so many questons, That is what happens when you sit back and wait in the wings. Please ask, suggest and anyone tell me what I may have missed...
thanks,
Thomas
Junior User
Joined: Sep 2007
Posts: 57
Likes: 0
How did you do the compression check?
I once put a truck up for sale and two guys that came to look at it pulled one plug at a time and started the engine and let the truck run (on 5 cylinders).
The way my auto shop teacher (and horsepower TV) taught to do it is to pull ALL plugs, disconnect the ignition coil, hold the throttle open (foot to the floor) when you are cranking, and make sure the battery is fully charged.
If the starter is not cranking the same speed on every cylinder test, or the throttle is not open (forgot to put foot on the gas pedal) for one cylinder test, you could get a false reading.
Also do it with a warm engine (ALMOST hot enough to burn yourself when pulling plugs), then the rings should be oiled. As long as all cylinders are within 20% of each other you are O.K.
It sounds like you have tried to clean or replace almost every sensor or valve; but two of them you didn't mention are the O2 sensor (if it is bad your computer will not know if it is rich or lean, thus making it run rich giving you bad gas mileage), and the Throttle Positioning Sensor or TPS (if the computer doesn't know what position the throttle plates are in, it can not know how much fuel to give, then it has to rely on the other sensors, thus giving you poor perfomance).
I once put a truck up for sale and two guys that came to look at it pulled one plug at a time and started the engine and let the truck run (on 5 cylinders).
The way my auto shop teacher (and horsepower TV) taught to do it is to pull ALL plugs, disconnect the ignition coil, hold the throttle open (foot to the floor) when you are cranking, and make sure the battery is fully charged.
If the starter is not cranking the same speed on every cylinder test, or the throttle is not open (forgot to put foot on the gas pedal) for one cylinder test, you could get a false reading.
Also do it with a warm engine (ALMOST hot enough to burn yourself when pulling plugs), then the rings should be oiled. As long as all cylinders are within 20% of each other you are O.K.
It sounds like you have tried to clean or replace almost every sensor or valve; but two of them you didn't mention are the O2 sensor (if it is bad your computer will not know if it is rich or lean, thus making it run rich giving you bad gas mileage), and the Throttle Positioning Sensor or TPS (if the computer doesn't know what position the throttle plates are in, it can not know how much fuel to give, then it has to rely on the other sensors, thus giving you poor perfomance).
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New User
Joined: Dec 2006
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From: Round Rock, TX
Originally Posted by cowmilker
How did you do the compression check?
I once put a truck up for sale and two guys that came to look at it pulled one plug at a time and started the engine and let the truck run (on 5 cylinders).
The way my auto shop teacher (and horsepower TV) taught to do it is to pull ALL plugs, disconnect the ignition coil, hold the throttle open (foot to the floor) when you are cranking, and make sure the battery is fully charged.
If the starter is not cranking the same speed on every cylinder test, or the throttle is not open (forgot to put foot on the gas pedal) for one cylinder test, you could get a false reading.
Also do it with a warm engine (ALMOST hot enough to burn yourself when pulling plugs), then the rings should be oiled. As long as all cylinders are within 20% of each other you are O.K.
It sounds like you have tried to clean or replace almost every sensor or valve; but two of them you didn't mention are the O2 sensor (if it is bad your computer will not know if it is rich or lean, thus making it run rich giving you bad gas mileage), and the Throttle Positioning Sensor or TPS (if the computer doesn't know what position the throttle plates are in, it can not know how much fuel to give, then it has to rely on the other sensors, thus giving you poor perfomance).
I once put a truck up for sale and two guys that came to look at it pulled one plug at a time and started the engine and let the truck run (on 5 cylinders).
The way my auto shop teacher (and horsepower TV) taught to do it is to pull ALL plugs, disconnect the ignition coil, hold the throttle open (foot to the floor) when you are cranking, and make sure the battery is fully charged.
If the starter is not cranking the same speed on every cylinder test, or the throttle is not open (forgot to put foot on the gas pedal) for one cylinder test, you could get a false reading.
Also do it with a warm engine (ALMOST hot enough to burn yourself when pulling plugs), then the rings should be oiled. As long as all cylinders are within 20% of each other you are O.K.
It sounds like you have tried to clean or replace almost every sensor or valve; but two of them you didn't mention are the O2 sensor (if it is bad your computer will not know if it is rich or lean, thus making it run rich giving you bad gas mileage), and the Throttle Positioning Sensor or TPS (if the computer doesn't know what position the throttle plates are in, it can not know how much fuel to give, then it has to rely on the other sensors, thus giving you poor perfomance).
The O2 sensor was replaced before my engine was wasted so it could be bad and I had the TPS changed years ago dont know about that one.... BUt right now I feel like I am throwing money at it and time. I can change both of them but never did the TPS myself is there any thing I need to do when setting that up? Calibration?
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Joined: Sep 2007
Posts: 57
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The only TPS I've ever changed was on an '87 Ranger (2.9 v-6), and it was just as simple as taking out the 2 mounting screws, unpluging the old, pluging in the new and replacing the 2 mounting screws.
I know sometimes it feels like you are just throwing money at a problem, but in my opinion it's a LOT better than making a $400+ a month truck payment, for a new one.
I know sometimes it feels like you are just throwing money at a problem, but in my opinion it's a LOT better than making a $400+ a month truck payment, for a new one.
