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Engine Compression very low, options

  • Thread starter Thread starter Trebor
  • Start date Start date Jul 20, 2021
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Trebor

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7991LXnSHO said:
You have a closed throttle body in the picture. Was it closed during the compression test?
Click to expand...
Yes closed as in picture
 
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Trebor

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Trebor said:
Yes closed as in picture
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Well. I assume it would have opened? The mechanic turned the car over using a washer on the starter solenoid.
 

7991LXnSHO

wanna catch the space herp
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#23
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If the throttle was closed, the engine could not suck in air to compress, and the numbers will be false lows. The throttle has to be held open somehow or the test is invalid. I hope the mechanic knew better.
 

HemiRick

I'd be looking at jacking under the house
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#24
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no, the engine can suck enough air thru a throttle body that will idle....a leak down test can tell you much more about the condition of the inside of the motor than a comp. test.
 

7991LXnSHO

wanna catch the space herp
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#25
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HemiRick said:
no, the engine can suck enough air thru a throttle body that will idle....a leak down test can tell you much more about the condition of the inside of the motor than a comp. test.
Click to expand...
It also pulls a vacuum at idle. Holding the carb open was a step that came with Dad’s compression gauge. I do not know why that would be different now.
 
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7991LXnSHO

wanna catch the space herp
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#26
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HemiRick said:
no, the engine can suck enough air thru a throttle body that will idle....a leak down test can tell you much more about the condition of the inside of the motor than a comp. test.
Click to expand...
I agree about the leak down test. You can tell where the air is going.

The online steps do not seem to include holding the throttle open anymore. WTH? I guess If the other plugs are out, it is sucking air around the throttle butterfly only for that one cylinder, plus past whatever intake valves are partly open.
 
Last edited: Jul 23, 2021
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General karthief

wonder how much it would cost to ship you a pair
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#27
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Either way can detect the problem aside from valve overlap and ring gap that I think can effect result, remember, he may not know the engine history. If all the cylinders are within what? 15-20% of each other send it, at this point you're looking for possibly zero or very little compression one one or two cylinders, there is also the possibility of the SC pushing air through where under normal conditions would be hardly noticeable but not with the added boost. Then I'd do a leak down test, I'm just spit balling here and in no way claim to know anything about anything. This is the beginning path I would take.
 
Last edited: Jul 23, 2021
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Trebor

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Well. Here is an update. My SC looks like it’s needs a lot of love. Do this look like stock lower intake?
 

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General karthief

wonder how much it would cost to ship you a pair
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#29
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Cobra or explorer lower
 
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Trebor

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General karthief said:
Cobra or explorer lower
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I don’t know. Unfortunately I don’t know anything about the engine. Mechanic said he can probably tell me after it’s cleaned up
 

Mstng93SSP

You have a nice rear end there Dave.
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#31
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Like the General said, it is an explorer or Cobra/GT40 lower. The Cobra, GT40 and explorer all are very similar. Same bolt pattern and you can bolt any upper (Cobra, explorer/gt40) to any lower (Cobra, explorer/gt40). Mix and match wouldn't matter.
 
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Trebor

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Mstng93SSP said:
Like the General said, it is an explorer or Cobra/GT40 lower. The Cobra, GT40 and explorer all are very similar. Same bolt pattern and you can bolt any upper (Cobra, explorer/gt40) to any lower (Cobra, explorer/gt40). Mix and match wouldn't matter.
Click to expand...
Sorry. I misread the statement as a question.
 

Mstng93SSP

You have a nice rear end there Dave.
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#33
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It's O.K. Sometimes @General karthief talks while standing on his head....it's hard to figure out what he is saying. You should see him do it while he is juggling bowling pins.....
 
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Trebor

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#34
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Trebor said:
Sorry. I misread the statement as a question.
Click to expand...
So assuming my SC is shot.
If I don’t care about max HP could I just go for some new heads and get back to driving?
 
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Trebor

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#35
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Trebor said:
So assuming my SC is shot.
If I don’t care about max HP could I just go for some new heads and get back to driving?
Click to expand...
Here is where we are today. Looks decent to me???
 

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