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Fresh Engine. Low Compression

  • Thread starter Thread starter a91what
  • Start date Start date Apr 14, 2014
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GroverDill

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#21
  • Apr 15, 2014
  • #21
I have never seen an EFI car do an actual "wash down" Always thought that was a carb thing from leaking primaries and such.
 

a91what

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#22
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noid light showed alot of activity in the fuel injector circuit. how much should one injector pulse during normal cranking? will a bad pip cause this?
 

mikestang63

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#23
  • Apr 15, 2014
  • #23
Gotta say I've not heard of washing down the cylinders on an EFI setup. You'd need to crank that sucker over 1000's of times with the injectors firing. Cranking with the starter is maybe a few hundred rpms. Now on a carb yeah maybe. Your oil would smell of gas and plugs fouled.

Sounds more like either bent or wrong length pushrods, or the valves not adjusted properly. Have you squirted some oil in the spark plug holes and rerun the compression test? That may do the trick.
 

a91what

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#24
  • Apr 15, 2014
  • #24
i dont mean to be a dick but........ the oil reaked of fuel. i pulled the dip stick and could smell fuel.
I agree though i have never heard of it happening myself. now i did try to get her to start for the better part of an afternoon pulling my hair out.... thought maybe it was a timing issue, the dizzy is stock from an 87. the plugs were fouled out. blew her dry with compressed air and new plugs newer dizzy redropped dizzy. shoulda fired right up. then the compression test. i have checked the push rods and rockers that was my first thought. the heads have all new parts.
thanks for the advice i will try the oil and see if it fires.
 

DesertDawg

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#25
  • Apr 15, 2014
  • #25
90lxcoupe said:
Is your name Richard by chance?
Click to expand...
Ahh, ya doesn’t has to call me Johnson! You can call me Ray, or you can call me Jay, or you can call me Johnny or you can call me Sonny, or you can call me RayJay, or you can call me RJ… but ya doesn’t hafta call me Johnson
 

DesertDawg

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#26
  • Apr 15, 2014
  • #26
a91what said:
and see if it fires
Click to expand...
up with a mighty thirty pounds of compression in each cylinder! I just know that shortly there is going to be one of those Doh Moments
 

89oem

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#27
  • Apr 16, 2014
  • #27
heres a thought, a long time ago in high school i helped a friend rebuild, we were excited to get the engine reassembled... went well... never noticed they gave us the wrong rings for a non bored 302.... similar wtf.... just a thought....
 
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a91what

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#28
  • Apr 16, 2014
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That is possible that the wrong rings, i bought the pistons as a kit and used the rings supplied.
DesertDawg said:
up with a mighty thirty pounds of compression in each cylinder! I just know that shortly there is going to be one of those Doh Moments
Click to expand...
When you put oil or trans fluid on top of the ring it acts as a seal. look up wet compression testing this is not some far fetched practice. it is the correct way to test for bad rings, other than a leak down of course. i am going to use it as a way to get enough compression to fire the engine and retry the break in. if it does not work i will then rebuild again.
 

FoxMustangLvr

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#29
  • Apr 16, 2014
  • #29
a91what said:
That is possible that the wrong rings, i bought the pistons as a kit and used the rings supplied.

When you put oil or trans fluid on top of the ring it acts as a seal. look up wet compression testing this is not some far fetched practice. it is the correct way to test for bad rings, other than a leak down of course. i am going to use it as a way to get enough compression to fire the engine and retry the break in. if it does not work i will then rebuild again.
Click to expand...

Hopefully they gave you the correct kit for a 306 (4.030") and not a 302 kit. It'd be difficult for a bad hone to get the same low compression in all 8 cylinders. Seems like a problem with the rings IMO.

You didn't use synthetic oil for break in right? Is it possible your injectors are stuck open? Have you checked to see if you have good spark?
 

90lxcoupe

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#30
  • Apr 16, 2014
  • #30
Did you check piston to valve clearance during the build?
 

FoxMustangLvr

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#31
  • Apr 16, 2014
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I'd like to know more about this 306. Does it have H/C/I? Stock? What injector size and MAF?
 

a91what

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#32
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  • #32
i checked ptv with stock pistons it was a no go with the new heads so i broke it down and balanced the assembly with new sealed power pistons hyperutectic .030 over... heafs are ported gt40s with a new valve job and 2.02 valves e303 cam and 1.72 rr. port matched cobra lower and upper ported for 75mm tb. 32 lb injectors feom cyote motor lightning maf and sct tune. i have done the injector leak down test. they passed. during build i shimmed the rockers. i even did the leakdown test with the rockers off the head.
 

84Ttop

They make new pistons every day, so why worry?
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#33
  • Apr 16, 2014
  • #33
90lxcoupe said:
How exactly did you do that?
Click to expand...
pour a cap full in each cylinder and crank it over with all the plugs out... The stuff works.. How exactly, now thats the mystery part!
 

FoxMustangLvr

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#34
  • Apr 16, 2014
  • #34
a91what said:
i checked ptv with stock pistons it was a no go with the new heads so i broke it down and balanced the assembly with new sealed power pistons hyperutectic .030 over... heafs are ported gt40s with a new valve job and 2.02 valves e303 cam and 1.72 rr. port matched cobra lower and upper ported for 75mm tb. 32 lb injectors feom cyote motor lightning maf and sct tune. i have done the injector leak down test. they passed. during build i shimmed the rockers. i even did the leakdown test with the rockers off the head.
Click to expand...

32# injectors are pretty big for your combo but not so big it'd flood it so long as the tune is good. What size fuel pump? Are you customizing the tune yourself? Seems that maybe the injectors are dumping too much fuel possibly and your not getting enough spark. What duty cycle are the injectors set for?
 
Last edited: Apr 16, 2014

a91what

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#35
  • Apr 16, 2014
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fuel pump stock. have new 155 waiting. the tune was burned by bama tunes worked fine before i tor it down. i only had e7 heads and an untouched cobra intake previously. idk what the duty cycle is cant be much for now. hopefully if all goes well a supercharger in the future.
 

90lxcoupe

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#36
  • Apr 16, 2014
  • #36
a91what said:
i checked ptv with stock pistons it was a no go with the new heads so i broke it down and balanced the assembly with new sealed power pistons hyperutectic .030 over... heafs are ported gt40s with a new valve job and 2.02 valves e303 cam and 1.72 rr. port matched cobra lower and upper ported for 75mm tb. 32 lb injectors feom cyote motor lightning maf and sct tune. i have done the injector leak down test. they passed. during build i shimmed the rockers. i even did the leakdown test with the rockers off the head.
Click to expand...

You really lost me here... So did you check PTV with the pistons that are currently in the motor?
 

a91what

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#37
  • Apr 16, 2014
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yes. same pistons we used in our 450hp nitrous car with a 620 lift cam.
 

a91what

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#38
  • Apr 16, 2014
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thanks for the help guys but its gonna come apart......... there is so much air coming fromthe crank case im sure the damage is there.
 

a91what

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#39
  • Apr 16, 2014
  • #39
i will keep you posted on what the cause was.
 

FoxMustangLvr

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#40
  • Apr 16, 2014
  • #40
a91what said:
thanks for the help guys but its gonna come apart......... there is so much air coming fromthe crank case im sure the damage is there.
Click to expand...

Sorry to hear that, good luck and post some pictures along the way!
 
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