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Old 09-07-2005, 03:12 PM   #51
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Just as I said earlier he can get a new gasket and clean the TB.. I'm sure it could use it...

Right now what has me most concerned is the Low 95psi readings from the compression test... I'm wondering if thats acurate... I would like to see him do the compression test, so we can get a good idea of what shape the valves and piston rings are in... we are looking for better than 100 psi in all 6 cylinders... Say we find a cylinder at 150psi and its the highest reading cylinder, that would mean that the lowest reading cylinder would have to be 105 psi..

I have seen 3800'* with almost 300,000 miles test out with no more than a 5 psi diffrence between all 6 cylinders..

When Vital has more time, I'm sure he will look deeper into the problems... I'm hopeful that it will be a simple problem..

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Old 09-07-2005, 03:19 PM   #52
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I'll clean the throttle body this weekend and report back. I've done that job several times on my old L27 and on the L36. No problems....

Should I clean the sensors too, or just leave them alone? And, if we think the IAC is suspect, is there a test I can do on it?
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Old 09-07-2005, 03:23 PM   #53
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Quote:
Originally Posted by vital49
I'll clean the throttle body this weekend and report back. I've done that job several times on my old L27 and on the L36. No problems....

Should I clean the sensors too, or just leave them alone? And, if we think the IAC is suspect, is there a test I can do on it?
At the very least, using Throttle body and intake cleaner, you will want to spray the tip of the IAC, don't spray the IAC motor, just the tip...

Not sure about the MAF...

Good Luck

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Old 09-08-2005, 09:14 AM   #54
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Wow, I missed a lot - haven't been around in a couple of days - I'm with jr on this one - sorry I didn't chime in earlier, but as I was reading 95 psi today, it made me think... back when I put a new head on the shadow, I was getting a solid 130+ psi per cylinder...

and when I had a bad head on, it ran like CRAP at idle (if you could get it to idle at all), but it ran like a top at higher RPM'*. I wish I had some video of it, because you'd be shocked...

of course, it was far worse than what yours might be right now, as it was pushing a scant 35psi or so on the gage... the valves had carbon all over them (and two were cracked) and I couldn't get decent compression to save my life.

but at top end, it ran like a dream.
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Old 09-08-2005, 09:41 AM   #55
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JR.. can you give us the correct way to compression test.

I've got one and have used it a couple times and believe I may not be testing properly. Although I thought it was put puppy in and start it up.
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Old 09-08-2005, 10:57 AM   #56
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Quote:
Originally Posted by BillBoost37
JR.. can you give us the correct way to compression test.

I've got one and have used it a couple times and believe I may not be testing properly. Although I thought it was put puppy in and start it up.
Not sure it the totally proper way...

I dissconnect the ECM-PCM fuse... Take out all 6 plugs, Block the throttle plate open, insert the threaded fitting( I hate the ones you have to hold in place ) spin the engine over for I think 3 cranks... You should generally see good compression quickly, and it should hold too... If the compression builds slowly with each successive compression stroke then we've got problems... If the compression is low, we could squirt some oil in the cylinder, and try the test again, if the compression improves after the bit of oil, the rings are not happy, if there is no change than the valves are most likely not happy...

For **** and giggles one day we decided to check my friend old 3.0 buick V6... It has 9.0 to 1 compression... I think we got 175-180psi for compression... At the time it had 200,000 miles on it... and all cylinders held pressure...

We have check other engines... Blown head gaskets... Betweeen cylinders... Both reading 30-35 psi.... The other 2 reading 160ish....LOL... Man gotta love a compression gage

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Old 09-08-2005, 10:58 AM   #57
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Quote:
Originally Posted by BillBoost37
Possibly consider an additive that will clean deposits in the oil and then maybe some Lucas stabilizer for a while..maybe some upper cylinder/valve lubricant once it'* cleaned out well.

Has the IAC tube and TB been cleaned...sorry I haven't read teh whole thread.
i highly reccomend giving Auto-RX a try for cleaning an engine or trans, the stuff works miracles

http://auto-rx.com
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Old 09-08-2005, 11:37 AM   #58
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Thanks for the clarification on how to do the compression check, Don.

How long should the cylinder "hold" pressure? If you think about it, it can only hold compression for so long because as the ring cools and retracts, the expansion slit in the ring will expand; thus allowing an air space. That air space will decrease the compression, right?

I'm getting my father-in-law'* test kit this afternoon and will do the compression check this weekend.
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Old 09-08-2005, 11:45 AM   #59
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If the rings are in good shape, it should hold for a bit.... You may hear some leak down when you do this from the piston rings... If it builds pressure quickly, as in the first stroke almost gets it there, and the second pushes it a little further and it stays pretty solid without dropping like a rock, than I'd say you have decent compression...

Look for 140-160 psi... I have pretty much never seen a 3800 FUBAR piston rings...

I have seen some motors that hold good compression for a while, but like you said they will loose some... I should test mine one of these days and see what I get

If the test comes back clean than we can say the engine is ok...

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Old 09-08-2005, 12:15 PM   #60
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Ahhh so then pulling a single plug at a time and cranking it up isn't the right way

The tester I have has a one way valve to hold the pressure to show you the highest pressure established. I think this is pretty common. On leak down.. what if a valve was partially open when you stopped cranking...then it won't show the pressure.
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