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86 2.8mpfi 140k mi compression check/results

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Old Jul 19, 2017 | 04:14 AM
  #1  
1WheelerPeeler's Avatar
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Joined: Feb 2011
Posts: 1
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From: Portland (under the hood)
Car: 1986 Pontiac Firebird
Engine: 2.8 MPFI
Transmission: 700R4
86 2.8mpfi 140k mi compression check/results

Last time i logged in was 2k13...crazy.

Top of the mornin' to ya, rest of it to me.

Short story long- been driving this beast for 2 years without the guage fuse in.
I might get into why later, cuz its a great story in itself, but car started dying, like a fuel starve. Noticed fuel pump stopped priming at turn key. Checked pressure @ rail like a true...shade tree mechanic. Squirt was non impressive. Autozone rented their fp guage to some dip that never brought it back yet.
Changed filter and checked squirt, much better. Still dying while hot and denied a restart for 5 mins to 6hours- crap shoot.
Anyways, decided to check compression, cuz really, with no guages and a loud stereo, who knows whats going on under the hood.
Results
(front pass to rear)
Cyl 1 120
Cyl 3 140
Cyl 5 110

(front driver to rear)
Cyl 2 135
Cyl 4 150
Cyl 6 150

All dry tested, cold engine numbers.

Since 2004 when i got the damn thing, pump primed on turn key. Now since it started dying, and being rediculous, pump primes on turning key OFF.

Idk. Are my numbers ok? Ill elaborate on the guages thing later. Possibly be a sober type story, so it all comes out in English.
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Old Jul 24, 2017 | 07:42 AM
  #2  
drdave88's Avatar
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Joined: Feb 2003
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From: Waterford, MI
Car: 1998 Camaro Z28
Engine: 6.0L
Transmission: 4L60E
Axle/Gears: 3.73
Re: 86 2.8mpfi 140k mi compression check/results

Little variation and 2&6 seem a bit low on the passenger side. You usually don't want more than about 20psi variation between the cylinders.
Try doing it with a warm engine, you'll get more accurate readings. When your engine is cold, your numbers will be off since your pistons have not expanded and everything (including your rings) are moving around causing a less consistent seal. If you're still getting low numbers on the pass side, then shoot some oil in there and see if they come up or not.
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