Low compression

[desertt5]

My S decided not to start last week in the cold ( 0* ). Found the starter had a cracked housing, replaced that. I am getting fuel, and what appears to be good spark at the plugs, and it is good enough to trigger a timing light on each wire too. Also verified timing is still good. Even swapped the DME just to see. No start.

Checked compression: 1- 140 2- 80 3- 130 4- 140. Rod bearing #2?
Head gasket a slim possibility? Will compression that low cause a no start?

No way to do a leak down test. Not sure what I am going to do. My suspension is also shot, I have been shopping for thsoe parts but now......

[John_AZ]

Due to the cold weather in ABQ, I would repeat the compression check.

Did you remove the DME relay when you did the compression check---must be done or you wash the cyl walls with gas.

Squirt a few drops of conventional oil in the #2 cyl and retry.

Does the tach needle bounce 1/16th of an inch when you crank??? It must....or the sensors or sensor connections on top of the rear engine are dirty/corroded.

Are you using a synthetic oil?

Worn piston rings will cause the low compression reading not a #2 rod bearing.

GL
John

[desertt5]

Did the check in the garage. About 50*. Tried some oil from my POS, no change in the reading.

My tach only moves when it wants. Bad connection somewhere. Would I have any spark if the senors were bad?

I am running synthetic oil.

Am I right in assuming I will end up pulling the head or more to really find out?



Thanks, John

Wish i was in AZ right now. Down to 10* again tonight.

[John_AZ]

Yes, you could have spark if the sensor/sensor connections are bad.

The DME/fuel pump relay was removed during the compression test-right?

You now need to do the "Leak Down" test.
If your ear lobes are not frozen, you might hear the hissing at the exhaust pipe, or the oil fill tube (cover off). If the leak is via the cooling system, you will see bubbles in the coolant overflow reservoir when you check .

Harbor Freight has a kit.

Compression-leakdown test

Cross your fingers and hope it is a bad/rotting HG. If you added enough conventional oil to the low cylinder, it should have brought up the reading when you did the compression test (with DME relay removed) by sealing the cyl wall & piston rings a little.

Has your car ever had the HG replaced? There is a nonproven fact that the HGs used in the '87 cars deterioated sooner. I replaced my "87 HG about 3 years ago. Not a hard job.

Again GL
John

[desertt5]

Yep, DME relay pulled.

I could deal with a head gasket. There are a couple things under the intake that probably need done anyway. (would have rather spent the money on Koni's)

Will look into the leak down tester. Will also try more oil with the compression test and see what happens. At least the "thing" is in my garage.

Never had a HG done as far as I know on this motor. PO had this motor put in with ~60 or 70K on it (I'd have to look at paperwork to be sure). It came from Cananda. He lost the the chain tensioner if I remember right. All I have done inside is a new tensioner.

[Vicious]

for a single cylinder to be that low its not likely a head gasket. have a higher chance of it being caused by bad valve or piston rings. but that alone is not enough to cause a no start it would only make it misfire. you need to check elsewhere

[hpaulb]

Just did mine. I believe the factory was in the 170 lb/cyl range. Mine is reading ~150 each. Home made Leak down tester is reading 5% At-10deg. C. No oil added to cylinder. Realy cold, so i anticipate it should go to~4% if worm. Factory at nom temp. should be ~3%

[rick13]

if your tach doesn't bounce consistently you have an electrical problem. as you crank it, it should bounce, oh...i'd say 3 times per second, at about 1/16 of an inch. anyhow, the car should be able to start and run on 3 cylinders.

rick