fj 60 good compression/low leak down help (1 Viewer)

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Making a very long story short, 157k mile 1987 fj60 2f engine was running crummy w. low vacuum (<10 in).

Determined a gasket leak. Determined cracked intake manifold.

New manifold assy installed, vacuum lines routing good, smog stuff good.

Here are the numbers.

Vacuum at 12 in with following compression/leak down data.

Cylinder # 1 -145 PSI, leak down within 10% (Good)

Cylinder # 2 -135 PSI, leak down within 10% (Good)

Cylinder # 3 – 132 PSI, leak down at 30% (excessive)

Cylinder # 4 – 145 PSI, leak down within 10% (Good)

Cylinder # 5 – 140 PSI, leak down at 30% (excessive)

Cylinder # 6 – 140 PSI, leak down within 10% (Good)

Need held in determining what's going on.

Why would only 2 cylinders have low leak down while compression good all around?

Is low vacuum associated with bad leak down numbers?

Would there be flutter in vacuum gauge readings?

All advice welcome!
 
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Interestingly, the mechanic says that he is hearing air at the egr valve. That typically indicates rings, correct?

Valves would be my guess too, but those manifest with air sounds coming from either the exhaust or the carburetor.

I'm not entirely confident in the mechanics skills, and I haven't verified personally any of the information.

If in fact the valves are the problem, I suppose I could drive it until it dies, no?
 

1911

chupacabra
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Interestingly, the mechanic says that he is hearing air at the egr valve. That typically indicates rings, correct?

No, exhaust valves. Air in the crankcase from bad rings would be heard through the oil dipstick tube (or the PCV valve).


Valves would be my guess too, but those manifest with air sounds coming from either the exhaust or the carburetor.

Yes this is true; you did not say in the original post if you heard air in those places or not. Did you check your compression wet or dry?


I'm not entirely confident in the mechanics skills, and I haven't verified personally any of the information.

It's difficult to diagnose something 3rd hand.


If in fact the valves are the problem, I suppose I could drive it until it dies, no?

Yes, if they're not too bad they may last a long time. Try adjusting them for one thing - if any are too tight, they will burn quicker and leak when hot. If/when they do go bad, you will just lose power over time.
 
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I suspect compression was checked dry. But I will check on that.

The valves were supposed to have been adjusted. But I will check on that as well.

Once I get verification on above. I will post for advice.

Thanks
 

rchalmers3

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Interestingly, the mechanic says that he is hearing air at the egr valve. That typically indicates rings, correct?

Valves would be my guess too, but those manifest with air sounds coming from either the exhaust or the carburetor.

I'm not entirely confident in the mechanics skills, and I haven't verified personally any of the information.

If in fact the valves are the problem, I suppose I could drive it until it dies, no?

An air leak at the EGR valve during a leak down test indicates the EGR valve may not be seating correctly. However, a leak at the valve would affect all cylinders due to the connection location on the intake plenum. You will definitely need to investigate the EGR valve leak further, by cleaning the valve and passages to make sure it is functioning properly.

Regarding the low vacuum, is the gauge needle steady at 12 inches or does it fluctuate like the 2 cylinders with leak down are the main source of vacuum loss?

A low steady reading indicates a discreet set of probable causes. A fluctuating needle indicates cylinder specific issues.

I would not yet condemn the cylinder or valves without further information and diagnostics. Depending on your reply to the guage reading question, you may have multiple problems affecting proper performance.

Rick

Rick
 

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