I'm doing a dry/wet test on my wifes 84 vette today. But I have a quick question.
I disabled the ignition by removing the wire that feeds the coil on the HEI distributor
I also opened up the butterflies on the TB's.
What about the fuel pump... do I disable that as well or just let it be?
thanks

 

I dont bother with the fuel pump, so long as you have the TBI wide open that puts the comp in "clear flood" mode and it wont fire the injectors..

Shane.

 

Thank you. These were my results


Cyl Dry Wet
1 130 90
3 110 100
5 120 90
7 128 90
2 122 100
4 100 120
6 139 100
8 100 100


Overall I don't think its to bad by I'm going to retest Cyl 4
In my directions it states that if the pressure goes up could be a piston/ring problem. but it doesn't say anything about when the pressure goes down. Still be ring blow by?

 

Those numbers seem backwards, usually the wet test will give a higher number.. Like you said with the wet test if the pressure goes up its usually a sign of worn rings. If there is no change then its usually a valve problem. I would retest it just to make sure.. Make sure to go five or six compression cycles so you get the max reading. Also you should have someone watch while you are cranking it to see if the pressure jumps up fast or slowly builds up.. It should jump up to near max psi within 2 or 3 compression cycles..

The normal spec for a compression test is that all cylinders are within 20% of each other. So that would mean your lowest should be within 28 Psi of the max which you are close but 3,4 and 8 are a little low.. Ive seen engines run for a long time with way worse numbers so its not super critical.. Its just not optimum..

 

I certainly appreciate your help. I did it again slighty colder engine.

Cyl Dry Wet
1 150 152
3 140 155
5 160 158
7 145 150
2 155 155
4 150 150
6 180 180
8 155 179

These make a bit more sense. I'm doing this because on my vette I put new heads on last spring, then I took my orginals in to get them reconditioned and plan to use those on this car (my wifes 84). So I want to be sure that don't make the bottom end worse by putting them on. I can see I must have some blow by on the rings. But overall for a car that has 219k on it I don't think its to bad.

 

That looks better.. I would be very happy with those numbers with that kind of mileage..