Compression Test results

[Eastcoast SHO]

Ok so i finished putting high temputure tape ove the entire back cp harness, didnt see any obvious burn throughs, but some were tough to pull apart. after i was done with that i did the compression test and here are the results

#1 #2 #3 #4

Test 1 90 100 90 90

Test 2 90 100 100 90

Test 3 90 100 100 100

Test 4 100 100 90 100

Test 5 100 100 100 100


so is this good or not good?

if this is good and there is nothing wrong with my rings, checked cp wires redid them, new coil packs and spark plugs, if there is still a misfire what would it be next?

 

[jmpSHO]

It's good that they are all consistant but I thought they should be higher, maybe 120-140 but I am probably wrong.

 

[jmpSHO]

Any reason why you didn't check the other four?

 

[Eastcoast SHO]

Any reason why you didn't check the other four?

i have been trying to find out why i still have a misfire on 3, just wanted to eliminate bad piston rings

 

[ThatShoGuy]

i have been trying to find out why i still have a misfire on 3, just wanted to eliminate bad piston rings

i have a misfire on cylinder 7 at least mine if up front. but i can feel the car lose it and come back. only sometimes is it a turd. i havnt figured it out quite yet.

let me know if you figure yours out.. sorry not much help but if it stopped raining here i would work on mine some more

 

[Bob Gervais]

Looks good to me Peter. As mentioned above I would have expected to see higher cylinder pressure, but they're all within 10% of each other so you're good.

I wouldn't worry too much about the cylinder pressure, especially if it's a borrowed or rented gauge. A lot of times they can be off a little.

 

[Eastcoast SHO]

Looks good to me Peter. As mentioned above I would have expected to see higher cylinder pressure, but they're all within 10% of each other so you're good.

I wouldn't worry too much about the cylinder pressure, especially if it's a borrowed or rented gauge. A lot of times they can be off a little.

no bob, it was a brand new tester, i bought it.

 

[bacernate]

Did you check it with the throttle fully open? If not the cylinders can get washhed down with fuel. Even with a even compression test there is still a chance of a valve train problem. The only way to know for sure is a running compression test which is impossible on the rear bank of the sho.
Is this a cam fail car?
Switch injector #3 and coil #3 and plug # 3 with another cylinder in the front and see if the misfire travels. Just cause it's new doesn't mean it's good!!! Also did you apply dielectric grease inside the coil boots?

 

[Bob Gervais]

He did run a compression test on the rear bank, cyls 1-4. Why would it be impossible to run a compression test on the rear bank?

 

[ThatShoGuy]

He did run a compression test on the rear bank, cyls 1-4. Why would it be impossible to run a compression test on the rear bank?

he means motor running!

 

[Bob Gervais]

he means motor running!

You can't do a compression test with the motor running. Have you ever done a compression test? Do you know what a compression test is?


Pete, I pm'd you my phone number in case you have any problems. Too much misinformation here.

 

[Eastcoast SHO]

1. i did hold the throttle wide open on each test
2. it didnt get washed down with fuel as the lower intake and fuel injectors were completely out of the car(did pauls test version)
3. this is not a cam fail car, it was one on the first cars welded by kirk

the numbers may not be high, i am not sure but, i have read not only on this thread but in others from doing a search that being within 10% of each other is good

and i think when removing coil packs and spark plugs, it is near impossible to get the motor running

 

[Eastcoast SHO]

i have a misfire on cylinder 7 at least mine if up front. but i can feel the car lose it and come back. only sometimes is it a turd. i havnt figured it out quite yet.

let me know if you figure yours out.. sorry not much help but if it stopped raining here i would work on mine some more

well as of right now i havent thrown a code for a misfire, but i will wait to confirm, i never uplugged the battery just reset the codes with my scanner, so i assume the misfire should have already shown up but i will at least 10 cycles before conformation, i reinsulated the rear coil pack wires with high temputure tape, then swapped out the coil pack and see if a misfire travels, but as stated i will wait, the only 2 codes that showed up were p0171 and
p1518, i have done everything minus change the o2 sensor, i will do that and see what happens

 

[ThatShoGuy]

You can't do a compression test with the motor running. Have you ever done a compression test? Do you know what a compression test is?


Pete, I pm'd you my phone number in case you have any problems. Too much misinformation here.

yes i do!!!! and i dont know why you couldnt do it with the motor running?your only pulling 1 plug 1 coil... not to say it would help but im not sure about that!

 

[Bob Gervais]

yes i do!!!! and i dont know why you couldnt do it with the motor running?your only pulling 1 plug 1 coil... not to say it would help but im not sure about that!

Maybe it's just me and my inexperience, but I don't get what the advantage of doing a compression test on a running engine with a spark plug missing would is. Honestly, and I'm not busting balls (any more), I've never heard of anyone doing that.

 

[jmpSHO]

I suppose a compression test could be done while the car is running but i have never heard of it being done that way.

 

[SHOZ123]

Maybe it's just me and my inexperience, but I don't get what the advantage of doing a compression test on a running engine with a spark plug missing would is. Honestly, and I'm not busting balls (any more), I've never heard of anyone doing that.

Doesn't Kirk have that special LIM that has the 8-1bbl Weber downdraft carbs on it and the special linkage for the SHO?????

 

[1995mtxsho]

yes i do!!!! and i dont know why you couldnt do it with the motor running?

Not on the back bank of a Gen 3 SHO. There is no physical way.

 

[Bob Gervais]

Doesn't Kirk have that special LIM that has the 8-1bbl Weber downdraft carbs on it and the special linkage for the SHO?????

Thanks, Mr. Letthecatouttathebag.

 

[bacernate]

The purpose if doing a running compression test is to tell how the engine is breathing. When you do a non running test all you are testing is whether the rings and valves are sealing. A running test can tell how far the valve open, so it would be feasible to have a good compression test on a cylinder but a valve not opening enough[ie a weak spring bad cam lobe etc] to cause a misfire.
But as I said it would be impossible to do on the rear bank.
Any access to a sscanner?