Hi

I’ve recently sold my 996 in favor for a mid 80s generation. Found a car I like, an 86 3.2 and one of the things I want to do is run a compression test. Last time I did this it was 15 years ago on a completely differently vehicle and I just want to run by you guys how this is done safely, since it is not yet my own car…

process, please feel free to correct me:
1) get the motor to operating temp
2) remove fuel pump fuse - which one? Somewhere in the front on the drivers side but which?
3) disconnect spark leads
4) remove all spark plugs
5) disconnect coil? Where and how?
6) thread/insert compression tester gently and crank 4-5 turns and repeat six times for each cylinder.
7) reassemble and put fuse back.

sound good? Not sure about how to disable spark and where fuse for fuel pump is.

thanks

 

i would suggest a thorough PPI and have a compression test included as part of it. If you are not familiar with the air cooled family there is a lot to check for such an investment.

 

Hi

thanks, the car has a decently documented history, not concerned, but I want to be sure, and I like to do things myself. Was looking for the specific info related to the fuse and how, if it is necessary, to remove the signal or power to the coils.

 

not sure on a Carrera, someone might chime in ..

 

First off, only pull one plug at a time, that is the hole you're going to test.

The coil is pretty obvious just pull the center wite off the distributor.

I, too, recommend an impartial independent you trust and pay them. Pulling plugs on a 911 is easy enough but it can go horribly wrong. Since you don't own the car how would you handle it if a plug snapped off? Good luck.

 

that's what i was trying to say .. but figured i pressed the issue enough lol.. if it were my car, he wouldn't be doing it for sure.

are you going to take his valve covers off and check studs too ?

 

Appreciate your tips and concerns

It is supposed to be in really good shape. If a plug snaps that indicates there are larger issues…

why should I leave the other plugs in? Since I’m looking for differences across cylinders it doesn’t matter I guess.

the car is pretty far away, dont have any independents I really trust. Different cultures and all that. Its good advice but I’m sort of out of options. First car in many years that ticks my list and there are very few Targas for sale where I live at the end of the earth. Have seen a LOT of youtube renovations so I know where they typically rust, my biggest concern next to engine and transmission.

 

Pull the DME relay. It will cut both fuel and spark to allow for the test.

-Todd

 

Ah, naturally of course. Duh, should’ve thought of that.

cheers 🙂

 

Make sure the spark plug areas are free of debris so nothing gets sucked in to the other cylinders during testing.

I'd let it crank until the pressure stops changing. Figure out how many that is, and keep it repeatable for each cylinder.

I put a battery charger on the car to maintain consistent voltage throughout the testing. You don't want to find pressure dropping as you get to the last cylinder if it is due only to the battery running down.

Gas pedal held floored to allow no restriction of intake air.

And if there is any doubt, repeat some cylinders to see if you get the same numbers on the second try.

Main thing you're looking for is a variation where one or more cylinders is significantly lower than the rest.

If you're going through the trouble to do this, a leakdown test is not much more effort, if you have an air compressor.