Compression Test Procedure Questions.

[thejapino]

Hey guys, so I did a compresson test on my car today and got even readings through all four cylinders. However, after doing some research, I've found that 155-160 across is eh-common for high mileage 93 DE's. I did every step while performing the test:

*Engine at operating tempurature
*Pulled the coil wire
*Pulled the fuel pump relay and depresserized the system

Except:

*Cranking the engine at WOT

My question is how different would my results have been if I did this. Would my even compression #'s be higher? It sounds logical that they would be but Im hoping that someone who knows for sure could chime in. Plus I already returned the tester. THanks:rawk:

[kandyflip445]

They would probably have been higher. But the important thing is that you have even numbers across the cylinders.

[Neejay]

Ditto^

When I remembered to do it at WOT, my numbers jumped up about 20+ psi. But like kandyflip445 said, the main concern is that they're all within spec to each other.

[thejapino]

Cool, the only thing I was worried about was LOW even compression across all cylinders. Thanks alot guys. Autozone doesn't charge to rent the tool so I may pick it up again just to see how much it goes up! Well, my compression is OK, now time to diagnose fuel problem. My DE is running on 3 cylinders right now so I've narrowed it down to injector, injector wiring, ecu.

BTW if i do retest the compression, I'll post the difference here.

[kandyflip445]

Turn the car on. Unplug each injector, 1 at a time. The one that doesn't change the idle is the one that is the problem. Make sure you have spark in that cylinder. If you do, it's probably your injector.

My #3 cylinder did this to me. Got a new injector and everything was good again. If you want to get more into it.

You could check to see if you have signal to your injetors using an oscilliscope to watch and see if the injector is getting a signal. But who has one of those laying around. I haven't tried using a multimeter to do it, but my guess is that it would be to slow to catch it.

[thejapino]

thanks for the tip. Im gonna unplug each injector one by one in a few hours. I already know the #1 cylinder is the culprit. Now i just have to prove it.

[Dream240]

You can do a simple resistance check on your injectors to see if they're faulty. If you have a volt meter just check resistance on each injector from prong 1 to 2. Do this with the engine off and cooled. You should get approx. 11.5 ohms for each injector, if not then it's bad.

Also just because you are getting spark doesn't mean you have a good running ignition system. If you've got a stumbing idle or acceleration then replace your spark plugs wires with FACTORY wires. Again I insist on factory wires for the KA engine. For some reason they just don't like aftermarket wires. I went through 3 different brands of wires before I just ordered stock OEM wires and they fixed the problem.

I would definitely go there next just because it's a cheap fix, especially if you're not throwing any codes and you are just stumped.

GL