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914World.com _ 914World Garage _ How to find which cylinder is not firing and why?

Posted by: velum Sep 9 2010, 04:01 PM

Hi!

I had to change my FI Wire-Harness ('73 914-4 2.0L), because the old one wasn't good anymore. Barely moving wires broke them. So I installed a brand new harness. However, my engine is not running smoothly at all. It sounds as if it would be running on three cylinders only. You can hear it on this video I posted on YouTube:

http://www.youtube.com/watch?v=Uu6K7P4bpQk

How can I test weather all injectors are receiving impulses from the ECU? Can it be done with a multimeter? I also have an extra set of injectors taken out from a more recent car ('74 I believe. They are green). Should I just connect each injector wire to one of these extra injectors in loose air one by one and see what happens? Even if there is no gas line connected to the injector?

Also, is there an easy procedure (without special tools) to ensure that all injectors are working properly? And if I find an injector that is not working properly can I swap it with one of the extra ones I have. All injectors in my car, and the extra ones are green (sometimes they look black, maybe because of the age).

Cheers!

JF

P.S. I also changed the injector o-rings recently...

Posted by: underthetire Sep 9 2010, 04:33 PM

You can check the pulse with a old analog (dial type) multimeter at idle. The digital ones are just not fast enough. There is also a "noid" light you can buy to test them. Easiest way to find a dead hole is with a thermal gun. Find the cold exhaust.

Posted by: dlee6204 Sep 9 2010, 04:36 PM

One way to test the injectors is to unbolt all four from the manifolds and place each one in a small jar. Disconnect the coil, then crank the car for a few seconds. Each injector should spray a small amount of gas into each jar and you can tell if they are all firing and flowing evenly.

Another way is, while the engine is running, disconnect each spark plug wire one at a time. If you pull one and your engine doesn't change, you know that cylinder is not operating correctly.

Posted by: Vacca Rabite Sep 9 2010, 04:40 PM

To find wich cylinder is not working, just start the car and let it idle. lay down and feel near the exhaust pipes (don't touch them, they will be HOT). The bad cylinder will be way cooler then the others - maybe flat out cold if it is not firing at all. No special tools needed.

Zach

Posted by: Andyrew Sep 9 2010, 05:05 PM

I have always liked the wire pull method.. Pop the hood, Pull the wires one at a time. done.

Posted by: 9146986 Sep 9 2010, 07:42 PM

QUOTE(Andyrew @ Sep 9 2010, 03:05 PM)

I have always liked the wire pull method.. Pop the hood, Pull the wires one at a time. done.

Make sure you use insulated pliers, or plug wire pliers.

Posted by: yeahmag Sep 9 2010, 08:20 PM

Eh... If your plug wires are OK and you are wearing tennis shoes you'll be fine. If your super paranoid don't ground yourself. Then again, I'm an idiot...

Posted by: plays with cars Sep 9 2010, 09:55 PM

QUOTE(yeahmag @ Sep 9 2010, 07:20 PM)

Eh... If your plug wires are OK and you are wearing tennis shoes you'll be fine. If your super paranoid don't ground yourself. Then again, I'm an idiot...

You'll know it if you do accidentally ground yourself. Its an eye opening experiencing.

Posted by: velum Sep 10 2010, 09:39 PM

Many thanks for all that input!

I think I'll use insulated pliers + rubber gloves + tennis shoes!

Cheers!

JF