Fuel injector testing

rmcdonnell · 01-22-2009, 04:23 AM

Hi,

I think I may have a dodgy injector, in my 1989 2.7L 944, and would like to rule it out.

I also think it should be possible to disconnect the fuel rail and expose the injectors, so that the spray pattern can be observed. Is this as simple as it sounds, or have several other components got to be removed first, and the whole lot then reconnected, and bled, to operate in a different position, slightly away from the head?

Presumably removing the low voltage feed to the coil should prevent any sparks whilst cranking.

Clarks mentions injector and fuel rail removal, nothing about testing them; (probably because it is a bit dangerous if you are not aware of the hazards).

regards
Rissole.

earlr85944 · 01-22-2009, 01:04 PM

you can do it as described

rmcdonnell · 01-22-2009, 01:33 PM

Is this the answer to my question or just an observation?
Could you just spell it out..?
Cheers
Rissole

SolReaver · 02:23 PM

Y...E...S...

In other words, just take the injectors out still attached to the rail and crank the engine. They will fire. I put little cut out cans or something to catch the spray. If you use a shot of either down the horn you can actually see them up to about 3k, pretty interesting to watch.

Mr. Safety says have a fire extinguisher handy and wear eye protection. Good job to have an assistant for.

If one is still dodging...check for signal using a noid before replacing it. OR...swap an injector from another cyl and repeat the test.

Which one is giving you problems?

rmcdonnell · 01-22-2009, 03:31 PM

Thanks Sol,
That's quite mad: starting the car on ether, while squirting petrol about from disconnected injectors:- but I want to live !! (I was wondering if I was being paranoid about safety when I mentioned disconnecting the coil, and now I know I was :g)

It's no2 pot thats periodically gumming up a new spark plug with carbon (about 3-6 months), and the car has a lumpy idle if left for a few days that goes away after 10 minutes drive. I thought I might have a weepy or poor injector, and this should tell me loads about the health of the fuel injection system, or better still, rule it out as a problem.

Anyway, thanks: I will experiment at the weekend and see what I can see.
Cheers
Rissole.

HondaDustR · 01-22-2009, 04:39 PM

To rule out any leaking, jumper the fuel pump relay to run the fuel pump, or make it run by simply cranking the motor the same way you did while checking the spray pattern, only just with all the injectors unpluged

SolReaver · 11:28 PM

Mad? Mad you say? Well, now that I think of it......
Yes, It is a dangerous procedure. You are wise to be concerned.

You can just disconnect the coil wire and crank the engine. It will tell you if an injector is firing. However, by your description, it is possible the injector is firing all too well. Removing the spark plugs helps the engine spin faster. I would place 4 cans, cups, bags, Tubes, or other suitable receptacles on the individual injectors and see if Number 2 is putting out the same amount as the rest. Also check the current flow diagram and verify that the FI signal and ground wires are all sounding out. With the age of the car it is possible that the wires or connections are not what they used to be.

Lastly, you could just switch the injector with another one and see if the carbon fouling stays with the cylinder or with the injector. If it stays with the cylinder, wiring is the most likely candidate. If it stays with the injector, get a good used injector or have the Witch Hunter guy clean the old one. As the other 3 may not be far behind you might want to think about having the set cleaned, tested and flow rated should this be the case.

Have you replaced the fuel filter and checked the screen in the gas tank?