EFI Injector testing

[Matt Evans]

> Subject: Testing EFI injectors
> 
> I'm working on a Bosch L-Jetronic (EFI) equipped car that has been sitting
> unused for a couple of years. Initial no-start diagnosis was no fuel
> pressure. Cleaned out the gas tank and replaced the fuel pump and filter.
> Now I have good fuel pressure. When I crank the engine it fires for a few
> seconds and then dies - presumably the cold start valve doing its thing. The
> obvious diagnosis is that the injectors are gummed up but how do I test
> them? By the time I have got the injectors out of the car I have pretty much
> torn the intake system to pieces so I can't simply crank the engine and look
> at the injector output. I hate to spend several hundred dollars on new
> injectors and then find out that they weren't the problem. Is it possible to
> dunk the injectors in carb cleaner or some such to clean them?
> Also -  is it possible to monitor the signal to the injectors with a basic
> voltmeter (I don't have an oscilloscope) and if so, what sort of values
> would I expect to see?
> Thanks
> Vic Norman  1996 A4 2.8 1989 Alfa Spuder Veloce

Vic,
the Bosch EFI book talks about L-Jet in great detail.  I have moderate 
experience with it as it was used in my '80 BMW 528i. (L-Jet + Lambda)

You don't need new injectors necessarily - you can send them off and have
them cleaned/"balanced" for less than the cost of a new set of injectors.

the objective measurement of injector performance is flow rate.  If it shoots
the right amount of gas in the right time, then its fundamentaly working
(ignoring issues such as spray pattern).  The "book method" of testing this is
to stick the injector in a jar, and bridge the injector terminals to hold it
wide open (iirc).  After you've done this for some time interval, see how much
gas is in the jar :)

I don't see why you cant crank the engine and look at the injector output -
just disconnect the coil and crank away happily, with one of the injectors
in a jar.  Typically with injector failure you should see one of the injectors 
performing differently than the rest.  This might reveal itself if you were to
pull the plugs and look at the plugs.  One running richer or leaner than the
others might point to a singular faulty injector.  

Are you _positive_ fuel pressure is correct ?  I.e. you've put a FP gauge on
the rail, and have watched it during prime, start, and cold idle conditions ?

If you know its fuel system related, the first thing is to verify rail pressure
(for _all_ stages of engine operation).  Then verify fuel is coming out of the injectors.  Optionally, verify it's the right amount of fuel :)

It could be the injectors are dirty, faulty, or the ecu->injector interface is
faulty (or the ECU is faulty)