GM TB injector questions, HELP!

[Frederic Breitwieser]

Hey George!

> At 10:56 AM 6/17/97 -0500, you wrote:
> >I put a DMM (I have a cheesy little Radio shack analog meter) on the
> >injector leads

A meter, digital or analog has a sampling time associated with it.  DMM's 
are typically a few times a second, and analog meters depend on how much 
the needle/pointer weighs.  The only realy way to do this is with an 
occilloscope, spelling not included.  I bought one used a few years back 
for $20, which only goes to 5Mhz, which is great for automotive 
applications.  Computers, Nah.

> >  Their is a high pulse width at start
> >up right?  the DMM should integrate the signal and show around 12V,
> >right???

Yes, but its still too fast for any kind of meter... an occiliscope will 
help you out tremendously.  For example, at 1000 RPM, each cylinder fires 
twice, which means you have 500 pulses per minute divided by six cylinders, 
which translates to 125 pulses per minute.  Meters just don't cut it... 
still way to fast.  That's assuming the injectors are open during the 
intake cycle, and not modulated, which someone else could answer better 
than I.  If its modulated, you have several sharp pulses per cycle.

> >solenoid
> >be stuck?  How common is it for these injectors to go bad??

Did you check all of them?  Or just the cylinder closest to you?  What's 
the chances of six being bad?  I have heard that injectors that sit for 
long periods of time after use tend to corrode somewhat.  Its my 
understanding that the gasoline, as obnoxious as it is, keeps them clean.

> >I see no evidence of fuel being sprayed into the throttle body when
> >I crank the starter, I don't smell it or see a trace of it.  Is it
> >the injectors, or the computer...  HELP!!:)

I would check the crank sensor, which on your engine (and mine) is a 
magnetic hall sensor, if you rotate the engine with a large pry bar and 
socket on the flywheel, it should pulse several times per rotation.  Also, 
make sure the computer is getting 12-13V, excessive cranking kills the 
battery quickly as you know, and computers generally don't work well in 
undervoltage situations.  Next, I would measure voltages along the spark 
plug wires (wear gloves), just to double check that has voltage too... make 
sure all your grounds are good, and your computer is grounded as well. 
 Lastly, make sure your fuel is getting into the injector rail, and there 
is no air sitting around.  I went through some of this stuff when I started 
my 3.8L on the engine crane.  But I got it.  My issue was the computer 
wasn't grounded correctly.


Frederic Breitwieser
Homebrew Automotive Mailing List
Website: http://members.aol.com/fjb203/index.htm
Email: frederic.breitwieser at mcione.com & FJB203 at aol.com
Bridgeport, Connecticut