Injectors sick?

[Michael Skolones]

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     I've been having simialar troubles with my LH-Jet '84 Volvo 240; I 
     think the system is somewhat similar to L-Jet.
Cold running is "open-loop," meaning the 02 sensor hasn't come on line yet.  In 
this mode the computer guesses at the correct mixture (the factory default 
mixture calculations work great for new cars) and controls the injectors 
accordingly, using the air mass signal, block temperature and engine speed as 
inputs.  Others have told me that vacuum leaks and dirty/worn out fuel injectors
are the chief culprit to poor open-loop performance, and so far their advice has
borne out.  The theory is that in closed-loop mode, the FI computer can 
compensate for vacuum leaks and bad injectors, within limits, by telling the 
injectors to give a little more or less fuel as necessary; setting the air mass 
meter mixture screw when the car is fully warmed up also helps compensate for 
the vacuum leaks.  In open loop mode the mixture is set to a factory default, 
and if any extra air gets into the system past the flow meter there can be no 
compensation for it, and so forth for  malfunctioning injectors.

Trouble spots on the LH-Jet for vacuum leaks seem to be:
fuel injector o-rings;
throttle body gaskets and butterfly valve rod seal;
idle speed adjuster o-ring;
on the Volvo, passenger compartment air circulation flaps are controlled by 
vacuum, and they are prone to leakage;
power brake booster, ignition vacuum advance control, etc.


The RPM-related sluggishness might improve with clean fuel injectors; it sounds 
like they're not pushing out enough fuel.  Could also be a clogged fuel filter, 
bad pressure regulator or fuel pump.

Mike Skolones
michaels at telerobot.com



______________________________ Reply Separator _________________________________
Subject: Injectors sick?
Author:  diy_efi at coulomb.eng.ohio-state.edu at Internet
Date:    9/5/97 11:23 AM


     
I have a Fiat L-jet and it seems to be a little sluggish sometimes at lower 
rpms, picks up around 3500 or so.  Can't really floor it or it cuts out.  Is 
it possible the injectors are working well only in the mid-range rpms and 
not at low or high extremes.  Is it common for injectors to have this sort 
of pattern or is it maybe something else?
     
Also, what would be the likely cause of cold drivability problems with the 
L-jet system?
     
Ed Hilker aka "Chief"
84'SS - 700R4
     
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