How to tell a bad injector?

ZRS90sc

Registered User
I have a 90sc that runs 33psi while idling and 40+ when revved, after i shut the car off the fuel pressure slowly dwindles down to 0, could it be a bad FPR leaking into the manifold? or i was also told an injector could be stuck open, if so how can i tell which injector is the culprit?
 
ZRS90sc said:
I have a 90sc that runs 33psi while idling and 40+ when revved, after i shut the car off the fuel pressure slowly dwindles down to 0, could it be a bad FPR leaking into the manifold? or i was also told an injector could be stuck open, if so how can i tell which injector is the culprit?

Pull the vacuum line off the fuel pressure regulator and see if there's gas in it. If there is, the regulator is bad. If not, the pump may be bad. You should have around 35-40 at idle and it should hold it for 10-15 minutes after shutting the car off.
 
If the car seems to run fine chances are its the check valve in the fuel pump. If you had a leakky injector the car would run realll cruddy
 
Same goes with abad regulator...Pull the vacum line off and fuel should come out if the diaphram is bad.

I;m still thinking fuel pump checkvalve
 
I'm bout to change the regulator, and the car does run like crap, starts hard sometimes and bucks at WOT, the car sat for about an hour b4 i pulled the vacuum line off the fpr and it was a little moist, so thats where i'm going to start. so i hope the FPR does the trick and i dont have to touch the injectors. oh and it has a new 190 lph fuelpump

thanks guys
 
Injector Testing Device

There are little devices that can individually check each injector. I borrowed the tool from my neighbor. You hook a pressure gage to the injector rail at the fitting that is on it, pressurize the line, hook the tool up the the injector where the injector harness plugs into it, and press the button all while the key is in the on position. This sprays/cycles the injector for three seconds. You check the pressure gage for the pressure drop of each injector. They must all drop pressure within a certain range of each other - much like a compression test must indicate a certain range of readings. This is how you can check if one or more is out of spec.

You could also test them by sight with this method using the manifold if the heads are off the car. Doing it this way was easy when I had the heads off my truck. Its quite easy to diagnose a bad injector when you can see it spray. Usually, the bad ones just trickle or have a very weak spray thats obvious when compared to ones working well that give the nice big broad spray. May be harder here though if everything is together. The pressure gage thing would be your best bet in that case. They are too damn expensive to be replacing all of them if its not needed.
 
What I also heard is getting one of those mechanic's stethoscopes (cheap at ur local parts store) and hearing the injector pulse when its operating. IF its not pulsing its either clogged or open all the time.
 
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