TBI Throttle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.

TBI question

Old 03-14-2019, 09:59 AM
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TBI question

I have a 5ltr crossfire injection vin 7 dual throttle body 1982 TransAm. When the engine is cold it is very hard to start. When started cold I notice when the initial 2 second fuel pump run I get fuel spray out of the front injector but not the rear injector during this prime cycle, is this normal?
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Old 03-14-2019, 10:45 AM
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Re: TBI question

Not normal, likely have a bad o-ring. There are two that seal the injector so fuel doesn't leak.

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Old 03-14-2019, 03:37 PM
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Re: TBI question

If I disconnector the front injector it does not spray and if I put a volt meter on the connector it shows a voltage across the terminals so the ECM is sending the pulse signal, how can that be, wouldn't you lose the pulse before you would get an errant pulse signal. I am confused , where do I look next?
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Old 03-14-2019, 04:21 PM
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Re: TBI question

The prime cycle is to pressurize the lines with fuel, the injector sholdn't spray until you start to crank the car. I'm not sure if both injectors fire on the crank cycle on a cross fire or not, they did on my LO3 89 TBI. I think what RBob is saying is the one injector is either leaking or the o-ring is leaking and its spraying the fuel out during the prime cycle. This means the pump then has to bring the fuel pressure back up as you are cranking the car, which will prolong the crank cycle.

I would say that first things first re o-ring/gasket the throttle body, and if its still slow to crank, test fuel pressure, if that is good likely gummed up injectors I can't tell you how many threads I've seen lately where the answer has been new injectors. Seems ethanol has taken its toll on these older injectors and they are dying en masse.
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Old 03-14-2019, 04:53 PM
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Re: TBI question

This car has never seen ethanol, it is a perfect survivor that has been in storage for 25 years. I have changed the gass tank and pump even though it was rust free. The fuel pressure is 14.5 and if I disconnect the injector power source they do not leak with 14.5 psi of pressure on them. When the car starts the injectors work normally. I put an Excel ignition coil and module on the car and the spark is good. When I try to start the car when cold it just cranks and cranks, as I said , I can see the initial spray of fuel when I turn the ignition on and again when the motor cranks but seems like it is flooded and finally will fire. I have changed the fuel filter and will try the injectors but I don't think that will do it , I will let you know. Mine looks just like yours, white and black with factory alloy wheels and a few years older.

Last edited by kens727; 03-14-2019 at 04:57 PM.
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Old 03-14-2019, 04:53 PM
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Re: TBI question

Originally Posted by kens727 View Post
When started cold I notice when the initial 2 second fuel pump run I get fuel spray out of the front injector but not the rear injector during this prime cycle, is this normal?
No.
Originally Posted by kens727 View Post
If I disconnector the front injector it does not spray
So this is an electrical problem.

Originally Posted by kens727 View Post
and if I put a volt meter on the connector it shows a voltage across the terminals so the ECM is sending the pulse signal,
Voltage is probably supplied by the fuse and wire harness any time the key is "on". The ECM supplies pulsed ground to fire the injector(s). I bet your vehicle has false ground issues--bare or pinched wire between injector and ECM, something like that.
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Old 03-15-2019, 08:10 AM
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Re: TBI question

Just so I understand, at key-on, engine-off, the front injector produces a single spray of fuel. Then stops until you crank the engine? If so replace the Accel ignition parts (coil & ICM) with AC Delco parts.

If at key-on, engine-off, the injector sprays continuously, the ECM is likely bad. Or as Schurkey mentioned there is a pinched/shorted wire.

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Old 03-15-2019, 09:28 AM
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Re: TBI question

That is correct. I will try that thanks
Ken
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