ntruck wont fire

[TJ79Cheyenne]

Hey guys i need some help here. My truck 87 chevy silverado will not fire. It has a 350 tbi setup and i noticed that the injectors arent spraying fuel. I pulled one line off the tbi and turned the key on and im getting fuel to the tbi. Could it be that the pressure regulators bad or even possibly the injectors? And how would i go about testing these things?

 

[chengny]

Attached are the injector circuit diagnostic charts for 1987 MY.

I excluded the pump/relay operation and regulator tests (chart A-5) because you have demonstrated fuel pressure at the TBI inlet as indicated below:

I pulled one line off the tbi and turned the key on and im getting fuel to the tbi.

 

[chengny]

Same stuff here, just easier to read - maybe:

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[TJ79Cheyenne]

Well i just rented a noid lite set n tested my injectors for pulse but no lights flashed or turned steady on either injector harness... I tried it with my original computer and one i picked up at the junkyard yesterday... Anything else you can think of?

 

[chengny]

Here is a link to the entire manual (1987 GMC Light Duty Truck Fuel and Emissions Including Driveability Manual):

http://depositfiles.com/files/rblr611g2

I just uploaded it about a month ago - it should still be viable.

 

[Stewzer55]

The ignition module could not be giving the signal for the injectors to fire, go ahead and clean/rebuild your injectors while they're apart because they like to gum up if they've been sitting too long.

 

[chengny]

As per Stewzer55;

Along with a power supply input from the battery, the ECM needs to see 2 things before it will allow the injectors to open and allow fuel into the throttle body. One of the following two permissives must be met at all times:

1. A crank signal (from the starter solenoid) that an attempt is being made to start the engine. This is only needed until the ignition system fires up - after that it goes away because you release the ignition switch from the START position and the solenoid is de-energized.

2. After the crank signal drops out, the pulsed signal from the distributor module takes it's place. As long as the ECM senses an operational ignition system it will permit injector function.

It is often possible to start the engine without a crank signal because the ignition system will fire up and provide the input to the ECM even without fuel.

But, as you can see, the opposite is not true. If the distributor module is not firing the plugs, the engine won't fire up regardless of whether you have fuel flow or not.

Bottom line - you can probably start an engine without a crank signal, but not without a functioning module due to the accompanying lack of spark in the ignition secondary (i.e at the plugs).

As a test, just pull and ground a spark plug and observe whether you get an arc across the electrodes. No matter what ever else, no spark = no start.

If you get a good spark at the plugs and you have tried 2 other ECM's - start looking at power supply issues to the ECM.



With the key on and the engine not running, do you get a steady Service Engine Soon light?

 

[TJ79Cheyenne]

Gosh darnit its always somethin stupid with my trucks! A plug for the ignition module somehow wiggled its way loose! Thanks for the help though man!