Hi..im new to the forum also do not know much mechanically i have replace the fuel pump changed the fuel filter and still nothing..when I pour gas in the throttle body it runs until the gas is gone..any suggestions thanks

 

I have a problem in my 2002 4x4 blazer, the engine turns but normally does not start. There is no spark. I changed the following parts for new components: coil, cables, complete distribution, ignition module, crankshaft sensor. Now, seeing a tutorial on the internet to test the ignition module, specifically if the computer sends an intermittent signal to the ignition module, I disconnected the cable and placed an LED spotlight on it, after verifying that the signal did arrive, I reconnected the cables and there the vehicle to start, turn on. Now every time the vehicle doesn't turn on, I disconnect the cable, put the LED light on, reconnect and turn on again.... what could be happening? I make the connection in the following way, positive led bulb to battery positive and negative from led bulb to cable that goes from computer to ignition module, all the cables of the connector remain in place except the cable where I connect the negative of the bulb led.

 

I need clarification on the problem that you are having.

So it cranks but no spark. Where did you check for spark? Did you check the coil output cable for spark?

Did you check the ICM and coil power wires and the ICM ground?

Please explain " Now every time the vehicle doesn't turn on".

George

 

I check the spark directly at the coil, why a spark meter.
The coil has its 12 volt supply (correct)
The ignition module has 4 wires,
1) 12 volt power supply (correct),
2) ground wire (correct),
3) cable carrying signal from ICM to coil (wrong),
4) cable carrying signal from computer to ICM (wrong).
I connect the led bulb to cable 4), to check the crankshaft sensor and it works fine. After testing, I connect all the cables, check for spark and if there is, I turn on the vehicle and it starts.
I wait a few hours and again it doesn't turn on.
For the vehicle to turn on, I must place the LED bulb on the cable 4) again for about 10 seconds, I remove it, connect the cable normally and the vehicle starts without problems.
How do I connect the led bulb? With the ICM connector disconnected, I place the led bulb negative to the cable that goes from the computer to the ignition module (ICM) and the led bulb positive to the battery positive, when connecting it the bulb does not turn on or it makes it very weak, After 10 seconds the light from the led bulb becomes intense, I remove the led bulb, I place the connector normally on the ignition module, turn on the vehicle and it turns on without problems.

 

What do you mean that the vehicle does not turn on? Do you mean that there is no 12V somewhere with the key in the run position or no dash lights? Or do you mean that it cranks but wont start?

George

 

YES, it cranks but won't start.

 

Testing for power, ground and signals is the right way to go about this. That said, there is an opportunity for confusion regarding the wires. I am going to use the GM wiring labels and colors so that we can be clear.

The ICM has 4 wires labeled with letters not numbers in the GM diagrams and most tutorials. The GM wiring diagram has the wires out of order at the ICM and both have black and white colors so the colors are the best check:

A: Pink, 12V
B: White, Ign timing sig (from the PCM to ICM)
C: Black w/wht stripe, ground
D: White w/blk stripe, Tach signal (coil control)

When you checked for ICM power at the pink wire on the ICM (A), what voltage did you get? Was the ICM connector in place? Where did you ground the meter?

How did you check the ground to the ICM (C) on the black/wht wire?

When you checked the signal from the PCM to the ICM on (D) the white/blk wire the connector needs to be in place on the ICM? BTW, this does not check the crank sensor, it tests the signal from the PCM. The PCM gets its crank sensor input elsewhere.

Have you checked the integrity of the white wire between the PCM and ICM?

For all of these tests when you say LED spotlight do you mean an LED test lights? An LED test light will put almost no load on the circuit. If LED spotlight means an LED lamp, that can put substantial load on the circuit depending on the wattage of the LED lamp.

George

 

For reference here is the GM test procedure:



George

 

Hi Geoge, thank you for your comments.
Respect your questions:

A: Pink, 12V
B: White, Ign timing sig (from the PCM to ICM)
C: Black w/wht stripe, ground
D: White w/blk stripe, Tach signal (coil control). (Here its my problem too - this model donīt tachometer signal on coil conector)

When you checked for ICM power at the pink wire on the ICM (A), what voltage did you get? Was the ICM connector in place? Where did you ground the meter? Yes I have 12 V. ICM connector out place. Ground meter on alternator case.

How did you check the ground to the ICM (C) on the black/wht wire? Yes I have good ground. With meter negative on conector and positive on battery postive.

When you checked the signal from the PCM to the ICM on (D) the white/blk wire the connector needs to be in place on the ICM? BTW, this does not check the crank sensor, it tests the signal from the PCM. The PCM gets its crank sensor input elsewhere. When I checked this sigmal the conector is out the place. If correct, the crankshaft sensor signal is tested at another point (pin # 12 on PCM), but if the computer does not send the timing signal to the ICM, it could be determined that there is a fault in the crankshaft sensor.

Have you checked the integrity of the white wire between the PCM and ICM? Yes.

For all of these tests when you say LED spotlight do you mean an LED test lights? An LED test light will put almost no load on the circuit. If LED spotlight means an LED lamp, that can put substantial load on the circuit depending on the wattage of the LED lamp.I say an LED test light. Now to get an idea, if I measure the voltage out of this LED test light (conect positive LED light to battery positive and negative LED light to meter) teh voltage is 10.7 volts. Now, when conect the negative LED light to white wire (Ign timing sig from the PCM to ICM) the voltage down to 4.3 volts.

Thanks for sending me the GM test method I'm going to use and let you know the results.

Truly, my great unknown is why when I make the connection described in previous messages (led test light to white (B) wire), desconet these led test light, conect white wire to ICM, the vehicle works normally. Only with that.

 

Try doing your procedure but do not connect the led test light, just everything else and see if the truck starts:

"For the vehicle to turn on, I must place the LED bulb on the cable 4) again for about 10 seconds, I remove it, connect the cable normally and the vehicle starts without problems. How do I connect the led bulb? With the ICM connector disconnected, I place the led bulb negative to the cable that goes from the computer to the ignition module (ICM) and the led bulb positive to the battery positive, when connecting it the bulb does not turn on or it makes it very weak, After 10 seconds the light from the led bulb becomes intense, I remove the led bulb, I place the connector normally on the ignition module, turn on the vehicle and it turns on without problems."

George