98 G3500 with no spark

[boilrman]

I came back to visit family and found myself trying to help fix this thing. Here is what I know.

My brother in law owns the van and when purchased it was smoking badly and barely moved. (vehicle has just over 500K on it) Motor and trans have been rebuilt. I was told there was no spark from coil. Also told coil was checked and checked out good, but replaced anyway. New plugs and wires.

I pulled #1 plug and verified TDC/distributor setting. Checked for spark coming from coil - nothing. pulled connector from coil, turned on key have power on one wire(purple or brown - cant remember) I can hear the fuel pump running and can smell fuel while cranking. I have a couple of more days here before heading south again. My brother in law really would like to get this going as it has been sitting for over 1 year now. The mechanic who helped do this is a family member and has became stumped and just forgot about it.

Any help would be greatly appreciated.

Chad

[rhandwor]

I would take the module to Advanced or Auto Zone and get it checked they will do this free. Check the rotor button and distributor cap. Unplug the pickup use a analog DVOM and put one lead in each connection the gage should sweep as the engine is cranked.

[boilrman]

Originally Posted by rhandwor

I would take the module to Advanced or Auto Zone and get it checked they will do this free. Check the rotor button and distributor cap. Unplug the pickup use a analog DVOM and put one lead in each connection the gage should sweep as the engine is cranked.

The module checked out ok. Button in top of cap has small amount of wear on it, does not move. Cap looks to be in good shape no cracks noticed, small amount of oxidation on tabs. rotor looks to be ok.

I put a digital meter(no access to an analog meter) to the wires from the pickup coil and from the outside 2 wires got 11.9 volts with key on and about a 9.4 - 9.6 while cranking. while touching center to right I got about 11.8 with key on and 8.5 - 8.6 while cranking. Is this bad? Where is the voltage feed coming from?

Chad

[ctwright]

If the module is good then I would check the crankshaft position sensor. If it is bad then the ignition module won't send any ground pulses to the negative terminal on your coil because it's not getting the signal from the sensor.

[boilrman]

Originally Posted by ctwright

If the module is good then I would check the crankshaft position sensor. If it is bad then the ignition module won't send any ground pulses to the negative terminal on your coil because it's not getting the signal from the sensor.

I checked the ohms thru the pickup coil and got 1682. I have read where it should be between 500-1500, with this being high is it bad? will do some looking into the crank position sensor.

chad

[boilrman]

found out there is no way to test the crank position sensor. When I look up a cam position sensor(Parts house website) it shows the pick up coil. Is there a cam sensor on this? I believe the motor is a 5.7L.

Without being able to test the crank sensor do I bite the bullet and spen $60, or send it to a shop and have a diagnostic done? Or is there something else to look at first?

Thanks, Chad

[MT-2500]

Originally Posted by boilrman

found out there is no way to test the crank position sensor. When I look up a cam position sensor(Parts house website) it shows the pick up coil. Is there a cam sensor on this? I believe the motor is a 5.7L.

Without being able to test the crank sensor do I bite the bullet and spen $60, or send it to a shop and have a diagnostic done? Or is there something else to look at first?

Thanks, Chad

Did it ever set any codes?

Crank shaft sensor needs tested with a lab scope or with good engine capable scanner watching rpm signal.

I am not much on throwing parts at it but it will cost as much to have it tested as just putting on on it.

If coil and module is good go for it.
Good luck and.
Let us know how it goes.

[rhandwor]

The ground wire for the coil should be pulsed for the coil to fire. Try a logic probe on the ground wire it should blink as the engine is cranked. The coil has 12 volts and fires when grounded as the distributor turns into the proper position.

[boilrman]

Originally Posted by MT-2500

Did it ever set any codes?

Crank shaft sensor needs tested with a lab scope or with good engine capable scanner watching rpm signal.

I am not much on throwing parts at it but it will cost as much to have it tested as just putting on on it.

If coil and module is good go for it.
Good luck and.
Let us know how it goes.

I asked at the parts store about renting an OBDII and checking for codes, but was told that if it does not run, it will not set a code. So no I have not checked for codes.

Originally Posted by rhandwor

The ground wire for the coil should be pulsed for the coil to fire. Try a logic probe on the ground wire it should blink as the engine is cranked. The coil has 12 volts and fires when grounded as the distributor turns into the proper position.

I will try to do this before the crank sensor. What is next if I dont get a pulse from it?

[ctwright]

Originally Posted by boilrman

I asked at the parts store about renting an OBDII and checking for codes, but was told that if it does not run, it will not set a code. So no I have not checked for codes.




I will try to do this before the crank sensor. What is next if I dont get a pulse from it?

Normally if you do not get the ground pulses to the negative side of your coil when trying to crank the next step would be to check your ignition module which you say is already tested good, and from there I would suspect the crank sensor.

[rhandwor]

Most shops charge $85.00 for an Hours diagnostic. If your wires look good around the distributor replace the pickup if you have no pulse.
On these I use a Thexton plug adapter for a place to hook up my scope. If you use a bed of nails or straight pin coat the hole with silicon. The wire will be hard to get a place to get to a tester attached.

[boilrman]

I appeciate the help folks. I will be looking into this after lunch and will post some sort of results.

Thanks

[ctwright]

I agree with Rhandwor, I was thinking about a different system when I was giving advice, sry for the bad info about where the ignition module gets the signal from on your vehicle. The problem like he said is more than likely your pickup coil.

[boilrman]

well no luck today. I am out of time. My brother in law is going to let me know what it is when he gets things looked at. Will post here at that time.

[rhandwor]

What did you find was the cause?