shawn87gta

iTrader: (1)

This isn't third gen related but could be pertinent to someone having a similar problem. I searched but couldn't find anything helpful. I have a 1990 GMC 1500 with 350 TBI motor. I drove it to lunch Friday and when returning from lunch it started and moved about a foot then died. It was low on gas but not empty, but to be sure I put more gas in it and it still didn't start. I went backed today and checked and it's not getting power to the coil and the injectors are not firing - I don't see any gas going into the TBI as the motor cranks. The fuel pump is working. I pulled the connectors off the coil and checked for voltage there, nothing, so I pulled the connector off the distributor and checked and it did not have 12 volts at any of the four terminals on that connector; I only saw ~.8v on one terminal and nothing on the others. I suspected the ignition module but once I found there was no power to the distributor I figured the problem might be upstream from there. I pulled fuses out of the fuse panel and all were good. Is there another fuse or relay that would prevent the distributor from getting power? Should there be 12v at the distributor connector? Thanks for any help.

steve8586iroc

I hope someone can give you a quick answer here, but you may get one quicker on the Tech / General Engine Board. I wish I had a better answer for you.

Steve

dimented24x7

iTrader: (2)

Do you hear the pump runnign while the motor cranks? If its not then there arnt any reference pulses getting to the ecm. You can also see this if you have a tach. It goes dead. The simplest explanation is its probably jsut a faulty module.

shawn87gta

iTrader: (1)

Yes, the pump runs when I turn the key. I debated on replacing the ignition module but when I didn't see any voltage at the dist. connector I thought the problem would be something else.

ledhead96

is the starter working?

RBob

iTrader: (1)

If this is an external coil small cap distributor, the power feed is the heavy pink wire going to the coil. The two wire (pink and white IIRC), between the coil and the distributor feeds power to the distributor from the coil.

With the ignition on the heavy pink at the coil should have +12 volts.

RBob.

dimented24x7

iTrader: (2)

If teh pump runs while cranking then there is at least power to the module and its doing something. If not and the problem still persists with a new module, then its time to look into the wiring. I dont know teh pinouts of the 4 pin connector for the dist. off the top of my head, maybe someone can post them? Ill have to check later on to see what they are.

EDIT NVM, RBob has it covered.

shawn87gta

iTrader: (1)

"I don't see any gas going into the TBI as the motor cranks" From my original post. Yes the starter is working fine. I'm not getting any spark or fuel, and not seeing voltage at the distributor connector. I assumed that I should see voltage at the distributor, but I wanted to ask rather than assume. I guess I'll pick up an ignition module this evening and see if that works, if not I'll take it somewhere for repair as I'm a lost ball in high weeds when it comes to electrical problems. Unlike my GTA, the electrical relays are not obvious in the engine compartment of this truck so I don't know where to look to find out where the power distribution loss is, if any. In any event, thanks all for taking the time to look and offer suggestions!

Edit: I rechecked the voltage at the coil per Rbob's input and I have 12v there. I guess I wasn't getting good ground on the Fluke meter probe yesterday when I checked it. Hopefully the ignition module is the culprit and I'll have it back on the road this evening. Thanks again for your help.

Green92RS305

my car acted the same way bout a year ago, the fuel pump was running but the dist got no power. after replacing all the wires, rotor/cap, and coil i found out it was the ICM (Ignition Control Module). $50 later the car was up and running, might be your fix too.

gnatshop

A follow-up on this subject - hope RBob is following this.

Regarding the external coil small cap distributor - yes, the heavy pink wire to the gray connector is the direct 12V power supply to the coil.

However, from what I can tell from the factory manual wiring diagrams, this 12V supply should also feed through the coil to the small pink wire in the black connector going to the distributor 2 wire connector. You have to pull the 2 wire connector on the distributor to check the voltage flowing thru to the distributor.
Is this correct or does something in the coil cut down the voltage to the distributor?
I'm currently trouble-shooting a similiar situation. Don't seem to be getting 12V to the distributor.

The 4 wire connector the original poster referred to are all from the ECM if he has the same set-up.
Again, correct me if I'm wrong.

Also, the white wire from the 2 wire connector at the distributor flows back to the coil black connector and on through the coil to the tach through the gray connector.

No wonder folks get confused on distributor/external coil wiring!

David
gnatshop@bellsouth.net

rgarcia63

If the distributor has one 4-wire connector, and one 2-wire connector. The 2-wire connector is feed "hot at all times" 12 volts through the ignition switch in the run/start positions through one of the two wires regardless of color (pink get my vote.)
Zero volts at this wire means faulty wiring/connectors/ignition switch. Faulty wiring, the "hot at all times" 12 volts originates at the starter through a fusible link.

RBob

iTrader: (1)

You are correct. Inside of the coil the two connectors are tied straight across. Pink to pink and white to white.

The heavy pink goes to the primary coil winding and also right out the other connector to the distributor (via the pink wire). The white wire that is paired with the heavy pink goes to the tach. The white wire that goes to the distributor is tied to that tach wire AND to the primary coil winding (other end of the winding from the pink wire).

The distributor gets power via the small pink (+12v), and pulls the coil down (charges) via the white wire (it grounds it). When it's time to fire a spark plug the distributor releases the grounding from the white wire and the coil fires.

Note: if you measure the voltage on the white wire (to ground), as the module current limits the primary side of the coil, the voltage will increase. It won't sit at ground. Need to keep this in mind when troubleshooting.

RBob.

Driveshaft

double post

Driveshaft

shawn87gta

did you solve your problem yet
I am in same situation at the moment. was looking for your solution before I spent money chasing the fix.