1991 K5 no spark

[swettysblazer]

I just got the new motor in my truck, and now I have no spark. New coil, new cap and rotor, new plugs, and still nothing.

I get 12 volts in to the coil, and 12 volts out of the coil into the ignition module. Any ideas what this could be? I've been working on this thing till midnight every day to try and get it ready for a wheeling trip this weekend and I'm at the end of my rope. Thanks

 

[rampage]

12V out of the coil? Should be 10’s of thousands of volts which your meter more than likely can’t read or will blow the fuse in it/damage it. Just because it’s new doesn’t mean it’s good these days. You can check the resistance of your primary and secondary coil, and also the make sure the primary and secondary coils aren’t shorted together but other than that I don’t know how to check them. Also make sure all grounds are in place and in good condition.

 

[swettysblazer]

Sorry, should have clarified... I am getting twelve volts out of the coil plug into the ignition module, not out of the coil wire itself.

 

[Blue85]

Is this a TBI setup with ECM control or HEI with weights and vacuum can? Are any of these parts carry-over from the old motor? Any left-over parts to swap for troubleshooting or friend with a similar setup?

Do resistance checks on the coil primary (connector to module) and secondary (carbon button spot to ground lug) to make sure the coil isn't broken. Check the pick-up coil where it plugs into the other end of the module. I thought on TBI you could bypass the ECM via the test connector and get straight base timing. The fact you see 12V on the low side of the coil means that primary isn't open. Make sure you have something pretty close to 0V on the low side of the module as well. There are also some checks you can do with the DMM in AC volts mode. The pickup coil should produce a small voltage when the engine is spinning, when it's not connected to the module, anyway (it's just a permanent magnet so you should also see the ohms flipping around when the dizzy spins). If the module is driving the coil, you'll see an AC voltage on the primary (you know, the terminal hooked to the module and not to straight 12V).

Also retrace your work to make sure you didn't do a late night snafu, like leave out the carbon button or line up one of the coil terminals wrong in the distributor cap. I think it's also possible to get the dizzy dropped in "wrong enough" that the rotor terminal isn't lined up with any of the cap terminals when it's trying to spark.

 

[swettysblazer]

Is this a TBI setup with ECM control or HEI with weights and vacuum can? Are any of these parts carry-over from the old motor? Any left-over parts to swap for troubleshooting or friend with a similar setup?

Do resistance checks on the coil primary (connector to module) and secondary (carbon button spot to ground lug) to make sure the coil isn't broken. Check the pick-up coil where it plugs into the other end of the module. I thought on TBI you could bypass the ECM via the test connector and get straight base timing. The fact you see 12V on the low side of the coil means that primary isn't open. Make sure you have something pretty close to 0V on the low side of the module as well. There are also some checks you can do with the DMM in AC volts mode. The pickup coil should produce a small voltage when the engine is spinning, when it's not connected to the module, anyway (it's just a permanent magnet so you should also see the ohms flipping around when the dizzy spins). If the module is driving the coil, you'll see an AC voltage on the primary (you know, the terminal hooked to the module and not to straight 12V).

Also retrace your work to make sure you didn't do a late night snafu, like leave out the carbon button or line up one of the coil terminals wrong in the distributor cap. I think it's also possible to get the dizzy dropped in "wrong enough" that the rotor terminal isn't lined up with any of the cap terminals when it's trying to spark.

Hey @Blue85 , this is all TBI stuff. The only carryover is the harness. I swapped the cap, rotor, and ignition module from the old motor as it was fairly new and put that on to rule that stuff out.

I didn't take the distributor out either, so I am assuming the timing is right as this thing ran perfect when I pulled it in the shop last week.

I'm confused as maybe as I am calling it a different thing, but what is the carbon button? Should the coil have a dedicated ground to it or is it based off the intake?

 

[miniwally]

I would try two quick things, #1 charge the battery I've dealt with a battery being low enough it would turn the engine over but not have high enough voltage for the TBI to send spark. Then I would also just change out the ign. module as those are temperamental and seem to go out easily and at odd times.
Beyond that I'm assuming it was a running TBI replacing a non running TBI. Just double check grounds, power etc. as it's going to be something odd and silly.

 

[diesel4me]

On the older HEI's a common issue was the ground strap (metal bent thing) to ground the ignition coil got left out when someone did a tune up..also one of the prongs on the wire connector didn't align and actually connect to the coil terminals in the cap..

I'm not much help on TBI ignitions,mostly I've only had the old 4 prong module HEI's they used up until '86...on those,a quick simple test was to put a 12V test lamp to the "tach" terminal and ground the other lead,and crank it over,if the pick up coil & module were ok,you'd see the lamp flash on and off..do not crank it more than 5 seconds though or it may damage the module..

Usually the module is the first thing to fail,and I believe on TBI's the module can still have spark,but not pulse the injectors,and vice versa,sometimes only one half of it craps out..they can also come back to life temporarily ,only to die on you again later on ,usually in a bad place!.the pick up coil can "come and go" too,or fail completely..

 

[Blue85]

The carbon button sits underneath the coil, passes through the cap and touches the terminal on the top of the rotor. Easy to forget if you have the coil out or swap the cap.

 

[Chevman88]

Are you sure spark is the issue? If you pull a plug and ground the threads to the block while still connected to the plug wire and have someone attempt to crank it over (hold with a nice pair of insulated pliers or you may be in for a shocking surprise) do you see spark? Another probably safer way is to connect a timing light to one of the wires and see if you get any light output.

The reason I ask is the connectors on the TBI injectors break pretty easily and don't always like to seat all the way to make a good connection.

Just a reminder to check all the basics and make sure they're all there - fuel, air, and spark. I frequently skip the basics and my problems usually turn out to be something silly I should have caught...

 

[swettysblazer]

Are you sure spark is the issue? If you pull a plug and ground the threads to the block while still connected to the plug wire and have someone attempt to crank it over (hold with a nice pair of insulated pliers or you may be in for a shocking surprise) do you see spark? Another probably safer way is to connect a timing light to one of the wires and see if you get any light output.

The reason I ask is the connectors on the TBI injectors break pretty easily and don't always like to seat all the way to make a good connection.

Just a reminder to check all the basics and make sure they're all there - fuel, air, and spark. I frequently skip the basics and my problems usually turn out to be something silly I should have caught...

This is the newer style HEI where the coil is not on the cap, so I don't think grounding is an issue. I have the intake connected directly to the battery and the block goes right to the frame.

I am definitely getting fuel- I can see the injectors pulsing and can see the fuel spraying. I am going to go back tonight with a spark tester and go from there.