OK...

1991 L98 6 speed.

Over the winter, i installed cam, heads, intake base, intake, headers, etc etc...

I had just the bare block in the car with pistons in it.

I get everything back together, and the car turns over, but does not start. I did not change the ICM, Coil, Cap, Dist, or Rotor. All looked new when I pulled it apart, and i feel they were recently done. I did do plugs and wires. They are all hooked up correctly.

Some may say timing, but there is no spark when checked by putting another plug in a wire and holding it against the block.

Is there a chance that a component died over winter? All wires are hooked up at the dist, etc.

Any ideas where to start? Fuel pressure is at 44ish and plugs are wet when pulled.

I did have the dreaded C41 then H 41, but now the C12 pops up when i check the codes. C41 and H41 are gone.

WHen I put it diagnostic mode, the fans do not come on as they should.

I had mseven write me a tune to start it, and the no spark happened with the stock and new tune.

Any help would greatly be appreciated. I am really thinking it is going to be something simple, just need ideas where to check.

Thanks,

Mike

 

If you have 12 volts at the pink wire to the HEI dist. w/key on and you're sure the dist. rotor is turning when cranking the engine. Then it sounds internal to the HEI dist.--could be module-ign. coil or pick up coil. However if you had spark before the engine work--I think I'd recheck the connections etc. inside the Dist when you were checking your "new" looking ignition parts to be sure you didn't leave anything loose or disconnected. question--does the tach needle move while cranking the engine?

 

Use your multi-meter to check the hot + wire coming into the distributor. With the key on and the engine not running you should have 12 volts in. If you do, then the next thing to check should be the distributor cap, coil and ICM. Also, with the cap off, crank the engine and see if the rotor goes around.

Let us know what you find...

 

Once, I fried the the ICM in my Yukon by turning over the engine without the plug wires connected but with power to the coil. Did you happen to do this while adjusting the valves, etc? Just a few cranks and it was dead. I put a new one in the distributor and all was well. Maybe the FSM will have the test procedure for the ICM if you don't like throwing parts at your engine.

 

I did not start the car at all until it was ready to fire, or so i thought.

I;ll have to buy a multimeter and test for the 12 volts at the dist. What wire am I checking? If you could hint at the connector and the color of the wire it would be really helpful.

I'll check on the rpms when cranking and see if the tach moves. WHat should I be looking for?

Its weird the fans dont turn on in diagnostic mode anymore. I am thinking this may be a computer problem...The computer tells the dist when to spark right? Or is that bypassed when you disconnect that wire used to base timing?

I dont see how parts would go bad when they were removed and put on a shelf. I'll pull the cap and see that all is connected properly. Where is the ICM in the distributor? In the cap under the coil?

Thanks for all of your help. I am this is a stupid mistake on my part and all is well once it is found.

Mike

 

There are 3 connectors on the cap. 1 big connector with wires going into the base of the distributor. The 2 smaller connectors are for the tach and 12v. 12v wire is possibly red if I recall correctly. The cap might be labeled if you look closely.

The ignition control module is mounted inside the distrubutor to the base. It sends signals for the tach, coil, and possibly the ecm. If the tach needle moves at all while cranking then at least that part may be working.

The ignition control module and coil are a maintenance item (maybe every 100k) and should be replaced as a set as one bad part can damage the other.

The spark advance wire only controls the advance mechanism.

 

Try reading above --hmmmmm could it be pink ??

 

Sorry Twisterup...just overlooked the color part. What plug is that on? The 4 prong one that connects behind the distributor or one of the 3 that plug into the side of the cap/coil?

Im pretty sure the icm and coil are original. I'll check that tach and see if I get 12 volts or a test light to light up and go from there.

Am I way off on my thinking that the computer could be the issue? That part was fine before too though.

 

The 12V input wire for the coil is the single pink wire. The white wire is output to the tach. You might also make sure you did not accidently catch the pink wire under the corner of the valve cover during reassembly.. It happened to me and when the insulation cut through, I lost all spark. Also double check the grounds on the block above the oil filter G106, G108, etc. It is one of the grounding points for the ECM.

As far as the fans not coming on with the ALDL jumpered, you might check the 10A Gauges fuse in the fuse panel. It provides "control" power to the fan relays..

 

I had 12 volts with the key on at the pink battery wire which plugs into the cap.

On my way home i bought a cap, rotor, icm and coil knowing i could return if necessary. Once i found power to the dist i replaced all above parts and it fired right up. I have no idea what was bad or how it went bad over the winter.

I am still wondering about the fans in diagnostic mode and that random c41 and h41 code.

Thanks for all of your help.

Mike

 

You either had a bad ICM or a bad coil. I'd bet it was the ICM which as mentioned above, GM recommends changing out every 75000 miles or whenever you get stranded along the highway, WHICH EVER COMES FIRST.