Hi all,

I have my engine out on a homemade test stand, and this is where I would like to do the initial start-up and break in. I don't have spark and I'm hoping to get some troubleshooting advice before I do anything else. Here is where I am at...

Starting system is hooked up and working. New starter and starter relay. Not new battery, but tested good and is charged. No ignition switch or panel wiring in use here - I'm just jumping the battery "+" post of the starter relay with the "S" post. Again, starting system seems to be working fine. Battery is grounded to engine block.

Charging system (alternator and voltage regulator) hooked up, but I don't know if they are working yet. Not really my problem right now.

Ignition system: new distributor (I don't have the old one anymore), never ran before. Old coil, was working the last time the truck was running (3 years ago). Old ignition module (blue connector), was working the last time the truck was running. Ignition module and distributor connected via short harness removed from engine compartment (known working). In addition, I have a jumper wire running from the "s" terminal of the starter relay to the white wire of the ignition module. I also have a jumper wire running from the battery + terminal of the starter relay to the red wire of the ignition module. Normally these would come from the ignition switch wiring. But essentially I'm just bypassing the instrument cluster harnesses and switch. One comment on the red wire - I don't have the resistor in my setup, so it would supply full battery voltage and not the 7-9 I've read it is supposed to supply. Not sure if this will be a problem later, but don't suppose it would cause my 'no-spark' condition because this is for "run" (essentially hot at all times for my test stand) and not "start"...? Or, is it important that the ignition module only sees one of these voltage inputs at a time (eg. start and run voltages don't happen simultaneously)?

Checked the diagrams for grounds, and it looks like the distributor is grounded 'internally'. Also, it looks like the coil is grounded through the radio noise capacitor - which grounds through the mounting screw, into the coil bracket, and into the engine block. I cleaned up these connections. I don't see any other grounds on the 'ignition' side of the electrical? No MCU in my year engine.

I checked for spark by removing plug #6, leaving it in the boot, and holding it against one of the exhaust manifold bolts. Then I jumped the starter relay for enough time for the distributor to make a couple rounds and looked for spark. Nothing.

I feel like I'm missing something obvious but I've looked at the wiring diagrams and I can't imagine that the instrument cluster harnesses, etc, are 100% necessary for a 'simple' test stand setup. Just the white and red jumper wires for the ignition module... or????

I could replace the coil and ignition module, but I'd like to hear some intelligent recommendations before I do that. I'm still very inexperienced with this electrical system. Thank you in advance! PS let me know if pictures would be helpful.

PSS - yes, it's been 1.5 years since I updated my build thread

 

*edit* I am changing my answer until I can find my wiring diagrams, computer is giving me a hard time. Is your setup grounded? New wires or old? Can you check for spark at the coil? The ICM should switch the ground and that's what makes it fire, but I want to look at my diagrams before I have to edit out another silly response.

 

Thanks for the reply. I have new plug/coil wires installed. The ICM isn't explicitly grounded. From what I've read, the ICM housing is not a ground source, but it is grounded through the distributor (black wire). That being said, 'some people' say they added a ground by splicing to the black wire and connecting it to a good ground elsewhere - because the distributor ground 'can be weak'. I don't know if this is accurate.. but I could always try it.

I really need to sit down and draw out my wiring diagram because I'm pretty sure I'm missing something obvious. Talking it out on here helps.

I'm also thinking I will buy a 3 or 4-position switch just to wire up for the test stand so that I can correctly simulate the run vs start circuits to the ICM. With that, I would also buy a ballast resistor to reduce the running voltage to the coil. All "official" diagrams show 1.1 Ohms, but I read 1.35 in a couple forum threads. Looking at the local parts stores, I could get a 1.2 or 1.35 (but not 1.1). Shouldn't really matter much, as the shop manual says that any resistor that tests between 0.6 and 1.6 is OK.

I think having the switch and resistor will help make the wiring more straightforward and similar to the actual truck. Plus, it's relatively inexpensive.

Thank you again for making me think harder about this one, and I appreciate the feedback. I'll keep you updated on what I find.

 

Not sure that it matters, but the diagram I looked at shows one wire to the icm is powered during start, the other during run. Makes me think only one is powered at a time. A one off, and not one I would pursue unless all else fails, is the reluctor in the distributor, think it won't fire if it's 180* out. But being new, I would assume it's right. Have you checked for power at the coil?

 

I had my nose in a few books yesterday, looking at wiring diagrams, and also sat down and mapped out all connections I have on my test stand. My suspicion about it being something obvious was confirmed; I have no power going to the coil. So, to answer your question, no

Being very unfamiliar with my truck's electrical, I had misunderstood the diagrams and assumed I had power going to the coil through the ICM. I've since learned that I was wrong.

I haven't made any physical changes to my test stand yet, but I'm pretty clear on what I have to do. I've ordered a 4-position key which should arrive today. I've also ordered a 1.35 Ohm ballast resistor wire from my local blue and yellow store, which is available for pickup today. I will redo my wiring a bit, incorporating the resistor in the 'run' position for the coil, and having separate 'start' and 'run' connections to the ICM (white and red, respectively). In addition, I am thinking I will add a ground (besides the distributor ground) by grounding the black wire of the tach connector. This black wire is already connected to the distributor ground and goes into the ICM as well. I figure this can only help ensure I have a good ground on the ignition side of the system.

If it is helpful to someone else down the road, I've attached the diagrams which helped me the most. I hope to make my changes in the next days and do another spark test. I'll keep you updated.

 

I thought you said you took the harness from the engine bay to connect the distributor to the icm?

 

Yes, correct. Three of the four pictures I posted unfortunately don't show this accurately in that they don't show a break between the engine bay harness and the ignition key. In reality, this harness connects the ICM / Distributor / Coil together of course, but also has a 4-pin connector which connects to the instrument panel harness and key to coil (+). The orange-ish diagram from Gary's site does show it accurately, and has connector C325 which is the 4-pin. I don't have the IP harness in my test stand setup, so this 4-pin connector is not hooked to anything at the moment - and the power from the battery to the coil (+) terminal goes through this. Therefore, to correct my issue, I need to connect the battery (+) to the pin in this connector which goes to Coil (+). The other 3 pins are for the coolant sensor, oil pressure sensor, and the 4th I'm not sure yet lol

Anyway, I will actually have 2 wires going to the coil (+); one from the "run" position of the key with ballast resistor, and one from the "start" position without ballast resistor (full 12V). I gave myself a big headache yesterday, but I feel confident that I've looked at the diagrams long enough now to understand what I did wrong, and how to correct it.

 

Resistor bypass during cranking. Mine was disconnected when I got the truck, haven't gotten around to adding it back to the coil + yet.

 

RESOLVED!!

Good news! I have spark! seems that having power to the coil is important

My resolution was as expected; I added a 4-position ignition switch (although "accessory" wasn't necessary) and fed battery (+) to it, and ran wires from the "start" position of the ignition switch to the starter solenoid "s" terminal, to the white wire of the ICM, and to the red wire of the coil (coil (+)). I then ran wires from the "run" position of the ignition switch to the red wire of the ICM, and again to the red wire of the coil but with the 1.35 Ohm resistor in line (resistor bypass during cranking).

I also added a ground from the tach black wire to the same ground as my solenoid and battery. Not sure if this made any difference but I could always disconnect it to test.

Next it is time to add fuel to this fire!!! Stock carb was rebuilt and has been bench adjusted, but I'm sure it's not in tune. Distributor was stabbed with 10 degree advanced timing, but again this will probably need to be fine tuned once it is running. I'm just hoping everything is "close enough" to last the 20 minute cam break-in period. I have coolant and oil in already. I need to temporarily hook up my exhaust so I don't go deaf (or anger the neighbors too much) and to get the fumes out of the garage.

I thought about making a more detailed write-up on my home-made test stand and wiring in case someone else down the road wants to do the same. Good idea or waste of time?

 

Too easy, tear it apart and do it again lol

Write ups are always worth it, just put the description in the title so it's easier to search for.

 

Well, you get your wish... sort of. Tried starting it today and realized I have starter run-on. Meaning, the starter engages when the key is turned to the “start” position, but does not disengage when turned back to the “run” position.

I have a few things to check...

Motor started well, considering the tuning is just in the ballpark right now. No bad noises or leaks. 55 PSI oil pressure at 2k RPMs. I had a quick disconnect to bypass the starter run-on issue, but only ran the motor for 2-3 minutes, tops. I had a minor issue with my upper radiator hose, so I didn’t get to run as long as I wanted. I want to correct the starter issue before I give it another go. But in general the first start in 3 years was promising!!!

I’ll keep you posted.

 

It's probably just your connections. Bad, loose, or corroded connection adds enough resistance to increase amp draw passed what the relay can switch. Low battery can do it as well. Instead of the switch, just keep a screw driver nearby and wop it between the eyes with the handle. My cables are bad enough that I'm right there at the switch limit, so if underhood temps are up, or it takes an extra tenth of a second to start, mine will run on. I have the door open, hood pop, reach into console for special screwdriver technique down to a fluid motion. They also smell fear, like bees and dogs.

 

I agree, it gets to be muscle memory after a while I always tried not to look at mine too intently, it might take that as a challenge and decide to make me walk home thinking about the consequences of my actions.

The PMGR starter upgrade is worth it for that exact situation. I was really impressed just doing my break in last night. Engine kicks over much faster and easier than it ever has before, even when the relay and starter were both brand new. And the old fender relay is just operating the solenoid on the PMGR starter. I did have to get a 60" 4 AWG cable from AutoZone as my factory one was too short. But I think I will sleep a little easier.

 

Yeah, been thinking about it myself. And those things do smell fear. If you hesitate with the key and your cables are as bad as mine, it'll do it every time.

 

I think (hope) I’ve solved my stuck relay issue! All tests with my meter show all the right voltages in all the right places at all the right times haha! And a live test with the starter connected also worked as expected (no run-on).

The cause; I had voltage back feeding my start circuit through the run circuit. This is because both have a common connection at the coil. But, since the run circuit has a resistor, and only gives 6.6 Volts to the coil, it was not enough to open the relay when the key was first turned to run. However, this 6.6 Volts was enough to hold the relay open (or prevent it from closino) after the full 12.8V was applied in the start position.

My solution; I installed diodes in both circuits to prevent any voltage back feeding. I used a diode normally intended for use on an alternator (Chevy I believe).

I have a couple small unrelated tasks to do before I attempt my cam break in again. I’ll keep you posted!