Sleuths Needed: The Intermittent Start Devil is on me again!

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FWIW, the starting circuit on this truck is pretty simple.

The power side of the starter motor solenoid is a direct run from the positive battery terminal.

THe logic side of the circuit is battery/fusible link/ignition switch/NSS/starter.

If you are hearing the starter solenoid close, then the logic side checks good. Either you have bad starter contacts/plunger in the starter or there is no direct connection to the battery or there is a bad ground from the starter motor to the block.
 
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Nice. Can you post a drawing or an explanation with details of how you went about installing the relay? Like a schematic of your circuit, or just written details. I'm always at a loss of how to tap into, or splice into wires properly.

In the link, there are installation instructions that you can click on and follow.
 
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FWIW, the starting circuit on this truck is pretty simple.

The power side of the starter motor solenoid is a direct run from the positive battery terminal.

THe logic side of the circuit is battery/fusible link/ignition switch/NSS/starter.

If you are hearing the starter solenoid close, then the logic side checks good. Either you have bad starter contacts/plunger in the starter or there is no direct connection to the battery or there is a bad ground from the starter motor to the block.


Nope. That's not any of it. I've been through that many many times
 
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I think I have finally fixed my intermittent start problem, hopefully this will help you with yours. I found this thread from last year:

https://forum.ih8mud.com/80-series-tech/211786-starter-ignition-circuit-thought.html

which basically says that the stock ignition wiring degrades over time, and that the intermittent start with the click at the starter might occur when there is not enough power to activate the solenoid on the starter. The suggested remedy was to add a new solenoid with heavier guage wire going to the starter solenoid.

I had already replaced the starter, battery, battery cables and grounds, so the ignition circuit was my last hope.

I bought a 50 amp fuse, an ST 81 starter solenoid switch from NAPA, and some 10 and 12 gauge wire with connectors. I ran the 10 gauge wire through the 50 amp fuse to the new solenoid and from the new solenoid to the solenoid connector on the starter. I connected the ignition circuit to the new solenoid with 12 guage wire.

For the first time in as long as I can remember the truck starts as soon as the key is turned.

there is an extra post on the ST 81 solenoid that is not used so I taped it off. It also grounds to the body instead of a dedicated post. The original thread lists some better options(ST 80, ST 85 and others) that ground to a post instead of the body, but this was the only one in stock so I bought it.

I still have to clean up the mount and wiring but here are some pictures to give a better idea of what I did.

View attachment 370606

View attachment 370607

Funny... in the link you posted... someone in that thread posted a link to my original thread :)
 
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Nope. That's not any of it. I've been through that many many times

LOL. Well since there is nothing else in the circuit I'd say it's definately one of those...

Its possible that the logic side is not getting a good +12 to the solenoid logic and the solenoid isn't engaging all the way. That needs to be checked under load with a meter. Pull the +12 line off the battery so she doesn't crank the motor.

I don't see what adding a relay where there was none can help anything. That's adding another contact point. The only advantage that would bring to the table would be if the plunger got jammed in the start position as is the case on older starters.

If the +12 run from the battery is suspect then simply run a new one and be done. You can make your own for a few sheckles.
 
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Jon,

In my case I had already replaced everything that was not on the logic side. New Battery, new starter and battery grounds, new +12 to the starter, toyota reman starter - the only thing left was the logic side. It was much easier for me to run a new +12 to the solenoid logic than it was to go through and rewire all of the ignition circuit. Also, checking the voltage with a meter would have taken more effort than wiring in the new relay and would have required a helper.

I haven't had a single no start episode since I added the new relay, so I feel pretty certain that I found the problem with mine.
 
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I find these 2 statements very interesting.

Adding a relay will get good 12v to the solenoid logic.

Repairing/replacing the ignition wiring would also get a good 12v without adding something else to fail, but it would be a lot harder than just adding the relay IMO. But the relay/solenoid does add something else that can fail, and I feel pretty sure the solenoid I added won't last as long as the stock ignition wiring.
 
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Jon,

In my case I had already replaced everything that was not on the logic side. New Battery, new starter and battery grounds, new +12 to the starter, toyota reman starter - the only thing left was the logic side. It was much easier for me to run a new +12 to the solenoid logic than it was to go through and rewire all of the ignition circuit. Also, checking the voltage with a meter would have taken more effort than wiring in the new relay and would have required a helper.

I haven't had a single no start episode since I added the new relay, so I feel pretty certain that I found the problem with mine.

Aha. Maybe I should have read your posts more carefully. I was assuming you put a relay in line with the +12 from the battery to the solenoid. Couldn't figure why you did that one...sorry.

In your setup what throws the relay? The existing start logic I assume. Where did you tap in?
 
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You diagnosed where the problem is, but you didn't fix it. That start logic circuit feeds the ECU in 3 different places, the cold start injector, the cold start injector time switch, and the circuit opening relay. If there is a problem somewhere in there, the correct choice (in my opinion) is to fix it. It's possible that you are masking another problem that can come and bite you at a later date.

I'm not busting on you for what you did, I'm just saying I would have taken a different approach. There are only a handful of connectors between the battery and the starter and they're not too hard to get to.
 
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You diagnosed where the problem is, but you didn't fix it. That start logic circuit feeds the ECU in 3 different places, the cold start injector, the cold start injector time switch, and the circuit opening relay. If there is a problem somewhere in there, the correct choice (in my opinion) is to fix it. It's possible that you are masking another problem that can come and bite you at a later date.

I'm not busting on you for what you did, I'm just saying I would have taken a different approach. There are only a handful of connectors between the battery and the starter and they're not too hard to get to.

There's one connector that's a bitch to get to. The connector that leads to and from the PARK/NEUTRAL POSITION SW is a bitch to get at in a '94. It's located above the starter and below the PHH. I unplugged the NSS side of the connector with one hand barely. You can snake it back out with some effort. The other side of the connector is next to impossible to do anything with unless you drop the transmission or something like that. It'd be easier to wire the relay circuit in and be done with it.

I'm all about practicality at this point, but also the efficiency of my dollar and time. If it was easy to fix the problem properly, I'd definitely do it without a doubt. Relay install sounds practical on just about every level.
 

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