1088A1 Starter Problem

[abfisher1798]

No response from start button, same for the remote start switch.

I jumped the auxiliary solenoid and it started right up.

I've looked through older posts and found a lot of info that applies mostly to 1078. My M1088A1 has a the printed circuit PDP and the relay ID's are different.

Can someone point me in the right direction?

 

[SausageGuy]

No response from start button, same for the remote start switch.

I jumped the auxiliary solenoid and it started right up.

I've looked through older posts and found a lot of info that applies mostly to 1078. My M1088A1 has a the printed circuit PDP and the relay ID's are different.

Can someone point me in the right direction?

Swap relays around till one lets you start.

 

[Ronmar]

Yea, they do it different on the A1. When you turn on the main switch do K11(alt excite) and K26(neutral start) energize? K11 gets it’s power from CB77 via the neutral start relay K26. K26 gets powered by the transmission controller and feeds K11 pin 86.

The K11 coils path to ground is thru the oil pressure switch on the block. So if the trans is in neutral when you turn on the main switch, K26 should energize and with no oil pressure K11 should also energize. The energized contacts of K11 feed the power to the start switches which in turn feed power to the aux start relay to crank the starter when they are pressed. Once the engine starts, the oil pressure switch opens, de-energizing K11, which shifts the starter switch power to the alternator, disabling the starter on the now running engine, and energizing the alternator...

 

[Ronmar]

There is a A1 schematic up in the tech manual section near the manuals for the A0...

This page shows the start control circuit...

 

[abfisher1798]

Yea, they do it different on the A1. When you turn on the main switch do K11(alt excite) and K26(neutral start) energize? K11 gets it’s power from CB77 via the neutral start relay K26. K26 gets powered by the transmission controller and feeds K11 pin 86.

The K11 coils path to ground is thru the oil pressure switch on the block. So if the trans is in neutral when you turn on the main switch, K26 should energize and with no oil pressure K11 should also energize. The energized contacts of K11 feed the power to the start switches which in turn feed power to the aux start relay to crank the starter when they are pressed. Once the engine starts, the oil pressure switch opens, de-energizing K11, which shifts the starter switch power to the alternator, disabling the starter on the now running engine, and energizing the alternator...

Awesome! I’ll get to work on this in the morning.
After I jumped the solenoid and let the engine run for about 20 minutes, the voltage gauge began to show a decrease. With the engine running, I put a meter to the 24v and 12v lugs on the PDP and noticed a decrease (23.5 and 11.9). Is this related? Is there another potential faulty relay that is preventing to alternator from charging? Or do I have a bad alternator?
Thanks for the help!

 

[Ronmar]

Awesome! I’ll get to work on this in the morning.
After I jumped the solenoid and let the engine run for about 20 minutes, the voltage gauge began to show a decrease. With the engine running, I put a meter to the 24v and 12v lugs on the PDP and noticed a decrease (23.5 and 11.9). Is this related? Is there another potential faulty relay that is preventing to alternator from charging? Or do I have a bad alternator?
Thanks for the help!

No, this is the same problem. Pin 30 on K11 gets power from CB77. When energized, K11 sends power to the start switches From it’s pin 87. When it de-energizes after engine start and reaching 15PSI of oil pressure, it sends that same CB77 power thru it’s de-energized contacts(pin 87A) to turn on the alternator... this symptom tells me you probably have something wrong with CB77 power or the switched 24v ignition power which comes from K1, but K1 would cause other issues as well. If the CB77 power is missing, it would cause both your problems...

 

[abfisher1798]

No, this is the same problem. Pin 30 on K11 gets power from CB77. When energized, K11 sends power to the start switches From it’s pin 87. When it de-energizes after engine start and reaching 15PSI of oil pressure, it sends that same CB77 power thru it’s de-energized contacts(pin 87A) to turn on the alternator... this symptom tells me you probably have something wrong with CB77 power or the switched 24v ignition power which comes from K1, but K1 would cause other issues as well. If the CB77 power is missing, it would cause both your problems...

You are Man of the Hour!
A few days ago I was about to give up on this project. After some troubleshooting with the relays per your suggestion, I drove that same truck through town, and it runs like a champ!
No other outstanding electrical issues that I can see. It operates as it should. What a great machine!

Thanks very much for your help. You are among those that make this forum work.

I owe you!

 

[Third From Texas]

You are Man of the Hour!

He keeps providing all these amazing answers.

We suspect that he may be the inventor.