I'm having some trouble with this one. My B+ latch relay is receiving power to its coil as it should when the car is running or in run mode, it is receiving approximately 12v. The latch relay works and switches when power is received from the ECU to its coil. However, when I turn the car off from a running state, the 12v on the coil immediately goes away and does not stay for 3-5 seconds as it should. I was suggested to check pin B7 on the ECU to make sure that the ECU is receiving a direct supply of 12v from the battery, so I backprobed the ECU connector and it is receiving 12v. I am becoming more and more convinced that this is an ECU problem. What do you guys think? In anticipation that the ECU might be the issue, I do have the opportunity to purchase an 89' ECU.

early 87 Wagoneer, 4.0, AW4

Thank you all..

 

You might try the RENIX group on Facebook. Nick Risley often will reply to ECU related questions.

 

While pin B7 gets power from the battery, Pin B10 provides power to the B+Latch relay on Pin 5. Pin 2 on the relay (ground) then goes back to Pin A9 on the ECU. Battery voltage through a fusible link from the starter relay provides power to the switch side on the relay Pin 1. Pin 4 on the relay also runs to the diagnostic connector D2-5.

If you don't have it, you can find the Renix manual and the 1988 FSM on Cruiser 54's site.

 

Thanks for the reply! I'm getting 12v from Pin B10 to Pin A9 (I've been measuring from the Diagnostic Port). The relay is also working and switching the battery voltage. The whole system is working except for the fact that when you kill the car, the 12V across B10-A9 goes away instantly, rather than staying for 3-5 seconds and then disappearing. Essentially, the "time delay" function does not appear to be working. I've got the 88FSM, and also found the Renix MPFI manual on Cruiser's website, the latter is priceless information..

The other day, I found an 89 ECU for a decent price, so it will be here sometime next week.

 

B+ Latch issue is solved. New ECU fixed the problem. I guess the time delay function inside the old ECU was bad. Interesting failure.

What's interesting, is that when measuring from D2-5 to D2-3 on the diagnostic connector. With the old ECU, I was getting around 12v when running, and with the new one, I'm getting close to 15v. Then when I kill the engine, the 15 drops to 12 and stays around 12 for 3-5 seconds.