ISA not working , 2.5 L

[HellCreek]

I know this topic has been beaten to death, but this one is a little strange.  I changed my ISA with a new one, replaced my intake/exhaust gasket and torqued the bolts, changed all of the vacuum hoses, cleaned the TB and replaced all the gaskets and o-rings. 

 

The problem is, as the title suggests, the ISA is not working.  It does not fully extend when I shut off the motor like it is supposed to.  I can extend and retract the shaft  with a 9 volt battery, so the motor is working.  With the ISA unplugged, I have extended the shaft with a 9 volt battery, left it unplugged and started the engine.  It revved up to 3500 RPM, so I shut off the engine, plugged the ISA back up and restarted the engine.  The RPMs stayed at 3500 and would not come down.  I took it for a test drive, and when I returned, the RPMs were still 3500.  I order to be able to drive it, I unplugged the ISA, retracted the shaft with the 9 v battery, and the RPMs now are at 800. 

 

I hate it when things don't work properly, so I would really appreciate some help figuring this out.  I suspect an electrical issue.  I have already checked the Closed Throttle Switch, and it is in spec according to the FSM.

 

This is a 1989 MJ Sporttruck with a 2.5L engine and a manual transmission.

 

Thanks,

Tom

[eaglescout526]

Ok. ISA. There. IAC is for the 4.0L which is the Idle Air Control. 
2.5L has the ISA which is the Idle Speed Actuator. 
Yes I’m making a stink cause there is a difference and 4.0L guys would get confused and try to help you with something they have never touched. 
 

Anywho! If it’s not working like you should and since you verified the motor is working, I would highly suspect the wiring to have damage to it. Either heat or corrosion somewhere. If someone doesn’t post a pin out of the ISA to ECU plug I will get one this evening so you can do a continuity check to make sure there is a break or not. 
 

Worst case is there is a exposed wire, it grounded to the engine or intake and fried the circuit that controls the ISA in the ECU. 
 

Unless you did an HO swap where you would have the IAC.

[HellCreek]

Thanks for fixing that.

 

ISA, I stand corrected.

[eaglescout526]

No problem. Just thought of this. Check to see if you have good continuity to ground. 
 

Once I get home I’ll find the pin out for the ECU so we can test continuity from the ECU to the ISA 

[eaglescout526]

 

Pins 23, 24 and 25 along with making sure it has a good ground. 

[HellCreek]

I will check that when I get a chance. 

By the way, how do you jumper the diagnostic sockets (near the battery) to cycle the ISA motor?  I'm having to do that at the motor itself.  I can completely overhaul an engine, but I know nothing about electronics.

 

Thanks,

Tom

[eaglescout526]

3 hours ago, HellCreek said:

By the way, how do you jumper the diagnostic sockets (near the battery) to cycle the ISA motor?  I'm having to do that at the motor itself.  I can completely overhaul an engine, but I know nothing about electronics.

 

[HellCreek]

When I said that I knew nothing about electronics, I meant it.  I need to know the basics, like - connect one end of the jumper wire to "x" and the other end to "y".

[HellCreek]

Does any one know where the jumpers go?

[eaglescout526]

2 hours ago, HellCreek said:

Does any one know where the jumpers go?

Actually don’t test it from there. I fried an ECU doing that. You’ll need to either take it off the throttle body or you can get it to extend and retract while it’s still installed. 

[HellCreek]

HI,

 

Thanks.   Actually, I did remove it from the throttle body, and the motor does extend and retract the shaft.  It won't activate on the truck when I turn the key off though.  Also, if I extend it manually, it won't retract and idle down on its own either.

[Ωhm]

Check B+ Latch Relay. Used for resetting the ISA at ENGINE OFF. Use a known good relay or swap your relays around with one another. See if problems follow relay.

[HellCreek]

I swapped both relays for new ones, since I didn't know which one was which.  The ISA still did not extend. 

[Ωhm]

B+ Latch Relay is a tough circuit to figure out. B+ Latch Relay will have two (2) pink wires in C215_4 and C215_5. Use this to help with ID.

KEY OFF

Check for voltage at C215_1. Looking for 12vdc (HOT at all times).

 

 

[HellCreek]

C215_1 has 12.2 volts.  It was the relay towards the cab.  The one in the front is the fuel pump relay.  This is backwards per the FSM.  Since I switched both relays, they both should be good.  ISA is still not working.

 

Thanks,

Tom

[eaglescout526]

We will have to suspect theres a break in the wire from the diag connectors or a break from ECU to ISA. Or worst case, the ECU circuit that controls the ISA is no longer able to function. I.E. a resistor blew.

[HellCreek]

Hi,

 

The ISA functions manually, that is, I can make it extend and retract using a 9 volt battery wired directly to the motor.