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On the passenger side engine compartment on my 89 yj 2.5 liter there is some diagnostic plug in connectors. which one is the connector for the isa motor control?  Which one is D-1 and D-2?   How are each individual holes in connectors numbered ( 1-2-3-4-5-6 etc>)?

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Thunderbolt1078...Below is a PDF layout for the diagnostics ports, which outlines the ISA motor terminal you want to access.  Ports and plug terminals are each numbered...Note that your 1989 Jeep YJ Wrangler is the Model 81 (2.5L TBI equipped) plug layout (Fig. 97 at bottom of the page); the XJ/MJ Cherokee and Comanche 2.5L TBI is the upper layout (Fig. 96 for Models 60/70). 

I also included the ECU plug layout, as that could be another need.  The ECU plug layout is for a Model 81 with a 2.5L TBI engine like yours:

Jeep YJ-XJ 2.5L TBI Diagnostics Ports.pdf

Moses

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Thank you Moses the diagnostic port Diagrams were very helpful. I just have one more question. I hooked up a Snap on MT2500 scanner to my 89 jeep yj and everything checked out and read "ok to drive" but the EGR valve read "open" the whole time the engine was running at idle(idle read 880 rpm) and i removed the vacuum hose at the EGR valve with no change to the reading. Shouldn't the valve read closed at idle?

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Thunderbolt1078...You're welcome...Below is a PDF of your 2.5L TBI engine's vacuum circuit.  Zoom into the (upper) Fig. 8 for details. 

Note that for vacuum to reach the EGR valve, it originates at the throttle body (a ported vacuum source) and goes to the EGR/Canister Solenoid.  After the solenoid, vacuum goes through a vacuum "T" to 1) the EVAP canister Purge Signal in one direction and 2) the EGR Valve in the other.

Jeep YJ Wrangler 2.5L TBI Engine Vacuum Circuit.pdf

The vacuum source is the throttle body, and for vacuum to reach the EGR valve, it must pass through the EGR/Canister Solenoid without any vacuum loss or bleed-off.  The same applies at the canister purge.  Vacuum must not bleed off here.  If there is a vacuum loss, the EGR valve will not have adequate vacuum.

Check the vacuum each step on this circuit.  Begin at the throttle body:  Confirm whether this is manifold vacuum or ported vacuum.  Ported vacuum means that the vacuum only applies as you open the throttle, then vacuum tapers off around 1/4 throttle opening.  Confirm and test the TBI vacuum port shown in the diagram.  Note whether this is ported vacuum or manifold vacuum (continuous vacuum regardless of throttle setting).  The function of the EGR/Canister Purge solenoid suggests that this TBI port is manifold vacuum, present at all throttle settings and highest at an idle, tapering off as the throttle opens wide.

The EGR/Canister Purge solenoid is the gateway for vacuum to the canister purge port and the EGR valve.  Factory statement:  "The solenoid is energized during engine warm-up, closed throttle (idle), wide open throttle and rapid acceleration/deceleration." 

Note:  Energized means the valve is closed!  You don't want EGR function during engine cold start and warm-up, when closed throttle/idling, during wide open throttle or under rapid acceleration and normal deceleration.  Yes, the EGR valve should read closed when the engine is idling if the solenoid is working properly.

If the solenoid is disconnected or always open, vacuum will flow continuously to the EGR valve and Canister Purge.  Make sure the EGR/Canister Solenoid opens at the right time to allow vacuum pull past the solenoid.  Check vacuum at each side of the solenoid.  Test the solenoid's function.  This system depends upon the EGR/Purge Canister Solenoid to activate the EGR valve at the right times.

Finally, make sure the EVAP system works properly and that the canister purge vacuum does not leak off to atmosphere.  Check the EVAP's vacuum system for any leaks or disconnects...Each vacuum section must be intact and functioning properly for vacuum to reach the EGR valve.  

Moses

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