# 1988 Z24 EGR problem Fails NOX



## coinoprus (Jan 21, 2015)

1988 Nissan Pickup 4WD Z24 engine (California version). Can’t pass CA NOX test. EGR valve tested and is functioning normally. No vacuum from BPT to EGR with engine RPM at 2-3k. BPT Solenoid tests good. With solenoid connection removed, vacuum gets to BPT and EGR. Connect the solenoid and no vacuum. What controls the solenoid? I have been told the throttle position switch tells the ECU to break the ground to the solenoid. Is this correct? BTW by pulling the hose from the EGR to the bottom of the BPT exhaust gas does escape. Engine runs fine btw and passes everything except the NOX level. Watching the screen during the 15 and 25mph test I can see the level bouncing all over the place, but reads high on the readout.



Country: United States
Make (manufacturer): Nissan
Model: 4WD pickup
Year: 1988
Engine (optional): Z24
What have you tried so far? (optional): First problem showed check engine light with EGR and Exhaust gas temperature sensor codes. Pulled, examined and reinstalled sensor and code for it went away. Found distributor cap cratered, replaced it and rotor and check engine light is gone. EGR system still not working correctly as described in question.


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## coinoprus (Jan 21, 2015)

*Need help from Super Tech*

Really need some help here. We've tested the EGR valve, EG temp sensor, BPT, EG cut solenoid, throttle position sensor, water temp sensor and all test good. However, we cannot get the disconnect from the ECM to the EG RC solenoid valve at high rev. Thus the EGR does not get the vacuum from the BPT valve to activate. Thus we can't pass the NOX test. If we disconnect the EG RC solenoid from the ECM everything functions normally. 

What else can be controlling the signal from the ECM to the EG RC solenoid?

How does the throttle position switch play into all this and the SVC control valve solenoid? BTW the ECM only throws the EGR code once the check engine light comes on and that takes a while to happen. Certainly never during testing.


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