Mechanics

POOR PERFORMANCE

1989 Nissan Truck • 4 cylinder 2WD Automatic • 139,000 miles

My 89 nissan D21 Z2.4 with automatic seems to be in the "limp home" mode. Engine does not rev normally and transmission shifts hard - much like the old auto's with a bad vacum modulator. It starts and runs smoothly, but has reduced power, poor acceleration and poor fuel economy. In checking the wiring I found wires from what appears to be the thermostat housing that are tied together. There is a plugin connector that looks like it would have connected to the "connected" wires from the thermostat. Why would someone do this?
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Cactus50
May 9, 2011.




The thermostat is not electrical in any way. You might be looking at a temp sensor or something and if so, that will have a major effect on you fuel mixture.

Wrenchtech
May 9, 2011.
There is also no power to the wire going to the base of the distributor, so if a sensor is disconnected does the system default to the "limp' mode?

Tiny
Cactus50
May 9, 2011.
In some cases it will ignore the sensor reading and substitute a default reading for it but not all sensors or computers are programmed that way.

Wrenchtech
May 9, 2011.
Checked the wires a little closer and they go to a temp sensor below the thermostat housing. Also, they are not wired together but directly to other wires without a plug. Which sensor/s would be suspect here?

Tiny
Cactus50
May 10, 2011.
You would have to see the data from every sensor to answer that question.

Wrenchtech
May 10, 2011.
Should the ECM provide codes for this and how would you access them? I looked at the ECM and it has a switch on the side and a window with red/green lights, but could not get it to respond.
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Tiny
Cactus50
May 10, 2011.
Those early computers did supply a whole lot of info compared to today's. They wouldn't necessarily set a code.

Wrenchtech
May 10, 2011.
The haynes manual says to set the switch to the "display" mode (switch only has 2 positions -run & display) in the display mode the red and green lights are supposed to flash one at a time to generate the stored codes, but nothing happens.

Tiny
Cactus50
May 10, 2011.
That probably means that there are no codes stored. If you didn't have a check engine light on, I wouldn't expect any.

Wrenchtech
May 10, 2011.
OK, then my main concern is for the lack of power to the distributor. This engine has the double plugs and 2 coils -which are obviously working as the engine does run. However the only other wire to the distributor goes to a spade plug at the base of the distributor. I assume this goes to the crank angle sensor - anyway, the manual says it should have voltage and it does not at any time. Using ohm meter traced the wire back to a relay which has power but must not be getting activated or something. Relay has been checked and is good. Am thinking it must need a signal to energize the circuit. If this is the crank angle sensor and it does not work, it would explain the symptoms shown. How can I test the sensor/relay or?

Tiny
Cactus50
May 10, 2011.

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