POOR PERFORMANCE

  • Tiny
  • cactus50
  • 1989 Nissan Truck
  • 4 CYL
  • 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?

Monday, May 9th, 2011 AT 3:05 PM

18 Answers

  • Tiny
  • Wrenchtech
  • Expert
  • 19,583 posts

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.

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Monday, May 9th, 2011 AT 4:03 PM
  • Tiny
  • cactus50
  • Member

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?

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Monday, May 9th, 2011 AT 4:21 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,583 posts

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.

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Monday, May 9th, 2011 AT 4:23 PM
  • Tiny
  • cactus50
  • Member

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?

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Tuesday, May 10th, 2011 AT 4:08 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,583 posts

You would have to see the data from every sensor to answer that question.

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Tuesday, May 10th, 2011 AT 4:12 PM
  • Tiny
  • cactus50
  • Member

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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Tuesday, May 10th, 2011 AT 4:55 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,583 posts

Those early computers did supply a whole lot of info compared to today's. They wouldn't necessarily set a code.

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Tuesday, May 10th, 2011 AT 4:57 PM
  • Tiny
  • cactus50
  • Member

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.

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Tuesday, May 10th, 2011 AT 6:57 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,583 posts

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

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Tuesday, May 10th, 2011 AT 6:59 PM
  • Tiny
  • cactus50
  • Member

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?

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Tuesday, May 10th, 2011 AT 7:30 PM

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