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?

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

18 Replies

Tiny
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
Tiny
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This isn't something that you're going to be able to diagnose over the Internet. It's going to take some in-depth on site testing.

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Tuesday, May 10th, 2011 AT 7:41 PM
Tiny
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Well, the ecm did flash a code of sorts. It went through a sequence of 1, 2, 3, 4, 5 then repeats. However haven't been able to locate a list of codes for this model. Also, found that disconnecting either of the two coils makes it run much smoother. Close examination of the plug wires shows several spot that are worn thin on the insulation so will replace wires, plugs, cap& rotor.

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Wednesday, May 11th, 2011 AT 1:48 PM
Tiny
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Worn thin? Plug wires have to be in perfect condition. Any exterior damage at all and they have to be replaced.

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Wednesday, May 11th, 2011 AT 2:03 PM
Tiny
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Replaced plugs, wires, rotor & cap: still runs rough with both coils active, smooth with just one - doesn't matter which one is unplugged or if you run it on the intake or exhaust side plugs. Also noticed that the large "biscuit" round 6" dia. With large hose connecting to the AVI controler and the exhaust gurgles like it has water in it. There is also large water drops beneath this unit

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Thursday, May 12th, 2011 AT 2:07 PM
Tiny
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Check your firing order.

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Thursday, May 12th, 2011 AT 2:36 PM
Tiny
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Did for both sides and it is correct. I am having trouble understanding why it will run smoothly if you disable either set of plugs. I thought there might be some cross firing from wires running
adjacent to each other, but have the new wires spread out so that should not be an issue.

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Thursday, May 12th, 2011 AT 4:03 PM
Tiny
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That is exactly why I said to re-check the firing order.

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Thursday, May 12th, 2011 AT 4:44 PM
Tiny
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Re-checked firing order and it is correct for o both intake & exhaust sides. When running rough it is producing black exhaust - lots of carbon - and smells almost like raw fuel- not oily. When running smooth the exhaust is clean.

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Monday, May 16th, 2011 AT 11:42 AM

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