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87 2.5L Hesitation At Crusing

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Truck:  1987 2.5L 2WD Manual (AX-4)


Symptoms:  When driving in 3 & 4th gear, the engine starts to "stall", looses power.  Push in the clutch and rev it a few times, and accelerate seems to cure it 50% of the time. but when cruising again, starts to stall.  Seems ok under hard acceleration.  But then there are times it ran ok.  On the way home tonight kept rev'ing at stop lights since I didn't want it to die and not start.  At home seemed to idle fine.




1) All four spark plugs look similar and of a light brown.  They are "E3" plugs.

2) Checked TPS per Cruisers guide.  Results:

1. Ground test: 0.9 ohms, stable on the "B"terminal.

2. A-B (reference) with key on: .33 volts

3. C-B (Output) with Key on: 5.07 volts.


This seems wrong me since Cruiser's guide indicates my measurements are "opposite".  I checked it twice: once and then again when I couldn't believe the numbers.


I don't want to start adjusting until I figure out what's up with those TPS voltages.


Also, anything else I should check first?

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Temp test: air temp 60 deg (no deep freeze here)


I placed a thermocouple into the radiator hose where it enters the radiator (down stream from the thermostat).


60 deg (start up): idles good, using finger, actuate throttle cable about 3/16 inch to kick up the RPMs to 2000?


135 deg:  I noticed the symptoms returned.  Really chunky running. wants to stall.  if i let it idle, it would have died.  rev it a few times and it was okay.


160 deg. seemed to smooth out


190 deg.  noticed some chunkiness again.


200 deg.  shut it off


This was done in the driveway, parked.  Note, my Thermostat is a premium Gates 195 deg. I replaced last weekend or so.

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I have an infainfrared   is there any way you can take your readings from the line to the throttle body.......that seems to be the angry one with mine.... :dunno:


edit.....just seems to have "cold start" symptoms.....even though you ambiant temp is warmer than the room i am in now.... :thumbsup:

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The coolant temp sensor (CTS) reads "open circuit" ; should be less than 1000 ohms.


The manifold air temp (MAT) reads "open circuit" ; should be less than 1000 ohms.


That seems really strange to the point I wasn't sure if I was doing it right:


1) I disconnected the sensors and probed across the pins at the connector

2) I confirmed the ohm meter was working properly by touching probes together ( 0.00 ohm).


->same result "open circuit".


O2 sensor was replaced last year. I have never tested the CTS before. No idea if they worked previously or not. Engine worked ok for the longest time; but these symptoms got really bad today all of a sudden. So bad I will need to drive my wife's truck to work tomorrow...

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I replaced the CTS with the Autozone SU332.


Note, after getting some erroneous readings from my cheapo Multimeter, I used the calibrated Fluke 87V here at work.  The MAT sensor reads 3.4k ohm at 70 deg F.  which agrees dead-on with Hornbrods spec table .  So the MAT "seems" to be good.  Driving to work today, it ran great.  Ill report back in a couple of days.


Note to self:  make sure test equipment is reliable before spending money on parts!

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