I'm helping my son with a problem he's having with excessive gas
consumption (6 mpg average) on his '87 Wrangler YJ with 2.5L and TBI.
I have the Chilton's and Haynes manuals for the YJ and armed with my
limited knowledge of auto mechanics we're looking for the cause of the
problem.

In addition to the low mpg, it also starts hard and has a strong
exhaust smell so I suspect it's getting too much gas but I'm not sure.

He has 33 x 12.50 tires, a 3-3.5" suspension lift and a 1" body lift
installed. When I tell anyone the size of his tires they tell me that
is the cause of the bad mileage, but I don't want to assume that's the
whole cause. He has a friend with a '92 YJ with 2.5L and the same size
tires and he gets around 17mpg.

It had an O2 sensor shorted, which has been replaced by a repair shop.

There is a missing hose from the air filter box to the manifold. I'll
replace it since it looks like it could cause problems running while
the engine is cold.

The big mystery is a sensor that is still wired in but removed from
the engine. From the diagrams and pictures I think it's the air
temperature sensor but I'm not sure. It has two wires connected to it;
one comes from the wiring harness (tan) to one side of the sensor, and
the other side of the sensor (brown) goes back to the harness and to
another sensor which might be the coolant temperature sensor. From my
limited description, can anyone tell what this sensor is, and should
it be in the engine? The YJ had gauges added to it, and I suspect when
they were added, this sensor was removed to install the one for the
new gauge (there is a sensor in the vicinity of the loose sensor with
a red wire on it going to the gauges).

This sensor does not have the typical connector on it. It appears
someone has spliced the connections, possibly after removing the
connector.

I don't have the equipment to determine what codes are being reported,
is it worth buying or is it less expensive to have a shop check this?

 

The codes you can get out of th '87 are so limited that a reader is
useless. All of the (limited) info is available at the plug in's on the
rhs hood hinge using a voltmeter.

I have the factory wiring manual for an '87 that shows the wire colors as
well as all the plugs and pin out's at the plugs. There is a wire pair
tan and brown with trace that goes to the Coolant temp sensor. If this
puppy is removed, the computer thinks the engine is not up to proper temp
and makes the mix extra rich to compensate. Gas mileage goes to zero! This
is a different sensor than the temp sender for the gauges.

There is also an air temp sensor that uses tan with trace and brown with
trace.

I can scan a page or two, contact me off line.

Cheers.

dgassocdelete@pobox.com wrote:

> I'm helping my son with a problem he's having with excessive gas
> consumption (6 mpg average) on his '87 Wrangler YJ with 2.5L and TBI.
> I have the Chilton's and Haynes manuals for the YJ and armed with my
> limited knowledge of auto mechanics we're looking for the cause of the
> problem.
>
> In addition to the low mpg, it also starts hard and has a strong
> exhaust smell so I suspect it's getting too much gas but I'm not sure.
>
> He has 33 x 12.50 tires, a 3-3.5" suspension lift and a 1" body lift
> installed. When I tell anyone the size of his tires they tell me that
> is the cause of the bad mileage, but I don't want to assume that's the
> whole cause. He has a friend with a '92 YJ with 2.5L and the same size
> tires and he gets around 17mpg.
>
> It had an O2 sensor shorted, which has been replaced by a repair shop.
>
> There is a missing hose from the air filter box to the manifold. I'll
> replace it since it looks like it could cause problems running while
> the engine is cold.
>
> The big mystery is a sensor that is still wired in but removed from
> the engine. From the diagrams and pictures I think it's the air
> temperature sensor but I'm not sure. It has two wires connected to it;
> one comes from the wiring harness (tan) to one side of the sensor, and
> the other side of the sensor (brown) goes back to the harness and to
> another sensor which might be the coolant temperature sensor. From my
> limited description, can anyone tell what this sensor is, and should
> it be in the engine? The YJ had gauges added to it, and I suspect when
> they were added, this sensor was removed to install the one for the
> new gauge (there is a sensor in the vicinity of the loose sensor with
> a red wire on it going to the gauges).
>
> This sensor does not have the typical connector on it. It appears
> someone has spliced the connections, possibly after removing the
> connector.
>
> I don't have the equipment to determine what codes are being reported,
> is it worth buying or is it less expensive to have a shop check this?

 

I would say the same as Roy. If that coolant temp sensor is diconnected
it won't tell the intake to turn off teh choke setting. Just like
running a lawnmower with choke on.

But one more tidbit of info for you. The motor in your 87 is a Puegot
(sp?), the one in your biddies 92 is a Chevy. Just a side note for
future reference. I believe they switched in 1990.

dgassocdelete@pobox.com wrote:

> I'm helping my son with a problem he's having with excessive gas
> consumption (6 mpg average) on his '87 Wrangler YJ with 2.5L and TBI.
> I have the Chilton's and Haynes manuals for the YJ and armed with my
> limited knowledge of auto mechanics we're looking for the cause of the
> problem.
>
> In addition to the low mpg, it also starts hard and has a strong
> exhaust smell so I suspect it's getting too much gas but I'm not sure.
>
> He has 33 x 12.50 tires, a 3-3.5" suspension lift and a 1" body lift
> installed. When I tell anyone the size of his tires they tell me that
> is the cause of the bad mileage, but I don't want to assume that's the
> whole cause. He has a friend with a '92 YJ with 2.5L and the same size
> tires and he gets around 17mpg.
>
> It had an O2 sensor shorted, which has been replaced by a repair shop.
>
> There is a missing hose from the air filter box to the manifold. I'll
> replace it since it looks like it could cause problems running while
> the engine is cold.
>
> The big mystery is a sensor that is still wired in but removed from
> the engine. From the diagrams and pictures I think it's the air
> temperature sensor but I'm not sure. It has two wires connected to it;
> one comes from the wiring harness (tan) to one side of the sensor, and
> the other side of the sensor (brown) goes back to the harness and to
> another sensor which might be the coolant temperature sensor. From my
> limited description, can anyone tell what this sensor is, and should
> it be in the engine? The YJ had gauges added to it, and I suspect when
> they were added, this sensor was removed to install the one for the
> new gauge (there is a sensor in the vicinity of the loose sensor with
> a red wire on it going to the gauges).
>
> This sensor does not have the typical connector on it. It appears
> someone has spliced the connections, possibly after removing the
> connector.
>
> I don't have the equipment to determine what codes are being reported,
> is it worth buying or is it less expensive to have a shop check this?
>
>

 

In message <3F03908F.6010401@mail.no>, "Cash" wrote:

>I would say the same as Roy. If that coolant temp sensor is diconnected
>it won't tell the intake to turn off teh choke setting. Just like
>running a lawnmower with choke on.
>
> But one more tidbit of info for you. The motor in your 87 is a Puegot
>(sp?), the one in your biddies 92 is a Chevy. Just a side note for
>future reference. I believe they switched in 1990.

Where do you guys get this stuff?


>
>dgassocdelete@pobox.com wrote:
>
>> I'm helping my son with a problem he's having with excessive gas
>> consumption (6 mpg average) on his '87 Wrangler YJ with 2.5L and TBI.
>> I have the Chilton's and Haynes manuals for the YJ and armed with my
>> limited knowledge of auto mechanics we're looking for the cause of the
>> problem.
>>
>> In addition to the low mpg, it also starts hard and has a strong
>> exhaust smell so I suspect it's getting too much gas but I'm not sure.
>>
>> He has 33 x 12.50 tires, a 3-3.5" suspension lift and a 1" body lift
>> installed. When I tell anyone the size of his tires they tell me that
>> is the cause of the bad mileage, but I don't want to assume that's the
>> whole cause. He has a friend with a '92 YJ with 2.5L and the same size
>> tires and he gets around 17mpg.
>>
>> It had an O2 sensor shorted, which has been replaced by a repair shop.
>>
>> There is a missing hose from the air filter box to the manifold. I'll
>> replace it since it looks like it could cause problems running while
>> the engine is cold.
>>
>> The big mystery is a sensor that is still wired in but removed from
>> the engine. From the diagrams and pictures I think it's the air
>> temperature sensor but I'm not sure. It has two wires connected to it;
>> one comes from the wiring harness (tan) to one side of the sensor, and
>> the other side of the sensor (brown) goes back to the harness and to
>> another sensor which might be the coolant temperature sensor. From my
>> limited description, can anyone tell what this sensor is, and should
>> it be in the engine? The YJ had gauges added to it, and I suspect when
>> they were added, this sensor was removed to install the one for the
>> new gauge (there is a sensor in the vicinity of the loose sensor with
>> a red wire on it going to the gauges).
>>
>> This sensor does not have the typical connector on it. It appears
>> someone has spliced the connections, possibly after removing the
>> connector.
>>
>> I don't have the equipment to determine what codes are being reported,
>> is it worth buying or is it less expensive to have a shop check this?
>>
>>

 

On Thu, 03 Jul 2003 05:28:54 GMT, bllsht <nospam@invaliddot.net>
wrote:

>In message <3F03908F.6010401@mail.no>, "Cash" wrote:
>
>>I would say the same as Roy. If that coolant temp sensor is diconnected
>>it won't tell the intake to turn off teh choke setting. Just like
>>running a lawnmower with choke on.
>>
>> But one more tidbit of info for you. The motor in your 87 is a Puegot
>>(sp?), the one in your biddies 92 is a Chevy. Just a side note for
>>future reference. I believe they switched in 1990.
>
>Where do you guys get this stuff?
>

We all belong to a secret club, and are endowed with all jeep
knowledge from the dawn of time......some of us in here have forgotten
more about jeeps than most people will ever know.

;-)

I'm not one of them mind you, I have a hard time finding the doorknob
to go to work in the morning.

Hope that answered your questions

Tony

 

Yup, Jeep used both the Chevy four cylinder:
http://www.off-road.com/jeep/tech/engine/gm151.html and V6:
http://www.off-road.com/jeep/tech/engine/gm173.html and of course the
Buick V6: http://www.off-road.com/jeep/tech/en...ntless225.html and
V8: http://www.off-road.com/jeep/tech/en...ntless350.html
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Tony wrote:
>
> Uhhh, a chevy motor?
> In a Jeep? From the factory?
> Does GM know about this?
> Or Chrysler/Jeep/Eagle?

 

On Wed, 02 Jul 2003 22:10:23 -0400, Cash <email@mail.no> wrote:

>I would say the same as Roy. If that coolant temp sensor is diconnected
>it won't tell the intake to turn off teh choke setting. Just like
>running a lawnmower with choke on.
>
> But one more tidbit of info for you. The motor in your 87 is a Puegot
>(sp?), the one in your biddies 92 is a Chevy. Just a side note for
>future reference. I believe they switched in 1990.
>

Thanks for the tip on the engine, we thought it was an AMC built
engine.

I checked the diagrams from Roy and I think it's the manifold air
temperature sensor. See my post to him.

 

On Wed, 02 Jul 2003 17:48:27 -0500, Roy Jenson <rkjenson@qwest.net>
wrote:

>The codes you can get out of th '87 are so limited that a reader is
>useless. All of the (limited) info is available at the plug in's on the
>rhs hood hinge using a voltmeter.
>
>I have the factory wiring manual for an '87 that shows the wire colors as
>well as all the plugs and pin out's at the plugs. There is a wire pair
>tan and brown with trace that goes to the Coolant temp sensor. If this
>puppy is removed, the computer thinks the engine is not up to proper temp
>and makes the mix extra rich to compensate. Gas mileage goes to zero! This
>is a different sensor than the temp sender for the gauges.
>
>There is also an air temp sensor that uses tan with trace and brown with
>trace.
>
>I can scan a page or two, contact me off line.
>
>Cheers.
>

Thanks for the scans Roy. I disconnected the sensor from the circuit
to check it and found it's open.

I don't see any other places in the engine that are open to plug it
into except for the location in the manifold where the temp gauge is
plugged in currently. I'm looking in the book to see where they
normally sensed the temperature for the gauge.

The book said the sensor should measure less than 1000 ohms when the
engine is warm (450 ohms at 160F, 1600 ohms at 100F) so yesterday I
temporarily plugged a 470 ohm resistor in place of the sensor. I know
it may throw off the ECM since it never changes. Last night when he
drove it, he thinks it seemed to run better once he'd driven it for a
few minutes. We'll see how the mileage reacts.