Update on mystery problem changed....

'91 Wrangler with a 4.0 and manual tranny

Had some trouble about two weeks ago with cutting out as I was driving
down the road. Changed the Crank Position Sensor, and it worked fine
for a couple days, then cut out once more, waited 10 seconds then it
started up again and ran excellent for another week, no more cutting
out...Then, some other problems started. The engine now has
drastically reduced power. It won't go over 60 on the higway, and at
highway speeds it sounds kind of like one of those import cars with an
aftermarket exhaust pipe. The mechainic can't figure out whats
wrong...

After a week of leaving it with him, the only thing his computer would
tell him is that the timing would not increase as it should. - Does
this new info tell anyone anything?

Please help me!
Phil

Also, the fuel filter was changed, even though he (mechanic) said it
was clear. As for the fuel pump, his computers showed that it had the
proper fuel pressure and volume. He did mention that some people have
that done every 100,000 miles as preventative maintenance, but I don't
want to put another of those in if I don't have to.

Thanks again for all the help (I'm stumped), you guys are great,
Phil

Hi Phil,
The computer (Powertrain Control Module) is responsible for spark
advance, so it is either in the safe mode because one the sensors like
the Cam Position Sensor in the distributor is bad, or it's self.
God Bless America, Bill O|||||||O
http://www.billhughes.com/

Mariner15 wrote:
>
> '91 Wrangler with a 4.0 and manual tranny
>
> Had some trouble about two weeks ago with cutting out as I was driving
> down the road. Changed the Crank Position Sensor, and it worked fine
> for a couple days, then cut out once more, waited 10 seconds then it
> started up again and ran excellent for another week, no more cutting
> out...Then, some other problems started. The engine now has
> drastically reduced power. It won't go over 60 on the higway, and at
> highway speeds it sounds kind of like one of those import cars with an
> aftermarket exhaust pipe. The mechainic can't figure out whats
> wrong...
>
> After a week of leaving it with him, the only thing his computer would
> tell him is that the timing would not increase as it should. - Does
> this new info tell anyone anything?
>
> Please help me!
> Phil

In message . com>, "Mariner15"
wrote:

>'91 Wrangler with a 4.0 and manual tranny
>
>Had some trouble about two weeks ago with cutting out as I was driving
>down the road. Changed the Crank Position Sensor, and it worked fine
>for a couple days, then cut out once more, waited 10 seconds then it
>started up again and ran excellent for another week, no more cutting
>out...Then, some other problems started. The engine now has
>drastically reduced power. It won't go over 60 on the higway, and at
>highway speeds it sounds kind of like one of those import cars with an
>aftermarket exhaust pipe. The mechainic can't figure out whats
>wrong...
>
>After a week of leaving it with him, the only thing his computer would
>tell him is that the timing would not increase as it should. - Does
>this new info tell anyone anything?

Yes. You need a new mechanic.

>
>Please help me!
>Phil

Phil,

I agree with Bill. The PCM can fail. I've replaced mine twice since I've
owned my 91YJ 4.0L. Since the PCM is rather expensive ($600-800) depending
on the dealership (cheaper at a junk yard if you match the VIN), you would
do well to take your Jeep to a Jeep dealer and let them do full diagnostic
on the PCM rather than let a local mech do it. Most folks don't want to
hear that, but you have to do what you have to do.

My PCM failures were different than your symptoms. All 91YJ 4.0L
functions are controlled by a myriad of sensors that feed the PCM. So
either one of those sensors has failed or its sensor circuit, or the PCM
itself. The only other items that could possibly cause your problems a

Bad sparkplugs
Bad rotor
Bad/cracked distributor cap
Bad plug wires
Bad/faulty fuel injector
Bad engine ground
Fuel filter
plugged/dirty fuel lines
Plugged/faulty/wornout/dirty catalytic converter (If it rattles, it's toast)

BTW, the 91YJ PCM does not have a "safe mode" like later TJs. I do not
suspect the fuel pump since the pressure check showed normal. However,
while at the dealer, have them check pressure at the fuel rail and do a
leakdown test. The 4.0L are increditably reliable motors and will last a
very long time if properly maintained, but they do have they're quirks which
are mostly the sensors and PCM.

Scott
91YJ 4.0L
256,000 original miles and still running strong

"L.W.(Bill) Hughes III" > wrote in message
...
> Hi Phil,
> The computer (Powertrain Control Module) is responsible for spark
> advance, so it is either in the safe mode because one the sensors like
> the Cam Position Sensor in the distributor is bad, or it's self.
> God Bless America, Bill O|||||||O
> http://www.billhughes.com/
>
> Mariner15 wrote:
>>
>> '91 Wrangler with a 4.0 and manual tranny
>>
>> Had some trouble about two weeks ago with cutting out as I was driving
>> down the road. Changed the Crank Position Sensor, and it worked fine
>> for a couple days, then cut out once more, waited 10 seconds then it
>> started up again and ran excellent for another week, no more cutting
>> out...Then, some other problems started. The engine now has
>> drastically reduced power. It won't go over 60 on the higway, and at
>> highway speeds it sounds kind of like one of those import cars with an
>> aftermarket exhaust pipe. The mechainic can't figure out whats
>> wrong...
>>
>> After a week of leaving it with him, the only thing his computer would
>> tell him is that the timing would not increase as it should. - Does
>> this new info tell anyone anything?
>>
>> Please help me!
>> Phil

Bummer!
God Bless America, Bill O|||||||O
http://www.billhughes.com/

reconair wrote:
>
> Phil,
>
> I agree with Bill. The PCM can fail. I've replaced mine twice since I've
> owned my 91YJ 4.0L. Since the PCM is rather expensive ($600-800) depending
> on the dealership (cheaper at a junk yard if you match the VIN), you would
> do well to take your Jeep to a Jeep dealer and let them do full diagnostic
> on the PCM rather than let a local mech do it. Most folks don't want to
> hear that, but you have to do what you have to do.
>
> My PCM failures were different than your symptoms. All 91YJ 4.0L
> functions are controlled by a myriad of sensors that feed the PCM. So
> either one of those sensors has failed or its sensor circuit, or the PCM
> itself. The only other items that could possibly cause your problems a
>
> Bad sparkplugs
> Bad rotor
> Bad/cracked distributor cap
> Bad plug wires
> Bad/faulty fuel injector
> Bad engine ground
> Fuel filter
> plugged/dirty fuel lines
> Plugged/faulty/wornout/dirty catalytic converter (If it rattles, it's toast)
>
> BTW, the 91YJ PCM does not have a "safe mode" like later TJs. I do not
> suspect the fuel pump since the pressure check showed normal. However,
> while at the dealer, have them check pressure at the fuel rail and do a
> leakdown test. The 4.0L are increditably reliable motors and will last a
> very long time if properly maintained, but they do have they're quirks which
> are mostly the sensors and PCM.
>
> Scott
> 91YJ 4.0L
> 256,000 original miles and still running strong