1990 4.0L Cherokee Stalling and Bucking Problems

I have a 1990 4.0L Cherokee that is having stalling and bucking
problems. While driving or coming to a stop the engine would stall, I
would hear a slight puff sound and then smell fuel in the engine
compartment. At other times, usually on acceleration, the engine would
buck. I had the vehicle towed 3-4 times to a shop and they checked the
fuel system, the fuel pump (it was bad and replaced), and the fuel
system power cleaned.

I have had the fuel pump replaced, the CPS replaced, the fuel system
(injectors cleaned), and had a rebuilt PCM put in. The intermittent
stalling continued and the engine would "buck" on acceleration like I
did not know how to drive a manual transmission vehicle. The PCM was
taken out and the original replaced (The reason the PCM was replaced
was that at times after the engine was turned off the fuel injectors
kept firing.)


After reading a number of posts on this group, I cleaned the
connections on both the Throttle Position Sensor (TPS) and the Input
Air Sensor (IAS) on the throttle. Upon restarting the vehicle, the
engine stopped stalling in my garage (Yes!) and I was able to drive it
without it stalling out for about 5 miles. It did buck a little and a
few times the RPM level dropped a little but did not stall. On the
drive back home it did not buck at all and the RPM level stayed
consistent even at stop lights.

I am hoping that the cleaning of the contacts on the TPS and IAS has
solved the problem, but I fear that it might be the PCM unit (see note
above).

Finally, after I had the Fuel Pump replaced, the fuel gauge stopped
working, at times it does come back on for a second, (which leads me
to think a short, or an electrical (ground) problem. Does the PCM have
anything to do with the Fuel Gauge? Should I request the shop that
replaced the fuel pump to fix the fuel sender or could this have
occured separately.

Thanks in advanve for any help or suggestions.

Otherwise this has been a great vehicle and I do not want to give up on
it! Any other suggestions would be greatly appreciated.

You likely have found the trouble.

Yes, go after the bozo's who put the pump unit in. The gauge sender is
part of the same unit.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

wrote:
>
> I have a 1990 4.0L Cherokee that is having stalling and bucking
> problems. While driving or coming to a stop the engine would stall, I
> would hear a slight puff sound and then smell fuel in the engine
> compartment. At other times, usually on acceleration, the engine would
> buck. I had the vehicle towed 3-4 times to a shop and they checked the
> fuel system, the fuel pump (it was bad and replaced), and the fuel
> system power cleaned.
>
> I have had the fuel pump replaced, the CPS replaced, the fuel system
> (injectors cleaned), and had a rebuilt PCM put in. The intermittent
> stalling continued and the engine would "buck" on acceleration like I
> did not know how to drive a manual transmission vehicle. The PCM was
> taken out and the original replaced (The reason the PCM was replaced
> was that at times after the engine was turned off the fuel injectors
> kept firing.)
>
> After reading a number of posts on this group, I cleaned the
> connections on both the Throttle Position Sensor (TPS) and the Input
> Air Sensor (IAS) on the throttle. Upon restarting the vehicle, the
> engine stopped stalling in my garage (Yes!) and I was able to drive it
> without it stalling out for about 5 miles. It did buck a little and a
> few times the RPM level dropped a little but did not stall. On the
> drive back home it did not buck at all and the RPM level stayed
> consistent even at stop lights.
>
> I am hoping that the cleaning of the contacts on the TPS and IAS has
> solved the problem, but I fear that it might be the PCM unit (see note
> above).
>
> Finally, after I had the Fuel Pump replaced, the fuel gauge stopped
> working, at times it does come back on for a second, (which leads me
> to think a short, or an electrical (ground) problem. Does the PCM have
> anything to do with the Fuel Gauge? Should I request the shop that
> replaced the fuel pump to fix the fuel sender or could this have
> occured separately.
>
> Thanks in advanve for any help or suggestions.
>
> Otherwise this has been a great vehicle and I do not want to give up on
> it! Any other suggestions would be greatly appreciated.

Mike,

Thanks for your response. This morning when I drove to work, it was
doing it again. The RPM was fluctuating and it stalled once, but I was
able to start it rather quickly. I am wondering if I should purchase a
new TPS and/or IAS from the dealer or try to get one from a local
junkyard. Or I might clean the contacts a little better. Do you have
any suggestions on what I should use to clean the contacts. I am also
thinking of getting a PCM from the same jyard if I can find my year and
manual tranny.

Thanks again for your help it is much appreciated,

Tim K

Mike Romain wrote:
> You likely have found the trouble.
>
> Yes, go after the bozo's who put the pump unit in. The gauge sender is
> part of the same unit.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
> Canadian Off Road Trips Photos: Non members can still view!
> Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
> (More Off Road album links at bottom of the view page)
>
> wrote:
> >
> > I have a 1990 4.0L Cherokee that is having stalling and bucking
> > problems. While driving or coming to a stop the engine would stall, I
> > would hear a slight puff sound and then smell fuel in the engine
> > compartment. At other times, usually on acceleration, the engine would
> > buck. I had the vehicle towed 3-4 times to a shop and they checked the
> > fuel system, the fuel pump (it was bad and replaced), and the fuel
> > system power cleaned.
> >
> > I have had the fuel pump replaced, the CPS replaced, the fuel system
> > (injectors cleaned), and had a rebuilt PCM put in. The intermittent
> > stalling continued and the engine would "buck" on acceleration like I
> > did not know how to drive a manual transmission vehicle. The PCM was
> > taken out and the original replaced (The reason the PCM was replaced
> > was that at times after the engine was turned off the fuel injectors
> > kept firing.)
> >
> > After reading a number of posts on this group, I cleaned the
> > connections on both the Throttle Position Sensor (TPS) and the Input
> > Air Sensor (IAS) on the throttle. Upon restarting the vehicle, the
> > engine stopped stalling in my garage (Yes!) and I was able to drive it
> > without it stalling out for about 5 miles. It did buck a little and a
> > few times the RPM level dropped a little but did not stall. On the
> > drive back home it did not buck at all and the RPM level stayed
> > consistent even at stop lights.
> >
> > I am hoping that the cleaning of the contacts on the TPS and IAS has
> > solved the problem, but I fear that it might be the PCM unit (see note
> > above).
> >
> > Finally, after I had the Fuel Pump replaced, the fuel gauge stopped
> > working, at times it does come back on for a second, (which leads me
> > to think a short, or an electrical (ground) problem. Does the PCM have
> > anything to do with the Fuel Gauge? Should I request the shop that
> > replaced the fuel pump to fix the fuel sender or could this have
> > occured separately.
> >
> > Thanks in advanve for any help or suggestions.
> >
> > Otherwise this has been a great vehicle and I do not want to give up on
> > it! Any other suggestions would be greatly appreciated.

When our 88 acted like that, it turned out to be a rotted mesh ground
strap from the engine head to the firewall. The Jeep would steal
grounds from other routes and act up.

I use a spray contact cleaner on the TPS plug and socket. WD40 will
also work fairly well, but the proper contact cleaner sold at electronic
shops is the best.

You can take a multimeter and put it on resistance to measure the TPS
with the engine off and the TPS unplugged. As you increase the
throttle, the resistance should change smoothly. If it jumps around,
the TPS is likely in need of an internal clean or replacement.

Mike


wrote:
>
> Mike,
>
> Thanks for your response. This morning when I drove to work, it was
> doing it again. The RPM was fluctuating and it stalled once, but I was
> able to start it rather quickly. I am wondering if I should purchase a
> new TPS and/or IAS from the dealer or try to get one from a local
> junkyard. Or I might clean the contacts a little better. Do you have
> any suggestions on what I should use to clean the contacts. I am also
> thinking of getting a PCM from the same jyard if I can find my year and
> manual tranny.
>
> Thanks again for your help it is much appreciated,
>
> Tim K
>
> Mike Romain wrote:
> > You likely have found the trouble.
> >
> > Yes, go after the bozo's who put the pump unit in. The gauge sender is
> > part of the same unit.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> > Canadian Off Road Trips Photos: Non members can still view!
> > Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
> > (More Off Road album links at bottom of the view page)
> >
> > wrote:
> > >
> > > I have a 1990 4.0L Cherokee that is having stalling and bucking
> > > problems. While driving or coming to a stop the engine would stall, I
> > > would hear a slight puff sound and then smell fuel in the engine
> > > compartment. At other times, usually on acceleration, the engine would
> > > buck. I had the vehicle towed 3-4 times to a shop and they checked the
> > > fuel system, the fuel pump (it was bad and replaced), and the fuel
> > > system power cleaned.
> > >
> > > I have had the fuel pump replaced, the CPS replaced, the fuel system
> > > (injectors cleaned), and had a rebuilt PCM put in. The intermittent
> > > stalling continued and the engine would "buck" on acceleration like I
> > > did not know how to drive a manual transmission vehicle. The PCM was
> > > taken out and the original replaced (The reason the PCM was replaced
> > > was that at times after the engine was turned off the fuel injectors
> > > kept firing.)
> > >
> > > After reading a number of posts on this group, I cleaned the
> > > connections on both the Throttle Position Sensor (TPS) and the Input
> > > Air Sensor (IAS) on the throttle. Upon restarting the vehicle, the
> > > engine stopped stalling in my garage (Yes!) and I was able to drive it
> > > without it stalling out for about 5 miles. It did buck a little and a
> > > few times the RPM level dropped a little but did not stall. On the
> > > drive back home it did not buck at all and the RPM level stayed
> > > consistent even at stop lights.
> > >
> > > I am hoping that the cleaning of the contacts on the TPS and IAS has
> > > solved the problem, but I fear that it might be the PCM unit (see note
> > > above).
> > >
> > > Finally, after I had the Fuel Pump replaced, the fuel gauge stopped
> > > working, at times it does come back on for a second, (which leads me
> > > to think a short, or an electrical (ground) problem. Does the PCM have
> > > anything to do with the Fuel Gauge? Should I request the shop that
> > > replaced the fuel pump to fix the fuel sender or could this have
> > > occured separately.
> > >
> > > Thanks in advanve for any help or suggestions.
> > >
> > > Otherwise this has been a great vehicle and I do not want to give up on
> > > it! Any other suggestions would be greatly appreciated.