1990 Cherokee won't run over approx. 1500rpm
 

Almost giving up..

Renix ECU (replaced couple of years ago with Bendix)Multi point fuel
injection, 4.0 litre inline six with manual transmission, 110K miles.
It has been doing this over a year now,it feels like this Jeep has a
mind of it's own...sometimes good day,sometimes bad day (mostly bad
days recently).
Problem is, that sometimes it just dont run over 1500rpm, it doesnt
matter how much i press
the gas pedal,it just sputters and rpm gauge drops to zero,it does not
matter what gear i'm using,if i depress the gas pedal slightly then it
keeps going slowly and rpm gauge comes back alive.

But when it runs fine it really runs like it should (almost like a
sportscar)..

CPS sensor is brand new and giving nice pulses,O2 sensor is brand
new,TPS sensor is giving smooth voltage,coolant temperature sensor is
ok,manifold air temperature sensor is ok,MAP sensor seems to be ok,EGR
seems to work, stator in the distributor is giving nice pulses,fuel
pump ballast resistor is 1 ohm, (every sensor checked according to Jeep
Renix Fuel Injection Manual) i have checked the sensors using digital
multimeter (and oscilloscope for pulse giving sensors). I have done
measurements near to ECU connectors (by cutting/peeling the wires).
One strange thing is, that there is no noticeable difference if knock
sensor wires are connected or not.. and it it was also giving knock
pulses..more rpms,more and higher pulses. Basically my question is,what
should i try next...
could this problem be fuel related ?
what are the reasons which can make rpm gauge drop to zero?
For me it just seems to be electrical...i dont know anymore..

Please answer if someone have a clue about this.

1990 Cherokee won't run over approx. 1500rpm
 

I don't see fuel filter in there.

Also there is a body ground that runs from the rear of the head to the
firewall. If it goes bad, the vehicle has to steal grounds. Sometimes
it can get a good one, sometimes not...

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:
>
> Almost giving up..
>
> Renix ECU (replaced couple of years ago with Bendix)Multi point fuel
> injection, 4.0 litre inline six with manual transmission, 110K miles.
> It has been doing this over a year now,it feels like this Jeep has a
> mind of it's own...sometimes good day,sometimes bad day (mostly bad
> days recently).
> Problem is, that sometimes it just dont run over 1500rpm, it doesnt
> matter how much i press
> the gas pedal,it just sputters and rpm gauge drops to zero,it does not
> matter what gear i'm using,if i depress the gas pedal slightly then it
> keeps going slowly and rpm gauge comes back alive.
>
> But when it runs fine it really runs like it should (almost like a
> sportscar)..
>
> CPS sensor is brand new and giving nice pulses,O2 sensor is brand
> new,TPS sensor is giving smooth voltage,coolant temperature sensor is
> ok,manifold air temperature sensor is ok,MAP sensor seems to be ok,EGR
> seems to work, stator in the distributor is giving nice pulses,fuel
> pump ballast resistor is 1 ohm, (every sensor checked according to Jeep
> Renix Fuel Injection Manual) i have checked the sensors using digital
> multimeter (and oscilloscope for pulse giving sensors). I have done
> measurements near to ECU connectors (by cutting/peeling the wires).
> One strange thing is, that there is no noticeable difference if knock
> sensor wires are connected or not.. and it it was also giving knock
> pulses..more rpms,more and higher pulses. Basically my question is,what
> should i try next...
> could this problem be fuel related ?
> what are the reasons which can make rpm gauge drop to zero?
> For me it just seems to be electrical...i dont know anymore..
>
> Please answer if someone have a clue about this.

1990 Cherokee won't run over approx. 1500rpm
 

clogged exhaust maybe?
did you hook a vacuum gauge to the intake manifold to see what it reads?

Bad distributor rotor/cap, weak ign coil?
clogged vacuum tube/hose to MAF sensor?

did you check the fuel pressure with a cheapie tire gauge or fuel pressure
gauge? BE CAREFUL and use common sense please!!!

is this a USA model or an import to you?
--
later,
dave AKA vwdoc1

> wrote in message
oups.com...
> Almost giving up..
>
> Renix ECU (replaced couple of years ago with Bendix)Multi point fuel
> injection, 4.0 litre inline six with manual transmission, 110K miles.
> It has been doing this over a year now,it feels like this Jeep has a
> mind of it's own...sometimes good day,sometimes bad day (mostly bad
> days recently).
> Problem is, that sometimes it just dont run over 1500rpm, it doesnt
> matter how much i press
> the gas pedal,it just sputters and rpm gauge drops to zero,it does not
> matter what gear i'm using,if i depress the gas pedal slightly then it
> keeps going slowly and rpm gauge comes back alive.
>
> But when it runs fine it really runs like it should (almost like a
> sportscar)..
>
> CPS sensor is brand new and giving nice pulses,O2 sensor is brand
> new,TPS sensor is giving smooth voltage,coolant temperature sensor is
> ok,manifold air temperature sensor is ok,MAP sensor seems to be ok,EGR
> seems to work, stator in the distributor is giving nice pulses,fuel
> pump ballast resistor is 1 ohm, (every sensor checked according to Jeep
> Renix Fuel Injection Manual) i have checked the sensors using digital
> multimeter (and oscilloscope for pulse giving sensors). I have done
> measurements near to ECU connectors (by cutting/peeling the wires).
> One strange thing is, that there is no noticeable difference if knock
> sensor wires are connected or not.. and it it was also giving knock
> pulses..more rpms,more and higher pulses. Basically my question is,what
> should i try next...
> could this problem be fuel related ?
> what are the reasons which can make rpm gauge drop to zero?
> For me it just seems to be electrical...i dont know anymore..
>
> Please answer if someone have a clue about this.
>

1990 Cherokee won't run over approx. 1500rpm
 

My '88 did that one on me - your MOPAR replacement should be similar.
Seems that when I replaced the CPS I didn't tie the CPS sensor lead
close enough to the firewall. It had just enough slack for the cable
to make contact with the ehhaust, which naturally melted the
insulation on the wire and would tempporarily short out the CP against
the exhaust. One wet day, the intermittent became chronic and I made
the last 5-6 miles home with the engine revving to a max of about 1250
RPM and no real power above 1000 RPM. Same thing you describe - I
basically had a little more than idle RPM. Got some real funny looks
as I accelerated ever so slowly away from stops shifting when I felt
it start to bog. Changed the CPS and problem was gone. Moral: check
the CPS and all related connections.

On Fri, 25 Aug 2006 20:45:01 UTC wrote:

> Almost giving up..
>
> Renix ECU (replaced couple of years ago with Bendix)Multi point fuel
> injection, 4.0 litre inline six with manual transmission, 110K miles.
> It has been doing this over a year now,it feels like this Jeep has a
> mind of it's own...sometimes good day,sometimes bad day (mostly bad
> days recently).
> Problem is, that sometimes it just dont run over 1500rpm, it doesnt
> matter how much i press
> the gas pedal,it just sputters and rpm gauge drops to zero,it does not
> matter what gear i'm using,if i depress the gas pedal slightly then it
> keeps going slowly and rpm gauge comes back alive.
>
> But when it runs fine it really runs like it should (almost like a
> sportscar)..
>
> CPS sensor is brand new and giving nice pulses,O2 sensor is brand
> new,TPS sensor is giving smooth voltage,coolant temperature sensor is
> ok,manifold air temperature sensor is ok,MAP sensor seems to be ok,EGR
> seems to work, stator in the distributor is giving nice pulses,fuel
> pump ballast resistor is 1 ohm, (every sensor checked according to Jeep
> Renix Fuel Injection Manual) i have checked the sensors using digital
> multimeter (and oscilloscope for pulse giving sensors). I have done
> measurements near to ECU connectors (by cutting/peeling the wires).
> One strange thing is, that there is no noticeable difference if knock
> sensor wires are connected or not.. and it it was also giving knock
> pulses..more rpms,more and higher pulses. Basically my question is,what
> should i try next...
> could this problem be fuel related ?
> what are the reasons which can make rpm gauge drop to zero?
> For me it just seems to be electrical...i dont know anymore..
>
> Please answer if someone have a clue about this.
>


--
Will Honea

1990 Cherokee won't run over approx. 1500rpm
 

One out of many daves wrote:
> clogged exhaust maybe?
> did you hook a vacuum gauge to the intake manifold to see what it reads?
>
> Bad distributor rotor/cap, weak ign coil?
> clogged vacuum tube/hose to MAF sensor?
>
> did you check the fuel pressure with a cheapie tire gauge or fuel pressure
> gauge? BE CAREFUL and use common sense please!!!
>
> is this a USA model or an import to you?


I second a clogged catalytic converter.
(or muffler, although I've gone through more converters then mufflers)

1990 Cherokee won't run over approx. 1500rpm
 

Thanks for all about the replys !
It is import model, i live in Finland.

I added extra ground cable from head to the firewall.
CPS wires are ok (not melted),i replaced the wires some time ago.
Exhaust/catalytic is not clogged,but i'll take a closer look.
I havent check manifold vacuum or fuel pressure yet.
Fuel filter,distributor rotor/cap are on the list to replace,right when
i can get them.
Where is MAF sensor located ?

Sami

1990 Cherokee won't run over approx. 1500rpm
 

Hmm....

In my book, the distributor cap, rotor, and the fuel filter would be the
'first' things to replace, not the last.....

You could have a 16 year old distributor cap in there and I will bet the
fuel filter 'is' 16 years old....

My 88 bogged down like that once. When I went to replace the fuel
filter, it literally crumbled to pieces.

The MAP sensor is on the firewall center on those I believe with one
vacuum line running to it.

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:
>
> Thanks for all about the replys !
> It is import model, i live in Finland.
>
> I added extra ground cable from head to the firewall.
> CPS wires are ok (not melted),i replaced the wires some time ago.
> Exhaust/catalytic is not clogged,but i'll take a closer look.
> I havent check manifold vacuum or fuel pressure yet.
> Fuel filter,distributor rotor/cap are on the list to replace,right when
> i can get them.
> Where is MAF sensor located ?
>
> Sami