does anyone know ??

[flyboy]

1045341

I recently exchanged my 2.5 tbi with a 4.0 mpi that i salvaged from an 89 cherokee. I have everything wire up except the fuel pump which i have connected to a straight 12v switched. Now when I start it up it constantly revs at 5000rpm. does the computer communicate with the fuel pump or is it just throttle positioning sensor?

[addsig]

 

[ktrip]

1045360

You have to remove the AIS motor and housing from your old throttle body and put it on the new one. They are different sizes. This should clear up your problem.[addsig]

 

[flyboy]

1045431

does this still apply even though i've taken the motor trany, wire harness and the computer from the cherokee and rammed it all in the yj?[addsig]

 

[Bounty__Hunter]

1045445

No, I think Ktrip thought you only swapped the throttle body from a 4.0L to a 2.5L jeep. The fuel pressure from the pump should stay constant, so this doesn't sound like your problem. You've got a problem somewhere else, maybe the TPS. Wiring, computers, and sensors are not my strong points

[addsig]

 

[jprtroy]

1045465

What I can tell ya, is that my Mopar kit ( modeled after a 94') has the fuel pump controlled by the computer. (ecm)A green wire comming out of a wire harness. When I turn the ign key to on, the pump starts and goes for about 10 to 15 sec, ( builds up pressure) then shuts off. When the motor is started, it then runs continuosly.

Not really sure about the 88' if it's fuel injected, maybe the fuel pump is bad.



[addsig]

 

[flyboy]

1045472

here is an update. When I disconnect the vacuum line to the map sensor it idles down to around 1500rpm, plug it back in goes back to 5000rpm. Hmmm... something do do with vacuum lines. the egr valve3 is pouched but i will be replacing that soon.

[addsig]