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T.B.I. Not Functioning, at Injector/Etc.


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The '87 MJ I4 2.5L  I have was running and then stopped.


There IS: Air Intake to the cylinders,


           &  Spark


  There is a fuel delivery problem.


I have fuel pressure to the Throttle Body Injector.


If I provide the injector with 12V then it does respond (like a Solenoid should) 

Opening and Closing/ Moving Correctly with the correct voltage supplied.


So, the trouble seems to be that the Jeep is not supplying the T.B.I. with the Voltage required to actuate that injector

and so provide fuel to the cylinders.


The Jeep was running recently then died; I have only been ablt to get it to run by pouring fuel into the intake myself.


I did replace the Crank Position Sensor Today with a new part.

Battery voltage is fine.  Cranking is fine.

The Injector is not opening when I turn the key.


Where to look next, right?





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It seems like #21 from the E.C.U. should be sendig the 12V nominal to the injector, from what wiring diagrams I've been able to see.


Is there something besides the Crankshaft Position Sensor signal to the E.C.U.  that would keep the E.C.U. from suppling 12V?..

seems like there must be suposing the new part installed was well and installed correctly; it really only did fit one wa so what's next.


I may have to trace wires and connections to determine continuity; I am not trying to miss a correct step.







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I will have to find a way to post some of these wiring diagrams I've been looking at. 

An older Chilton gave Me a heads-up to check voltage at the Fuel Pump Relay Connections;

 -- looks like that is with the ignition on and system Not cranking.


' Will see what I can find


I did clean the terminal(s)/ connection block from the Engine Bay to FirewallWires thouroughly,

after the non-start function began (and noticed no difference in response).




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Not the answer you're looking for, but have you considered dumping the TBI? If you have to replace that injector, it's scary expensive compared to the individual injectors for the 4.0L and later 2.5L engines. And it's not an especially efficient form of injection anyway. I've been toying with the idea of just scrapping the TBI setup and reverting to a 2-barrel carburetor (or maybe even a very small 4-barrel, but for an I-4 that's probably overkill). It shouldn't be too difficult to find or make an adapter to mount a 2-barrel on the TBI intake manifold.


You would also have to use a new fuel pump, because a carburetor only needs about 7 psi. The TBI pump puts out enough pressure that it would defeat the float and needle valve in a carburetor.

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Thanks very much for that reply.


I really like the idea of a Carburetor on the Comanche, and I think a 2BBL does make sense for the I-4.


For the time being, I'll have to find my multi-meter then check a few more connections and take a few more readings;

if I can repair what is there then that would help to move things along.


And, if you/(someone) happen/(s) to figure out a nice match of a carburetor for the  I-4 then that would definitely interest me.


I'll have to put some time into researching that, when I've got some more time to.


Thanks again for the thought.

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To be more accurate; I was unaware of there being a Camshaft Position Sensor.


I have not had to work on that before.


I've worked on many types of Engine configurations; thanks-again.


Also, Is That Cam. Pos. Sensor a ready-made part?

I have not found a listing of a Camshaft Position Sensor yet, online.


And Maybe I can take a look and see what is in and about the distributor, later from now.


I wonder if the Cam. Pos Sensor is Built into the Distr., or otherwise independently replaceable from the rest of that assembly.


Thanks again.

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I apologize; the wiring diagram images so far posted are less accessable than I had intended.


I do:understand carburetors, Maybe, a bit more because I also Breath, and so forth and so on.


Digital signals make some times Way Better, from my experience.


Attempting to Supply Better photo/data links:



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Where-ever I set my multi-meter, I haven't found that yet today.


I took a look at the distributor ( 1987, MJ I-4 engine, Throttle Body Injection), and after at least tripple checking

I found that there was not a sensor at the distributor on that engine.


I did find a BWD part# ME79 (Distributor Ignition Pickup) listed at Oreilly's site; the part looks like it would probably fit my Jeep.

(So I can understand that some Comanches may have such a sensor).  And thanks, "Sync Sensor" and so forth helped me to find that data.


Again, I found no sensors connected/installed/ and so forth at the distributor on this Jeep; I do not think any such parts

were ever equipped on this Jeep.


At the interior, driver's side I found the:  Renix S100801-103


I would like to test if there is a 12v signal from the ECU to the TB Injector, after I find my multi-meter and have the time for the test.


I have some tree work to do today more immediately; the Comanche in operational condition would really help with that.


'have to go to work with the XJ for right now.


'until next.


Thanks very much.

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The Comanche started the day before yesterday.

And I went to work with the Comanche Today.


I would love to provide more specifics about the work/repairs as I may.





'Almost Forgot; I found my multimeter; the mulit-meter and propper data helped me.'

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