yet another rough idle, missing, and running rich thread

okay i just swaped a 4.0 out of a 93 grand cherokee that had been rolled into my 88 xj. the old motor that was in the 88 ran fine besides the knock when u first started it up. i reused all of my old accesorys, intake, exhast, water pump, all my sensors, my old oil pan, and old distributer. i pretty much only used the new shortblock and head. the new motor carries 120 lbs of compression in the first 4 cylinders and 130 in 5 and 6. it also carries about 50 pounds of oil presure going down the road. i just put new plugs in the new motor also. since we got the motor in and running, it has had a miss thru the whole rpm range, is running rich(im assuming this since it is puffing just a tiny little bit of black smoke) and has a very rough idle, and if in park or neutral and you hit the throttle up to about 2500 and let off completly *sometimes* it will stall. i dont know what could be the problem, since it sounds like the tps, iac, o2 and who knows what other sensors are bad. but realy what is the possibility of all the sensors going bad at the exact same time when i did the motor swap. is there anything i might be overlooking? when i searched some said that cleaning out the throttle body made a huge diff but i wouldnt think that is the problem because the old motor ran fine.

kolby

Try re-indexing your distributor

It will run very rich if the MAP sensor is not connected to the throttle body.

If there is a miss over the whole rpm range, your problem is most likely not a sensor. You most likely have a single cylinder that is not firing either at all or at least most of the time.

Troubleshooting 101

Start the engine and pull each spark plug wire, one at a time and replug it. You will find the cylinder that is misfiring when you get to a cylinder that when you pull the plug wire, the rpm's do not go down as far or it doesn't run quite as rough as the other cylinders. Once you find that cylinder, the real troubleshooting through swapping starts. First swap the spark plug wire with another cylinder and see if the problem tracks the wire. If they don't, try swapping the spark plug.

My bet is on the fuel injection side. The injection on a 4.0L is sequential. I have seen a screwy miss caused by swapping the wires on a couple of injectors, much like swapping sparkplug wires but not as pronounced. Do you have the wire color code sequence for the injectors? I will list them below. If the wires are not swapped, you most likely have a defective or plugged injector. By injecting at the wrong time, you will cause the equivelent to running too rich because raw gas can be being injected into the exhaust.

cyl Color
-------------------------
1 - Light Blue
2 - Light Green
3 - Tan
4 - Yellow
5 - White
6 - Brown

anybody can stick the distributor in at tdc, but it has to be indexed properly.

we looked up the injector wire sequence when we put the motor back together so im 99.998% sure thats not it, sorry to be an idiot but how exactly do you properly index a distributor?

i forgot to add earlier that when u stop at a stoplight it will rev up and down about 200 rpm differnce back and forth making the jeep kind of want to pulse forward a little each time.

kolby

lankchevy said:

...sorry to be an idiot but how exactly do you properly index a distributor?

Click to expand...

This'll help: http://www.angelfire.com/my/fan/dist_index.html

Do the troubleshooting proceedure and see if you can pinpoint a particular cylinder.

when my dad and grandpa put the 88 distributor in the 93 block, they didnt use the holddown, they just tightened the bolt down the aluminum ears on the dist. and the ear broke off yesterday, i got it home and found the holddown and put it on. what im wondering is if i could take the sensor (cam positioning sensor) out of the 88s dist. and put it in the dist. we got with the 93 motor? physicaly the tow look the same, just have a diff plug on the sensor. does anyone know if this would work?

kolby