help - burning a lot of fuel - Needs fixing ASAP

[sinnaevd]

So i put an 87 YJ 4 cyl into an 86 comanche.

 

When the engine was in the YJ, it ran beautifully, had no problems at all.

 

I have put it into the comanche, it is now missing a bit and I can't figure out why. I used the TBI unit off of the comanche as well as the vaccuum lines to make sure everyhting was the same.

 

The engine has a new oxygen sensor, new cap and rotor, sprak plugs and spark plug wires.

 

The gas was old, I added octane booster to try to see if that works at all.

 

 

But I am still missing, and it is still burning a rediculous amount of gas. The idle isn't the best, but it is better.

 

What else am I missing that could be causing this?

 

Should I maybe look at using the computer from the 87 in the 86?? would that affect it??

[Confedneck]

yes... easiest to try

[JeepcoMJ]

and also check your injectors, that sounds kind of like an injector fault. and your ICM should be checked along with the distributor etc.

[sinnaevd]

injectors?? its a TBI unit??

 

whats an ICM? Ignition control module?

 

where is that located? Or is that the same thing as what the coil is attached to?

[JeepcoMJ]

injectors?? its a TBI unit??

 

whats an ICM? Ignition control module?

 

where is that located? Or is that the same thing as what the coil is attached to?

 

TBI is throttle body injection. there is an injector (singular, sorry) there. check it, it may be pouring too much in.

 

the ICM (ignition control module) is what you think is your "coil pack". it powers the distributor.

 

let me ask, what all did you swap over when you did the swap? did you just yank the motor (complete) and drop it in, or did you put all the distributor/accessories/crank position sensor/ICM from the 86 motor on the 87 motor?

 

I just put an 88 4 cylinder into an 86 and while I do have some high idle problems and a sometimes-miss, I don't have any other issues with it. I don't really care regardless...this motor is temporary for me and it's just a DD. *shrug*

[sinnaevd]

I used the 87:

 

block

head

exhaust man

intake man

water pump

most sensors

 

I used the 85 tbi unit, oxy sensor, starter, transmission, cps, distributor

 

any idea how to check the injector in the 86?

 

do you think the computer might be the problem as well JeepcoMJ?

[JeepcoMJ]

probably not the computer, more likely a bad sensor on the TBI unit.

 

swap some sensors off the 87 unit, they're interchangeable.

 

the injector...just pour cleaner into the gas tank and see what happens

[sinnaevd]

so you mean the TPS sensor might be crappy?

 

I just swapped over t he TBI unit from the 87, nothing chaged with it, smoke wise but the idle was nicer (the unit was cleaned to begin with)

 

I also changed over ICM, that didnt help either.

 

The only part I have left from the 87 to change over is the brain itself, which i thought would be a big job based on where it came off of the YJ, but its a lot nicer on this comanche, underneath the steering wheel.

 

I can also change over the TPS sensor from the 87 ( i used the top half of the TBI unit from the 97 and the 86 base)

[JeepcoMJ]

change over the TPS sensor swap out the crankshaft sensor, you should check the ignition control module, and it's probably the computer.

 

it's kinda hard to use the lower of the 87 tbi since it only has 2 vacuum outputs unlike the 86's 4 vac. outputs, but seems like you're getting somewhere.

[sinnaevd]

computer will be swapped today, then virtually everything from the 87 will have been used (minus the wiring harness itself)

 

Hopefully that will cure the last problem.

 

Now i still have to refix the exhaust as the engine backfired and the muffler blew up like a granade....my ears are still ringing from when it happened :roll:

[sinnaevd]

I found an intake leak, which helped a bit. Its idles really really well now. I had it capped off before, but the cap must have fell off somehow.

 

I still haven't changed the computer over. My back has been giving me troubles today

 

hopefully tomorrow I will get it all patched up, and get the new tires on it.

[carnuck]

Check the hose on the MAP sensor, as when they get clogged or cracked, the fuel economy goes in the dumper! (4.0L too!)

[sinnaevd]

it's cleaned itself out quite a bit now. I changes everything on it, and still can't get it running just right

 

At about 50 MPH it runs beautifully, but still idles absolutally terrible.

 

I found an intake leak, it's been fixed and helped quite a bit. the computer has been changed, helped some but not too much. I still think that the vaccuum's may be the culprit, but to the best of my knomwledge, they are correct.