I just finished replacing a blown head gasket on my 87 Cherokee 4.0 caused by over heating. Now the engine seems to idle smooth and on rev in the engine compartment, oil pressure is good and temp is holding its own. The problem is that at the tail pipe it sorta sounds like a puf puf puf and no smoke. When I test drive it there seems to be a loss of power and it dies if I turn on the AC. Turn off the AC and it starts back up. Any ideas on what I can check for?

 

According to your descriptions..

Check the catalyst

Check to see if AC compressor is partly seized up without turning it on. Take the belt off and see if you can turn the compressor over by hand for free smooth rotation or if it is partly difficult.

While you have the belt off check to see if you can turn the water pump by hand.

 

Sounds like he's got a misfire... Any cel codes?

 

I believe that the water pump and ac unit are both fine and are turning freely.

I'm not sure what cel codes are in a Jeep this old or how to read them and there's no trouble light on the dash. I do have a code reader but I can't find where to plug it in. My service manual isn't much help either. It kinda seems like a misfire to me too. I've checked the firing order and it looks OK, I marked the wires and put them back the same way they came off. So not sure what else to check.

 

Not sure if 87 jeeps had an on board diagnostics system...OBDII wasn't introduced to the jeeps until 1996, so if you're reader is meant for that system it wouldnt work on your jeep anyway...

http://www.jpmagazine.com/featuredve...e/viewall.html

 

It almost seems as if you have low compression in one cylinder...did all of the pistons look normal?

Oh and FYI, 87-90 had a renix-based diagnostic plug, not very easy to come by a reader unless you are a dodge dealer or your making serious bank

 

Its an 87 so its PRE OBD I.

It does not store codes.

 

Could be driving it with the bad gasket finished off your catalytic converter. (plugged up). Once on an old "K" car I was able to loosen the header pipe flange bolts enough to test it. Keep in mind there could be fire/sparks coming out of there, as well as deadly carbon monoxide.

As far as AC, you might look at your DC power. Could it be bringing voltage/ Ign. voltage down?

 

Catalytic converter is starting to look like the culprit. When I fired it up after changing the gasket I had coolant and oil shooting out the tail pipe at first then it stopped. From what I can tell coolant and oil can damage a converter. The engine is running smooth now except when I drive it, then there's a loss of power and it's sluggish. Almost like my old Camaro did when it's converter went bad.

 

I believe it is in the engine compartment the plug in(not 100% sure and would like to know for sure if anyone else knows), you can buy a obd1 ,obd2,can- code reader at sears, harbor freight etc for around 150.00 and up for the better ones.g/l

 

You can buy a obd1 ,obd2,can- code reader right from sears (order from cat.) or harbor freight, etc. FYI they are really quite widly avalible, even some of the better stocked auto parts store's will have them.$150.00 and up for the better one's.

 

All Renix XJs (87-90) are pre-OBDI. None of the code readers you mentioned will work on that. The only scanner that will work on a Renix XJ is DRBII, which is extremely expensive, as FiftySix56 said. With Renix, you need to either spend the $$$ on DRBII or test each sensor individually with a multimeter and manual.

 

Are you sure all the vacuum-type hoses and fittings are hooked up, and in the proper places?

 

The older Snap-on "brick" has a cord and card to read the computer also.

 

Fairly certain, there's a diagram on the firewall that matches the service manual which I followed.