1990 Jeep Cherokee: Leaving Soot and Gray Clouds Despite Maintenance...Leaky Injector Problem?

Just to clarify, I own a 1990 Jeep Cherokee with the Renix system. A couple days ago, I replaced the fuel filter, most parts on the ignition system and a general tune-up. In addition to that, I replaced my upstream O2 sensor (with a Denso, if that matters), fouled catalytic converter and muffler since the previous owner had a straight pipe. On my way home from the muffler shop, after the new O2 sensor, I still left a grayish cloud, that didn’t appear to be caused by oil or coolant, when I took off from stops. Today, I replaced the O-rings on a couple leaky fuel injectors and got them taken care of, since I figured they were the culprits.

Problem is, my wife, who was under the hood to check for any leaks when I started the Jeep, saw there was a new leak on a different injector. So I think I’ll just replace the O-rings on all the other injectors. Long story short, the couple of minutes it was running created a nice sooty spot on my driveway. Is there a good chance it’s simply due to a leaky injector? I’ve got no problem replacing the O-rings on my injectors, but I’d prefer to not have to spend $180 on 6 new injectors to avoid having my new catalytic converter fouled. Any input would be appreciated. FYI, it appears my fuel pressure regulator is okay and I spent most of the afternoon cleaning up grounds and electrical connections.

Thanks in advance, guys/gals.

The wife had a 90 Cherokee with the 4.0L engine. And when one of the injector O-rings started leaking I replaced all of them. You can purchase these as a kit.

As far as the soot and gray smoke, one thing to check for is a faulty Manifold Absolute Pressure (MAP) sensor or the vacuum hose going to it. This sensor basically takes the place of the vacuum advance and the accelerator pump that where found on vehicles before fuel injection. If this sensor is sending erroneous signals to the computer it cause the engine to run very rich.

Since this system is an OBDI engine management system, just unplug the MAP sensor and see if the engine runs better. This will cause the computer to go to default value for the missing information for the MAP sensor.

Also look for any breaks in the cheap, hard plastic vacuum lines used on this engine.


Not sure if just unplugging the MAP sensor will help on this. This is a pretty critical sensor. All the Chrysler vehicles I’ve had will instantly stall if you unplug this, but I guess you can try. Even if it doesn’t stall, it will run like utter crap with it disconnected, so not sure this is a viable test.

Thanks for the responses, folks. I figured the Jeep is running rich…which would obviously indicate a faulty sensor or vacuum leak, etc. Please correct me if my understanding is off, but if I have the vehicle running and removing the vacuum line from the MAP makes little difference in the idle, would it be fair to assume the MAP is faulty? My other question is whether bad injector O-rings would create the symptoms I’m experiencing or if new injectors are necessary? I wouldn’t mind replacing the MAP if I need be, but I’d hate to replace the injectors too if I don’t have to. Thanks again for the help!

Was there vacuum at the MAP when you disconnected the hose? If so your assumption is likely correct. The MAP is probably bad.

To be honest, I haven’t tested the theory yet by pulling the MAP sensor vacuum while running. The only thing I did test was the FPR, which had no fuel in that particular vacuum line. Since I’ve cleaned the IAC valve too, I’m inclined to think it’s the Map, though.

You don’t disconnect the vacuum line from the MAP sensor to see if it’s the problem. You unplug the electrical connector.


The MAP can’t be condemned until confirming that full manifold vacuum is reaching it.

Do what my buddy did with his Cherokee… swap in a Mercedes OM617 turbodiesel engine!