Novak Conversions Jeep Wrangler YJ radiator

94 Jeep YJ Check Engine Light Issues

heath

heath

New Member
Joined
Feb 2, 2026
Messages
3
Location
Riverton, Utah, USA
I am a newbie to this site, I have searched all over for this fix, and I cant seam to find it. This is my 3rd Jeep to own and it is causing me the most issues. I have a check engine light that comes on after the Jeep warms u,p but only when driving. If I stop and shut the engine off, the check engine light turns off for a couple of miles than it comes back on. I have tried to get the trouble codes by
  1. Insert the key into the ignition
  2. Turn the ignition On-Off-On-Off-On within 5 seconds
  3. Record the 2-digit DTC as displayed by the flashing MIL
But I get no codes. It seems as soon as I turn it off, it resets the code. When I am driving it, I have to have the gas pedal to the floor to get past 50MPh. I also noticed that I am getting some oil out of the exhaust when she is cold.

1994 Jeep Wrangler YJ 2.5L
All repairs have been done in the last 30 days..
New Fuel Pump
New Fuel Filter
Fuel Injectors Cleaned and Tested (Shop, not me)
New Spark Plugs (I verified Gap)
New Spark Plug Wires
New Distributor (Timing is good)
New Water Pump
New Thermostat (Tested before installation)
New Radiator
New Upper and Lower Rad Hoses
Rear Dif Serviced
All Vacuum Hoses replaced, and Vacuum checked
New serpentine belt
New O2 Sensor
Compression Test I am getting between 120 and 140 on all 4 cylinders

I have not tested fuel pressure yet. But when I release it on the rail, I get a lot of fuel.


I am at my wits' end, and any help would be very much appreciated.
 
Last edited:
no CEL before general points to PCM, most all wrangler that i am aware of use Champion 412{RC12lyc} the oil out exhaust could very be PCV,or bad oil seal. need to check fuel pressure at rail, you can borrow one from auto store. if PCM is problem, it probably effect timing, which could effect your speed. god luck.
 
I found a vacuum leak or O2 sensor can light the CEL but not show any codes. I read that you did replace both items but I would still check them.

Check the vacuum lines and connections by spraying them lightly with carb cleaner and see if there's an RPM change. Aftermarket O2 sensors can also be a common problem. They can be checked with a multimeter and show the right numbers yet have intermittent troubles. At least check it once or twice to be sure. Getting a light after two minutes does make it sound like a temperature related issue, again pointing to a faulty O2 sensor.

Today's new Jeeps will rarely work right with any aftermarket sensor. The new computers detect it's not an OEM product. Doesn't stop Amazon from selling them. Our 30 year old YJ's won't recognize them for what they are but can still trigger the CEL.
 
Novak Conversions Jeep Wrangler YJ radiator
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