Long time reader, first time poster. I have a '93 YJ 2.5L with a reoccuring issue I cannot seem to solve. I've read alot of posts but still looking for some help or ideas.
My YJ will run pretty good for a few weeks at time and then, while driving, I'll notice a little stumble and not long after that the check engine light will come on. I can continue to drive the Jeep with some lack of power and a stumble through acceleration. Over the course of a few days the issue will get progressively worse to the point that I have to hammer the throttle just to get through the gears. Eventually, when I shut the Jeep off and let it sit for a minute it won't start back up. At that point I disconnect the battery and pull a plug and it will start back up on 3 cylinders (I did the first time while checking for spark). After putting it back together it will run fine for a few weeks then the problem will start all over again. The check engine light throws a "27" code each time which is "fuel injector control". I'm not sure how to check each injector other than pulling the connectors (maybe check the voltage?) which hasn't helped me pinpoint the problem and I don't know how to diagnose a bad ECM. I'm considering pulling the fuel rail and inspecting the injectors and o-rings for obvious visible damage.
I've changed the fuel filter (have good pressure at the rail), plugs, cap and rotors. Cleaned the throttle body, AIC and TPS. Also put on new cat and exhaust.
In the end, I can fix the problem as it occurs to keep driving but I'm stumped on the underlying issue. Thanks in advance for the discussion!!
I have spark in all 4 cyclinders. Sorry for the confusion. I pulled a plug to check spark the first time I had this issue and it did have spark. I start the Jeep on 3 cylinders with with one plug out to check spark. Then put it all back together and it runs fine on four cylinders. Not sure if disconnecting the battery for awhile and removing a plug purges the system but after connecting the battery it will start back up with one plug out. Once all four are back in it runs fine for a few weeks then the issue starts all over.
It resets the ecu. If it was a injector or O ring issue it would be more regular and repetitve. The fact that a battery disconnect clears it means you are probably dealing with a bad ecu or a wiring issue. The ecu goes into a default that the battery disconnect clears. Try and move the wiring harness to the ecu and to the injectors around and see if you can get it to stumble. If not then I think you need to start looking for another ecu.
Que thanks for the reply. I have to tend to agree with you as the PO for this Jeep did some mods to the electrical, which I'm all for if they're done correctly, but I'm afraid this thing has issues. I wish there was a simple way to test the ECU before I replace the wiring harness. I saw a used harness on Ebay for $50, maybe I'll give that a shot first. If you have any tips on changing the wiring harness I'd appreciate any info. Also, is there any way to test an inidividual injector once it's pulled. Will a shop do that? Thanks again for your response.
The problem is it is intermittant so trying to test an issue that is not there will leave you spinning your wheels. You might be better off starting by cleaning all the injector plugs and the ecu connector, coat them with dielectric grease. Run the injector cleaner through it. If the problem is still there buy a single injector, they usually run around $40 and leap frog the injector until you have done all 4. Run it while it is in each of the positions on the fuel rail and see if the problem goes away. If the problem is still there then you go to the reading stuff with a meter and a Noid test light.
You can do this step at any point when you have the problem:
The injectors are all ground switched by the ecu. 12 volts is supplied by the asd relay. You can use a meter across the injector the next time it happens. First check for 12Vdc on all the injectors on the dark green orange wire going to each with the meter refrenced to ground. If the power is there then you need to check the ground of the injector and it is a little more tricky. The ground comes off of pins 13, 14, 15, and 16. The ecu is switching it so it is not constantly there and most meters do not switch fast enough to allow you to see the ground. This is best done with an oscope(Not a back yard tool) or a test light. Take a test light and hook up one side to battery positive and the other to the injector ground at the injector and see if the light flashes. That should be brown, yellow/white, tan, and dark blue. You can use a strait pin to push through the backshell of the connectors or through the wire itself to make contact to do the test. If you do go through the wire make sure you seal it up when you are done. Still not fixed then to the harness swap:
Flipping the harness is easy as long as you are getting a 93-95. The 91 & 92 are different so make sure you get the right one. The 2.5L and 4.0L are the same except the 4.0L has 2 additional injector wires so you can use the 4.0L harness and cut off the 2 you don't use. The harness on the YJ is really simple under the hood and shouldn't take more then a couple hours to swap. What kind of electrical "mods" did the PO do?
I think the ecu is last. I thought about it and if it really was the ecu the issue should be more consistent. If none of the other steps worked or you can't find a harness from the right year let me know.
I take it you are from Michigan! Going down in another 2 months! ......Sparty Fan though......Go Blue! LOL
Again, Great Info! I'm going to try and tear into this weekend as long as the weather holds up. I may just pull the harness out and clean/grease all the connectors and look for a short to see what I find, everything could use a once over anyway. The Jeep seems to be OK for now but if/when the issue reappears I will definitly do the test you mentioned and check the voltage/test light. I'll put up a post if I find anything of interest.
I really do appreciate the info! Seems like you know your stuff, makes me wonder how you ended up a Wolverine's fan. Haha! Thanks again!