So my zj is being ugly and horrible. it will start good and run fine until you get to 2k then it starts jerking and stuttering violently...

I checked firing order. looks right. The #2 on the cap is more in the 7 oclock position than the 6, but the order looks right... (maybe dizzy position off?)... how do I check?

I have codes 12, 13, 55...

It has new cap and rotor and wires and plugs from previous owner... it also has new fuel pump.

looking for some ideas.

 

check your idle control sensor. that's what it was in my girlfriends zj



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On an OBD1 jeep (up to '96), there aren't that many codes and they aren't all that complicated. Normally, the 12 code means that the battery has been disconnected within the last 50 "ON" cycles, and the 55 means that you're at the end of the code list stored on your ECU, so that means that you have one fault that's been recognized by the ECU - code 13. This code relates to the MAP sensor - No difference recognized between the engine MAP reading and the barometric (atmosphere) pressure reading from start-up. The OBD1 codes sometimes aren't very definitive, but they often give you a place to start.

First, I'd check to see if the hoses are attached to it and that there are no cracks or breaks in these hoses. The connections themselves may have dried out and could be leaking. Vacuum hoses are pretty cheap and should be changed every so often anyway, so for a couple of dollars, you could just replace them & see if that works. If it doesn't help, your MAP may be malfunctioning.

Around here, a MAP isn't cheap, but because it's not common to have one fail or malfunction, you could see if you can get one at an auto salvage yard or borrow a good one from someone you know that has an OBD1 jeep with the same engine.

OBD 1 codes are available on a lot of sites, but don't mix the code meanings between manufacturers, for example, with an OBD 1 Ford, the meaning could lead you toward the IAC motor (Idle Air Control Motor), which is a linear stepper that sets/controls your idle.