Shaky Xj

My 98 Xj has a strange fluke going on. It has done 5k since the engine swap with all the new parts (plugs, leads, dist cap, rotor, water pump, thermostat, fluids, o2, starter, brakes, fuel pump) I am likely forgetting some. However today when I started the truck after work it ran very poorly. Kind of like those old plymouths that didnt have a choke ran when you would try to start them in the negative temps. I didnt have to give it gas to stay running however I have no idea what this could be. Evened out shortly after. This has happened a few times before but never this badly. Because It only happens when the engine hasnt been running for hours (if it happens at all) I was thinking maybe when I derived timing for the dist I put it in a tooth off? Any thoughts?

Also after it evened out and the truck ran normal I did not notice any loss of power. Seemed to be in proper running order.

Check the wires going to the downstream O2.

Even tho you replaced the fuel pump, I would verify fuel pressure when you start it as a starting point. Also possible you have a lifter bleeding down causing a cold start misfire.

Why would the downstream o2 cause this? That monitors the function of the caddie but the upstream is what monitors the mixture. As for the lifter and the pressure I will have to look into that. Thanks

alexgalexg said:

Why would the downstream o2 cause this? That monitors the function of the caddie but the upstream is what monitors the mixture. As for the lifter and the pressure I will have to look into that. Thanks

Click to expand...

Yeah, that's what everyone says............


Until your DS eats your wires and it runs like shit.

Before I go through the expense of changing it would I see any signs on the plugs? Plugs have maybe 1k on them

Doubtful since it's only at start. I would not hold my breath for the rear o2 being the cause of this problem

My uncle owns a large mechanic shop. Full reports are done on every vehicle and every issue and how it was fixed so im going to take what I have found here and ask him as well to see if he can dig anything up

did a spark plug wire come loose? or maybe an injector wire not completely seated.

Before throwing parts at it I did a little poking under the hood. I think this was just a case of a dirty throttle body. This truck was a barn find and everything down to the air filter and coolant was original. When I put the new engine in I used the original intake and throttle body. Being out in 104+ degrees I must have forgotten to clean the inside of the throttle body when I cleaned the intake. Seems to have fixed my issue but if the fluke comes back I will update