Rough start only when cold
 

I've tried to search for a similar problem but I can't find anyone else who has the same problem without any symptoms while the motor is running. This whole hard starting when cold came out of no where but it seems to be getting more persistent.

Little history on my xj. 98 4.0 recent service done within the past 6 months...

New fuel pump assembly because when I bought it the check valve was bad.. new cap, rotor, plugs, wires, thermostat, coolant and heater core hoses, battery, new primary and secondary o2 sensors...on top of some gaskets and all the fluids changed.

Also cleaned the throttle body out a few times.

I am getting what feels to be a misfire when the truck actually starts up. It takes.an extra crank or so and stumbles to start for a second or so. Once its running its fine... almost feel like maybe the timing is off.. I'm really not sure.

Should I change the whole distributor? Should I change the tps sensor... what to do..

Oh and if the jeep is still warm and I hop back in it to start it...it starts up with out hesitation.

i know you replaced it... but its possible it could be the check valve again. do you have a tester to check the fuel rail? if so check once when its hot once when you first shut off and then again the next morning. pressure should remain the same if its lower in the morning then id go with check valve.

on a side note i doubt timing if it was more then likely it would do on both cold and hot starts, sounds like its losing fuel pressure.

My '98 has a similar issue, except it only starts rough when hot. I haven't replaced anything yet, besides a full tune-up.

One way to test the check valve is by doing the "Poor Man's Prime"--turn the key to ignition and wait for the pump to run, turn it off, repeat two or three times, and then start. This hasn't changed anything with my XJ though, and mine doesn't do it every time either. Puzzling!

I haven't tested the fuel pressure yet but it doesn't feel like it did when my check valve was shot..

Before I changed the fuel pump assembly it would crank and crank and crank and then start normal.

Now of cranks and it feels like one cylinder fires then it misses and then it starts..

This all started awhile back when my distributor started squeaking. I marked exactly how it was pulled it up and sprayed some white grease in there and it stopped making noise. For the month or two it was squeaking on start up it started doing this weird cold start thing


But like I said once running the jeep is great no misses no codes...runs like a top.

okay didnt know that, have you tested spark? sometimes it will give either a weaker spark or almost orangish color instead of blue when they go. they run about 80 bucks online with rotor camshaft sensor and cap included... money well spent.

Mine XJ had a rough start up the same as yours. Felt like a miss and stumble when starting. I just happend to order some 703 injectors for the 4 nozzle upgrade. Since I installed them it starts up so smooth. No more rough start....
When I took the old injectors out they were pretty dirty. That could have been my issue.

Worth a try....?

Good info I'm going to pull the injectors this weekend and see how they look. Maybe I'll try changing the plugs and if not I'll suck it up and try a new dizzy

if you are going to do injectors, please... please please clean the intake manifold when you do it. its going to have more burnt up gunk then you believe and the new injectors likely will rub some of it on them. take the extra hour or 2 and clean it out might as well clean iac and throttle body while your at it. no point doing it half way.. also new injectors get new orings and put a dab just a light coat of motor oil on lower seals before putting it in.

My manifold was pretty dirty when I removed them. I cleaned out the ports that the injectors go into with Q-tips and rubbing alcohol. They were not perfect but way better after cleaning.