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Wierd start up issue (every time)

Kmack23

NAXJA Forum User
Location
Kansas City
First off I have searched the forums for an issue like mine but haven't quite come up with anything, some are similair in nature.

I have a 99 XJ with a wierd "start up' issue. When I start it up it fires right up and runs\idles fine. After about 45 to 60 seconds it will start bucking, bad hesitation, etc. After about a minute of this sometimes butterflying the accelerator, stomping on the gas, it comes out of the up and down hesitation, bucking. The issue completly goes away and the XJ runs fine, actually great until the next time I turn it off. This happens every single time I start the Jeep. It doesn't matter if it sits for 5 minutes or 5 hours. So I know it isn't a cold start issue. I've run into a convience store for a few minutes and it will start this all over again and the vehicle is still warm (operating temp). I've tried a new Map sensor, cleaned the IAC (carbon build up), new plugs, wires and cap. It shows no check engine light on the dash. The jeep is high mileage but runs perfect other than this??

Anyone have an idea what this would be???
 
Goin out on a limb here (with my limited experience), but when is the last time you changed the fuel filter? Had similar problems with a minivan my dad had, but once that filter was changed, it was fine. Doesn't sound like a cracked manifold issue - that would be temperature evident. But overall, fuel filter would be my guess.
 
no help here but another question i had a similiar problem but now it shit on me and when i star it up it turns over and cranks up but when it goes to the run position on the igniton switch it dies immediately. any body have a clue on mine too
 
The same thing was happening to my '96 and I put it in the shop day before yesterday.
It came down to the ECU.
Signal voltage in, sensor voltages ok, but no output voltage to all the systems.
Some time ago duing a search on this site I read where you should un-plug each component individually until you find the bad one. Try some deep searching on this web site for more info.

The local parts shop said they could get mine rebuilt for $225+-, but no time estimate.:bawl:

We ordered a used ECU from the local salvage yard($340+-), 2-3 day shipped from ?? :mad:

'96 is a one year run for this ECU #, so the price is high.:rtm:

Now I'm stuck for the weekend (no 4-wheeling) to boot. :(
 
Check your fuel pump ballast resistor - should be forward on the driver's side fenderwell.

It can cause exactly the symptoms you describe - when you turn the key to START/CRANK, the ballast resistor is bypassed, and fuel pump gets full power.

When the key is in RUN, the ballast resistor is in the circuit, and serves to limit current into the fuel pump (mainly, to reduce noise.) If the ballast has failed OPEN, you won't have a circuit to power your fuel pump with the key in RUN, but it will still get power in START/CRANK.

The nominal resistance for the ballast, in ohms, should be stamped onto one of the terminals - making it easy to locate a replacement (they're typically less than 10 ohms, mostly less than 5.) They're cheap, so don't worry if you have to get one.
 
Mine was doing something like that. but it would keep bucking at crusing speed. No matter how fast or slow you would be going hot or cold. would throw a MAP sensor voltage low code. just replaced map, front 02, plugs, wires, cap, rotor, airfilter. Still doing it. Went up to the jeep dealer and graped their scanner again and scanned it. Same code. My buddie told me to check for a vaccume leak. Sure enough I have a large leak. The leak is usually on the rear hose off the valve cover into the intake. You have to squeeze it and move it around to find it. Mine waas a lack of vaccume canister. Since it was hit there they never replaced it. i ordered a new one will be in monday. I capped off this line and it is not at 85%. it will cruise and not buck. but from a slow take off it will still buck some. I will put the VC on Monday and see if that fixes it all. And look for another leak. If that dosent work we will call STAR and see if they know something.
 
Thanks for the replies so far. I'll check the hose and the ballast first. I'm hoping it isn' the ECU but who knows. I was wondering about fuel filter but I would think it would do it all the time just not right after it starts?? No?
 
Kmack23 said:
Thanks for the replies so far. I'll check the hose and the ballast first. I'm hoping it isn' the ECU but who knows. I was wondering about fuel filter but I would think it would do it all the time just not right after it starts?? No?

The fuel filter on your 99 is, as I recall, in the fuel tank. Rather than have a "sock" prefilter, then the pump, then an external filter; they decoded to do a "lifetime" filter on the OBD-II XJ (no, I don't know why, either.) Theoretically, you don't have to change it.

Given that you'd note fuel starvation more at startup than at idle or operation, that's not the first place I'd look. Check the ballast, and check for vacuum leaks (as someone else mentioned.)
 
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