Engine Bog On Start Up

I have a 99 xj, sport model with 58k. A while back it started taking longer for the engine to start when turning the key. Not a long time but two to three chugs compared to the normal one and good. Also after starting the engine would idle fine but then bog down when I pressed on the pedal.

After searching and writing down all my options I tried a few things. First off I want to let it be know that the jeep has new plugs wires cap and rotor within the lask 4k or so. Everyone mentioned iac when I searched so that was the first to get cleaned. And in the process I got over zelous in figuring out how it worked and broke it. So i have a new iac and a cleaned throttlebody. I used probably 100 qtips and stp throttle body cleaner. I cleaned my k and n intake and used put a bottle of dry gas in. The problem went away but the weather was also much warmer. It went from 50 and rainy here to 90 and hot at night. I used to only have the problem when the engine was cold. If it was fifty it woud start, bog, then i would kill the engine. Start it up no bog.

Last couple days its been cold and rainy again. Starting hasn't really improved since the cleaning but just the other morning it bogged when I touched the pedal. I doesnt stall just kinda chokes. One last thing, I put a bottle of chevon techron fuel system treatment in the last tank. Any ideas?

Thanks,

Tyler Forbes

i know it sounds funny but change the coolant temp sensor. mine was getting real bad and finaly put the cel on changed it truck runs good again. $15 fix if you can wrench

Im not doubting the sensor chance which I will try for $15 but can you try to describe the relation between the problem I'm having and a coolant sensor which appears to be working based on the internal gauge. I can see how there might be a link but cant quite vision it. Thanks.

Tyler

I grabbed a new coolant temp sensor on the way home from work. I then pulled the old one and threw the two in the fridge. After a cold soak for about a half hour i pulled the two put them in some helping hands and took measurements over the next 1/2 or so every 5 minutes. Both sensors from 40 degrees to 80 degrees were with 5% of each other and 5% of the published values throughout the cold range. I installed both took them up to temp and they both measured within 8% of what my dash gauge said. My guess is it isnt the coolant temp sensor but I will replace it anyway since there probably arnt returns on "tested" stuff.

When I started thinking about it there are three temp sensors, correct me if Im wrong. Coolant temp, intake temp, and block temp. My guess based on the fact that if I let the engine run for ~1 minute or pedal through the bogging is that the engine block sensor is the only one that could heat up that fast. Problem is I could not find it in the dark. I checked the intake temps sensor and it seemed to read normal.

Any ideas or help? Thanks.

Tyler Forbes

Does the 99 xj have a TPS?

My '89 did the exact same thing....as soon as the weather turned warm my jeep was hard to start and would stall and die on the first push of the gas pedal...this was with a cold engine. Was fine after engine warmed up.

The fix for stalling/hard starting in warm weather was to adjust the TPS properly which I didn't do at the time of installation in December.

They do have a TPS, but I believe they are non-adjustable. Can't remember the year they became that way off the top of my head.

I will try and diagnose the tps. Thanks for the idea. For the heck of it I rented a n autozone obd2 scanner. Hooked it up no codes. I will try it tomorow morning if it is cold but I dont think ill have any other results. Any other ideas guys.

Tyler

Guys,
New news. Its good to find a problem but not always what you want to hear. Just checked fuel rail pressure. Idle was ~49 psi. Shut if off and it stayed at ~47 psi. Four hours later 8 psi. Next morning nada, yep the guage read zero.

Started it up the pressure jumped back up to ~49, I got on it quick and watched the pressure drop to ~20 while I was on it good. I didnt bog on my but I was reving in park not drive or reverse. After the first drop I could not get the pressure to drop when reving the engine. Looks like pressure is bleading back into the tank. There is no visible leakage up front nor can I smell anything.

The funny thing is I have also been trying to diagnose a clunk in the back when I hit bumps. I tried the hatch, pulled everything out of the trunk, exhaust, shocks e brake lines. Still does it. Im thinking I have something loose in my pump assembly. O joy. This will be an adventure.

Anyone wanna confirm my ideas or thinks other wise.

Thanks,
Tyler Forbes

My 97/98 does/did the same thing. Its the fuel system. Fuel Pressure Regulator and or fuel pump/filter. The bog will occur mainly for the first few minutes, after a long, drawn-out start up. Go mellow on the throttle until you get some pressure built up. You'll prob get some Check Engine codes on occasion soon, since I'm guessing your starving one or more of the cylinders from gas for a spell. It won't be a big deal. I'm guessing you may also have evidence of fuel starvation from idle and hard left turns as well. Be prepared for this, since a quick start to cross ahead of traffic can be a killer if it suddenly goes "dry." More pronounced on 5-speeds like mine. I've heard it helps to keep the tank full, or to not let it get super low. On the long starts, Its embarassing, but you can actually live with it for quite a while. DON'T listen to the pre-97 folks on the fuel system. Its an entire unit (FP reg, pump, filter) and it's all in the tank. PITA. Gotta drop it, clean it, etc. to do right. Much worse if you have the tank skid/trailer hitch set-up like mine. Have it done by a shop, with a lift and knowledge of what they're doing. every late(last) model XJ owner has to go through this deal. Don't skimp on the replacement "module" but get the factory unit. After its done, have your codes cleared and you'll be fine. Not as bad in cold wx, or right after you shut it off, since the fuel press is still high enough. Its a Daimler-Chrys thing, they should have put an access panel in the floor, but that prob cost another $1.22 in labor when designing.buidlign the XJ. Couple hundred bucks to fix. sorry for the bad news. Good luck.