Stumbling on hot start
- Thread starter casm
- Start date
If you guys are getting codes then there is something else up. Misfire on six seems like a faulty CPS. I wouldnt go dropping money on a new ignition rail just yet. What is the exact code for misfire on 6? Interesting...
Here is the underlying problem...It is just a heat soak problem related to all 2000's with the thinner 0331 head. It happens to all of us with 2000's but you shouldnt be pulling codes on this. It should happen only if you run it for a while then turn it off for 5 to 10 minutes and then try to restart. (at least that is what I have found when reading about it).
Here is the underlying problem...It is just a heat soak problem related to all 2000's with the thinner 0331 head. It happens to all of us with 2000's but you shouldnt be pulling codes on this. It should happen only if you run it for a while then turn it off for 5 to 10 minutes and then try to restart. (at least that is what I have found when reading about it).
i only get the misfire codes when it misfires real bad..
basically it happens all the time when i restart it after about 5-10 mins, sometimes it stumbles a little real quik, and sometimes real bad, but always goes away after about 20 sec or so..
most of the time I get a misfire on #3 one time on #4
basically it happens all the time when i restart it after about 5-10 mins, sometimes it stumbles a little real quik, and sometimes real bad, but always goes away after about 20 sec or so..
most of the time I get a misfire on #3 one time on #4
NighthawkXJ
NAXJA Forum User
- Location
- Salina, KS
I had the same problem with my 97, and according to a very good mechanic friend of mine, most of the jeep 4.0s and alot of the dodge dakotas have the same hot restart problem.
Here is what he told me:
Rather than having the fuel presure regulator on the intake fuel rail, jeep put them in the tank with the pump, as well as the return fuel line that would normally run from the main regulator back to the tank. When you shut it off hot, the gas in the fuel rail vaporizes, but keeps the pressure in the rail. So when you start the jeep, it runs rough, cause the lines are all still under pressure, but you have to burn off the vaper before the good fuel will get there. This is where your misfire codes come into play, while trying to burn off the vaper, the motor stumbles, and the computer sees it as a misfire and causes the cel to come on.
If you give it a sec, and dont floor it, just let it try to burn it out, or shut it off real quick and then turn it back on, then it will clean out the vapor, and get fresh fuel to the rail. My cel will come on during this crap when im wheeling, and that is the only time it happens to me, just when im wheeling hard, but after a few more stops (air up at end of run, get gas, etc.) the cel will go out on its own, i have never had to have the code cleared or unplug the battery to get it to clear.
Hope this helps, sounds like it is a standard issue, he says make the fan run longer after shut off by grounding out the relay for it with a switch( you have to shut the jeep off, then turn the key back to on) hood vents, hood spacers, or cowl hood.
He works on the local PD Cherokees and that is one of the biggest problems the local PD has with the jeeps, they shut them off to do something, and then need to go again real quick (ie speeder in speed trap :flamemad: ) and they cant get the jeep running to go fetch the ticket.
If he is wrong, let me know, cause im also anoyed by it. Out of the 4 xjs that wheeled in our group last week end, both of us that have sealed hoods had this problem, and the other two had spacers or vents, and claimed they had had the problem right up till they modified the hood or added spacers.
Here is what he told me:
Rather than having the fuel presure regulator on the intake fuel rail, jeep put them in the tank with the pump, as well as the return fuel line that would normally run from the main regulator back to the tank. When you shut it off hot, the gas in the fuel rail vaporizes, but keeps the pressure in the rail. So when you start the jeep, it runs rough, cause the lines are all still under pressure, but you have to burn off the vaper before the good fuel will get there. This is where your misfire codes come into play, while trying to burn off the vaper, the motor stumbles, and the computer sees it as a misfire and causes the cel to come on.
If you give it a sec, and dont floor it, just let it try to burn it out, or shut it off real quick and then turn it back on, then it will clean out the vapor, and get fresh fuel to the rail. My cel will come on during this crap when im wheeling, and that is the only time it happens to me, just when im wheeling hard, but after a few more stops (air up at end of run, get gas, etc.) the cel will go out on its own, i have never had to have the code cleared or unplug the battery to get it to clear.
Hope this helps, sounds like it is a standard issue, he says make the fan run longer after shut off by grounding out the relay for it with a switch( you have to shut the jeep off, then turn the key back to on) hood vents, hood spacers, or cowl hood.
He works on the local PD Cherokees and that is one of the biggest problems the local PD has with the jeeps, they shut them off to do something, and then need to go again real quick (ie speeder in speed trap :flamemad: ) and they cant get the jeep running to go fetch the ticket.
If he is wrong, let me know, cause im also anoyed by it. Out of the 4 xjs that wheeled in our group last week end, both of us that have sealed hoods had this problem, and the other two had spacers or vents, and claimed they had had the problem right up till they modified the hood or added spacers.
RickyN29
NAXJA Forum User
- Location
- San Jose, California
Yeah, this is the only problem my Jeep has and it drives me crazy. This is on a 1990 Renix XJ.
It happened immediately after an ignition tune up. So I went and re-replaced everything with another brand. Still there.
Upon hot restart, any blip of the throttle will cause a severe hesitation, low idle upon return, and sometimes a stall after quick blip.
I have a whole list of things to check because this problem drives me crazy.
One thing I will throw out there, could a exhaust manifold leak cause this? Right about the same time I noticed this hot start problem, I noticed noise from the manifold (sounds like a leak). Perhaps the expansion (from heat) of the manifold could be exascerbating the leak and causing a idle issue.
It happened immediately after an ignition tune up. So I went and re-replaced everything with another brand. Still there.
Upon hot restart, any blip of the throttle will cause a severe hesitation, low idle upon return, and sometimes a stall after quick blip.
I have a whole list of things to check because this problem drives me crazy.
One thing I will throw out there, could a exhaust manifold leak cause this? Right about the same time I noticed this hot start problem, I noticed noise from the manifold (sounds like a leak). Perhaps the expansion (from heat) of the manifold could be exascerbating the leak and causing a idle issue.
I read in another thread that this is caused by the fuel vaporizing before it gets to the injectors, and that the fix was to use injector insulators from DCC, I cant remember the P/N but also, maybe insulating the fuel line is a good plan also. And as far as checking for recalls and if they have been performed there is a weblink on the chrysler (for newer jeeps) website that will look for you if you enter your vin.
FubAr4x4
NAXJA Forum User
- Location
- Dingmans Ferry PA
it sounds like a fuel injector, when my #6 went it had the same problem but it was fine on cold starts
YMMV
NAXJA Forum User
- Location
- New Jersey
Ben, I will have to pull the code again but I know the desc. on my Snap-On scanner says cylinder #6 misfire. I noticed this most during when the vehicle runs for awhile, I will shut it off and then restart (hot), it will stumble and misfire for a min but then corrects itself. Mine also does this sometimes if it is idling for a long period of time-like when Im on trails and I leave it running-but again it corrects itself.
I sometimes wonder if its a leaking injector. Changing plugs has made no difference.
I sometimes wonder if its a leaking injector. Changing plugs has made no difference.
Ben H said:
98XJSport
Destiny is the rising sun
- Location
- Western Maine
Sounds similar to a problem my 98 had, but it did it cold and hot, and time after it was off for 10+ mins. Turned out to be the upstream O2 sensor. No codes, either.
I just had a chat with my father inlaws cousin, hes a shop teacher..
He said it sounds like a leaking injector, he said something about puttinga gauge on the rail, turn the jeep on, not started, just to pressurize the system. Then turn it off.. He said it should hold pressure for a little bit, if it goes down fast, there could be a leak... Im going to try this as soon as I find a gauge
He said it sounds like a leaking injector, he said something about puttinga gauge on the rail, turn the jeep on, not started, just to pressurize the system. Then turn it off.. He said it should hold pressure for a little bit, if it goes down fast, there could be a leak... Im going to try this as soon as I find a gauge
YMMV
NAXJA Forum User
- Location
- New Jersey
spcustoms said:
I was thinking the samething. I am going to do the same. LMK your results.
RickyN29
NAXJA Forum User
- Location
- San Jose, California
I did the above test, no luck. Fuel pressure held for a few hours.
I scored a new O2 sensor at Pick N Pull, so I am going to swap that in for fun and see. (I currently have a Bosch O2 and from the day it was put it, the jeep ran worse.)
I scored a new O2 sensor at Pick N Pull, so I am going to swap that in for fun and see. (I currently have a Bosch O2 and from the day it was put it, the jeep ran worse.)
- Location
- Coshocton, OH
I have experenced this on my 2000 also. When I had spacers under my hood it would only happen when it was quite warm out, and after a hot restart. I have had it happen while wheeling without the spacers (the temp was close to 55*), but have never had it light the CEL. At least not yet.
YMMV
NAXJA Forum User
- Location
- New Jersey
Well.. mine seems to be a leaky injector causing my problem. I will be replacing it. I will keep this thread updated with my results.
RickyN29
NAXJA Forum User
- Location
- San Jose, California
Well, I will be attacking this issue headstrong. In the next few weeks, each of the following items will be replaced, one at a time, and tested:
All parts are on hand.
MAP (Manifold Absolute Pressure Sensor)
CTS (Coolant Temperature Sensor) for ECM, not gauge
IAS (Intake Air Temperature)
O2 (Oxygen Sensor)
KS (Knock Sensor)
EGR will be cleaned
Leaking exhuast manifold will be replaced with a Pacesetter header
New power cables/grounds.
And more that I cannot think of at the moment.
I will keep updated (expect a couple weeks)
All parts are on hand.
MAP (Manifold Absolute Pressure Sensor)
CTS (Coolant Temperature Sensor) for ECM, not gauge
IAS (Intake Air Temperature)
O2 (Oxygen Sensor)
KS (Knock Sensor)
EGR will be cleaned
Leaking exhuast manifold will be replaced with a Pacesetter header
New power cables/grounds.
And more that I cannot think of at the moment.
I will keep updated (expect a couple weeks)
- Location
- Coshocton, OH
The easiest way to check if it is the hot start stumble is to just open the hood on a hot day after you get home wait about ten minutes, and go try it. If it doesn't stumble then thats what you have. I would test it several times though to be shure.
ok, last night i did a good tune up- oil, new plugs, cleaned the contacts on the coil rail.. I also swapped the #3 injector with #1, well see what happens this week, if it does it again and throws a #1 misfire code, ill definatly know its the injector, if it does it again on #3 ill change the coil rail..
YMMV
NAXJA Forum User
- Location
- New Jersey
Any updates with any of you guys? I ended up not replacing my injector after doing some more diagnose. My fuel pressure is def holding. I am going to try to rewrap my injectors (part #56028371AA) and see what happens. Damn this is annoying.
