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Missing out on hot starts- odd symptoms

96 Cherokee

NAXJA Forum User
Location
Indiana
Recently the 4.0 has been missing out on hot starts, like its running on 4 or 5 cylinders. Cold or cool starts, like after it sits for over 30 minutes, and no problem. Also, it takes from 15 to 60 seconds to clear up after it starts missing, ususally- sometimes longer. After searching this forum and talking with the mechanic at the dealership, it sounds like it may be a leaky injector. However, here's the kicker: it only misses out when the ambient temp is above 70 degress F, or thereabouts. It's been in the 50's here lately and when it is, no problem with hot starts. Could a leaky injector be temp sensitive? I am taking it in to the dealership Monday to have the fuel rail pressure checked, and whatever further diagnosis thay can do. 223,500 mostly rural mail route miles, almost everything on the engine(injectors, electronics, etc.) is untouched since new. Recently replaced the plugs, wires, cap, rotor, and forward O2 sensor.
 
96 Cherokee said:
Recently the 4.0 has been missing out on hot starts, like its running on 4 or 5 cylinders. Cold or cool starts, like after it sits for over 30 minutes, and no problem. Also, it takes from 15 to 60 seconds to clear up after it starts missing, ususally- sometimes longer. After searching this forum and talking with the mechanic at the dealership, it sounds like it may be a leaky injector. However, here's the kicker: it only misses out when the ambient temp is above 70 degress F, or thereabouts. It's been in the 50's here lately and when it is, no problem with hot starts. Could a leaky injector be temp sensitive? I am taking it in to the dealership Monday to have the fuel rail pressure checked, and whatever further diagnosis thay can do. 223,500 mostly rural mail route miles, almost everything on the engine(injectors, electronics, etc.) is untouched since new. Recently replaced the plugs, wires, cap, rotor, and forward O2 sensor.
What about the engine temp sensor, it's different than the gauge sensor.
It may not read a warm engine and may be always in cold start mode.
 
langer1 said:
What about the engine temp sensor, it's different than the gauge sensor.
It may not read a warm engine and may be always in cold start mode.

If that were the problem, then it seems to me that hot starts on a 75 degree day would be the same as hot starts on a 60 degree day. But, they are much different. Come to think of it, when it is missing out, I can smell unburnt fuel in the exhaust. If it is a leaky injector, how long shoud it take to clear out after then engine starts? On these problem hot starts, the engine starts easy, then in 1 to 2 seconds it starts missing out, sometimes real bad. That part just does not sound like a leaky injector to me.
 
96 Cherokee said:
If that were the problem, then it seems to me that hot starts on a 75 degree day would be the same as hot starts on a 60 degree day. But, they are much different. Come to think of it, when it is missing out, I can smell unburnt fuel in the exhaust. If it is a leaky injector, how long shoud it take to clear out after then engine starts? On these problem hot starts, the engine starts easy, then in 1 to 2 seconds it starts missing out, sometimes real bad. That part just does not sound like a leaky injector to me.
I didn't say it was not working at all, it could just be off by 20 deg's or so.
 
I know this is an old thread, but I see I did not post the resolution to the problem. It was a bad fuel pump. It was pumping air bubbles into the rail. Less than 2 years old and it failed. Had it replaced and all is well with the engine since. Wish I could say the same about the transmission.
 
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