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Losing power and lurching when engine warms up

2K views 37 replies 10 participants last post by  JStMarie 
#1 ·
Cruising down the road today and out of no where I felt like my clutch was slipping so I headed home. The jeep was lurking kinda jumping when getting up to speed, I also noticed a huge decrease in power, today was the hottest day of the year so far here. Cut it off and let it cool down a minute and fired up fine and idled fine. Ran great with full power no lurking for about 5 mins then started doing it again. I've searched and searched with many people leaving the thread unanswered to what the problem actually was. I have no cel, so don't know what sensors to check or anything, just curious as to where I should start. Any help is appreciated.
 
#4 ·
fuel pump will not set off code... have the pressure tested..
Also look up to see if your injectors have the heat wrap around them..
just some ideas that dont set codes... But go have your computer read to see if any stored codes
Fuel pump won't set any codes?? Bullsh**! It can cause a P0171 and/or a P0174 which is bank 1 and/or bank 2 lean. And you'll lose power too. But as mentioned above a plugged cat is a better fit for the description given. Try removing the O2 sensors before the catalytic converter and see if you still lose power in the same way. The Jeep will be quite loud once you remove the sensors so avoid doing that late at night.

If the problem is the cats then the best fix is a new Y-pipe. The weld-in aftermarket cats can be a can of worms and oftentimes do not have a warranty since the maker has no control over who welds the cat in or how they do it.
 
#8 ·
Jeepsr4me said:
fuel pump will not set off code... have the pressure tested.. Also look up to see if your injectors have the heat wrap around them.. just some ideas that dont set codes... But go have your computer read to see if any stored codes
my injectors and fuel rail aren't wrapped and never have been but I may try that. Would a 02 sensor going bad telling my computer to send more fuel?
 
#9 ·
Yes, the O2 can cause rich running, and your symptoms do match a bad O2. I just had a bad O2, and did not get an engine light. To diagnose, disconnect the O2 sensor and drive for a few miles. If it runs better the sensor is bad.


You can purchase the OEM NGK sensor from Napa. It's expensive, but I can tell you from first hand experience that it will last a long time. I got about 130,000 miles out of mine, and the original lasted about 150,000.
 
#12 ·
Jeepsr4me said:
fuel pump will not set off code... have the pressure tested.. Also look up to see if your injectors have the heat wrap around them.. just some ideas that dont set codes... But go have your computer read to see if any stored codes
Any more info on this fuel injector wrap? I live in a pretty hot area where the next few months will be 100+ without a doubt, keeping things cool is always a good idea.
 
#15 ·
Over the past two days I've noticed my temp gauge reading normal , the drop down to like 140ish just under the the quarter mark. Could the temp sensor on the thermostat housing be bad causing this? Also it has started idling too rough and cutting off to be able to drive. It'll start and idle rough for about 20-30 secs and cut off.
 
#19 ·
This is not normal, and really it isn't possible (meaning the temp can't run at 140ish after the engine has heated up, the cooling system just isn't that efficient). The PCM (computer) uses the temp input to determine whether the engine is heating up or has heated up to normal (fuel trim, etc...) If the computer suddenly thinks it's "warming up" when it is really at temp then it could signal the injectors to dump more fuel as more fuel is needed during warm up. This is a problem and needs to be addressed before chasing anything else as it may be causing all your other symptoms.

Good Luck. :cheers2:
 
#17 ·
Upon more searching I found that I had gas in my oil, and it was getting into my exhaust somehow. If I pulled the fuel rail and it has pressure would the leaky injector be leaking?
 
#20 ·
bobjp said:
Did you ever disconnect the O2 sensor? How did you determine that there is gas in the oil? You should be able to see which injector is leaking by pulling off the fuel rail and turning the key on (not to start) so that the fuel pump turns on.
my oil smelled like gas and was really watery. And if that's the case then I don't have a leaky injector. And yes I disconnected upstream o2 with no change then downstream o2 with no change.
 
#21 ·
I missed your post about engine temp. JSTMarie has a good point that the engine runs richer when trying to warm up. Perhaps your engine temp sensor is bad. I know others have complained about rough running due to an engine temp sensor, but I don't recall complaints of gas in the oil.

I've never tested a temp sensor, but got some hits with a brief search. Here's one discussing a YJ.
http://www.jeepforum.com/forum/f12/testing-coolant-temperature-sensor-3717241/

Are you sure there isn't a head gasket leak that is allowing coolant into the oil? Was the oil level excessively high?
 
#25 ·
I know for a fact that it wasn't coolant, coolant levels are fine, the oil still looked like normal oil just watery and smelled like straight gas. I'm getting oil into my exhaust too. I dropped the exhaust from the manifold and the manifold was full of oil..
 
#27 ·
Pull all of the spark plugs out and look inside each cylinder at the top of the pistons. The piston tops should have a fair bit of black on top of them. If any of the pistons look like shiny aluminum then that's where the leak is.
 
#29 ·
xxdabroxx said:
It sounds like you might be getting a lot of blowby. Oil in exhaust, gas in oil. Is it running on all cylinders?
it was before, ran fine and idled fine except the occasional lurking while driving, but never a cel for a misfire. But then all of the sudden yesterday, it decided to idle rough and sound like a drag car with a big cam, then eventually fouled the plugs and won't run.
 
#30 ·
I'm still thinking your coolant temp sensor is crap (that's the technical term) and causing your mix to be out of whack.

First thing is stop cranking the engine until that oil is drained and replaced.

Change the temp coolant sensor and your oil and oil filter (or at least pull the filter and dump it).

Post back what you find.
 
#31 ·
JStMarie said:
I'm still thinking your coolant temp sensor is crap (that's the technical term) and causing your mix to be out of whack. First thing is stop cranking the engine until that oil is drained and replaced. Change the temp coolant sensor and your oil and oil filter (or at least pull the filter and dump it). Post back what you find.
I'll have to change the plugs too, it fouled those out pretty quick. Also I don't have good fuel pressure I opened up the valve on the fuel rail and fuel just trickled out.
 
#32 ·
Also I don't have good fuel pressure I opened up the valve on the fuel rail and fuel just trickled out.
You checked turning the key to the on position? The fuel pump only kicks on for 2 to 3 seconds when key is turned to the on position and then will run when the engine is cranking only if the PCM has a good crank sensor output.

It's counter intuitive to have both a fuel pressure issue and too much fuel delivered when the engine is running.
 
#33 ·
JStMarie said:
You checked turning the key to the on position? The fuel pump only kicks on for 2 to 3 seconds when key is turned to the on position and then will run when the engine is cranking only if the PCM has a good crank sensor output. It's counter intuitive to have both a fuel pressure issue and too much fuel delivered when the engine is running.
my only guess is it not reading much fuel pressure so it keeping my injectors on longer to make up for the lean mixture, and yes I checked the pressure after flipping the key to the on position and back off a few times to makes sure it built up pressure. It's reading right at 9psi.
 
#35 ·
my only guess is it not reading much fuel pressure so it keeping my injectors on longer to make up for the lean mixture, and yes I checked the pressure after flipping the key to the on position and back off a few times to makes sure it built up pressure. It's reading right at 9psi.
The engine management system on a TJ does not have a fuel pressure sensor. Therefor it does not know how much fuel pressure is present and is not capable of trying to compensate for that.
 
#36 ·
The problem is the fuel pump. The plugs are fouled and the cylinders are washed and the oil is full of gas because you've been cranking the engine without it starting for so long. Replace the engine oil, replace the fuel pump, replace all of the spark plugs and before you start cranking again put a little ATF in each cylinder. Engine oil will work too but ATF will flow into the ring lands much easier to help reseat the rings. Another thing before cranking is to cycle the key about 3 - 5 times to be sure the system is primed. Once the engine starts it'll smoke really good for a moment and will probably misfire a few times. Let it run and clear its throat.
 
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