Q: im fuel injected. acts like no gas is coming through system. once i pump pedal it starts up alright

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So I am seeing this is a common thing with Jeeps. I have a 1999 Jeep Cherokee sport 4.0L V6 straight 6, and a little over 182k miles. I have already changed the plugs, replaced the ignition coil (coil pack), wires, tps, air change sensor, radiator, oil pressure sensor, brake flush and I am still having the same problem. When I first start it up it runs fine. After the engine warms up periodically it will run rough and then die/ stall at times. If I am parking it dies losing all rpms to 0 I have to turn the key off and sometimes it will start back up immediately and sometimes it takes up to a minute. I have noticed that if I sit with my foot on the gas and break and keep my engine at at lease 1,000 rpm it will not die. but if I don't do that it will usually die on me. However, if I am on the interstate, I can get on it and it runs perfectly. It has a lot of power and runs great. It's just when it dies it's like I am out of gas. The fuel pressure is normal and the pump is fine i believe.

My car has 183000 miles.
My car has an automatic transmission.

It’s either a fuel or ignition issue, however you do have to check the air induction system, such as any idle air control valve, mass air flow sensor, and so forth. With regard to the fuel possibility, it’s relevant that you note that it runs well cold. When a car engine is cold, the PCM is programmed to enrich the mixture. That may explain why when cold, it runs OK as there is adequate (extra) fuel. Once the engine warms up though, and it goes into closed loop operation, the PCM uses the oxygen sensors to adjust fuel supply. I would use am automotive scope (oscilloscope) to verify the operation of the oxygen sensors, however if the sensors have never been replaced you might consider just replacing them outright as they would be pretty old. Of course, it is always good to test with a scope as that gives you more diagnostic data to understand what is going on with the engine. Often, what will happen in case like yours is you there is a combination of problems, so I would check the fuel injectors as well. Ideally, if you are really trying to "restore" the engine, the injectors should just simply be removed from the fuel rail and sent out to one of the many labs that test, refurbish, clean, and install new internal filter baskets. Mr. Injector is an example of these labs. If you service the injectors, obviously put a new fuel filter in. If the oxygen sensors and injectors are OK and yet you still have a problem, check engine compression and scope the cylinder secondary firing patterns which diagnostic will let you know if you have a fuel or ignition system problem. If you desire that a certified mechanic walk you through all of this and identify (and repair) the faulty components, simply request a rough running engine diagnostic and the mechanic will get this resolved for you promptly.

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