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Very often this is caused by a faulty crankshaft position sensor , but I've also seen this a problem caused by a faulty PCM . When this loses power we need to checked the crankshaft sensor using a lab scope and see if the pattern is consistant
My research indicates a faulty Crankshaft Position Sensors tends to cause the vehicle to stall and not allow it to be restarted - not just caugh, and temporarily lose power and then come back to life with no further issues. I've found no other evidence to support your reply.
I don't have access to the scope you refer to and haven't the means (money) to take the truck to a dealer. I will, however, replace the sensor and if it resolves the issue, I will reply to the e-mail you sent, accept your answer and thereby authorize payment for your time.
As for the PCM, I don't have any way to program the VIN or Milage in a new one so I hope I don't have to go there.
Thank you for your time. I will let you know if the Crank Sensor solves my problem - that's one I haven't had to replace yet.
I tried to send you a message but I guess I don't know how to work this site. The egr valve seems to function normally. When vacume is applied to it, it moves and remains in the new location until the vacume is removed. The new Crankshaft position sensor was very difficult to access but had no effect on the problem. When the truck was cold, it started fine, ran fine for about two or three minutes. As the temperature guage behan to indicate that the engine was warming, it lost power with the natural increase in pressure on the gas peddle by me. The truck caughed and backfired several time and then began running normally once again. I drove the truck a couple hours later without the loss of power. It seems it only happens after the truck has been sitting over night or for serval hours. I keep thinking it has something to do with the transition from 'cold' operation to 'hot' operation. The only sensor I am aware of that tells the PCM when that should happen is the Temperature Sending Unit which was the first thing I replaced.
This was what I tried to tell you earlier when this website erased my typing and gave me a short list from which to choose my reason for wanting more ideas. I'm sorry I've wasted your time but this is getting really frustrating. I appreciate your efforts and if you have any other ideas, I'd love to hear them. I'm going to be at work until Monday and won't be able to address any additional steps until then.
I have no way to read fuel pressure. It is approximately 48psi when idling and during start. I believe the backfiring is caused by excess fuel in the manifold when the transition is made from 'cold' (rich fuel) to 'hot' (lean fuel). Once the truck backfires (and it's not a loud 'bang', it's a muffled 'thud' or 'pop' sound) a few times, it begins running fine and will continue to do so until it has an opportunity once again to cool several hours.
I do know that my fuel pressure regulator needs replacing because pressure in the fuel railing bleeds off within about 30 minutes of shutdown. The are no leaks in the fuel line. I always have to crank the engine 1 or 2 seconds, pause and then crank it again. The second crank ALWAYS fires in less than one second - virtually immediately. Once started, it idles and runs fine until the temp gauge begins to indicate it is warming. Then comes the loss of power, the caughing, muffled backfires and then it runs out fine again.
I'm sorry I don't have the answers to your questions - I'm sure my local dealership could answer these but I would have to leave the truck there at least overnight and it's the only form of transportation I have - and I can't afford their diagnostic costs ($125 per hour).
As I mentioned in my first question - it is backfiring up through the intake manifold and the throttle body. It is caused by too much fuel in the intake manifold from the fuel system delivering the 'cold' amount of fuel when in fact the timing has converted to the 'hot' opperating mode.
I'm on my way out the door and won't be back until Monday. I'll see what you have then.
Your problem sounds like a weak heater on the upstream oxygen sensor. This is a problem common to all Jeeps, trucks and Ram vans from '92 to 2003, anything that used a JTEC engine controller.
The oxygen sensors have a built in heater because the exhaust doesn't heat the sensor enough to properly monitor oxygen content, and the heater also helps it get into closed loop operation quicker from a cold start.
The sensor has a 5v pullup voltage on it for circuit diagnostics. When the key is first turned on the sensor reading will be at 5v. As the heater starts to work it bleeds off this voltage until the voltage is in the normal operating range.
When you start your engine it's in open loop mode. This means that the oxygen sensors are ignored and fuel control is managed basically by software alone. After it warms for a few minutes it will go into closed loop, when the oxygen sensor readings are then used. If you have a weak heater on your upstream oxygen sensor the pullup voltage will be bleeding off too slowly, and when the truck hits closed loop the sensor is still reading the higher pullup voltage instead of the actual sensor reading. The engine controller sees this and thinks its running rich and leans it out, giving you rough running, hesitation, and often some lean backfiring in the intake.
Also if it's already warm and you park it and let it idle for a few minutes the sensor will cool back off. The longer it sits and idles it will run worse and worse, usually you can hear the idle air control motor opening farther and farther to keep the engine running, giving a large sucking sound under the hood. This is more likely to happen in cold weather.
You would think this problem would set a code, but the software used in these engine controllers let this slip by without setting a code normally, because the voltage is still within normal operating range (not shorted to ground or an open circuit). It simply believes the wrong voltage is the true signal because it's still within it's voltage window of not being shorted or open.
I'd recommend replacing the upstream oxygen sensor, the one on the front of the catalytic converter. After you do, disconnect the battery to clear the stored fuel control adaptives out that have been falsely learned by the bad sensor. This step is just as important as replacing the sensor, since the controller has been adapting fuel lean because of the incorrect signal.
Time will tell but it would appear that changing the O2 sensor might have helped. Because this only happens once a day (during the first time the engine is started), and because this is intermittent, it will take several days to confirm but there was no studdering or loss of power today after swapping the sensors. I replaced both upstream and downstream since I was under there - I figured it couldn't hurt.
I'm confident that it's fixed! Thanks for the update and the Accept. I saw your feedback, HERE is a link to my profile page, you can open new questions right from there with a request for me. It would be best to have my username in the question too. It would be greatly appreciated!