Background: 2001 5.9 Magnum out of a 1500 Sport swapped into a 1999 Jeep Wrangler TJ with Jeep 5spd manual. Runs on truck computer and wired so that the Jeep thinks it's a Ram. HemiFever tunes to eliminate the auto trans and give power. No internal mods. Wiring looks factory and all connections were soldered and heat shrinked.

I did all of the work myself and know this thing is right. It has ran for 2+ years with no issues until now. The only codes I get are coolant temp sensor and evap canister. Can't find the right sensor and haven't bothered to eliminate the evap circuit.

Problem: It will start, idle, run and drive fine when cold. When it reaches operating temp the idle speed will increase 2-300 rpm. Then if you even breath on the throttle it will die immediately. It will sometimes restart when you floor it, but misses and backfires. Will run rich enough to dump raw fuel.

I've replaced every single sensor. I've traced and tested wiring. It doesn't throw any new codes. It just effing dies.

Fuel pressure is constant 43 psi when running. Drops as soon as it dies.

TPS voltage is normal.

Fuel pump relay sees 11.6 volts at distribution center, and pump sees 11.6 at pump. I can't figure out why though.

Alternator tested well, but I wonder if it's dying off when warm.

Ideas?

 

Fuel pressure should be around 49 at idle.

Coolant temp sensor would definitely give you the problems you are seeing. It's a two-wire sensor, might be on the passenger side of the intake, right behind the alternator, or, it also might be by the thermostat housing, between the alternator, and a/c compressor. (if it's there. can be a drag to see if both are there.)

Temp sensor for 01 ram *should* get you the correct one.

How old are the O2 sensors, and what brand?

 

I've always suspected fuel, so maybe it's just a touch too low. I've traced and retraced the wiring and find nothing wrong with it. The pump is only a year old or less even, but maybe it went bad on me.

Coolant temp sensor has been that way for 2 years and it ran fine, so that's not the issue. It only allows the engine to adjust fuel trim, and should not cut fuel completely out of the system. I've replaced it 2x thinking that I had a bad one, but for whatever reason it doesn't read the signal until the engine nearly overheats, then it registers as hot. I've always assumed it's a wire impedance issue.

It only has one O2 sensor, right after the y-pipe, and it's new within the last 2 years. I can't recall the brand, but I do recall buying a specific brand because of what I learned about how sensitive these engines are to O2 brands. I only put about 2-3k miles on it a year as well. However, O2 should only adjust fuel trim, not cause it to not run at all. They don't have that much control.

I'm not sure why low fuel pressure would cause the idle speed to increase once it reaches operating temp. Maybe you have some thoughts on that?

I know that I have a plenum leak because there is a small pool of oil in the back of the intake, and because they all do. That should effect performance and economy, but from what I understand should not kill it. I've sprayed starting fluid all over the intake looking for leaks and the engine doesn't even flinch.

Here are all of the sensors I've replaced, just for certainty:

• Throttle Position
• MAP
• IAC Motor
• Coolant Temp
• Distributor Pickup
• Crank Position

I do not intend to be dismissive of your suggestions, but since I built the entire wiring harness by hand for the swap I had to learn exactly what each circuit is for and what each sensor does. I came here for fresh eyes on the problem and appreciate your response. Please keep them coming.

 

Coolant temp sensor can have a profound affect on fuel. If the sensor tells the PCM it is -40 degrees, it will positively DUMP fuel into the cylinders, and too much, is just as bad, if not worse, than not enough. If you have a scanner available that will do data logging, I would be real tempted to do a warm-up cycle while logging, and see what sensors do what.

On an 01, you should have two O2 sensors, one before, and one after the cat. It is rumored that the rear O2 can indeed cause some interesting driveablility issues.

No pinched wires in the harness anywhere? I have crunched some between engine and trans on more than one occasion.

Basically, what you have is something getting warm, and screwing up. Given that you have seen the same behavior with multiple coolant temp sensors, makes me wonder if the PCM isn't getting too hot..... Where do you have it mounted?

 

Boy! An interesting problem, sorry, but I have nothing to add, just following this thread to see how it all turns out.

Since I got rid of my '03 TJ to make room for the ram, I figure you have the best of both worlds there, once it's running again. (I still had the I6 though it was enough for me)

 

Your'e on to something! My scanner does have a logger and it showed -40C, but I wasn't sure that it had ever shown that before because I honestly never looked. I may have to eat my words about the sensor.

I had the rear O2 tuned out since I don't have a cat. The rear O2 is just to determine if the cat is working properly and fine tune fuel trim based on its performance.

The PCM is mounted in factory Jeep location on firewall, and since they are exactly the same size/shape, etc. it should be fine and has been for the last 2+ years.

 

An idea. I know that you have been running it this way for a couple of years now but...


Do you have any hood vents? What type of fan system are you running (elec, no doubt)?
Just thinking that the under hood temps may also be getting up higher than they used to.

 

Well, this is my 3rd built Jeep. The first was a 4-cylinder YJ, which wheeled like no other, but the lack of power sucked. The next was a CJ with a Vette LT1, but I bought it that way and it had too many bugs for my liking. This one started out as a nice daily, but the I6 wasn't nearly enough after the Vette motor. I tossed a 505 Performance turbo setup on it and after blowing through 2 engines decided to swap in the 5.9. My wife used to have a Durango RT and I loved that thing. When I found the wrecked Ram for cheap I knew exactly what I wanted.

No hood vents, but the fender wells are wide open. Has a 16" electric fan on a thermostat.

The exhaust started to get really hot in Colorado when I was there in September. I rolled it a few days before and figured out that a wiring harness had gotten close to the exhaust and melted the loom. I've inspected it thoroughly and it doesn't have any bare spots. Some of the wires were stuck together and had to be separated, but they weren't completely melted and I could just separate them with my fingers. When it was running so hot I assumed it was probably running lean and that the pump wasn't getting enough voltage.

I still suspect the pump isn't getting enough voltage (11.6v), but it only has 11.6v all the way back at the PDC, which has no sign of heat damage.

I wonder if it's a combination of the coolant temp signal and fuel pump voltage? Guess I have some new places to focus on this evening.

Thanks for the thoughts on this!

 

just another thought, if your fuel pressure is only running 43 psi, then id imagine the duty cycle of your injectors is nearing 100% to make up the difference, check your fuel trims with the scan tool and see if there pushing +20%..

 

Is the fuel pump volts measured under load or is it a constant 11.6? If you upgraded (to a larger pump) it may be pulling more amps than the old, not getting enough voltage then to do the trick. Remember, volts-amps is an inverse relationship, if one goes up the other goes down. Drawing more amps= dropping the voltage more. Now, if this is a static measurement, pump on but not pumping, 11.6 may be okay (but it does sound low). Still assuming you have a bigger pump in there, trying to draw more amps through the smaller wire gauge will bring on heat, bringing on more resistance, greater drop in voltage.

As long as all of your "melted" wires are separated,that should be no problem. Were any connectors near the headers, got too warm?

Still thinking...