4.0 l bogs down after 15 to 20 minutes of driving if key off for 2 minutes will drive another 15

[bob m]

2002 XLS has got me puzzled 200k miles 4.0L
Starts well idles great
No codes
Hot here over 100F
Drives fine for 15 to 20 minutes and then acts like a minibike with the choke on. Lacks almost all power but still will idle perfectly. Also out of gear engine will rev up. When you key off for a couple of minutes it will go for another 15 -20 minutes before the same thing will happen. If you lay into the gas when it is happing it will spit and sputter a little but I am thinking I may be hitting the wot cutout when pushing the gas trying to get something out of it.

So far I have
Searched all the forums I could find
Cats have been replaced (most common cause found for lack of power)
Fuel Filter replaced
Fuel Pump is new and running at 68psi
checked for vacuum leaks and found none

With Forscan I checked
MAF voltage - good across the range with the reference numbers I could find
TPS voltage- good across the range with the reference numbers I could find
Pulled cleaned and tested the EGR - was not dirty and used hand vacuum to check movement
Pulled and cleaned IAC since i was there but it Idles great
ECT in forescan matches the temp gage and is running in the middle
It is not happening in the transition open and closed loop as I made sure it was closed before and still the same
Fuel trims look ordinary within a few percent of 0

initial thought was it was temperature related but with the 2 min key off the engine only gets hotter from the short soak.

All ideas or insights would be appreciated

 

[Rick]

You have checked everything that I would have checked. Troubleshooting can be really miserable. Please keep us informed if you should solve the issue.

 

[bob m]

You have checked everything that I would have checked. Troubleshooting can be really miserable. Please keep us informed if you should solve the issue.

Thanks I half and thinking PCM but was hoping for some type of confirmation. the only thing I could think of that may reset something with a short key off but I was hoping someone would say the same before I spent the money on it. But honestly not sure that Key off resets anything involved.

 

[410Fortune]

This is an odd one
Does the truck roll okay? Meaning it will coast downhill,
No brake drag or anything like this

There are no trouble codes no flashing od light when it occurs?
Theft light?
Have you tested fuel pressure when it acts up? Meaning when it’s sputtering then see what fuel psi is maybe it’s falling off, it sure sounds like a fuel delivery issue
Weird that it re sets w the key!!

 

[CallMeSyd]

This is the same thing a guy just asked in my FB group. I'm going to tell you what I told him. It sounds like your coil pack is getting hot and weakening. I've seen it plenty of times before. If you let it cool down, back to normal until it gets hot again.

 

[bob m]

This is an odd one
Does the truck roll okay? Meaning it will coast downhill,
No brake drag or anything like this

There are no trouble codes no flashing od light when it occurs?
Theft light?
Have you tested fuel pressure when it acts up? Meaning when it’s sputtering then see what fuel psi is maybe it’s falling off, it sure sounds like a fuel delivery issue
Weird that it re sets w the key!!

I cant seem to find the fuel pressure on the forscan and I swear I had it in the past. I took fuel pressure using a manual gage attached to the fuel rail connection. No trouble codes the only light I have is and airbag light that came on before the issue started. I was half wondering if it could be something in auto 4wd loop that is locking or loading something. It is the only thing that I can think of that completely resets when the key off. struggling to think of something else.

 

[bob m]

This is the same thing a guy just asked in my FB group. I'm going to tell you what I told him. It sounds like your coil pack is getting hot and weakening. I've seen it plenty of times before. If you let it cool down, back to normal until it gets hot again.

Odd part is that it does not cool down key off for a minute and it will run for another 15 would figure it is only getting hotter under hood for a short key off.

This is an odd one
Does the truck roll okay? Meaning it will coast downhill,
No brake drag or anything like this

There are no trouble codes no flashing od light when it occurs?
Theft light?
Have you tested fuel pressure when it acts up? Meaning when it’s sputtering then see what fuel psi is maybe it’s falling off, it sure sounds like a fuel delivery issue
Weird that it re sets w the key!!

seem to roll just fine like it runs completely normal in15-20 minute intervals post key on weather hot or cold and will restart again no issue no stall idles well

 

[bob m]

This is the same thing a guy just asked in my FB group. I'm going to tell you what I told him. It sounds like your coil pack is getting hot and weakening. I've seen it plenty of times before. If you let it cool down, back to normal until it gets hot again.

i dont seem to get any misfire per say unless i push the throttle wide open. it seems to act better to a point if I slightly feather the throttle even a little pick up when I let off the throttle. I would figure if it is the coil I would have some misfire. maybe I am thinking about it wrong. any additional explanation would be appreciated.

 

[CallMeSyd]

i dont seem to get any misfire per say unless i push the throttle wide open. it seems to act better to a point if I slightly feather the throttle even a little pick up when I let off the throttle. I would figure if it is the coil I would have some misfire. maybe I am thinking about it wrong. any additional explanation would be appreciated.

I had one like that years ago. Turned out to be the MAF sensor. Running too lean under throttle. It really sounds like a MAF or TPS issue but I saw you already checked those. On a 2002, the only other thing I can think of is the DPFE sensor.

 

[410Fortune]

It could be pcm or fuel pump relay
It seems like something relay or pcm because a key off resets it

 

[bob m]

I had one like that years ago. Turned out to be the MAF sensor. Running too lean under throttle. It really sounds like a MAF or TPS issue but I saw you already checked those. On a 2002, the only other thing I can think of is the DPFE sensor.

when you had the MAF sensor issue did you get code? I had the dpfe issue prior and replaced it but it was few years ago.

 

[bob m]

It could be pcm or fuel pump relay
It seems like something relay or pcm because a key off resets it

I would think if it was the fuel pump relay that I would get a stall condition. It doesn't it will sit at a stop light and idle just fine but when you take off it is like a 10000lb trailer is attached to it. i keep thinking it is something related to the pcm as it resets with key off. but the only thing i found that completely resets with the key off is transmission 4wd auto. I am sure there are other things but not sure what.

 

[bob m]

It could be pcm or fuel pump relay
It seems like something relay or pcm because a key off resets it

I would think if it was the fuel pump relay that I would get a stall condition. It doesn't it will sit at a stop light and idle just fine but when you take off it is like a 10000lb trailer is attached to it. i keep thinking it is something related to the pcm as it resets with key off. but the only thing i found that completely resets with the key off is transmission 4wd auto. I am sure there are other things but not sure what.

 

[410Fortune]

I had the catalyst break free from the housing on a cat converter once. It gave me fits for months! Eventually even a slight incline I would have no power from my 4.0 bronco ii. I finally found it by tapping on the exhaust and dropping the exhaust mid pipe
The catalyst honeycomb was free and would slide back inside the converter housing, plugging the exhaust output!
That was an odd one to sort out

The pcm relay and ignition switch turn on and off with every key on/off those two things power many other things
Seems logical it would be something electric that resets
It would be nice to see what fuel pressure is when then occurs, just to rule it out.
Idle does not take as much psi as under load and the returnless systems will run okay even with low pressure (like 45) and then fall flat instant

 

[410Fortune]

one more thing to add
Every single time over the last 20+ years with these trucks and I mean every single time I had a truck that died on the road then would start back up like
Clockwork it was fuel related

Either the relay gets hot and stops sending power or the pump gets hot and cannot keep up with demand,

one time it was a faulty connection at the inertia switch, paper clip got me home.

Except one time it was purely electirc, and on that ranger it was his faulty wiring a splice in the power distribution on my stepsons v8 ranger so it does not really count

Would be awesome to check fuel psi when it happen and also check for spark

I’ve never had a faulty crank sensor do this “restart 15 min later” routine… once they go they usually go intermittent and then nada

 

[CallMeSyd]

when you had the MAF sensor issue did you get code? I had the dpfe issue prior and replaced it but it was few years ago.

I don't remember. I think you should try an obd2 scanner with live data. Watch your live data values when it's happening and you should be able to narrow it down pretty easily.

 

[bob m]

I had the catalyst break free from the housing on a cat converter once. It gave me fits for months! Eventually even a slight incline I would have no power from my 4.0 bronco ii. I finally found it by tapping on the exhaust and dropping the exhaust mid pipe
The catalyst honeycomb was free and would slide back inside the converter housing, plugging the exhaust output!
That was an odd one to sort out

The pcm relay and ignition switch turn on and off with every key on/off those two things power many other things
Seems logical it would be something electric that resets
It would be nice to see what fuel pressure is when then occurs, just to rule it out.
Idle does not take as much psi as under load and the returnless systems will run okay even with low pressure (like 45) and then fall flat instant

does anyone know if you can see the fuel pressure on forscan on a 2002? to connect my gauge I need to pull the coil out of position and the hose on it is only about a foot so trying to catch live data would be the only way I could read it. It has some type of sensor on the right side fuel rail but not exactly sure what it is. I am along the same train of thought as most fuel or air MAF TPS Fuel pressure but struggle on which resets with the key. Trying to avoid the parts cannon on such and old vehicle. Thought maybe the MAF if it was on the switch between closed and open loop but that change seems to have nothing to do with it and the voltage on the MAF and TPS seem to follow the numbers I have seen published on them when i test them. Cats were intact when they were changed. The odd thing is it never stalls pull over and it idles just fine and the engine will rev up just fine with no load on it.




I do appreciate the feedback from everyone.

 

[410Fortune]

There is no fuel pressure sensor on 02 that im aware of! But then you said yours has the sensor on the rail! Show me the sensor! If it’s not avail as live data then chances are the pcm is not monitoring it

 

[bob m]

I don't remember. I think you should try an obd2 scanner with live data. Watch your live data values when it's happening and you should be able to narrow it down pretty easily.

Thanks that I could do. What exactly would I be looking for? Air in excess with the fuel trims going wacky or a very low reading? The odd is that it always idles fine and if I put it in park when it is happening the engine will rev up with no load so if one of the sensors is bad I would think that the condition would carry over both in park or in drive.

 

[Turdle]

I wonder if the iac valve is sticking open