Acts like I'm running out of gas after engine warms up

[rfields109]

94 explorer with stock 4.0 liter runs great when cold, after it warms up a bit it acts like it's out of gas when I push the accelerator down.

Would the fuel pressure regulator be a likely suspect? I've replaced the fuel pump relay, the fuel pump, filter etc... this vehicle sat for 5 years before I got it. I cleaned the gas tank out and the lines while I had it apart.

This seems to have gotten worse over the last few times I've driven it. Runs OK while cold, the warmer the engine gets worse the power gets until it's not safe to drive. Unless I feather the accelerator and then I can get around slowly..

Thanks for your help guys and gals

 

[Roadrunner777]

No check engine light? Beg, borrow, or buy a fuel pressure gauge and do some testing. If fuel is ok, I would run OBD-IV sequence to verify sensors. Potential issues:

1. One thing that happens when the engine warms up is it goes into closed loop mode, using MAF and O2 sensors to meter fuel. Maybe something there.

2. Possibly intake temp or coolant temp sensors, since it is temp related.

3. Something in ignition system failing when it warms up, happens with electronics sometimes. That would be the coil pack, ignitor module, or the PCM computer.

 

[lounge lizard]

just an easy check ( sometimes ) try dropping the cats out on the exhaust. maybe the cats are plugged up.

when cold they work but as they heat up they constrict the flow. till it can't spew out the exhaust.

easy check it cost nothing to remove a couple bolts if they come out.

for the age of the truck this seems to be something that is starting to show up more and more on older trucks.

 

[rfields109]

Checked fuel pressure and it ran from 29 psi to 40 psi based on RPMS.
Replaced Fuel Pressure Regulator
Cored the CAT, replaced the muffler too, original one and it was in rough condition.
Does not look like this is fuel related.

Checked codes and they pointed to O2 sensors which I attributed to running badly.
More codes for EGR valve and sensor (so I replaced them)

Found a bad air leak on the bottom of the duct coming from the Air Flow Sensor to the intake, ordered an aftermarket replacement however I mucked around with sealing it and it did change he attitude of the condition but did not fix it.

I'm gaining on it but so for no joy !

Open for ideas and suggestions
Thank you for your help!
Rusty

 

[colintrax]

When cold the "choke" is on, riching the mixture. Once it's hot, the mixture leans out, so that air leak is probably the problem. It's just to lean

 

[LXNavajo_94]

I agree that the biggest issue you have is the intake air tube. I had a similar problem with mine. Chased it for a while found a rather large say half dollar sized hole on the bottom side. I went to advance and picked up a replacement 3inch air hose for like 14 bucks did have to put a filter on the oil fil vent hose. I found one on clearance in the store for 7 bucks. I also had to buy a couple of hose clamps the ones off the old air tube would not open up enough to fit over the connector on the end of my new hose.

 

[SLOW RIDER]

I had your problem not to long ago it felt like it was trying to cut off i had to hit the gas to keep it running i changed my fuel filter and it helped a lot i think they should be changed every 30,000 miles

 

[unclemeat]

I would look for a intake manifold gasket leak, or idle air control valve. Cold engine, rich condition, additional air. Warm engine less gas more air, lean condition.

 

[rfields109]

Thanks guys for the feed back, I'll replace the Idle Air control valve, at it's age it might be time anyway. I have a new air duct to install and in general I've replaced the EGR, mechanical and electronic parts, fuel pump, fuel regulator, fuel filter, muffler and cored the cat. Thus I'm pretty certain it's air related. I'm going to run the intake bolts as well to make sure we don't have a leak there. I have sprayed EVERYTHING with starter fluid and can't find any place that changes the behavior. TEARING into it tomorrow if the weather is decent.

I appreciate the help everybody, When I get it READY I'll be looking for some trails

 

[rfields109]

OH YEAH, fuel filter was the 1st thing replaced when I put in the new fuel pump.

 

[MrShorty]

Out of curisoity, when you checked the fuel pressure, did you check it while the engine was stumbling? I had a fuel pump in mine that would only act up when hot, and the symptoms were similar to yours. If I tested the fuel pressure while "cold", it was normal. But, if I tested the fuel pressure while it was stumbling, that was when I could see the pressure drop to ~20.

 

[rfields109]

I think Mr Shorty might be right. I reconnected the fuel pressure gauge and the hose was long enough to run out to the windshield so I could see it.
Ran it at Idle and it held at around 29psi, drove around the block, pressure dropped to 25 psi and if I tried to accelerate it dropped a little and never went up, started cutting out and back firing a little... looks like my 8 month old rebuilt O'Reilly fuel pump was defective. I'll replace it this weekend and HOPE like heck it fixes things. Thanks guys

 

[rfields109]

Thanks guys, put a Carter fuel pump in and ditched the Airtex and it's running great again.

 

[Currency]

Glad you got things squared away. Hopefully you'll find some decent trails.

One local spot a lot of locals are my area head to is about to be logged out and then divided up for a subdivision. I'm looking to legal ways of stopping them since there is a historical tomb located on the property.

 

[rfields109]

Try getting denoted as a Historical Landmark, probably already thought of that but either way it would tie it up for a while.