A quick correction on what I just said about fuel pressure:

On the new pump I installed, it was showing 50 pressure but idling bad. When I shut off the engine the fuel pressure stays at 50.

I put my old pump in and it's showing 40 pressure (used to show 50 before I changed the fuel pressure regular on it). But with this the truck is idling great and starts right up. When I shut off the truck the fuel pressure drops immediately.

Evil, evil truck...

 

ttt

I still can't figure out the problem Another idea I have is that something could be clogging the cat, so I may take off the exhaust system on it and run the truck to see what happens.

Alex

 

Just pull out the pre-cat O2 sensor, and see how the truck runs.

 

sounds like the cat

 

Your still chasing it. It's running you all over the map. There's definitely a problem here. I've been out of town for a bit and I come back here to see your not making any progress. You need help here for sure. I know what your going through and, what is happening to you is, you've got yourself an intermittent problem. This is quite difficult to diagnose.

I'll come back on tomorrow eve and help you root this out. I would get a test method together and start knocking each one off the pad ASAP vs. just swapping things around. Not to knock what your doing- we've all done that at one point or another but, this could go on and on for months at this rate.

I will help you but, you've got to follow along with the method and, it must be executed in the sequence of events in order for it to work. If not, it will be a huge waste of time.

First thing I want you to test ASAP is your FUEL PUMP RELAY. Start with the simplest and check it off your list first. A simple, cheap part may be the root problem. I always start off with the relays, connections, and wiring PRIOR to checking the pump itself.

If you do not know how, you can find the information online or, you can buy a Chiltons or Haynes manual and in there, you'll find the test procedure. I can also walk you through with complete instructions as a last resort.

Now, you must have a DMM to do this test. Do you own / have access to a Digital Multimeter? (DMM)

More tomorrow eve.

CM

 

Look at the key things the OP said in his first post

It drove fine for 20 miles. Check, plenty of time to determine if the cat was bad (clearly is not with this information)

From what I gather, the culmination of the fuel lines, the pump's built in cavity (the thing that prevents it from running dry) and then fuel rails that is about 15-20 miles worth of fuel to be honest.

The OP states the person he bought it from put in old gas from another car so he could get it home. Hmmmm.

Drain your tank, put in a bottle of gas dryer and fill it up with 5 or 6 gallons of good fresh gas. Repeat your tests.

Your engine will throttle up without any TPS reading by the way. But if your map sensor is disconnected... or faulty, it will behave exactly like this, except throwing a code as well.

 

It could be any number of things. Everyone is focusing on the fuel system here but, it could be something else. I've worked on this system many times and know it inside and out down to the PCM level as well as building my own fuel delivery system for my Dodge.

I wouldn't look at the old gas as a possible cause because, he's had issues with the new pump as well. I would only check the inside of the old pump for signs of contamination. If none is seen, that's a non-issue. At 50 PSI and, with the ID of the fuel delivery system, the fuel is cranking through the system. It takes more than one gallon to go 25 miles and, the amount of fuel that the entire system holds is much less than the gas required to go that distance of 25 miles.

The pump is constantly drawing gas from it's inlet and maintains constant pressure regardless of it's internal cavity. The fuel rails hold nothing for volume of fuel and, if it ran dry- it would die.

The CAT would not show up in that amount of miles if it was partially restricted. <IF> the CAT were totally impacted- YES, it would show up. However, that's ONLY in a totally plugged condition. I've gone miles and miles on a partially restricted CAT. IT would start out fine and work fine for a while until, it began to slow down and bog uphill with an occasional backfire along with a rising ECT. It did run rough however. I'd shut it down, let it cool, and it would be fine again.

He has an intermittent issue here where, it runs rough sometimes and sometimes it doesn't - regardless of what's been done. He's chasing it and, nothing in any of these posts confirms nor rules out any failure modes.

If the FUEL PUMP relay is intermittent- the same exact failure mode will occur. It will run extremely rough due to impedance mismatch thus causing a voltage drop at the pump thus, the pump will not rotate at the spec'd RPMs thus, a drop in pressure thus, it runs like crap.

Same applies with a bad fuel harness- same failure mode- runs like crap.

Now, if the driver CKT inside the PCM is going south and / or is faulty, the same exact failure mode will occur.

If the coil is low at the output or if the PCM coil driver CKT is faulting or intermittent, same exact failure mode will occur- runs like crap, sputters - same thing.

If the O2 sensor is way out of whack- same exact failure mode can happen according to some posts on this forum- sputters and runs like turd.

If there's backfiring *he said there was*, this also can be many things such as:

-faulty CAT / partially restricted
-CPS intermittent
-Dwell CKT / Hall (but, I think on the 99 they rid of that type and went to solid sensors instead)
-A/F ratio is out of whack due to many various sensor faults, PCM errors, O2 sensor out of range.
-Ignition Timing sequence at the PCM drifts out of range- bad ground

There's many things here that all induce the same exact failure modes :

Rough running, sputtering and occasional backfiring.

Now, if it were rooted at the sensor level, there would be a code thrown.

If it were in the coil- a code would be thrown.

If it were the coil driver CKT- no code is thrown.

If it's the injector driver CKT- no code is thrown

If it's a fuel wiring harness issue- no code is thrown.

If it's a plugged CAT- no code is thrown. NOTE: only if the temperature exceeds the upper limit threshold will the dummy light come on.

If there's a fuel leak, gas cap leak, filler tube leak or a clogged injector- no code will be thrown.

IF the wrong injectors are put into the vehicle- this will also not trip a code and, it would cause it to run like crap if they are outside of the fuel trim upper and lower range limits.

This could even fishbone out beyond what I've listed here.

So, in order to determine the root cause for failure here, it needs to be rooted out in a systemic method one by one. And, I always start with the most simplest to the most complex providing the simplest components pass OEM specs / tests.

CM

 

Actually, when I re-read his initial post just moments ago, he clearly stated that it drove fine for 40 miles. So, that rules that out completely- throw that out. As for the old gas- that's a non issue and, to further add to his initial comment / question regarding it would have run like s-hi-t from the beginning if the gas was bad so, throw that out as well. His logic was correct.

Now, in light of re-reading the very first post again, it sure sounds like a clogged CAT. The gradual bogging, the REV limiter due to serious back-pressure applied etc etc.

I read that over a few times and, after doing that, the first thing that comes to mind is a spent CAT.

See, the thing is, this can also be caused (as I stated earlier on) a clog or restriction somewhere in the fuel supply. Either at the pump level and or, rusty fuel rails in which, I am going to explain in detail next.

TOPIC: Restriction at the fuel rails and injector baskets.

Whenever a vehicle sits for a long period of time, moisture takes it's toll on the components. Now, the fuel rails are made of cheap ****, cold rolled steel which, if not pressurized, ends up rusting on the inside.

When this happens, the inside walls (base metal) starts to break down due to oxides forming on the surface. Despite being coated with either a super thin film of Teflon or other surface treatments, the base metal starts to bleed through this barrier through tiny microscopic pores. It then starts to connect from pore to pore until the entire wall surface is coated in particulates / rust. Eventually, it starts to break down and flake off, thus losing more and more of the protective coating on the inside which in turn exposes more and more base metal thus expediting the corrosion process.

At that point, this rust is very large in particulate size. When the truck is run, the fuel pressure acts as a pressure washer and breaks the surface tension of the rust free thus dislodging it. This loose material / debris makes it's way into the fuel filter baskets of each injector to more or lesser degree.

When the truck is run, the pressure forces more and more particulates into these baskets and, over time, it restricts the fluid flow thus, the longer it runs, the worse it gets.

Conversely, when the truck is <OFF>, the pressure is not pushing forward as was when running. The loose particles now float around as if in a suspension thus, allowing to run fine upon start for a short period of time.

This condition will also induce a backfire condition due to a lean condition being present.

Other scenario:

Now, the other thing that will cause the same exact thing to happen is when you've got a gross vacuum leak at the intake level. Since it happens after driving for a bit, it is quite possible that after warming up, there is compliance in the gasket at the intake to head interface thus allowing large amounts of air into the system to enter undetected thus leaning out the A/F ratio. This would bog it down, cause backriring, loss of power etc. In this case, the PCM has no way to monitor that air coming in. The O2 sensor is the primary sensor that is going to provide that fluctuating voltage for a lean condition at which point, the PCM is going to adjust the fuel trim to bring it back within nominal range.

When it is first started, it is running on preset values so, the fuel trims are fixed for three minutes until it reaches the setpoint temp at which time, it starts to adjust for that after the exhaust temp reaches it's temp range programmed at the PCM and, the ECT reaches it's set-point value programmed at the PCM and lastly, the timer counts down and triggers the switch over to closed loop mode. This is when your O2 sensors are input into the PCM to adjust fuel trims based on the output.

This is a basic explanation of how this system functions. By determining the output at the O2 sensor, the PCM can determine fuel flow rate and, it adjusts it accordingly.

I wanted you to have a better understanding of the system level function so, this is why I explained that above. If you know how it works on a system level, you can get your head wrapped around it and learn where the problem may be rooted without the need for extensive testing / probing etc.

Now, going back to focus on that gradual slow down and rev limiter- in my experience and, in my mind, it sounds like you've got a CAT issue. With that in mind, what happens over time is, serious back pressure is built up and maintained during operation thus not allowing the engine to breath. If nothing is coming out, not too much is going to get sucked in.

It works on displacement. For whatever the piston is displacing, nearly the same amount of intake is consumed during the down stroke thus creating a vacuum. If there's a plug at the output section, the input section has no where to go thus slowing down the entire combustion process thus causing the engine to fight itself just to keep running.

This back-pressure keeps a near constant force applied thus making it difficult for the motor to rotate thus, the drop in RPM load speed.

It's also very damaging to the metallurgy. The excessive thermal loading on the combustion chamber as well as internal components is greatly increased thus compromising them. This is what causes cracked heads, cracked valves and cracked rings and cyl walls. If the thermal properties of the components is exceeded, the material starts to break down thus inducing permanent damage.

I would have that looked at before anything else. Now, in your case, removing the O2 sensor is most likely NOT going to improve the condition due to the small orifice and, in this case, it takes a really long time- about 40 miles, before it starts bogging down.

I would remove the CAT 100% and drive it w/o it to test it properly. If it improves, root cause: restricted / partially clogged CAT.

IF it does NOT improve: back to ruling out one system at a time.

CM

 

CM,

thank you again for the time you're taking to give suggestions. I spent some time at home trying to remove the cat on the truck, but I just don't have the necessary tools on me. As of yesterday the truck was towed to a local shop. The shop's owner specialized in Dodge work vans and trucks, so he should be able to diagnose the problem quickly. I will keep you all updated on what he finds. Hopefully this information will help someone else in the future.

Alex

 

Sorry to hear ya had to take it to a shop. Good luck on finding out what the problem is. I know I'm anxious to know.