Is my cat getting plugged up? P0171 and P0174.

[rfingon]

My 98 Ranger has been throwing codes P0171 and P0174 for a while now, but only during in town driving when running errands (not on the highway traveling long distances). Also of note, one of my cats is getting hot. I have melted carpet under my mat on the passenger side. I haven't used an IR thermometer on it yet, to see how hot it is getting.

This is what I have done so far. New heads, pushrods, rocker arms, lifters, LIM gasket, plenum gasket, all 3 O2 sensors, coil, ignition wires, plugs, valve cover gaskets, fuel rail gasket, IAC, DFPR sensor. All torqued to specs and in correct sequence. MAF sensor cleaned (new more than a year ago).

I have looked for vacuum leaks with carb cleaner, and I cannot find any. After all that I have done, I should have kicked those codes' asses. BTW, she did have a burnt exhaust valve on cyl 5 (fixed that P0305!). No codes for a misbehaving catalytic converter, but she gets hot down there. Today, I threw a whole can of Seafoam through the PCV tube into the intake, in two different steps. Truck runs smoothly, but still throwing lean codes.

If anyone can shed some light in this, I would greatly appreciate it! Thanks in advance.

 

[rfingon]

I took the truck for a little spin after clean slating codes today, got it warm (normal operating temp) and used the IR gun on the pipes and cats while the truck was idling. The exhaust pipe going into the first cat reads 300° F, the first cat read 280-300°F, the entry into the second cat read 300° F, and the exit out of the second cat (and the exiting pipe) read 400-450° F. The exhaust pipe connected to the "cat" pipe before the muffler was 300° F. I am wondering if anyone knows what is normal, and if that second cat is out of whack.

The crappy thing is that if the back cat is going bad, I will have to have someone do it. I live in CA, and I cannot find a direct fit dual cat that meets CA state standards (only 49 state direct fit cats). I cannot weld, so I will have to bring the Ranger somewhere. Who knows, maybe this is normal operation for the Ranger, and there is still a vacuum leak that I haven't found yet.

 

[adsm08]

I think the cats are OK. IIRC cat light off is at about 400*, so you aren't even getting them hot enough for normal operation.

I'd keep looking for leaks.

 

[rfingon]

Thanks for the input. I will keep looking for a leak. Since it is throwing both codes, I wonder if that rules out a vac leak from the valve covers (unless both of them are leaking somewhere)?

 

[adsm08]

Valve covers keep oil in, not air out. PCV valve could cause an internal leak.

 

[Dune Runner]

CATS get hot. That's how they work. I had the same codes and tried everything under the sun. Ended up being the vent hose was off on my fuel tank. It was sucking fresh air into the system and causing the lean codes. It could be any number of things. keep plugging away at it and you will find it. Good luck.

 

[Bigstick1973]

Best thing for you to do is get it on a scanner where you can see your fuel trims and O2 sensor reading. I had the same problem on my 98 4.0l ranger. I did have a upper intake vac. leak. it was in the very front of the intake. i had to spray it with the carb cleanner tube on the can to be able to reach the leak or i wouldnt have found it. i sprayed the front drivers side on the intake. I did take the time to right down my fuel trims before i replaced the gaskets and after the leak was repaired. to see the difrence. if you do find a leak and decide to repair it your self there are a few postings on here with photos on how to do it. Heres a tip that i did when i did mine that i didnt see posted.
Make sure that you get a tube of vaseline like used on chaped lips just a small tube. you will need it to lube the Fuel Injector O rings and the Fuel rail where the injector go into the fuel rails. also the EGR tube where it goes into the intake. and the fuel pressure Dampner O ring. I didnt lube thiese and ended up with a pinched on ring and had to tare it all back apart to fix the oring. also i left my IAC on the intake to use as a handle. After you remove the intake nuts stand on the passanger side of the truck grabe the IAC and pull to get the EGR tube to come loose.
Good Luck! took me about a hour and a half.. second time around. lol

Here are my fuel trims with the leak
ST1 35.0
LT1 25.0
ST2 32.0
LT2 25.0

Heres my fuel trims after the leak was fixed.
ST1 1.8
LT1 2.3
ST2 1.6
LT2 2.0
These were taken at Idle. 850 rpms

 

[rfingon]

Thanks for all the input, everybody. Very scientific, Bigstick, to do the before and after readings on a scanner. I do have an Autotap, circa 2007, but I didn't record any values before and after. Smart move on your part. I do know about the Vaseline on the O-rings (definitely nothing should be used that is silicone based). I previously had all the injectors cleaned and checked, and that is what the shop recommended. I was very careful upon reassembly.

One place that I apparently neglected to check closely with the can of starting fluid at first was the EGR tube/valve interface. Even though I bought a new gasket for it, I may have not double checked tightening the two bolts on the EGR valve connecting it to the tube. When I hit the area with a liberal amount of starting fluid, it took a few seconds to make the engine idle go down. When the idle stabilized, I hit it again with the fluid. Again, the engine bogged down. Funny, I expected the idle to increase when the starting fluid got sucked into the intake, not decrease. After tightening those two bolts, I couldn't get the engine to bog down when I hit it with the starting fluid. So I think I got it. I did soak the PCV valve and contoured vacuum tubing connected to the upper intake, and that connection seems leak free.

Tomorrow's test drive into town should reveal if I was successful or not. I think I nailed it, and I sure as hell don't want to see any codes tomorrow. I am pretty sick of those two!

 

[rfingon]

Today's test in town revealed my codes again, but in different order. Got the P0171 first, then the P0174. Still on the hunt for leak(s). Unfortunately, a lot of stuff came off of my truck to put those heads on, so a buttload of variables of where the vac leak is exist. DOH!

 

[rfingon]

Here's a little update on the top rebuilt 4.0L Ranger. I have a new symptom. The DPFE hoses keep popping off under load, such as climbing up hills on I-5. Either one, but usually the larger diameter silicone tubing. I bought a suitable high-temp silicone set (Dorman), and still a hose will pop off while climbing up hills. Also, I now have a noticeable decrease in power while climbing up the hill. It is as if someone kicked this truck in the balls when going uphill. I then put hose clamps to hold the tubes on both the DPFE sensor and the nipples off of the tube to the EGR valve. Even with the clamps, I had one hose pop off of the larger diameter nipple last night while driving home.

Thinking that I have some serious back pressure in the system, this morning I placed a vacuum pump on the EGR valve to determine if the EGR tube is plugged up. After applying vacuum while the idling truck was at operating temperature, I could get the engine to sputter but not die. So it seems that I have a working EGR valve. Does this indicate that the EGR tube is not clogged, or could it be still partially clogged?

At this point, I decided to use some Seafoam in the intake (1/3 can sucked thru the PCV tube). After 10 minutes, I took the truck down the hill and back up (2.6 miles). I then used the IR gun on the cats again. This time, the pipe entering the first cat was about 450° F, the first cat was 500-550° F, the second cat and the exiting pipe was 650-700° F, and the muffler was 550-600° F. I should have ran my first IR temp test like this, after a little drive.

I have no problem ripping the plenum and EGR tube to check and rule out a possible clogged EGR tube. I however don't know how well Seafoam will clean a cat (or if it will clean it at all). I am crossing my fingers for a plugged EGR tube. Any input would be greatly appreciated. Thanks in advance.

 

[rfingon]

I have confirmed that the EGR tube is clear and open. So I am guessing that my back cat is having issues. Not happy. Time to put the intake back on and open the wallet.