CR-Snow

Ok guys and girls, I've done a few searches and I'm needing some input from the community on this one. I'll start with some basic info.

-01 4x4 4.0
-motor was replaced ~12k miles ago by PO
-supposedly a Jasper long block installed
-I've owned the vehicle for appx 3 months, of which, its been in the shop about half that time. The guy working on the jeep builds my boss' drag racing cars. he is a very skilled fabricator and domestic v8 guy, but not a jeep tech by any means.

So here are my symptoms: Jeep initially presented with Intermittent rough idle, poor gas mileage, a CEL, and very infrequently, a flashing CEL indicating a misfire. eventually the rough idle turned to a consistent issue, the misfires started happening more frequently so I took it to my guy. normally I would do this type of work myself, but I was in a time crunch so I was hoping with his expertise, we could solve the problem quickly. Not the case.

Codes:
initially had misfire codes for the rear 3 cylinders, O2 grounded to chassis code and lean mixture code.

Right away we were thinking vacuum leak. did the brake cleaner or carb cleaner or whatever he used test by spraying around vacuum lines and ports. tested the brake booster for leaks, sprayed all around the EVAC system **which apparently was replaced right before I bought the jeep, PO told me the CEL it had when i bought it was from that EVAC solenoid being replaced and that the code hadnt been cleared. This seems fishy to me now. someone clear that up for me if possible** anyway, no obvious vacuum leaks could be found.

did a compression and leakdown test. I think i may still have an 0331 head, so i was terrified at the thought of the expensive jeep i just bought having a cracked head but those two tests turned out fine. so...

we pulled the plugs, rear 3 were black from running so darn rich (im guessing), replaced the rear O2 sensor, and replaced a coil pack. I left the jeep with him for nearly a month. he would drive it around, check the symptoms, replace something, wait for symptoms to return, then repeat. finally after a month, I asked him if i could just have my truck back. he told me that it had run good for the last 4 or 5 times he'd driven it, no CEL, no misfires but because of the intermittent nature of the problem, he couldn't guarantee it was completely resolved. So, I took it home. It ran good for a day. Third time I started it after getting it back, CEL came back on. Rough Idle returns. No misfires or flashing CEL, but it smells rich and is sort of sputtery in general.

I ran the current CEL codes at Pep Boys yesterday. getting code PO174 - Lean Condition code

So.... Things I'm considering as problems... first, it still seems like a vacuum leak to me. maybe intake or exhaust manifold gasket?? I would think that with the motor being out so recently, that the gaskets would be fine but given the complex nature of those gaskets, maybe someone screwed up putting those gaskets on.. what you think?

also, I've read on here that some of these symptoms are similar to crank position sensor malfunction symptoms. maybe cam position too? any other sensor issues that this could be coming from? I'm really not excited about pulling the manifolds in 99 degree Kentucky heat, or about paying my guy to do it either.

if you guys have ideas on sensor replacement, could you include brands to go with too? Thanks for reading this novel of a post. People that have had these tricky little issues know how hard it is to track down the culprit, so I've tried to be as detailed as possible.

Thanks guys

CCKen

Could be a defective upstream O2S for that bank of cylinders or a defective O2S heaters relay for that bank of cylinders.


A scanner that shows live data would show the defect.


This pic shows the Oxygen Sensors you should be using.

CR-Snow

Upstream o2 for that bank was replaced. Can you explain o2 heaters?

CCKen

Each O2S has a heating element in it that assists in bringing the O2S up to operating temperature. The heater is operative from the time the engine starts and as long as the engine is running.

There are two relays in the PDC, as seen in the diagram below. There's only one fuse for both heater (relay) circuits. Pic below.


If one relay fails, both O2S's heaters associated with that relay will be inop.




.

CR-Snow

Thanks for the replies man. Can I test those relays with a meter? If so, what's the protocol?

Anyone else have any ideas? What's the sensor that meters air coming in called again? Could it be malfunctioning? Probably not the case given the rear bank is the only one having issues??

CR-Snow

So I went out to the jeep today and went over as many vacuum lines as I could find. Didn't find any leaks or breaks in the lines. Inspected the EVAC system from front to back and everything seems fine.
Pulled the relays suggested from above and looked at the connections, all clean. I seriously doubt that helped anything at all. How do you check a relay with a meter? Or should I just buy a couple and drop them in?

Anyone else have any other ideas? Could any other sensors be contributing to this lean condition?

CR-Snow

Dang, quiet day on the forums. Maybe tomorrow someone has some ideas.

wanna-be-a-wheeler

I had an issue very similar on my 96 xj. It became undriveable the issue got so bad. Mine did turn out to be the upstream O2 . Just throwing out some info hope this helps man .

CR-Snow

Thanks for the info. I just replaced the upstream o2 on the rear bank. I'm starting to think it's the intake or exhaust manifold gasket. I was hoping maybe a crank position sensor could be the culprit. I suppose it couldn't hurt to throw one on.

CCKen

Here's some data pertaining to P0174, taken from the 2001 FSM diagnostics manual:


P0174-2/1 FUEL SYSTEM LEAN


When Monitored: With the engine running in closed loop mode, the ambient/battery temperature above 20 deg. F and altitude below 8000 ft.


Set Condition: If the PCM multiplies short term compensation by long term adaptive and a certain percentage is exceeded for two trips, a freeze frame is stored, the MIL illuminates and a trouble code is stored.


^ This is where you need to use a scanner that shows live data.


POSSIBLE CAUSES


INTERMITTENT CONDITION


RESTRICTED FUEL SUPPLY LINE - I don't think so


FUEL PUMP INLET STRAINER PLUGGED - I don't think so


FUEL PUMP MODULE - I don't think so


O2 SENSOR


O2 SENSOR SIGNAL CIRCUIT SHORTED TO GROUND


O2 SENSOR HEATER OPERATION


TPS VOLTAGE GREATER THAN 0.92 VOLTS WITH THROTTLE CLOSED - I don't think so


TP SENSOR SWEEP - I don't think so


MAP SENSOR OPERATION - I don't think so


ECT SENSOR OPERATION - I don't think so


ENGINE MECHANICAL PROBLEM


FUEL FILTER/PRESSURE REGULATOR (HIGH) - I don't think so


PCM


In addition to these possible causes the intake manifold gasket may be defective or the manifold isn't seated properly, clogged or dirty fuel injectors, exhaust restrictions such as a clogged Cat.
This dual Cat/dual upstream O2S system is tricky. The PCM may be seeing a lean condition from an O2S and is compensating by adding fuel and in the process is causing the other three cylinders to be flooded. The O2S bank that shows lean remains lean because of an intake leak on that manifold, or the injectors on that bank are clogged, or the Cat on that bank is clogged. Why it would show a lean on the 2/1 system I don't know, when it could be 1/1 that is lean.

CR-Snow

Right on. Thanks much for that post. I've been keen to do the injector upgrade anyway so I suppose I'll start there. I'll Just do a little search for those newer style Bosch single hole injectors. Thanks again. I'll keep this thread updated.

CR-Snow

New injectors came in. Planning to take the truck back in to my mechanic tomorrow to get the manifold gaskets done. I was going to wait till the results from the gasket change were back before putting the injectors in.

Is this a good idea or should I get those injectors in ASAP.

CCKen

Generally, folks use four hole Bosch injectors, not single hole.

CCKen

It's best to do one corrective action attempt at a time.


There's no need to spend money needlessly.

CR-Snow

I like the one corrective thing at a time idea too. I'll wait till this gasket goes down to see how it's running.

I bought those newer style Bosch single holes. Read probably 20-30 pages worth of stuff from several threads about the 4 hole and these newer style single holes. Seems like they both achieve the same desired results. Quicker start up, smoother idle and throttle response etc.. But I'll wait on putting those in. Got some bushings to do this weekend and some steering u joints too. Can't wait to work on this thing on Saturday.