OK, so I've been driving my Ram since purchase, and when I bought it the poor thing needed EVERYTHING. It's a 96 2 wheeler 3/4 ton, 5.9/OD. So far, did the plenum, full tune, both 02s, IAC, coolant temp sensor, new cat, new cat back duals, cleaned the throttle body and put a new gasket under it, that's about all I can think of but I bet there's more. Cleaned the crank position sensor and replaced the cam position sensor also.

Now I have a constant p0171 and p0172. I CANT get rid of it. When I start it it's terrible, really no fast idle at all. If it's a cold morning (by cold I mean really 60 or below) if you start it and take off before it's good and warm, it backfires through the intake and won't get out of it's own way until 2000 RPM's or so. It will randomly backfire through the intake when given throttle and has practically no power at all. I can't use overdrive as it shakes my teeth out when the lockup engages.

Now, I went to a friend's shop yesterday and hooked the hi tech scanner up to it, and drove it around. On open throttle when I'm getting no power and backfiring the 02s got as low as 0.0 volts, which I would assume is basically just air passing out the exhaust. It had a lean condition almost throughout except for spikes where it would detect rich. I got back and sprayed carb cleaner into the TB and watched the 02 sense it, so I don't think the 02's are out of the box bad.

I emptied 2 cans of carb cleaner looking for a vacuum leak, found one, fixed it, nothing. I let it idle and drove it around watching all 8cyls for misfire, nothing was detected. It FEELS like there is a dead miss or two, but nothing was detected on the scanner, and it throws (usually) no p0300 codes.

Now, a few months ago I was pulling my trailer and it FREAKED OUT. Flashing CEL, and backfiring, power loss to a halt. Threw p0300-p0308. Happened for a day or so, figured it was a freak incident, and maybe I got bad gas. In that timeframe I hooked a fuel pressure gauge up to the rail and had 50psi at idle, then took it around the neighborhood (with gauge hooked up and extended into the cab) and while beating it, couldn't get fuel pressure to deviate from the 50 psi. A day or so later, nothing, it was like it never happened.

Fast forward to last nite, I have had it with this thing, and not being able to pull my car trailer it's worthless to me, I put a for sale sign in it. It got pissed. I went to get pizza last nite and on my way home bam, flashing CEL was back, power loss like a madman. All of the sudden, the CEL went out. Drove further home and this thing was MAYBE able to reach 20 mph while popping out intake, surging etc (and I had my code reader hooked up the whole time) and after about 20 readings while driving, NO CODES. This thing is a freak.

So...now I'm really starting to think that the computer is kicked. What drives the injectors? What makes them work? I can't figure out why the computer didn't throw a code for all the drama last night?

I obviously took the for sale sign out, I don't want to sell it, I LOVE this thing, but if it can't pull, I might as well take it off the insurance. But I am not comfortable passing my problems to someone else so I think we are stuck together.

Sorry about the long post but wanted to be as thourough as I could be, anyone have any ideas?

 

To add to this mystery, it has been running lean for as long as I can remember, but after our little spat last nite, I started it right after posting this to go get some firewood from our yard, and while parked it was SO rich I could see grey smoke coming out of the tailpipes and it smelled like a car with the choke cable pulled. Straight gas. The code came up for running rich but it didnt turn the CEL on. This is the first time that I can remember of it just sitting running for 20 minutes completely rich. Im really leaning to whatever is controlling the injectors flow, as it seems to now get stuck on both sides of the spectrum but never lands in the middle. Any ideas throw em out! Greatly appreciated!

 

sort of a quote...
So far, did the plenum, full tune, both 02s, IAC, coolant temp sensor, new cat, new cat back duals, cleaned the throttle body and put a new gasket under it. Cleaned the crank position sensor and replaced the cam position sensor also.



yeah, i can see why you're about sick of owning this truck...

i've learned to pay attention to the codes, because the computer is telling you what it sees to be wrong. p0171 =LEAN and p0172 = RICH conditions in the exhaust. the pcm senses this and attempts to alter the fuel mix by dumping more or less gas through the injectors, up to its limits.

i've got a question for you. has it always acted this way, or did it possible start this problem when you fixed the plenum. shaking and missing can = lean (intake gasket leak ?) you could have an intake leak.

backfiring through the intake usually means that it either firing the plug out of time, or you have an intake valve problem. so i was going to suggest replacing crank position and cam position sensors. i see you replaced cam pos already. i think i'd replace the crank pos, and do that first to see what happens.

if that doesn't fix it, then you should do a compression test on all cylinders to see if you have a major problem or not. probably not, but you need to rule it out.

p300-p308 is telling us you have misfire on all cylinders, not just one. crank position sensor has a lot to do with this, so it might be related. also, since its not just one cylinder, i don't think its a single valve or injector problem.

the combination of the 171 (lean) and 172 (rich) tells me the pcm is swinging the mix back and forth, and is then surprised by the results. i see that you've replaced the 02's already, and you're not getting an 02 related code, so.....

my last random thought is that you have no fast idle when cold. thats the responsibility of the IAC, which works in combination with TPS sensor and temperature sensor. i think your 96 might have 2 temp sensors, one for the gauge and one for the computer. something is still wrong here.... i'd check/replace the IAC again. most places offer a 90 day, 1 yr, or lifetime warranty on those things. just say... it worked great for xxx long and now its stopped giving me fast idle. they'll replace it, but you have to take in the old one for exchange. see if you can use the scanner to temp signal to the pcm. make sure it know that the engine is cold.

what i've learned to do on these stupid expensive sensors is to keep a spare of each. sometimes you have to replace on based on a guess. if it fixes the problem, then i assume the old one was bad and throw it away. if it doesn't fix the problem, then i keep the old one and mark it as used/good, and swap it back in as a troubleshooting guess.

http://www.obd-codes.com/p0171 = LEAN
http://www.obd-codes.com/p0172 = RICH


edit - i'd blindly replace the front 02 sensor again. it and the PCM aren't seeing eye to eye.
remember, the PCM only knows what the sensor tells it. it can't see the true result of black smoke and smell.
it only listens to what the 02 sensor tells it, which can be faulty.

 

My thought with the o2, the manual says when at operating temp it is supposed to read between .1 and .9 volts, and at cold startup between .1 and .2 volts. Now, if I am at operating temp (and the computer has switched to closed loop as visible on the scanner, so the coolant temp sensor is doing its job presumably) and the front 02 is reading as low as mine was reading, 0.0 and usually hanging around 0.04, NOT 0.4 which sounds like it should be reading, is that low reading a lean reading? IE, the lower the voltage in millivolts is the leaner the condition? Or the richer condition? Im wondering if the 02 is reading backward of what I think it's reading. On the other hand, and there is always an other hand, the scanner had a little graph setup that said in plain english what the fuel/air mixture was, and it was nearly always reading "LEAN" which I figure gathers its info from the front 02. Both front and rear 02 were reading around 0.04 volts harmoniously so I am hard pressed to think it is an 02 issue.

I just ran out and removed the PCV valve, don't know why I didn't think of it before, replaced it with a bolt just to take it for a ride and it's still terrible. Would have been cool tho, really cool.

Do the MAF sensors have anything to do with this? It looks like a simplistic piece of plastic, is there a chance they go wrong and read the air flow incorrectly? It's wierd too, because on cold startup I can hear (what I think is the) IAC surging, there is a hissing sound coming from the throttle body, and it's almost as if the IAC is extending and retracting, unable to find a decent mix. Up and down, up and down.

Some other things I noticed here. It is caca on the road until around 2k RPMs, then it wakes up a little, almost always.

Beyond that, I just revved it in the driveway after the PCV brainfart and noticed it would rev up to almost the desired RPM, then drop a second and hesitate (up and down) and then head back up. So, let's say I was shooting to hold it at 2k RPM, it would rev nicely up to there, once I got about there, it would waver a tad like it was stumbling, then head back up to 2k. It was only a 100+/- RPM waver, but it was consistent every time.

I've never thrown a TPS code with this thing, but I'm wondering if it would be possible for that to cause this? I really don't see how, but I am all about learning. At this point I have a pretty well rounded Mopar EFI education, but like everything else in my life, I learned from broken crap hahaha. Thanks!

 

Take what dhvaughan said into good consideration. He had a lot of good information. Since we are suspecting that the o2's might be part of the problem, lets give this a shot first. Since you already have your codes documented in this thread, lets try this.

1. Disconnect the negative battery cable to reset the computer.
2. Disconnect the front o2 sensor connector
3. Start your truck and see how it responds. It should also high-idle when you start your truck after resetting the computer (at least mine does).

When an o2 sensor goes bad, the computer runs on its default value which is slightly rich if I remember correctly. The purpose of reseting the computer is to get rid of the values it created with your rich/lean condition. At minimum, doing the above will give you a consistant mixture to work with if the o2's really are bad. But then again like dhvaughan said, you arn't throwing o2 codes.... This may not help, but it certainly won't hurt either.

 

I will do that, even if it doesn't do anything, anything is worth a shot! It is unreal how much time I have spent with this truck. I get up in the morning and have my coffee, let the dogs out and gaze into the back yard at my forlorn car trailer, it seems like a previous lifetime when we had something goin' on.

What does the TPS do? I haven't replaced that, yet haha...and Im wondering what it does? I thought it just had to do with how far the throttle was pushed, but dvaughn, you said that the IAC works w/ the TPS? That may be a new avenue to look into.

 

I doubt the TPS is your issue, and you are correct it it has to do with how far the throttle is pushed. I tested mine a long time ago using a volt meter. There are three wires that go to it (ground, 5v+, Signal) You put the black lead to the black wire while the connector is still plugged into the truck, then take the red to the signal wire and back probe that one as well. Turn the meter to... 20v or so (i forget if the lower setting is to little). As you push the gas pedal, the numbers should incrementally increase. If you have a dip in voltage but you pushed the pedal further to the floor, then the tps is bad.

Edit... haha forgot to add that you need to turn the key two clicks to give power to the sensor. Also if you probe the wrong wire with the red lead, then it will just show up 5v constant no matter what, switch to the other wire.

 

Did that, and it was worse! Floored it would go about 4 feet at a time before just stopping, sounding like it wanted to rev and backfiring. This thing is killing me.

I got another CEL tho...go figure, p0171 and p0172 for a change haha.

Im really thinking something MAJOR is wrong here. The truck rarely acts the same twice.

What controls the IAC? ie...what gives the IAC it's info? I can hear the thing, it sounds like hissing, no hissing, hissing, no hissing. It's just going in and out of the pintel well (I think that's what it's called) and has no idea how to get the right amount of air. Does the PCM directly control this?

 

http://www.obd-codes.com/p0172

Check out this link.

Dave

 

Interesting... how can you throw a p0171 and p0172 to tell us a rich/lean condition with no o2 sensor. As far as the IAC, as far as I know it is controlled directly by the pcm to maintain idle. If it is moving, that tells me its functional.. just the computer is trying to idle and moving it to see a change.

I guess it is possible for a computer to go bad... expecially our style JTEC pcm's... However I know when my computer went bad it threw a P0601, but the truck still runs fine on the default values. I'd like to think in your case it is not the computer... but certainly shouldn't be ruled out.