Fuel trims bank 1 suddenly show lean

MikeP

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#1
Make
Jeep
Model
Grand Cherokee
Year
2004
Miles
156k
Engine
4.7 v8
Hi! Thanks for reading this! Bank one setting intermittent lean code. Hooked up scanner and both banks st and lt trims normal and fluctuating. Running good. After running 15 minutes or so, suddenly st jumps to 32 and sits there. Lt follows suit in about 10 seconds, both at 32. Dash light comes on (of course) truck still running good. Clear the code and might go 3 days or 3 weeks fine. Then it does it again. Thoughts? Thanks!
 

nickb2

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#2
Would be good to get FP pressure when 32.

But since I like being the devils advocate. I rarely if ever see +32% LT ST trims and
After running 15 minutes or so, suddenly st jumps to 32 and sits there. Lt follows suit in about 10 seconds, both at 32. Dash light comes on (of course) truck still running good.
 

nickb2

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#3
Normally, @ - or + 15%, engine will run rough.
The not so normal trims limits are -/+10%, but code at 15 or so if they stay that way for an excessive amount of time.

-/+32 is almost unheard of and seeing a smooth running engine.

So, I must ask, are you sure about your pid data? If you are, can you tell me what software and hardware you are running?

Running lean on both banks is pretty indicative of a restriction of some sorts or a major vac/exhaust leak and algorithm is trying to correct. But, again, I never see +32% for long periods of time, and if I do, probably a cat cooked for sure.

Since I don't know what scanner you are using, or what method you are using, maybe you are getting a 15% swing both ways accounting for a gross 30 or so%. An ecu/pcm can calculate that far. But with a differential of +32% and calculating for the odd -%, you are way out of what normal ecu's can calculate for fuel correction and I have no idea how that engine is running "good"

When I see 30% on any car, air leak is the first thing that comes to mind, and those cases we can barely get the vehicle in the bay without some sort of help.

Ford has a sweet way to confuse the UN-initiated, they calculate fuel trims as a whole swing, from - to + and them determine long term for that. But mopar uses a different strategy unless something has changed since the last time I picked up a scanner, which is all day every day.

Now, who am I to say this, I am just a master tech. Does that sound condescending, yeah maybe, but no way that engine is running right with +32% enrichment due to a lean engine probably due to a massive air leak somewhere.

If you can even make to closed loop, that is astounding.

With those percentiles, no way the ecu will even let the engine into closed loop, will code way before that, which is why I am amazed you can even read that type of enrichment and consider this engine is

truck still running good.
.
 

nickb2

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#4
I have been waiting for this type of thread to make a point. Fuel trims are an awesome tool that should be learned by techs in this ever evolving trade.


But the best way, is to understand PID data limits. Once you understand that, the numbers you see on your scanner screen make more sense.

A car/truck running at +32% can almost if not run at all. But put into a different PID data scale, the ECU will see this as a differential of the two and calculate a whole, and the stratagem for the algorithm makes sense at this point. Now I know I am a french guy, my english is good enough, but my main point here is to help you decipher what you are seeing.

If this was a race car, we wouldn't even see this type of limit.

This is where a scope, or bi directional scanner shines. If you could injector kill a few, trims would go down. But I don't think this is your problem.

So here is where you need to listen. What are the O2's telling you in voltage scale. Since you have live data capability, you can surely post a graph, or screen shot at time of event of +32%. I would love to see those numbers and bring that to my master tech night course just to chew the fat with fellow techs on how this mopar POS is still running "good".

@Mike P, we have talked before, an you know I don't blow smoke out of my arse. SO make sure you tell me what software and hardware you are using, maybe you are just not using the right pid data format to read proper integration algorithm.

I want to see load, rpm, maf, tps and all o2's and of course lt and st trims in the same table. Is your scanner capable of doing that in a fast baud rate, depends on what you using.
 

nickb2

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#5
I highly doubt you will get an accurate reading as the ecu will code way before entering closed loop. This is a sick engine to say the least.

ECU need alot of info to get into closed loop. Such as O2 temp, ect temp, air flow (MAF) and load and other various pids. The shit part here is that often, a situation such as this will erase itself as the ECM/PCM/ECU tries to correct itself because it only goal is to get into closed loop.

NickD says it best here, automotive is the worst kind to work on as it has a self preserving code.
 

nickb2

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#6
Point of fact, which I wanted to post in the other forum for imports, but will do here and post pictures of how I fixed it.

Audi quattro 2.0l turbo, in with massive lean codes, misfires on all cylinders, manufacturer codes telling me it cannot attain closed loop.

I took time to take pictures. They will come shortly as I left my laptop on my tool box friday as I was more keen on beer than hauling my laptop home. I have my I7 pc here to have more than enough fun with.

I could hear a massive whistling noise, when dip stick removed from engine oil verification tube, it wanted to suck my index in. Hauled out the tranny cooling hose I keep aside for vac leaks. I use this to listen. Kind of like Beethoven when he started going deaf. So vac leak was present at crankcase pressure regulation valve. My vac gauge told me the dip stick was sucking 16-18hg. Guy's at the shop thought the engine was blown. So did I at one point, but when I would cover the dip stick with my index, engine ran somewhat capable.

When it would die or try to die, that and only there would I see trims go high, nothing even close to +32%.

Long story short, and pic will prove it, just a major vac leak from the pressure regulation valve which had a torn diaphragm.

Safe to say, client was lucky, because the intake was literally sucking all the oil out of the engine and throwing it back in the combustion chambers.

I did an oil change, put a combustion chamber clearner in there (for you american guy's, got seafoam on hand now, better than the VIC shyte carquest was selling us) and laughed seeing the smoke coming out the exhaust. changed the OEM plugs with new ones, and saved that engine/turbo cuz it would have starved from lubrication very soon. When client saw pictures and proof of part in her hands, and she had told me she went to 4 other shops with no joy for that check engine light, she had no idea she was this close to buying another audi. safe to say, my beer this weekend is on her dime.

Her tip was that fat:p
 

MikeP

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#7
Hi again, long time no talk! I can get freeze frame data, and watch live data. Everything else seems normal to me, and ues it really does run fine. This is all why I posted here after all these years, because it is certainly very strange. The fact that the trims bounce back and forth either side of zero like normal for 15 minutes while in closed loop at idle, part throttle, etc. Then in a blink of an eye bank 1 sensor 1 short term and long term jump and sit steady at 32 all while the truck runs fine makes me think electrical glitch.
 

MikeP

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#8
Further testing.. it is in closed loop, b1s1 is pegged at 32 both st and lt. And yes, it runs good... maybe a little rough at idle, but really not bad. Anyway, adding propane has no effect on this reading, but the other bank ABSOLUTELY responds to the extra fuel. I pulled a plug from both banks, the good bank looks great. The bad bank is black, clearly running rich, yet being told it's lean. So I'm thinking the O2 sensor is faulty. Solid deduction?
 

MikeP

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#9
Something happens when it gets good and warmed up. I cleared the codes, started it up, watched the live data. Idles perfect in open loop. Closed loop in about 60 seconds, still smooth. Both banks switching normally and responding normally to throttle spikes, etc. Both banks in the same range. Coolant temp gets to 200 and levels out. Still all good for about 2 more minutes, then in a blink of an eye, bank 1 st starts to climb and in 15 seconds is at +32.8, with long trim reaching 32 about 10 seconds later. Bank 2 continues to act normal. Idle roughs up a little, which makes sense since it is probably running rich due to the false lean. Could the sensor do that? Or is something triggered at 200 degrees that is messing with the sensor or the pcm? This is strang to me.
 
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#10
Been a Seafoam nut for years, one ounce per gallon of gas helps keep the fuel system clean, one ounce or quart, about 300 miles before changing the oil keeps your lifters clean, can also pour a full can in the TB, let it soak to clean off the face of the injectors and junk off the intake valves.

Other AF ratio problems are caused by the PCV, was not much of a problem when returned to the base of the carb, sure is now returning it to the TB input sticking the TB vane. Yet another one is a sticking EGR valve, these two things really have to be kept clean.

When I run into problems like this, don't stare at a scanner, time to do some housekeeping.
 

MikeP

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#11
NickD!!! Long time no "see"... Way back when, blown head gaskets on a '91 taurus 3.8, our first daughter was a toddler... Well that toddler is now married!
Anyway, this jeep has been house-kept, I am only having the issue with one bank, so I am pretty sure I have a sensor issue (whether it be sensor, wiring, pcm) on that bank. All cyls are firing, all injectors are working, all 4 plugs are now dark, so the lean code and +32 stft is very false. I'll check actually voltages with my DVOM in the next day or so to figure what's what. Hope all is well.
 
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#12
MikeP did kind of ring a weak bell, wow, time sure goes by fast, youngest daughter turned 27 last year and left home, now just my wife and I. With our wonderful economy, my kids are scattered all over the country, two of them in foreign countries to find jobs. 16 grandkids, three I have never met yet.

Yeah, that 89 Continental kept me going, new problem every week, but still have my 88 Supra yet.

Erratic does spell electrical
 

MikeP

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#13
Time flies.... I hope all your family, and you, are doing well... I still have the '93 Bonneville, that Transman helped me rebuild on this site. It only comes out in sunshine.
 
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#14
To the best of my knowledge, O2 sensor is the only one that deals with AF ratio running lean or rich. So is yours lying, or is there an injector misfiring providing excess oxygen?

Ha, one friend came over with a rough running engine, lean after spending 1,500 bucks at his shop replacing this or that. Put my vacuum gauge on it, low, his intake manifold bolts were loose.

That new GM compound EGR valve almost drove me nuts, maybe it did, top half was working perfectly, but the bottom half was opening it when it wasn't suppose to killing the idle.

Another car was an 80 Horizon misfiring, pulled the carb three times to find bits of neoprene blocking the main jet, finally found a sharp edge on the tubing, whenever I connected the hose, was peeling off bits of neoprene.

Did purchase a new Hyundai Elantra Limited with an engine over cooling problem, Hyundai said a recall on the thermostat, not a darn thing wrong with it. But has a heater inside of it to expedite production in adding coolant. Hooked up my digital scope and hit the starter, found the voltage was dropping belowe 8.5 V, was not getting a proper POR. found one loose screw, been working properly ever since. Other guys and dealers were going nuts with this problem.
 
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#15
Filled my tank in around 2007 for winter storage, did see ethanol on the pump, had no idea what that meant in my 88 Supra. Back then, this is all we could buy. But sure found out next spring, entire fuel system was corroded, about a thousand bucks worth of parts at internet prices, and sure had to watch my language.

Can buy ethanol free gas now, but cost more than E10, but it costs more to make a gallon of E10 than pure gasoline, just saying you can have problems by our nuts running this country, also can't afford to eat a hamburger anymore.

Some owners manuals state you can use E10, but not E15! What's the difference? E10 will just take a bit longer to screw up your injectors.

Ha, was talking to my son's father-in-law, says his riding lawn mower is running fine with E10, but then I learned he was laying out 150 bucks for a new carburetor every season.

What are you running in your Jeep?