Ok, this is another post about my idle problems (sorry guys). The symptoms are an idle stumble/missfire, with occasional stalling. I hooked up a scanner (again, Snap-on ), and noted the BLM adn Integrator readings. The BLM reading cruises around 111 this is tellling me that the ECM is leaning out my mixture for some reason (even though the plugs always show signs of running lean). The Integrator readings dip as low as 108, or as high as 122 (but WHY?). If it was running rich enough to pull that much fuel out, it would at least show SOME signs on the plugs. At part throttle the BLMs dip the most, holding a steady 2000 rpm is where it hits 111. The only other odd sensor data I notice is the Timing advance numbers, they read "0" and don't change reguardless of rpm. I have no codes in the memory, the ignition checks as being fine. Balance test fails to isolate a cylinder. Vaccum reading are normal (except when it stumbles/misses, then they drop slightly).

 

You said the ECM will not adjust timing. Is your EST wire connected? Just wondering.

-Buck

 

Of course (but it's always good to check the obvious stuff)
If the engine runs with that connector disconnected, it throws a code. I have NO codes. EVERY sensor on the car is giving data within normal parameters (for the most part...) Also, they have all been replaced (save for the CTS).

 

They shouldn't show signs of running lean because it is actually leaning it out to compensate for a rich condition. When it finally levels out and stays consistant at one number, that means that everything is right around 14.7:1...so they won't show lean signs because you might not actually be running lean.

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The Integrator readings dip as low as 108, or as high as 122 (but WHY?).

Because it is still rich. you should be hovering within 5 - 10 points of 128 in the integrator at all times. It should change just about as quickly as the O2, in the opposite direction. If it's higher, it's running it richer because it thinks lean, if it's lower it thinks rich and is leaning out. You might have an O2 that is biased rich. Very possible.

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If it was running rich enough to pull that much fuel out, it would at least show SOME signs on the plugs.

No, see the first part

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At part throttle the BLMs dip the most, holding a steady 2000 rpm is where it hits 111.

Is this under load or sitting in the driveway being revved?

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The only other odd sensor data I notice is the Timing advance numbers, they read "0" and don't change reguardless of rpm. I have no codes in the memory, the ignition checks as being fine. Balance test fails to isolate a cylinder. Vaccum reading are normal (except when it stumbles/misses, then they drop slightly).

Did you actually check the timing by holding an advace light on the engine and revving it to see if you actually are advaning OK? You should be somewhere about 35 to 40* at about 2500 rpm.

Have you checked your TPS??? if you have a glitch there, then you could be getting the stumble from there.

Do you have a graphing multimeter/DSO?

 

I've been through all of the obvious things (TPS for one). I have verified timing advance with a light, the computer isn't registering it, that's all. I work on auto's for a living, so I've been through all of the flow charts. The problem isn't easily traceable, that's for sure. I went ahead and took it to Grease Monkey here in Houston. They will figure it out hopefully, they have the diagnostic toys for the ECM and a smoke machine to hunt vac leaks/cracks. I pray it's somthing simple like a cracked head (therefore giving me an excuse to add my ported heads....).

 

 

Well, i can tell you that you don't have a cracked head...well at least that that isn't your problem. A cracked head wouldn't cause the rich condition that your BLM is showing a correction for.

You are definitly looking at a fuel control problem for that. Here are things that they SHOULD checkout.

Load Sensor - If the MAF or if sending out too high a voltage for what it actually should be, then it'll run too rich and could stumble.

TPS - Obvious...you said you already checked that.

IAT - Could be telling the computer that you have colder air coming in than you do, both messing with the MAF and the mixture.

CTS - You said in the first post that it hasn't been checked, so if it's reading too low, then you could get a rich mixture for what the collant temp really is.

Did you change injectors when you did the 3.4 swap to bigger ones? What size are they. How about fuel pressure? Have you actually looked at the O2 voltage on a scope? You must have access to one of those since you said you work on cars for a living.

Something else you have to consider, unfortunatly, you can't always trust the PID data you see on a scanner. What you are seeing is what the computer THINKS the value is/should be, not necessarily what the computer is getting from the sensor itself. If in doubt, always phisically check the voltage you are getting at the sensor.

 

I've checked )2 volts with a DVM (we don't have a scope at the shop). And the computer only THINKS it's running rich, it is NOT RUNNING RICH. It's pulling fuel because of sensor data for some reason. My Fuel pressure is dead on (55 without vac, 45 with vac at idle-4000 rpm). But the car is running lean, not rich (reguardless of what the computer says). The plugs are bleach white, not like lean white, more like BRAND NEW, Never fired, white. All sensors have been checked and verified multiple times.

 

Ok, I think we are having a problem with mis-communication. Here's how the BLM works.

The O2 tells the computer what it sees as happening. The integrator goes down(signaling that the computer is pulling fuel because it was rich) when the O2 voltage is high. The oposite occurs when it's lean. This changes very quickly, but should hover around 128 all the time.

When the integrator is either high or low for a period of time(usually a few seconds) that information transfered to the BLM. So if the O2 reads rich(high voltage) all the time, the computer is going to pull fuel out(cut PW) and decrease the integrator. Since this is happening for more tahtn a couple of seconds, it transfers to the BLM and the BLM number heads south.

You said that your plugs don't look lean, nor do they look rich, that is because the computer is in proper fuel control and it is niether, it's right where it should be. The ONLY thing that affects the integrator and BLM is the O2. If the BLM is low, that means that the O2 said you were rich. If you looked at the O2 voltage and it said that you are fine now, then your BLM is correct, you were rich, but are now correct.

Do you have access to a 4 or 5-gas analyser???

Don't get me wrong here, I'm just trying to help you out. I'm a smog technician here in california and see this all the time, but unfortunatly, it's very hard to diagnose a car over the internet. If you have really properly checked all of the sensors and all of the readings match what the PIDs are saying, then you are leaving out some important info.

If all of the sensors are correct, then the only thing that could make you rich is high fuel pressure, or leaking injectors.

How old are the plugs.

 

PLugs are about 4 months old, theya re as white as a piece of paper. I don't have access to a gas analyzer (the shop i took the car to for diagnostics does however). I'm sure they'll find the problem, but it's always nice to figure out stuff yourself first (or with assistance of others). If the car was TRULY running rich (leaking injectors etc.), the plugs would show signs of this after idling in closed loop for a time. I had a similar~ problem about a year ago with this car. Only difference was a random miss at all RPM's, and a code 44. Ended up being a fault on the O2 sensor circuit in the ECm. ECM thought the exhaust was lean so it was dumping extra fuel causing the plugs to fuel foul and misfire.

 

not if the Computer is correcting for it and dropping the BLM. As long as the car can correct for the rich condition, it will and you won't run rich anymore. And as long as you are closed loop, then it is correcting. That's what I'm saying. To see if you actually have a rich problem, you have to find a way to keep the PCM in OPEN loop and let it run, then pull the plugs, because even if you were open loop, running rich, and then went closed loop, the mixture cam down, the plugs hit there self cleaning temp, and cleaned right off. Plus, when you're crusing, it runs you just barely on the lean side anyway, so it cleans the rich deposits right off.