Running very lean

[bimas]

I just recently resolved running rich issue, and passed smog. Unfortunately, I have the exact opposite problem now.

To preface the situation, I have had an intermittent running lean issue at times - sometimes at start up, sometimes at full operating temperature - but I could never diagnose it as the problem cured itself within seconds. Now, my car idles so poorly, that it is on the brink of stalling. As I still have an AFR monitor running, I can observe that the car runs lean overall most of the time. It will never run rich, even under a good load and WOT, it runs perfect close to 14.7AFR (at this point, it should jump to 12-ish). As soon as I let go of the accelerator, I get lean condition somewhere in the vicinity of 18AFR. When I stop and idle, the AFR climbs as far as 28.

As far as I know the normal range of AFR is 12-16 in at various loads and throttle position, with keeping with the ideal mix at 14.7 mostly (that's how the car ran until today).

Could this be a bad ICV? Do I have a fuel delivery problem? I feel like the engine is trying to idle well, but due to improper mix, it can't. I will test fuel delivery and pressure.

Any other suspects?

Recently replaced items: spark plugs, distributor and cap, wires, AFM, FPR (used), fuel pump (used), cat, O2 sensor.

[FernandoBunster]

Did you try swapping the ECU with a known good one?

[alpinacsi]

You mentioned replacing the AFM: why? Did you install a used one and did you check the calibration?

[bimas]

I will try the ECU, although the nature of the problem is not a sporadic one, which was my experience with a bad ECU before. I had my AFM refurbished less than 2 years a go. I had a bad running condition that improved when I smacked the AFM with a blunt object. I do have another AFM laying around that isn't completely shot, so I will try swapping it. It does make sense that my fuel trim is just shifted toward lean via a bad AFM, right?

EDIT:
Swapped AFMs 2x to no avail.

Swapped DME, which didn't start the at at all (I know it worked last time I used it).

[bimas]

So I touched up the power transistor solder points on the spare DME that didn't work, and it runs the engine as badly as the original one.

I also dug up another good DME, and 2 more ICVs. Same results.

Unplugging the O2 sensor makes no difference. Could that be a culprit?

I need a new direction. Unless the engine harness is bad, the DME and AFM function ok.

[tschultz]

Are the injectors all clean and flowing properly? They could be clogged and only flowing partially.

But really if the O2 sensor is hooked up and working, it should adjust and compensate somewhat.

To me it would point to the O2 sensor providing the wrong signal in the narrowband... IE something that happened to me with somewhat clogged (or maybe they were incorrect/non OEM) injectors.

[bimas]

Are the injectors all clean and flowing properly? They could be clogged and only flowing partially. But really if the O2 sensor is hooked up and working, it should adjust and compensate somewhat. To me it would point to the O2 sensor providing the wrong signal in the narrowband... IE something that happened to me with somewhat clogged (or maybe they were incorrect/non OEM) injectors.
I had the injectors cleaned las year, and they worked like a charm until this sudden change.

I have a pretty instant idea of the fuel mixture due to also having the LM-1 still running off of the wide band O2 sensor. I didn't know the AFR can run as high as high as 28 and keep the engine (barely) running.

I don't think that the problem is in the injectors, as the entire fuel mix just seems shifted to lean. Mind you, if I rev to 5,000 rpm while parked, and to 2,500 under load, the engine runs great, and the mix is perfect 14.7AFR - although, it should fluctuate to rich while accelerating and and compensate to as perfect ratio as possible - it doesn't. It just crawls to the ideal number, and stays there. The same goes for WOT up a steep hill. Again, the car should run a bit rich under such load. It's hard to tell how much power I'm losing, since there isn't much to begin with. But the engine under load runs smooth with a perfect stoichiometric mixture.

Also, there is maybe a two second delay when I stop revving the engine, when it doesn't run crazy lean, before turning to starvation.

I'm lost. But I can test the injectors, or even swap them with a known good set.

When I think about it, this almost sounds like a giant vacuum leak. I'll take a better look at the tiny hoses (they are recent), and the intake boot. Does that sound plausible? My fuel economy is definitely not better, in fact, it may be worse. Is it possible that I'm sucking in a bunch of unmetered air?

[tschultz]

A good idea, check for leaks.. maybe the vacuum hoses under the intake manifold?

What about calibration of the throttle position sensor? It should click with a slight tough, indicating off idle conditions.

[bkats]

I vote vacuum leak. No way your luck is that bad with those parts you've checked. The vacuum connections to the intake manifold are not a very good design. I might just replace all the vacuum hoses anyways if they could use some TLC. It's a relatively cheap and easy way to eliminate vacuum leaks as a cause.

[bimas]

Tom and bkats get a ribbon. I get an idiot award.

I tightened the negative battery terminal, which was pretty stretched out.

I also found fired vacuum hose under the intake manifold (not sure if it was off, or if I pulled it off). After snipping the ends off and ending up with hose too short, I swapped the evap and breather vacuum routing. They seem to connect almost in the same place in the intake:)

Knock on wood. Idle purrs like a kitten, and stoichio ratio is on the money. Now, let's fix the other 72 non-emergency items on my list, like AC!

[bkats]

Tom and bkats get a ribbon. I get an idiot award.

I tightened the negative battery terminal, which was pretty stretched out.

I also found fired vacuum hose under the intake manifold (not sure if it was off, or if I pulled it off). After snipping the ends off and ending up with hose too short, I swapped the evap and breather vacuum routing. They seem to connect almost in the same place in the intake:)

Knock on wood. Idle purrs like a kitten, and stoichio ratio is on the money. Now, let's fix the other 72 non-emergency items on my list, like AC!

My shelf has a lot of idiot awards on it...very few ribbons. No matter how many hours I waste, I will always trade looking like a fool for a simple fix. Go get 'em!