Running lean after 30 mins

ZV8888 · 10-02-2010, 05:19 AM

After 30 mins of motorway driving or 50 mins of local driving, my 79 euro SC starts to run lean. I can't figure why. Surely all the warm up bits are fully warm after 10 mins? Could it be a faulty AAR?

Walter_Middie · Walter_Middie's Garage

What makes you think it's running lean? Exhaust gas probe? Fuel pressure check?

If it is going lean - most likely a vacuum leak.

ZV8888 · 10-02-2010, 05:46 AM

I have a LM2 with wideband sensor hooked up. A great piece of kit for the CIS system.

Can't figure why a vacuum leak would only start after 30 mins of hard driving...

914efi · 10-02-2010, 05:52 AM

Likely the WUR is too 'tight'. As it warms up it leans out by design, very common that it goes too far.

If you eliminate vac leaks, etc then maybe take a look at adjusting the WUR, but this is involved. Have you checked control pressure, system pressure?

914efi · 10-02-2010, 05:54 AM

Just saw your post about the a/f meter. What are your air/fuel ratios? I have a lean condition (read via a wide band 02) under load that I am scratching me head over.

ZV8888 · 10-02-2010, 01:13 PM

At this stage I am intimate with my WUR. You are right, I could drop the control pressure a bit. Checked fuel pressures a couple of weeks ago and they were on the button. My WUR is now the adjustable type, after I got fed up stripping it every few days.

Cold: 10.5 - 11
Idle: 13.5 - 14
Acceleration: 12.5 - 13

After a good run, they change to ...

Idle: 16 - 16.5
Acceleration: 13.5 - 14

So the idle gets rough and the revs drop to about 750 too.

Hope this helps you. In my opinion, idle should be on the rich side ..... seems happier there.

stlrj · 10-02-2010, 01:27 PM

So why not enrich the mixture by turning the CO screw?

ZV8888 · 10-02-2010, 01:57 PM

If I enrich, I have the following problem .....

Cold start too rich, hunting. Then after a few mins, Idle is too low and starts and hunting or stall. Hesitation on acceleration also.

Am starting to think I should drop the WUR warm control pressure about 1/2 a bar and see if that helps. This should richen it a bit when warm, but not affect the cold start.

ossiblue · 10-02-2010, 04:08 PM

What exactly is your warm control pressure? If you have been rebuilding a WUR, it's usually best to set the warm control pressure first by moving the position of the large plug that holds the fuel fittings. Once the warm pressure is set (and you are certain the WUR heating element/bimetallic arm is fully extended), then you can reset the cold pressure. I can't recall you mentioning your control pressures--either warm or cold--in your posts, so this would be the way to go, IMO, before touching the mixture screw.

914efi · 10-02-2010, 05:14 PM

How do you set the warm CP without changing the cold?

stlrj · 10-02-2010, 05:40 PM

Quote:

Originally Posted by ZV8888

If I enrich, I have the following problem .....

Cold start too rich, hunting. Then after a few mins, Idle is too low and starts and hunting or stall. Hesitation on acceleration also.

Am starting to think I should drop the WUR warm control pressure about 1/2 a bar and see if that helps. This should richen it a bit when warm, but not affect the cold start.

I think you might try just the opposite. You need to raise the cold control pressure so you will be able to richen the base mixture in order to deal with too rich cold and too lean warm.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by 914efi

How do you set the warm CP without changing the cold?

914efi,

Moving the 'block' (big circular plug) slightly down increases the warm control pressure. While moving the small plug (that holds the bi-metallic arm with heater) down decreases the cold control pressure. But it all depends on the deflection and condition of the bi-metallic arm including the heating element for the cold control pressure to be manageable.

To answer your question: You can't!!!! Any movement (up/down) by the 'block' would directly affect the cold and warm control pressure settings.

Before you do any adjustment, it is important to measure the cold and warm control fuel pressures. Then make the necessary adjustment as needed. HTH.

Tony

ZV8888 · 10-03-2010, 12:31 AM

stlrj, good point.

I checked the pressures a couple of weeks ago ...

Cold @ 12C - 1.5 Bar
Warm - 3.3 Bar
Warm without vacuum - 2.6 Bar

So they should be okay - but probably worth re-checking.

I have the WUR with the diaphragm and the block now has a nice little hole to let me get a 4mm allen key in at the height adjuster.

Do you really think that it should take 30+ mins of motorway driving to get the WUR Fully warm? I suppose I should check that too.

psalt · 10-03-2010, 03:32 AM

If your pressures are within spec after the 30 min run, I would start looking elsewhere, you will only be masking the problem. Look for vacuum leaks with propane at the injector sleeves and boots, the Orings are usually baked and the leaks vary with heat. If you find no vacuum leaks, I would be testing the injectors for flow.

ossiblue · 10-03-2010, 07:22 AM

Quote:

Originally Posted by psalt

If your pressures are within spec after the 30 min run, I would start looking elsewhere, you will only be masking the problem. Look for vacuum leaks with propane at the injector sleeves and boots, the Orings are usually baked and the leaks vary with heat. If you find no vacuum leaks, I would be testing the injectors for flow.

Agree. You need to recheck your warm control pressure after your symptoms appear. The objective here is to eliminate areas at fault--in this case, the wur. Run your car until the problem arises, take a reading of your control pressure. If it's in spec, the wur is doing its job and you can begin to look elsewhere.

ZV8888 · 10-03-2010, 07:53 AM

Fair point, thanks guys.

dicklague · dicklague's Garage

Quote:

Originally Posted by ZV8888

I have a LM2 with wideband sensor hooked up. A great piece of kit for the CIS system.

Can't figure why a vacuum leak would only start after 30 mins of hard driving...

Is the LM2 calibrated? Is the O2 sensor fairly fresh? the LM2 is a 5 year old design. Maybe something is happening to it when the exhaust and sensor really warms up.

Just a guess.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by ZV8888

stlrj, good point.

I checked the pressures a couple of weeks ago ...

Cold @ 12C - 1.5 Bar
Warm - 3.3 Bar
Warm without vacuum - 2.6 Bar

So they should be okay - but probably worth re-checking.

I have the WUR with the diaphragm and the block now has a nice little hole to let me get a 4mm allen key in at the height adjuster.

Do you really think that it should take 30+ mins of motorway driving to get the WUR Fully warm? I suppose I should check that too.

ZV,

Check the control pressure change over time. To do this test, run the FP without the engine running. Record the control pressure reading @ start, 1, 2, 3.....5, 7,10,15,20 mins......until the control pressure stabilizes (warm). You could get the warm control pressure without running the motor just the FP.

What's the heating resistance of your WUR? Do you have the correct WUR for your engine? Keep us posted.

Tony

stlrj · 10-03-2010, 11:57 PM

If I am not mistaken, it should not take more than 5 mins to reach fully warm control pressure from stone cold.

ZV8888 · 12-14-2010, 03:54 AM

Got it figured out. WUR bimetalic strip / heater is faulty. When I thought it was fully warm (like after 15 mins driving) the strip wasn't fully lifting away from / releasing the pin. It only opened fully after 45 mins of driving OR 15 mins of driving and left standing for an hour or so (I presume heat radiation from the engine keeps heating it up). So the warm start component of the WUR was running the car too lean when it had unrestricted access to control pressure tit thing in the WUR. Once re-calibrated and mixture adjusted it is pretty happy again. I don't think the solution makes complete sense as the original Lean warm start would come back into spec after running the engine for a few mins. But such is the idiosyncrasy of the CIS system.

Thanks for all the help - Again.