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Rich/Lean condition - What do they feel like?

C

ck42

CEG'er
Joined
Jun 4, 2005
Messages
99
Given everything else is working correctly, what does it feel like when an engine is running rich or lean?

What would be an easy way to artificially (temp) produce a rich/lean condition for testing purposes?

Chris
 
if you were running rich or lean your car would throw a rich or lean code in a certain bank. You can really watch it all of the time with a gauge.
 
That's harder to do than in the old days before fuel injection.

Back then you could artificially enrich an engine with an unlit propane torch or even momentarily with choke cleaner spray.

Leaning it down in an even manner was more difficult but sometimes you could create a vacuum leak. The power brake booster hose is usually a well distributed vacuum source. Pull it off the booster and clamp it with vice grips, then loosen the vice grip in a controlled manner to try and control the quantity of air allowed in.

With fuel injection, the system try to overcome your efforts to make it rich or lean. If you succeed, you are likely to set an oxygen sensor code that you will need to clear when you are finished.
 
ck42 said:
Given everything else is working correctly, what does it feel like when an engine is running rich or lean?

What would be an easy way to artificially (temp) produce a rich/lean condition for testing purposes?

Chris
Click to expand...
If it has a massive vacuum loss, you should hear hesitation or loping (i.e., idle not steady, going fast then almost stalling, then going fast again).
Open up the air filter housing. That will cause a lean condition "almost immediately" (actually more like a few drive cycles). Broken vacuum hoses and clamps which not loose will sometimes also cause lean conditions :eek: .

Rich conditions, you can usually smell the gasoline or the "pungent" sulfide smell from the exhaust. You can cause this by removing the ECT connector. That will have the engine run rich all the time. Note that this is a recipe for disaster. The precatalytic converters and main cat will wear out and you will be looking at a $2500 repair very soon. In addition, you might also cause and engine fire. :crazy:
 
I guess what I was looking more for was 'what does it feel like when actually driving the car' when in a lean/rich condition. e.g., does it run rough, skip, just feel weaker, etc.

Also, for testing purposes, If I block off the vacuum line (not the one going to the brake booster - assuming there's no leak there) what will be affected, besides the EGR system? Is the vacuum used for anything else or is it all EGR system related?

Chris
 
Yea, I am a little curious of this as well. I have a lean code that keeps popping up on my car. It feels no different from when the code wasn't present. I can't hear or feel any leaks in the engine bay for unmetered air so I don't know what to do. I know all the things to check, but ripping stuff apart and replacing isn't much fun when you dont know exactly where the problem lies. Is this lean condition causing any problems for me, or wll it grow to a catastrophe?
 
A slightly lean engine tends to have a light throttle miss or surge, often most noticable in high gear with light throttle. A severly lean engine will be done on power. If severly lean from a bad fuel pump or plugged fuel filter, it won't run at all, starting to fog out at higher engine speeds or under load.

A rich engine runs fine until the plugs foul then you get roughness from fouled plugs.
 
That helps, Big Jim.
I'm curious though....can you explain "fog out" and what that means and what it feels like when driving?

Chris
 
...one more:

What would happen and what would it feel like if the ECU lost its signal from the CAM sensor?

Chris
 
Wow....OK, so then it should be pretty definitive if either the connection is lost of the sensor goes bad. cool. I like ones like that :)
 
Big Jim said:
A slightly lean engine tends to have a light throttle miss or surge, often most noticable in high gear with light throttle. A severly lean engine will be done on power. If severly lean from a bad fuel pump or plugged fuel filter, it won't run at all, starting to fog out at higher engine speeds or under load.

A rich engine runs fine until the plugs foul then you get roughness from fouled plugs.
Click to expand...

Good explanation there Jim. I still have a lean condition going on, it will pop up when im cruising under 3500 rpms, and I have driven it hard once or twice with the code present, and I noticed no difference at all. It's weird. But none the less, I will start doing some maintenence on this car in the coming weeks. New fuel filter, some injector cleaner, some new wires, and see if any conditions improve.

The only other problem I know I have, is where my -ypipe meets my cat-back, hat gasket has gone bad. In cold temps I can see the gases escaping pretty good, and not to mention I can hear it ticking when the music is off.
 
i mean you want to run your car as lean as possible, to get the best performance. but its also dangerous. and your cars more likely to throw a lean code than rich. lean is more of whats it worried about.
 
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