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Old 12-25-2012, 12:17 PM   #1 (permalink)
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Messing with Egr on 94 Volvo

I have been playing around with the vacuum lines using a vacuum gauge.
I plugged up some other vac lines that I did not need. I may have increased vacuum pressure to EGR.

With the vacuum gauge on

0 at idle ... egr off
6 psi on cruise, partial throttle
3 Psi while accelerating

When I'm cruising and the EGR line is at 6 psi ( Full Open). I can slowly play the throttle pedal, (Slight in or out) and the engine will start missing. After a second or two and the engine shows a burst of power. (like a turbo)

My theory is that the mixture is leaned ( Full Egr). The 02 sensor reads this and tells the injectors I need Fuel . Does that seem logical? Have I acheived a poor mans lean burn lean burn? Am I thinking wrong?.

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Old 12-25-2012, 12:24 PM   #2 (permalink)
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Increasing the EGR flow doesn't create a lean burn condition. It introduces more inert gas into the engine which dilutes the intake charge (effectively displaces oxygen). The O2 sensor will sense this and compensate by lowering the amount of fuel injected to maintain stoichiometric 14.7:1 fuel ratio. If you're getting misfires you're running too much EGR which will lower your engine's efficiency. You'll have to back it off a bit.
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Old 12-25-2012, 04:31 PM   #3 (permalink)
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EGR displaces the air fuel mixture , all of it

Quote:
Originally Posted by Daox View Post
Increasing the EGR flow doesn't create a lean burn condition. It introduces more inert gas into the engine which dilutes the intake charge (effectively displaces oxygen). The O2 sensor will sense this and compensate by lowering the amount of fuel injected to maintain stoichiometric 14.7:1 fuel ratio. If you're getting misfires you're running too much EGR which will lower your engine's efficiency. You'll have to back it off a bit.
the load sensor either MAF or MAP sees / calculates less incoming air and this what reduces the injector pulse to maintain desired air fuel ratio .

EGR when active displaces the air fuel mixture
EGR when active dilutes the air fuel mixture
but
EGR does not and can not change the Air Fuel RATIO , the mixture DOES NOT become lean or rich
when EGR is active

and now
the next part
02 sensors as in Oxygen sensors
DO NOT SEE OR MEASURE OXYGEN content
02 sensors as in Oxygen sensors
DO NOT SEE OR MEASURE OXYGEN content
02 sensors as in Oxygen sensors
DO NOT SEE OR MEASURE OXYGEN content
02 sensors as in Oxygen sensors
DO NOT SEE OR MEASURE OXYGEN content

02 sensors / oxygen sensors see only
combustibles
and they report presence of combustibles to the ECM

Lambda sensor is a better word to describe 02 sensors
and if this word is used , there would be much less confusion in the ranks of the mortals pondering their use
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Old 12-25-2012, 05:00 PM   #4 (permalink)
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Bosch invented the things and they call them oxygen sensors too... Don't they generate a voltage proportional to the difference in partial pressure of oxygen across the platinum-zirconia electrode?

In any case it sounds like your volvo is running rich and surging when the egr is open, then it leans out after a few seconds and feels like a big power boost. If it were running lean with the egr open then you would have backfiring in the exhaust and not so much a surge feeling but just a big lack of power.

Try it while accelerating at WOT and measure the vacuum pressure and report back. The lambda or O2 circuit is not in the closed loop during WOT in Bosch Motronics.
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Old 12-26-2012, 09:27 AM   #5 (permalink)
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Thx everyone for your input

KennyBobby, Running rich seems logical. My Mpg got up to 27 mpg in the summer and the last few tanks are 21-23, with alot of coasting in N. I figured it was cold weather. The CEL is not on. I wonder what I can do on the cheap to lean out this engine. I will do the WOT test and report the egr vac psi.

BTW. the timing belt skipped 2 months ago and I reset it. The engine seems smooth so I figure its set right. If I'm off a tooth would that make it rich? Would'nt run rough if the belt was off?
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Old 12-26-2012, 01:22 PM   #6 (permalink)
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Interesting, Ive seen the newer insight motor described as a stoichiometric engine.
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Old 12-26-2012, 05:47 PM   #7 (permalink)
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I drove the Super Volvo today. Floored it. lots of hesitation. wimpy..down shifted etc.. The Egr vac PSI goes to zero but needle bounces around between 0 and 2. That makes me think I'm loading inert gas to the cyl when I accelerate.

Next test was to disable the vacuum to Egr. The engine accelerated smooth , no missing. The car is still slow.. but it accelerates smoother.. interesting.. My Egr valve maybe acting funny. I almost want to have the emissions checked to see if I am running rich.

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Old 12-27-2012, 07:09 AM   #8 (permalink)
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As a former mechanic we use to disable those to give more power. This was back when both gas and diesel was under a dollar a gallon.

I unplugged it on my insight and the herky jerkys went away at 20-40mph, but my fuel economy dropped by 20 mpg and after 300 miles generated a check engine light.
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Old 12-27-2012, 08:01 AM   #9 (permalink)
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We had a Honda that had a egr manifold . It would stumble also. It turned out the manifold was clogged on some cyl. And the egr was not evenly applied to all pistons, which caused the missing.
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Old 12-27-2012, 09:47 AM   #10 (permalink)
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Did you replace the belt or reuse the old one--the old one has probably stretched out and that would retard your timing such that it runs sluggish at low rpms and runs great at high rpm.

If you have one of those hand-operated vacuum pumps you could try adding some more EGR while driving down the road at cruise to feel how it affects the power. The whole concept of EGR has never made much sense to me--pollute the charge air to weaken the power...oh yeah that's a great idea...?

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