Carburetor EGR port question

No problem Bob. I just don't remember seeing it. My guess would be that I was watching the NOx readings because that was the problem being worked on at the time. Since the new OBD II emissions test no longer uses an exhaust analyzer in this area it has been a while since I have been able to use one. Our emissions testing here is done using the diag connector under the dash, basicly if there are no trouble codes stored and the monitors are run it passes.

Reply to
Mike
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Next time, don't open it so far. Try a 10% or 20% command on your scn tool instead of 80% .

No, it wouldn't be a lean misfire. Lean misfire comes from too much air and not enough fuel. Opening the EGR does not add more air. The exhaust gasses displace what would have been combustible mixture in the combustion chamber, the actual ratio of that combustible mixture doesn't change. If you have an engine with a leaking EGR valve at idle, fattening up the mixture doesn't improve how the engine will idle. Comparing secondary spark lines on a ignition scope, a lean mixture looks completely different than a stuck open or leaking EGR valve.

Yup.

Reply to
aarcuda69062

Ultradrive innovation?

Reply to
beerspill

The air pump is original equipment. I bought the truck new and I have done all my own work on it, including changing the lifters and changing a blown head gasket, two separate operations. So I know the air pump is original. Whether it's working as it should today, I can't say. I tested it a few years ago according to the manual and it seemed to be working then.

What has me puzzled at this point is which of the 4 operations I performed on the fuel and ignition systems contributed to the skyrocketing of CO emissions on the third test (test results reprinted below). HC and NO came down significantly, as did O2, but at the expense of CO.

Only the enrichening of the idle mixture and the widening of the canister purge line ports in the wall of the carb throttle body could have fattened up the mix, which would have resulted in the higher CO and lower O2 readings. Assuming no freakishly timed breakdown of the air pump, it's operation would have been the same for all 3 tests, whether working or not.

If the guy who owns the smog shop will allow it, I would like to run another pre-test and see if clamping down the canister purge hose changes the readings mid-test.

I leaned out the idle mixture screws just a bit after the third test. They were pretty close to lean best idle as it was. I can't imagine that the small change that I made to the idle mix could have such a strong affect on the emissions with the engine running at 1325 rpms. So the enlarging of the canister purge line ports into the venturi just above the throttle plates is the likely suspect, IMO.

%CO2 %O2 HC PPM %CO NOx PPM

15mph

1st test 10.8 5.9 34 .01 3641-FAIL

2nd test 10.4 6.7 132* .01 626 3rd test 12.2 3.6 82 1.02-FAIL 358

25mph

1st test 10.7 6.0 26 .01 3225-FAIL 2nd test 10.7 6.1 65 .04 606 3rd test 12.5 2.9 73 1.14** 191

1st test - 1. EGR run from EGR port on carb resulting in essentially no EGR function 2. MSD ignition hooked up

2nd test - 1. EGR run from spark advance port on carb 2. MSD ignition not hooked up

3rd test - 1. EGR run from modified EGR port on carb 2. Idle mixture enriched slightly 3. The ports entering both barrels from the canister purge hose were enlarged to correspond to those in the original stock carb. 4. MSD ignition hooked up

  • passing is 134, measured 132
** passing is 1.14, measured 1.14

Reply to
Simpson

Yes.

Reply to
aarcuda69062

It does add gas which displaces air. That would mean less air going into the cylinders. At least that is what would happen in the first fractions of a second. So for a very brief period of time you get a rich condition.

How can the mixture not change if you just took away some of the air. Of course in about the time it takes you to blink the dynamic system that controls fuel, air, timing and idle speed is going to react to those changes - so any conclusions you draw from this experiment are more than likely to be completely wrong.

-jim

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Reply to
jim

Displaces air -and- fuel.

Less air -and- fuel going into the cylinder.

What makes you think that EGR only takes away air. What makes you think that EGR takes away anything? EGR displaces a volume in a cylinder.

None of what I've said are mine nor are they conclusions. IOWs, you assume wrong again They are the physics of the internal combustion engine, documented and published (but probably not in Popular Mechanics).

Don't take my word for it, feel free to run Simpson's non operating EGR valve gas readings and his operating EGR valve gas readings thru a Lambda calculator. You'll find that the air fuel ratio changes by .01 which is well within the expected sampling error of the type of equipment being used for his tests.

Reply to
aarcuda69062

One can only guess what it is you are talking about. Let's assume you were talking about a modern car with fuel injection. Air gets displaced meaning less will enter intake (at least for an instant). The fuel at the same time doesn't get displaced. There is nothing physical to cause the fuel to be displaced. If the end result is less fuel is delivered it is only because the engine's control system delivers less fuel (but it could deliver more air or both). On a vehicle with carb it's different because airflow is part of the physical process that delivers fuel. But that still doesn't mean the air/fuel ratio will stay the same without some engineering effort to make that happen.

Maybe or maybe not. All depends how a particular system is designed. Hopefully it's designed well enough that it won't change the air/fuel ratio very much in your scenario since EGR failures are not rare occurrences.

That was your terminology. Air is a gas. So is the exhaust coming from EGR

- fuel is not. If you say some of the volume of gas is displaced that equivalent to saying some is taken away.

It sounded like it was your experiment. It also sounded like your conclusion or at least you hoped others would reach from the experiment. The only reason your experiment would lead to that erroneous conclusion is because that is the way it is engineered to work. If the controls are working as they should then it won't affect air/fuel because it is designed not to.

I suspect that Chrysler had a good bit of data on the vacuum controls for EGR in the 80's also. And that data is what they used to design EGR controls so that didn't throw the air/fuel ratio out of wack. But when you start doing your own design on an engine as the OP is doing it is extremely unlikely that you will end up not changing air/fuel ratio if you just slap any EGR control onto the system any which way and simply hope.

-jim

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Reply to
jim

jim wrote in news:1206456252 snipped-for-privacy@isp.n:

I'd think the engine's computer would sense the decrease in fresh air intake and reduce fuel delivery accordingly.

Reply to
Tegger

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