Carburetor EGR port question

Good point, Mike. There is a 'open loop' mode that this computer may default to if it senses a value outside of its programmed parameters. This computer controls spark advance timing and fuel mixture, but now that the carb no longer has a mixture control solenoid, that aspect of control is gone and only the spark timing is left.

Your post raises an important point for me. I have the code reader for this beast. It's almost prehistoric but it works great. I got it used on eBay because good luck trying to find one new. When I had the old original feedback carb installed, the mixture control solenoid would get stuck. At one point, I screwed down the allen screw on top of the solenoid to close the auxiliary main jet and the auxiliary air bleed in an attempt to convert the feedback carb into a convention carb. Even with the solenoid modified so that the electrical pulses to it were doing nothing, the computer failed to set any codes. I would have expected a code set for the the O2 sensor perhaps because it was no longer controlling the fuel mix, but the computer seemed not to mind. When I disconnected the wires to the feedback solenoid, however the computer set a code for it.

Getting back to the 'limp-home mode' question. The only thing that the computer now controls is the spark advance. The service manual spells out the procedure for testing the spark advance at 2000rpm. After setup, it says that I should be reading 38 degrees plus or minus 4. The only trouble is, how will I read 38 degrees I don't have a magnetic timing unit, which I assume will allow one to read that far off the scale used with a timing light, which only goes plus and minus 10 degrees from TDC.

I guess I can wire the failed solenoid the computer. The windings are still good. This way the computer will still read it as working and, if the computer is working okay, the advance timing should working okay. If I read the service manual correctly, there are only two spark advance curves, one for cold and one for warmed up. I had a problem with the coolant temperature sensor recently that caused the vehicle to only operate in cold mode which was too retarded. Gas mileage sucked until I discovered the problem. If there are only two modes I should be able to tell if the computer is ignoring the absence of the mixture solenoid and continuing to use the warmed up spark advance curve.

How does the situation you are describing dealing with spark advance? Is this controlled by the 'ignition control modules' you mentioned?

Sounds like a real party :-)

Actually, I'm doing quite well, thank you. I appreciate your suggestion about advancing the timing. Perhaps you should limit your posts to asking questions and making suggestions instead of trying to correct what you seem to regard as my inappropriate posting methods in my communications with others.

I don't particularly care much how you do it. I was trying to empress upon you that the advice you get is only as good as the information you supply. For instance why is it you changed the carb in the first place? And how much have you driven with the new one? If someone cared, they might guess that the old carb was running very rich and you haven't driven very many miles on this one. It may pay off to just drive it a few hundred miles. It may take a while to recover from whatever was previously wrong. Also fiddling with the idle mixture is not likely to help much. When your going down the road the throttle is usually open enough that the idle circuit is no longer doing anything.

-jim

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And he wasn't satisfied with "barely." I wouldn't be either. The frickin cut points are so loose that if it's not below 50% of cut point, something isn't right.

Okay, publish the vacuum specs for both types of EGR systems. That ought to help him considerably.

It's the twenty first century Jim, the old beliefs that you're subscribing to here have been long refuted.

Main Entry: dis?place Pronunciation: \(?)dis-?pla?s, di-?spla?s\ Function: transitive verb

Main Entry: al?ter Pronunciation: \?o?l-t?r\ Function: verb transitive verb

Do you think a boat floating in water makes the water different?

Your wet sidewalks cause rain fan club membership card is in the mail.

Really? The results of his third test show differently.

Couldn't figure out how to fix them, 'eh?

Not even close to plausible.

Cite?

Gee, I'm pretty sure there was a carburetor change in there.

It might if the CO weren't so low. I will admit to not having fully realized that he connected the EGR to the vacuum fitting for the spark transducer which well would cause an over EGR condition. Should have run like crap at cruise though...

And he has since modified the carb and tested it configured with ported vacuum with positive results.

True that.

Not necessarily due to there no longer being any service parts.

I don't know what your problem is, Simpson has demonstrated amazing ingenuity, intuition and desire to learn and understand.

You can go crawl back into your hole, jim. You've expended your good will.

I can assure you I haven't given much thought to your posting methods. I did ask a couple of questions and have made some suggestions.....

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File under 'forgot to note':

For the 3rd test, I reconnected the MSD Blaster Ignition. It was present on the 1st and 3rd tests, but not on the 2nd.

Simpson wrote: The only

The newer timing lights have a digital display that gives the advance also

Yes, you can get stand alone distributors and/or ignition modules to put in so your timing works like the pre-computer engine does.

Someone on AADT should know what ones plug in or what junkyard swaps are easy?

I have the PCV and canister (gas tank and carb float vent) hooked up, the EGR, the distributor advance and the air filter flaps all properly plumbed for a manual tune. I am set up to pass emissions with my feedback carb manually set.

I got on one ASM 2525 test, 589 NOx, 16 ppm HC and 0.11% CO and my 1986 CJ7 'Utility Vehicle' doesn't have nor need a Cat up here in Canada...

But the point was that only under certain load and RPM it was well within limits.

The reason they introduced the vacuum amplifier was not because they changed the way the EGR worked but because they changed the location that the vacuum signal that operated the EGR came from. The EGR valve for his vehicle probably was the same for a 10 or 15 year period. During that time they had all sorts of different carbs and vacuum line configurations. The signal from venturi vacuum was to weak to operate an EGR valve in a reliable way so it needed to be amplified and then the same old EGR could be used. The reason it was tied to the weaker venturi vacuum was that would allow for more accurate metering of air and fuel under a wider range of operating conditions. The feedback carberator wouldn't need that because the feedback system itself would be able to compensate for any changes in airflow that affected the air/fuel mixture. As for the Chrysler lean burn crap - that was easy to fix. What was so incredibly stupid was it took Chrysler engineers 10 years and near bankruptcy to figure out how to fix it.

-jim

Air fuel mixture is controlled by the flow

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No one drives at only 15 and 25 miles per hour. There is no data for other speed ranges so, the word "only" is a bit disingenuous.

It couldn't possibly be. His was the first year of production for both the chassis and the engine, the year following his was throttle body fuel injection and used a SMEC controlled pulse width modulated solenoid and back pressure transducer to control the EGR.

No they didn't. One year only. 4 cylinder or six cylinder.

That was Chrysler's way of doing it. That's all that can be said.

Love to hear about it some time. Hope you research it better then your claims about the 10-15 year spread where they used that exact EGR valve/scheme on a vehicle that was produced in that configuration for only one year.

That's the way innovation is.

Quite easily.

Hand turn the engine until the #1 TDC timing mark on the balancer is aligned with the minus 10 mark on the front cover scale. Make a mark (sharpie) on the balancer adjacent to the plus 10 timing mark on the front cover scale. Hand turn the engine again until your new balancer mark aligns with the minus 10 mark on the front cover timing scale. Make another new mark (sharpie) on the balancer adjacent to the plus 10 mark on the front cover scale. Take a knife edged file and make this last mark more permanent.

You've just marked your balancer 40 degrees advanced from the TDC mark. The 2 degrees error you can work out easy enough.

Some times the simplest solution is the hardest to see.

Thanks for all your help and patience.

As long as you do the run/ chop the throttle/ and shut down a plug reading is pretty good. The problem is that you don't want it to idle much if you want a good reading. Now if you really want to play with it at idle a gas analyzer works. So does a set of color tune plugs. But on an installed engine where you can't see the plugs real well they are no fun to use. But they do show how well the manifold actually spreads the mix around, or not in the case of some engines.

The explanati>

Yep.

Didn't run at all, they don't run well on an inert gas.

Being the engine wouldn't stay running I would say it went down. ;) If it would stay running it would have a lean misfire that would lead to an increase in HC.

Yes, I'd like to see the results with the air pump disabled.

Yep, I see your point here. My experience has been that aftermarket emission parts are junk.

They sure were, but living in the rust belt they don't last very long and are long ago rusted away.

That's hilarious coming from someone who's above statement describes the EGR as metering air and fuel.

Must be why they all had the same part number (not).

Now you're getting it. Did the 87 Dakota V-6 use a vacuum amplifier?

Sounds like something the guy at the junkyard would say.

Never said otherwise.

Indeed.

Which is not the same as asserting that the EGR changes the air fuel ratio.

Absolutely.

For someone who claims to know something that is as good as saying you don't. I didn't say chrysler used the same engines for all those years I said the EGR's were all pretty much the same in that era. The means of controlling the vacuum, which determined how much exhaust gas was delivered and when it was delivered is what changed depending on make, model and year. That was the purpose of vacuum hose configurations, vacuum amplifiers or transducers and different vacuum ports. The difference in the valve itself had more to do with how they fit on the engine rather than how they behaved.

At any rate EGR clearly has a huge effect on NOX emissions and does completely change the way air and fuel burn inside an engine. That mains the entire way the engine is tuned needs to change to accompany the changes that EGR creates. For the most part EGR is beneficial. It is a lot like getting an octane boost (at no extra cost) and does allow for better fuel economy as well as overall better emissions *if* the engine is tuned to accommodate the changes in burn characteristics. That means changing air/fuel ratio as well as timing. The modern vehicle's computer takes care of all of that for you so yes you can get along quite nicely with any knowledge of it.

-jim

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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.