Carburetor EGR port question

Simpson wrote:.

One more way, a fresh oil change using conventional oil.

High HC's can come from oil getting past the rings also so a really thin oil or old oil that goes 'thin' can bump them up.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
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Reply to
Mike Romain
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Oil is fresh and the rings seem to be in good shape. I can go all the way between oil changes at 3,000 miles without having to add a quart. I bought it new and changed oil and filter fairly regularly.

Reply to
Simpson

Page 8D-10 of the

Chrysler Motors 1987 Shop Manual

2WD and 4WD Pickups

Dakota Trucks

Like the one shown here:

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From the manual:

CABLE RESISTANCE CHART

Minimum---------------------Maximum

250 Ohms Per Inch 600 Ohms Per Inch

Right... I went and re-read what you wrote about it in your first post.

I feel certain that the reasoning for this must be in one of your past posts. It appears counterintuitive at first glance, though... a richer mix to lower HCs at the tailpipe.

Would you suggest bigger main jets or a higher float?

Mike suggested leaning out the idle mixture screws to get lower HCs.

At this point I am a bit more knowledgeable, but not quite sure what to do with it. What I need is tailpipe emissions wand like the one at the shop so i can monitor the changes that take place for a given tweak.

Will do, and thanks for all the input.

Reply to
Simpson

Yep, the EGR valve allows exhaust gas back into the combustion chamber, but, it is only a very small percentage of the total combution chamber volume. The exhaust gas was already burnt once in the combustion chamber, how does running it through the combustion chamber a second time cause the HC to increase even further ? Isn't the HC reading from the smog test unburned hydrocarbons ?

Yep, that's how the power enrichment works as well but why such a jump in HC ? This is the first time I remember seeing a NOx problem fixed were the HC reading jumped up like that. Does this have anything to do with the vehicle being equiped with an air pump ? We don't see too many air pumps on the east coast.

Reply to
Mike

Okay, if Chrysler says so.

When a cylinder gets lean enough it begins to misfire and HC goes up. The whole thing is a teeter totter balancing act.

I'd play with the main jets. A higher float can cause other not so desirable results. (like dripping upon shut down)

Both of you should look at the chart on the first page of this PDF

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See what I mean about teeter totter?

Which side of the bold black line is your high HC on?

Then look at the chart on page 2, pay attention to where O2 and CO converge at stoichiometric, like I said earlier, .5% give or take tenth.

Mike is certain that your high HC is because the mix is rich, based upon -what- I have no idea since your gas numbers are skewed by the false air from the air pump. I'm saying that I "suspect" that it's actually too lean, maybe in part because I thought you had mentioned that the plugs were white.

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e (sorry about the line wrap)

This is (IMHO) the best deal out there.

Reply to
aarcuda69062

Mike,

I just popped the top off the carb and removed the boost venturi to get at the area around the throttle plates. The barrel that has the designated EGR port has a perforation just above the closed throttle plate just as I expected. When I attach a hose to the designated EGR port I can blow air through the perforation. When I plug up the perforation inside the venturi with my finger, the air flow stops. This is the case with the other barrel that has the designated spark vacuum port. The only difference between the two seems to be the relative size of the venturi perforations, the EGR side being slightly smaller and the height relative to the closed throttle plate.

three hours later... I just got back from ripping the carb out of its moorings and teraing it down and comparing it with the old original. Same body - different porting. I cut a new slot for the EGR port and widened the holes that feed the canister purge line into the the venturi just above the throttle plates, both mods to conform to the original.

The new carb also differed from the original through a hole in the gasket that connects the throttle body to the main body. This hole in the gasket on the new carb connected the EGR hole in the throttle body just above the throttle plate in one barrel to a hole in the base of the venturi. The original carb did not have this hole in the gasket or the hole in the base of the venturi, so I flipped the gasket to put the hole on the other side where nothing is happening and the hole is not connecting anything to anything.

I am about to go out now and take it for a test drive to see what happens after it warms up and the EGR circuit kicks in. I have a vacuum meter teed into the vacuum line to the EGR valve so I should be able to see if the mod works like the original. If not, I will negate that particular mod in some fashion and go back to running the EGR valve from the park vacuum port, which is what got me passed smog.

It's a frikken obsession, but I bought this truck new and I refuse to let it die for want of a replacement mixture control solenoid.

Thanks Chrysler.

Thanks Holley.

Way to stand behind your products.

Reply to
Simpson

So? If the air fuel mixture is lean to begin with, how does adding exhaust gas make the flame propagate better?

See above.

Yes it is. Ever open an EGR valve at idle? Did the engine run better or worse? Do you suppose HC goes up or down if you open the EGR at idle?

Not for me. It's very common on some engines to repair a non functioning EGR for a NOx failure and have the car fail on HC. Typical 4 cylinder where the EGR feeds into the intake ports individually (4 separate EGR passages) and 2 or 3 are plugged. The 1 or 2 that do flow EGR are over fed and cause a misfire. Roto-Root the passages and everything is fine...

The high HC? Maybe yes, maybe no. That's why there's a thing called 'diagnostics.' I'd watch the reading with the air pump disabled. The OP has a 21 year old truck, what are the odds hat the air pump is original? I couldn't get the air pump on my bought new 85 F-150 to last more than three years. Air pumps tend to have a generic universal design, what if instead of a

4 CFM air pump made for a 3.9 liter engine, he got a 10 CFM replacement pump made for a 7.4 liter engine. You -can- pump too much air into a catalytic converter and snuff out the fire.

Dunno why, they were pretty common in the day that the OPs truck was built. Now they're likely to be electric.

Reply to
aarcuda69062

I just got back from modding the carb. See my last reply to Mike.

While I had the carb off, I removed the limiter caps and will try readjusting the idle mixture screws as I have a rough idle. Apparently, this truck has always idled rough, from what I hear and read. The HCs on the successful test at 15mph test are double those at 25mph test - 132 to 65. The engine rpms for both tests reads virtually the same, though, which is a mystery. But that mystery aside, I would guess that the idle circuit plays more of a part in the fuel mixture at 15mph than at 25mph and this transmission will go all day in third gear at 15 mph. Anyway, what I guess I'm trying to say is that I will try riching up the idle circuit first. Being as it would cost me up to 30 bucks for a dry run on the dynamometer, I want to try everything that I can to get the ideal adjustments lined for a try.

I have some smaller jets from the old carb that worked in conjunction with the mixture control solenoid. I hear that it's not always a good idea to drill out jets because the shape of the jets is important to the flow of the fuel, but is it always a bad idea?

I guess I should mention again that the carb that I put on this 3.9L (239 cu) V6 was designed for a 318 from the early seventies. It probably was designed for a Lean Burn system as it had a throttle position sensor on it, which I took off, as this 87 Dakota is not a Lean Burn system, I don't think. Anyway, there was no throttle position sensor on the original carb, so off it came from the new one.

In any case, this 2280 Holley that was used on the 318 V8 is the same body and capacity as the 6280 that came original on the 239 V6, so I am assuming that it can be tweaked to run the 239 just fine.

Wow, love it! Thanks for posting that!

The 15mph test, 132 PPM, is on the left, but the HC line on the graph does not come down to 65 PPM, which was the result of the 25mph test.

I will pay this the attention it deserves after I get back from a test drive, or maybe tomorrow morning after a big mug of tea

Not a problem.

Yeow! Prices are on the high side for shade tree mechanic.

Reply to
Simpson

Mine has read high HC's with a lean miss on mine once.

Reply to
Mike Romain

I have had that happen to mine once.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
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Reply to
Mike Romain

Ya gotta do what ya gotta do.

Last fall had a guy bring me one of those kit cars that's a replica of a

20s something Mercedes Benz, the drive train is 78 or 79 Mustang V-6 with a 2 barrel Motorcraft carb. All stock engine wise, all emissions equipment present and functioning. The car couldn't pass the state IM-240 test. The only thing non-stock emissions related was the exhaust, he had one of those small universal catalytic converters on it. The original Mustangs had a 3 cat system. Thing is way rich, CO is sky high. No way to fit two more cats on it. Shoot the moon, pull the carb top off, remove the jets, solder 'em shut and re-drill them .008" smaller. Why .008"? That was the next smallest drill size in my number drill set. Re-assemble and took it to the test station 2 miles away. The car fast passed which means it's running significantly cleaner then it was before. Is soldering and drilling a set of jets a kludge repair? Absolutely! Did it fix the car? Hell yes. It passed the emissions test and he called back 2 days later and said the car had never ran so good.

So, a lean jetted carb is high on HC.

How do you know that? Maybe your HC reading is to the right of the bold black line. The HC graph represented on that chart is "U" shaped isn't it? High rich of stoichiometric, drops near stoichiometric and rises again lean of stoichiometric.

Your test sample was taken after the catalytic converter. so naturally the numbers would be lower. The specific number aren't what I was pointing out, it's the relationships of the different gasses at different air fuel ratios, i.e., is the HC high because it's too rich or because it's too lean. Some here seem to think that HC can only be high due to a too rich fuel mixture. The only way to know which side of stoichiometric your HC numbers represent is to know what the actual unadulterated O2 measurement is.

Reply to
aarcuda69062

Got it! Using that way of looking at the graph, especially for CO, CO2 and O2, which are expressed in percentages, I can easily see that my passing test was on the lean side, the CO being a dead giveaway.

Okay, now I see why you place so much store in the O2 reading. I need to richen up the mix a bit. The only tool I have at my disposal to judge The mix is the color of the ceramic insulators on the plugs and they have been pure white of late.

Is plug insulator color a good indicator of proper fuel mix? That's all I have for now. If it's a good indicator, when I get a good color I will take it to the smog shop for a dry run.

Reply to
Simpson

Your issue may be timing. The vehicle is designed to run with EGR. It sounds like your engine performs well without it (ignoring NOX) and with EGR it does not do as well (other than NOX). That suggests you may be able to advance the timing a degree or 2. Doing that will probably increase NOX a little but may bring the other readings back in line.

-jim

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Reply to
jim

Your response was to ignore the advice given. The suggestion was made that the EGR was designed to run off the very low vacuum port. From there it goes to a vacuum amplifier which uses the low vacuum signal to control the EGR using vacuum coming from intake manifold. If I understood your response - you ignored that advice and hooked it up in a different way.

The low vacuum plus amplifier may or may not be how your engine vacuum lines are supposed to be configured. But it does sound like the carb was designed to work with that configuration. Is there an under-the-hood vacuum line diagram?

-jim

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Reply to
sjedgingN0sp"

My response was to investigate what a vacuum amplifier was and then to determine that the EGR system on the 87 Dakota V6 did not incorporate one.

And that is *all* that it was... a suggestion.

that

But not in this case.

I hooked up the EGR valve the way it was hooked up stock. There is no vacuum amplifier. The vacuum hose from the EGR port on the carb goes directly to the CVSCC (coolant vacuum switch cold closed) which prevents the EGR system from kicking in when the engine is closed. The vacuum line then goes directly to the EGR valve.

You're starting to repeat yourself.

I hooked it up in such a way that passed the smog inspection.

Now you're getting it.

It may be that the *carb* was designed to work that way, but the EGR system on my truck was designed to to work without a vacuum amplifier.

I made it clear in the thread that the mixture control solenoid for the original, stock carb can longer be purchased and that the carb I am working with is the non-feedback version of that carb. I also made it clear in my last post to Mike Romain that I modified the carb to work like the original as far as the EGR function goes and that the mod was successful.

Of course there is. There is also one in the shop service manual.

Are you the hall monitor for this group? Do you go around busting people for not following the advice of others to the letter? If so, you have too much time on your hands.

Reply to
Simpson

When we mod our Jeeps to take out the feedback carb, we can run the ignition module or even a replacement stand alone distributor or ignition replacement without the rest of the smog computer controls.

The reason is or 'ford' emissions control box goes into 'limp home' mode basically clamping down on the timing advance.

When we wire our ignition control modules directly to the distributor in whatever form, we bypass this, our timing jumps about 15 deg and has to be reset and we get a sweet 'seat of the pants' 25% boost in power.

We can have 'fun' with the new vacuum line layouts as well.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
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Reply to
Mike Romain

Your reply made no mention of that. That is you completely ignored the advice and didn't explain why you ignored it until now. You didn't even give a hint that you comprehended what was said.

Maybe - Maybe not. How the hell would I know.

When people fail to indicate they understand the advice the tendency is to repeat it. No??

Then why are you trying to do additional modification? You've made a half dozen posting since you passed the test asking for help with modifications. What's that all about?

You still don't "get" that when you fail to provide adequate information the reader has no choice but to guess what the actual facts are.

But given that you now have a different carburetor the range of vacuum coming from the EGR port will not be exactly the same as the original and it is possible that the way it was hooked up in connection with a vacuum amplifier might give you better performance. The EGR affects the mixture that the carb delivers. If the flow thru the EGR is not in synch with the carb mixture controls you may not be getting optimum mixture at all the different possible engine loads and RPMs. So the original advice to hook the EGR thru a vacuum amplifier still may have produced better results than you got.

You implied that you replied to the advice given. You did not reply to that advice you ignored it completely. You didn't even give the slightest hint that you understood what the advice was. Since my crystal ball is in the shop for repairs this week - I thought maybe you didn't understand the advice and perhaps maybe you would want to be aware of that. But apparently you're not interested.

-jim

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Reply to
sjedgingN0sp"

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Reply to
aarcuda69062

He has already stated that with the replacement carb installed the HC emissions are barely within limits.

He has already explained that he reconfigured the vacuum slots to match the old carb. And what's to say that his current EGR valve is calibrated to be used on a system that employs a vacuum amplifier? Where does it end? It's a 21 year old truck.

Actually, no. When you say mixture associated with carburetor (or any fuel metering device), It's assumed you mean the air/fuel ratio. Exhaust gas is neither air nor fuel, it's supposed to be inert. EGR doesn't alter air/fuel mixture, it displaces it.

He's not getting optimum mixture because he's using a lean burn carb in a non lean burn application. But what do I know, I only worked on them every day in a dealership in the late 70s.

And if there's an underhood inspection involved with the emissions test, he gets an automatic fail.

Reply to
aarcuda69062

Atta boy!

Plug color is a method, it's naturally not going to be as accurate as a gas analyzer. Hell, it worked for Smokey Yunik for years.

Reply to
aarcuda69062

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