I am a real idiot when it comes to emissions control stuff so here is my question. Exactly what is the EGR valve supposed to do. The one on my Duster is still hooked up so will I do any harm by unhooking it and plugging the vacum line?

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Just take it off, and turn it 180 degrees, that will block it off, and look stock.
But why do you want to?
It doesn´t work at full throttle anyway, as it use vacuum to open, wich you don´t have much of at wot.
What it does is: to put some exhaust in the intake, so there is less oxygen in the mix, so it burns cooler.

Don't make the error of thinking that admitting exhaust gas into the intake tract just has to be bad and couldn't possibly be any good. The purpose of the EGR system is to cool the burn, as has been stated. This reduces NOx emissions, but more importantly from a performance standpoint, it reduces the tendency for spark knock. Depending on the rest of your setup, you may get optimal running with the EGR in factory configuration, with the EGR disabled, or with the EGR system tweaked and reworked to give you just enough EGR to allow the use of a more aggressive spark advance curve. Disconnect the vacuum line and plug it if you want to try it out, but keep a very careful ear open for spark knock.

Dan is correct. I tried defeating the EGR on a 5th Avenue I used to have, without changing anything else, wham-o, bad spark knock.

Someone had defeated it on my '88 truck when I got it. Had a spark-knock problem. Reactivated it and repaired some associated EGR vacuum lines and controls - no spark knock. However, the truck (TBI 318) then ran crappy off idle, and had a bog. Dan, you can go into what thing(s) I overlooked in the computer/sensor/vacuum control/nightmare system (there is some kind of backpressure sensing valve that I replaced, but I think because my truck has had duals added and the "cataclysmic converter" removed, it threw off the setup), but my solution was pretty cool and food for thought here with /6, too. The aftermarket replacement EGR valve that Idiot Auto Parts sold for my truck had a bag of different orifices so that it could fit a variety of applications... One is supposed to find the one that matches the diameter of the stock valve. Huh huh, yeah, rite! I progressively reduced the EGR orifice size until I got driveability and spark knock under control - kind of made an EGR adjustment, if you will. I throw that in, because that is a third option. I doubt you can get the "adjustable" EGR for the slant 6, but one could easily fabricate a little restrictor plate...

D/W

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If it ain't broke, fix it!

I'm going out on a limb and guessing it was an '85-'89 civilian (318-2bbl) M-body 5th Ave. These later cars with the Holley carb ran significantly poorer than the '84-down models with the Carter carb. The biggest complaint was a persistent surge under steady throttle at normal road loads. Very irritating. It is fixable by some clever and knowledgeable tweaks to the EGR system, but yeah, just pulling the EGR hose won't get you anywhere on those.
I might be able to comment on this, given that I drive a nearly identical truck. It is possible to finesse many of the driveability faults out of this TBI setup. I'm running with the EGR disabled, spark plugs one or two heat ranges colder than stock, upgraded coil, premium plug wires and specially modified distributor rotor, timing set to spec, and don't get any spark knock on regular gasoline. And yeah, the backpressure transducer is calibrated for the stock exhaust system. The previous owner of my truck put in a low-restriction muffler and phony-duals, one pipe into the muffler, two out with mullet pipes straight out the back—I scraped this mess off the truck when I got it, capped off the extra muffler output and put the factory tailpipe back on. But since the backpressure transducer gives more EGR with less backpressure, going to a low-restriction exhaust increases the amount of EGR, which can really mess with driveability. (Sometimes those "Use only factory exhaust components!" warnings are there for a reason).
Ayup. Aftermarket EGR valves are handy that way, since you can dial in your setup. I have a complete table of EGR valve orifice plates to hole size (from which flow rate can be calculated).
But you can. How surprised would you be to learn that it is the selfsame EGR valve that fits the '88-'91 TBI trucks? True! There are only relatively few EGR valve assemblies in the aftermarket for RWD Chrysler vehicles. The proliferation of different part numbers is because "different" valves come packaged with a different selection of orifice plates.

Correct again ('85 Holley equipped 5th Ave). I had driveability probs, but not as you described, no surging. I solved my problems by a combination of carb tweaking (to the enrichment piston spring tension) and a defeat (ground) switch for the 02 sensor. It ran fine out on the highway and got slightly better gas mileage with the 02 functional, but for around town, I would defeat the 02 sensor and put the feedback carb in full rich mode.

D/W

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If it ain't broke, fix it!

Yep, very similar. My '88 is in outstanding shape too, but not quite as crisp as yours. Mine had a so-so repaint before I bought it in '97, but it is still very eye-pleasing, the white paint doesn't show the little imperfections unless you get up real close or sight down the sides. Is that EFI badge stock, or something you added? My truck has no such emblem. The original owner didn't even realize it is fuel injected! He thought the Throttle Body Injector was just a fancy carb (which, in a way...).

Well, I hope you're still around when I get ready to do the motor swap on this truck. The 318 is still running good, but at 120,000mi it is starting to show it's age. Oh yeah, I could put on some valve seals and change a few gaskets and proabably drive it another 100,000 but I like to do things a little differently from standard folk. I'm collecting up the pieces I need to build a 4" stroker polyspherical small block (based on an "old-style" 318) and I want to retain all the TBI stuff. I plan to modify a "poly" intake to accept the Holley TBI. I'm going to "sensorize" the motor exactly like the current LA mill, my main question mark is going to be the computer, and of course the cam. There is a cam grinder up the street from me (Reed), I plan to work with them on the grind. Pistons will be custom units, fly cut for the "polyangle" valves. I want to try a 360 computer first, I think that will be closer than the current one. The cubes are going to work out to something like 398 (if I remember correctly). This motor will be all about torque, not top end hp. I plan to build it and make it appear as it would have if the factory had offered a polyspherical motor in an '88 truck - bar code stickers on the valve covers and all! Dan, stay tuned, I'm sure I will have lots of spark and fuel management questions for you... (although we may have to move it over to the polyspherical TBI truck board!

D/W

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If it ain't broke, fix it!

Wow, what a cool idea! I look forward to hearing about your results. I really like this kind of unconventional stuff.

I must say, though, if you're going to all this custom-build work, you could do a lot better than to use the '88-'91 TBI. It's really a pretty shïtty system. How 'bout programmable MPFI and DIS fromSDS? Or, if not, you may want to talk with Sandy In BC; he's had good results with the less-cruddy GM TBI setup and has a source for custom chips for it.

Point well taken, but I figure all the '88 TBI stuff is already extant, working well and ready to go under the hood, plus TBI in general should be a relatively easy adaption onto the old-style "A" motor.

D/W

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If it ain't broke, fix it!

It was on the truck when I got it. Given that there was bizarre blue tape striping down the side of the truck, and cheesy "clear with increasingly-dense black dots" striping about 18" below that, it's entirely possible a previous owner applied that badge. I saw a nifty "AUTOMATICO" emblem on the Argentine eBay site the other day; that would make an interesting addition...or maybe the nice "TorqueFlite" badge from an Australian R/S model Valiant...
Ooh yah, yabetchya, doon'tchyaknoow. I'll be here. You may have to rattle my cage a little, but I'll be here. It takes more than a brandished snowboard to make me go away.

What does spark knock sound like? And what exactly is Carbon knock? The only knocking that I have ever hear is the ticking lifter in my F-150 when it is cold.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Spark knock ("detonation", "pinging", "pinking", "preignition") sounds like ball bearings being rattled around in an otherwise-empty soup can.

"Carbon knock" can mean either of two things: (1) Carbon builds up in the combustion chamber, heats up and holds its heat, so the incoming fuel-air charge ignites before it's supposed to (preignition, see above). (2) Carbon builds up in the combustion chamber to such an extent that the carbon on top of the piston makes physical contact with the carbon on the underside of the cylinder head when the piston reaches top dead center.

Certain engines (e.g. Chrysler 2.2 and 2.5) are rather prone to the second kind.

That might be what I am experiencing in my D-150. It makes a dull clattering noise between 30- 45 MPH. I can either back off the gas or press it further down to make the noise go away. I has been doing this for over 3 years and it apparently has done it no harm. The EGR valve on it must have quit working.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

That does sound like spark knock. You really should track down the cause and fix it, because spark knock is very hard on the engine. It's possible the EGR system has a fault, certainly, but many other things can cause spark knock.

Is there a difference between spark knock and detonation? And how do I know if it has damaged my engine or not?

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2