Very specific questions about EGR... Using Howell system on Jeep 4.2 6cyl

Hi All:

(Been gone awhile, but I'm back now)


I have an old Howell system (10-11 years or so) on my Jeep Wrangler. It's a fuel-only system that I am trying to update. One of the things I did recently was get an EGR solenoid and hook it up to (I think) terminal A4 (or whatever the diagram said for the 1227747). The idea, as I understand it, is that the ECM grounds the circuit and causes the solenoid to open, so that vacuum from a ported source goes to the EGR valve. I have a negative pressure valve and I put this together in accordance with the FSM.

The problem with this is that I really didn't test it before I datalogged with it. Right after I hooked it up, I placed a vacuum gauge on the outlet of the solenoid. As I revved the engine, the vacuum would increase (after I went past about 1000 RPMs), then, when it got to about 10psi or so, the solenoid clicked and the vacuum went to zero. Now, I should have stopped right there and logged some, but instead, I made up a new chip with some adjustments to the EGR settings. More on those in a minute...

Two things happened during my 30 minute drive:

(1) The fuel became VERY rich. My BLMs were all 94's except near idle, and my integrators were around 118 or so, suggesting that the BLMs could go even lower. I had previously changed the BLM limit so that values could go below 108. Now, the engine ran pretty smoothly, which told me that either the original EGR system was on all the time and the switch to ECM control fixed it (not true - see #2) or there was no EGR happening at all).

(2) I had wired an LED in parallel with the two wires going to the solenoid (inside where I could see it) and it never ever not once came on, saying that whatever I changed on my PROM probably messed stuff up.

Settings (all scalars) I changed before driving were:

> MAP threshold EGR ON: from 255 to 40 - my thinking was that 255 eliminated EGR, but maybe 255 means it's enabled at any MAP?

> RPM Min for EGR%: from 1000 to 1300 - just because it sounded right

> On Hi VSS: from 0 to 74 - not sure what the number means, but I ASSUMED "Hi" made me think that the number needed to be above zero MPH for the thing to work. Maybe I'm thinking backwards? Will it work right if this is zero?

> On Hi TPS: from 1.95 to 3.3 - I ASSUMED that this meant EGR would not work above 1.95, and since I spend a lot of driving time ABOVE a TPS of 1.95V, then 3.3 sounded about right. Is this backwards like my 'On Hi VSS' thinking?

> Min kPa for EGR% - from 69.92 to 40 - figured this would make EGR work more often, but might change it back to the higher number.


If anyone can PLEASE explain this stuff to me and tell me where I went wrong (or right), I would GREATLY appreciate it. The reason I am changing some of these values is this: I know Howell disabled some things in their setup, but I don't know what I need to change to get these functions back (like EGR, ECM controlled timing, whatever else). I even discovered that even though I had a California kit which should have had a VSS, the wire in the loom did't go to the ECM - it just disappeared in the tape somewhere, and I had to put a wire in the connector for it. Same thing for EGR.

I have made my VSS work - I'll put a little write-up on the forum sometime since it's a little unorthodox. I am attacking the EGR now, and I plan to change my timing to ECM control next. (If anyone can point me to a good write-up about the timing change, that would be great. My searches usually show me something about going the other way.)

PLUS: is there a better way to learn this stuff, like a book or something? I have the FSM, but it's not much good for things other than wiring and troubleshooting. I would LOVE to see a write-up on what every little scalar and table in the BIN file does. Maybe I'll do that one day when I learn more.

Anyway, I anxiously await your answers. I have to make a new fuel table so I can drive to work tomorrow.

Dan.

OK - Here's a brief update on the above:

I changed the fuel table based on the very low (RICH) BLMs.

I also changed some of the EGR settings back:

- MAP Thresh EGR On -- back to the original setting of 255 from the 40 I had changed it to.
- On Hi VSS -- original was zero - I changed it to 74, then back to 1 (almost zero).
- Min kPa for EGR% -- original 69.92 - changed it to 40, and now to 50.

On a short test drive (without logging) the following happened:

- Nothing for about a mile, then...
- The light started working, indicating I now have ECM control of the EGR. The light comes on at some slower speed - maybe 10-15 MPH. It goes off lower than that and at idle, it goes off an deceleration, and it goes off under heavy acceleration. With the light on (indicating the EGR valve solenoid is open) it accelerates like crap - lots of stumbling, coughing, misfiring, whatever. If I stomp the gas, it smooths out very briefly, then commences to farting again. I think this coincides with the port vacuum behavior: sudden throttle opening makes the vacuum almost disappear, then it comes back most of the way. This in turn tells me that when the EGR is on, it makes the thing lean, and since I just decreased my fuel, I am very lean.
- I got an SES light when it started running badly. I don't know what code it gave since it turned off right before I got home.

So now...

What do I do about this? It seems like the EGR is working about right - comes on and goes off as I would expect. But with this going on, how the heck do I tune it? Datalog with the EGR OFF, and let the ECM sort it out when the EGR is working? Or do a new datalog with the EGR working via ECM control?

And... My EGR valve is fairly new. It isn't a Delco one, it's from Advance - probably a BWD - but it is a 'negative pressure' one as specified. Could it possibly be that I have a valve that lets too much gas pass (hence the farting?)

Help, please!

Dan.

SMALL amount of progress (this is like being a detective).

The FSM says that the vacuum going to the EGR valve after the solenoid should be 2" to 10". I tested this and discovered that at higher RPM I have about 15.5" to 16".

Two things are wrong with this. First, obviously there is too much vacuum going to the valve. Whether this causes the valve to open more I don't know, but if they specify no more than 10", then I am certainly above that. Second, and much stranger, is the fact that vacuum increases as the throttle opens. This of course seems backwards to me - the amount of vacuum should decrease as the throttle opens.

What caused this? Don't know, but it could be related to at least one of the following: (1) I have an open spacer between the throttle body and the intake - I stuck the gasket (a closed one) to the throttle body with goo - maybe there is some weird bleed-through; (2) With the ported port right in the venturi, maybe increasing velocity as the throttle opens increases the vacuum at that port - it should; (3) This particular 4.3 throttle body did not come with manifold vacuum ports - just the two humps with no holes. I drilled those out and inserted steel tubing so I could attach hoses. I don't think I screwed up that part as the manifold vacuum works right.

So this problem causes me two more problems. Number one: the EGR valve gets a backwards signal plus too much vacuum, and this may be screwing up my fueling. Number two: I have my vacuum advance hooked to the same port. I would guess that this causes my timing to advance with throttle opening rather than decrease.

All of a sudden I have a bunch of reasons for sputtering when I push down on the gas pedal. I'm going to rework the vacuum hoses and uses manifold vacuum only, plus try to reduce vacuum to the EGR somehow.

More later.

facing the throttle body the egr hose should be to the left of the pcv hose, does your egr valve use washer to meter how much it flows into the intake?

Hi 'ony':

Well, it's there as of about an hour ago. It is now on one of the manifold vacuum ports that I had to drill in this particular throttle body. I am assuming it's from a later model 4.3. I got it off of ePay - it was advertised as being "recently professionally rebuilt", so naturally I had to take it apart, clean it, carefully put it back together, install an adjustable fuel pressure regulator (dead set on 12psi), and add those two ports. Originally it had only the big PCV port and the smaller 'port' port below and a pinch to the right of the PCV port when viewed from the front.

The EGR is now on that left port you mentioned, as well as my distributor vacuum advance. Howell said to use ported vacuum, and I have been going back and forth for years with that. It seems to run the same either way, except that maybe I can get a hair better mileage with all the extra advance at idle that manifold vacuum provides. (Like that will matter with a brick-shaped Jeep anyway.)

After changing ports earlier I went for a long logging drive - it ran fine but the BLMs were WAY high in most places, so I refined the tune with those and will make a new chip later.

The EGR valve is not one of those that takes washers, but I don't know if it's a top shelf piece either. It's a BWD from Advance. I did notice earlier, however, that in the FSM the specification for 2" to 10" vacuum after the solenoid is only for over 8500 GVW vehicles. The regular (under 8500 GVW) vehicles do not have a specification for a vacuum level, other than the valve must open.

Thanks VERY much for responding, and please continue with advice!

By the way, I came from Texas about ten years ago, lived in Abilene, then in Weatherford from 2005 to 2007. I can't wait to get back there.

Dan.

There should be some kind of table or tables to adjust the fueling with the EGR on. If you mess with the VE table with it on, then the fueling will be off with the EGR off. Related to this, you probably can't use ported vacuum to turn the EGR off at idle when the ECM thinks it's on or else the EGR fueling correction will be applied when the EGR is closed which will mess up the fueling. So, you need to setup the VE table with the EGR disabled and then go back and work the EGR correction tables once you enable it if the fueling is off when the EGR comes on.

When there are high and low threshold value pairs it's likely that instead of simply being between to operate, the ECM will only turn on when you go above the higher threshold and then it only turns off when you go below the lower threshold. For example, if you have speed thresholds the EGR would only switch on once above the higher speed value and it would only turn off once below the lower speed value. When between the speed values it stays in whatever state it was in.

Hi 'lionelhutz':

Thanks for the reply!

In the BIN I am using there is a table called "EGR - VE Comp Table":

0 6 13 20 25 31 38 44 50 56 63 69 75 81 88 94 100
8 0.89 0.84 0.80 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76
16 0.89 0.84 0.80 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76
24 0.89 0.84 0.80 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76
32 0.89 0.84 0.80 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76
40 0.89 0.84 0.80 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76 0.76

(I can't get this crap to line up no matter what I do, but you can see how everything from MAP 38 over is 0.76, and the correction factor is the same for all RPMs.)


The numbers down the left column look suspiciously like RPMs, the top row looks a lot like kPA values with some extras thrown in for better resolution, I guess, and the values on the table are probably multipliers to be used on VE1 when EGR is operating. Of course these are all guesses, but they seem to make sense.

I tentatively plan to do the following:

- Get a good fuel map with EGR off
- Get a fuel map with EGR on
- Use the data (BLM deviations or something) I get from the EGR 'on' run and modify the multipliers above so that the BLMs I get with EGR 'ON' match the good EGR 'OFF' fuel map.

This may take some time. Lots of time.

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I like what you said about high and low values. This makes sense especially in those tables where the value in the 'low' cell is higher than the value in the 'high' cell'. They are more like 'entry thresholds' when you are going up or down in whatever table is in question.

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As far as turning off the EGR with ported vacuum / throttle closed, I think it's a moot point. From what I gather when trying to watch my "EGR indicator light" and the TunerPro dash while trying to drive makes me think that EGR is based on ECM programming. The EGR turns off when I decelerate even a barely noticeable amount, and it is never on when the "dash" says "Idle" mode is engaged. It turns on at a lower MAP than I think I programmed, but it does turn OFF at my specified TPS voltage. There is some work to do on the ON/OFF side, but the real work will be getting that compensation table to work right. I noticed while driving that the EGR on/off threshold seems to be the line between 80 and 90 MAP - it's on at 80 or less, and it's never on at 90 (and of course I've never seen numbers appear in the 100 column).

Keep the advice coming! Thanks!
Dan.

Hi, Dan...

My time to reply is limited. Ported vacuum will seem to make increasing vacuum with increasing throttle angle. The throttle plate limits the port exposure to full manifold vacuum at lower opening. Use two vacuum gauges to see relationship between the two types of vacuum sources.

Ported vacuum for spark is a way to retard the spark and decrease NOx at idle and in decel conditions in a vacuum/mechanical spark advance system.
Ported EGR is a method to more easily prevent EGR operation during idle and decel. At idle adding EGR can unnecessarily complicate tuning. During decel adding EGR reduces engine braking.
Adding Exh. Gas displaces O2 so O2 sensor reports less O2 as "rich" operation to ecm. VE - EGR compensation table adjusts fuel delivery to account for displaced fresh air entering engine. There is also an EGR spark adder. Exhaust gas is inert. It doesn't react with fuel and slows down combustion so spark must be started sooner to make peak pressure occur at proper time.
Hysteresis pairs, like "min TPS to enable EGR" and "Max TPS to enable EGR" usually work so values must be between min and max. Sometimes limits are labelled as HI and LO which can mean variable must go above HI to enable, then EGR will stay enabled until variable drops below LO. It's best to get a stock .bin to use for comparison and instruction.

Reading the GM EFI FSM system descriptions and trouble code notes are a great way to learn. Emissions controls were new in the '70s and '80s and some old books do a great job of telling mechanics of the day how these "new fangled" systems worked.

Hi! Thanks for that response - it's full of good little nuggets of information.

Some things I am wondering about.

With the vacuum gauge on the ported port, the vacuum does seem to increase with throttle opening - at least for awhile. Near full open it catches up with manifold vacuum and then starts to decrease. It is acting on some kind of curve, but only past 50% or more. I am guessing that just above closed throttle (when vacuum appears on the gauge), the larger portion of the vacuum is created via Bernoulli principle due to increasing velocity past the little bitty port drilled horizontally into the side of the throttle body's intake cylinder (whatever it's called - I hate to call it a 'venturi' like on a carburetor since it isn't tapered). As manifold vacuum decreases with increasing throttle angle, the velocity must increase, hence the ever increasing port vacuum. Then at some point, the increased velocity past the port vacuum hole is diluted by the greater exposure to manifold vacuum, and the port and manifold vacuums merge.

Considering the above (increasing port vacuum with increasing throttle angle), what does this do for vacuum advance on the distributor? Doesn't higher vacuum cause greater advance? Wouldn't ported vacuum therefore be opposite of what I need, assuming that advance should decrease with RPM? Mine might be one of the weirder cases. I know some people prefer manifold vacuum for the advance, while others prefer port vacuum. This may be an example of why one may be preferred over the other. I have gone back and forth over the years, but with this latest switch to manifold vacuum it certainly runs more smoothly.

One thing I am fairly certain of: this whole thing will get better when I move to ECM controlled timing.

As it is, my EGR goes off at idle and deceleration, and it goes off with fairly large throttle openings, so I guess that part works right.

What I don't know is this: does the VE - EGR Comp table need to be "turned on"? I get two very different BLM tables when logging with and without electronic EGR. That makes me think either the values in the table aren't right for my engine, or else the whole table is being ignored. At this particular time I am running on a VE table modified by BLMs collected when EGR was being used. I believe this is working for me because I hit closed loop at 26.25C (79F) and my Jeep engine with all its internal friction warms up very quickly.

Am I missing the mark here? Any suggestions about adjusting the EGR Comp table, or whether I should at all? My BIN is mostly AKDX - I've changed several of the usual things but so far the EGR Comp table is untouched.

By the way, I have made a huge spreadsheet which contains every item in the BIN, plus columns for four different BINs to enable comparison. I've done this mainly for my benefit so I can compare my changes with the original Howell file, with AKDX, and with another one. I will upload it sometime soon so other people can use it for comparison without opening millions of table in TunerPro.

Dan.

It's been many years since I last tuned a 7747 equipped vehicle. Some ecm specific details may be accidentally omitted. :(

Fuel is generally decreased through VE compensation since less O2 is present with EGR on. Should be a BPW with EGR ON variable also, make sure it is correct. Scale it by the same amount as the base BPW variable. I would expect values in the VE Comp table are not correct for your engine. I do not remember a "Switch" for the table. I remember the table will be used when the ECM determines EGR should be operating.

Spreadsheet sounds cool. I usually end up falling asleep somewhere in the middle of a project like that.