87-95 TBI EGR code 32

[jameslleary]

Hi guys,
I was not sure exactly where to post this, so I will stick it here, and the Mods can move it as they see fit.
This post is intended for anyone in my situation, where they have to pass emissions tests, and have swapped in a GM TBI system.
Since I have decided to stay with TBI, i have been chasing down a problem with the EGR system, throwing code 32.
Today I found the problem.
I am still running the dual cat exhaust, with magnaflow mufflers inline, and dual 2" tailpipes, like what came on the 86 trucks from the factory.
This exhaust configuration is entirely too free flowing for the TBI EGR system to work properly, as this particular EGR system is disigned to operate with the help of back pressure from the original single cat ehaust system, found on un-molested 87-95 GM light Trucks.
I have cured the problem by stuffing one of the tailpipes with tightly rolled shop rags....no code 32.
I have confirmed this by removing the rags, and then driving at 55 mph, and code 32 comes back up, when pressing on the accellerator to maintain speed.

[EagleMark]

Code 32 is a PIA sometimes to cure and your test and cure here is awesome! :thumbsup:

But I don't think it was because of back pressure needed for EGR, I think you changed something to increase or decrease engine vacuum to put it in boundries of test. Either way you found a cure and with this finding we may be able to make a simple change in bin file so EGR test can occur and pass with changed engine vacuum because of free flowing exhaust...

Here read the GM manaul for Code 32 and you'll understand what I am saying... the complete TBI manual in pdf can be found bottom of this post.
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?52-GM-ECM-Reading-Error-Codes-CEL-SES-Light

http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=1382&d=1325807601

[jameslleary]

Thats an ok idea, only problem is, the TBI EGR valves will not work solely on vacuum, like the TPI, and earlier carbed EGR valves do.
I dont know if this is true with TBI fuel cars, but the truck valves act as if they have a metered leak in them, which requires sme exhaust pressure to help it out...I dont know what GM engineers wer thinking when they decided to make it this way...but they did.

[EagleMark]

When EGR opens it's passage is to engine vacuum (vacuum drops for test) so it sucks a little exhaust in.... I've never heard or read anything about EGR operation that mentions exhaust pressure? But you have obviously proved something here with code 32, but code 32 tests for MAP reading. And it's only a test when the 3 qualifiers mentioned above are met? Not that the EGR has failed...

So I looked in the $42 hack, then $42-1227747-V3.xdf and sure enough, there it is, first one in Flags. "Options @ 0x0005 - Bit 7 - EGR" Checked! Uncheck it and test is off, no more code 32 with free flowing exhaust.

[jameslleary]

Yeah, but they pull the plug on the egr solenoid here to make sure it throws a code during bi annual inspection.

[EagleMark]

That would set a differant code, I think. What mask?

EDIT: On $42 I was talking about would turn off the bit for the test, not the error code after test failed! So code 32 would still work, but won't because the test would never happen. Not sure but if you pull the wire off EGR it should set a code.

Or have 2 chips. One stock for inspection one with Code 32 test off? Besides other cool stuff...

[jim_in_dorris]

James, is that a P or N EGR? And my smog guy just told me yesterday that if your vehicle came with single exhaust, that dual exhaust even with 2 cats will be an automatic fail next year. I have true duals with 2 1/2 " pipes on my 87 with cats, and don't throw an EGR code.

[jameslleary]

I was thinking 2 chips as well, i would like to get a chip with your hwy mode.
Jim, the truck had TPI, CA certified with dual cats, i will be changing it to a single cat system...Yup, its me, from FSC.

[jameslleary]

p or n?

[EagleMark]

I was thinking 2 chips as well, i would like to get a chip with your hwy mode.
I just revived it, RBob is the one to credit!

[jim_in_dorris]

There are 2 types of EGR valves. TBI uses a Negative pressure EGR, and has an N in the part #. Using a P (Positive) part number will cause EGR codes and other strange behavior.

Yeah I figured it was you... What are you switching from TPI to TBI?

[93V8S10]

I wounder if the coding could be changed to work with the P valve. This would depend upon whether the P and N valves look similar or not. Would have to get a replacement P valve and write in the old N valve part number. Of coarse all of this would be pointless if it's an automatic fail with duels.

I'm not sure, but I believe that the $0D code will run P, N, and Digital if set-up correctly. Don't know about $42 though.

[jameslleary]

Yep, The Burb has become more of a family cruiser now, and i just wanted to go with something reliable, that i can work on easily on the road if I have to. If i get another project truck, I want to maybe get a 73-74 longbed with a 292 I6, and do something multiport to it. I went by the oem info that i was able to find for the system I am using, and matched up the correct orofice that came with the Egr valve. I am thinking that i may need to cange the solenoid, as i am still using the one from the TPI.

[EagleMark]

Thats an ok idea, only problem is, the TBI EGR valves will not work solely on vacuum, like the TPI, and earlier carbed EGR valves do.
I dont know if this is true with TBI fuel cars, but the truck valves act as if they have a metered leak in them, which requires sme exhaust pressure to help it out...I dont know what GM engineers wer thinking when they decided to make it this way...but they did.


There are 2 types of EGR valves. TBI uses a Negative pressure EGR, and has an N in the part #. Using a P (Positive) part number will cause EGR codes and other strange behavior.
Ahhh! That's what he was talking about in above quote? I hadn't realized there were 2 kinds... this would explain a lot of Code 32 issues!

[EagleMark]

I wounder if the coding could be changed to work with the P valve. This would depend upon whether the P and N valves look similar or not. Would have to get a replacement P valve and write in the old N valve part number. Of coarse all of this would be pointless if it's an automatic fail with duels.

I'm not sure, but I believe that the $0D code will run P, N, and Digital if set-up correctly. Don't know about $42 though.We are lucky to have a very nicely written $42.xdf by Robert Saar that has many, many more options then others I have seen, probably 3-4 times as many parameters then TunerCat. Lots of EGR settings.

But it may not be a scaler or table. But in bitmasks we have:
Options @ 0x0005 - Bit 7 - EGR which I believe would turn off Code 32 test! Not the Code 32 error code.

Then these 2 I do not know what they are for?
Options @ 0x0005 - Bit 4 - EGRIN = Not checked
Options @ 0x0005 - Bit 3 - EGRDC = Checked

[jim_in_dorris]

The difference between a N and a P EGR is how they work, not in the code. I can't find the thread from fullsizechevy.com that had a really good write-up on how they work and how to test them. Something like 99% of TBI trucks would use the N type EGR. The type of EGR valve is reflected in the part number.

[jameslleary]

17056181 was the part number for OEM, Then i had to figure out which orofice to use.

[jim_in_dorris]

There will be a N or P right on the EGR, I have a couple of them to look at.one has a p, the other an N. the P style on a tbi causes all sorts of problems. IIRC the p type uses exhaust reversion pressure to hold it closed, while the N type doesn't rely on exhaust to hold it closed.

[EagleMark]

The difference between a N and a P EGR is how they work, not in the code. I can't find the thread from fullsizechevy.com that had a really good write-up on how they work and how to test them. Something like 99% of TBI trucks would use the N type EGR. The type of EGR valve is reflected in the part number.I guess we were thinking code could be changed to opisite. But from the explination above it's a mechanical process of operation.

And both look the same?

[jameslleary]

The one i have is an Airtex/Wells replacement.
EGR126

[jim_in_dorris]

This pdf from airtex would seem to indicate that you have a positive type EGR. Another thread (the one I can't find) poster had problems with the positive EGR and dual exhaust also. Every Chevy mechanic I talked too (not that many really) indicated the they are not interchangable.

http://www.airtexve.com/custom_searches/pdf/instruction_sheets/990700686.pdf

[93V8S10]

OK, so no coding difference. I did some rummaging through my storage and found my original valve for my 91 Caprice TBI 305.

The original valve is stamped: DFX 17088125 095 01N. I'm assuming that this is a N valve, correct?

The instructions that came with the NAPA replacement valve have this statement:

NOTE: GM valves are marked with a "P" or "N" indicating the type of transducer incorporated. All functional tests of GM valves should be made using service manual procedures. All clockable style EGR valves incorporating internal transducers are of a positive backpressure style. Due to their design and precise calibration, negative backpressure valves can be replaced with positive backpressure style replacement valve. The replacement valve calibration is further controlled by the size of the opening in the washer to be mounted in the exhaust gas inlet where required (see step 3, below). Physical appearance of replacement valve may differ from the valve on the engine; however, both perform the same function.

This replacement valve is marked as "POS", as well.

So, could the real problem with running free flowing exhaust be with the valve calibration and not with the valve design itself? Or could it be that the "N" valve won't work but the "P" will if calibrated correctly? It would be possible to test this by trying the different size washer supplied with the replacement valve.

Jim, I'm not trying say your wrong or anything negative at all. I don't really know how these work and I value your opinion.

[jameslleary]

so, I have the P valve. Its what was listed on rock auto, I am using 89 v1500 lookups. i will probably be going with a walker quietflow3 muffler as well, and the light came back on yesterday.

[jim_in_dorris]

I understand James, I'm just trying to help here, nothing personal. I don't know anything about calibrating them, The instructions would seem to indicate that they are replaceable, but with free flowing exhaust, perhaps the calibration washer needs to be different. Keep updating us, as this is valuable information. I had code 32 problems with my truck for a while, but it cured itself when I went to hotter plugs to stop an oil fouling problem.

[jim_in_dorris]

Just found this explanation online

Exhaust Gas Recirculation
The purpose of the EGR system is to control oxides of nitrogen which are formed during the peak combustion temperatures. The system feeds small amounts of exhaust gas back into the combustion chamber. Feeding back the exhaust gas lowers the combustion temperature which in turn lowers the oxides of nitrogen. If to much exhaust was reintroduced into the intake stream, combustion would not occur or would be inhibited. Symptoms of a open valve would be stalling after a cold start, engine stalls after deceleration, engine surging during a steady speed and rough idle. If the valve was always closed spark knock, engine overheating and possible emission test failure might occur.

The EGR valve is operated by engine vacuum and generally is open only when the engine is warm and is operating above the idle speed. There are three types of valve control systems used to control EGR valve operation in General Motors trucks; the positive exhaust backpressure type, the negative exhaust backpressure type and the ECM vacuum solenoid controlled type. The ECM controlled EGR system is generally found only on trucks (http://www.justanswer.com/chevy/06wno-1987-chevy-silverado-5-7-egr-valve-inop.html#) built for use in California.

Both the negative and positive backpressure type valves use a thermal vacuum switch to prevent operation before the engine has warmed. The switch prevents vacuum from being applied to the valve when the engine coolant is cold. Both the negative and positive valves are designed to insure that the valve only operates above the engine idle speed and the amount the valve opens is not excessive. The choice of either a positive or negative backpressure valve is determined by measurement of the engine's normal backpressure output. Negative valves are used on engines with relatively low backpressure; positive valves are used on engines with relatively high backpressure. If the valve is to be tested or replaced, it is important to know the type of installed. To identify the type of valve used, look on the top side of the valve. A "P" will be stamped on the valve after the part number if the positive type is used or an "N" for a negative type valve.

The positive backpressure type valve has an internal vacuum bleed hole that is open when exhaust pressure is low. As exhaust backpressure builds, the bleed valve closes allowing engine vacuum to be applied to open the EGR valve. The negative backpressure type EGR valve has an internal bleed hole that is closed when there is low exhaust backpressure. Engine vacuum opens the EGR valve. When engine vacuum increases combined with negative backpressure the vacuum bleed hole opens and the EGR valve will close.

The ECM controlled EGR valve uses a solenoid valve to control the operation of the EGR valve. The ECM monitors the coolant temperature sensor signal and the throttle position sensor to determine when to operate the valve. Based on the coolant temperature and throttle position, the ECM will pulse the EGR vacuum solenoid on and off many times a second and varies the amount of "on" time to vary the amount of gas recirculated. Since the ECM determines when the system operates, the level of exhaust backpressure is not important and therefore the system can use a simple standard ported EGR valve.

On 6-cylinder engines, the EGR valve is located on the intake manifold adjacent to the carburetor. On small block V8 engines, the valve is located on the right rear side of the intake manifold adjacent to the rocker arm cover. Mark IV V8 EGR valves are located in the left front corner of the intake manifold in front of the carburetor.

[EagleMark]

Good article! But I don't remeber ever seeing an EGR on a TBI engine that was not controlled by the solonoid? Maybe wrong?

It says there are 2, P and N. But then it goes on to say:

The ECM controlled EGR valve (http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dautomotive&field-keywords=egr+valve&x=0&y=0&ih=6_0_1_0_0_0_0_0_0_1.95_260) uses a solenoid valve to control the operation of the EGR valve. The ECM monitors the coolant temperature sensor signal and the throttle position sensor to determine when to operate the valve. Based on the coolant temperature and throttle position, the ECM will pulse the EGR vacuum solenoid on and off many times a second and varies the amount of "on" time to vary the amount of gas recirculated. Since the ECM determines when the system operates, the level of exhaust backpressure is not important and therefore the system can use a simple standard ported EGR valve.

So the above test of plugging a free flowing exhaust proved that wrong...

[jim_in_dorris]

That's actually for a different style of EGR, it is an ECM controlled EGR (linear Pintle under computer control)

[jameslleary]

I understand James, I'm just trying to help here, nothing personal. I don't know anything about calibrating them, The instructions would seem to indicate that they are replaceable, but with free flowing exhaust, perhaps the calibration washer needs to be different. Keep updating us, as this is valuable information. I had code 32 problems with my truck for a while, but it cured itself when I went to hotter plugs to stop an oil fouling problem.
Whoa! LOL! Where did that come from! Did I say something wrong, If I did, sorry bout that.
I am thinking that I will get the N type, just to keep from having any problems in the future....anyone have a part number?

[EagleMark]

Well I knew what a thermal switch was. This is what is used on carburetors vehicles to ensure EGR only operated when vehicle is warmed up. It has a vacuum source but won't let it through until set temp.
http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=1413&stc=1&d=1326080177


================================================== ============================

But with all the GM TBI engines I have seen use this solenoid to control the EGR valve via ECM. It too has vacuum from engine but ECM controls vacuum to EGR. The extra open vauum port on this one is suposed to have a filter on it..
http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=1412&stc=1&d=1326080177




================================================== ============================
Found this picture of Positive EGR.


Positive Back pressure EGR (BP/EGR) Valve
This type uses both engine vacuum and exhaust back pressure to control the amount of EGR. It provides more recirculation during heavy engine loads than the single diaphragm EGR valve. A small diaphragm-controlled valve inside EGR valve acts as pressure regulator. The control valve gets an exhaust back pressure signal through the hollow valve shaft. This exhaust backpressureexerts a force on bottom of control valve diaphragm. The diaphragmplate contains 6 bleed holes to bleed air into the vacuum chamber when back pressure valve is in open position.

http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=1411&stc=1&d=1326080177




================================================== ================
Found this picture of Negative EGR.


Negative Back pressure EGR (BP/EGR)
Valve This type has the same function as the positive BP/EGR valve except valve is designed to open with a negative exhaust back pressure.The control valve spring in the transducer is placed on the bottom side of the diaphragm. When ported vacuum is applied to the main vacuum chamber,partially opening the valve, the vacuum signal from the manifold side(reduced by exhaust back pressure) is transmitted to the hollow stem of the valve. This enables the signal to act on the diaphragm, providing a specific flow. Thus, the EGR flow is a constant percentage of engine airflow.

http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=1410&stc=1&d=1326080177






So there's the difference. An extra spring and a vent.


================================================== ===================
Digital EGR

http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=1409&stc=1&d=1326080177

[jameslleary]

Thats the solenoid i need to get....right now i am using the one from my original 86 e4me setup.

[jim_in_dorris]

James, I might have over-reacted to you comments earlier, no sweat. It's late here now, but tomorrow after work I will try to get under the hood of my truck and get the part number for an N type EGR, do you need a part number for the solenoid also?

[jameslleary]

Jim,
just the valve would be good, I have the part number for the solenoid as of an hour ago. It would ba wonderful if I could get the egr to work, and still run dual inline magnaflows with the single cat setup.
I also need to look into modding my ecm so I can use the flashable chips....dunno if I have the balls to start de soldering pc boards though!

[jim_in_dorris]

I just got my EGR # off my truck.. What a pita, its upside down on the back bottom side of the EGR as it is mounted. Anyways, I have a 17087196 EGR

The 17087194 = EGV627 says GVW Under 8,500 Lbs.; w/ m.T.

the 17087196 = EGV628 says GVW Under 8,500 Lbs.; w/ a.T.

http://www.summitracing.com/parts/SMP-EGV628/Application/?prefilter=1

This looks like the one you need, but rockauto is probably a lot cheaper.

[jameslleary]

Thanks Jim!

[EagleMark]

Did the trucks end up being N? Wondering if cars are P? I've never thought of comparing intakes as that may tell why/if there is a differnce...

[jim_in_dorris]

Mark, almost all TBI trucks are N type.. Apparently they have a low negative pressure exhaust and thus require the N type EGR. Adding dual exhaust makes them even worse.

[EagleMark]

Earlier I had mentioned changing in the bin the MAP ratings to meet qualfiers for Code 32, it's not in the xdf but maybe could be found in hac and added for a simple change.

Today I'm playing with my LT1 and in xdf is this paremeter option "Error 32, Min Diff. MAP Test Value " it is set to 11.88 kpa expecting that much change. But in $42 I think it has a high and low and must be inbetween.

[EagleMark]

Found some interesting EGR stuff in $42 hacs. One mentions Back Pressure EGR?


; 5.7l LD w/Back Pressure EGR (asdx)
;
; This tbl provided a corrected value of
; effective cyl vol/Inj flow rate when EGR
; is active.
; 1. Inj Flow is per bank, in gms/sec
; 2. Cyl vol is liters/cyl
; 3. Ratio = cyl vol/Inj flow
;
; The resulting value is used to predict
; fuel flow using the speed density method.
;
; {During EGR off/on transients the value is
; filtered between the value at LD2B4 and the
; table value for smoothing}
;
; 189.48 = .7125L / 7.713 g/sec TBI
; TBL = 1461.5 * Volume/rate
;=============================================

The other thing is qualifiers that have to be met to enable a code 32 test. Looks like it is not a MAP reading that fails the test but an Integrator count? Several hacs have test fro 30 sec to 90 sec and Integrator change from 4 to 8? So this would be a simple fix so code 32 is still active but fixed to pass test, but if I read this right it could be that fueling is off to begin with because as it closes EGR for test it is looking for Integrator change? Less integrator would pass test easier!


;---------------------------------------------
; ERR 32
; >> EGR <<
;---------------------------------------------
LD52B FCB 90 ; 90 Sec's DIAG CYCLE TIME
;
; ENABLED IF IN MAP WINDOW
;---------------------------------
LD52C FCB 96 ; 45.8 Kpa, LO LD DISABLE
LD52D FCB 208 ; 87.1 Kpa, HI LD DISABLE
;
; ENABLED IF IN TPS WINDOW
;---------------------------------
LD52E FCB 17 ; 6.6% LO TPS LIMIT
LD52F FCB 64 ; 25% HI TPS LIMIT
;---------------------------------
LD530 FCB 250 ; 98% EGR ON THRESH
LD531 FCB 25 ; 2.5 SEC'S EGR ERR DELAY TMR
LD532 FCB 3 ; 3 CNTS FAIL CNT'T THRESH
LD533 FCB 10 ; 3.9% TPS, CHNG TO DISABLE TEST
;---------------------------------
LD534 FCB 28 ; 2.8 Sec's TEST DURRATION
LD535 FCB 4 ; INTIGRATOR CNT LESS FOR EGR FAULT
LD536 FCB 45 ; 45 MPH REQ TO ENABLE TEST
LD537 FCB 255 ; 99.6% EGR D.C, DECREMENT FOR TEST IN WORK
; (Big Blk IS TYP 50%)
;---------------------------------------------



LD52B FCB 15 ; 15 Sec's DIAG CYCLE TIME
;
; ENABLED IF IN MAP WINDOW
;
LD52C FCB 104 ;
LD52D FCB 208 ;
;
; ENABLED IF IN TPS WINDOW
;
LD52E FCB 25 ;
LD52F FCB 64 ;
LD530 FCB 250 ; 98% EGR ON THRESH
LD531 FCB 32 ; 3.2 sec's EGR ERR DELAY TMR
LD532 FCB 2 ; 2 CNTS FAIL CNT'T THRESH
LD533 FCB 10 ; 3.9% TPS, CHNG TO DISABLE TEST
LD534 FCB 30 ; 3.0 Sec's TEST DURRATION
LD535 FCB 8 ; 8 CNT'S, INTIGRATOR DIFF FOR EGR OK
LD536 FCB 30 ; 30 MPH REQ TO ENABLE TEST
LD537 FCB 255 ; 99.6% EGR D.C, DECREMENT FOR TEST IN WORK
; (Big Blk IS TYP 50%)
;-----------------------------------------

[wokeupdead]

I know this is an old thread, did you resolve it? My suburban used to throw that with headers and three inch single exhaust. Egr worked normally, and no light. All about flow.

Edit: Without EGR will probably have nox too high.

Mike

[jameslleary]

Yup, sure did. Replaced the valve with the egv628 mentioned above, and no problems since.

[Tralam]

For anyone who might run across this looking for a solution to their EGR error code (like me), I found a different solution following EagleMarks lead.

I put a vortec 5.7 in my 94 k1500, and used the fancy GMPP intake manifold so that I could keep the EGR for emissions reasons. I would always get a code 32, even though everything seemed to be correct and working. Looking at the $0D hac, I found that the way the test works is by closing the EGR, and keeping track of the Int count. If it increased a certain amount (4 counts) within a time limit (2.5 seconds), the test passes, if not, error 32.
10999

I looked at the datalog the moment that the error was thrown, and this is what it looked like.
10998
In between the two red vertical lines is where the EGR closed for the test (which failed right after). You can see that the int count (green line) started to increase, but toward the end of the test. Based on the Map (blue line), it looks like the EGR was closing too slow for the test to pass within the time limit.

To remedy this, I modified my XDF to allow me to increase the time limit (I think I increased it to 4 or 5 seconds), and I haven't had an error 32 yet.

[billygraves]

.............

[SKFengineer]

Billygraves, thanks for your reply... Are you saying that the TCC solenoid could be going bad? I have Code 32 but only when the air temp is between 65 and up. Also to be clear the TCC is the torque converter lock-up, correct?

[1project2many]

Billygraves... I wish I'd heard this back in the dealership days!

[billygraves]

..............