90 350 TBI Vacuum Lines

[Stringer]

Newbie here. Again. Recently bought this Suburban and will replace EGR later today. But there's a T'ed line from the vac tank. Don't know where it oughta go. Everything seems plugged in. Just got a service manual but don't even see this type of vac tank in the book - and no vaccuum line map. (Maybe it's in the emissions manual.) Symptoms: Runs fine...no defrost, brakes are grabby.

Thanks in advance. Oh yeah...I didn't pay extra for the custom painted valve covers and block! I hope.

I think I've figgered it out. I have a 72 with the same TBI set up. I ain't that sharp, but I was able to copy enough of the plumbing to hook it up.

[rfmaster]

That system was hacked 10 times over - I am surprised that it it runs at all. This is what it supposed to look like.



//RF

[Stringer]

Thanks for the diagram. I bought a shop manual but your pic is easier to read. Thought I had it taken care of but I'm having trouble getting air to blow out of the defrost (I posted another question about that) and, even though I replaced it, I'm still getting an intermittent code for EGR. Only happens sometimes after driving at highway speeds for a while.

[rfmaster]

Originally Posted by Stringer

Thanks for the diagram. I bought a shop manual but your pic is easier to read. Thought I had it taken care of but I'm having trouble getting air to blow out of the defrost (I posted another question about that) and, even though I replaced it, I'm still getting an intermittent code for EGR. Only happens sometimes after driving at highway speeds for a while.

The EGR code is one one of the most annoying SES codes to get rid off. 1st off disconnecting will not fix it -so forget about that approach. The way ECM checks for EGR functionality is when operational conditions are:

-Throttle position (TPS) is between 10% and 25%
-Steady throttle with no more then 2% change in throttle position.
-Vehicle speed is above 32 MPH
-ECM in closed loop operation
-Max short term fuel trim less then 6 counts for 3.2 seconds
-desired EGR command greater then 40% duty factor
-MAP above 47.5 kPa or less then 15 kPa.

Basically the ECM cuts the EGR OFF and expects to see a predetermined outcome. After failing the test twice a code 32 will be set. Usual suspects are:

1) Wiring harness - disconnected, damaged, etc
2) EGR solenoid - broken or disconnected vacuum lines.
3) EGR diaphragm is defective ( very common)
4) Intake manifold EGR passages are clogged with oil and carbon deposits (common in high millage engines)


Do you have AC or heater only in your burban??

//RF

[Stringer]

Truck has A/C and heat. Thinking "out loud here":

Clogged EGR passages=distinct possibility. EGR holds a vacuum...causes truck to die if diaphragm is pushed. Wiring...uh, it runs is about all I can say!

When time allows - hopefully within the week, I'm going to try to make sure the vac lines are where they ought to be and working right. As of now, all I can say is "I think they are right". Still - not sure about under the dash since I have that vent door/actuator problem.

[Stringer]

Also, I'm thinking the EGR solenoid must be okay since the new EGR valve got me through a state emissions test. It had failed NOx before the EGR.

[rfmaster]

Originally Posted by Stringer

Also, I'm thinking the EGR solenoid must be okay since the new EGR valve got me through a state emissions test. It had failed NOx before the EGR.

How much of the NOx delta did you get before and after EGR swap - you should see it in your test results print out. Usually a partially clogged EGR passage will drop NOx, but not dramatically. If the NOx readings dropped a little bit, just below test threshold you still may have obstructed EGR passages or leaky EGR diaphragm (not applicable since you have new EGR).

A clogged CAT may cause increased exhaust back pressure which will effect EGR test.

//RF

[Stringer]

If I'm reading this right, at 1793 RPM I failed @ 2317 ppm. New EGR...at 1467 RPM, I passed at 1205 ppm. I passed the high speed emissions test even with the old stuck EGR.

[rfmaster]

Originally Posted by Stringer

If I'm reading this right, at 1793 RPM I failed @ 2317 ppm. New EGR...at 1467 RPM, I passed at 1205 ppm. I passed the high speed emissions test even with the old stuck EGR.

Test #1____#2
RPM 1793 1467 (RPM)
NOx 2317 1205 (ppm)

I can tell you that pass limits are very generous when compared with eco-nazi limits that we have to deal with here in Cal. Ours are about half of what yours are ~735ppm limit! My guess is that you may have clogged EGR passage...

//RF

[Stringer]

Thanks. I sorta tried to clean the port when I put the new EGR on but I'll try to do better than sorta. And I'll let the opportunity to comment on CA's regulations and regulators pass. It's a beautiful state and I lived there for 3 years. Can't tell you how happy I was to get back to Texas!