90 350 TBI Vacuum Lines
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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. |
Re: 90 350 TBI Vacuum Lines
That system was hacked 10 times over - I am surprised that it it runs at all. This is what it supposed to look like.
http://forum.73-87chevytrucks.com/sm...0;attach=15212 //RF |
Re: 90 350 TBI Vacuum Lines
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.
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Re: 90 350 TBI Vacuum Lines
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-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 |
Re: 90 350 TBI Vacuum Lines
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. |
Re: 90 350 TBI Vacuum Lines
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.
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Re: 90 350 TBI Vacuum Lines
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A clogged CAT may cause increased exhaust back pressure which will effect EGR test. //RF |
Re: 90 350 TBI Vacuum Lines
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.
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Re: 90 350 TBI Vacuum Lines
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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 |
Re: 90 350 TBI Vacuum Lines
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!
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