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Old 09-18-2006, 03:53 PM
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91 TBI 350 EGR problems

i bought a 91 GMC C1500 with a SBC 350 and i drove it for about 200 miles and then noticed the engine light came on. didn't notice any difference in the truck so i kept on driving it for a few days(i know i know) and then i decided to look into it today and found it was giving codes 32(EGR Failure) and 42(ignition module). i found that the vacuum hose to the EGR was not hooked up so i hooked it back up and made a trip to the auto wreckers, picked up lots of EGR vacuum valves(electronically controls vacuum to the EGR), 1 good EGR valve, and 1 good tested ignition module. on my trip the engine was running poorly, with just the throttle cracked open it was cutting in and out badly and died once. sounded like the motor had a huge cam in it until i got like 1/4 throttle. i pulled the vacuum hose off of the EGR valve and then the motor was running fine again. so i pulled the EGR valve off and pushed in the diaphragm and with my finger over the vacuum hookup it held its suction and doesn't seem like there is anything wrong with it. i also changed out the ignition module and did not help, i took my original one to get tested and its fine. i also tried 3 different EGR electronic valve controllers and they all worked the same, i tested them with a Vacuum gauge while the engine was running.

anyone have any ideas? im currently sea foaming a EGR valve from the wreckers and going to install it to see what happens.

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Old 09-18-2006, 04:33 PM
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Sounds likr vacuum hose connections may be wrong. I would ge a vacuum schematic and validate alll the connections before you replace any more parts. You also may want to pull the egr valve and clean out the ports in the intake. They are known to plug up and cause problems.
Those egr control valves seldom go bad. I would put the original back on nless you can prove for sure it is no good.

An egr valve that is open when it shouldnt be will cause the car to run like crap.
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Old 09-18-2006, 05:12 PM
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i just installed the other EGR valve and reseted the computer and it is still the same.

Right now i got the vacuum line blocked off after the egr control valve and it seems to run fine but i dont consider it fixed doing that, least i can just get to work and back.
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Old 09-18-2006, 05:56 PM
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I agree with T-Bucket vacuum hook up has to be wrong.

Should be hooked to ported vacuum source. There arent that many choices to hook it up should be an easy fix.


EGR Control Solenoid
The solenoid controls when EGR is open by grounding gray wire, when grounded EGR is activated.

Wiring EGR controler
A Pink w/ black stripe 12 volt power from ignition switch
B Gray ground through computer (controls EGR solenoid)
C not used
D Black w/ white stripe ground for solenoid





If that tests out ok and its still acting up check for the control solenoid being on all the time. Should get 12 volts supplied to solenoid but only ground the circuit when computer says so. Not at idle for sure.


There are 3 different types of EGR valves negative exhaust backpressure, positive exhaust backpressure, and ported (ported doesn’t rely on any backpressure condition in order to open).
All heavy-duty trucks rated over 8500 lbs use ported type. I think the others are on pick-ups but not 100% sure.
To test apply vacuum directly to valve idle should become very rough (this will only work on the ported type valve).


EGR Valves Types
Negative has a “N” stamped on back of valve
Positive has a “P” stamped on back of valve
Ported has only the part number stamped on back of valve




Code 42 Electronic Spark Timing = open or short to ground in the EST or bypass wires


Hope that helps you out some.
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Old 09-19-2006, 10:24 AM
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well turns out the EGR was hooked to a Full vacume port, swaped it with the Charcoal canister wich was on a ported vacuum and now it seems to run good all hooked up.

Not to sure about the Code 42 Electronic Spark Timing, it hasnt come up on the computer since. should i be worried about this?

i am also replacing all the coolant hoses and the 1 heatcore hose has got me into a bind, it is a 1 peice rubber hose into a metal pipe wich is bolted into the Intake in the rear(supposed to be some sort of quik release?) and my parts guy told me i have 2 options of removing the pipe and installing a fitting and just using some hose from there to the heater core or else cutting that metal line off and hooking up a hose to it. What would you reccommend me doing? the metal hose seems to be kinda rusty and isnt Solid, seems to have a bit of play in it. but removing it alltogther i was told may be risky as the fitting is hard to get out of the intake and can shatter easily.

Thanks guys!
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Old 09-19-2006, 10:36 AM
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Quote:
Originally Posted by montea
it is a 1 piece rubber hose into a metal pipe which is bolted into the Intake in the rear(supposed to be some sort of quick release?) and my parts guy told me i have 2 options of removing the pipe and installing a fitting and just using some hose from there to the heater core or else cutting that metal line off and hooking up a hose to it. What would you recommend me doing? the metal hose seems to be kinda rusty and isn't Solid, seems to have a bit of play in it. but removing it altogether i was told may be risky as the fitting is hard to get out of the intake and can shatter easily.

Thanks guys!

Glad to hear that the EGR problem is fixed.

As far as the coolant nipple in the intake, you can either change it now or later, it will start to leak.

Chances are it will brake off leaving the threaded end in the intake, A tool is made to remove the broken ends. I have used a hack saw blade and a hammer and chisel to remove before I bought the correct tool.

What I did is use the hack saw blade to cut the fitting (after the head is broke off) down to the threads, in four or more spots, then use the hammer and chisel to knock out the "little" pieces of leftover fitting. Try not to bugger up the threads in the intake, then just replace wit a GM part or use a slip on coolant nipple that has been used for many years to connect hose from intake to heater core.

Hope this helps

Steve
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Old 09-19-2006, 11:36 AM
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Would it help to heat up the fitting before trying to remove it?
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Old 09-19-2006, 11:47 AM
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It's hard to say, the intake is aluminum, if it gets too hot it will melt and be destroyed. I would soak it down with some good penetrating oil for a day or two (drive it with the pen oil on it if you can) then give it a go, and see what happens.

You might try tightening it first to break away some of the crud in the threads, then try to back it out. If it stops coming out try going back in with it, then back it out some more. You may have to work it back and forth to get it out, unless it breaks off.

Steve
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Old 09-19-2006, 07:38 PM
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Quote:
Originally Posted by 1931 steve
Chances are it will brake off leaving the threaded end in the intake, A tool is made to remove the broken ends. I have used a hack saw blade and a hammer and chisel to remove before I bought the correct tool.

You too? For a while, it seemed like every GM with a coolant leak was either the intake gaskets, or that stupid connector.

Montea, GM used cheap, pot metal to make said coupler, and still does. GM will stop production to make a change to save 1/4 of one cent. IMHO, replace it with a pipe fitting.
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Old 09-19-2006, 07:45 PM
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Quote:
Originally Posted by montea
well turns out the EGR was hooked to a Full vacume port, swaped it with the Charcoal canister wich was on a ported vacuum and now it seems to run good all hooked up.

Not to sure about the Code 42 Electronic Spark Timing, it hasnt come up on the computer since. should i be worried about this?

i am also replacing all the coolant hoses and the 1 heatcore hose has got me into a bind, it is a 1 peice rubber hose into a metal pipe wich is bolted into the Intake in the rear(supposed to be some sort of quik release?) and my parts guy told me i have 2 options of removing the pipe and installing a fitting and just using some hose from there to the heater core or else cutting that metal line off and hooking up a hose to it. What would you reccommend me doing? the metal hose seems to be kinda rusty and isnt Solid, seems to have a bit of play in it. but removing it alltogther i was told may be risky as the fitting is hard to get out of the intake and can shatter easily.

Thanks guys!
Its gonna break, they usually do. The good news is it will come out easily with a large easyout. You look at these types of things and you know why GM is in trouble. Did some engineer realy think that that connector was a good idea.
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Old 09-19-2006, 09:09 PM
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Originally Posted by T-bucket23
Its gonna break, they usually do. The good news is it will come out easily with a large easyout.
I don't know if I would use the term easy or not, even with the proper tool.

Steve
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