Im hoping someone can help me here. I have an 85 Vette showing codes 32,34. Currently the EGR solenoid is passing vacuum without it being grounded by the ECM ( I'm getting 12V on both wires). N0 one seems to know whether this should pass vacuum without power or not. Basically I can blow through it when its in my hand disconnected. Is this normal? Weird thing is...car seems to run pretty good. I would think if the sol is passing vacuum the EGR should be opening some and causing idle problems but that doesnt seem to be the case.I guess the next step is to take off the intake plenum and start checking EGR temp switch etc. How hard is it to get he plenum off the engine to get at the EGR etc. What should I be watching for here. Thank guys for lookin maybe someone can point me in the direction. Frank

 

I believe 12v on both wires is normal when EGR is not being requested. The ECM switches one wire or the other to ground to open and close the solenoid. As far as passing vacuum through the solenoid all the time, it shouldn't. Try hooking a vacuum gauge to the out port on the solenoid (solenoid to valve) and see if it is truely passing vacuum at idle.

The pelnum is very easy to pull and can be done in less than an hour. Just have a rubber mallet handy once you get the bolts for it out. It'll need a whack to break it free of the gaskets.

Also, code 34 isn't EGR, it is MAF voltage reading too high. On an 85 there are really 3 possibilities. 1) Bad MAF sensor. 2) Bad MAS module 3) The PROM chip in the ECM is the original one from the factory. There was a service bulliten out on them back in the later 80's. The bulliten was for... False code 34, cold drive away hesitation, torque converter cycling and a couple of other minor annoyances.

Oh, and a service bulliten isn't the same as a recall...you have to pay for the new PROM and installation (if you can't do it yourself).

 

The EGR valve in an '85 Vette is a negative back pressure valve; so it should close when the engine is started. This means that it will pass vacuum when disconnected.

Are you getting the code 32 at startup or after crusing for a few minutes?

You can simply open the connector in the line from the Temp Switch and measure resistance of the switch, or probe the wire with a pin and measure voltage. It is a NO switch so, at idle you should read 9-12 Vdc on the line to the switch.

 

If I puy my finger on the other port of the solenoid it wont let me blow through it anymore. I havent actually put voltage to it out of the car but i will tomorrow to see if its working in reverse (ie stopping flow when its on) This solenoid is relatively new...6 mos or so but maybe its bad (Thx Autozone) lol. Anyway where is this MAS sensor you speak of?
And while Im at it, is there any special sealer I should be using when I reinstall the plenum? Or is RTV blue OK? I think Im just going to get a new solenoid from Mr Chevy tomorrow and then go ahead and pull the plenum. Am I smart to go ahead and change the EGR Valve while its apart? Got almost 160K on it...sounds like maybe a good idea. Any thoughts?? Thx Frank

 

I don't think you will need to pull the plenum unless the valve or switch is bad. In which case it isn't difficult; I like to remove the MAF, the TB and then pull the plenum. The MAF is located in the intake stream just after the air filter and before the bellows to the TB.


I suggest you get new gaskets for the upper runners and the TB to plenum; AutoZone will have them. Do not use RTV on this application.

 

Im always getting the Code 32. Anyone had any experience with SAS rebuilt ECM's. I see them at Rockauto.com for like 35 dollars. also they have have rebuilt MAF sensors for 35 bucks as well...Can this be for real?? I may have to try one out heh . Thx guys

 

There are actually 3 "ports" on the EGR solenoid, one is the vacuum source, another is vacuum to the EGR valve and the last port (opposite the other 2), is an atmosphere port and is supposed to have a small piece of foam over it to act as a filter.
No RTV should be needed on the plenum gaskets. Go to the parts store and get an "upper intake" gasket set for your car. It has just the throttle body, and runner gaskets in it and is a little cheaper than the whole set (it is made by ROL, a very high quality set).
For a vehicle as old as yours you need to get some "special" diagnostic tools. first would be a Mityvac vacuum pump. Hook it to the EGR valve and with an inspection mirror look at the underside of the valve as you apply vacuum. It should open and remain open until you release the vacuum. The Mityvac costs much less than an EGR valve and is worth its weight in gold when troubleshooting.
Other tools you'll want to get, a digital volt meter, a noid light, timing light and shop manuals for your year of car.

The MAS is a module, not sensor. It provides the power and burn off function for the MAF sensor which is located in the inlet tract and has an electrical connector going to it. The MAS module is in the "bread box" and you DO NOT want to buy one from GM. GM wants $700+ for them (they were only used in 85).

 

I was a little confused because I have always heard it called the MAF burnoff relay, but now I know what your talking about. I do hear it click for about 1 second when I shutoff the car so I assume it is is turning on the MAF sensor to burn it off..At least I hope it is. I will go out tomorrow and get the Vac Pump. Hope I can see that EGR move ..It sure is tight in there. I will let you know tomorrow what I find. Thx

 

You can avoid buying a vac pump by using engine vacuum to test the EGR valve and solenoid; see the diagnostic method on my site.

 

Did more checking today...Found the EGR Temp switch is in fact shorted to ground and no voltage coming out of the C15 line on the ECM because of it. Ive ordered a new switch along with plenum gaskets. I dont see any way of changing it other that pulling the plenum. While its apart I'll take out the EGR as well and check it and look for carbon build up in there.