[QUOTE=Adams' Apple] toptechx6,  that's some good basic info on EGR systems.
I don't think Dave's car has had any exhaust mods, but....it may be that the wrong EGR valve has been installed. That's something I haven't considered...

[/QUOTE]

Huh, are we reading the same thread?  From his first post:

" when i installed the exhaust i eliminated the precats, put a hi flow converter on it and low backflow mufflers."

If the light is coming on under 'cruise conditions' , it is most likely the "diagnostic temp switch" that is located adjacent to the EGR valve.  This switch must be detected 'closed' after 4 mins of cruise. It is a single black wire, 13MM hex body.

I have had this code and symptom on both my 85 and 88.  On the 88, the center pin had come loose, and backed out of 'adjustment'. Using a VOM I screwed it in until it made contact, then backed it out just a bit, and put a dab of Devcon on it to 'lock' it in adjustment.

Worked for me on two cars.  Your results should be similar.
Dave

Dave told me his car doesn't have the temp switch for the EGR...that's one of the first things I asked about, but I wasn't sure the '90 cars had it...

[QUOTE=Adams' Apple]Dave told me his car doesn't have the temp switch for the EGR...that's one of the first things I asked about, but I wasn't sure the '90 cars had it... [/QUOTE]

Maybe they don't have it. Never heard / noticed that the 'hardware' changed on the L98. I assumed it was the same until the end in 91.. I'll have to look next time the hood is up on a 90 L98.

Dave

I don't know for sure, either! I did ask about the switch, and he said his car didn't have that system, so I went with that info. I remember pulling all the t-shooting info for the code, and the schematics, but I honestly can't remember if it showed the switch or not. I know my '85 doesn't have the switch...they started using it in '86, but no clue for how long it was used for the L98.

[QUOTE=Adams' Apple] I know my '85 doesn't have the switch...they started using it in '86, but no clue for how long it was used for the L98. [/QUOTE]
Interesting. MY 85 has the switch. It is located at the base of the EGR valve, under the plenum.  I thought all L98's have it.  In 86, the position of the switch changes, because of the external tube for EGR on aluminum heads.

Can't believe your 85 doesn't have it, unless it's been removed. Even so, the green wire should still be in the harness.

By golly I think yer right! I went and looked at the pics I took while I had the intake off installing new injectors a couple of years ago, and sure enough...there she be! I think where I was getting confused was with the external tube used, as you say, for the later '86 lum heads. That's the place that I'm most used to seeing the temp switch, so....
For anyone else looking for the EGR temp switch on their '85, click on the image below. You'll see the switch and the wire going to it at the lower right end of the EGR valve.
Thanx Dave!!


                                                                   Click

that is why this forum is the best. this has made a very interesting meeting of the minds. on my 90, there is not any wires as you describe. the only wire i disconnected was the mat sensor on the bottom of the plenum when i removed the intake. i misunderstood what joel was asking when he asked me about it. i thought he was asking if i had the heated o2 sensors.i have not seen any type of connection like that but i will be checking in the service manual to see if they even mention anything about it and the location. hope something shows up on it. thanks again for all the input.

5 posts for something so darn simple.  Here's a picture of it.  It's in the EGR hot pipe, directly behind the RH valve cover. Sheesh.


DaveP85C42009-04-05 15:26:45