I'm going to be installing new injectors soon and when its all apart, should I install a new EGR valve when I'm at it or am I wasting money? :seeya

 

TTT

 

My EGR was replaced last summer, it was giving my driveability problems. 10+ years on an EGR valve seems like a pretty good run, it was time for a new one anyway. If the plenum is gonna be off anyway drop in a new one and save yourself a headache later, IMHO.

drj

 

Going to be changing my intake gaskets (LOWER)....guess this is a good idea also since I will be in it........How much do the EGR valves run??

 

Thanks, that is what I kind of thought too.. I know there is an EGR solenoid, I wounder if I should change that too? :confused:

 

They run about $50, its better than doing all that work and then find out later that you have to take it apart again.

 

I think I paid about $50 from Ecklers or Mid America.

 

By the way, the EGR solenoid is located on the left side near the rear corner of the intake. They are about $20 I think and my feeling is, replace both.

 

I looked at both Ecklers and Mid America and I could not find a listing for a 1991
:(

 

And while you are under there, a new Intake air temp sensor and EGR temp sensor might be cheap insurance too :yesnod:

Make sure you have plans to replace the hard, brittle vacuum lines which will most likely snap on you. Antisieze for the plenum bolts, a good cleaning of the TB with throttle body cleaner (remove IAC valve as per the tech-tips), and a soaking of the upper plenum would all be a great weekend project. -Matt-

 

I am going to move my Intake air temp to the cold air box while I am at it.

 

Ecklers only list a EGR Temp sensor for 86-89, I don't think there is one on a 1991 Vette. As far as a "Intake air temp sensor ", I looked for that and can't find a listing for it anyware. :confused:

 

ep...the EGR temp sensor might be an early part only.

The IAT sensor is also called the Air Charge Temp sensor, Manifold air temp sensor, etc. It is located on the bottom of the upper plenum unless someone has relocated it to the air filter housing.

 

I replaced the solenoid too while it was open - though in a pinch I think it can be removed w/o pulling the plenum (but just barely).

Try this place - good service and reasonable prices:

http://www.tld-corvette.com/

NB: 91 has no EGR temp sensor - it uses different logic. IAT and CTS are same sensor on a '91 - if I remember right, oil temp sensor is also the same piece.

Re relocating the IAT sensor: it will make a stock L-98 run more rich (more fuel). The one thing a stock L-98 does NOT need is more fuel.

 

Let me give you something to think about. I am working on a 90 right now with reducing exhaust back pressure and what can be done to help prevent a code 32 from setting after this is done. Well so far it looks like I may have a solusion to this problem. As anyone with a 90 or 91 may know when you reduce exhaust back pressure it reduces the ability of the stock EGR valve to work correctly so when you go on a good highway cruse you wind up with a SES light and a code 32. Well the problem is that up to know the only fix was to eather add pack pressure back into the exhause to get a reprogramed chip. Now that's all good but the chips are not cheap and with many states going to an IM240 emission test many could now fail for NOX because the EGR is not working correctly. So I am on a quest right now trying to come up with a fix for this that people can do with out spending a lot of money and that is were I am right now. The car is a 90 6spd I have removed the catilist from the front cats, the main one is still there and I have removed the inner tail pipes muffler plugs, this should have been enough of a reduction in back pressure to triger the code to set, but what I have done also is to replace the stock EGR with an EGR from a 86 to 89 which is just a little different, using the Tech 1 I was at high idel ablet to prove that the EGR does work better then the stock one by using output funtion of the Tech 1 to turn the EGR on at about 1,500 rpms and by doing this I was feeling and seeing(watching MAP siginal) the EGR working more than the stock one was when I did this after the changes were made and it wasn't untill yesterday that I was able to take a highway trip with the car to see what would happen took a trip to down town Atlanta an about a 60 mile round trip and most of it highway and so far no problem. I would like to do a few more long trips to know for sure but so far it looks like the cure for the code 32 problem with modded exhausts on a 90 and 92 could be just to install a 86 to 89 vette EGR. You see one of the problems is I have not been able to find anything on what it is in the program of the stock chip that says just what has to happen to set the code. On a 85 to 89 there is an EGR temp switch that closes from the heat of the recycled exhaust gasses, but if you go to the GM manual for code 32 in 90 to I think 93 there is nothing there except just how to test the EGR not what has to happen to set the code in the first place, I think they are using MAP siginal change to test the EGR that is what is done many other GM cars at the time but it is not stated so I am also looking at if needed hooking up a relay to help fool the ECM MAP siginal if this doesn't work. But I just though this would be a good time to put this out there so other people can look into doint the same thing so we can finaly come up with a workable solution to this.

David Fulcher

 

WOW, this sounds like something I should do when I replace my injectors because I'm changing out the front "Y" pipe with one that has no pre-cats and also installing a new main cat. I already have a low restriction exhaust system and the main cat is a low restriction type too. You guys think I should do this? Sounds good..

 

Just get rid of the EgR system :yesnod: :D

 

1991C4 & David F

On a '91 the EGR self-diagnostic routine involves cycling the valve during cruise to check for a change in MAP signal. If the ECM sees no (or not enough) MAP change in the specified range it throws a code flag. This flag does nothing in the system except light the SES indicator.

The EGR valve itself requires some positive exhaust pressure to operate, and some report this code when they change mufflers. I've never seen it myself, but if it occurs (provided the MAP sensor is operating properly and the EGR passage isn't plugged with carbon) the quickest fix is to turn off the flag in the PROM. A piggy-back adapter like the one Motes is selling over on the DIY forum, plus a new chip without the flag, make this an easy band-aid and require no change to the engine or stock ECM/chip.

Using an EGR from '89 (presumably with bigger Cv) could also solve the code flag, though I've never tried it. A little more EGR gas flow probably has no downside, except you might (?) need to run more throttle opening at cruise.

To disable the EGR system requires a complete rework of the part-throttle spark tables. While expensive this is doable; but it results in less throttle response at cruise, and raises fuel consumption with no corresponding performance benefit. In NYS it may also give you a problem at the emissions test station.




[Modified by DOCTOR J, 2:06 PM 2/12/2002]

 

Can I plug off the EGR in an 85 vette without having problems

 

I would recommend an actual ACDelco valve if you do get one. I went to Autozone and got a replacement but as soon as I put it on-with NO other changes- the temp shot thru the roof. It was very obvious exhaust was going into the intake in a very wrong way. You are supposed to do something with a bunch of little washers they give you, but it isn't worth the hassle and risk IMHO.