Howdy!

Still working on my year long project, and got to the point of putting the plenum on.

Get it installed, and realize there is a one wire weatherpack connector I seem to have ignored during my whole install process.

So I check the '88 wiring manual, sure enough, there is supposed to be a temp sensor. Odd thinks I, I didn't see anything on the EGR valve. So I pull the plenum back off, and sure enough, the EGR valve doesn't have the temp sensor.

So going back and reading all the posts I could find on it, when the change was made to SD, the sensor was removed. The intake and plenum were both SD, so that explains that "problem"...the EGR is off of a SD intake.

My question then is, since I will be burning PROM's to get this running
"perfect" (355/Vortec Heads/Mild Crane Roller Cam/full length headers/"stock" TPI components) can the temp sensor safely be "deleted" from the PROM when I get to that point?

I'm not looking to screw things up here, I want to eventually try running highway mode, and I already have the SDPC EGR feed stuff hooked up so I can run it with the Vortec heads, this temp sensor issue is really the last major thing I have to figure out. Once I get all this hardware stuff figured out I will start working on the software issue, but I'd like to know if I can just forget about the temp sensor for now and take care of it with the PROM? I'd rather not have to change the EGR valve and get the sensor, that is my only concern here really. If thats the right thing to do, I will, but if it can be "worked around" in a totally functional, intelligent manner, I would be interested.

As an aside, the SDPC EGR feed kit uses I believe a Corvette pipe, which has a fitting on it for a sensor. I'm *guessing* that in the MAF EGR valve, the temp sensor is on the "intake" side, so that when the valve opens, thats when the heat is seen...OR, would there possibly be enough restriction with the valve closed, that the fitting in the pipe before the EGR valve could be used, and once exhaust started flowing through it, the temp would change enough to satisfy the ECM?

 

Ugh, well, in a fashion.
It would be best to do it all as designed.
Yes, you can bypass the EGR.
yes, you could install a resistor in leiu of the sensor and then set the enable temp to above that reading. Not perfectly legal, but it would just mean having EGR with a cold engine. Once warm it would all act according correctly.

If all the manifolding is for a SD system, then you might consider running SD. It's been covered in detail several times.

 

Appreciate the response.

So essentially, just run it the way GM intended.

I'm not in an area where legality is an issue, so that was never a concern. I want to run EGR because it will do nothing but help in my case.

After making numerous changes to my plans, from carbed to TPI and beyond, I've now realized that in my application SD WOULD have been the best choice. But when I initially purchased this setup, Vortec heads were already a reality (also a bad choice IMO) and MAF was where I thought I needed to be. I figured I wouldn't want/need to get into PROM burning.

Unfortunately, I already spent money getting the MAF plumbed right and realized that after spending that money and more importantly, time, I didn't want to undo all the work I had done.

I've still got the plenum off, so changing the EGR valve and adding the sensor isn't going to be an issue, it's just going to add more cost. At this point, $50 or anything even near that is nothing.

 

Had to think about this one for a bit, and do some research. The sensor in question is a thermal switch. It is just on or off. It is used in the ECM diagnostic routines to check whether the EGR is flowing exhaust gases or not.

If the EGR feed tube sensor fitting is not close to the exhaust manifold it should work. As you surmised there will not be any EGR flow until the valve opens. The switch will then activate keeping the ECM happy.

Regarding your post above this one, if the engine is mostly stock (other then the Vortecs) and not wanting to get into PROM burning, the MAF just may have been the better choice. There is a good possibility that it will run satisfactorily with a stock chip.

Changing heads on a SD system will darn near guarantee that you would have to do PROMS to tune it in.

RBob.

 

RBob, do you think there will be any issue with the fact that now the exhaust is routed through an external tube, and then into the lower intake? I just finished the whole vortec/SPDC deal, and wondered if the extrnal plumbing would drop the temp enough so that the thermal switch won't actually kick on, due to heat loss. I guess it did work on the corvette though right??? Anyone happen to know what temp that switch works at?

 

Couple of replies then...

With the SDPC piece, I wonder if that is WHY the Corvette EGR tube has the fitting where it is, and not at the EGR valve...heat would be higher there than at the valve with the "remote" feed tube. I kind of doubt this though, it is probably more of a space issue.

Rbob, that EGR fitting is probably 8" to a foot from the exhaust source. On my setup, since only one runner is feeding it, and the feed itself is pretty small diameter, that it might work plumbing it like that. Guess I can always try it!

Engine is far enough from stock that I want to make sure by getting into PROM burning that I am losing nothing power/economy/driveability-wise with this swap.

I don't recall that my electrical manual makes mention of the temperature required for the switch, but I suspect it may be shown in the driveability section of the service manual. Even if not, probably wouldn't hurt anything to put it in water of a known temperature to see when it "switches".

So which is it? A sensor or a switch? If it's a switch, then that means that EGR operation is governed by the temperature the ECM sees from the coolant temp sensor, not the EGR itself, which makes sense...EGR solenoid doesn't work independently of the ECM. EGR temp switch would have no bearing on anything other than for the ECM to determine if it is working or not, correct?

Having an actual sensor in the EGR to determine when it should operate would be redundant, no?

 

I thought that was the diagnostic sensor?. With the ecm commanding the EGR, on, and then the ecm looks at that to make sure the EGR is actually on, and flowing.

OK, Doc just found our wiring book.
89, 305, Vin F,
C12 is the MAT sensor.
E4 controls the EGR valve.
C15 is the EGR diagnostic switch input.

 

Yes, used by the ECM for malf code 32 diagnostics. The switch will open or close dependent upon the exhaust gases flowing through the EGR valve. With the EGR open and flowing the exhaust heats up the switch and it changes state (I don't know if it opens or closes with EGR heat).

RBob.

 

According to the '88 manual, the EGR switch is normally open. It's also on the "intake" side of the valve, so only sees "heat" when the valve is open.

Can't find any temp specific info though, only reference to coolant temp.