'burning' EGR question (1 Viewer)

[tblume]

made you look!

I posted last on this thread (post #51)
https://forum.ih8mud.com/80-series-tech/281596-who-has-removed-their-egr-valve.html
RE: 2/93 '80, non california emissions, no temp sensor in the EGR valve.

anyone have this and is there a lot of difference from one with the sensor? I'd like to trick the CPU using the 1K OHM resistor, but does my truck look for the signal or what?

partly melted plug is the jumper that Mr. T put there from the factory, and the bolt/plug that fills the port where the sensor ought to be is just that. I have to assume that the EGR system is functional or the plug would not be melted, but can I presume that without a watchdog on the EGR valve/temp the CPU does not care if it sees the right temp, and it will not throw a code or CEL?

I need to OHM the plug now that I think about it, could it be a factory fooler????

nope- 0.2 ohm

 

[Ebag333]

Bigger picture of the 2nd one please.

That looks suspiciously like where the EGR Modulator is supposed to go.

If so, that's the EGR Valve right behind that empty bracket. On the exact opposite side of that (walk around to the other side of the engine bay) is the EGR Temp probe.

 

[tblume]

you're right Gabe- the modulator lives in that bracket, I popped out of the way to take the picture. the plug/bolt visible behind the bracket is the only opening for any kind of temp probe, nothing on the drivers side. (USDS)

I have not disabled the EGR yet, but thinking about doing it and seeing if I get a CEL this weekend; I am headed to the coast so I figure it will come up if it is capable. My guess is that the ECU does not care what the EGR temp is, but may throw a code for something else if disabled?

in the first picture the melty plug was installed in the pigtail from the second picture, it is a straight jumper (0.2 ohm)

 

[Ebag333]

you're right Gabe- the modulator lives in that bracket, I popped out of the way to take the picture. the plug/bolt visible behind the bracket is the only opening for any kind of temp probe, nothing on the drivers side. (USDS)

Finally found a pic.

Right smack dab in the middle, to the right of the "Vac line to vac guge [sic] in cab", and below the "T".

Easy to miss.

 

[tblume]

aww hell, I thought it was in the EGR body itself. Still not sure about if the ECU looks for a signal, I assume not with a factory jumper in there that is not a fooler, I'll see about mod'ing the plug with resistors if I throw the CEL this weekend.


any thought as to what I am looking at in that second picture? (the plug) can you look at yours and compare when you have a shady minute?

thanks for the picture, although from the FSM it appears the probe is in the EGR- I need to look further

 

[Ebag333]

The picture is looking from the DS side towards the PS side. You can see the intake on the left, and the EGR Valve is in front, the Modulator (which you removed) is behind it.

The FSM is not entirely clear on this.


You going to be down this way anytime soon? If so, hit me up. I'm pretty flexible on my schedule.

 

[tblume]

Photographic proof!

proof of the lack of something I guess

so if gnob is right:

Quote:
Originally Posted by Ebag333
What do you mean you have no temp sensor? How does the ECU know if the EGR is functioning or not?

>if the ecu actually cares, it would use the data from the o2 sensor to see if the EGR is functioning. <gnob's quote

where do I put my resistors to fool the o2 sensor

I will be experimenting with removing the vacuum from the modulator/EGR valve tonight- what could possibly go wrong?

 

[retrofive]

LOL, so Ebag33 - How many 93-94 trucks do you work on or know about?

Same as T's on mine.

 

[alia176]

Vacuum plug- all you're doing is plugging any vacuum lines that are coming out of the intake manifold to y prevent any unwanted vacuum leaks is all you're doing.

Since it's OBD-I, I wonder if your EGR is purely mechanical? In the post 94 (or is it 95?), the VSV under the intake tells the EGR system to open up and start operating. This is based on the feedback from the EGR temp sensor to the ECU. I wonder if you have this VSV?

 

[retrofive]

The funny apart about T's pic compared to Ebag's is 93 vs 97. I have a 94 and have the exact mssing part but looks like the form on the intake for fitting.... (sorry for the lack of techy terms).

 

[Ebag333]

Does the 93-94 FSM have any ECU codes for the EGR?

LOL, so Ebag33 - How many 93-94 trucks do you work on or know about?

Smart ass. I'll remember that next time you ask me a question on your truck.

 

[tblume]

mr.T gearing up for probing that boss, boss.

and I'll look Gabe...

 

[retrofive]

Does the 93-94 FSM have any ECU codes for the EGR?




Smart ass. I'll remember that next time you ask me a question on your truck.

Hehe and yes.

 

[retrofive]

mr.T gearing up for probing that boss, boss.

So back to the matter at hand. With that out of play, is that where the later year truck use the resistor to trick the ECU?

The only ECU code Ive thrown from the EGR system was a 71, and was the EGR modulator.

T - Im interested in the outcome if you cap it off, let us know.

 

[tblume]

Does the 93-94 FSM have any ECU codes for the EGR?


71 pops into my fragile little mind but I'll get the book out now...

 

[retrofive]

IIRC when i got my CEL 71, the FSM (and later years) its a simple test. Mine failed miserable, ordered a green top, no more issues 4k later. I know this isn't the topic at hand but....

 

[tblume]

here's why I thought the temp probe was in the EGR valve itself,

and the code 71 for EGR trouble. any help or more 'MUD?

if it has to have 60 seconds of EGR operation under 158*F and I have no temp probe, I have to assume there is no code 71 logic in this ECU. I'll have to make two trips to find out I guess...

 

[Ebag333]

Okay, so the trick to the '93-'94 trucks should be the same as the '95-'97.

According to Gotmud, his FSM showed:

122 (F) - 64K -97K Ohms
212 (F) - 11K - 16K Ohms
302 (F) - 2K - 4K Ohms

This is the same for the '97. So the resistor trick should work the same.

Here's how Gotmud did it on his '94. You do not have to block off the passage, it's easiest to simply disable the EGR Modulator.


It's interesting to me that Mr. T changed the location of the temp probe to closer to the cylinders, and closer to what the true temps would be. I wonder if they did that in response to the head gasket issue, and cylinder 6 popping, in an attempt to better modulate the flow of exhaust.



tblume: I realize now that the mystery bolt I was wondering about in your second pic (in the EGR valve) is where they blocked off the EGR temp sensor.

Have you thrown an EGR code since that has been unplugged? I wonder if the ECU doesn't get info from that sensor if it will just ignore it. I think I'm going to go unplug mine, and see what happens over the next few days.

That would make a certain amount of sense as not all trucks had the EGR system....one less ECU variant to produce.

 

[tblume]

tblume: I realize now that the mystery bolt I was wondering about in your second pic (in the EGR valve) is where they blocked off the EGR temp sensor.

Have you thrown an EGR code since that has been unplugged? I wonder if the ECU doesn't get info from that sensor if it will just ignore it. I think I'm going to go unplug mine, and see what happens over the next few days.

no code in the year plus I have owned it, and it was never plugged into anything; there is just that factory jumper plug completing the temp circuit. also no mention of testing the temp probe in my FSM that I can find...

[/QUOTE]
That would make a certain amount of sense as not all trucks had the EGR system....one less ECU variant to produce.[/QUOTE]

SO ,,,, put a BB in the single line from modulator to EGR valve, effectively stopping it's ability to open and after three stop start cycles I have no CEL, but, that was only a couple short runs to the store and back with a side trip stop/start for good measure.

If I read the FSM right I need 60 seconds of EGR temps lower than 158*F (who's measuring though) at intake temps above 32*F and rpm above 1200. Check on both the last items, but how would the thing know without a temp factor? Tyler had the #71 CEL on without a temp probe, so there must be something else like the o2 sensor like gnob said?

After the weekend I should have more than enough miles to pop a 71 if I am able, and if it does I'll try the resistor trick, and if that does not work, back to factory- looks like 93-94 only run the EGR on deceleration at open throttle and the EGR valve cycles at not quite closed throttle position.

 

[Ebag333]

Tyler has a temp probe. His isn't in the '95-'97 location, but in the EGR Valve spot (same as yours).

So that cap that fits into the EGR temp sensor plug....does that just connect one side to the other? Basically making it an open circuit?