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EGR Stuck?

longbedder

longbedder

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Well, I got my ALDL cable today, and downloaded TTS Datamaster. I must say, it's like I was blind and now can see. If you've got TBI/MPFI, you NEED a cable and laptop.

Anyway, my EGR Raw is stuck at 14% when 0% is being commanded. I assume this means my EGR valve is stuck open.

Has anyone else encountered this, and does it generally indicate a problem that can be solved with cleaning, or is component replacement required? I've been having idling and stalling issues, and this seems like a likely contributor.
 
Ive seen a mechanic tap on the EGR with a screw driver to knock out carbon temporary fix. It was an S-10 blazer that had stumbling/running problems.
 
Which vehicle is this, OBD1 I'm assuming?

I don't believe OBD1 is capable of measuring EGR any other way than on/off. Temp switch, or change in manifold vacuum are the two ways I am aware of that GM monitored EGR operation.

Can't hurt to manipulate the EGR valve by hand, while it's running, see if idle changes, and that it moves smoothly. Pull off/plug the EGR vaccum line, see if your readings change.
 
Pull the EGR off and clean it. Use carb cleaner or what ever. It is fairly common for them to get carboned up and stick open. Choppy idle and stalling is common with open egr. If you cant get it to work with cleaning. replace it.
 
I assume this is on the 94 suburban since it's the only one with an electronic EGR. Lots of different causes. What kind of supercharger are you running? How about a little history on other mods and any codes that are stored.
 
Yeah, it's the '94 Burb. It's got a Whipple supercharger and chip. Pretty much stock, otherwise. No codes are stored.

I'm just now learning the software, and sifting through my first set of data.

TTS Datamaster outputs:

EGR Actual
EGR Duty Cycle
EGR Raw
EGR Target

EGR Actual is showing 0.0, while EGR Raw is showing 14% (when target and duty cycle are both 0.0). Not sure what this means yet.
 
Sounds about right for EGR position at idle. Usually when an EGR valve is hung open the percentage will be 30% or more.
What are your BLM and INT numbers? You may have a vacuum leak at the t-body adapter on the charger or the base of the charger may be leaking as well. I've had to reseal mine a couple of times.
 
I'll have to check when I get home tonight on the BLM and INT numbers. Any idea about the difference between the EGR Actual and Raw numbers?

The engine has 132,000 on it, but does not use oil and runs strong in general.

I did notice that the manifold vacuum at idle looks low (about 11 inHg but steady at operating temp idle). This would be consistent with a vacuum leak.

I think that I am going to pull the TB off and clean it thoroughly - if nothing else this is good from a maintenance perspective. That would be a good opportunity to reseal the TB to blower surface. I assume you used some sort of RTV, or did you order new gaskets from Whipple?

I probably won't resolve this before next year. I fly out to my wife's folks' place on Saturday...
 
The raw number is EGR actual position the computer then figures out what the at rest position is from that number. The raw number varies from sensor to sensor because of tolerances and can be anywhere from 6 to 15 at rest. Once the computer knows the at rest position it calculates positions from there which is your "EGR actual" position.
Your vacuum sounds a little low for your low altitude, but the BLM numbers will tell us for sure.
Don't use RTV on any of the surfaces, gasoline will attack it and turn it to mush. Originally they were sealed with O-rings which I have never been able to get so I use anaerobic sealer to seal mine up.
 
Sorry...I knew what I meant. I tend to use the term RTV universally for goo coming out of a tube :D

My main question was did you find new seals or use goo, and you answered that.
 
At operating temp idle (in gear, 675 RPM), my BLM is holding steady at 124 counts. The integrator fluctuates slowly between 128 and 129.
 
Pretty doubtful you have a vacuum leak with those numbers. If you did I would expect BLM numbers up in the 140s.
Your rough idle may just be tune-up related.
 
Yeah...that's kinda what I thought, based on my newfound internet knowledge. Someone should write a consolidated book on GM fuel injection, PROM's, etc. Right now it's just scattered info on forums, etc.

I do think that a TB cleaning is a good start in my case. I bought the truck used, so I don't know when that was done (if ever). Then I'll evaluate idle stalling again and try and capture my other problem on a data log. Reference this post: http://coloradok5.com/forums/showthread.php?t=213923

Anyway, thanks for the help so far. Have a Merry Christmas.
 
thirdgen.org's "ECM" board has a few decent articles, but unfortunately, since the ECM's were so different, there tends to be a lot of assumptions or whatever. '7747 and '7730 are the two ECM's that have a LOT of data out there on them.
 
I joined Thirdgen earlier this week...lotsa good knowledge there.

Like I say, it's just a lot of googling trying to track down good info on this stuff. Oh well...
 
I talked to Whipple today and learned a couple new things. I had bought my Burb used with the blower already installed, so was in the dark a little bit.

1) There is supposed to be a higher-than-stock-pressure fuel pump installed in my truck, if the install was done according to Whipple's instructions.

2) The funny looking can on the driver's side next to the blower is a variable fuel pressure regulator that ramps up fuel pressure with boost...so it's NOT a static fuel pressure situation under throttle.

3) The injectors are stock.

4) The guy who wrote the code for the Whipple chip has his own company now: Powertrain Electronics.

I'm sure this isn't much use to anybody here, but...whatever.
 
Are you still trying to track down the mysterious backfire problem?
You need to start with checking your fuel pressure to make sure the pump is still good and strong. Fuel pressure at idle should be about 24 psi. WOT fuel pressure will depend on the amount of boost you're getting, I'm going to assume 5 psi which will put fuel pressure up to at least 40 psi. The fuel pressure regulator ups fuel pressure 3-4:1, meaning for every pound of boost you get an additional 3-4 pounds of fuel pressure. If your pressure isn't changing with boost inspect the vacuum lines from the regulator to the intake manifold, if they leak you don't get pressure rise. If that checks out ok the fuel pump is probably weak and needs to be replaced. You also need to replace all of the plugs, wires, cap, rotor and coil with new. Make sure you use only conventional spark plugs. Platinums DO NOT work in this application, don't even try. Any weak ignition components will cause strange drivability issues especially under boost so make sure you buy good stuff.
 
Thanks, BB72. You've been a big help. As far as I know, you're also the only other guy on here with a 94 454 with a Whipple.

Whipple was supposed to email me the owners/install manual, but so far that has not happened.

What heat range of plugs do you use (or what specific plugs have you had good success with)? I'd assume one range colder than stock?

Incidentally (and way off topic), I saw an article yesterday about some gal named Mary that lives in American Fork. She married some guy with the last name Christmas. Hah!
 
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