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Where can I get an EGR modulator?

04-16-2012, 09:36 PM
'92 XFi. The mod is no good per the GM manual test procedure.
Or can I somehow clean/repair it?

Metro Mighty Mouse
04-17-2012, 03:12 AM
If you are looking for the part that is held by the big clip, it's available at Rock Auto for $100 new and there are several used on ebay for around $25. If you are looking for the part held on by 2 bolts ebay has new and used for similar pricing. If it's electrical there is one on ebay used for $40.

04-17-2012, 12:03 PM
Yeah it's the biscuit up top in the clip with all the hoses going to it.
The valve works when you put vacuum to it.
But ain't no vac getting to it from the mod.
I'll check eBay.

04-23-2012, 12:30 PM
I got one off eBay for $20 but the EGR still ain't working (when you rev the engine with all the vac hoses hooked up per the FSM, the EGR valve diaphragm doesn't move).
I think maybe the port (on top of the EGR valve, connected to the bottom of the modulator with the fat hose) is blocked with soot - again... gonna take my drill bit and compressed air to it this week...
I'm afraid of burning valves, although this is a 3tech cam/head rebuild, with his exhaust valves that are supposed to be better, I think... got 3500 miles on it with no EGR flow...

04-25-2012, 12:17 PM
Don't buy an expensive new one or "just as bad or worse" old one! Just clean your own! Here's how I have done many of them: Get a can of carb cleaner with the little snout pipe on it. Clean the intake and output ports very well with a small screwdriver and lots of carb cleaner which will loosen up the carbon crud. The most important part is the controller ports. The one on the vac diaphram never gums up, but give it a test suck anyhow, and you should hear action, like a small thunk, when vac is applied and released. The control/sense port near the front (intake) side is the one that always gets impacted, but it can be fairly easily cleaned with the carb cleaner snout and a small flat blade screwdriver just small enough to get into the passage, but not so small it leaves too much crud on the side. Use the carb cleaner to blast crud out and loosen the underlying crud, then mine it with the screwdriver. After 6-10 drilling operations, it will open up and you will feel your screwdriver break through into the input chamber. Clean it all up good and you will have an EGR as good as new.

Now, that said, about half the time the real problem is with the input passages gumming up from the exhaust manifold, through the head. That is a whole nuther story, but can be fixed, too. To test if that is the problem, start it up with the EGR off the car. The pipe to the ex manifold should blast out a pretty healthy rasty blast of exhaust. If it feels weany, shoot in some carb cleaner (with the engine off), let it sit, and then start it back up and it will blow some crud out. Usually the port through the straight distributor side of the head is what gums up worst, or the horseshoe on the intake manifold on the 3 cyl. Most times you have to pop the manifolds to get it cleaned totally out. Note that with the EGR off, I have ALWAYS had these cars run at very high idle, and hunting up and down at about 5 second intervals. It will sometimes hunt too high for comfort and you will have to shut it back down, but usually you can get out and do some engine testing. It will be fairly loud, but tolerable.

About 5% of the time it is actually the INTAKE MANIFOLD passages that plug up! So if everything else is open, the gas still won't move through the EGR into the vacuum of the intake, because a booger is in the back of that passage. You can clean that out with a small wire and some carb cleaner, too. Test it by starting it up and plugging the intake manifold EGR hole on the intake manifold with your thumb. If the idle goes down then the passage is open. Don't worry, it won't suck your thumb off, but you WILL feel it (hopefully) with the passage open.

Some of the early Geos had NO EGR, proving that the common myth that a plugged EGR will cause valve damage (especially in Cyl 2) is UNTRUE. You can run a Metro with a plugged EGR and it will not damage your engine. You might not even notice any difference except the dang check engine light and test code coming from it. But I generally keep mine cleaned up.


05-10-2012, 11:57 AM
OK. What you're describing is cleaning of the EGR valve, and that is very importatnt to do if one wants to keep EGR flowing. Many threads on here about that. There are even some posts saying that you can clean all the passages out thoroughly, even if very gunked up, without removing manifolds.
But what I was describing here is an EGR modulator that wasn't working. This is the vacuum biscuit up top mounted in a bracket and having three vacuum hoses connected to it (the big one going to its bottom is actually an exhaust hose that applies pressure when the EGR valve is closed - and also when open?).
I knew my valve was working and my passages were open. (Applying vacuum to the valve caused its diaphragm to move. Moving the diaphragm caused the engine to want to die.)
But testing the system per the FSM procedure told me that the modulator was not working. (Revving the engine did not make the EGR valve diaphragm move.)
Long story longer: I got the used mod, installed it, and still no worky.
So I looked at the ports labelled "P" and "Q". Did it matter which of the two vacuum hoses was connected to which? Hmm. The off-the-car test of the mod says to apply vacuum to a specific one (I forget if it's P or Q), so it must matter! So I put the "new" mod back on the car rotated 180 degrees from where it had been (reversing P and Q). Voila! Rev engine, EGR valve operates. Note that it returns to closed position when I hold the engine speed at a high idle - I guess that's normal and the main thing is that when the engine is revving up, teh valve opens. I'm guessing that if there were a load on the engine at steady speed, the valve would stay open(?). But the main thing appears to be that the valve didn't move at all before, and now it does!
ATTENTION Moderator: You may want to move this into the Indexus Metroglodotus or whatever as a LESSON LEARNED:
Lesson learned: The EGR Modulator apparently needs to get vacuum to one specific port, and it is not a "poke-a-yoke" design. That is, it can be installed the other way, in which case it won't work.

05-10-2012, 12:19 PM
So are you saying that:

1 - things were working fine, then one day the vac lines magically moved on their own?

2 - things were NEVER working, and you forgot to mention that fact in your first post? My assumption was that this was a new problem. I have seen the controller go bad exactly once in 63 Geo Metros. I have seen the EGR valve go "bad" about 45 out of 63 Metros.

3 - if one of the two vac ports on the very frequently plugged EGR itself gets plugged that it would not throw exactly the same code?


05-11-2012, 11:31 AM
What I'm saying is:
1. No, the lines didn't switch themselves. How long they've been that way I don't know. It may have been since I got the car in 2005...?!
2. Again, I don't know if it was working and somehow I then inadvertently swapped the biscuit position and reversed the vac lines at some point (I've pulled the engine once or twice & done a bunch of other work...).
3. I have never gotten any fault codes about EGR, although I have had this vac line switch-up that appears to have disabled EGR, and earlier I did have the top "vac" port on the valve (actually a hot exhaust port) all plugged up to where I needed a drill bit to open it up.
Bottom Line: I guess I'm trying to verify what I've observed - that if the vac lines to ports "P" and "Q" are reversed, (a) EGR will not work no matter how clean the valve/passages are, (b) there may be no fault code letting you know, (c) there is no poke-a-yoke design prohibiting someone from reversing the P and Q lines, nor is the FSM very clear as to how they should be oriented on the car.

05-11-2012, 11:56 AM
Oh - I also wanted to mention that, simply because some earlier Metro models ran no EGR on the "same" engine, one cannot say conclusively that there will be no adverse effect of disabling EGR on one of these later models (mine is a '92 XFi).
Although the basic engine design was the same, EGR cars are going to run a different calibration from the factory for this and other reasons, mostly having to do with emissions. Calibration can affect everything from spark timing/advance to fueling, etc. Further, cam profiles and timing can change from configuration to configuration.
Each cal is set up for its particular engine configuration.
EGR is there to lower peak flame temperature, and in turn to reduce formation of oxides of nitrogen (NOx). When a mfr does that, it's always a factor in the engine calibration, and also things like catalyst loading in the converter. At some point in the engineering process, engine component testing takes place, and there is the chance that something like an exhaust valve/seat material will be specified for that configuration that will not be well off under a higher temperature condition. I don't know about these G10 engines, but since I get 50+ mpg with EGR, I don't want to take a chance that I may get a mpg or two more (actually I don't think it will make much difference in fuel economy) at the expense of valve, and hence engine, life. What I DO know is that I've gone through two sets of valves on this engine; I cannot prove that it had anything to do with lack of EGR, but if I have to choose between higher peak flame temp or lower, I'll take the latter in the absence of any engineering data as to the behavior of the alloy in the valves. I have a 3tech 10deg advance cam and "premium" exhaust valves now, so maybe I could disable EGR w/o adverse effects - who knows? - but I don't have enough data to tell me it's OK. I do know I'm getting better performance out of this setup, with little or no effect on fuel economy (although I haven't hit my pre-overhaul record of 58mpg yet, just close to 56, but those are not super-scientific values either).

Note: I'm not saying EPA is right about stuff, or that emission regulations always pass the cost/benefit test. I'm just talking about the implications of this hardware/software on our cars that we need to deal with (or not, at the possible risk of things like burned valves or whatever...).

05-11-2012, 12:06 PM
NOTE: I went out and looked under the hood, and the way I have this hooked up now (which appears to matter and doesn't appear to be explicitly stated in the FSM) is:
Vacuum to the modulator, from the EGR VSV, is connected to "Q" (toward front of car).
Vacuum from the modulator to the EGR valve is connected to "P" (toward firewall).
BTW I also measured resistance across the VSV terminals, which I guess could also affect EGR operation, and it was within the normal range.

05-12-2012, 05:38 AM
If you're not getting a "Check Engine" light, then why bother?

EGR is more likely to gain you 1 or 2 mpg than to loose it. It has the effect of artificially reducing the size of the engine when it is in operation. This causes you to open the throttle farther, thereby reducing the pumping losses caused by the engine trying to suck air past the throttle body.

There were no changes to the cat or the valves or seats having to do with EGR, the only obvious change was retarding the ignition timing to a ridiculous setting. I believe that this is the biggest reason that the exhaust valves burn. Advance your ignition timing to 10 BTDC and enjoy better mileage, more power, reduced hesitation, and longer valve life. If you have emissions testing in your area, mark the original location of the distributor so you can rock it back for the test.

05-15-2012, 12:19 PM
Thanks Woodie
If what you say is true about no component changes (namely valves) with EGR engines, then you may well be right about the retarded timing being more of a possible culprit in burned valves.
I don't know if I'm at 10 deg BTDC; I just set the timing by ear while we were driving hard through the hills outside Pittsburgh. And I'm using 89 octane ((R+M)/2) fuel. It has a 3tech 10 deg advance cam wheel and his "economy" cam. It seems to run very well. I'm getting 50+ mpg, I guess about the same as before the overhaul, but for sure there is a performance improvement from the stock setup.
I don't notice much change since re-activating the EGR. I'm pretty sure it was not working for the first 3000 miles after the OH.
But I think your contention that EGR might increase fuel economy due to wider throttle openings may overlook some other factors, the main one being a probable drop in the BSFC (brake specific fuel consumption) curve due to lower combustion temperatures, which could offset any gain due to lower pumping losses - or not - who knows? With the advanced cam and spark timing it's even more anyone's guess as to what my fuel economy advantage (or disadvantage) might be. Too many variables have changed.
So I'll just be happy as long as the engine is running well, not using oil, not burning valves, and getting 50+mpg. Which it is...

05-15-2012, 07:39 PM
Is this car exempted from emission laws?
If yes, you could put a blank gasket to block the egr port & put a tourniquet on vacuum hoses going to the egr valve.

05-15-2012, 09:52 PM
Right. I know. But it's a whole lot of people on here posting about keeping that EGR passage open, how important it is, rod it out every 10,000 miles, etc.
Is that really a good idea?

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