The computer controls how much voltage is sent. Just like the e-fans. When the temp gets too high, the computer will send more voltage to the e-fans to draw more cfm. This is how it is on the Gen III motors. What you have may be different so Im not real sure. The regualtor works off vacum. At wide open throttle the regualtor has no vacum applied so it is free flow. Thats why some guys will disconnect it to get free flow all the time at the track.

 

Thanks Ruffneck. That helped to fill in some of the blank spots in my mind. (plenty of those )

What constitutes a Gen III motor? 1996 and newer?

 

The 99-06 vortec motors. The Gen IV started with 07 till present. The ignition set up is different from what you have. No distributor, it uses crank and cam sensors, individual cylinder coils, MASS sensor, heated O2 sensors, computer has more control over all. So they are more efficient and precise as for like air/fuel ratio and timing.

 

Again, thanks for the education. It sounds like the Gen IV engines have systems I'm more familiar with from working on my bikes. They don't have the MASS or O2 sensors, but the other elements are present, and the bikes are ten years old.

I had a chance to spray some starter fluid around the TB and such today. I had to run it with the MAP sensor disconnected and capped because that is the only way it will idle - around 900 to 1000 rpm. The only "sensitive" area I could find was when I sprayed on the EGR valve. However, the RPMs did not increase, but rather, after 2 or 3 seconds the rpms dropped signifcantly and a couple times nearly stalled if I hadn't given it more fuel. I did this repeatedly to make sure it wasn't just a fluke. Every time the rpms would drop.

Now, my question is, does this indicate a flaky EGR valve or am I merely introducing a condition that would affect a fully functional engine the same way? I know the EGR valve is supposed to recirculate exhaust gases into the intake, but is it also normally open to the "outside world?" I'm just trying to avoid needlessly buying yet another part, only to have someone tell me later that, "Yeah, when you spray starter fluid on your EGR valve it will make your engine stall. I thought everyone knew that?"

I'm not cheap, but I would just rather spend my money on fixing the problem - not replacing a serviceable part, as I have done three times already up to this point.

Let me know what you think. Thanks for your input.

 

Ok when the EGR valve starts to become faulty, it builds up carbon. Therefore it cannot close or open fully. When it gets stuck open, it will cause the motor to run sluggish. You will also see some black smoke from the exhaust. Sometimes it will not throw a code for the EGR if it stays open, but a rich code. If you rev it up a lot check your exhaust for excessive black smoke. If it stays closed then nothin will really happen except a EGR code. On the other hand faulty O2 sensors can cause this too. On my 2001 I can take the EGR off and clean it. A lot of folks do that for maintainance. You will need a new EGR gasket too. First, have you gone to Autozone and had it checked for codes? The computer will store codes and run default settings until the problem is fixed. Do that first if you have not already. Even if the CEL has not come on.

 

I replaced the O2 sensor just before the MAP sensor because it was relatively cheap and I have heard they can fail and cause symptoms similar to mine. The new one made no improvement.

I checked the codes myself per the Haynes manual I have been using. It only flashes the "12" code (continually) which Haynes says merely indicates that it is in the diagnostic mode. Whereas, if a fault code were stored, it should flash "12" three times and then flash any stored codes in succession - each one three times. Also, the only time the "check engine" light comes on is when I have the MAP sensor disconnected.

During the weeks leading up to this failure - even the day before- it ran fine - not sluggish at all. I've never seen any black smoke from the exhaust, even during the rare times that I ride it hard. The tail pipe has some "color" on it, but not what I would call sooty or carboned from a rich mix.

When I was testing it with the starter fluid and had to rev the engine to keep it running, I could see the EGR shaft/diaphram actually moving. However, it didn't travel very much. It looked like maybe a 1/16 or 1/8 inch. I'm not sure what is typical movement on those valves, but it was doing something. If nothing else, I guess I'll have to pull it off to inspect it more closely. If I apply my own vacuum to it, do you have any idea how far it should be moving? When it is closed does it rest against a seat in the intake manifold? The valve operation will probably be obvious once I get it out to look at it.

 

Im really leaning more towards a vacum leak. Even a bad PCV valve could cause this. Take your throttle body off and look all around. Even those flaps sometimes do not close all the way and more air enters thus causing the computer to try to keep a constant idle but becomes more of a surge.

 

Those flaps?? I'm not following you on this one.......
Pull the TB, eh? That will be a project for Monday. I'm booked for tomorrow, but maybe I can pick up the gasket kit.

The PCV valve. That's certainly a cheap part I can eliminate. Although I didn't suspect it because when I had it disconnect and capped, and then reintroduced it to the system, nothing changed - at least nothing apparent.

Another question, though likely unrelated: The PCV valve is in the right hand valvel cover, but on the left hand valve cover another tube (about 1/2" diameter) comes up and enters just above the TB but below the air filter. Is that simply a crankcase breather similar to what was installed on older GM vehicles with that small filter inside the air filter canister?

I appreciate your time and effort Ruffneck.

 

Hey no problem. That tube is mainly for vapors that rise from within the motor from heat. Even though there is no water inside, heat will cause some condensation from the oil and internal moving parts. This creates vapor and will rise. So it is set up to be vacumed and thrown into the intake. If not then that condensation will settle, which will create water within the motor. The flaps Im referring to are the ones that open when throttle is applied to allow more in. They sit just below where the injectors spray in the throttle body. When some gunk builds up inside the throttle body, mainly from that hose and PCV valve line, it will sometimes not allow the flaps to fully close therefore letting more air in and throwing the TPS off. Most of the time a can of Throttle Body Cleaner sparayed into really well the throttle body will do the job. But taking it off and cleaning by hand with a brush and cleaner is better. You can inspect without taking it off. Just take the air cleaner off and look down inside the throttle body(with the motor off), and open the flaps by hand. If its dirty you will see black sludge build up.

 

Oh, the "BUTTERFLIES!" Those are the "flaps" you are talking about. Why didn't you say so?

Actually, I was looking at those just today while I was spraying the starter fluid around. There were some cruddy deposits around the inlet where that breather/vapor tube comes in, but the butterflies and venturies themselves look pretty clean. I noticed because I had read one of your other posts where you mentioned that the injectors should produce a nice conical spray down toward the valves, and mine were doing just that.

Based on your experience, when it comes to vacuum leaks due to a failed intake manifold gasket, is there any typical location where they fail? This particular gasket was replaced back in 1996 by a Chevy dealer here in town, but they did a sloppy job. I can't say they didn't put the new gaskets on right, but they did a poor job of "removing" the old one. I say this because about six months later a friend of mine noticed a low end knock right after starting the engine. So I had another friend, who was into auto repair at the time, pull the oil pan to see what he could see. Guess what he found clogging the filter screen for the oil pick up? That's right - pieces of intake gasket material! I don't know exactly what the lifter valley on my 350 looks like, but those pieces of gasket material made it down to the oil pan some how.

I'm sure there are shops out there that care about the jobs they do, but I no longer have the patience or courage to find them. Hence, I do what I can myself. Along with that, internet forums have been an incredible resource!