Poor MPG. Tune-up suggestions?

[GerryLP]

Gerry,

That vacuum hose has been replaced, as well as any others that looked cracked or dodgy. I even traced the entire lengths of the headlight hoses and couldn't find any problems, though I still realize there could be a leak. So, that picture was before the hoses had been changed. Still getting an intermittent rough idle, followed by ~100 rpm drop. I ordered a new EGR valve, so we'll see if that's the problem soon enough. Also ordered a vacuum pump so I can do the more in-depth vacuum tests. Thanks for all your help!

-Tatortot

Well do a consumption drive. Fill the tank, reset the trip-o-meter, and drive it a couple of gallons worth. Then, fill the tank again, and divide the miles on trip-o-meter by the fuel taken. See if she is doing better.

The tackle the next problem.

 

[22229stingray81]

Roger that, Gerry. EGR should be here Wednesday, and the fuel consumption is what I'll do next.


-Tatortot

 

[22229stingray81]

New AC Delco EGR arrived. This design looks a LOT more like the one in the shop manual. The one that was on the car didn't have an exposed rear diaphragm, amongst other variances. Anyways, once I had the old EGR off the 'vette, I'm 100% positive it was bad. It would not hold vacuum at ALL, and the diaphragm was extremely difficult to move. Instead of a gasket, the old EGR was attached with some orange goop that I had to scrape off the manifold port. What a pain.

I put the new EGR on, and went for a long drive. Guess what? No change. :ugh

So here's what I did: I tested the new EGR with a hand vacuum pump and it moves great, but it does NOT take the 20 seconds to move back in place like the shop manual describes. It only takes a couple of seconds. Next, I had the motor warmed up and idling, and I opened the throttle by hand to about 2500rpm, and I could NOT see the diaphragm move on it's own. I put a vacuum gauge in line, and I observed 20" hg, so that is MORE than enough vacuum to open it. It only took 5" hg with the hand pump. When I move the diaphragm by hand, the idle speed lowers as it should and described in the shop manual. Hmmm.

I also hooked up the dwell meter, and I think I have some conclusive results, but I don't know what the hell they mean: When the 'vette is idling normally, no engine vibration and the idle is at 700rpm in park, the dwell meter reads a steady 2.9 degrees. Then, every minute or so, the idle will drop by ~100 rpm, and the engine will shake and vibrate, though you'd probably only notice it if you were looking for it. When that happens, the dwell meter spikes to the ~27 to ~46 degrees. Does this mean that the engine only runs well in open loop? Still might have a vacuum leak, I guess. I'm going to do a consumption test to see how the fuel economy has been effected when the weather turns nice again.

To sum up what I've done:

-Replaced visibly broken and cracked vacuum lines
-Installed new EGR valve
-Cleaned and properly oiled the K&N air filter
-Replaced PCV valve
-Replaced Crankcase breather element
-Took the EGR solenoid off the car to inspect the wobbly bottom port (front clip has apparently broken off, but back half is still attached and pulling vacuum). The coil on the red top section also looks to have some corrosion, or something on it, but they seem to be working.

Man, am I getting tired of pulling off that air cleaner assembly :L

-Tatortot

 

[GerryLP]

Tattor,

The EGR valve has that plate shaped the same as the base of the valve. The valve takes one gasket and the plate takes another. This should seal your EGR.
once you attain the 20 seconds or better test, your Vette's engine should pick up engine speed. Once you adjust down the curb idle, it should begins to run much better. Again, when is working correctly, it should vary short needle sweeps of 28 - 32 degrees (approximately)

 

[22229stingray81]

Tattor,

The EGR valve has that plate shaped the same as the base of the valve. The valve takes one gasket and the plate takes another. This should seal your EGR.
once you attain the 20 seconds or better test, your Vette's engine should pick up engine speed. Once you adjust down the curb idle, it should begins to run much better. Again, when is working correctly, it should vary short needle sweeps of 28 - 32 degrees (approximately)

Gerry,

Are you saying I need to remove the plate (attached to the intake manifold) and replace that gasket as well? I pried up on the plate and it is REALLY stuck on there, so I let it be. I should mention that I have an Edelbrock Performer intake manifold.

I guess you're also saying that since I couldn't achieve the 20 seconds test, that I still have a vacuum leak?


-Tatortot

 

[GerryLP]

Gerry,

Are you saying I need to remove the plate (attached to the intake manifold) and replace that gasket as well? I pried up on the plate and it is REALLY stuck on there, so I let it be. I should mention that I have an Edelbrock Performer intake manifold.

I guess you're also saying that since I couldn't achieve the 20 seconds test, that I still have a vacuum leak?


-Tatortot

Yes, the gasket on that plate (between manifold and plate) is likely deteriorated and leaking. Use a scrapping spatula (flat piece of metal with a handle and a narrow edge use to spread putty or scrape paint or pry in between two surfaces).

if the valve is new, and the gaskets are replaced, when the engine is running, it won't leak vacuum signal from the manifold side. I did notice your manifold looked differently, but I am sure designed to work with your Vette.

The EGR valve redirects the diluted gases containing unburned compounds, into the intake runner to re burn them. The diaphragm opens the valve (the round port) by pulling it away from it's sitting (spring loaded position) and the unburned gases loop through the base of the valve & through the rectangular port. The computer, through the solenoid, decides when that happens (which is programmed for deceleration times and cruising while in no load (not climbing a hill) conditions.

To make sure you are testing the valve correctly, place the vacuum pump's hose directly to the EGR vacuum port (on top of valve). You are basically checking that the diaphragm in the valve is not leaking. If it were to be leaking, then the valve port at the manifold (the previously mentioned round port), won't open, and it won't redirect the diluted gases. However, this condition would cause a vacuum leak whenever the computer told the solenoid to apply vacuum signal to the EGR valve, and when it did, having a leak, your engine would run rough, just as it would whenever you disconnect and not plug/cap a vacuum hose.

So you could have a vacuum leak between the top of the valve and the solenoid (including a solenoid stuck open), and you could have a vacuum leak from the bottom of the valve between the valve and manifold.

i am proud of you taking the leads and investigating it on your engine. Keep up the good work. So new gasket between plate and manifold, and test valve direct to its vacuum port (at top of valve) with a vacuum pump.

keep us posted.
p.s. Just remember that vacuum signal is ALWAYS present (when engine is operating) in the hoses that go from the right-front of carburetor's vacuum (at base of carb level) and through the red "Y" connector to both solenoids (bottom port of top solenoid and top port of bottom solenoid.) If the solenoid is stuck open, it will activate the EGR valve all the time and cause high gas mileage consumption that way; and if it is stuck closed, then the valve won't operate and your Vette would likely fail the emissions test.

 

[22229stingray81]

Gerry,
I understand you 100% now, thanks! I was explaining to my buddy the other day that I have the shop manual, AIM, some tools, and the CAC, so there's really nothing I can't tackle :L.

Wow, having a vacuum pump sure makes things easier! I can't believe I didn't pick one up sooner.

I already did the test on the EGR as you described: vacuum pump directly on the EGR. It held vacuum and opened perfectly. That was NOT the case with the old EGR, which we know now was bad.

So I'll pick up a couple new gaskets tomorrow and pry that stuck-on plate off and report back. Thanks again for all the help and explaining it in a way I can understand.


-Tatortot

 

[Peer81]

Very promissing the work you did so far. My advice would be, do not go into to much detail (examply the egr) that way you loose track of the real problem. Remove egr and close off the egr opening in the intake with steel plate and new gasket, also plug the egr vacuum hose. This way you know quickly if the egr is the problem and if not move to the next. Dwell around 2 degrees is compensation at full rich (for lean condition) so to much air or not enough fuel. Sorry lately i just don't have the time to read this forum as much as i like. Lucky for the members Gerry has a lot of technical knowledge!

Greetings Peter

Verstuurd vanaf mijn GT-I9195 met Tapatalk

 

[22229stingray81]

Thanks Peter. Going out of town this weekend so hopefully I'll get to tackle the EGR within the next few days and report back.

-Tatortot

 

[22229stingray81]

Okay, I managed to pry off the EGR spacer. After cleaning it up, I can see a fair amount of corrosion on the upper-side of the plate. Do you think this would be cause for a leak? I have searched extensively online and I cannot find a replacement. A few "already sold" listings on eBay are the closest I found. Am I worrying too much about the corrosion causing a leak even with a new gasket? Thanks.

-Tatortot

 

[Peer81]

Put it on a big belt sandingbench and it will be flat and new as never before. Normally any metal workshop will have a belt sandingbench somewhere

Greetings Peter

 

[bill81vette]

Do you have a sand blaster???
you could try that instead of a belt sander....
just a thought...

 

[22229stingray81]

Thanks for the suggestions. I do have a hand-held belt sander that may work. No sand blaster.


-Tatortot



Edit: I found the spacer part #: 14031368

 

[22229stingray81]

Okay, I put everything back together today with 2 new gaskets. No change at all. The idle was a little bit lower, actually.

For whatever reason, I CANNOT get the EGR to work. At idle, while revving the engine, I can't see the diaphragm move with a mirror behind the EGR valve. I can move it by hand, and with a vacuum pump, but it seems the engine vacuum can't. Like I previously stated, I'm getting more than enough vacuum at 20" hg (the shop manual says you only need 5" hg). Regardless, the EGR should be closed at idle anyways, so I guess that can't account for the problems I'm having.

I'm going out of town tomorrow, so I'll have a lot of time to think about what's next. Is it possible I still have a vacuum leak somewhere else? Probably. I need to test every single flippin' hose, me thinks. Then there's the possibility it's leaking at the carb base, manifold, or valve covers like Gerry said. Arg.


-Tatortot

 

[GerryLP]

Okay, I put everything back together today with 2 new gaskets. No change at all. The idle was a little bit lower, actually.

For whatever reason, I CANNOT get the EGR to work. At idle, while revving the engine, I can't see the diaphragm move with a mirror behind the EGR valve. I can move it by hand, and with a vacuum pump, but it seems the engine vacuum can't. Like I previously stated, I'm getting more than enough vacuum at 20" hg (the shop manual says you only need 5" hg). Regardless, the EGR should be closed at idle anyways, so I guess that can't account for the problems I'm having.

I'm going out of town tomorrow, so I'll have a lot of time to think about what's next. Is it possible I still have a vacuum leak somewhere else? Probably. I need to test every single flippin' hose, me thinks. Then there's the possibility it's leaking at the carb base, manifold, or valve covers like Gerry said. Arg.


-Tatortot

Tattor,

Yes, the EGR is not activated at idle (see post #32).

We were trying to figure out your Vette's high consumption cause. So sealing the EGR was on the list. But you seemed distracted by the rpm change issue.

I recommend you take the Vette next opportunity and drive it and see if the consumption gets better.

 

[22229stingray81]

Gerry,

I understand the EGR is inop at idle, but the EGR doesn't seem to be opening when I open the throttle (by hand) either. Maybe I'm misreading the shop manual, but it says to "open the throttle to 2000 rpm and observe the diaphragam moving," or something to that effect. Regardless, I'll do the consumption test when I get back in to town and shelve the EGR for now. Thanks!


-Tatortot

 

[Peer81]

Alright, this is what I would do.

I think you have two possibilities,

Or you have a vacuumleak somewhere so the ECM is compensating for a lean condition
Or your ECM THINKS you have a lean condition.

So far we're still at option one:
First plug all the vacuum lines that come out of the intake. (brake, headlights, egr, tvs etc etc) This only leaves you with a possible vacuumleak around the carb base or at the intake/head connection.

On mine I have somewhat the same problem but I'm at option two:
Dwell close to zero but at startup it's fine around 25-30 degrees. So the ECM thinks the engine is running lean and is compensating to a rich mixture. My wide band O2 bugs say I'm already running way rich (as consumption also tells me) Send my ECM to Cor, he tested my ECM on his 81, same problems on his 81 as I have on mine, as his vette is doing fine on his ECM I concluded the problem is or the ECM or the PROM. Changed the ECM, no change in problems so now want to change the PROM and see if that helps. Not that you have the same problem but I would say begin with big steps that way you can exclude some uptions fast. After that you can zoom in and pin point on more detailed stuff.

Greetings Peter

 

[GerryLP]

Gerry,

I understand the EGR is inop at idle, but the EGR doesn't seem to be opening when I open the throttle (by hand) either. Maybe I'm misreading the shop manual, but it says to "open the throttle to 2000 rpm and observe the diaphragam moving," or something to that effect. Regardless, I'll do the consumption test when I get back in to town and shelve the EGR for now. Thanks!


-Tatortot

Tattor,

Maybe I have been confusing you. It is not that the EGR is inop at idle entirely. Once the coolant temperature reaches 195 degrees, the computer de-energizes the EGR solenoid. This allows application of vacuum signal to the EGR valve; however, that vacuum signal may be the minimum required or not, depending on the vehicle, idle speed, and what not.

When I run Gail's engine, it takes a while, sometimes up to a half-hour, for her to really warm up. I have done this several times, and with blocked wheels, on drive, and waiting to see the dwell gage to oscillate, does take a while. It could be because I am at 5,000 feet of altitude. But I am not a 100% sure of this.

Anyway, it is likely that you WIll NOT see a full deflection on the EGR valve just by accelerating the engine while on Park and at 2,000 rpm. What the shop manual is saying is that you should have minimum vacuum signal to actuate the EGR valve, but again, that does not happen at full deflection. All it takes is for the EGR's round port to unseat the needle valve, and it is redirecting unburned compounds to the combustion chamber.

If you (with engine turned off) apply vacuum directly to the EGR valve of 5 in-hg (inches of mercury), the EGR on your engine will perhaps deflect visibly or perhaps not. That is why the test procedure tells you to manually pull up on the diaphragm and look for rpm drop. The rpm drop tells you that 1) the valve is opening and 2) that the port itself is not clogged (I cleaned the carbon from that port on my Vette, and it took me a while to do; of courser, oven cleaner works pretty good).

As your Vette's engine idles, there are processes that are continuous and some are cyclical. The EGR activation is cyclic. So it will open, until a condition changes, and them it will close.

In fact, I believe that the RPM drop you video'ed is likely to be caused by your EGR cycling through. So that is why I am suggesting for you to do your consumption test drive, to see if your mileage has improved.

Now, was the dwell check on the carburetor passing or failling?

 

[22229stingray81]

Okay, I think I understand better now Gerry, thanks. We know that the EGR was bad, so at least I didn't waste time/money on something that wasn't broken. I will still say, just to be clear, it is not the RPM change that bothers me, but rather the engine vibration when the idle drops. Regardless, a consumption test is indeed next.

And as for if it passed the dwell test... I dunno! :L This is what I do know: After going for a drive (so it is sufficiently warmed up), there is a constant 2.9 degrees dwell. Then, every minute or two, the rpm drops slightly and the engine vibrates, and THAT'S when I get the dwell "flux" between ~27-37 degrees. So, the dwell appears to be changing with the engine vibration I'm chasing my tail over. This happens every time I've checked it. Engine smooth = 2.9 degrees. Engine rough = normal "flux."

Consumption test is next. I promise

-Tatortot

Tattor,

Maybe I have been confusing you. It is not that the EGR is inop at idle entirely. Once the coolant temperature reaches 195 degrees, the computer de-energizes the EGR solenoid. This allows application of vacuum signal to the EGR valve; however, that vacuum signal may be the minimum required or not, depending on the vehicle, idle speed, and what not.

When I run Gail's engine, it takes a while, sometimes up to a half-hour, for her to really warm up. I have done this several times, and with blocked wheels, on drive, and waiting to see the dwell gage to oscillate, does take a while. It could be because I am at 5,000 feet of altitude. But I am not a 100% sure of this.

Anyway, it is likely that you WIll NOT see a full deflection on the EGR valve just by accelerating the engine while on Park and at 2,000 rpm. What the shop manual is saying is that you should have minimum vacuum signal to actuate the EGR valve, but again, that does not happen at full deflection. All it takes is for the EGR's round port to unseat the needle valve, and it is redirecting unburned compounds to the combustion chamber.

If you (with engine turned off) apply vacuum directly to the EGR valve of 5 in-hg (inches of mercury), the EGR on your engine will perhaps deflect visibly or perhaps not. That is why the test procedure tells you to manually pull up on the diaphragm and look for rpm drop. The rpm drop tells you that 1) the valve is opening and 2) that the port itself is not clogged (I cleaned the carbon from that port on my Vette, and it took me a while to do; of courser, oven cleaner works pretty good).

As your Vette's engine idles, there are processes that are continuous and some are cyclical. The EGR activation is cyclic. So it will open, until a condition changes, and them it will close.

In fact, I believe that the RPM drop you video'ed is likely to be caused by your EGR cycling through. So that is why I am suggesting for you to do your consumption test drive, to see if your mileage has improved.

Now, was the dwell check on the carburetor passing or failling?

 

[22229stingray81]

THANKS Peter! So we're still thinking it's a vacuum leak; got it! Makes perfect sense. I really do need to check every inch of vacuum hose for a leak with a pump, as well as the TVS, etc. I'm moving on from my obsession on the EGR!

Good point on the computer, too. Just because it says it's working fine doesn't mean it is! I know mine is a replacement ECM. No reason why it couldn't go bad again.


-Tatortot

Alright, this is what I would do.

I think you have two possibilities,

Or you have a vacuumleak somewhere so the ECM is compensating for a lean condition
Or your ECM THINKS you have a lean condition.

So far we're still at option one:
First plug all the vacuum lines that come out of the intake. (brake, headlights, egr, tvs etc etc) This only leaves you with a possible vacuumleak around the carb base or at the intake/head connection.

On mine I have somewhat the same problem but I'm at option two:
Dwell close to zero but at startup it's fine around 25-30 degrees. So the ECM thinks the engine is running lean and is compensating to a rich mixture. My wide band O2 bugs say I'm already running way rich (as consumption also tells me) Send my ECM to Cor, he tested my ECM on his 81, same problems on his 81 as I have on mine, as his vette is doing fine on his ECM I concluded the problem is or the ECM or the PROM. Changed the ECM, no change in problems so now want to change the PROM and see if that helps. Not that you have the same problem but I would say begin with big steps that way you can exclude some uptions fast. After that you can zoom in and pin point on more detailed stuff.

Greetings Peter