E4ME tuning help

[Wajulia]

Hello all.

I am trying to tune my carb in after a rebuild. In general the car runs fine, idles fine, but not consistently. This is what I found out so far.

After the car is warm, start the car and the dwell reading goes to about 25. I have tried to adjust the idle air bleed -- I will discuss that a little later. The idle is good, but a little lumpy. After a minute or so, the dwell goes to 5 degrees and idle smooths out. Bringing the revs up the dwell goes up to about 30 then slowly goes back to about 5

When the idle is at 5, I can choke the carb and the dwell SLOWLY climbs up to about 50, where to my amazement, the idle smooths out again!!. removing the choke the dwell goes back to 5

Idle air bleed screw. I start that at 4.5 turns from the bottom. When the idle is at 25, i can turn it all the way to the bottom with no change in dwell. When turning it out to about 5 turns, the dwell goes to 5 degrees and does not react at all till I restart the engine.

The car also sometimes gets a code 44 (lean)

I realize this is a lot of data, but I am stumped as to where to go next? Any ideas?

 

[Peer81]

Can you also post your engine setup. Cam spec's etc?

Greetings Peter

 

[Wajulia]

Bone stock L81

 

[LannyL81]

Has anyone been into the carb ever?
Suggest starting from the beginning.
Do you have the carb setting tools?
Will need these to set the mixture control solenoid and idle air bleed screw....without them you are guessing.

The air mixture screws should be at around 3 1/2 turns out. If the idle air bleed screw is out of adjustment, then trying to set the air mixture screws is really going to be a challange.

You should be able to get the tools off of ebay or a Google search for E4ME carb tools.

Good luck....

 

[GerryLP]

Read the following thread. Try the same steps I tried. Also, when you turn the air valve screw, do so 1/8 of a turn at a time, and wait two minutes between adjustments. Also, you have to make sure that the engine gets up to operating temperature fully before turning the air valve for adjustment.

http://www.corvetteactioncenter.com/forums/l81-vette-registry-forum/126234-i-have-question-experts-folks-who-have-dealt-e4me-carb.html

 

[Wajulia]

Has anyone been into the carb ever?
Suggest starting from the beginning.
Do you the carb setting tools?
Will need these to set the mixture control solenoid and idle air bleed screw....without them you are guessing.

The air mixture screws should be at around 3 1/2 turns out. If the idle air bleed screw is out of adjustment, then trying to set the air mixture screws is really going to be a challange.

You should be able to get the tools off of ebay or a Google search for E4ME carb tools.

Good luck....

Yes, Many times. In its younger days (80's and 90's) It would never pass emmisions, to rich because the computer had a constant error code of speed sensor. Every year some bubba (even genuine GM bubbas) would rebuild the carb, then give me a sticker -- but of course the problem was never fixed because it was the speedo sensor was never corrected letting the computer go open loop. The car has been sitting since then and I recently got it running again. I fixed the speedo, and opened the carb up myself to sort out all the previous bubba work.

It seems to be running quite well now -- the computer rarely throws a code and it is always 44 (lean). I would like to tune it in, but it does not do what I think it should be doing, So I am not sure where to start.

I started with the idle mixture adjustment screws out 3.5 turns. Stumbled really bad, so I turned them both out one additional turn. It idles pretty good now, but acts as I described above. Should I keep backing out the

As for the mixture control solenoid adjustment -- I measured the total movement on the solenoid from the "D" vent hole on the top of the carb and it is 4/32nds. The service manual says It shoud be from 2 - 4/32nds So I think I am ok there.

As for tools, right now I am using some makeshift tools and everything seems accessible so far.

 

[Wajulia]

Read the following thread. Try the same steps I tried. Also, when you turn the air valve screw, do so 1/8 of a turn at a time, and wait two minutes between adjustments. Also, you have to make sure that the engine gets up to operating temperature fully before turning the air valve for adjustment.

http://www.corvetteactioncenter.com...n-experts-folks-who-have-dealt-e4me-carb.html

So from the thread, it sounds like you had an air leak in the exhaust and when you fixed it the carb began to meter as expected. That is consistent with my code 44. I will check the headers and the exaust connections.

Thanks.

 

[Bills money pit]

I have rebuilt several E4ME carbs and believe one step in the rebuild is often overlooked. There is usually wear in the area where the butterfly shaft rides in the body of the carb. Cliffs performance and others make a bushing kit to eliminate the slop. If this area is not addressed then a rough idle is experienced as air is pulled in around the shaft.

Also the dwell issue will be affected if there is a vacuum leak. I failed to connect one of the hoses to the carb and the dwell went crazy.

My 81 now runs better than ever before.

Something to consider....Good luck!

 

[Peer81]

Like Bill says, do you know or can you measure how much vacuum HG you have at idle? Could be you have a vacuumleak that is causing the lean condition.

Greetings Peter

 

[Wajulia]

I don't have a vacuum gauge -- I will see if I can find one. What would I be looking for?

 

[Peer81]

You can connect the vacuum gauge to one vacuum port or line that is connected to the intake. Check the reading and move to the next line. As you are sure the vacuum gauge holds the vacuum and your lines are a big question, you can find if one vacuumline is pulling air into the intake.

Greetings Peter

 

[Wajulia]

Vacuum
I measured the vacuum at a few carberator ports at idle, 18mm hg varying about 0.5mm
I measure an intake port (headlight motor line) 20mm hg

Does that vacuum indicate a leak?

I backed out the idle adjustment screws and it does not seem to make any difference

Any ideas?

 

[Peer81]

No it doesn't. Now I don't have the original cam anymore and I'm at 16mg vacuum but I have about the same problem you have. At idle very lean but when you drive it's about normal. I'm thinking about the EGR valve not closing properly anymore so it's pumping exhaust gas into the intake when the valve should be closed.
And I think it isn't that difficult to make a EGR block off plate to see if that is the problem.

Greetings Peter

 

[GerryLP]

Vacuum
I measured the vacuum at a few carberator ports at idle, 18mm hg varying about 0.5mm
I measure an intake port (headlight motor line) 20mm hg

Does that vacuum indicate a leak?

I backed out the idle adjustment screws and it does not seem to make any difference

Any ideas?

Maybe...did you mean millimeters of mercury???

millimeters of mercury x 0.03937 = inches of mercury


At sea level you should have about 18 -19 Hg In. So if it is true that you meant millimeters, then you got about 7.8 Hg In. But if you get the saem on all rubber hoses connected to the manifold, then you do have an intake gasket leak, most likely. While the engine is running, spray WD-40 on the mating surfaces between the cylinder heads and intake. If the engine RPM goes up while spraying the WD-40, then you have a leak there.

How's your engine's oil consumption? Do you have to add oil every two weeks or so, and you don't see a huge amount of oil on the garage floor? Then you have an intake gasket leak. The oil is usually coked on the intake/exhaust valves.

GerryLP:cool

 

[Wajulia]

I want to go back to something I mentioned earlier, but tried again this weekend. If I put a rag on top of the carb, It coughs and hesitates, but then I watch the dwell meter continue to rise until it gets to about 35 -- the engine smooths out and the dwell moves from between 30 and 40 -- like I would expect it too.

Does anyone think this is signifying a vacuum leak?

I will spary carb cleaner (this is what I have -- will it work?) at the base of the carb and some of the vacuum hoses. If there is a leak the RPM will change when I do??

 

[GerryLP]

I want to go back to something I mentioned earlier, but tried again this weekend. If I put a rag on top of the carb, It coughs and hesitates, but then I watch the dwell meter continue to rise until it gets to about 35 -- the engine smooths out and the dwell moves from between 30 and 40 -- like I would expect it too.

Does anyone think this is signifying a vacuum leak?

I will spary carb cleaner (this is what I have -- will it work?) at the base of the carb and some of the vacuum hoses. If there is a leak the RPM will change when I do??

Yes, a vacuum leak is when air is being sucked in. This sucked in air dilutes the fuel charge and makes it a lean condition (too much air for the fuel amount).

That is exactly what my L81 was doing. If I place my bare hand (a rag can be swallowed though the carb). You can see how the computer continues to meter the mixture, because it has the mean to do so. An air leak can be so large (relatively speaking) that the computer has no way to compensate, and then switches to open loop based on saved data from earlier engine operations. Is as if it knew that if it encounters problems metering the fuel and air mixture, that it will revert to a time in which it "knew" that it was running better.

Once I knew that the intake gaskets where GTG, I began by sealing the carb from its gasket base. I inspected the gasket, and I found the plastic inserts in which the bolts go through were loose, so I used some permatex RTV and sealed the bottom and top of gasket (a little messy). Then, I checked all the vacuum lines that connect to the carb or manifold. And in between efforts to seal it, I would start up the engine and see if the computer would meter on its own.

This process led me to the leaky exhaust doughnut on the left side upstream of the oxygen sensor.

Now, it was probably the fact that since I was resealing the different areas systematically, once I tightened the left side of the front "Y", there were enough corrections made to satisfy the computer into not quit metering the fuel, but it worked (it other words, it may not be to factory specs, but the computer is happy).

 

[Wajulia]

Update

Well, it has been a while and I just wanted to close the loop and perhaps get a little advice on how to proceed from here

Spent the summer tracking down lots of vacuum leaks and some loose bolts on the exhaust manifolds. Still had code 44 (lean)-- Decided to bring both the lean and rich mixture stop screws up a little to bring the control point a little richer -- when I did that, I noticed the air horn gasket in the carb was wet with gas. Realized that all the screws on the airhorn where loose, Tightened them up and have not got a check engine light since. Thought about putting the screws back down to see if the problem was the loose screws or the adjustment, but figured I would leave well enough alone.

The car idles like silk, and runs great, BUTTT -- I still can not get the dwell right. I get a dwel of 27, and turning the idle air screw does NOTHING. it seems to be in close loop, revving the engine changes the dwell, everything seems to be working ok. Strangely, after a few minutes of idle, the dwell drops to about 7 and will not come back up. If I turn the car off and start again it does the same thing.

Another thing I noticed -- I can not get the idle below about 700. The idle screw is backed out so that it does not touch the liknage and idle stays at 700. Can that be an issue with the butterfly being installed incorrectly?

Any ideas on what I should continue to look for to get the dwell above 30? I keep telling myself just to leave it alone since it is running so good, but it is against my nature:eyerole Any advice will be appreciated!

 

[GerryLP]

Well, it has been a while and I just wanted to close the loop and perhaps get a little advice on how to proceed from here

Spent the summer tracking down lots of vacuum leaks and some loose bolts on the exhaust manifolds. Still had code 44 (lean)-- Decided to bring both the lean and rich mixture stop screws up a little to bring the control point a little richer -- when I did that, I noticed the air horn gasket in the carb was wet with gas. Realized that all the screws on the airhorn where loose, Tightened them up and have not got a check engine light since. Thought about putting the screws back down to see if the problem was the loose screws or the adjustment, but figured I would leave well enough alone.

The car idles like silk, and runs great, BUTTT -- I still can not get the dwell right. I get a dwel of 27, and turning the idle air screw does NOTHING. it seems to be in close loop, revving the engine changes the dwell, everything seems to be working ok. Strangely, after a few minutes of idle, the dwell drops to about 7 and will not come back up. If I turn the car off and start again it does the same thing.

Another thing I noticed -- I can not get the idle below about 700. The idle screw is backed out so that it does not touch the liknage and idle stays at 700. Can that be an issue with the butterfly being installed incorrectly?

Any ideas on what I should continue to look for to get the dwell above 30? I keep telling myself just to leave it alone since it is running so good, but it is against my nature:eyerole Any advice will be appreciated!

Wajulia,

Is the dwell needle steady at 27 or is it moving to the right and to the left small distances (as an analog Gage would when it hunts for a signal)? If it is steady, it is in open loop and utilizing previuosly saved values. Also, if you have a sticky pcv valve, it will read it as a leak.

GerryLP:cool

 

[Wajulia]

It is steady, But it does change if the engine is revved. I will check the PCV valve.


If it where running open loop, would it eventually kick out a code?

 

[Peer81]

I had the same thing with my carb. Running great but after a few minutes the dwell dropped to almost zero. But I forgot what the problem was.
Also had the same problem with the idle speed, couldn't get it under 700 rpm.
Did you put bushing in the thottle shafts? This is a way to get air in. Your butterfly isn't the problem as it isn't the border between outside air and engine vacuum. Your throttle blades could be the problem, but repositioning them isn't easy.

Greetings Peter