The Sweet Sound of an L81+

[Barry08]

Gerry,
Go to this link and read all the comments.
Looks like you will have to richen up your main metering rods as they did there.
You should be able to get it close by doing what they did.
http://forums.corvetteforum.com/showthread.php?t=1428712

Barry

 

[Peer81]

Very nice topic Barry thanks

Just one thing to clarify

Looks like you will have to richen up your main metering rods as they did there.

Primairy rods are controlled by the ecm. In a way the only thing the ecm does is keeping the fuel/air ratio as close to perfect as possible. So changing the primairy rods will have no effect. You have to change the secondairy rods like stated in the topic. But as I read it Gerry is going to check his E4ME step by step so everything is going to be just fine

Groeten Peter.

 

[GerryLP]

ERROR ERROR (Alarms blaring)

Barry et al,

The dyno results show that I have a problem with the carburetor...Take notice on the bottom fuel mixture chart how LEAN the engine is running. That's is why I am starting with the calibration of the E4ME procedure from the Rochester E4ME book (page 15).

View attachment 12630

I guess that I have forgotten some of the basics in carburetors' functions. I wish I could say that I caught my own error, but the truth is that communication exchanges with Lars Grimsrud made me realize that the L81 is running RICH NOT LEAN. My sincere thanks go out to Lars for helping me realize my error.

I read-up some more in my Holley book on the Air/Fuel Ratio and Ratios for Power and Economy, and I was confusing the stoichiometric Air/Fuel ratio of 14.7 for optimum, with the A/F ratio for max power of 13.3:1 to 12.5:1 or even as low as 12.0:1 (that red dash on the Dyno chart, I guess). An economy-best setting would be at or near 16.0:1.

So it appears that my L81 begins heavily enriched, then leans (near 12.0:1) at around 4,180 rpm, and the enriches again to-wards 10.0:1.

I am awaiting for the remaining E4ME tools to arrive, so that I can set the Rochester back into a calibrated setting IAW the procedure in page 15 of the 9D-5-1 E4ME manual.

 

[Barry08]

I'll be damned! We all missed that on the dyno sheet!
Lars is pretty much a god when it comes to tuning!
I take it you have checked for vacuum leaks?
I believe if your vacuum is too low it can also screw up the mixture as the ecm thinks you are opening the throttle quite a bit even though your not. Because of the low vacuum signal it's causing a rich condition.
Maybe too much cam for the computer.... if it was installed straight up ?Advancing it 4 degrees may help.
Keep us posted!

Barry

 

[GerryLP]

Ready for another Dyno run

Hello everyone,

I just got finished today adjusting the E4ME carb parameters. Basically, I took advantage of a nice couple of days of spring-like weather to work the issue.

Replaced the EGR valve (the old one needed too much vacuum signal to make it move), and I set the TPS to 0.56 volts with the throttle at curb idle (engine off). The TPS was set at little over a volt.

I returned the initial timing to the stock 6 deg BTDC. I had set it to 13 deg during the last dyno run, but I wanted to start from square one, and so I set it to stock.

The idle mixture screws are set at 3 3/4 turns out. The shop manual says 3 1/3, but the AC-Delco SD-100A manual says 3 3/4 turns out for the 17081218 E4ME carb. I tried needle settings from 3 turns to 3 3/4 in 1/4 increments, and when the 3 3/4 turns on the idle needles was set, it was relatively easier to set the idle air valve at a 30 deg Dwell.

With all the settings done, I even had time to the idle speed-up solenoid (for when the A/C is turned on).

Took a 15 mile drive, and the adjustments have really awaken the Vette. I did not drive it hard, but it just felt stronger and more responsive.

I will call ahead and make an appointment for another Dyno run.

 

[Peer81]

Sounds great!
Good luck on the dyno, I'm very curious what a dyno results will be.

Groeten Peter.

 

[Barry08]

Gerry,
Glad to hear you are making progress.
Where did you get the specs and the tools to set all that up?
Waiting for dyno results

Barry

 

[GerryLP]

Gerry,
Glad to hear you are making progress.
Where did you get the specs and the tools to set all that up?
Waiting for dyno results

Barry

Barry,

It took me a little while. I had the E4ME carb manual (electronic version bought in eBay). Then I bought some of the supplemental manuals mentioned in the carb manual. One of them is the 9A-100-3 which contains the part numbers for some of the carb component (i.e. carburetor, parts, power kits, and emission control parts). This one was hard to find, but I finally found one on the web in some hot rod website. The AC-Delco SD-100A has the tune-up specifications by carb part number. It also has carb adjustments like the idle and the other special adjustments.

I also gathered some of the many tools needed. Thexton makes some of these tools. Thexton tool #370 is becoming difficult to find, and it is even discontinued, but it has the lean and rich stop screws tools, the M/C travel gage, and the initial setting tool for the idle air valve.

The Thexton #362 has the jet tool and it also adjusts the TPS, M/C stop screws and other settings. This one still available from many vendors. What this one is really missing is the M/C gage and the idle air valve. The M/C gage can be made from a ruler with 1/32" markings and shaved to fit the "D" vent slots at either side of the idle air valve screw. The idle air valve initial setting tool could probably be made by setting up a shadow shape on a wood board with solid studs and a wire that can be hardened later. I bought my #362 tool from ETW Corporation, Washington. They're on the web.

If any CAC members need a few pages scanned and e-mailed from the SD-100A and the 9A-100-3, then please let me know by sending me an e-mail.

 

[Peer81]

Good luck tomorrow!

Groeten Peter

 

[GerryLP]

Good luck tomorrow!

Groeten Peter

Thanks, Peter.

I am really curious how rich or lean is really running now, but if the dwell was any sign of it, the computer seems to be controlling that well, since I managed to set it very close to 30 degrees dwell on the 6-cylinder scale.

After the first pull, I will change the initial timing to 12 deg, and we'll see what that nets.

 

[GerryLP]

Lack of common sense won't help your Karma

Well folks,

On a beautiful "almost spring" day, I arrived at my dyno appointment 5 minutes late (My Flight Commander had a last minute task handed-out). However, as luck would have it, Chris, the dyno guy, had to rescue a buddy of his who had blown his F150 Lightning way out in the west-side of Albuquerque. So he didn't show-up until about 4:30 p.m....but at least he showed-up. Chris is a real cool guy, so he began setting everything up for the L81's run.

We got the Vette up there, and the plan was for after the first pull, I would be adjusting the initial timing to about 12 -14 degrees. However, the first pull sucked. It is the one in red. Notice the red fuel mixture line how it goes up and down until it gets real close to the 10 to 1 air/fuel mixture (best is about 13.0 to 1).

View attachment 12920

Before the second pull, I adjusted the initial timing to 14 degrees. I also turned the idle mixture screws in about 1 turn (the wide-band sensor was showing 12 to 1 at idle). Since I had to remove the air cleaner, I placed a cap on the carburetor tube for the Thermac hose and removed the air cleaner assembly all the way. So I "checked" everything, and I told Chris to go for the second pull. The second pull is the blue one. Notice how the fuel mixture improved to about 12 to 1.

With me dragging my deflated spirits like remnants from a shredded balloons, I headed to my Vette and loaded my tool box in it. I got myself in the Vette, and I started the engine.....wait a minute...now what????....why is the "check-engine-light" on???? I suppressed my frustration, for I now was hoping to make it home 25 miles away...looking...looking...Hey! what tha heck??!!

I found the four wire connector from the distributor disconnected....I must've forgotten to reconnect it after adjusting the timing...now, I felt like I should be changing my name to "Dumb A$$"....so that means that my second pull was not correct....so there's hope...hnoes

Driving home, I kept thinking why was the fuel mixture so close to 12 to 1??? The computer was not controlling much at that time...perhaps the fuel mixture only...and it was not scheduling timing advance. So what could it be? running rich...running rich...hummm...I wonder if I am having a problem with the Thermac?

I got home, and I decided do a simple test. I checked everything to make sure that it is hooked-up correctly...it was. So I disconnected the flexible cold air ducts, and at the same time, I rev-up the engine and see if the snorkel doors are doing anything....left front snorkel is wide open during the entire revving-up and down. I do the same on the right hand one, and it is closed at idle, at part throttle, and at about 4k rpm...hummm....that should cause a rich condition, so the good news is that I found what is causing the L81 run rich.

Did I mentioned that the bad news is that today's Dyno run sucked!

 

[Peer81]

Hello Gerry,

Sorry to see the dyno isn't what it should be, but you're getting closer and closer to getting it spot on! Are you reffering to the flaps in the aircleaner snorkels? And how are you going to correct this problem?
I don't know if you have an old laptop or something. With some effort you could make or find an ALDL cable to have an instant readout of your ecm program. I find it ashame to spend all that money on a dyno run to find out the air/fuel ratio isn't good. These numbers should also be monitored by your ecm so you should be able to get a readout (same as with the c4 vette's).
Good luck!

Groeten Peter.

 

[GerryLP]

Hello Gerry,

Are you reffering to the flaps in the aircleaner snorkels? And how are you going to correct this problem? I don't know if you have an old laptop or something...
Groeten Peter.

Peter,

I am suspecting the it should not be too difficult. The Thermac has that temperature air valve inside the air cleaner that when the engine is cold at first start it should redirect vacuum to one or both snorkels to close the flaps (one snorkel closing makes more sense that both). Then when it reaches the temperature, the snorkel previously closed should open and fresh air should reach through both snorkels.

As far as a lap-top, I could not even begin how to do that...

 

[LannyL81]

Gerry,
You know you could just cap-off that vacuum line that controls the doors in the intake cleaner. Just pull the line off the front of the carb and cap it off with one of those rubber vacuum line caps. That way both doors will be open all the time.

Just a suggestion.

Later,
LannyL81

 

[rbell@idtfla.com]

Gerry:
I went to purchase the CL12-238-2 Cam from Summit that you recommended in this thread which Comp also said was good and summit states that it will not work with the computer on the L81??? Do you have any input. Do you know of anyone ruinnig this the 238??

Thx,

Bob

rbell@idtfla.com

 

[GerryLP]

Bob,

The Cam I have in the L81 is the XE268H....http://www.compcams.com/information/Products/Camshafts/DynoSheets/XE268H-10_001.asp

The CompCams catalog says the following:

HYDRAULIC-Great for street machines, largest
cam for stock converter, better with 2000+ stall

Operating range: 1600 to 5800

P/N 12-242-2

XE268H [cam grind]
268 [advertised intake]
280 [advertised exhaust]
224 [intake duration @ 0.050"]
230 [exhaust duration @ 0.050"]
.477 [intake gross lift]
.480 [exhaust gross lift]
110° [lobe separation angle]


Did they tell you why you should not use the XE268? The P/N you posted is the XE262H. You may want to ask CompCams directly.

As far as the computer is concerned, I can tell you that it has not set any error codes in my L81, and it seems to be working within specifications.





​

 

[Peer81]

Gerry,

Did you check how much vacuum the engine produces? I don't know which cams the ECM tolerates but if the cam is to big (produces to little vacuum) the ECM thinks the carb valves are a little open (throttle) so the ECM will correct this with more fuel. This could also be why the engine is running rich. Maybe something to check..
Good luck

Groeten Peter

 

[GerryLP]

Gerry,

Did you check how much vacuum the engine produces? I don't know which cams the ECM tolerates but if the cam is to big (produces to little vacuum) the ECM thinks the carb valves are a little open (throttle) so the ECM will correct this with more fuel. This could also be why the engine is running rich. Maybe something to check..
Good luck

Groeten Peter

Peter,

Good point! By coincidence late yesterday I was planning to come back and elaborate on the vacuum signal as listed on the CompCam's torque/power graphs for the different cams.

If one compares the XE262 and XE268, the XE262 will yield a little higher vacuum signal at 800 rpm than what the XE268 will yield.

The XE 262 yields approximately 17.5 inches of mercury at 800 rpm...

http://www.compcams.com/Technical/DynoSheets/XE262H-10_001.asp

The XE268 yields approximately 2 inches less of mercury at the same rpm...

http://www.compcams.com/Technical/DynoSheets/XE268H-10_001.asp

So the XE 262 will perhaps be more appropriate for an L81 with stock compression (versus the true (measured) 9.5:1 in my L81).

But to answer your question, Peter, my L81 produces approximately 14.5 inches of mercury, but I have not measured it lately, so I'll let you know when I do. Nevertheless, I am at 5,000' of altitude, so the vacuum signal is also affected by the pressure altitude.

The problem with my L81 running rich does not manifests itself at part throttle. It does manifests at WOT, and I believe that the computer is by-passed in WOT mode. ...Que no? :confused

 

[Peer81]

True, at WOT your carb is on its own
Good luck!

Groeten Peter

 

[GerryLP]

Correction...

Peter,

I was looking at my notes after work, and the 14.5 inches of mercury is wrong. That was a different set-up (XE268 cam, 650 Holley, 900 rpm curb idle).

So I started the L81 and connected a vacuum gauge. The L81 set-up produces 11.5 inches of mercury at 650 rpm no load (in parking setting).

So this is more consistent with the fact that at sea level, one should get about 18.5 inches of mercury with the stock cam. But with the XE268 cam, the cam will produce a vaccum signal of 15.5 inches of mercury at sea level and at 800 rpm, but the cam at 5,000 feet of altitude produces 11.5 inches of mercury at 650 rpm.

The bottom line is, however, that the computer does not seem to be affected. In fact, I got the dwell pretty steady (relatively speaking steady..the dwell meter needle should keep moving slightly) at 30 degrees dwell in the 6-cylinder scale as per AC-Delco instructions.