Q-Jet: Rich at cruise, lean under slight accel - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
LinkBack Thread Tools Display Modes
post #1 of 7 (permalink) Old Oct 9th, 02, 04:29 AM Thread Starter
 
Join Date: Feb 2001
Location: Wylie, TX
Posts: 15
I'm running a 383 with AFR 195 heads, Team G street ram (#7525) intake and a Comp Cams solid roller cam XR274. I also have a heated O2 bung in my driver's side collector and have been monitoring my A/F ratio lately and I can't get it to keep from leaning out on slight acceleration. My carb is about 1 1/2 years old and is an Edelbrock 800 cfm QJet with 74/48 jet/rod combo.

I'm using a Summit O2 sensor which looks like an unbadged Nordskog (sp?) 10 LED bar graph gauge. One light is lit up for each .1 volt of O2 output. I have also verified my reading with 2 different O2 sensors and they are consistant.

When driving at cruise with no wind on a level surface, the car runs a bit rich at 7 to 8 lights. When I *barely* touch the throttle, it leans out to about 1 to 2 lights. The throttle is pressed just to change the exhaust note and I'm not really accellerating more than 1 mph per 5 seconds, or maintaining speed on a very slight hill. It will stay lean until I increase the throttle enough (30% open?) to pull the power piston up and then it runs at 7 to 8 lights again. Also, the higher the revs, the leaner it seems to run. So, at 2000 RPM (44 mph), I'm seeing 1 to 2 lights and at 3000 RPM (70 mph) all lights go out.

Now, if I didn't have the O2 sensor and gauge, I'd never know that it's running that lean. There is sometimes a very small stumble when going from cruise to the slight acceleration, but it is only occasional and is ever so slight. Other than that the engine runs great. I believe there is a problem in the main circuit, but I'm not sure where to look.
Amblefinie is offline  
Sponsored Links
Advertisement
 
post #2 of 7 (permalink) Old Oct 9th, 02, 06:48 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 32,180
Garage
I would probably write everything down just to have a reference to return in case one took a wrong turn.

The first item on the agenda I would do is to increase main jet size, and/or decrease rod diameter. I think the piston spring is a given and can't change the rate (stiffness) as in maybe try a lighter spring.

Maybe increasing idle mixture screws a tad might help, just a guess.

One might adjust float level alittle higher. This would allow the venturi, creating a high pressure area, to allow the atmospheric pressure to push more fuel into the air stream.

In the older days before computer control, one looked at the inside of the tailpipe. A gray color sygnified a properly tuned engine. The lighter the color, closer to white, the leaner the engine was running. Now days, with O2 sensors, the pipes are dark, can't really tell by visual examination if the engine is in tune. Need test equipment to read O2 sensor voltage for rich/lean condition.

Maybe some others will give their thoughts.

------------------
Everett "OBJECTS IN THE MIRROR DISAPPEAR UPON RAPID ACCELLERATION"
Everett#2390 is offline  
post #3 of 7 (permalink) Old Oct 9th, 02, 07:03 AM
DjD
Retired
Dennis
 
DjD's Avatar
 
Join Date: Apr 1999
Location: Fortuna, CA
Posts: 26,550
Garage
Just thinking out loud here but with the slight increase in throttle you are giving maybe the condition is normal. Each time you open the throttle bore the acel pump supplies a squirt of fuel to aid in the transition to the new mixture. I believe that pump shot is needed as air is the first part of the mixture to arrive when the throttle is opened. With a very small throttle change you may not be getting a squirt or enough squirt to over come the lean condition you are seeing. Does the lean condition go away as you level out the throttle and maintain a faster but steady speed?

------------------
...Dennis
"The '69, the '96 our local club"
and the "daily driver"
DjD is offline  
 
post #4 of 7 (permalink) Old Oct 9th, 02, 08:56 AM Thread Starter
 
Join Date: Feb 2001
Location: Wylie, TX
Posts: 15
I have played around with jets/rods, but I'm hesitant to go with bigger jet or smaller rod as with my current setup, I'm a little rich at cruise (assuming level ground). I also played around with the idle screws but that didn't make a signifigant change to the cruise or slight accel readings. Changing the power piston spring will not do anything as I'm pulling about 15" of vacuum when I'm getting the leanness. I did not change the float setting, that may be something I'll try.

The leanness I'm experiencing continues until I either let off the throttle, or push it to the point of pulling up the power piston, so it is not a transition type problem.

Thanks for the replies
Amblefinie is offline  
post #5 of 7 (permalink) Old Oct 9th, 02, 09:48 AM
 
Join Date: Nov 2000
Posts: 84
Hey everret, could you go over that rule of thumb for looking in the tail pipe. What happens if you are running rich. What part of the tail pipe do you look at, just the end or do you remove the manifold? I have an older 73 with no sensors and I dont know the specs on the cam. I am trying to figure out if it is running rich or lean but dont really know the tell tale signs. Also, I am having to guess at the timing due to not knowing anything about the cam. What a pain.
gateruner is offline  
post #6 of 7 (permalink) Old Oct 10th, 02, 01:03 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 32,180
Garage
Gaterunner,

Look at the end of the tailpipe, the first few inches when bending over and looking into the tailpipe. Black is rich, silver gray is good, white is lean.

In adjusting timing, use a vacuum gauge to monitor full time vacuum and tune for max (higher) vacuum. But then, too much advanced timing will probably buck the starter when hot, then have to back off timing. Use timing light to see where timing is. Adjust idle mixture using the same method,

Remove spark plugs and check their color, black = rich, tan/beige = correct mixture, no color/white = lean. This would be after driving for 100 miles, not all at one time, to "color" the plugs.

------------------
Everett "OBJECTS IN THE MIRROR DISAPPEAR UPON RAPID ACCELLERATION"
Everett#2390 is offline  
post #7 of 7 (permalink) Old Oct 11th, 02, 10:10 AM Thread Starter
 
Join Date: Feb 2001
Location: Wylie, TX
Posts: 15
Thinking about this some more, what is the chance that I'm still in my off-idle circuit for the cruising and then going to the main circuit during the slight accel?

The more I think about this, the more it makes sense to me since the cruising A/F has not changed regardless of which jets/rods I'm running. I've run alot from a 77/50 down to a 73/50. The 77/50 was rich everywhere and the 73/50 was rich a cruise and dead lean (ie. no lights) at slight accel. Is there any way to lean the off idle other than playing with the idle screws? I've already leaned out the idle to see if it made a differnce at cruise, but it didn't do much (if anything).
Amblefinie is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome