Dailing in E4ME carb.

[Peer81]

Hello everybody,

I'm in the proces of dailing in the Q-jet, I have some ideas about correcting some problems but would like others to comment on that.

This is what I have:
1981 Corvette with almost stock 350ci engine. 200hp or something like that, so nothing fancy.
Stock rebuild E4ME carb (rebuild with Cliff's parts)
Electronic solenoid and stock main jets and rods (can't be changed anyway)
Acc. pump shaft length is stock, openings are also stock.

Secondary rods are stock CH's (I also have richer and leaner rods)
Secondary hanger is stock (think it's a Y but need to check that, also have other hangers)
Opened up the secondary fuel wells a little (as discribed in Cliff's book)
Cut a little half moon out of each secondary upper air valves on the side that faces the discharge holes.
The secondary vacuum pull off is at 2 or 3 seconds, also need to check my book to know.

Idle mixture screw holes are opened up to pre emissions dimensions, also cut the spring on the mixture screws to still get them to be fully seated. Screws are 3 turns out.
The fuel inlet in the carb is the bigger then stock opening also from Cliff.
Floatlevel is set to .420 below.

I have a wide band connected on the passengers side and this is what I get.
Idling around 650rpm or 550 in drive the mixture is around 14.3:1 (ideal is 14.7:1) As this is computer controlled I think it's just right.
Under light load up to 1/2 throttle the mixture is still around 14.3:1. When pushing the throttle the mixture drops a few seconds to 10.5:1 and then backup to 13:1 and then back to 14.3:1.

-I'm thinking about using another acc pump to deliver a small shot to lean out the initial mixture?

When driving in one gear second or third and slowly (around a minute or more) up the rpm range above 3500 rpm the engine begins to hesitate a little and you can see the mixture bouncing from lean to rich and lean again. Further up the rpm range only makes it worse, shifting to the next gear and the hesitation is gone.

- We are thinking the fuel bowl is empty around this time so the engine gets a little fuel. The fuel pump isn't that old. Maybe checking and resetting the float level?

When at WOT.
First a little rich around 10.5:1 after that it goes back to between 12.5:1 and 13.5:1, above 3500 it begins to lean out to 15:1 - 15.5:1.

-First going with a little richer rods would bring the upper rpm A/F ratio up to the disired 12.5:1 to 13.3:1 and after that I can tune the secondary butterfly to get the quickest openingrate without going into a lean condition.

If somebody could also explain what effect changing the secondary hanger has on the mixture then I can also take that into account.
Thanks!

Greetings Peter

[jjr]

 Peter, I can address some of this...

 Idle and main metering systems are under control of the ECM and so
it is driving your air/fuel mixtures based on read only software in the
PROM chip.

 Unless you rewrite those tables the system will keep trying to attain
factory values.

 The system is dependent on accurate TPS values, O2 sensor voltages,
MAP voltages and some systems even had a BARO sensor.

 The TPS in particular generally returns about .5 volts to nearly 5 volts
and the ECM will use this in scheduling. I've seen some TPS sensors
well over a volt in the idle position, and that will shift things a bit.

 Also the oxygen sensor is a limited life part. The original Delco's are
the best, but they can all get lazy then go flatline.

 About 30,000 miles is the best life span for the O2 sensors, and sure
some will perform beyond this.

 I find that today's replacements are NOT consistent, with some becoming
useless in a matter of days.

 I tune the 1981 system cars with the Dwell meter procedures that I showed
in the other thread. But...

 All of that assumes the ECM is getting good data from it's sensors!

 Sorting this out isn't hard, it simply requires the use of a 1981 capable scan
tool. Actually, these aren't very expensive, typically $40 or so on eBay.

 So, I scan the sensors first to ensure the ECM is getting good info, then
use the Dwell meter for tuning.

 Obviously the ECM sends a GO rich command at WOT and doesn't run
the show.

 Does this help?

 Joe

[Peer81]

Hello Joe,

Thank you for the explination but no it doesn't help. It's not your fault but mine! Let me say it like this, i think as we're talking about theoretical knowledge about these systems we are on the same page. I've been working on this car for more then 10 years and know it from bottom to top and inside out. I can almost rebuild the Q-jet blindfolded so to say.
But back to the subject. All the sensory input is fine, the dwell meter shows clearly when the ECM is in open loop and when it goes into closed loop (hunting of the needle). I also setup the carb with the dwell meter for idle control but from that point on I use the wideband oxygen sensor as it is way more acurate. The way the carb is right now about 95% of the people would be very happy with it but I want to get it right so that's why I'm asking this if I'm thinking in the right direction with the changes I'm want to make.

As above 80% or so throttle opening the ECM system goes into WOT condition it doesn't matter what the sensory input is it's just like setting up an old Q-jet and that is what Im asking about. What is the easiest way to setup the carb to get it right in WOT conditions. What do I change first or where to I begin? I know I need to dail-in the primairy side first but I think except for the acc pump it is running fine on the primairies. Then the secondaries, I think the best way to set it up is to first change the rods, then the airvalve spring tension and secondary vacuum pull off and after that the secondary hanger but I don't know if this is correct and what the consequences are when for example I change the hanger has on the A/F ratio and on other parts.
I can also take a few afternoons and test it while changing different parts but this is much easier to get it right.
I hope this helps

btw. I see now I put it in the diagnose section and not the dail in section..   

Greetings Peter

[Cliff Ruggles]

Are the M/C solenoid and upper metering rod height limits at the original settings?

I like to remove the factory plugs and slot the adjustments with a fine hacksaw blade so we can set them externally when custom tuning.

I tap the airhorn for 1/4-20 set screws for easy access to those adjustments. 

For secondary tuning, first you have to make sure that the carb is staying full on hard runs.  In most cases leaning out at high rpm's is insufficient fuel delivery, so no amount of tuning with metering rods or hangers will improve that deal.....Cliff