HighPressure

Hi!

I mounted yesterday my AEM LSU 4.9 wideband sensor.

I use a E4ME Quadrajet (the computer one) on a L69 from a L69. So its not the small 600 cfm, its the I think 700cfm one? (checked it when I was rebuilding it)

I use DR, K Hangers and Rods.

With DR & K it runs like a charm, but has a little little hole at ~ 3000/3500 rpm where the secondarys open. If I run through all gears the hole where acceleration gets stuck at ~3000 is a little longer.

DR & K =
Idle @ 12.0 - 13.5 (mostly @13.0) | 13.12 = Lambda 0.896
Cruise @ 13.5 - 14.7 (mostly @14.5) | 14.68 = Lambda 1.003
WOT @ 10.3 - 12.0 (mostly @ 11.5) | 11.56 = Lambda 0.790

Gauge info:
10 - 18.50 is the total range
10 - 11 is rich area
17 - 18.50 is lean area

So I guess WOT is too rich, or why is it laging at ~3.500 rpm ?

My vacuum reading is also low, but I guess this is also caused by the cam ? Thats what I read on the board as possible cause, as I dont have vacuum leaks (Cam 208/210@.050, cam lift .299"/.300", LCA 112°)


thanks for suggestions

*edit*
BTW: I´m in Austria / Europe. We run on 95 Octane Gas here, 100 is available but I dont think that this brings any gains or changes in performance with this engine

mlbinseattle

Is that O2 sensor connected to the ECM and gauge or is it a second O2 sensor that you installed and connected straight to the gauge?

HighPressure

It is an additional 2nd sensor.
It has an 1 volt emulation wire for the ecm aswell, but I read on the board, that it brought troubles in some cases.

So I monitor the wideband with the gauge and just checked the heated narrowband for proper function with the computer/aldl cable

mlbinseattle

Yes, the broadband O2 sensor connected to both the gauge and ECM could cause a possible problem because of parallel resistances.

Since the QJ gets feedback from the ECM depending on what the O2 sensor (one connected to the ECM) tells it, have you checked the output of that O2 sensor? A faulty O2 sensor can cause the carb to run rich.

Disconnect the lead and read with a DMM. The output should be .3 - .9 VDC and varying back and forth from one end of the scale to the other. Ensure the engine has warmed up to operating temp.

mlbinseattle

Also, I'd like to add that I don't know what the gauge should show since I've never dealt with that setup. I do know that, if the main O2 sensor, CTS, and ECM are all working properly, then it should be going into closed loop. If the QJ primary is properly tuned, the ECM won't throw any rich or lean codes. I'd ensure all this is properly operating, first. If you've already done this, then someone who is familiar with the wideband sensor and gauge will need to comment.

Damon

A "hole" in the mid RPM range on a QJet can be a bunch of things, but if it's when the secondaries are opening there are 3 things that are the usual culprit. Almost all of them are due to going lean:

1. Too much or too little air valve tension. 3/4 of a turn from the zero tension point should put you in the ballpark.

2. Vacuum dashpot on the pass side/front of the carb acts like a "shock absorber" to slow the opening of the secondary air valves (in combination with spring tension mentioned, above). Too fast you get a noticable stumble. But too slow hurts as well. It won't ever bog, but it will "lay flat" if it opens too slow. A lot of replacement canisters can take as much as 3 full seconds to fully extend! That's just way too slow for a performance application. 1 second or so maximum from fully retracted to fully extended. (Yes, you can bench test this with a hand vacuum pump or just using a vacuum line and your mouth to draw vacuum).

3. The brass secondary-side pull-over enrichment tubes in the airhorn have fallen/vibrated out of the casting. They act as a sort of crude secondary accelerator pump system and the carb will always lay flat upon secondary opening if they aren't installed. If they fell out it will be obvious- they'll be laying inside the carb in the little fuel wells they draw from.

mlbinseattle

I have the exact same secondary metering rods and hanger in mine. However, I'm running a stock cam. IMO, at WOT, it should be going rich, anyway, and since you're using an over-sized cam, it may not be pulling enough vacuum. Yes, you probably need to adjust your secondary air flap spring tension and check your pull-off as Damon suggested.