Halltech

We have received a few emails regarding leakage around the MAF sensor tower on our new Killer Bee II plastic intake bridge. The MAF tower is now integrated into the bridge, and our initial 20 or so units last year that went out had screw size #8 X 1/2" for the two screw holes that clamp the MAF to the tower.



Our tower has a recess rectangular O-Ring receiver for the stock o-ring which completely seals off MAF to any leakage. We initially recommended using the stock screws, but they have proven to be inadequate due to the larger size of the hole in the bridge.

After working with two customers with idle issues, and one lean code, we found that the fix was to send #10 sheet metal stainless steel screws with each unit, which have much more clamping force to adequately seal the o-ring.

If you have these larger screws we recommend you use them in place of the stock screws. The other key to this is using the Viton rubber washers on the reverse side of the MAF to keep the MAF alignment accurate. Both have been shipped with all systems over the past two months.

If you cannot find these screws and washers we can mail you a set.
This is what the screw looks like. Part number 91675A353:


email debbie@halltechsystems.com for a set of both.

0Myhardtop

Jim,

Good job on stepping up and sharing with the vette community.

Thanks,
Carlos

TARANTULA

I have the #10 screws on mine but no Viton rubber washers. Do you have a picture of them?

Halltech

They fit tighter in a #8. The purpose is to provide a positive stop for the aluminum tabs on the sides of the MAF meter shown above. You are ok without them, but it makes a complete sealed package this way. The holes do not go through anyway, so no vacuum leak will occur without them.

Knowles's Z06

How about CF version...same issue or no issue?

THX

Halltech

Completely different system. It uses threaded stainless inserts.

Zero issues with the Carbon version.

Knowles's Z06

THX...mine went in great...and looks Great

HP ADDICT

How do you check for leaks. I have the new bolts but mine still seams to hunt around at idle alot more then it used to before then intake.

Halltech

As long as the screws are tight, there will be no leak. If you had even a pinhole leak, there would be a lean code pop. No codes, your car is running perfect trims.

We had a GM Tech here in Wisconsin test our KB II on his personal Z06 for a month now. The Long Term Fuel Trim averages settle around +3 to +5% on his factory stock 2007 Z06. His data logging shows very stable short term fuel trims, but as with all GM computer settings the stoichiometric value for E10 is incorrect in the ECM.

All GM products are factory set to 14.7:1 stoichiometric in closed loop. That is the chemically correct burn (all O2 and gas are burned in the combustion chamber) for E0 (no ethanol) fuel only, not E10.

In most of the states now, the fuel oxidizer MTBE (Methyl tert-butyl ether) has been banned from all fuels here in the USA due to the ground water poisoning issue. The replacement for the oxidizer is grain ethanol. All states as far as I know now run E10 (up to 10% ethanol) in all of the gasoline or gasohol fuels. Guess what? Your Non-Flex Fuel Corvette cannot reconcile the Long Term Fuel Trims averages, EVER since the stoichiometric value is incorrect.

The EPA is happy that there is more O2 in the burn than necessary, since a lean burn promotes clean air, increases fuel mileage with very little downside, or so they think. When too much O2 is left over in the burn, the Cats overheat, and guess what GM has to keep them cool. COTP safety protocol has been around since the early 2000, which has three fuel enrichment thresholds which monitor the cat temps and add tons of fuel at a specific cat temp. When does this occur? Try a dyno room at around 90F, and a very hot motor. Then take off the stock intake and add one that is less restrictive with around 20% more air-flow, and you have a recipe for 9.9:1 air fuel ratios from the COTP circuit kicking in. All hopes of evaluating the gains from the intake are shattered due to this intervention of fuel. Now if this happens on the road on a very hot day and aggressive driving, you might smell the sulfur from the cats, but not for long. 9.8:1 a/f ratio pukes raw fuel into the atmosphere, which is the exact opposite of the EPA goal.

The correct burn for E10 is between 14:1 and 14.1:1, not 14.7:1. Having additional non metered, and irreconcilable O2 levels at the O2 sensors all the time, make your car just another EPA special.

Here is how closed loop works. The factory stoichiometric value, or lambda 1.00 set in the ECM is a static value that the adaptive closed loop system strives to reconcile at all times during closed loop operation. On the Z06 closed loop is MAP, rpm, and throttle position dependent. The MAF meter estimates the volume of O2 by mass, and communicates that value to the ECM, which in turn adds the estimated fuel for the metered air. If the estimate is off (like a leak after the MAF sensor) then the estimated value is corrected by the rear guard, or O2 sensors. The delta between the estimated MAF values and actual O2 at the O2 sensors, is instantly changed by adding or deleting fuel, reflected by the Short Term Fuel Trims. The Long Term Fuel Trim averages shows each of the cell's adaptive value over a few miles of driving. When one cell hits 25% added fuel, a lean code pops in that bank, or sometimes both banks. That simply means that the estimated airflow is underestimating 25% of the actual O2 showing up in the burn.

When you are driving under 49% throttle position, the O2 sensors are in the loop, commanding the ECM, in each of the 15 or more fuel cells, to either add pulse width (more fuel) or deleting pulse width (deleting fuel) to keep the Lambda 1.00 preset value. Once you pass 49% throttle position under 3,000 rpm, the ECM snaps out of closed loop, and into open loop (sometimes referred to as WOT), but you do not have to be at WOT to be in open loop. At 4500 rpm, for instance, 25% TP will put you in OL.

Open loop is the commanded fuel enrichment table which adds fuel to help stave off pre-ignition, or worse, detonation. The factory preset for OL at full tilt is around 11.55:1, or Very Very rich. This is the area most tuners go after to bring out more power by running .85 lambda to .89 lambda instead of .76 to .78 factory settings. Timing has to be carefully logged on the dyno to assure that KR is not present, or the leaner air fuel mix, might be too lean for conditions. Older Z06s, will likely not be candidates for lean OL tuning, since carbon deposits over time create hot spots and the problem of detonation follows.

Since Lambda 1.00 for E10 is 14.1:1, and the computer is allowing 14.7:1 levels of O2 to enter the combustion chamber, or more than it can burn, the leftover O2 causes surging, and erratic idle issues, and keeps your car running on the lean side all the time.

Flex Fuel vehicles have a 60 second window in which the ECM reevaluates the short term fuel trims on each fuel fill up to determine the amount of O2 in the fuel. E85, for instance carries up the 35% more oxygen in the ethanol part of the fuel, thus the stoichiometric (Lambda 1.00) is 9.7:1. This is why you cannot just fuel up with E85 and have a go of it without destroying your motor. The entire ECM has to be programmed for the specific fuel as I have done on our Z06.

When we tune vehicles, the E10 stoichiometric value table is changed to the proper burn for this fuel, which increases throttle response and torque, and keeps the short term fuel trims more stable, and long term fuel trims on the mark.

Our Killer Bee II was designed to mimic the exact MAF area scaler read zone, so no additional trimming or MAF recalibration is necessary. Getting a tune by someone who really understands the fuel issues and timing curves will definitely help bring out even more power than the 15/14 found on the Katech Engine dyno.

Hope this helps.

Jim Hall