6.8 V-10 stalls and dies when slowing down

SERVICE BULLETIN

RE: Ford 6.8L E-series cutaway bus chassis with PennTex charging systems.

Bulletin date: Sept. 3, 2010 Information and Bulletins

Service Issue: 6.8L V-10 stalling out at idle or when decelerating to a stop with PX-5 alternator.

Ford E-series Throttle Body replacements that include a new Throttle Position Sensor may cure a drivability problem, but on vehicles with a PennTex heavy-duty high amperage alternator already installed a new problem may occur that makes the throttle body change seem ineffective.

Background:

There are two styles of throttle position sensors: Potentiometer and Hall-effect. Ford has been using a potentiometer style TPS sensor in the E-series until recently when they changed to a Hall-effect style, which determines throttle plate angle by sensing the rotary angle of a small internal permanent magnet.

The old style triangular-shaped potentiometer TPS is immune to magnetic fields. A rectangular-shaped Hall-effect TPS can be affected by external magnetic fields unless it is properly shielded. Alternators always produce magnetic fields when energized and if a heavy-duty high amperage alternator like a PennTex is mounted close to a rectangular-shaped Hall-effect TPS, the sensor will pick up the magnetic field the alternator is producing.

This interference problem initially started occurring in 2010 Ford E-series Super Duty van chassis with the 6.8L gas engine and a new PennTex alternator install. However, it will also occur on an earlier model year Ford 6.8L gas engine chassis that's had a recent throttle-body replacement.

The new throttle-body comes with a magnetic-style Hall-effect TPS. A vehicle drivability problem in the older vehicle may have been corrected by replacing the throttle-body. But, because of the alternator magnetic interference with the new unshielded magnetic TPS, the drivability problem is now changed to "dies at idle or when decelerating to a stop".

Replacing one rectangular magnetic TPS with another rectangular magnetic TPS won't change anything.

Diagnosis:

If a new vehicle with a Penntex charging system (or an older vehicle with a new sensor replacement) is stalling out at idle or when decelerating to a stop, disable the PennTex alternator from charging by disconnecting the regulator harness plug from the regulator (for info click here.) If the vehicle will run properly after disabling the charging system, this can confirm that the magnetic interference is causing the problem. (This assumes that no other drivability problems exist at the time of the test.)

Solution:

TPS sensors on new 2010-up vehicles with a PX-5-Series alternator will need a magnetic shield applied. PennTex has a TPS Sensor Shield available that covers the Hall-effect style TPS and protects it from the alternator magnetic field: Part Number PX-7010. Older vehicles can either use an older potentiometer-style TPS sensor or also use the PX-7010 TPS Sensor Shield. The shield is designed for the rectangular-style TPS only, as the triangular-style TPS isn't affected by magnetic interference. The PX-7010 Shield kit is available from PennTex Distributors by clicking here.

Note: Ford had discontinued sales of the older style TPS sensor, but as a result of this issue, they were making a service replacement for the older vehicles. We've since found that this part number may be either style of TPS so this page doesn't list the part number any more to avoid confusion. The most reliable fix is the PX-7010 Shield kit.

If the replacement TPS is spring-loaded it's the older style potentiometer TPS that's immune to interference. If the inside portion that fits on the throttle shaft just spins freely, it's the magnetic style that requires the PX-7010 Sensor Shield.

PX-7010 Sensor Shield information with PennTex and Ford Bulletins