Surging Stallion

Troubleshooting Always Evolves

Any person who has worked in or around the field of automotive service and repair knows that a technician without a personal library of fact-finding and problem-solving skills is prone to continual frustration and possible failure.  The best and most capable technicians are the ones that are willing to tangle with the tough-to-find concerns and hang in there tooth and nail until they unravel the mystery and win the fight. These techs must be willing to exhaust everything the TSB’s and hotline engineers have to offer and go it out alone until they eventually slay the dragon.   In a word, good technicians must have real experience with unusual problems, along with the smarts to go beyond the obvious when looking for the answers.  And we all know tough problems will inevitably come to a serious technician. The difference is made with the right attitude, necessary aptitude, and downright grit, and those factors usually determine who will prevail and who will fail.

Some concerns naturally lead to a particular troubleshooting practice, and each tech generally has his or her own way of finding the cause of a particular concern.  We’re all familiar with just how fast the world of automotive service is changing.  Last month’s 6.0L Power Stroke situation is a good example of how necessary it is to develop new techniques.

When multi-point fuel injection became the order of the day on so many engine platforms of the early eighties, we had to come up with new procedures in order to pinpoint the new problems that came with that particular change.  Almost overnight (it seemed) we moved from dealing with old fashioned carburetor concerns to the point where we were struggling with high pressure fuel pump failures, dirty injector nozzles, and octane-absorbing carbon/olefin deposits on intake valves.

Complex electronics infiltrated transmissions, suspension, steering, and braking systems. Simple electrical systems evolved into a maze of modules and multiplexing, and a technician without a scan tool and a multimeter could be compared to a soldier without weapons. Developing an understanding of the strengths and weaknesses of new technology in the field has become as necessary as understanding the basics of how the technology operates.


 Aggravating EGR

One of the most problem-causing subsystems on emission-friendly engines has been the EGR system.  Some smaller powerplants have been able to satisfy NOx emissions standards without recirculating exhaust gas; for example, some of the old 2.9L and 3.0L Ford V6’s were produced without EGR systems.  GM went to electronically operated EGR valves years ago, but problems with carbon clogging can still produce driveability concerns and MIL lights.  The earliest EGR concerns were related to stalling and surging.

This month’s title concern outlines an aggravating surge at road speed that would totally evaporate with the EGR disabled.  The Mustang was nearly new, with a little more than 11,000 miles showing, and the surge was instantly noticeable.  The standard troubleshooting technique for a surge is one of the simplest; disable the EGR and resume the test drive.  Re-enabling the EGR and studying the scan tool, we studied the EGR system PIDs.

With a vacuum operated EGR system like the one on this Mustang, EGR activity varies with engine load and vacuum availability; this DPFEGR reading might be higher or lower depending on throttle angle and load. 4.0L SOHC Explorers actually have a vacuum reservoir for the EGR system. This EGR flow reading didn’t seem excessive enough to cause a surging problem, and since the DPFE sensor was a new one, we discarded the idea that the signal was inaccurate. Exhaust is, however, inert, and can cause misfires if the spark is weak or forced to fire abnormally.

The EGR system on this vehicle is basically the same system Ford has used since 1991.  The three-wire feedback sensor (DPFE) is a pressure-sensitive device that measures a differential on each side of a fixed orifice in the EGR exhaust supply tube.  At rest, the DPFE voltage signal will rest at about 1 volt on the newest units (0.60 on the older ones).  The EGR valve itself is vacuum operated by the PCM through an electrical solenoid called an EGR Vacuum Regulator (EVR).  By monitoring the duty cycle of the EVR and the corresponding feedback signal from the DPFE, we hoped to gain an understanding of why the vehicle was surging.  An improper feedback signal could have been the root cause, but in this case, it wasn’t.   EGR should be totally inactive at idle and at Wide Open Throttle, and one anomaly we noticed was that the PCM indicated that it was commanding a 44 percent duty cycle with the engine idling, in spite of the fact that the engine idled smoothly (EGR will usually stall an engine if it’s flowing at idle).  Replacing the PCM removed the confusing duty cycle concern, but the surge was still present.  Removing the foam filter from the EVR (it sometimes clogs and can cause excessive EGR) made no difference.

“Donnie,” I said, as we were returning from a test drive, “remember how the old 3.8 liter engines would develop a surge that could be cured by disabling the EGR?  Remember how sometimes the spark plugs would be loaded with puffy brown oil consumption deposits from the valve stem seals?  The problem was the spark plugs, not the EGR.”

Since EGR feeds inert gas back into the mix, a cylinder with a weak spark due to spark plug problems might fire just fine without EGR.

Fueled and Fouled by Additives

My brother once owned a beautiful silver 1971 Thunderbird that really liked high octane gas.  In order to save money, he started buying regular gas and pouring octane booster into the fuel tank at each fillup.  After about three tanks of this vile concoction, the 429 ran like a sick joke, and when I pulled the plugs, they were coated with a fine layer of strange red dust that was playing havoc with the spark.  A new set of plugs and a fresh tank of gasoline reawakened the 375 horses in that tough old engine. My brother never used octane booster again.

Removing the spark plugs from this 4.6 Mustang GT revealed two obvious problems.  One problem was the same type of fine red dust I had seen on my brother’s plugs, and the other was that the spark had found an alternate path to ground by firing from the center electrode across the ceramic to the side of the spark plug shell.  Heavy carbon tracking was evident, actually having painted the ceramic around the center electrode a glossy black; these strange little sparks would light the mix unless EGR was flowing, but adding inert exhaust gas would cause multiple misfires and an EGR-related surge.

This fine red oxidation wouldn’t seem to have any effect on the firing of a spark plug, but it does, and I’ve only seen it in vehicles where fuel additives are used in excess. In this case, the spark was forced to find a path to ground in another direction. Notice the glossy black ceramic insulators around the center electrodes on the two left hand spark plugs in the group photo. Carbon tracking on the insulator around the center electrode is evident in this detail shot of the first spark plug that was removed. The spark was lighting the mix as long as no EGR was present, but adding recirculated exhaust gas to the cylinders produced annoying random misfires. Eliminating the EGR fooled us into thinking the EGR was the problem when actually it was only magnifying a concern that was, in effect, unnoticeable when EGR wasn’t flowing. Any deposit that weakens the spark of a particular plug can cause a surge/skip that EGR may magnify.

The tried and true troubleshooting procedure of disabling EGR usually points to an EGR problem, but not in this case.  It turns out that the owner was an elderly man who had added at least one bottle of injector cleaner to his fuel on his last fill up. Whether or not he had been using it on several tanks like my brother did is possible, but unknown.

Don’t misinterpret what I’m saying here; not all injector cleaners are bad, but the manufacturer of this particular injector cleaning additive apparently added some octane booster to the product in hopes that the customer would feel an immediate difference in the way the vehicle ran, and any additive, no matter how good, can be overused.  By the time Donnie drew the work order, the plugs had been coated with red stuff, and the surging condition had taken hold.  A new set of spark plugs and a Keep Alive Memory (KAM) reset produced a smooth test drive that was extremely satisfying.

Another Problem

While we’re here, let’s have a look at a couple other vehicles.

A 2001 5.4L F150 with 58,000 miles on the clock came in with an intermittent misfire.  This isn’t an unusual concern; I saw two vehicles with this same problem on different cylinders in one day, and while the coil-on-plug ignition coils and their boots are frequently at fault, it isn’t always healthy to toss a coil in the hole and put the truck outside.  What is a good idea is to replace the boots whenever you do a tune up on a Ford COP system.

Using the WDS (Worldwide Diagnostic System) Power Balance screen to pinpoint the misfire (if no misfire code is present and you can access Mode 6 data on your scan tool, a misfiring cylinder can be found that way), I removed the #7 hardware and inspected the coil itself along with the boot.  While the coil is potted, it doesn’t take much water to destroy it, but I didn’t see any sign of water on the coil or problems with the boot, and there was nothing visibly wrong with the spark plug.

This is the IDS Power Balance screen, which tracks rpm changes between cylinders at virtually any engine speed. Even one misfire at high speed will make a gray track like the one you see here. This particular vehicle was misfiring on cylinder number 1.

But when I measured the resistance of the center electrode, I got a reading of only 200 ohms.  The spark plug was practically shorted internally, which may have damaged the coil, as strange as that may sound.  A new spark plug measured 3500 ohms; Ford’s specs call for less than 10,000, but the blue oval guys give few guidelines beyond than that.  I’ve actually repaired intermittent misfires by replacing plugs that measured infinite resistance through the center electrode.

While one spark plug engineer sent an e-mail criticizing the practice of measuring spark plug resistance, one CD base Ford training program includes this practice in diagnosing misfires. Most spark plugs will have from 3,000 to 9,000 ohms. I’ve repaired intermittent misfires by replacing plugs that measure infinite resistance. While it seems like the spark could bridge internal spark plug resistance, it may be that the spark has burned away enough material and created enough spark-resisting residue inside the spark plug to create more of a problem that simple air gap type resistance. In this case, the spark plug wasn’t open, it was more nearly shorted; a new plug like this one measured 3,500 ohms, and while the intermittent misfire on this cylinder wasn’t as severe after the spark plug was replaced, it took a replacement ignition coil to finish eradicating this misfire.

(I once got a nasty e-mail from an engineer who worked in a spark plug manufacturer’s lab after mentioning the fact that I check spark plugs this way, but with a Coil-on Plug system, most shops don’t have a way to scope the ignition system and measuring the resistance of the plug is a good test.)  In this case, a new plug and a new coil worked just fine.

And One More…

Near the end of my tenure this week at the dealer, I was handed a “hurry up” work order on a new truck with only 28 miles. It was a 2003 Super Crew (4 full size doors), with an inoperative Rear Entertainment System (ceiling-mounted television.)   This unit has a VCR mounted in the console (most units have a DVD integral with the ceiling mounted unit), and on this one the TV was as dead as a hammer and the truck was already sold. The console-mounted VCR was wide awake and operating, but no audio from the inserted videotape was coming from the speakers, and the rear audio control panel, while it was illuminated, couldn’t be activated by pressing the 3 and 5 preset buttons on the radio, and was completely unresponsive.

Researching the wiring and pinpoint tests in the shop manual, I removed four screws and dropped the TV assembly loose from the ceiling.  I found that the TV assembly has only four wires leading to it.  One wire is 12 volt power, another wire is ground, the third wire comes from the VCR and the fourth wire comes from the rear control panel.  Ford Audio systems with multiple control panels or remotely mounted receivers have a circuit called “ASYSON” (Audio System On), which is a single wire that activates remote modules and control panels as soon as the driver turns on the radio.

The TV display panel had good power and ground feeds as well as good continuity to the VCR connector and the control panel.  Removing the radio and measuring the continuity of the ASYSON wire, we found it open somewhere between the radio and the rear control panel.  The control panel never received a signal thus never knew it was supposed to wake up and go to work.

Searching for the open ASYSON circuit became quite an adventure.  With the console ripped out, and the pins and circuits checked, we discovered that our ASYSON wire had an open circuit somewhere between the radio and the console.  This was a late-breaking problem, almost unsupported by existing shop manual info. All but the very newest editions of the shop manual had incorrect connector shapes and pinouts for this system, making the whole process something of an egg hunt.

This square C275 connector can be found behind the right hand kick panel. After we measured an open ASYSON (Audio System On) circuit between the radio and the rear control panel in the console, we went on an Easter Egg hunt for this connector, since the early release version of the shop manual didn’t have it properly located. Straightening the bent male pins and reseating the female pin that had been pushed back, we were able to reassemble the unit and watch a few minutes of video on the TV.

The problem surfaced when we finally managed to track the ASYSON circuit to the next connector on the map, a square plug over behind the kick panel where we found a pushed back female terminal and some bent pins in the mating shell.  It took a fine pair of needlenose pliers to straighten the pins, but when we reassembled the connector, re-mounted the ceiling unit, pushed PLAY on the VCR to test the system, we were able to watch John Travolta having his face removed on the flat screen TV.

Not For Lazy Wimps

The days when high school administrators automatically send low-achieving students to auto mechanics class should be fading fast.   What today’s auto repair industry desperately needs is some of the brightest and best that our schools have to offer, not recalcitrant troublemakers who don’t want to obey the rules and do their work.  ASE tests are getting tougher and more necessary.  Today’s auto technicians need to be clear-thinking, hard-working problem-solvers committed to the highest standards in automotive service excellence and achievement.   A half-hearted tech just can’t be expected get the job done.


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