 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Coil on Plug Ignition RepairPosted 2/17/2003By Jim Linder Many different system names pop up when discussing the coil on plug (COP) ignition technology. We may be discussing coil on plug, coil near plug (CNP) or even the double ended coil on plug (DECOP). Although terminology may vary by manufacturer, we still use a conventional spark plug and ignite the air fuel mixture just like before. I do agree that all aspects of ignition have improved over the years with the trend being short ramp and fire time, which yields longer plug life in most all cases. So the problem with these new COP systems doesn't seem to be the understanding of the system, as it still fires the cylinder using a spark plug. The problem becomes how does the working technician find and quickly fix the problem when one or more cylinders are misfiring? Now we have some issues to discuss. The advent of the waste spark ignition almost killed all the conventional ignition scopes and many times our old friend - the ignition test console - was pushed into the corner, never to be used again. This unit was replaced in many cases with lab scopes and smaller, handheld units and some manufacturers actually improved their scan tool products to incorporate test procedures for ignition systems. Unfortunately, many haven't upgraded the scope unit to hook up to and/or test these latest COP systems. In many cases, the problem is compounded by a lack of a secondary ignition hookup. This leaves us with only a primary waveform with which to make an analysis. As always, an article of this type is tough to get started and I had originally thought of covering as many vehicles as possible in this one, but after sitting in a COP class session taught by John Thorton, I decided to approach a single vehicle in this article. Other vehicles may be covered in future issues of AutoInc. A typical Ford problem vehicle may have two common concerns:
Thinking coil on plug with a single coil per cylinder, we have some new thoughts as to:
The Car: 2001 Mercury Grand Marquis equipped with a 4.6L engine and COP ignition system. The malfunction indicator lamp (MIL) is on. Misfire can be felt in the service bay. How do we approach this diagnosis? (thoughts) The approach would really be no different than before. We would first confirm the customer's concern. Yes, the engine is misfiring at idle and under load at higher rpms. The MIL is on steady with no flash (we will discuss this later in the article). A few observations are noted while pulling the car into the service bay:
Now, let's discuss some facts about this particular vehicle. Ford V-8s use the high data rate (HDR) of misfire detection and may allow up to a 40 percent misfire at idle prior to considering it a catalyst-damaging misfire. Note: A single cylinder misfire = 12 percent (this will be discussed later in this article). It appears that the A/C is disabled with a single cylinder misfire. We verified this condition after the repair was completed. When a single ignition coil was disconnected, the A/C was in fact disabled! In most cases of ignition misfire, the fuel injector is also turned off or disabled on the misfiring cylinder. Where is the best place to start? (actions) Because the MIL is on and this is an OBD-II equipped, late-model vehicle, the "weapon" of choice is a scan tool. The scan tool I chose was the Ford New Generation Star (NGS) Tester, which is the factory Ford scan tool. As mentioned later in this article, it was the ONLY tool with all of the "bullets!" Our NGS scan tool shows a diagnostic trouble code (DTC) of PO352, which is the ignition coil B circuit malfunction. After consulting the Jendham OBD-II manual, I retrieved the following definition: Ignition coil "B" or No. 2 primary/secondary circuit conditions: Engine running, power control module (PCM) did not receive a valid ignition diagnostic monitor (IDM) signal from the ignition module and/or the PCM was able to identify that coil "B" or No. 2 coil has failed. From this point, we have two very different methods of actual repair:
Being somewhat of a realistic person, let's explore method A: fix the car. Knowing the offending cylinder is in fact cylinder No. 2, let's perform a visual inspection of cylinder No. 2 COP and harness. Assuming everything is fine, let's remove the problem coil and spark plug and replace them both. Next, clear the DTCs and test drive the vehicle. We're done! Now we know, in all honesty, this is the easiest and most profitable fix and in many cases will work just fine. So, why work any harder on this vehicle? The answer is, simply, because we may want to know more. When and if this vehicle comes back (and it may), we will then have the need to look a little deeper into this system. With this in mind, let's explore procedure B: analyze and then fix the car. By going back to the scan tool, we find we have missed or skipped over a couple of functions or clues as to what was really happening with the Code P0352. Looking at the scan data using the Ford "black card," we find no misfire counters showing any degree of misfire and no support other than a specific cylinder code. (General Motors supports and shows misfire rate and specific cylinders.) The answer, at least for now, is to remove the "black card" and use the "red card." Generic or Global functions allow us to look further into what is being reported by the cylinder and recorded by the PCM. Note: Enhanced and Generic data is needed to fix an OBD-II equipped vehicle. We select OBD-II Testing Results and ask for the report on "Non-continuous tests." These test numbers start at 10:01:11 and end at 10:56:00. We are concerned with tests 10:53:01 through 10:53:08 as the J1979 mode $06 DATA reports. This is a misfire report shown on the scanner as the engine misfire occurs. This information can be found under the Ford section on iATN (www.iatn.net). See chart below:
Below is a list of the actual numbers recorded from the NGS scan tool:
From the chart above, we see the last two digits relate to specific cylinder number. In this case, cylinder No. 2 is the only one with a misfire. Referring to the iATN chart, it instructs us to multiply 8202 by 0.000015 to arrive at a percent. Let's do the math: 8202 x 0.00015 = 12.3 percent. Using the conversion, we know that not only do we have a misfire, it figures out to be a 12.3 percent misfire.
Should we now check for spark and coil output? YES, but how would we do this on a COP ignition system? Again, remembering this is a Ford COP system, we know the coil is a two-wire simple circuit with a power in and a negative wire out to the PCM for spark control. This coil is what we call a tapped transformer type of coil. The "secondary tapped to primary" method of winding allows the ignition diagnostic monitor to closely monitor secondary ignition performance and watch primary inductive kick (or flyback voltage as Ford called it in the past). Now having a good idea (knowledge) of how this system is wired and its basic operation, we need to check for spark. This may be done a number of different ways.
Simply remove the COP unit from engine, hook up spark tester and crank or run the engine. A low current clamp may be applied to a main fuse, showing all ignition events at once. A low current probe may also be used at a single coil harness location, showing only a single coil's operation. A quick observation shows this system is Ford's Multi Strike Ignition. This allows multiple ignition strikes below approximately 1800 rpm for cleaner emissions. Throttle must be opened up to a point above 1800 to return system to single strike conventional ignition. Note that the coil achieved approximately 6.5 amps of current (coil buildup) each time in all tests performed. This was an expected result for this system.
On this vehicle we elected to test using the BOB and the COP-III test tool for overall convenience. Now we have seen that although this new COP system seems somewhat different from the systems of the past, we may check spark and analyze waveforms much like we have done in the past. Also note the COP-III tool is shown using two indicator lamps: one for proper signal verification (the green one) and the other showing a good inductive kick at the coil. Using this tool and the breakout box we may quickly check the coil's condition and output for all eight cylinders (especially needed on the trucks). Also, if further evaluation is needed, with the push of the red button we can cancel or kill the spark to each individual cylinder if cylinder balance with gasses or injector flow testing was needed. Should we check for fuel? Sure, we can check for fuel and actual fuel delivery by using the COP-III tool (cylinder balance on a running engine) as above or by using the 4/5 Gas Analyzer in the case of a push in no-start condition as shown in the gas graph. A gas analyzer probe is placed into the tailpipe of this "cranks, but doesn't start" truck. The HC results (over 4,000 ppm) tell us there is plenty of fuel supplied to this engine. What may be considered the most efficient analysis path? Tough question, as many after reading and studying this article will quickly say the "just-fix-the-car" route may be the most efficient path to take. While I don't disagree with this thought, being quick to replace parts and ship the car may not be the best option to use in all cases! My goal here was to show you all the avenues a shop or working technician could take and use whenever considered practical. I have spent years of studying procedure-based vehicle repairs and have found that many things cause this "procedure" to vary. Knowledge of systems, service equipment and time schedules are three that come to mind as problems in many shops. The methods discussed in this article require some special tools and have been tested on Ford coil on plug systems. Read the article many times and apply the tips that work for you. Use the weapon that is needed for each repair!
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Copyright (c) 1996-2009. Automotive Service Association®. All rights reserved.
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
