Sell your truck while it's still running...
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| Yes, I know that I've used this image before. |
There's a lot of practical, real life advice in Country songs. I've repeated this bit of wisdom before, and I've consistently ignored it. At my peril!
Oh no, my Mustang just displayed the flashing check engine light!
The CEL or MIL light is usually an indicator of an emissions system related problem. These situations usually don't result in a major loss of drive ability.
In this case I had been noticing some problems while running. The engine seemed a little hesitant to spin up to higher revs, it sort of flattened out and felt a bit soggy. There was was also a slight shudder. I attributed it to a lack of use and hoped that it would go away on it's own as I started to use the car more.
Hope springs eternal, but it just got worse. I was leaving for a long trip of over a hundred and twenty miles when the car felt quite a bit worse and the CEL lit and started flashing. I was only a couple of miles away, not even to the freeway so I turned around and brought it back home. I took my truck instead.
I felt a little surprised and I'll even admit it, a bit betrayed, my Mustang has always been my no drama machine.
Emotions aside, I had to figure what the problem was and fix it.
I really had been considering selling the car only a few weeks ago!
I borrowed a code reader from my Son so that I could obtain any possible trouble code.
The first thing that I did was to take a careful look under the hood to see if I had disturbed any vacuum lines or wires when I removed the battery. I couldn't find anything noticeable, so I hooked up the code reader. The only code that was displayed was P0304, a misfire on cylinder #4. With this info I could concentrate on the problem cylinder.
It's time for more diagnostics. Of course it couldn't be as simple as a plug wire terminal coming loose, that just doesn't happen like in the old days. Modern plug wires have clip on terminals at the coil, and the plug boots are very long and buried several inches into the motor. Back in the old days, the plug boots were tiny and hanging out in the open, and would frequently loosen and fall off the side of the cylinder head.
The last time I saw a flashing CEL was because I failed to dry out the plug wells after the manifold leaked coolant. Drying out the well cleared that up.
Once I determined that the terminal caps were in place and I found no coolant in the #4 plug well., I thought that I would pull the plug to examine it. That's a bit of work so I began looking for a simpler course of action. I started thinking about what could cause the problem.
Trying to proceed in a logical methodical manner, I laid out what I knew.
The plug wire terminals are secure.
There is no coolant present in the well.
I had replaced both coils less than two years ago, Could the coil have failed? I had kept the old coils which were still working when I replaced them. I pulled the new coil and replaced it with the old unit. No improvement.
The plug wires had been replaced a couple of years before the plugs, that would be around four years ago. Could they have gone bad in that short a time?
I pulled the plug and found that it was dry, clean, with a white electrode. It didn't look like it was fouled and misfiring. These had been changed out the same time as the coils.
Back in the old days of carburetor equipped engines, a misfire usually meant that the spark was missing or intermittent. This usually resulted in a wet, gas fouled, spark plug.
Now, a misfire can result from a problem with the injector, if there's a lack of fuel, that also results in a misfire.
So, how can you tell if the injector is working? A working injector makes a steady clicking sound as it opens and shuts during operation. You can hold a long screw driver against the body of the injector while the engine is running and put your ear to the handle to amplify the sound. The result?
Number four was clicking away and after listening to the other seven they all sounded the same to me. This doesn't mean that it is working correctly, but it's obviously working somewhat.
I have found it be useful if I keep a written account of what I'm doing. I will start by listing the problem, then possible factors that I should check. Then I record the results of each action. It helps to keep my thinking organized and I can scan the sheet and quickly review my progress.
I will also record possible shops that might be helpful in my efforts, for example I listed a shop (including the address and phone number) that can clean and inspect injectors. I'll list the cost of replacement parts from RockAuto as a guide to the possible expense of the repair.
All well and good, but where do I find myself right now?
The component that I had not checked was the condition of the plug wire. They are a bit older than the plugs and coils, They might be around four years old. I am always very careful with their routing, and they are much better secured on this modern engine. Besides any obvious visual damage such as corroded or dirty terminals, cracks or burns, I know that it is important to check their resistance. That can be done with a multimeter. I'd never done this, so I watched a couple of videos to learn how to do that.
Besides a given range of values, the obvious thing is to see how much variation there is between the individual wires. The range that was given on the video was 5-8 thousand ohms per foot, the longer wires will have more resistance. It turns out that the #4 cylinder has the longest wire.
The #4 wire had a value of 12,750 ohms of resistance. I checked the #5 and #6 wires and they were 7,20 and 7,25, almost half the measured resistance. Is this going to be the problem? Do wires suddenly go bad on their own? Should I just replace the wire set? Maybe I should check all the wires before I do a compression check.
It's easy to just throw parts (and money) at a problem, but that isn't always the best course. Lot's of times a guy will just replace parts without testing them to determine if they are faulty. This is partly because the guy is a DIY guy with a pretty good understanding of what could be wrong, but he doesn't have the equipment or expertise to make a systematic or "scientific" diagnosis. He also doesn't want to take his car to a shop where he will have to pay for a diagnosis as well as the repair. He usually saves money by doing his own work. So he wings it. The problem is that randomly changing parts doesn't always fix the problem, though it often does. So I could just replace the wires and hope that will fix it.
I think that I might remove the #4 plug wire and recheck it as well as measure the length to be more accurate. But I might have another option. I have a timing light gathering dust in my tool locker. It is a better unit with an inductive clamp that I place on the plug wire. I remember the cheap old neon timing lights that had to be plugged into the plug terminal, those were so dim and a pain to use! If the wire is conducting the charge it will flash. With modern engines there's no need to set timing any more, but this might tell me something important.
I dug the timing light out of my tool locker where it's been sitting for many years. I hooked up the timing light to the #4 wire and ran the engine. There was a steady flashing light. I tried it on a few other wires and saw what looked like identical flashes. That indicates to me that it is working okay.
On Monday morning I called Ace fuel systems, they had once rebuilt the carb for my '66 Riviera and had done a terrific job. The shop informed me that it doesn't clean the injectors. They referred me to a shop in Campbell. All Auto and Truck. I phoned and they told me cleaning and inspection is 25.00 each. usually a day or two to get done. That sounded okay, but I will price out the cost of new injectors at my local Winchester Auto.
At the parts store I spoke with several countermen who have dealt with me over many years. The cost of their Echlin injectors was 81.00 each, or as a rail set of four for a slight discount.They asked me what the problem was, and I described what I had found. They told me that if the plug looked good and the injector had been determined to be working, then it was time for a compression test. If it wasn't the spark or malfunctioning injector, it was time to look for mechanical problems.
This was not what I wanted to consider, as it did not bode well for the future of my Mustang. If there is a burnt valve or bad piston it might mean that it might not be worth repairing. However worrisome it seems, the next step is do the compression test. I need to know the facts before I proceed forward with any plans. One halting step at a time.
Keep calm and carry on!
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