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Going Back to Basics Fixes Mazda MVP MisfirePosted 6/25/2004By Guy Dibble
Keeping up to date on new vehicles and technology is as difficult as it is important. And it requires me and my trusty scan tool to make occasional visits to the Mazda dealership. During a recent visit - just as I was leaving - I heard the service writer ask one of the techs to take a look at a "Check Engine" light on a 2002 Mazda MVP. He guessed the customer probably left the gas cap loose. I didn't have 15 minutes to let the Worldwide Diagnostic System (WDS) docking station charge up, so I talked the tech into hooking up the New Generation Scantool (NGS). I asked if it was an EVAP code. I learned it was a misfire code, which probably needed a set of plugs. Since it was just a misfire, I decided to leave. A week later, the same dealership tech called and refreshed my memory about the 2002 MVP with the intermittent misfire. The vehicle had 30,000 miles on it so he figured once he did the required service, it would take care of the misfire code. But the car was back again in the shop, and he wasn't able to duplicate the problem during test drives. He wondered if our car-line specialists had come across any common problems for this vehicle. Our IDENTIFIX database did not show any problems for the 2002. When he gave me the freeze-frame data for the code, it indicated that the vehicle was operating at a temperature of 198 degrees, was idling and had a speed of 0 mph. That should be easy enough to duplicate. The tech decided that next, he would check technical service bulletins (TSBs) and called Mazda's tech support line. He told me Mazda recommended replacing the coil pack since they had been seeing problems with coil packs causing misfires and setting codes. The tech promised to stay in touch. Another week passed before he called back. Yes, the Mazda MVP was back again, still setting intermittent misfire codes. Once again, freeze frame data indicated an idle of zero mph and a warm engine. Since this is a Ford-based product with a 2.5 liter Duratech engine, I decided to cross-reference it to Ford to see if any data turned up. No TSBs for misfire codes. Fuel trim was perfect. It did not appear to have a vacuum leak. The entire ignition system, including plug wires and coil pack, had been replaced. What was left? Fuel pressure checked OK. The problem still hadn't been duplicated, so the tech called Mazda's Tech Line again, and they advised installing a set of fuel injectors since there had been reports of fuel injector problems causing misfire codes at idle. Another round of parts. I forget how long it was before I heard the verdict on the fuel injectors, but I didn't forget how frustrated the tech sounded when he called to tell me that didn't fix it. When I asked if he had been able to duplicate the problem, he said it would act up if he drove it really hard, and the engine got really hot and he pulled up to a stop sign running the air conditioning. While it was idling at the stop sign, he could feel a very slight miss and the "Check Engine" light would come on as it picked up the misfire. In this case, it was for cylinder No. 2. It wouldn't set a code if he held the rpms a little higher. After hearing what it took to duplicate the problem and knowing all the parts that had been thrown at the car, I wondered if it was a mechanical problem with the engine. But with only 30,000 miles? It was time to charge up the WDS machine and do a relative compression test. On a fairly warm engine, the results came out good. When the test was run on a hot engine, the No. 2 cylinder had a lower compression than the others. A conventional compression test like we use in the real world also showed that the No. 2 cylinder was about 15 psi lower than the others. In addition, a cylinder leakage test showed a small amount of leakage into the intake. It had been about two weeks since I heard anything more on the MVP, so I assumed it finally had been fixed. When I stopped by the Mazda dealership to pick up some parts, I asked about it. Indeed it had been fixed; in fact, it had a burned intake valve on the No. 2 cylinder. I remember something my Dad always told me as I was growing up in the automotive industry - don't overlook the basics. In this case, the basic tests ended up finding the problem. The old valve had not been turned in for warranty so I took a look at it. It looked like pretty cheap material had been used on those intake valves, so I doubt that this will be the last one of these we see.
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