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Old 07-25-2013, 04:35 PM   #1
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2002 Zetec - surge/miss problem


This is my first post here. I've done a lot of reading here, but I'm stumped. Let me tell you this first- I know old cars- carburetors, flat tappet cams, and 3 speed autos- not new stuff- so I'm doing my best here.

My 2002 SE (Zetec) has been well maintained it's whole life. I have 171k miles on it. For the past few years, it would occasionally "miss." It felt like the motor lost power very briefly, then recovered. I mean- like 1-2 cylinders miss, not an entire round. This got worse a year ago. It got to feel like it would actually kick back on itself. Infrequently, no repeatable pattern. I changed plugs, wires, and the coil just as a matter of curiosity. No change.

Yesterday, it decided to get so bad it's hard to drive. It feels like the timing is so advanced it kicks back, but there is no audible knock, no pinging like I'd expect. No DTCs are thrown. And here's the weird part- the speedometer jumps around when this happens now. It can happen at any time, but it's easiest to create under load while accelerating. The speedo will kind of stall out, then jump up and bounce around, or just plain read high for a while. I put the dash in diagnostic mode, and the LCD does the same. The tachometer display does not seem to indicate any issues. At one point, it even fired out the muffler (never heard that before).

Figuring this might be the ECM, I checked my grounds in the engine bay. They seem fine. No issues with plug wires. My only thoughts are

1. Vacuum leak or PCV failure
2. CPS failure?
3. Can the VSS cause this? Does the ECM adjust fueling/timing based on speed?
4. ECM failing.
5. Fuel injectors failing (never replaced)
6. EGR? I don't know. Maybe.

Nothing really explains the whole deal, and whatever happened got dramatically worse in literally 1.5 hours of sitting after my commute. By the way, this is my commuter and I really need to fix it.

Any help or ideas would be greatly appreciated. Thanks for all the existing great information too.

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Old 07-25-2013, 07:57 PM   #2
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Need to barrow a SCT xcal and do some datalogging , could be TPS , front o2 , fuel psi etc etc

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Old 07-29-2013, 11:23 AM   #3
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After driving around with a scanner for a while, I saw nothing out of the ordinary. The only clue I got was that RPMs did in fact waffle when this misfire seemed to happen. It also looked like the ECU really thought it was seeing these weird VSS readings.

I disconnected the VSS and drove the car. No weird VSS readings, so I assumed this meant it was not some sort of electrical shorting/bus issue. So, I was back to ignition issues.

It turned out to be the coil. The epoxy was cracked, and changing the coil had me back on the road quickly. I did the plugs and wires first, because I thought that was more likely. I can only assume that the coil arcing was getting to the VSS or being picked up as EMI.

Hopefully this helps someone else too.
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