Autonerdz forums

I'm looking to locate a technician who uses Autonerdz diagnostic equipment to help diagnose an engine problem I'm about 30 miles West/North-West of Boston, MA and would like to find a technician within roughly 50 miles of my location.

The engine problem I'm having is misfiring in the 1.6 Liter engine in my 1983 Mercury LN7 (similar car to Ford EXP). Occurs mostly and probably only under about 2200 RPM.

Every obvious fix has already been tried (rebuilt carburetor, rebuilt distributor, spark plugs including proper gapping, spark wires, ignition coil, ignition module, timing adjusted, various adjustments tried on vacuum advance, new fuel pump, new fuel filters, new timing belt. There are no obvious vacuum leaks (but possibly there could be a hard to find one? who knows?). For other reasons, a brand new cylinder head and camshaft were installed (the head includes all the valves and lifters).

I've even isolated the ignition wiring from the rest of the car's wiring harness by running jumper wires between the ignition module/ground/+12 volts and the ignition coil.

When I installed the new cylinder head & camshaft, I visually inspected the firing chambers including pistons and saw and felt no holes or cracks, but did no checks beyond visual and how it felt to my hand.

This car has had this problem to one degree or another ever since I bought in new at the Lincoln/Mercury dealer in 1983!

My main suspicions are that there is a hard to detect vacuum leak or the fuel mixture is too lean at low rpm or there is a spark delivery problem.

I'd like the technician to first determine if the problem is spark delivery, vacuum leak, fuel delivery, breach of piston or cylinder wall, then continue on from there and further isolate the cause.

I believe the Autonerdz diagnostic scopes will be great for determining if this is a spark delivery problem. I hope it will be able to track all at one time the pulses from the pickup-coil inside the distributor, the pulses from the ignition module, and the high voltage spikes coming out of the secondary of the ignition coil and, if need be, the sparks going to all 4 cylinders.

If the problem is not a spark delivery problem, than I would like the technician to analyze if it is a lean or other fuel delivery problem hopefully with diagnostic equipment that measures the oxygen in the exhaust gas or some other suitable diagnostic equipment.

If all that is not the problem, search for vacuum leaks or anything else I haven't covered that the tech thinks is likely to be the problem.

A good technician will not be able to solve this problem. Neither will a very good technician. It is going to take a great technician!

I forgot to mention that I disabled the egr valve, removing the connection between the egr valve and the exhaust, blocking the port opening between the egr valve and the intake manifold (if I remember right, did this some time ago), and removing a vacuum hose from the egr valve. The car had the missing problem for  years before I disabled the egr and disabling the egr didn't seem to affect the missing.

I can't really tell if only 1 cylinder or more than 1 cylinder is missing. The misses happen very fast and are somewhat intermittent.

When a miss happens, it is easy to hear it and I can feel the car lose power for a fraction of a second and the tachometer dips down and then back up very fast. In maybe a quarter of a second or even less, maybe a tenth of a second, not sure, the tach might fall from, say, 1800 rpm to 1200 rpm and rise back to 1800.

Another thing I didn't mention is that last week I tried high test gasoline. That also made no difference in the misfiring, although the car doesn't ping on a hot day under load anymore with that gas.

Misses definitely will happen between 1500 and 2200 or so rpm, so if that definitely rules out a vacuum leak, thanks for that info, it is one less thing to worry about.

I've also in the past tried changing the timing all over the place and no timing change ever got rid of the misfiring although at times it made the engine run horribly as expected.

I've run out of parts to change and adjustments to make and I'm lost.