Recently my car developped a problem that no one seems to know how to solve. The car runs great exept when I am cruising between 45 and 70 mph. At those speeds the car has an intermittent miss. It's not a bad miss, just enough to anoy the **** out of me. I have changed the plugs, wires, cap, rotor, pickup coil, checked all vacuum lines, adjusted the valves, checked the fuel pressure, and changed the fuel filter. I have taken it to three mechanics, had diagnostics run, scanned, and had an engine analyzer put on it. No one can find a problem. I removed the egr to see if that was the problem, and that didn't help either. Anyone have any ideas?

 

Sounds like a pain in the ****. I will take a stab at it though. What are your cam specs and fuel pressure set at? Have you upgraded your ignition at all? How are your heads. I have an 86 and every once in awhile it will do the same thing. Mine has a couple of bad valve guides on the passenger side. They let enough oil seep through to temporarily foul out the plugs. I went a couple of steps hotter on the plugs and it solved my problem. I don't know what gears you have, I have 3.23's and stock rims/tires. So at 70 mph I'm only turning a little over 2000RPM and down around 45mph it's even less. If you have set your engine up for more performance you may need to follow suit with your ignition. I'm just wondering if you may be loading up with fuel. I am not even sure if this is possible, but if you have put in a bigger cam, the stage 2 chip, and a 170* thermostat you may be running a little rich. Or your car may not even be coming out of the cold start mode. What's your engine temp at when the miss occurs? I would turn my fuel pressure down a little bit and maybe even swap back in the stock chip just for a test drive to see if that cures it. If it does then I would heat up the igniton and put everything back the way I had it.
Like I said I just thought I would take a shot in the dark. I hope this helps or you find out what's going on.
Good Luck,
Jason

 

The cam is a Crane Powermax emissions legal cam with 204,214 duration and 423,446 lift. The fuel pressure is set at 40 psi. The timing is on 10*. I just changed the plugs from Splitfires to AC42's, and that didn't help. The ignition is stock accept the wires. It has 3.23 gears with stock 16" IROC wheels. It does run cool when driving at those speeds, but it always has. The heads were rebuilt and only have about 8 or 9k miles on them. The chip has been in there since the engine was rebuilt. The problem gradually escalated while I was comming back from a 200 mile trip about a month ago. I didn't change anything that could have caused it, the problem arose itself.