The Mystery Truck

Dear Roy, We have a Ford F-250 with a 5.4L engine and automatic transmission. The problem we are having is after it starts warming up as you accelerate between 1,000 and 2,000 rpm, it acts like it is hitting the rev limiter. If you can get it to go over 2,000 rpm, it runs fine. It will sometimes set a code p0340 cam sensor.

Some days it is worse than others. MAF sensor checks OK, and we tried a new cam sensor just for kicks (replaced it with a known good part). The ignition coils check OK, injectors check OK, the crank sensor checks OK and the grounds check OK. Any ideas?

Thanks for what you do.

David Tacoma, M&T Auto Service • Grandville, Mich.

Dear David, The symptoms that you are describing could come from many areas. I have had crankshaft sensors create this condition without throwing a code. I experienced one case where sludge had built up on the sensor reluctor wheel and created an erratic signal. Erratic fuel pressure is also a possibility.

However, my money is on one of those ignition coils creating the problem. I have seen Ford coils cause misfire, surging and false codes and even illuminating the ABS lamp. Place your scan tool in mode 6 and scroll down to view current misfires. Try to simulate the condition and look for a cylinder that is creating a misfire and replace that coil.

Good luck and keep us informed. Roy