Flashing engine light at highway speed

[96cheyene]

I have a 96 Cheyenne with a vortec 350 and have recently done plugs, wires cap and rotor, fuel pump and filter within the last 5,000 miles. When I'm driving around town truck runs fine till I get up to 70mph then it starts misfiring and engine light flashes till I slow down. The code stored is the p0300 random misfire, I can't seem to figure out what could be causing it, truck has almost 180,000 miles on it. Any suggestions would be appreciated

 

[skylark]

Did you have the p0300 before your tune up?

 

[evilunclegrimace]

Check your fuel pressure at speed, see if it is still within specs, hook a scanner up and have some one drive it so you can watch the data steam and see if any thing is out of the norm.

 

[Schurkey]

If the light is flashing, you need to fix this FAST. The light is flashing because something is wrong that is endangering the catalytic converter(s). You're heading for a catalyst meltdown.

Is the code REALLY P0300? Cheap consumer code readers will sometimes output the generic code instead of the specific code. Depending on the scan tool or code reader, you might actually have a cylinder-specific code. What tool are you using?

I'd be testing spark voltage (coil output) using a commercially-available spark tester for HEI ignitions. Fuel pressure as already suggested. I would also check the distributor gear for wear as well as the distributor housing/bushings, and the cam sensor.

 

[96cheyene]

If the light is flashing, you need to fix this FAST. The light is flashing because something is wrong that is endangering the catalytic converter(s). You're heading for a catalyst meltdown.

Is the code REALLY P0300? Cheap consumer code readers will sometimes output the generic code instead of the specific code. Depending on the scan tool or code reader, you might actually have a cylinder-specific code. What tool are you using?

I'd be testing spark voltage (coil output) using a commercially-available spark tester for HEI ignitions. Fuel pressure as already suggested. I would also check the distributor gear for wear as well as the distributor housing/bushings, and the cam sensor.

The light flashes till I slow down to a lower speed then it stays solid

 

[96cheyene]

If the light is flashing, you need to fix this FAST. The light is flashing because something is wrong that is endangering the catalytic converter(s). You're heading for a catalyst meltdown.

Is the code REALLY P0300? Cheap consumer code readers will sometimes output the generic code instead of the specific code. Depending on the scan tool or code reader, you might actually have a cylinder-specific code. What tool are you using?

I'd be testing spark voltage (coil output) using a commercially-available spark tester for HEI ignitions. Fuel pressure as already suggested. I would also check the distributor gear for wear as well as the distributor housing/bushings, and the cam sensor.

I'll get a guy with a scanner to hook up to it and see what it shows, I've got the one from oriellys for $60. You get what you pay for

 

[96cheyene]

Did you have the p0300 before your tune up?

Only when the fuel pump was going out, before that I just had a few codes pop up that were an easy fix

 

[skylark]

Only when the fuel pump was going out, before that I just had a few codes pop up that were an easy fix

That would point me to a new part that has failed. If you still have the old parts then I would swap them back on until the problem goes away. I'm always suspicious of vortec caps so I would start with the cap and rotor.

 

[96cheyene]

That would point me to a new part that has failed. If you still have the old parts then I would swap them back on until the problem goes away. I'm always suspicious of vortec caps so I would start with the cap and rotor.

That's kinda what I'm thinking. I haven't checked the cap and rotor yet, I even went with the more expensive brand for both