[backyard_ bandit]

i have a 98 GMC 1500 with the 5.7..now my problem is when the truck is under load like heavy aceleration or towing it throws a cylinder 3 misfire code and if i am on the interstate or just driving and i hit about 60 or so it starts to miss and if i go to 65 or higher it straightens out but if i am just driving around and not really getting after it it wont throw the code and runs fine.. now i have changed plugs and wires i have tried different brands i have changed cap and rotors..but still no change i am just kinda running out of ideas on this one so any ideas will help thaks guys..

 

[99'HEARTBEAT]

i have a 98 GMC 1500 with the 5.7..now my problem is when the truck is under load like heavy aceleration or towing it throws a cylinder 3 misfire code and if i am on the interstate or just driving and i hit about 60 or so it starts to miss and if i go to 65 or higher it straightens out but if i am just driving around and not really getting after it it wont throw the code and runs fine.. now i have changed plugs and wires i have tried different brands i have changed cap and rotors..but still no change i am just kinda running out of ideas on this one so any ideas will help thaks guys..

With a Random Misfire Trouble Code.........it may mean that one or more of the following has Happened.....beyond the Plugs and Wires take to look at the following,

• Faulty spark plug or wire
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector
• Burned exhaust valve
• Faulty catalytic converter(s)
• Running out of fuel
• Poor compression
• Defective computer

Also what brand of Plugs are you running with??

 

[backyard_ bandit]

well i am running AC Delco plugs right now but i tried autolight and a couple others..now i didnt know that my truck had coils like i see them on new trucks where would that be on my truck?

 

[judsteele]

that same thing happened to me!!! then my catalytic converter turn into JUNK!!! from all the raw fuel, now it rattles like a bolt fell out in my transmission, need to replace soon. but they are very expensive,so what to do??

 

[Ethan]

Sounds like a bad coil, my truck had a miss in it, and a host of other problems, all caused by a weak ignition coil. If you 98 is anything like my 94(idk) then the coil will be right next to the distributor cap, it'll be that square thing right in front of it. They are like $40 for a high performance one, and are a quick and easy replacement.

If you are getting plenty of power, then it's not a lack of fuel issue.

 

[repairman54]

Same issue in my Yuk. . Massive Seafoam clean out helped a little. My entire secondary igniton system is new, including the distrib. . Only tosses code when trailering uphill WFO throttle. No load it pulls WFO to 90 with no problem, runs smooth as silk, idles like a dream.
After lots of reseach the spider assy in the intake has been trouble some and has been redesigned.
I'm at the point that the spider assy has got to go, OEM has poppet valves at end, new repl style has the injectors at the end as poppet valves are known to stick/leak and be erratic. Just putting $400 for the assy off as long as I can.