engine miss
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Junior User
Joined: Sep 2000
Posts: 78
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From: Sonora
engine miss
Hey guys I really need your help. I have this posted on all the other related boards with no luck and I know I can always find the answers here.
My buddy's truck runs fine until you turn on a heavy electrical load (headlights,heater,etc.), then it begins to miss BADLY. It will idle fine with the lights-etc. on, it only misses when the engine is under load (while driving). Could this be a bad coil or something more sinister?
I need to help him get back on the road soon. Please help!!! TIA Bill
My buddy's truck runs fine until you turn on a heavy electrical load (headlights,heater,etc.), then it begins to miss BADLY. It will idle fine with the lights-etc. on, it only misses when the engine is under load (while driving). Could this be a bad coil or something more sinister?
I need to help him get back on the road soon. Please help!!! TIA Bill 
Senior User
Joined: Oct 2001
Posts: 222
Likes: 0
From: Las Cruces USA
engine miss
Need a little more info:
What year is the truck?
What engine?
Does it have electronic ignition (like Duraspark) or points?
Is the battery holding a charge (alternator working OK)?
There are several things that can cause such a problem, such as a bad coil (as you mentioned, tho not that often), a bad connection creating a high-resistance situation (can't draw enough battery juice when load increases), a weak electroni ignition module, and others.
With a high-resistance situation, the alternator can, in many cases, still keep the battery charged because most of the driving is done during the daylight hours.
Does the miss go away if (and as soon as) the lights or heater is turned off?
Given your description, my first effort would be to check the battery cables for corrosion. A prime suspect is the battery ground (where the cable bolts to the engine. If it is an original FE, it probably is on the exhaust manifold, which is highly prone to rust due to the high operating temps. I always move mine to the intake manifold bolt next to the thermostat housing. I clamp it to the inner fender and route it above and behind the alternator, so that it won't get into the alternator fan.
Just some thoughts.
Eddie
Bad! Bad! Electrics
What year is the truck?
What engine?
Does it have electronic ignition (like Duraspark) or points?
Is the battery holding a charge (alternator working OK)?
There are several things that can cause such a problem, such as a bad coil (as you mentioned, tho not that often), a bad connection creating a high-resistance situation (can't draw enough battery juice when load increases), a weak electroni ignition module, and others.
With a high-resistance situation, the alternator can, in many cases, still keep the battery charged because most of the driving is done during the daylight hours.
Does the miss go away if (and as soon as) the lights or heater is turned off?
Given your description, my first effort would be to check the battery cables for corrosion. A prime suspect is the battery ground (where the cable bolts to the engine. If it is an original FE, it probably is on the exhaust manifold, which is highly prone to rust due to the high operating temps. I always move mine to the intake manifold bolt next to the thermostat housing. I clamp it to the inner fender and route it above and behind the alternator, so that it won't get into the alternator fan.
Just some thoughts.
Eddie
Bad! Bad! Electrics
