Coil/Cap Swap - Now Low Power

[Charles B Schiele]

Hey guys - I've been struggling with understanding how to troubleshoot this.

Last week my truck suddenly wouldn't start. 77 K10, 350, HEI. Gas good, I really suspected ignition. Because I was going to do it anyway, I just bought a replacement cap/rotor/coil/ignition control, and swapped it out.

Parts: Echlin (NAPA) all around

Truck fired right up! Problem solved! But the power is super low. I took it all out, inspected electrical connections and such, and put it back in again. I even got out my timing gun to check that - not so far off as to cause this massive drop in power. It will hardly even shift into second. It does drive, however, and idle smoothly. Feels like what I'd think "low spark" would feel like. But I don't know.

Normally I'd suspect a coil, or try a different one at least. But this one is brand new! Curious if this situation seems obvious to someone else.

Thanks!

 

[Arkansas_V8]

Check fuel pressure. Could just be coincidental that fuel pump took a dump at the same time.

I also have an idle fuse in mine. Caused close to the same issue.

 

[1987 GMC Jimmy]

Get the probe end of an old test lamp, a screwdriver, etc., have someone turn the key for you, and hover it over one of the cap pins. If you’ve got a yellowish spark, your suspicions are correct. If you have a white spark, then I’d still get your timing light and check the base timing and total timing to make sure the advance is doing what it’s supposed to. I’d check for arcing at the plug wires because you may just be running on seven cylinders, but this is best done at night. I doubt you mixed up the order on two of the cylinders since it is running smoothly, but give it a glance anyway.

 

[Red Rex]

Check your battery post and cables for corrosion. I have seen them where they would run a starter just fine but not produce enough to fire the plugs

 

[Johnny Mac]

so where is the timing actually at?

very likely that something could be bad out of the box. probably even more likely a fuel pump is weakening.