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What is causing this intermittant ignition miss?

Jessie James

Jessie James

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My 1991 K5 has a weird problem. Some times when I am driving it, everything is fine. It has a perfectly smooth idle, plenty of power, and doesn't miss at all. I park the truck, do whatever, then come back and start it and now it has a really bad miss, loss of power, and a very rough idle. It's so bad I swear it's going to die.

The next time I start it there is a 50-50 chance things will be good or bad.

I have replaced many common tune-up parts, like car/rotor, plugs, wires, injectors, FPR, etc.

So, what's the part that is failing? :dunno:
 
ignition module sh*ttin the bed..... at some point, it just wont start...

AC Delco replacement only imo...
 
Ignition modules can act up intermittently as Ryoken said..I prefer oem ones over any other aftermarket or no-name brand...some have no dwell advance circuit or use cheap components that fail quickly,usually at a bad time..

Also a failing ignition coil can cause intermittent missing--if it has a crack in the insulation over the secondary windings, the spark can jump to ground there,instead of firing the plugs..often a coil only acts up when it is "hot" or the engine is fully warmed up--if there is a break in the secondary windings it can run perfectly at times and act up intermittently too...a failing pick up coil can cause the same thing too,if your truck uses one..
 
How does the injector spray pattern look when doing this?

I've yet to hear anyone with any other injection problem have the same issue I did, but mine would run fine when started cold, once warmed up it would randomly not restart. Long story short, turned out multiple injectors were bad. Can't recall if the thing would ever idle poorly though.

Luckily with TBI anything along those lines is easy to rule out, since you can physically check the injection/pattern to make sure it's decent.

Doubt anything along those lines is the issue for you, but for free, don't see why it shouldn't be checked.
 
ryoken said:
ignition module sh*ttin the bed..... at some point, it just wont start...

AC Delco replacement only imo...
Click to expand...
That is what I was thinking, thank you for the confirmation.

diesel4me said:
Also a failing ignition coil can cause intermittent missing--if it has a crack in the insulation over the secondary windings, the spark can jump to ground there,instead of firing the plugs..often a coil only acts up when it is "hot" or the engine is fully warmed up--if there is a break in the secondary windings it can run perfectly at times and act up intermittently too...a failing pick up coil can cause the same thing too,if your truck uses one..
Click to expand...
I am not sure if I have a pick-up coil. But this problem happens hot or cold.

dyeager535 said:
How does the injector spray pattern look when doing this?
Click to expand...
They were replaced only a few thousand miles ago with new (not rebuilt) ones, so I think they are probably okay.

Thanks for all the help guys. I found an OEM ignition module on Amazon for $43 instead of the $80 my local shop wants for it! :D
 
Jessie James said:
That is what I was thinking, thank you for the confirmation.


I am not sure if I have a pick-up coil. But this problem happens hot or cold.


They were replaced only a few thousand miles ago with new (not rebuilt) ones, so I think they are probably okay.

Thanks for all the help guys. I found an OEM ignition module on Amazon for $43 instead of the $80 my local shop wants for it! :D
Click to expand...

Make sure it is a Delco brand module.
 
Actually I pulled the part number from AutoZone first, then serached Amazon. :)
 
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