Help ! Engine issue

[badmix]

1984 K5 305cid 180k.

Engine feels like running on 4 cylinders. Taking off from a stop , there is vibration and lack of power like I'm pushing a wall.

Once up to speed it'll run but not well. At one point of steady driving, I got a "pop" from under hood, like a misfire. It happened 3 times and then stopped doing it. Was going up a slight incline

RPMs are lower at speed too, only running 1700rpm @ 55. Normally I'm at 1900-2000 rpm at these speeds.

I pulled plugs, they all were grayish, so not fouled. Plug wires weren't loose.

Going to do tune up but what else to look for ?

Is it possible for cats to be clogged/bad ? I had to do an hour trip with truck running bad and my eyes were burning from exhaust I believe, but not rotten egg smell

Can vacuum advance or dist. Cause these issues ?

No blue, black or white smoke from tailpipe

Truck cold starts just fine.

Thoughts?

 

[ZooMad75]

I'd look at the cat for being plugged. Original cats suck,to begin with, but I've seen them get worse as they heat up. If you can separate the exhaust from just in front of the cat easy at a flanged connection, I'd try to run it with it open. If the power is back you found the problem. If the power doesn't come back, you've got another problem.

 

[Kain]

does it smell like rotten eggs?

 

[Blue85]

RPMs are lower at speed too, only running 1700rpm @ 55. Normally I'm at 1900-2000 rpm at these speeds.

This is kind of impossible, so interesting to focus on for troubleshooting. If the cat(s) is plugged, it's a basic restriction of airflow, so idle will work, but higher RPM will be super weak. Do you have a vacuum gauge?

 

[badmix]

No vacuum gauge.

Cats are aftermarket catco from 20 years ago.

No eggs smell. No rattles.

 

[Blue85]

When did this vehicle last get plugs/wires/cap/rotor? Any chance some of the wires have touched the manifolds? Do you have a timing light?

 

[badmix]

Plugs/wires/cap & rotor have been done within a year or so..

Am gonna change fuel filter as that hasn't been touched in years

No timing light

 

[Wes Harden]

Run a compression test before you spend $ on tune up stuff

 

[ktmoutfront]

^^^^^^^^^This is what I was going to say.

The lower rpm at speed does not compute.

 

[88Silverado]

^^^^^^^^^This is what I was going to say.

The lower rpm at speed does not compute.

I was thinking the same thing. Only way I can figure that is the ignition (coil??) is misfiring so the feel of running on 4 cylinders is what the ignition is feeding to the tach.
If that made any sense!!

 

[Blue85]

Yes, if the pickup coil or module is bad, the dizzy can fail to create some ignition events, which effects the tach. A timing light can catch a bad wire/plug/rotor/button, while the tach can not. One with low compression will not affect the tach or the timing light.

BTW - 7 ignition events instead of 8 makes 1943RPM read 1700RPM.

 

[badmix]

UPDATE !!

Was cracked ceramic on back plug.

 

[tRustyK5]

Simple is good!

 

[badmix]

Yea. Also found out timing was off, was only pulling 15hg. Advanced timing and at 18 now, didn't want to go too far. Truck much happier now, no bog or flat spots on acceleration