tach rpm/not running right

[skyknight789990]

ok i have a l20b in my 79 620 have had this problem before it comes an goes dono what it is or whats making it happen last night my truck was running fine this morning going to work doing 60 steady at just over 4000 rpms then it starts jumping all the way from 4-6000 rpms but i am going the same speed an the motor is still just over 4000 rpms but sputters an has lose of power if i let off the gas the rpms drop to what they really are then i have full power again but not for long... also when i come to a stop it will die an when it dose idle its not steady its from 750-900 rpms sometimes will die can anyone help me with this problem thanks Damon

[datzenmike]

Loose wire at tach or at the dizzy.

[Boaty]

What distributor are you running?

 

Electronic? Single-Points? Dual-Points?

 

If you're running an electronic dizzy, make sure all the connections are in good shape, and make sure the distributor itself has a good ground.

For the sake of testing it out, take some gator clips and ground the distributor case. If it's a matchbox (late L-engine) distributor, make sure the

matchbox itself has a good connection to the distributor base. The back side can get corroded and cause issues.

 

If it's a points distributor, check the points and make sure they are gapped correctly (.017-.021, memory serves.). If it's a dual-points setup,

somebody else will have to chime in, as I've never had any hands-on with a dual-points dizzy. Always ran single-points til I upgraded to a matchbox.

 

You may also buy a new condensor. They are cheap, and can cause odd issues. Replace it anyways, just because it's cheap and eliminates a possibility.

 

As for the tach wire, believe it should be hooked up to the (-) negative post on the ignition coil. Make sure this wire isn't corroded and has a good connection.

 

 

If none of the above fixes or changes anything, you might try another coil to rule out a coil going bad. If it's leaking at all, replace it.

I used an Accel Super-Stock (Electonic Ignition) coil, without a ballast for the last 3 years of my L-motor escapades. Coil fixed a lot of 'comfort' problems,

specifically my bad miss at higher RPM's. Ran a LOT smoother.

 

Hope this helps!

 

[EDIT - make sure your cap & rotor are in good shape, too. Doesn't hurt to check wires and plugs while you're at it.]

[zerow]

Mine did the same thing, tracked down a loose wire from the + terminal to the rest of the harness (mine was at the fusible link wire to battery terminal). Locked it down with a new connector and the tach was right on target.

 

Clean your + terminal for a better connection too...

[skyknight789990]

What distributor are you running?

 

Electronic? Single-Points? Dual-Points?

 

If you're running an electronic dizzy, make sure all the connections are in good shape, and make sure the distributor itself has a good ground.

For the sake of testing it out, take some gator clips and ground the distributor case. If it's a matchbox (late L-engine) distributor, make sure the

matchbox itself has a good connection to the distributor base. The back side can get corroded and cause issues.

 

If it's a points distributor, check the points and make sure they are gapped correctly (.017-.021, memory serves.). If it's a dual-points setup,

somebody else will have to chime in, as I've never had any hands-on with a dual-points dizzy. Always ran single-points til I upgraded to a matchbox.

 

You may also buy a new condensor. They are cheap, and can cause odd issues. Replace it anyways, just because it's cheap and eliminates a possibility.

 

As for the tach wire, believe it should be hooked up to the (-) negative post on the ignition coil. Make sure this wire isn't corroded and has a good connection.

 

 

If none of the above fixes or changes anything, you might try another coil to rule out a coil going bad. If it's leaking at all, replace it.

I used an Accel Super-Stock (Electonic Ignition) coil, without a ballast for the last 3 years of my L-motor escapades. Coil fixed a lot of 'comfort' problems,

specifically my bad miss at higher RPM's. Ran a LOT smoother.

 

Hope this helps!

 

[EDIT - make sure your cap & rotor are in good shape, too. Doesn't hurt to check wires and plugs while you're at it.]

 

cap an rotor are maybe 5 months old i have a mallory supper coil the first time this happend i thought it was the tach i hooked up a second one an same thing but ill check the connections its electronic

[Boaty]

Still say try another coil. I went through an MSD Blaster 2 and a new Standard Motor Product's OE coil, before the Accel coil. The Accel fixed my woes... worst it can do is not fix the problem, slap an OE on really quicklike and see how it runs.

[flatcat19]

Punctuation will make your truck issues easier to decipher.

 

:P

[skyknight789990]

Still say try another coil. I went through an MSD Blaster 2 and a new Standard Motor Product's OE coil, before the Accel coil. The Accel fixed my woes... worst it can do is not fix the problem, slap an OE on really quicklike and see how it runs.

 

i dont really have the money to get another coil but last i went back to my moms an took sand paper to the connections on the dizzy an tried to clean the inside of the plug the best i could it runs killer now

[Boaty]

Righteous! I like hearing that.

 

One of the BEST things I've EVER done was vinegar bath the fuse box (510), go through all the terminals, hit them with QD cleaner, replace those that were screwed, and ran a fatty ground cable to the strut tower from (-) on the battery.

I reterminated all the connections for the coil with rings instead of the little spade fitments. Then, nothing can wiggle off, and it's uber hard for it to corrode.

[skyknight789990]

Righteous! I like hearing that.

 

One of the BEST things I've EVER done was vinegar bath the fuse box (510), go through all the terminals, hit them with QD cleaner, replace those that were screwed, and ran a fatty ground cable to the strut tower from (-) on the battery.

I reterminated all the connections for the coil with rings instead of the little spade fitments. Then, nothing can wiggle off, and it's uber hard for it to corrode.

 

hmm i might do that to i have a ton of ring connectors been wanting to clean up the wiring under the dash to