Help missing at idle

[CodeeB]

My truck is misfiring and running rough at idle, but when you rev it it runs fine. If you drive it it has good power. I was even able to climb a small hill in it today in 2wd ( I couldn't resist ) . I have changed the ignition module and spark plugs, Bosh Platinums ( I changed them before the spark plug post ). How do I check the wires ( MSD wires). I plan on changing the rotor button and cap tomorrow. Help I' m trying to clear this up before I leave for Tellico Friday. I have a 302 with dura spark B. C. Q-jet with and Edelbrock manifold. Changing the timing didn't help.Thanks

 

[Jeepster]

pull the wires one at a time to see if the miss stops.

 

[jims66]

[quote author=jeepster link=board=5;threadid=17862;start=0#msg136609 date=1053999308]
pull the wires one at a time to see if the miss stops.
[/quote]
I think what Jeepster means is pull the wires one at a time listening for a change. When you pull the wire off of a plug that DOES NOT make a change that is the one that is the dead hole. Then you can begin looking for a cause, plug, wire etc. If they all seem to make about the same difference look for something that they all have in common. Vacuum leak, carb adjustment, coil etc...

Jim

 

[74bronc]

I would start with the platinums. get yourself a set of el-cheapo autolites and throw them in there and see what happens. Just a hunch!

 

[75_Bronco]

hey man this may sound dumb, but i would double check that the plugs were gapped correctly... i did my own tune up and didnt gap my plugs just right and it was missing hardcore.... just a suggestion, gap the plugs according to the manual and then run the timing light and make sure its hitting the mark pretty dead on... good luck
Paul<><

 

[Rustytruck]

Here's where I would start. Put a hose on the vacuum can of the Distrubuter and suck on it to see if there is a vacuum leak. if there is a leak it needs to be fixed first if there is no leak then try this to check your system. Take an Ohm meter and do a resistance check on the wires set the resistance on your meter to get a reading and not just go to 0.00 Longer wires will have a greater resistance than shorter wires. no reading through the wire is a bad wire as is a wire with a reading greater than double your smallest wire. A reading of zeros just means you have conductivity through the wire same as shorting the test leads together set your meter higher up the scale or you have solid copper wires?. A bad wire will be obivious. Platium plugs suck get autolights. Are you gapping your plugs to .045 to as much as .055? the Duraspark need the wider gap and not the points setting of .032. If all of this checks out and the cap and rotor are good then i would check for a mis set carb. first pull a small vacuum line hooked directly to the manifold and create a small vacuum leak and see if the miss goes away or the rpms pick up at Idle. if it does then the carb needs eithor a float adjustment or the mixture screws reset as it is running too rich. if it runs worse then you are leaning it out and that is good so hook the hose back up. Now check if it is running too lean at Idle. Take a propane torch and without lighting it while the engine is idleing leak a very small amount of propane down the carb this will add fuel to the mixture and either make it drop rpm's if too rich like it should or raise rpm's if too lean. if it raises rpm's check carefully for vacuum leaks and a miss set carb. This is all easier if you have a vacuum gauge hooked up as any changes for the better raises the vacuum level and is a more sencitive way of checking these problems out.

 

[CodeeB]

Thanks Rusty Truck for explaining the procedures so well . I hope I can get running well enough for Tellico, I leave on Friday AM.
Cody

 

[Yellow75]

Just another thing to try but I was running rough as well. I pulled the carb apart while it was still on the truck. It's an edelbrock btw... they pretty much split in half. Once apart I hosed everything down with carb cleaner blowing out the jets and the idle air bleeds. The air bleeds were a bit clogged. Put it back together and it runs like a champ now.