Intermittent Random Missfire

[GOBR]

Well I have a random missfire when drivin around and at high rpm's the oil pressure fluctuates. I have good wires and everything on, good plugs, cleaned the cap and rotor. Im leanin towards a bad distributor. Maybe too much play in it? That would cause erratic oil pressure at high rpm? Its not bad, it bounces around from like 60psi to 55psi around 3000-3500 rpms when cruisin at steady rpm. At idle the oil pressure is solid at 42psi when warm. Its only higher rpms. I have no tach so Im guestimating these rpms.

 

[89Suburban]

I had brand new Auto Zone wires on my truck and they were leaking spark. Bought a better set and it cured it. I also get some kind of white sulfur crap on mu dist cap's contacts so I got to pop that off twice a year and knock the **** off with a Dremel and mini wire wheel. That's on a TBI setup. Also could be a sign of the ignition module going out.

Don't know what to say about the high rpm oil pressure. Maybe oil is dropping down due to the high flow? You got the right level in it?

 

[GOBR]

I have the black MSD wires but they have gotten real hot around the boots. Hard to keep em away from the headers. Its like a weird drivin down the road, 1/4 throttle miss. And on decel. Best way I can describe it is the way a cam acts at idle is how it acts with the missfire. It doesnt buck and carry on but I can hear it. Its a real deep "THUMP, THUMP THUMP, THUMPITY THUMP" kinda deal. I have one of those Flamethrower HEI dizzys and I guess stock ignition? Delco plugs, 7 MSD wires and 1 8mm Motorcraft (Ford) I had in my tool box. I replaced it with that cause the other one burnt thru on the header.

As for the oil pressure I think maybe Ill try an extra qt to see if its oil "slosh" goin on at higher rpms. Maybe its not comin back down from up top fast enough and sloshin away from the pickup?

 

[Jims86]

I have the black MSD wires but they have gotten real hot around the boots. Hard to keep em away from the headers. Its like a weird drivin down the road, 1/4 throttle miss. And on decel. Best way I can describe it is the way a cam acts at idle is how it acts with the missfire. It doesnt buck and carry on but I can hear it. Its a real deep "THUMP, THUMP THUMP, THUMPITY THUMP" kinda deal. I have one of those Flamethrower HEI dizzys and I guess stock ignition? Delco plugs, 7 MSD wires and 1 8mm Motorcraft (Ford) I had in my tool box. I replaced it with that cause the other one burnt thru on the header.

As for the oil pressure I think maybe Ill try an extra qt to see if its oil "slosh" goin on at higher rpms. Maybe its not comin back down from up top fast enough and sloshin away from the pickup?

I would check the play on the distributor first, since it is random. You took the TBI off your truck, right?

 

[LowOnGas]

Well I have a random missfire when drivin around and at high rpm's the oil pressure fluctuates. I have good wires and everything on, good plugs, cleaned the cap and rotor. Im leanin towards a bad distributor. Maybe too much play in it? That would cause erratic oil pressure at high rpm? Its not bad, it bounces around from like 60psi to 55psi around 3000-3500 rpms when cruisin at steady rpm. At idle the oil pressure is solid at 42psi when warm. Its only higher rpms. I have no tach so Im guestimating these rpms.

Dang my oil pressure at idle is around 15psi..? makes me nervous..As far as the misfire I had a friend with a similar problem and it ended up being his distributor. We loosened the clamp on it and wiggled it slightly while it was running and were able to make the symptoms appear and go away by pushing/pulling on it. Granted this was on a ford 460 with the distributor in the front which is more convenient for this kind of testing.. We changed coils, wires, regapped plugs several times..took us two days to figure it out..thats my experience

 

[GOBR]

Whoever had it before me converted it over to carb. I got it from somebody who drove it for 2 weeks before it spun a rod bearing. Its a Flamethrower HEI dizzy.

How do I check the play in the dizzy? Take the cap off and pull up and down on the rotor? The cap has 1 hot wire from bat/ign switch and 3 wires from module to cap.

I wish I could just buy a complete MSD setup and be done with it lol. Its the plan anyway. I just dont want it to wash a cylinder out but I honestly dont think its that bad. Its not a miss on the same cylinder constantly. I dont want it to burn a piston up either tho..... Either possible?

What kinda gap should I try with my plugs? Im pretty sure they are gapped for a EFI motor. I am carbed with an XE274 cam. Runnin 87 octane. Not sure on timing. We just brake tq'd and advanced till ping then backed it off slightly. Runs good. Would like to check gaps tho...

 

[Jims86]

Whoever had it before me converted it over to carb. I got it from somebody who drove it for 2 weeks before it spun a rod bearing. Its a Flamethrower HEI dizzy.

How do I check the play in the dizzy? Take the cap off and pull up and down on the rotor? The cap has 1 hot wire from bat/ign switch and 3 wires from module to cap.

I wish I could just buy a complete MSD setup and be done with it lol. Its the plan anyway. I just dont want it to wash a cylinder out but I honestly dont think its that bad. Its not a miss on the same cylinder constantly. I dont want it to burn a piston up either tho..... Either possible?

What kinda gap should I try with my plugs? Im pretty sure they are gapped for a EFI motor. I am carbed with an XE274 cam. Runnin 87 octane. Not sure on timing. We just brake tq'd and advanced till ping then backed it off slightly. Runs good. Would like to check gaps tho...

Check it side to side, back n forth. Stay stock with the ignition.
The anly gaines performance you will get, is with the weight it removes from your wallet. HEI is already a pretty stout setup.

 

[GOBR]

Check it side to side, back n forth. Stay stock with the ignition.
The anly gaines performance you will get, is with the weight it removes from your wallet. HEI is already a pretty stout setup.

Alright, Ill check it in the mornin. Yeah Im just sayin tho if I ever have to buy any new ignition components Ill go ahead and get aftermarket.

What about spark plug gap? .040? .035? Shorter gap save the plugs right?

 

[Jims86]

Alright, Ill check it in the mornin. Yeah Im just sayin tho if I ever have to buy any new ignition components Ill go ahead and get aftermarket.

What about spark plug gap? .040? .035? Shorter gap save the plugs right?

I would go with 0.035 to start.
If you go with aftermarket ignition, make sure you get the kit that comes with the tailgate warmer.

 

[GOBR]

You just gave me an idea lol.................. Only bad thing bout that is my beer would get hot...

 

[Jims86]

You just gave me an idea lol.................. Only bad thing bout that is my beer would get hot...

Buddy of mine made a coil for the low side of his a/c lines....he popped the hood when we were looking at something else, and i asked him what the coil was for. he goes to his cab, starts the truck, a/c on, and sumbitch pulls out a bottle of beer and sets it in the coil.

 

[GOBR]

Buddy of mine made a coil for the low side of his a/c lines....he popped the hood when we were looking at something else, and i asked him what the coil was for. he goes to his cab, starts the truck, a/c on, and sumbitch pulls out a bottle of beer and sets it in the coil.

Innovative lol Another good idea.

 

[GOBR]

So I pulled the plugs. All of em were white with a slight brown tint except for #3. It was all gunked up and had hard black **** stuck to it? WTF is this? Dont tell me the pistons comin apart in there........ Anyway I gapped em to .035 and it didnt stop the miss just made the truck real sluggish. I could def tell a difference. According to this spark plug chart I got the engine wants MORE FUEL? JEEBUS! I can damn near hold my hand under the exhaust then light it on fire afterwards lol.

Could not havin a engine to body ground strap cause this missfire? I just thought about this....... What is the engine grounded to? My battery goes straight to the from then from the frame to body.. Nothin to engine.

 

[Jims86]

Well, this happened all of a sudden, right?
The battery should be grounded to the block or head, and then a ground strap to the frame, and then another from the back of the pass side head, to the firewall, and may 'splain the gauge problem...you can never have too many grounds!

As far as the misfire, if the dizzy checks out ok, I would start looking to the carburetor, and make sure some **** is not clogging it.
Check for vac leaks.
Fill the crank casebwith propane to check for leaks under the manifold...you neednto plug the dipstick tube, the breather hole, and pipemthe propane in through the pcv hole in the valve cover, and listen for a change in idle.
Open up the gap till your happy with it. Maybe do a compression check, at least on that #3 cylinder.
How do 1 and 5 plugs look?
How does it idle?
Got video?

 

[GOBR]

Ive got a video of what the gauge was doin. I said what the hell and added a qt of oil and that fixed that problem. I think it was sloshin around in the pan and lettin the pickup go dry for a moment.

Its mechanical gauges so that wasnt makin it act funny. I heard tho without the engine bein grounded somewhere it could cause a crazy missfire.

Ive got a vid but its hard to tell from the idle cause I have that cam installed. The miss almost went away when I upped the fuel mix on the carb but its still slightly noticeable. Plugs look good now tho. Time to check wires with ohm meter. How many ohms am I suppose to see?