5.2 magnum options

[vitamindart]

I have changed the wires, and the plugs at separate times with zero change.
I have not checked the rotor Phasing and probably should.

 

[magnummopar]

i dumped the msd box, I have a re-man dist. and the GM 4 pin module ( petronix version ). never thought about it being bad, I have a stock 4 pin module and different dist. I can swap in. I will give all the wires a good look over as well.
maybe I will even just run a temp. hot wire from the battery to the ignition just to rule that out.
Magnum, do you have a suggestion for a cam upgrade in the 318?

Sure, I have lots of upgrades, do you want to use stock springs or go to larger springs. If you use stock springs you will have to keep lift under .475", our stage II spring kit is same as Hughes and will work up to about .550" lift.

GM HEI module could easily be problem. Rotor phasing is more for MSD distributors running FITech FI system or serious racing, not really needed with a street engine. Pull cap and roll engine up to TDC. Rotor should be pretty close to lining up with #1 post, depending on initial timing.

 

[magnummopar]

NEVER EVER pull wires off like this, for a couple of reasons. One is the reflected high voltage pulse can destroy ignition systems.

The second reason is that the fire can "crossfire" and lead you down the wrong path as to what cylinder might be missing

Rather, use a shorting probe to SHORT the voltage on each cylinder. You need two hands, one with the probe and one with insulated pliers. Pull the wire up out of the dist, and as it comes up, insert your grounding probe



A timing light won't tell you squat, especially with MS systems

HAVE YOU checked the wires and the plugs, or changed them?

Also........Google and check ROTOR PHASING

Not wanting to argue, but the spark jumping 1/4" from cap to wire will not hurt anything, if that were the case, you would blow a module if you had a bad wire....If the coil wont put out enough to jump gap, you have a bigger problem. If spark jumps gap, then thats pretty good proof that the module, coil etc are in good shape. What do you think happens when you use a cylinder balance tester? It certainly doesnt absorb the spark, nor direct it to the block...with that said, I would not do it on a modern computer controlled vehicle.

 

[vitamindart]

i am not opposed to changing the springs, I believe these are comp springs for the comp computer cam that is in it currently.

I guess I never suspected the module since it did it with the MSD and now this.
I will look the wiring over again ( supply & ground ) just to rule it out as well.

 

[vitamindart]

ok, thanks to the rain & cold I had a few minutes to mess with the car last night.
I pulled the dist. to install a advance limiter I had and to check it over. I found the roll pin for locking the pickup plate and vacuum advance missing.
this cant be helping the rotor phasing or the ignition in general. so thinking I may have found the problem I buttoned it back up and started it up.
no Dice, still missing same erratic miss as before. I tried to isolate one cylinder by pulling the wires one at a time off the dist. cap. zero difference between cylinders.
now I am really puzzled. compression test was even on all cylinders, pulling the wires doesn't identify any one cylinder. yet the engine has a noticeable shake at idle, you can hear it in the exhaust. I guess next is to pull the push rods and check for bent ones? look for broken valve springs?

 

[magnummopar]

ok, thanks to the rain & cold I had a few minutes to mess with the car last night.
I pulled the dist. to install a advance limiter I had and to check it over. I found the roll pin for locking the pickup plate and vacuum advance missing.
this cant be helping the rotor phasing or the ignition in general. so thinking I may have found the problem I buttoned it back up and started it up.
no Dice, still missing same erratic miss as before. I tried to isolate one cylinder by pulling the wires one at a time off the dist. cap. zero difference between cylinders.
now I am really puzzled. compression test was even on all cylinders, pulling the wires doesn't identify any one cylinder. yet the engine has a noticeable shake at idle, you can hear it in the exhaust. I guess next is to pull the push rods and check for bent ones? look for broken valve springs?

You may have a bent push rod or flat lobe but that would miss on a certain cylinder each time. I have seen people swap 5 & 7 by accident too and it will run ok but not rev. Did you ever get a known good carb?

 

[vitamindart]

I have not tried another carb yet. I will see if I can dig up a points distributor.
want to get this figured out so I can swap at least the cam out for a non-computer controlled version

 

[jos51700]

If your compression is that even across all cylinders, you do not have a mechanical problem.

Get a bottle of Windex, water, other rapidly evaporating non flammable fluid. Allow motor to idle normally until warm but not running temperature. If headers, begin sooner, if manifolds, wait a little. Spray each exhaust individually right at the head a couple times. Watch for how the fluid evaporates.

If the cylinder is running well, that cylinder will boil water/Windex right off, especially with headers. If not, it will be slow to evaporate. On a dead hole, it will still evaporate off but much more slowly. (Even a dead hole generates SOME heat. If it has any compression at all. )
the key is don't do this after a drive, the heat will spread to adjacent cylinders and the compression will heat everything.

This will tell you if it's one cylinder, or a roving issue, regardless of issue.

I suspect it is an ignition issue, as compression is even, a lower intake leak would result in oil consumption, and an upper intake leak would be found as tested.

I'd put in NEW plugs (they're cheap. Don't you be), fresh fuel from a different station than the one you go to for the cheapest smokes (drain the old and give it to your neighbor with the dogs that bark all night. )

If it's single cylinder, you'll know it by this point. If it's a roving issue and new plugs didn't help, install a stock ignition system, which points would be simplest. Reuse nothing. Ytest and follow-up

 

[jbc426]

ok, I put a 5.2 magnum in my 66 valiant. it has a 904 w/a small stall 22-2400.
I have a miss that wont go away. swapped carbs, and the entire ignition system with zero change. it was rebuilt before I got it ( about 8,000 miles ago ). I have a feeling this is why it was pulled. im thinking it has a sticky valve or two.
do I just upgrade to the EQ heads? will porting help the stock lower end?
any suggestions for a cam? it currently has a larger than stock comp computer cam ( not verified )
I am running a 600 holley on a air gap knock off intake and have a set of shorty headers to install when it goes back in.
really just looking for a cruiser with some grunt that we can enjoy. car barely was used last year because of the miss.

THese motors are extremely sensitive to spark plug wire routing. There is even a factory service bulliten for this issue. The motor will miss if you route them wrong.

 

[vitamindart]

pretty sure I have a points distributor I can give a try, swapped the plugs already, I have an 850 demon ( I know its Way to big ) but , I know its a good carb.
going to try these next and see what happens, I have had two sets of wires on it already ( both routed different ways ) one was a stock style magnum replacement.
really want to figure this out so we can enjoy the car.

 

[magnummopar]

If your compression is that even across all cylinders, you do not have a mechanical problem.

Get a bottle of Windex, water, other rapidly evaporating non flammable fluid. Allow motor to idle normally until warm but not running temperature. If headers, begin sooner, if manifolds, wait a little. Spray each exhaust individually right at the head a couple times. Watch for how the fluid evaporates.

If the cylinder is running well, that cylinder will boil water/Windex right off, especially with headers. If not, it will be slow to evaporate. On a dead hole, it will still evaporate off but much more slowly. (Even a dead hole generates SOME heat. If it has any compression at all. )
the key is don't do this after a drive, the heat will spread to adjacent cylinders and the compression will heat everything.

This will tell you if it's one cylinder, or a roving issue, regardless of issue.

I suspect it is an ignition issue, as compression is even, a lower intake leak would result in oil consumption, and an upper intake leak would be found as tested.

I'd put in NEW plugs (they're cheap. Don't you be), fresh fuel from a different station than the one you go to for the cheapest smokes (drain the old and give it to your neighbor with the dogs that bark all night. )

If it's single cylinder, you'll know it by this point. If it's a roving issue and new plugs didn't help, install a stock ignition system, which points would be simplest. Reuse nothing. Ytest and follow-up

A much simpler way is to use a now very common lazer temp probe which will give you an accurate temp reading on each cylinder. They are down below $70 now.

 

[easyrider]

A much simpler way is to use a now very common lazer temp probe which will give you an accurate temp reading on each cylinder. They are down below $70 now.

You said earlier that when you pulled the plugs, it was a little rich. Now you said you have a carb that you know is to big. To me, that sounds like where I would try to correct first. Fuel problems (carb) seem to be much more erratic than ignition problems. Just thinking.