Intermittent / Weak Spark

[CusTim]

Hi guys. I am looking for some ideas from all you gurus. I am experiencing what seem to be intermittent ignition issues. My Fury III has the 383 HP. Earlier in the year I was having issues with the ignition system (original points system). It left me stranded a couple times (stalled and would no start – sputtering, backfiring, etc.) After replacing all of the points system components I was still having issues. At this point I contacted a reputable local mechanic and decided change over to a Pertronix III. The car ran ok (not great) for a few days after the Pertronix install but eventually started acting up again (not starting, sputtering, backfiring, etc.).

Neither I nor the mechanic could find where the issue was and I decided to change over to an MSD 6AL set up. I had the parts installed by the mechanic due to not having much spare time and not wanting my cruiser stuck in the garage during our short cruising season in Canada. Anyway, the car ran much better after the MSD install. I was sure the problem was solved.

I was mistaken. Although the car ran fine for a few weeks, the issue seems to be back!! The car will run good for the most part but occasionally will miss randomly for a few minutes and then resume running ok. Once in a while it will be hard to start (sputtering / backfiring, etc.). Since the issue is intermittent it is difficult to diagnose. Last night she left me stranded again.

A buddy and I tinkered for a few hours (in the dark on the street). After using a backyard mechanic method of checking for spark on each cylinder (arcing a spark plug wire to the frame from the distributer) it seems that there are 3 cylinders not getting any spark, and the rest of the cylinders are getting weak spark. The 3 “dead” cylinders are all on the passenger side bank(2,4 & 8). I pulled the plugs from the “dead” cylinders and the plugs were badly fowled (plugs were new a month ago) while the plugs from the other side of the engine looked great.

All of the wires / connections were good / tight prior to the car stalling. Car has new MSD distributer, 6AL box, coil, wires, etc. The regulator is new and the resister is bypassed. I am going to spend some time this weekend troubleshooting. Any help / suggestions would be greatly appreciated. Thx in advance.

 

[Yatzee]

Hi guys. I am looking for some ideas from all you gurus. I am experiencing what seem to be intermittent ignition issues. My Fury III has the 383 HP. Earlier in the year I was having issues with the ignition system (original points system). It left me stranded a couple times (stalled and would no start – sputtering, backfiring, etc.) After replacing all of the points system components I was still having issues. At this point I contacted a reputable local mechanic and decided change over to a Pertronix III. The car ran ok (not great) for a few days after the Pertronix install but eventually started acting up again (not starting, sputtering, backfiring, etc.).

Neither I nor the mechanic could find where the issue was and I decided to change over to an MSD 6AL set up. I had the parts installed by the mechanic due to not having much spare time and not wanting my cruiser stuck in the garage during our short cruising season in Canada. Anyway, the car ran much better after the MSD install. I was sure the problem was solved.

I was mistaken. Although the car ran fine for a few weeks, the issue seems to be back!! The car will run good for the most part but occasionally will miss randomly for a few minutes and then resume running ok. Once in a while it will be hard to start (sputtering / backfiring, etc.). Since the issue is intermittent it is difficult to diagnose. Last night she left me stranded again.

A buddy and I tinkered for a few hours (in the dark on the street). After using a backyard mechanic method of checking for spark on each cylinder (arcing a spark plug wire to the frame from the distributer) it seems that there are 3 cylinders not getting any spark, and the rest of the cylinders are getting weak spark. The 3 “dead” cylinders are all on the passenger side bank(2,4 & 8). I pulled the plugs from the “dead” cylinders and the plugs were badly fowled (plugs were new a month ago) while the plugs from the other side of the engine looked great.

All of the wires / connections were good / tight prior to the car stalling. Car has new MSD distributer, 6AL box, coil, wires, etc. The regulator is new and the resister is bypassed. I am going to spend some time this weekend troubleshooting. Any help / suggestions would be greatly appreciated. Thx in advance.

View attachment 140947

First off, I'd put a timing light on it and see if the timing marks are "dancing" or hold steady a various rpm's. If they're all over the place the timing chain is stretched unevenly or shot, you have the wrong combination of drive gear material on the distributor shaft or your timing gears are shot. The drive teeth on the cam may also be damaged. You also have to check all ground connections at the MSD box, and ensure the main power comes directly off the battery. Also check the air gap of the pickup and it's alignment with the reluctor ring.But because this problem has endured both the old and new setup I would suspect there's an issue with the ignition supply voltage.

 

[Knebel]

With a dual plane intake, follow the runners of the cylinders not firing right. See if they are on one side of the carb, it could that the carb is out of adjustment or something other funky, sticky float on one side or something!? I had a similar issue where one bank was constantly fouled but i dont remember what i did to get rid of it

 

[C Body Bob]

Check your grounds. Make sure they are clean, tight & not frayed. THEN go from there

 

[CusTim]

With a dual plane intake, follow the runners of the cylinders not firing right. See if they are on one side of the carb, it could that the carb is out of adjustment or something other funky, sticky float on one side or something!? I had a similar issue where one bank was constantly fouled but i dont remember what i did to get rid of it

With a dual plane intake, follow the runners of the cylinders not firing right. See if they are on one side of the carb, it could that the carb is out of adjustment or something other funky, sticky float on one side or something!? I had a similar issue where one bank was constantly fouled but i dont remember what i did to get rid of it

That's a good point. I haven't really considered a fuel delivery problem. I will look into the carb / intake this weekend as well.

Thanks

 

[CusTim]

Check your grounds. Make sure they are clean, tight & not frayed. THEN go from there

Yes, best to start with the basics. I will check the grounds first. Thx.

 

[CusTim]

First off, I'd put a timing light on it and see if the timing marks are "dancing" or hold steady a various rpm's. If they're all over the place the timing chain is stretched unevenly or shot, you have the wrong combination of drive gear material on the distributor shaft or your timing gears are shot. The drive teeth on the cam may also be damaged. You also have to check all ground connections at the MSD box, and ensure the main power comes directly off the battery. Also check the air gap of the pickup and it's alignment with the reluctor ring.But because this problem has endured both the old and new setup I would suspect there's an issue with the ignition supply voltage.

I am pretty sure the timing is ok. I adjusted it after the MSD install and everything seemed fine at that time, but I will re-check the timing this weekend. The mechanic who installed the MSD said the gears looked fine and I assume he made sure the correct materials were used. I will check to make sure all of the ground connections are tight this weekend. The power to the box is directly from the battery. I also will look into the air gap, alignment and reluctor ring.

I also suspect the ignition supply voltage as a possible cause. Could the problem be in the ignition switch? I did replaced the fusible link from the ignition switch during the first go around with issues but it made no difference. The rest of the wiring seems to be ok, but I will dig around some more.

Thanks for the input

 

[68Nwprt]

I had an intermittent mis-fire caused from ignition wires. I would replace cheap after market spark plug wires with a good performance set.

 

[Davea Lux]

You will want to check your carb floats. The Carter AVS uses a dual float system. The fact that you are fouling one bank of cylinders suggests that the float for that side is mis-adjusted (set too High) or the float is deposit fouled (white or brown crud) or fuel logged due to corroded lead seams on the brass float. This is a common problem with the modern crap oxygenated fuels.

Dave

 

[CusTim]

You will want to check your carb floats. The Carter AVS uses a dual float system. The fact that you are fouling one bank of cylinders suggests that the float for that side is mis-adjusted (set too High) or the float is deposit fouled (white or brown crud) or fuel logged due to corroded lead seams on the brass float. This is a common problem with the modern crap oxygenated fuels.

Dave

I should mention the car has a 600cfm edlebrock. Do you think the floats could still be an issue? I guess they could be - I am going to look into fuel delivery issues as well. The carb is pretty old and could probably use a repair kit. A fuel pressure regulator and gauge have also been on my list for a while but it looks like hey might get bumped up higher on the list now lol. Thanks for the insight.

 

[Davea Lux]

I should mention the car has a 600cfm edlebrock. Do you think the floats could still be an issue? I guess they could be - I am going to look into fuel delivery issues as well. The carb is pretty old and could probably use a repair kit. A fuel pressure regulator and gauge have also been on my list for a while but it looks like hey might get bumped up higher on the list now lol. Thanks for the insight.

The Edelbrock carbs are mostly reproductions of the earlier Carter Carbs (Carter was bought by Edelbrock) so they will still have the two float system, one for the right bank and one for the left. Try starting the car and then shut it off and remove the air cleaner. Look down the carb throat and see if you can see fuel dripping form the air horns or seeping out of the cover gasket. Sure sign you have a float or needle valve issue.

Dave

 

[Davea Lux]

The Edelbrock carbs are mostly reproductions of the earlier Carter Carbs (Carter was bought by Edelbrock) so they will still have the two float system, one for the right bank and one for the left. Try starting the car and then shut it off and remove the air cleaner. Look down the carb throat and see if you can see fuel dripping form the air horns or seeping out of the cover gasket. Sure sign you have a float or needle valve issue.

Dave

If you find you have a float or needle valve issue, I would suggest that you pull the carb off as a unit so none of the small parts get lost. I usually set the whole carb on my kitchen table on top of a newspaper before I tear into it. (Drain the fuel out first) Saves a lot of misery with all those itty bitty parts and my old eyes!

Dave

 

[GregG48203]

the timing chain is stretched

The FSM (Factory Service Manual) should give a specification for timing chain stretch. Also, if you haven't yet, do a compression test.

 

[CusTim]

If you find you have a float or needle valve issue, I would suggest that you pull the carb off as a unit so none of the small parts get lost. I usually set the whole carb on my kitchen table on top of a newspaper before I tear into it. (Drain the fuel out first) Saves a lot of misery with all those itty bitty parts and my old eyes!

Dave

Good point Dave. Thx.

 

[CusTim]

The FSM (Factory Service Manual) should give a specification for timing chain stretch. Also, if you haven't yet, do a compression test.

I am planning on testing the compression tomorrow (gonna remove all the plugs anyway). Is there an easy way to determine the amount of timing chain stretch?

 

[Davea Lux]

I am planning on testing the compression tomorrow (gonna remove all the plugs anyway). Is there an easy way to determine the amount of timing chain stretch?

First, jack up the car enough that you can attach a breaker bar with a socket to the big nut that holds the harmonic balancer on.
Next, rotate the crankshaft until you are at TDC
Remove the distributor cap
Have a helper rotate the crankshaft back and forth until the rotor starts to move.
If there is more than 10-12 degrees of free play between the forward and backwards rotation of the crankshaft, the timing chain is out of spec and should be replaced.
Mopar timing chains usually go out of spec between 80k and 120k in mileage. Use this as a guide. The harder the vehicle is driven, the sooner the chain will fail. Poor upkeep,(Oil changes) also contribute as does severe operating conditions. Lots of short trips etc.
If you opt to replace the timing chain, do not replace it with a stock Mopar plastic coated gear, use an all metal one made in USA. Chinese knock-offs are crap as are the Brazilian ones. DuraLast or Mel Gear are both quality units. You probably do not need to worry about a double roller gear for a stock application as it will take another 100k to wear out an all metal gear system and by them you will need a re-build.

Dave

 

[CusTim]

First, jack up the car enough that you can attach a breaker bar with a socket to the big nut that holds the harmonic balancer on.
Next, rotate the crankshaft until you are at TDC
Remove the distributor cap
Have a helper rotate the crankshaft back and forth until the rotor starts to move.
If there is more than 10-12 degrees of free play between the forward and backwards rotation of the crankshaft, the timing chain is out of spec and should be replaced.
Mopar timing chains usually go out of spec between 80k and 120k in mileage. Use this as a guide. The harder the vehicle is driven, the sooner the chain will fail. Poor upkeep,(Oil changes) also contribute as does severe operating conditions. Lots of short trips etc.
If you opt to replace the timing chain, do not replace it with a stock Mopar plastic coated gear, use an all metal one made in USA. Chinese knock-offs are crap as are the Brazilian ones. DuraLast or Mel Gear are both quality units. You probably do not need to worry about a double roller gear for a stock application as it will take another 100k to wear out an all metal gear system and by them you will need a re-build.

Dave

Interesting. The car has 112k easy miles so it may be due for a new timing chain. I am going to bark up a couple other trees first (voltage supply & fuel delivery) but am definately going to look into this as well. Thanks for the info!

 

[traintech55]

With a firing order of 1, 8, 4, 3, 6, 5, 7, 2 seems like your misfiring cylinders are close in the firing order. Although rare check that the distributor shaft is not bent. Look at the inside of the cap for gouges on the lugs for the other cylinders.
Also look at the bushings for the shaft, they may be worn letting the shaft wobble.

 

[Yatzee]

Hi guys. I am looking for some ideas from all you gurus. I am experiencing what seem to be intermittent ignition issues. My Fury III has the 383 HP. Earlier in the year I was having issues with the ignition system (original points system). It left me stranded a couple times (stalled and would no start – sputtering, backfiring, etc.) After replacing all of the points system components I was still having issues. At this point I contacted a reputable local mechanic and decided change over to a Pertronix III. The car ran ok (not great) for a few days after the Pertronix install but eventually started acting up again (not starting, sputtering, backfiring, etc.).

Neither I nor the mechanic could find where the issue was and I decided to change over to an MSD 6AL set up. I had the parts installed by the mechanic due to not having much spare time and not wanting my cruiser stuck in the garage during our short cruising season in Canada. Anyway, the car ran much better after the MSD install. I was sure the problem was solved.

I was mistaken. Although the car ran fine for a few weeks, the issue seems to be back!! The car will run good for the most part but occasionally will miss randomly for a few minutes and then resume running ok. Once in a while it will be hard to start (sputtering / backfiring, etc.). Since the issue is intermittent it is difficult to diagnose. Last night she left me stranded again.

A buddy and I tinkered for a few hours (in the dark on the street). After using a backyard mechanic method of checking for spark on each cylinder (arcing a spark plug wire to the frame from the distributer) it seems that there are 3 cylinders not getting any spark, and the rest of the cylinders are getting weak spark. The 3 “dead” cylinders are all on the passenger side bank(2,4 & 8). I pulled the plugs from the “dead” cylinders and the plugs were badly fowled (plugs were new a month ago) while the plugs from the other side of the engine looked great.

All of the wires / connections were good / tight prior to the car stalling. Car has new MSD distributer, 6AL box, coil, wires, etc. The regulator is new and the resister is bypassed. I am going to spend some time this weekend troubleshooting. Any help / suggestions would be greatly appreciated. Thx in advance.

View attachment 140947

If you are doubtful of your ignition 12 volt supply I highly recommend a dedicated ignition relay to offload the ignition switch contacts. This is a very inexpensive upgrade and very easy to do. If you end up rebuilding the carb, the best kitt comes from Rock Auto. Do not, under any circumstances trust the cardboard float gauge that comes with the kit. It'll get you in the ballpark but it's not ideal. These carbs are sensitive to float levels and "trial and error" by removing the top of the air horn to reveal the exact fuel level in the bowl is the best way. I installed an MSD distributor once that required the gear to be removed and a brass gear installed. The information to do this came from the cam manufacturer and it can go the other way to. Has to do with premature wear or self destruction.

 

[CusTim]

The FSM (Factory Service Manual) should give a specification for timing chain stretch. Also, if you haven't yet, do a compression test.

I just finished the compression test. Some of the numbers look a little high so I am wondering if I screwed something up?? The only procedure I didn't follow was having the engine at operating temp. (engine currently not running). I'm not sure how a cold engine would affect the results:

Cyl. # PSI
1 158
2 165
3 152
4 168
5 169
6 149
7 152
8 167

I also bought a "spark tester" today and re-checked each plug wire - all wires indicated spark. So I am a little confused. I am thinking of installing new plugs and trying to start the engine (most of the old plugs were fouled). If the engine runs, would I be correct to assume the issue is too much fuel getting to the cylinders??