HotWheelsBurban
Gotta have 4 doors..... Rawhide, TOTY 2023!
At least on a van, you can get to the back of the engine without standing on your head!
Good ol' Random Multiple Misfire
- Thread starter 323kielr
- Start date
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Jeepwalker
I'm Awesome
Under the cap is an ozone-rich envornment (from the sparking) which causes corrosion. Caps aren't what they used to be either.
Yeah, I would definitely look into the O2 sensor and get that straightened out before digging too deep into other things.
On the scanner, what are you using now? Is it just a code reader? How much can you stand to invest? What other vehicles might you scan...or work on? Do you do all your own maintenance? Do you mind using your phone or tablet? (iPhone or Android?). I've heard people say a lot of good things about Torque-Pro app. Then you need an obd port dongle to connect it. Lot of guys like the OBDLink MX Plus [Here]. These phone apps are getting ever more powerful. Then there are Launch scanners which do a ton, almost as much as Snap-on scanners ...if you go up the scale a few hundred bucks. Snap-on's are great but cost prohibitive to upgrade for the home user. The better scanners allow ya to do bi-directional things and Launch scanners have that.
But the reality, IMO, good basic troubleshooting and internet scanning is a very powerful troubleshooting tool. Add to that a basic scanner that gives real-time readings...is all you really need. A super-fancy scanner isn't the end-all be-all they once were. Not with some of the good phone apps out now. Or a handheld Launch Scanner. Scanners help see things but you still need to find the problem. If your current scanner isn't giving you real-time readings then yeah, a tool that can give you that is going to be a step up. But in truth you can get that by back-probing sensors and/or using a vacuum/pressure gauge. But a scanner or phone software which gives you real-time readings is probably all you need. ...What are the sensor voltages, pressures, etc.
Yeah, I would definitely look into the O2 sensor and get that straightened out before digging too deep into other things.
On the scanner, what are you using now? Is it just a code reader? How much can you stand to invest? What other vehicles might you scan...or work on? Do you do all your own maintenance? Do you mind using your phone or tablet? (iPhone or Android?). I've heard people say a lot of good things about Torque-Pro app. Then you need an obd port dongle to connect it. Lot of guys like the OBDLink MX Plus [Here]. These phone apps are getting ever more powerful. Then there are Launch scanners which do a ton, almost as much as Snap-on scanners ...if you go up the scale a few hundred bucks. Snap-on's are great but cost prohibitive to upgrade for the home user. The better scanners allow ya to do bi-directional things and Launch scanners have that.
But the reality, IMO, good basic troubleshooting and internet scanning is a very powerful troubleshooting tool. Add to that a basic scanner that gives real-time readings...is all you really need. A super-fancy scanner isn't the end-all be-all they once were. Not with some of the good phone apps out now. Or a handheld Launch Scanner. Scanners help see things but you still need to find the problem. If your current scanner isn't giving you real-time readings then yeah, a tool that can give you that is going to be a step up. But in truth you can get that by back-probing sensors and/or using a vacuum/pressure gauge. But a scanner or phone software which gives you real-time readings is probably all you need. ...What are the sensor voltages, pressures, etc.
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L31MaxExpress
I'm Awesome
My distributor is vacuum vented. No ozone/moisture corrosion creating environment. My failures have never been corrosion at all. It is the plastic breaking down and burning through. This is the way the last MSD cap and rotor failed as well as just about ebery other cap/rotor I have had on this van. It was about 5 years old at the time of failure making it pre China made junk they make now. I think a big point of failure on this design is the fact that the rotor phasing moves up to 27° off its centerline as the timing varies between -10° and 44° advance as the engine runs throughout various rpm points. As the timing increases the gap increases, thus the voltage requirement and heat also increase. I have considered bringing the CMR well above spec, disabling the P1345 code and adjusting the injector timing to compensate for the cam synchronization point change. If I went to say 15° on the CMR, that would roughly center the rotor phasing with the midpoint of the timing range. That would align the rotor with the terminals at approximately 30° spark advance, which coincides with the highest cylinder pressure and voltage requirement at WOT. I would probably have to advance the distributor a tooth to get the range to do that given the limited rotation possible before the cap terminals hit the intake manifold.
When this happened the engine stalled with a massive backfire from the exhaust. It happened at midnight on a city street. Lets just say the police response was about 2 minutes in my hometown. I tow strapped it the 3 blocks to the house.
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323kielr
Newbie
Hi all,
It is FIXED!
I feel like a fool, but it runs great after swapping the cap and rotor. This cap and rotor are only 2 years old, WOW I guess the do wear out fast.
I did most of my diagnostic in the dark of a NAPA parking lot, so I did not see how bad it really was. Well that and I am used to working on a junky old 71 that seems to run no matter the condition of the distributor, or anything else really.
Thanks again for the help. I did what I had to do and kept driving to get my family home, do you think there is any lasting damage to the engine from driving WOT for 1,200 miles with low spark?
I will certainly be changing the oil, and I may throw in a new set of plugs... AGAIN.
Also take a look at the wicked pitting on cylinder 6 in the picture below. I discovered this with the heads off, must have sat with coolant in it for a while. Still runs great. Compression is nearly 150 all the way around minus cylinder 6 with is at 110 (YIKES) but I will keep it going as long as I can, then I am thinking it deserves a crate motor 383 from Blueprint.
Thanks again fellas,
-Zeke
It is FIXED!
I feel like a fool, but it runs great after swapping the cap and rotor. This cap and rotor are only 2 years old, WOW I guess the do wear out fast.
I did most of my diagnostic in the dark of a NAPA parking lot, so I did not see how bad it really was. Well that and I am used to working on a junky old 71 that seems to run no matter the condition of the distributor, or anything else really.
Thanks again for the help. I did what I had to do and kept driving to get my family home, do you think there is any lasting damage to the engine from driving WOT for 1,200 miles with low spark?
I will certainly be changing the oil, and I may throw in a new set of plugs... AGAIN.
Also take a look at the wicked pitting on cylinder 6 in the picture below. I discovered this with the heads off, must have sat with coolant in it for a while. Still runs great. Compression is nearly 150 all the way around minus cylinder 6 with is at 110 (YIKES) but I will keep it going as long as I can, then I am thinking it deserves a crate motor 383 from Blueprint.
Thanks again fellas,
-Zeke
Attachments
L31MaxExpress
I'm Awesome
I have seen worse run ok. Might re-adjust the rocker arms on that cylinder, if they are even slightest bit too tight in that cylinder compression will suffer.
No easy way to tell if any lasting damage happened, but if it sounds ok, it is probably ok.
I feel a 383 is awesome, but then again if you are not towing a new stock 350 will get you down the road engine wise for many years and the stock 350 is no slouch. Put an emissions legal set of shorty headers, the magnaflow replacement cats, magnaflow muffler and a Volant air intake on it to pep it up a bit. The SBC Vortecs make good power when you open up their breathing a bit.
No easy way to tell if any lasting damage happened, but if it sounds ok, it is probably ok.
I feel a 383 is awesome, but then again if you are not towing a new stock 350 will get you down the road engine wise for many years and the stock 350 is no slouch. Put an emissions legal set of shorty headers, the magnaflow replacement cats, magnaflow muffler and a Volant air intake on it to pep it up a bit. The SBC Vortecs make good power when you open up their breathing a bit.
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Hello 323kielr,
Would you happen to have taken a photo of the underneath of the replaced rotor?
I remember being fooled by a taking a quick glance of the top side of a rotor
on a misfiring SBC, and it looked good. But on the underneath it was obvious where the
sparks had blown through and made an easier path to ground than the spark
plug electrodes. (NOTE: The whole path between the coil > center of the cap > rotor
{center to end} is stressed 8x as hard (or 8x as often) because all sparks go through this path.)
Like @L31MaxExpress' 2nd photo showing the spark blow-through on the underside of his cap:
NOTE: The reason I ask is that I checked the photo of your cap & didn't see anything obvious?
If it was mine, I would seriously consider doing the following in order to make sure I get the
most I can out of the existing motor:
1) At the very least I would 2nd what @L31MaxExpress said about resetting the lash
on the weak (#6) cylinder. Actually, I'd remove the valve covers, wrap the upper half of
the rocker arms with aluminum foil (to minimize the mess from the oil squirters) and
set/verify *all* of the rockers at a slow hot idle. (You know, loosen slowly until tick tick tick,
then tighten *just* until it quiets, move to the next, repeat 15 more times.) Shut off
the engine, and *then* set the preload on all 16 to your personal preference. (1/4 turn,
1/2 turn, etc.)
I've done this many times, and most of the time all the preloads were similar. But sometimes,
I would find 1 or 2 that were set way deeper than the others. (Sometimes during
initial assembly the lifter(s) that didn't really pump up are hard to set correctly cold.
Seen this several times over the years.)
IMPORTANT CROSS CHECK: Here's some valuable data that you can glean from checking
the thread count above the rocker arm nuts after setting the hot lash like this. In a
perfect world, let's say that ALL 16 rocker arm nuts have (4) threads showing above
the nut. Perfect! But in Road Trip's world, I may have 14 rocker arm nuts showing
4 threads, the 15th rocker arm nut showing 2 threads above, and the 16th rocker
arm nut showing 6 threads above? What can we infer from this?
* 14 cam lobe / lifter / pushrod / rocker arm / valve / valve seat assemblies either no wear,
or similar wear. No worries.
* 1 rocker arm nut with only 2 threads showing? Think of wear that takes up valvetrain clearance?
That's right, think of a wearing exhaust valve seat and/or burnt exhaust valve
receding into the head, thereby making the valve stem tip move UP?
* 1 rocker arm nut with 6 threads showing? Think of wear that creates extra valvetrain clearance?
Think of a cam lobe that's starting to go away - we've seen those disappearing lobe pics
many times. (!)
Of course, this check by itself is only of limited value. BUT if you happened to have verified/photo'd/logged
that all the valvetrain was set to the same number of threads above all 16 nuts when you replaced
the heads a couple of years ago, well *now* we have something to compare today's observations
against.
You know, it takes longer to describe all this than to do it. It's just a cross-check, but I
have resorted to resetting the hydraulic lifter preload with a hot lash adjustment on a problem SBC,
and if I'm able to clear up the issue AND all 16 rockers now match up, height-wise, then I
tell the owner that the probability is that the problem shouldn't return.
On the other hand, if I adjust the valvetrain for minimum noise, and afterwards I observe 1 or
more obvious outliers, I tell them the truth -- something is on the way out, the noise will return, and this issue
will need to be addressed sooner or later.
****
* 2) OK, the above was the doom & gloom part. The pitting in #6? Depends on how many miles can you
drive before the engine needs another quart of oil? If it's 750+ miles per quart, then the cats can
handle that. (per several manufacturers) IF it's worse than that, then I would defer replacing
the cats until you replace the motor. (I think you said that you are cat-free, so the real answer
is if the oil consumption is above your threshold of pain, then I wouldn't worry about it.)
But do yourself a favor, get a small logbook from the $ store, keep it in the glovebox,
and keep track of how often you are adding oil -- that's valuable info.
3) I'm not looking to burn up your wallet, but you may want to consider putting this engine
back into closed-loop operation. (ie: getting the front O2 sensors back up and running.)
Obviously you are satisfied with the way your truck runs open loop, but with the price of gas
maybe the constant fine-tuning afforded by closed-loop operation will help to pay for the
cost of sorting that out? Anyone reading this, have you quantified the difference between
open loop vs. closed loop MPG on your GMT400?
If the factory default calibration is really close, the difference may not be all that noticeable...on
the other hand, maybe depending on where you live it's more like 2-3 MPG difference? If so,
this additional cost could add up over time?
****
Well, that was waaay longer than I wanted. But if you see anything on the underneath on the
replaced rotor that looks wrong, I'd love to see that. And if you find/do anything in
your valvetrain that would be of interest as well.
Congrats on the fix -- celebrate the win! And welcome to the forum...looks like you
have excellent taste in the color of your truck.
Cheers --
Would you happen to have taken a photo of the underneath of the replaced rotor?
I remember being fooled by a taking a quick glance of the top side of a rotor
on a misfiring SBC, and it looked good. But on the underneath it was obvious where the
sparks had blown through and made an easier path to ground than the spark
plug electrodes. (NOTE: The whole path between the coil > center of the cap > rotor
{center to end} is stressed 8x as hard (or 8x as often) because all sparks go through this path.)
Like @L31MaxExpress' 2nd photo showing the spark blow-through on the underside of his cap:
NOTE: The reason I ask is that I checked the photo of your cap & didn't see anything obvious?
If it was mine, I would seriously consider doing the following in order to make sure I get the
most I can out of the existing motor:
1) At the very least I would 2nd what @L31MaxExpress said about resetting the lash
on the weak (#6) cylinder. Actually, I'd remove the valve covers, wrap the upper half of
the rocker arms with aluminum foil (to minimize the mess from the oil squirters) and
set/verify *all* of the rockers at a slow hot idle. (You know, loosen slowly until tick tick tick,
then tighten *just* until it quiets, move to the next, repeat 15 more times.) Shut off
the engine, and *then* set the preload on all 16 to your personal preference. (1/4 turn,
1/2 turn, etc.)
I've done this many times, and most of the time all the preloads were similar. But sometimes,
I would find 1 or 2 that were set way deeper than the others. (Sometimes during
initial assembly the lifter(s) that didn't really pump up are hard to set correctly cold.
Seen this several times over the years.)
IMPORTANT CROSS CHECK: Here's some valuable data that you can glean from checking
the thread count above the rocker arm nuts after setting the hot lash like this. In a
perfect world, let's say that ALL 16 rocker arm nuts have (4) threads showing above
the nut. Perfect! But in Road Trip's world, I may have 14 rocker arm nuts showing
4 threads, the 15th rocker arm nut showing 2 threads above, and the 16th rocker
arm nut showing 6 threads above? What can we infer from this?
* 14 cam lobe / lifter / pushrod / rocker arm / valve / valve seat assemblies either no wear,
or similar wear. No worries.
* 1 rocker arm nut with only 2 threads showing? Think of wear that takes up valvetrain clearance?
That's right, think of a wearing exhaust valve seat and/or burnt exhaust valve
receding into the head, thereby making the valve stem tip move UP?
* 1 rocker arm nut with 6 threads showing? Think of wear that creates extra valvetrain clearance?
Think of a cam lobe that's starting to go away - we've seen those disappearing lobe pics
many times. (!)
Of course, this check by itself is only of limited value. BUT if you happened to have verified/photo'd/logged
that all the valvetrain was set to the same number of threads above all 16 nuts when you replaced
the heads a couple of years ago, well *now* we have something to compare today's observations
against.
You know, it takes longer to describe all this than to do it. It's just a cross-check, but I
have resorted to resetting the hydraulic lifter preload with a hot lash adjustment on a problem SBC,
and if I'm able to clear up the issue AND all 16 rockers now match up, height-wise, then I
tell the owner that the probability is that the problem shouldn't return.
On the other hand, if I adjust the valvetrain for minimum noise, and afterwards I observe 1 or
more obvious outliers, I tell them the truth -- something is on the way out, the noise will return, and this issue
will need to be addressed sooner or later.
****
* 2) OK, the above was the doom & gloom part. The pitting in #6? Depends on how many miles can you
drive before the engine needs another quart of oil? If it's 750+ miles per quart, then the cats can
handle that. (per several manufacturers) IF it's worse than that, then I would defer replacing
the cats until you replace the motor. (I think you said that you are cat-free, so the real answer
is if the oil consumption is above your threshold of pain, then I wouldn't worry about it.)
But do yourself a favor, get a small logbook from the $ store, keep it in the glovebox,
and keep track of how often you are adding oil -- that's valuable info.
3) I'm not looking to burn up your wallet, but you may want to consider putting this engine
back into closed-loop operation. (ie: getting the front O2 sensors back up and running.)
Obviously you are satisfied with the way your truck runs open loop, but with the price of gas
maybe the constant fine-tuning afforded by closed-loop operation will help to pay for the
cost of sorting that out? Anyone reading this, have you quantified the difference between
open loop vs. closed loop MPG on your GMT400?
If the factory default calibration is really close, the difference may not be all that noticeable...on
the other hand, maybe depending on where you live it's more like 2-3 MPG difference? If so,
this additional cost could add up over time?
****
Well, that was waaay longer than I wanted. But if you see anything on the underneath on the
replaced rotor that looks wrong, I'd love to see that. And if you find/do anything in
your valvetrain that would be of interest as well.
Congrats on the fix -- celebrate the win! And welcome to the forum...looks like you
have excellent taste in the color of your truck.
Cheers --
Last edited:
323kielr
Newbie
Had this happen to me on my 2000 C2500 7.4 a couple of months ago. Coming back from a car show, pulling a loaded trailer, it started missing, occasionally backfiring and loss of power. I was about 125 miles from home and decided to try and nurse it on in. When I got home, could smell the gas coming from the exhaust also. 175,00 miles on truck and I had replaced the spark plugs about 5000 miles ago, the plug wires about 100,000 miles ago and still had factory coil, rotor and dist. cap. This truck had also been having hard start issues when the motor was hot so I thought that might be an issue with the injectors or fuel press. regulator. Since the other ignition components were mostly old, I decide to go ahead and replace all of those mentioned above except the plugs, just to rule those out as the problem. Low and behold, that solved my issues from the road trip. I don't like to throw parts but considering the age on them, I figured might as well. About $225.00 total for all AC Delco parts from Rockauto. Still have the injectors and regulator I need to replace but truck runs great and the hard start isn't every time.
