MSD Atomic EFI: Tuning Tuning Tuning

[FSJ Guy]

If the miss was there BEFORE the EFI upgrade, it is not surprising that is it still there.

Have you checked cap and rotor for signs of carbon traces that could be shorting to ground and causing a weak spark? How are the plugs and plug wires?

HEI isn't a magic bullet. And even if it did "fix" the problem, it would only be masking the issue, not solving the problem.

[Dr. Marneaus]

Cap and rotor and plugs and wires are all fairly new. Cap and rotor are clean. Wires are in good shape, plugs were shown a page back, coil had been replaced at some point in the last few years, duraspark box has been replaced a number of times, etc.

My duraspark box doesn't get a full 12v because I believe it's fed by the coil. Maybe that's something to do with it? And my coil still is the externally resisted type. I'm not sure if duraspark and whatnot are supposed to get the full 12v, so maybe that's part of having weak spark? I'm kind of running half 1973 and half duraspark.

That's why I'm saying maybe the HEI could potentially be a solution, because it will be wired in correctly and getting full 12v from the battery etc.

[Stuka]

Cap and rotor and plugs and wires are all fairly new. Cap and rotor are clean. Wires are in good shape, plugs were shown a page back, coil had been replaced at some point in the last few years, duraspark box has been replaced a number of times, etc.

My duraspark box doesn't get a full 12v because I believe it's fed by the coil. Maybe that's something to do with it? And my coil still is the externally resisted type. I'm not sure if duraspark and whatnot are supposed to get the full 12v, so maybe that's part of having weak spark? I'm kind of running half 1973 and half duraspark.

That's why I'm saying maybe the HEI could potentially be a solution, because it will be wired in correctly and getting full 12v from the battery etc.

From the factory the duraspark box should have a large red wire (10g I think) coming from the firewall for its main power lead. I know yours is not a factory install, so would be worth double checking where it gets its power from.

[Dr. Marneaus]

Cap and rotor and plugs and wires are all fairly new. Cap and rotor are clean. Wires are in good shape, plugs were shown a page back, coil had been replaced at some point in the last few years, duraspark box has been replaced a number of times, etc.

My duraspark box doesn't get a full 12v because I believe it's fed by the coil. Maybe that's something to do with it? And my coil still is the externally resisted type. I'm not sure if duraspark and whatnot are supposed to get the full 12v, so maybe that's part of having weak spark? I'm kind of running half 1973 and half duraspark.

That's why I'm saying maybe the HEI could potentially be a solution, because it will be wired in correctly and getting full 12v from the battery etc.

From the factory the duraspark box should have a large red wire (10g I think) coming from the firewall for its main power lead. I know yours is not a factory install, so would be worth double checking where it gets its power from.

I don't really want to go down a tangent here, but the coil gets power through the normal ignition resistance wire and the duraspark box gets power from the starter solenoid, which if I'm recalling correctly is the same reduced voltage as the coil.

[Flip]

Yes, the HEI will help with the primary side ignition related miss.

What it won't do is control hunting.

[babywag]

Yes, Duraspark is run on reduced voltage compared to HEI, however the coil spark output is pretty much the same.
Functionally they operate pretty much the same as well.
That is why you can run a GM module like what is inside the HEI, with a motorcraft distributor.
It really isn't an upgrade, but some like the simpler wiring.

Some people have had issues with the quality of the HEI, even the more expensive brands.
They are all made offshore, and some are pretty much garbage.

If it was me, I'd get an MSD box, and keep the motorcraft distributor.

[Dr. Marneaus]

Yes, the HEI will help with the primary side ignition related miss.

What it won't do is control hunting.

Yeah. So do we have any ideas on what would cause it to hunt as such? It didn't seem so bad yesterday when I fired it up, but the day my jeep becomes consistent it will be a surprise to me, lol.

I can watch the AFR when it hunts, and it will start to increase when the vehicle starts to die, then it drops as it comes back, then if it almost stalls again it goes up, etc.

[Tatsadasayago]

AFR 'Hunting' is usually a symptom of the system reacting to rapid changes. If returning to idle from part throttle starts the system hunting it could mean that the O2 sensor is seeing a sudden leanout, increases the injector pulse width, sees an over-rich condition and leans out...wash, rinse and repeat.
A MAP sensor would contribute to this in a similar manner.

The miss issue could be a contributor as well; especially if the missing cylinder is on the side with the O2 sensor.
Having a wideband AF/R system on my jeep I played with the sensitivity to get a feel for what conditions would cause the AF/R to change noticeably.
Pulling one plug wire on the sensor side at idle caused a change from 14.5 to 12:1 every time I broke the circuit. Doing the same on the other side of the engine barely made the needle wiggle.

I would suspect that your EFI system is reacting to input levels far enough outside what it considers normal, that it is trying to adapt quickly, which is leading to rough idle/stalling.

As suggested earlier, taking an active sensor out of the loop and noting the effects will likely lead you to the cause of the problem.
When I initially installed the O2 bung on my jeep, I placed it on the drivers side head pipe about 12" downstream of the manifold flange. The AF/R gauge was all over the place. I added another bung on the other side, about 6" from the flange and VIOLLA! Accurate AF/R readings confirmed with an emissions test. If I'd been running EFI at the time, I am quite sure the engine would have acted similarly to how yours is.

[babywag]

Need to figure out why it is doing that (obviously). It is adjusting for something it is seeing from the sensors. Or a mechanical issue with the engine.
@ idle it should stay consistent, it obviously should not surge from lean to rich, rpms should hold steady and not rise/fall.
The ecm is adjusting too far rich/lean to compensate and it is having trouble correcting the issue.
It is virtually impossible to tune out an engine problem, you can sometimes mask it/compensate for it, but it'll still be there.

Have you tried to isolate the misfire to a single cylinder? If you have a timing light sometimes you can find it that way.
You put the trigger on each plug wire until possibly finding the one that is misfiring.
Can also pull one plug wire @ a time and see if one cylinder is the culprit. Problem is if it's intermittent hard to find.
However it's also crude test to see the balance of all the cylinders. Watching a tach the rpm drop should be roughly the same when each wire is pulled.

You can sometimes find a bad cylinder by spraying each plug wire by the plug with a spray bottle filled with water.
If you do it in a dark garage, or @ night, and get a light show on a single wire it's likely leaky/bad.
Sometimes you get a light show on all the wires, and obviously tells you they should probably be replaced.

A DVM w/ ohms can also find a bad wire, if one is very high resistance(compared to others), it's bad.

[Dr. Marneaus]

There is no RPM hunting issue present aside from startup.

At idle, RPM's are pretty consistent, the tach on the handheld reads out super fast so it shows maybe a 25rpm swing in either direction, so it may vary from 650 to 700, but overall in gear its right around the 675 mark, and in neutral its right around the 800 mark.

when I put the vehicle in gear, it doesnt hunt. It just drops a bit.

when i go into park from gear it instantly kicks up to about 1000rpm then within a second or three finds its way down to the 800ish area and stays there. This seems normal to me since the load is instantly released from the engine so it revs slightly higher then settles down to its programed idle target.

The only time I've had RPM hunting issues is when starting up, and its normally only really an issue on cold starts, but it has happened on warm starts as well.

If I'm cruising along on surface streets and let off the gas there is a minor jump in AFR but it instantly finds where it needs to be. I've not noticed any issues there. If I'm powering along the highway and all of a sudden let off the throttle 100%, the AFR skyrockets to like 34 or whatever maxes out the reading. It'll stay there until i touch the gas pedal (even just a tap) or until the vehicle slows down a bit and apparently something tells it to kick in fuel. In both of these situations everything still appears fine and function, no odd behavior other than the AFR gauge.

[Dr. Marneaus]

Need to figure out why it is doing that (obviously). It is adjusting for something it is seeing from the sensors. Or a mechanical issue with the engine.
@ idle it should stay consistent, it obviously should not surge from lean to rich, rpms should hold steady and not rise/fall.
The ecm is adjusting too far rich/lean to compensate and it is having trouble correcting the issue.
It is virtually impossible to tune out an engine problem, you can sometimes mask it/compensate for it, but it'll still be there.

Have you tried to isolate the misfire to a single cylinder? If you have a timing light sometimes you can find it that way.
You put the trigger on each plug wire until possibly finding the one that is misfiring.
Can also pull one plug wire @ a time and see if one cylinder is the culprit. Problem is if it's intermittent hard to find.
However it's also crude test to see the balance of all the cylinders. Watching a tach the rpm drop should be roughly the same when each wire is pulled.

You can sometimes find a bad cylinder by spraying each plug wire by the plug with a spray bottle filled with water.
If you do it in a dark garage, or @ night, and get a light show on a single wire it's likely leaky/bad.
Sometimes you get a light show on all the wires, and obviously tells you they should probably be replaced.

A DVM w/ ohms can also find a bad wire, if one is very high resistance(compared to others), it's bad.

I have not ever tried to isolate the miss, thats a good idea. I can absolutely check with my timing light and or by pulling individual plug wires.

[Stuka]

Cap and rotor and plugs and wires are all fairly new. Cap and rotor are clean. Wires are in good shape, plugs were shown a page back, coil had been replaced at some point in the last few years, duraspark box has been replaced a number of times, etc.

My duraspark box doesn't get a full 12v because I believe it's fed by the coil. Maybe that's something to do with it? And my coil still is the externally resisted type. I'm not sure if duraspark and whatnot are supposed to get the full 12v, so maybe that's part of having weak spark? I'm kind of running half 1973 and half duraspark.

That's why I'm saying maybe the HEI could potentially be a solution, because it will be wired in correctly and getting full 12v from the battery etc.

From the factory the duraspark box should have a large red wire (10g I think) coming from the firewall for its main power lead. I know yours is not a factory install, so would be worth double checking where it gets its power from.

I don't really want to go down a tangent here, but the coil gets power through the normal ignition resistance wire and the duraspark box gets power from the starter solenoid, which if I'm recalling correctly is the same reduced voltage as the coil.

Don't mean to derail this too much, but the ignition module should NOT be running on lower voltage.

EDIT: If it is getting power from after the resistor, it could definitely lead to some issues with it.

[Dr. Marneaus]

From the factory the duraspark box should have a large red wire (10g I think) coming from the firewall for its main power lead. I know yours is not a factory install, so would be worth double checking where it gets its power from.

I don't really want to go down a tangent here, but the coil gets power through the normal ignition resistance wire and the duraspark box gets power from the starter solenoid, which if I'm recalling correctly is the same reduced voltage as the coil.

Don't mean to derail this too much, but the ignition module should NOT be running on lower voltage.

EDIT: If it is getting power from after the resistor, it could definitely lead to some issues with it.

It's all good it's definitely something that needs discussed. I never realized it was running on lower voltage until I was doing all this EFI work anyway.

It's got the white wire which gets full 12v when cranking to trigger the spark retard, then the red wire is getting whatever resisted vtage that the coil is getting because it's connected to the I terminal on the solenoid.

[Dr. Marneaus]

I guess I could always temporarily rig the red wire straight to the battery to test if that makes any difference in anything

[Flip]

Hey, did you determine if you have an exhaust leak or not when cold?

If no exhaust leak, get that distributor poked in there (watch out for the gear match issue), get it timed, and get lets get to tweaking.

[Dr. Marneaus]

Hey, did you determine if you have an exhaust leak or not when cold?

If no exhaust leak, get that distributor poked in there (watch out for the gear match issue), get it timed, and get lets get to tweaking.

I listend around with a hose and looked as best I could immediately following a cold start, I see no evidence. I need to grab my little dentists mirror thing and take a peek up around the back of the flange, but pretty sure its good.

When i had the exhausters out for the bung install, i saw no evidence of leaks past or present.

I know these pictures suck but as mentioned there wer eno signs of anything wrong when i had it out, so i assume it;s still fine now.



(yes, there was a leak where the pipe entered the muffler, but we welded that up.)

[Dr. Marneaus]

I'll have to do the dist next week, I'll be traveling this week/weekend. Also I'll have to wire up a relay from the battery to power the HEI. I'll tap into the "on/off" wire for the Atomic as the trigger for the relay, since that is the one wire on my truck that has 12v cranking and running.

[Flip]

On the power issue, is it just during hard acceleration, or is the overall power down compared to when it was at 50psi fuel pressure.

I think it needs more fuel pump squirt and power valve, but if overall power is down, we probably need to do a global change, by changing displacement first. Then run it like that for a bit.
If you are going to be out for a while Probably best to start this when you get back.

[Dr. Marneaus]

On the power issue, is it just during hard acceleration, or is the overall power down compared to when it was at 50psi fuel pressure.

I think it needs more fuel pump squirt and power valve, but if overall power is down, we probably need to do a global change, by changing displacement first. Then run it like that for a bit.
If you are going to be out for a while Probably best to start this when you get back.

It was absolutely most evident under WOT or high load conditions (climbing an on ramp and trying to gain speed, etc). I felt like it was even better under highway cruise though, like with the 50 psi I felt I could just barely get into the gas and it would pull from 65 up to 75 with ease, but when it was lower fuel pressure I feel like I had to get into the pedal allt more to gain speed on the highway.

That all could have just been an illusion tho

[FSJ Guy]

I would definitely get your Duraspark module wired up correctly. As mentioned, it is not designed to run on less than 12V. That definitely could be the reason for your misfires. The EFI could be trying to compensate for this and that is why you're seeing erratic idle RPMs.

The engine must be in good running order so the EFI can do it job. :- )