Restarting My '70 Nova Project

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I got the hard fuel lines out of the car and the braided hose in on Thursday afternoon. I reset the EFI to factory settings and went through the setup process. Took it for a drive and it's no better than before so that was wasted time and hose.
I spent over an hour on the phone with MSD tech support, including about 45 minutes on Friday with the "MSD EFI guru". Seems like he is stumped too, the only thing he recommended was to change the IAC, the idle air control, which was acting strange sometimes. So I ordered one from NAPA, picked it up yesterday, and installed it this afternoon. It didn't make any difference at all as far as I can tell, so I'm going to call him back on Monday. If you rev it up over 2,000 RPM or more and then let it back to idle, it will almost and sometimes die for a few seconds before it recovers and goes back to idle speed. While at a steady speed with the engine turning 1,800 to 2,000 RPM, sometimes it surges like you are giving it more then less throttle. It has also started backfiring, mostly when shifting from 1st to 2nd and sometimes on the 2nd to 3rd shift. It never did that before, and is a sign of a lean mixture, or possible an exhaust leak. When I had it up in the air, after I got the fuel line installed, I started it up and checked the entire exhaust system for a leak and didn't find one.
If I can't get this sorted out, I'm just going to pull it off and get either a FiTech or Holley unit and put that on. I'm tired of messing around with this unit and want it running right so I can drive it without fighting it all the time.
I guess if I ran a return line to the tank, I could install a pressure regulator and slap on one of the Holley cabs I have setting on the shelf, it couldn't possibly be any worse.

Ok, hold on a minute.
It is my understanding that with the Snipers, you needed a fuel pressure regulator after the efi to maintain the required pressure (forget if it’s 56 or 58 lbs) but that system needs a return line to maintain constant flow and pressure. The internal one in the Sniper may be too small or on its way out. If you can get at it, I’d remove the Sniper diaphragm and put on an external regulator.
Currently you have no return line?
That could be the problem right there.
Too much pressure is building up as a result and the compensation is to shut down fuel delivery until the pressure equalizes. This will happen time and time again in sequence as soon as you try to come off idle and is probably why by increasing idle speed, it becomes mitigated a bit because the efi call is remaining more constant. The gas/rpm call will only go so far however if the system is always trying to regulate at low speed because of the fluctuation in fuel pressure.
I could be wrong but this is sounding more like a fuel problem that has not so much to do with the Sniper as it does the fuel regulation delivery.
It could be getting worse because the regulator is failing in itself.
Before I did anything else like switching efi’s or moving to a carb, I’d put in a return line anyway ands see what happens.

 

[BravoXray]

Ok, hold on a minute.
It is my understanding that with the Snipers, you needed a fuel pressure regulator after the efi to maintain the required pressure (forget if it’s 56 or 58 lbs) but that system needs a return line to maintain constant flow and pressure. The internal one in the Sniper may be too small or on its way out. If you can get at it, I’d remove the Sniper diaphragm and put on an external regulator.
Currently you have no return line?
That could be the problem right there.
Too much pressure is building up as a result and the compensation is to shut down fuel delivery until the pressure equalizes. This will happen time and time again in sequence as soon as you try to come off idle and is probably why by increasing idle speed, it becomes mitigated a bit because the efi call is remaining more constant. The gas/rpm call will only go so far however if the system is always trying to regulate at low speed because of the fluctuation in fuel pressure.
I could be wrong but this is sounding more like a fuel problem that has not so much to do with the Sniper as it does the fuel regulation delivery.
It could be getting worse because the regulator is failing in itself.
Before I did anything else like switching efi’s or moving to a carb, I’d put in a return line anyway ands see what happens.

I'm not running a Sniper system, I'm running an MSD Atomic EFI.
The single line system is allowed, as the EFI controls the fuel pressure using a PWM control on the in-tank pump.

The good news is that this afternoon I went through and set up the system from scratch, reset everything. After doing the software reset, I reset the throttle plates to 1 1/4 turns open on the stop screws, set the cam type at stock, idle RPM to 800 RPM, RPM limiter at 6,000 RPM, and a couple of other settings that apply to my setup. After making the changes, I turned the ignition off and waited about 30 seconds before turning it back on. I checked all the settings to be sure they stayed at the desired settings, turned it off again for another 30 seconds, then restarted it. It idled a little fast, around 1,000 RPM, so I closed the throttle blades 1/4 turn each, which brought the idle down to about 850 RPM, which is fine. Now, when you hit the accelerator, running it up to 3,000 RPM or more and let off it, it comes right back down to the idle speed, no drop down to as low as 300 RPM like it did before. The most obvious thing I noticed was that the IAC, is barely opening at all. Previously, on a rev up, it would jump up to 175 then gradually fall back to anything from 30 to 70, that large air bleed had to be what was bringing the idle down so low. Now, it only goes up to 20 or so at most and drops back to zero at idle. That was a great thing to see it behaving properly again.
Just to be sure, I put the air cleaner back on, closed the hood and took it for a drive. Amazing, it's behaving just like it did originally, it'll take off from a dead idle with no coughing or sputtering. Also gone is the surging while cruising at a steady speed, so that's great too.
I drove it over 20 miles, and it works perfectly again, finally.
I also called the tech at MSD that had spent over an hour on the phone with me and told him I had it running correctly again. He had no idea why it finally straightened out but said if it works that way, leave it that way. I plan on leaving it just like it is.

On to the next project.

 

[BravoXray]

As long as the Holley is at least 750 cfm you can certainly go that route. Too bad for not having a mechanical pump or else you could have eliminated the return.

I have 670 CFM and 780 CFM Holley carbs on the shelf, but that's all academic now, as I posted above, I got it running correctly again.
Also, the in-tank pump could be used with a carb if a pressure regulator was installed with a return line to bring the pressure down to 7-8 PSI. There's no way I would go back to a mechanically driven pump, I'd stick with an electric pump.

 

[Alan46]

I'm not running a Sniper system, I'm running an MSD Atomic EFI.
The single line system is allowed, as the EFI controls the fuel pressure using a PWM control on the in-tank pump.

The good news is that this afternoon I went through and set up the system from scratch, reset everything. After doing the software reset, I reset the throttle plates to 1 1/4 turns open on the stop screws, set the cam type at stock, idle RPM to 800 RPM, RPM limiter at 6,000 RPM, and a couple of other settings that apply to my setup. After making the changes, I turned the ignition off and waited about 30 seconds before turning it back on. I checked all the settings to be sure they stayed at the desired settings, turned it off again for another 30 seconds, then restarted it. It idled a little fast, around 1,000 RPM, so I closed the throttle blades 1/4 turn each, which brought the idle down to about 850 RPM, which is fine. Now, when you hit the accelerator, running it up to 3,000 RPM or more and let off it, it comes right back down to the idle speed, no drop down to as low as 300 RPM like it did before. The most obvious thing I noticed was that the IAC, is barely opening at all. Previously, on a rev up, it would jump up to 175 then gradually fall back to anything from 30 to 70, that large air bleed had to be what was bringing the idle down so low. Now, it only goes up to 20 or so at most and drops back to zero at idle. That was a great thing to see it behaving properly again.
Just to be sure, I put the air cleaner back on, closed the hood and took it for a drive. Amazing, it's behaving just like it did originally, it'll take off from a dead idle with no coughing or sputtering. Also gone is the surging while cruising at a steady speed, so that's great too.
I drove it over 20 miles, and it works perfectly again, finally.
I also called the tech at MSD that had spent over an hour on the phone with me and told him I had it running correctly again. He had no idea why it finally straightened out but said if it works that way, leave it that way. I plan on leaving it just like it is.

On to the next project.

Good for you bro!!!!!

 

[arrow]

I'm not running a Sniper system, I'm running an MSD Atomic EFI.
The single line system is allowed, as the EFI controls the fuel pressure using a PWM control on the in-tank pump.

The good news is that this afternoon I went through and set up the system from scratch, reset everything. After doing the software reset, I reset the throttle plates to 1 1/4 turns open on the stop screws, set the cam type at stock, idle RPM to 800 RPM, RPM limiter at 6,000 RPM, and a couple of other settings that apply to my setup. After making the changes, I turned the ignition off and waited about 30 seconds before turning it back on. I checked all the settings to be sure they stayed at the desired settings, turned it off again for another 30 seconds, then restarted it. It idled a little fast, around 1,000 RPM, so I closed the throttle blades 1/4 turn each, which brought the idle down to about 850 RPM, which is fine. Now, when you hit the accelerator, running it up to 3,000 RPM or more and let off it, it comes right back down to the idle speed, no drop down to as low as 300 RPM like it did before. The most obvious thing I noticed was that the IAC, is barely opening at all. Previously, on a rev up, it would jump up to 175 then gradually fall back to anything from 30 to 70, that large air bleed had to be what was bringing the idle down so low. Now, it only goes up to 20 or so at most and drops back to zero at idle. That was a great thing to see it behaving properly again.
Just to be sure, I put the air cleaner back on, closed the hood and took it for a drive. Amazing, it's behaving just like it did originally, it'll take off from a dead idle with no coughing or sputtering. Also gone is the surging while cruising at a steady speed, so that's great too.
I drove it over 20 miles, and it works perfectly again, finally.
I also called the tech at MSD that had spent over an hour on the phone with me and told him I had it running correctly again. He had no idea why it finally straightened out but said if it works that way, leave it that way. I plan on leaving it just like it is.

On to the next project.

Glad it’s all smoothed out and ironically at a stock cam setting to boot.

 

[arrow]

I'm not running a Sniper system, I'm running an MSD Atomic EFI.
The single line system is allowed, as the EFI controls the fuel pressure using a PWM control on the in-tank pump.

The good news is that this afternoon I went through and set up the system from scratch, reset everything. After doing the software reset, I reset the throttle plates to 1 1/4 turns open on the stop screws, set the cam type at stock, idle RPM to 800 RPM, RPM limiter at 6,000 RPM, and a couple of other settings that apply to my setup. After making the changes, I turned the ignition off and waited about 30 seconds before turning it back on. I checked all the settings to be sure they stayed at the desired settings, turned it off again for another 30 seconds, then restarted it. It idled a little fast, around 1,000 RPM, so I closed the throttle blades 1/4 turn each, which brought the idle down to about 850 RPM, which is fine. Now, when you hit the accelerator, running it up to 3,000 RPM or more and let off it, it comes right back down to the idle speed, no drop down to as low as 300 RPM like it did before. The most obvious thing I noticed was that the IAC, is barely opening at all. Previously, on a rev up, it would jump up to 175 then gradually fall back to anything from 30 to 70, that large air bleed had to be what was bringing the idle down so low. Now, it only goes up to 20 or so at most and drops back to zero at idle. That was a great thing to see it behaving properly again.
Just to be sure, I put the air cleaner back on, closed the hood and took it for a drive. Amazing, it's behaving just like it did originally, it'll take off from a dead idle with no coughing or sputtering. Also gone is the surging while cruising at a steady speed, so that's great too.
I drove it over 20 miles, and it works perfectly again, finally.
I also called the tech at MSD that had spent over an hour on the phone with me and told him I had it running correctly again. He had no idea why it finally straightened out but said if it works that way, leave it that way. I plan on leaving it just like it is.

On to the next project.

and here I’m thinking you were referencing msd as your coil/electronics.
I don’t even recall them making an efi system

 

[arrow]

On to the next project.

Oh no you dont
Not until you get a time slip

 

[BravoXray]

and here I’m thinking you were referencing msd as your coil/electronics.
I don’t even recall them making an efi system

It came out in the 2010s, I bought mine in 2013, I think. I installed it on the 434 when I built it, but it was never fired up until 2023. They were never widely used, and they have updated it with the Atomic EFI 2. I bought it because it connected directly with the MSD 6AL ignition box I was using and can control the ignition if you want it to.

 

[BravoXray]

Oh no you dont
Not until you get a time slip

Don't think so, at 75, my drag strip runs are behind me.
Back in the early 70s, we ran my '69 L78 Nova at the local strip one weekend after stripping the car down and putting a tune on it. My three run best was 12.52 at 106 MPH. I kept the time slip for couple of years, but when we moved to this house in '74 it came up missing. I think the wife tossed it, but she would never admit it. It was in an envelope with a couple of pictures taken at the track that day, and the pics disappeared too.

 

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Don't think so, at 75, my drag strip runs are behind me.
Back in the early 70s, we ran my '69 L78 Nova at the local strip one weekend after stripping the car down and putting a tune on it. My three run best was 12.52 at 106 MPH. I kept the time slip for couple of years, but when we moved to this house in '74 it came up missing. I think the wife tossed it, but she would never admit it. It was in an envelope with a couple of pictures taken at the track that day, and the pics disappeared too.

That was an underrated engine as the 428 Cobra jets got all the press.
That 396 was easier to pull twelves than the Cobra jets.
Your trap speed w yours isn’t matching your et. You musta had a hell of a sixty foot
I was doing 106 w thirteen flats and 4.30’s out back and 117 with 12.2’s and 4.56’s after a bigger carb, cam and headers.
All my slips from those days were lost in a garage fire.