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Converting to MSD atomic EFI

I like the MSD Atomic and Fast EZ-EFI systems much better than the FITech or Sniper systems. The reason is because they have a separate ECU that is not in/on the throttle body exposed to all the heat and vibration of the engine.

Terminator X Stealth is a step above that for throttle body EFI, because the ECU can also control MPFI if you decide to upgrade down the road.

After that I would just go full MPFI from the get go.

All of them can work great or have issues, but the separate ECU you can mount under the dash or at least off the engine seem to reduce the issues.
 
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I had a second to take a look at the top of the fuel tank today, the first pic is from the driver side, you can see the small vent tube sticking up and the small line running to the engine, the second pic shows the filler line and filler vent line. I was wondering if the filler vent line could suffice as the sole vent and I could run the return to vent line that stick up? It seems like there’s two vents, could I get away with one? If not I’m leaning towards just buying another drop in for the tank, will the tbi sending units drop into the older carbureted tanks? I’ll buy a new tank and drop in unit if need be..

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I believe the '87-91 K5 tank/sending unit will work with any of the '73+ K5's. GM changed the filter setup a bit over the years but I believe the tank side is the same.

There should only be one tank vent. The filler vent just dumps back into the fuel fill neck as its for fueling.

You'll likely need the GM fuel line fitting to -AN adapters for the TBI sending unit, unless you have one of the high end flaring tools that makes that style GM flare.

No one's really enamored with the (crappy) aftermarket TBI tank sump, as it's almost wholly ineffective compared to what GM did, but of course GM's sump was made of plastic and breaks. If I did a lot of steep hills and didn't want to ensure my tank was full all the time, I might look at other options.

Holleys hydramat is super expensive (IMO) and I don't recall reading any 4 wheeling EFI experience with them, but if they work as advertised, that in a pre-TBI tank would be hard not to go with vs the crappy aftermarket TBI tanks. I'd ask for real wheeling advice on tank options first however. I don't do anything that gets really steep, but even then I don't like going below 1/4 tank as I don't trust the aftermarket sump. There might be other options I'm not aware of.
 
The hydramat is overrated and disintegrates after a few years seeing e10
 
That is unfortunate then, I'd take it off the table. For the price of the hydramat you'd expect them to last for a very long time.

Someone could make a boatload of money if they would make the "bucket" integrated style sender/pump unit common to modern GM vehicles, just designed to fit into the same space as the stock earlier sending units. Adjustable depth would be one size fits all for essentially every vehicle GM made from 1973 or even earlier.
 
I’ve had my K5 for 18 years or so. I started with the quadrajet and went to a TBI setup for the exact reason you mentioned.

I ended getting new heads, cam, intake and went with the new MSD Atomic. I went full in with the MSD ignition control too. An exhaust leak near the O2 will play havoc with the MSD.

I tried the returnless system and it sucked.

The work to swap it over is significant so you don’t want to do it twice.
The TBI tanks drop right it.
You’ll need the adapters from the o-ring to AN fittings for the sending unit.
You’ll need to modify the pickup tube a little for the bigger fuel pump.
Spend the money now and get the correct fuel lines rated for the EFI pressure.
The stock distributor will work if memory serves me correctly.
I have to have annual emission tests and I failed the first time with the sniff test. I adjusted the a/f ratios and drove it back through with a pass.
I’ve passed with the system with no issues for the last three years.
The throttle response and ease of starting was much nicer than the carb.
The ability to drive at 1200 feet above sea level to 7000 feet is a nice bonus too.

Someone wrote that in hindsight they would have done an LS swap, but in reality, unless you get a good turnkey engine, you’re still in it for $2000-$3000 by the time you do all the basic swap needs.

A full LS swap can easily run $5-10k without too much work.

I went with the Atomic to do something a little different and so my K5 kept some look of the original engine. I wish I had the LS power and gas mileage.
 
HawK5 said:
I had a second to take a look at the top of the fuel tank today, the first pic is from the driver side, you can see the small vent tube sticking up and the small line running to the engine, the second pic shows the filler line and filler vent line. I was wondering if the filler vent line could suffice as the sole vent and I could run the return to vent line that stick up? It seems like there’s two vents, could I get away with one? If not I’m leaning towards just buying another drop in for the tank, will the tbi sending units drop into the older carbureted tanks? I’ll buy a new tank and drop in unit if need be..
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dyeager535 said:
I believe the '87-91 K5 tank/sending unit will work with any of the '73+ K5's. GM changed the filter setup a bit over the years but I believe the tank side is the same.

There should only be one tank vent. The filler vent just dumps back into the fuel fill neck as its for fueling.
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He is correct, the tank vent is to vent pressure delta when the fuel changes level or temperature. The filler vent is only to allow air to escape around the nozzle when refueling, and when the cap is on, that vent does nothing, it can't be used as a normal vent. The tank is the same except for the filler hose diameter is different on older models, which can be made to work.

dyeager535 said:
No one's really enamored with the (crappy) aftermarket TBI tank sump, as it's almost wholly ineffective compared to what GM did, but of course GM's sump was made of plastic and breaks. If I did a lot of steep hills and didn't want to ensure my tank was full all the time, I might look at other options.
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While I agree that the aftermarket baffle pan is not as good as the GM version, it is still better than nothing, and I have had mine in for 15 years without a problem. With a carb bowl, if you lose pressure for a moment during a bump or something, it doesn't matter, with EFI, if you lose pressure for a moment, the injectors won't work correctly and the engine can stumble or stall. I highly recommend you install the TBI tank to help keep the fuel pump/pickup submerged as often as possible. Also, if you know you are going to do some extreme hill climbing or something, try not to run the tank on the bottom half or less if possible. I've ran mine down to 1/4 tank without a problem with dunes and hills and such, but not rock crawling.
 
I ended up changing plans for the pump as I was able to pickup an external pump and filters from a member here, so all I need is a port to return the fuel. That’s why I was thinking I didn’t need to swap the whole tank, just find a drop in sending unit that had an extra vent to return the fuel. Or is the issue that the 1980 tank doesn’t have baffles and bc the fuel injection is more prone to starvation I should just swap tanks.. if I understand right, my tank is 25 gallons, but the TBI tanks come in 31 or 40 gallons? The 40 gallon seems like it would be the better choice for multi day off road excursions.. other than weight is there any draw backs or modifications?
 
HawK5 said:
I ended up changing plans for the pump as I was able to pickup an external pump and filters from a member here, so all I need is a port to return the fuel. That’s why I was thinking I didn’t need to swap the whole tank, just find a drop in sending unit that had an extra vent to return the fuel. Or is the issue that the 1980 tank doesn’t have baffles and bc the fuel injection is more prone to starvation I should just swap tanks.. if I understand right, my tank is 25 gallons, but the TBI tanks come in 31 or 40 gallons? The 40 gallon seems like it would be the better choice for multi day off road excursions.. other than weight is there any draw backs or modifications?
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K5's only got the 31 gallon tank as the "large" one.

I don't think there is a good solution to lack of tank baffling. If I was doing crazy angles, I would think very long and hard about how I did EFI fueling. While the aftermarket "baffle" is better than nothing, in terms of design theory, it's a million times worse than what GM designed.

Aftermarket (which is even better than the baffle in my spectra K5 tank): https://ls1tech.com/forums/attachme...tra-efi-gas-tank-yay-nay-fuel-sump-baffle.jpg

GM-style (except GM was cheap and used plastic, which invariably breaks): https://forums.hybridz.org/uploads/monthly_2021_02/images.jpg.cc07c966f7b691a62007e2ee8600099a.jpg

Yes, the aftermarket baffle has holes in the bottom. It's also nowhere near as tall as the GM one. And since fuel return dumps into the baffle setup, with the GM design, you aren't "losing" the returned fuel, its reclaimed right into the area next to the pump.

For most running EFI, it's probably not that big a deal. But GM almost never does something unnecessary, so there must have been issues they saw way back then. Losing 25% of fuel capacity when getting 10MPG means I'm losing 75+ miles of range. I'd be willing to bet with the angles I've seen some on here taking, even 1/4 tank wouldn't be enough to keep the pump in fuel with the aftermarket design, so even less range. People talk about filling back up at 1/4 tank. I'm an hour from the nearest station when I'm using the truck. I'd burn near a 1/4 tank just getting back from filling up. I'm pretty sure my K5 tanks baffle setup is even shallower than what is shown in the above pic of the aftermarket design.

To be fair, even with the most effective baffle, you don't want to run it to the minimum. And who knows, perhaps the aftermarket has improved their designs since I got mine?

FWIW, I once pumped 31 gallons into my Spectra tank, so at least it's very close to rated capacity. Surprised I made it, about 40 miles between stations. Nail biter lol.
 
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I can tell you that the tank will continue providing fuel for extended periods with the front of the vehicle dipped in a hole at about 45 degrees. I've also crawled slowly up grades of 100% or more without issue. I tend to think of sand dunes as kind of a worst-case because you combine angles with a lot of bouncing and sloshing, but it doesn't seem to be a problem. Jumping a rig puts the fuel at zero gravity, then splashes it all over. I don't jump it on purpose, but I don't think everyone catching air is running a baffled fuel cell.

On the flip side, point an Edelbrock uphill and the engine goes pig rich then stalls.
 
dyeager535 said:
K5's only got the 31 gallon tank as the "large" one.

While the aftermarket "baffle" is better than nothing, in terms of design theory, it's a million times worse than what GM designed.

Aftermarket (which is even better than the baffle in my spectra K5 tank): https://ls1tech.com/forums/attachme...tra-efi-gas-tank-yay-nay-fuel-sump-baffle.jpg

GM-style (except GM was cheap and used plastic, which invariably breaks): https://forums.hybridz.org/uploads/monthly_2021_02/images.jpg.cc07c966f7b691a62007e2ee8600099a.jpg

Yes, the aftermarket baffle has holes in the bottom. It's also nowhere near as tall as the GM one. And since fuel return dumps into the baffle setup, with the GM design, you aren't "losing" the returned fuel, its reclaimed right into the area next to the pump.

For most running EFI, it's probably not that big a deal. But GM almost never does something unnecessary, so there must have been issues they saw way back then. Losing 25% of fuel capacity when getting 10MPG means I'm losing 75+ miles of range. I'd be willing to bet with the angles I've seen some on here taking, even 1/4 tank wouldn't be enough to keep the pump in fuel with the aftermarket design, so even less range. People talk about filling back up at 1/4 tank. I'm an hour from the nearest station when I'm using the truck. I'd burn near a 1/4 tank just getting back from filling up. I'm pretty sure my K5 tanks baffle setup is even shallower than what is shown in the above pic of the aftermarket design.

To be fair, even with the most effective baffle, you don't want to run it to the minimum. And who knows, perhaps the aftermarket has improved their designs since I got mine?

FWIW, I once pumped 31 gallons into my Spectra tank, so at least it's very close to rated capacity. Surprised I made it, about 40 miles between stations. Nail biter lol.
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Have you had problems with your Spectra baffle?

I haven't with mine, I have romped on it hard up bumpy dunes down to about a 1/4 tank without issue. I am not saying that is the limit, just I haven't tested it lower. The TBI sending unit still dumps the return fuel back into the baffle pan whether you have a spectra or a GM tank. To say it's a "million times worse" is a gross exaggeration when I haven't had a single problem with it in 15 years fueling a 525 HP BBC with a Walbro in tank pump.

I think the biggest limitation would be idling up a very steep incline for long periods at a low fuel level, that would give the fuel in the baffle time to drain out the holes in the bottom. But you need to have them or then you can't use the bottom portion of the rest of the fuel in the tank. The GM design is better in that aspect, I think the rest of the time it doesn't matter because mine looks more like the one in your picture and it probably holds a couple gallons, which is enough to get through most situations before it slowly drains out.
 
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folkenheath said:
Have you had problems with your Spectra baffle?

I haven't with mine, I have romped on it hard up bumpy dunes down to about a 1/4 tank without issue. I am not saying that is the limit, just I haven't tested it lower. The TBI sending unit still dumps the return fuel back into the baffle pan whether you have a spectra or a GM tank. To say it's a "million times worse" is a gross exaggeration when I haven't had a single problem with it in 15 years fueling a 525 HP BBC with a Walbro in tank pump.

I think the biggest limitation would be idling up a very steep incline for long periods at a low fuel level, that would give the fuel in the baffle time to drain out the holes in the bottom. But you need to have them or then you can't use the bottom portion of the rest of the fuel in the tank. The GM design is better in that aspect, I think the rest of the time it doesn't matter because mine looks more like the one in your picture and it probably holds a couple gallons, which is enough to get through most situations before it slowly drains out.
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Mine has a spectra tank. It stayed in place even doing the “a-hole pass” over the rocks as. @fastazz81 called it

I think he was just mad because he didn’t think of it first
 
Mine stayed in place and it is a spectra tank as well.
And you are correct about the pass, had I known it was not highly frowned on it would have happened a lot sooner.
And honestly the year after that rally mode was probably a lot harder on the trucks.
 
fastazz81 said:
Having a senior moment?
I have a open seat to help remind you.
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I still won't get out of work. We're short 5 guys at the moment, and even burger flippers would be of some use
 
folkenheath said:
Have you had problems with your Spectra baffle?

To say it's a "million times worse" is a gross exaggeration when I haven't had a single problem with it in 15 years fueling a 525 HP BBC with a Walbro in tank pump.
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I haven't had issues. Well, I had it hiccup on me once, but was it an anomaly or was it low fuel? It happened right at 1/4 tank, long uphill, at decent speed. Never done that before, so I attribute it to fuel starvation, but was it? Pretty hard to know for certain...never happened with higher fuel levels.

But as I qualified, I don't do anything at extreme angles, and I baby the thing because I also try not to ever let it go below 1/4 tank when I'm off highway, because I don't trust the design. Stalling where I have nowhere to turn around and nowhere flat enough to get it restarted is not something I'm interested in dealing with.

It's no exaggeration to say it's a million times worse. It is. The only way to make a worse design is to leave it out. It has holes in the bottom of it. That is the exact opposite of what it's supposed to do, and I stand by that fact. Imagine a coffee cup with holes drilled in the bottom. Is that not a million times worse than a normal cup? Lol The return fuel dumps into the baffle...and drains out the holes. As is the norm, the aftermarket has made parts as cheap as possible because that's what most want to pay for, not because its the most effective or even replicates factory design.

I will also mention that I'm pretty sure my tank baffle is different than any shown thus far. I recall it being essentially a shallow rectangle with angled sides, with drain holes. It wasn't nearly as deep as the others I've seen, and there was no additional "wall" inside the baffle as one pic showed. As I mentioned before, perhaps there have been design changes.

In any case. If people aren't having problems with extreme usage, practical experience trumps theory, right? I can't argue results.
 
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I was recently at my local wrecking yard perusing and saw what I believe was a FI era K5. Didn’t happen to check if fuel tank was still there. I understand gm used plastic, but would it be worth dropping the tank and inspecting? I do not want to go the trouble of swapping to FI only to have starvation issues.. the truck dying on steep hills is the primary reason for the swap.. the carb needs a rebuild and tune too so instead putting money into that I’m going FI.. but it also sounds like a lot of you are running aftermarket tanks without issues..
 
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