New 393C running, Won't Rev Beyond ~3500 RPM

[Casey72]

Have you tried tossing a carb back on it and see if it fixes the problem? That would go a long way towards seeing what the culprit may be.

I always had a known good carb, distributor, and coil to first fire or to test a fidgety engine.

- Paul of Mo

I don't have a carb to fit the bill and the plumbing would require some modification. The other extras I have are Windsor parts, so I'm out of luck.

 

[Don C]

I don't know how sensitive the Atomic programming is to possible conflicts or how it resolves conflicting information. It seems to me that 9 inches of vacuum indicates more than a mild cam. Is it possible the program is interpreting input and data in two different ways? What are the choices for cam selection? If they are limited that may be your only choice.

 

[Casey72]

I don't know how sensitive the Atomic programming is to possible conflicts or how it resolves conflicting information. It seems to me that 9 inches of vacuum indicates more than a mild cam. Is it possible the program is interpreting input and data in two different ways? What are the choices for cam selection? If they are limited that may be your only choice.

The options come down to stock, mild and performance. My cam is within the "performance" range by a fair margin according to MSD. Since the engine seems to idle about the same with both mild and performance settings, I ended up going with performance. Manually setting the idle air control seemed easier on that setting, and was overall much easier than setting it for the milder Windsor I replaced.

Also, the firmware is all up to date on the FI. I checked that before swapping engines and did a system reset before firing up the new engine.

 

[barnett468]

Barnett, the atomic can simulate vac adv for both ported and non ported up to around 15*. It has a MAP sensor so it takes SL pressure minus the map reading while running to determine how much vac the motor is producing. So at KO if the MAP reading on the handheld is 29.92 and idle its 15 then the engine is making 14.2" of vac. To disable vac adv just set vac to 0 in the handheld.

Thanks for the explanation jbojo, but I have absolutely no idea what you are talking about. rofl

 

[Paul of MO]

Have you tried tossing a carb back on it and see if it fixes the problem? That would go a long way towards seeing what the culprit may be.

I always had a known good carb, distributor, and coil to first fire or to test a fidgety engine.

- Paul of Mo

I don't have a carb to fit the bill and the plumbing would require some modification. The other extras I have are Windsor parts, so I'm out of luck.

The carb would not have to be exact or even close for that matter - it would be easy to bolt on and gravity feed a few ounces of fuel to the carb - just long enough to rev the engine. Any carb from 600cfm to 800cfm will work

If there is an fuel pump eccentric installed in the engine then you could install a $20 mechanical fuel pump and feed it from a gas can sitting on the floor.

If it revs up to 6K then you know it is the EFI. If it tops out at 4K then it is something in the engine.

It may also "solve" your issue by taking the EFI TB off, unplugging everything, and reinstalling it. There should be a way to wipe all of the existing learned memory and start over clean.

- Paul of MO

 

[barnett468]

Casey, you do not want and do not need a simulated vacuum advance feature . Disconnect the vacuum advance as i previously mentioned.

Give it more gas . It will probably go fast . It really probably is that simple.

 

[Casey72]

Have you tried tossing a carb back on it and see if it fixes the problem? That would go a long way towards seeing what the culprit may be.

I always had a known good carb, distributor, and coil to first fire or to test a fidgety engine.

- Paul of Mo

I don't have a carb to fit the bill and the plumbing would require some modification. The other extras I have are Windsor parts, so I'm out of luck.

The carb would not have to be exact or even close for that matter - it would be easy to bolt on and gravity feed a few ounces of fuel to the carb - just long enough to rev the engine. Any carb from 600cfm to 800cfm will work

If there is an fuel pump eccentric installed in the engine then you could install a $20 mechanical fuel pump and feed it from a gas can sitting on the floor.

If it revs up to 6K then you know it is the EFI. If it tops out at 4K then it is something in the engine.

It may also "solve" your issue by taking the EFI TB off, unplugging everything, and reinstalling it. There should be a way to wipe all of the existing learned memory and start over clean.

- Paul of MO

I did install the eccentric for the pump (because why not?), but the only carb I have is literally a box of parts in the attic that's supposed to be most of a crusty Holley 750. I got it with some other stuff as an "extra" a dozen years ago.

Though I did the system reset and cleared out all the self-learning before running the new engine and after having run it on the "mild" cam setting for a while, it's probably time to go back to a clean slate again for the tuning process, or it should happen soon. Having to let it learn again is a PITA, though.

 

[Casey72]

Casey, you do not want and do not need a simulated vacuum advance feature . Disconnect the vacuum advance as i previously mentioned.

Give it more gas . It will probably go fast . It really probably is that simple.

Roger that. Your take on that has gotten me this far. And it can't hurt.

 

[Casey72]

Everyone seems to agree about more fuel. I'm going to try going to AFR of 12.5 from 13.0 (even more for WOT, from 12.8 to 12.0) and see how far I can go with idle timing and where it likes the timing to come in with vacuum advance turned off completely, going up from 2500 RPM in settings. Any suggestions I'm not remembering?

 

[barnett468]

Everyone seems to agree about more fuel. I'm going to try going to AFR of 12.5 from 13.0 (even more for WOT, from 12.8 to 12.0) and see how far I can go with idle timing and where it likes the timing to come in with vacuum advance turned off completely, going up from 2500 RPM in settings. Any suggestions I'm not remembering?

yes, set wot to 11.0, not 12.0 . it is thirsty . it wants to drink . you have a huge cam.

also, dont forget the compression test.

 

[tony-muscle]

Reading the FAQS for the MSD Atomic TBI says that a cam more aggressive than 250 wont work. Yours is borderline. However, i dont see why it will be an issue at 4k rpm. I would have guessed the problem to show up at near idle, but not sure. I just throw the thought out there for debate.

1971 M-code Mach 1

 

[barnett468]

Though I did the system reset and cleared out all the self-learning before running the new engine and after having run it on the "mild" cam setting for a while, it's probably time to go back to a clean slate again for the tuning process, or it should happen soon. Having to let it learn again is a PITA, though.

Ok, I have friends that deal with this and one of them drag races with a self learning unit and they have found that it is better to program the fuel curves themselves because the self learning is always changing and the guy that drag races went slower with the self learning system.

 

[Casey72]

Everyone seems to agree about more fuel. I'm going to try going to AFR of 12.5 from 13.0 (even more for WOT, from 12.8 to 12.0) and see how far I can go with idle timing and where it likes the timing to come in with vacuum advance turned off completely, going up from 2500 RPM in settings. Any suggestions I'm not remembering?

yes, set wot to 11.0, not 12.0 . it is thirsty . it wants to drink . you have a huge cam.

also, dont forget the compression test.

That's the way I'll go with it.

 

[Casey72]

Reading the FAQS for the MSD Atomic TBI says that a cam more aggressive than 250 won't work. Yours is borderline. However, i dont see why it will be an issue at 4k rpm. I would have guessed the problem to show up at near idle, but not sure. I just throw the thought out there for debate.

1971 M-code Mach 1

242 at .050" is borderline, but I also guessed that would be an idle issue, plus the extra 42 cubic inches can't hurt. The progress so far and the excellent quality of the idle makes me think it's OK with that much cam.

 

[Casey72]

Though I did the system reset and cleared out all the self-learning before running the new engine and after having run it on the "mild" cam setting for a while, it's probably time to go back to a clean slate again for the tuning process, or it should happen soon. Having to let it learn again is a PITA, though.

Ok, I have friends that deal with this and one of them drag races with a self learning unit and they have found that it is better to program the fuel curves themselves because the self learning is always changing and the guy that drag races went slower with the self learning system.

I don't really doubt that for the track. Seeing the cold and hot starts, idle and cruise all tighten up on the street is pretty impressive, though.

 

[barnett468]

Everyone seems to agree about more fuel. I'm going to try going to AFR of 12.5 from 13.0 (even more for WOT, from 12.8 to 12.0) and see how far I can go with idle timing and where it likes the timing to come in with vacuum advance turned off completely, going up from 2500 RPM in settings. Any suggestions I'm not remembering?

yes, set wot to 11.0, not 12.0 . it is thirsty . it wants to drink . you have a huge cam.

also, dont forget the compression test.

That's the way I'll go with it.

.

xlnt, my guess is that if that does not make a significant improvement, you likely have an additional problem and at that point i wouldn't rule valve float out, but again, it "should" spit and sputter some . been there, done that a few times.

exactly which weiand intake do you have?

if you have the 4v excellerator, do your self a big favor and buy a 1" open spacer from any auto parts store if you have hood clearance and tune with that . i can virtually guarantee you it will run better with that once it gets enough gas and may extend your rpm range by a few hundred.

a tapered 4 hole spacer sometimes works better than an open one so they need to be tested back to back, but a good 4 hole wilson or maybe jomar or hvh spacer is around $100.00.

.

urc

.

 

[Casey72]

yes, set wot to 11.0, not 12.0 . it is thirsty . it wants to drink . you have a huge cam.

also, dont forget the compression test.

That's the way I'll go with it.

.

xlnt, my guess is that if that does not make a significant improvement, you likely have an additional problem and at that point i wouldn't rule valve float out, but again, it "should" spit and sputter some . been there, done that a few times.

exactly which weiand intake do you have?

if you have the 4v excellerator, do your self a big favor and buy a 1" open spacer from any auto parts store if you have hood clearance and tune with that . i can virtually guarantee you it will run better with that once it gets enough gas and may extend your rpm range by a few hundred.

a tapered 4 hole spacer sometimes works better than an open one so they need to be tested back to back, but a good 4 hole wilson or maybe jomar or hvh spacer is around $100.00.

.

urc

.

The intake is the X-celerator, chosen for its low height. I'm running a half-inch open spacer and there's a small rub spot on the air cleaner from the hood, so I'm out of space at this point.

Rain may subvert my efforts to actually drive the car for testing today, but I'll plug in the new fuel and timing numbers and set the IAC if necessary. Idle hasn't been an issue at all, so it's a matter of seeing how much timing I can run before it has hot start issues.

 

[Casey72]

I played around and ended up with 20 degrees of timing at idle set in the handheld and it starts easily when hot. Due to the insane sensitivity of the IAC it's either IAC of 0 and the computer retarding the timing to around 18 degrees with a nice idle, or IAC of 50-60 with full timing and a rougher idle. I went with IAC 0.

For AFR, idle and cruise are 12.5, WOT is 11.0 now. Timing is 20 at idle (18 in practice), 34 total at 2800 and around 26 at 2000. I set the pump squirt to 40 and power valve to 10.

Ok, taking it for a quick ride to beat the weather, there was a marked improvement. A slight tumble when tipping into the throttle, but a quick half-throttle flashes the converter and results in tire spin. At 2/3-3/4 throttle it really screams, zero to 40 in about 2 seconds (or damn close to it), with 50 and the overdrive kicking in before I can shift to 3rd, all without going but a tick beyond 5000 RPM. Near or at WOT it rumbles and sputters a bit and won't rev much at all beyond 4500. No power and very sluggish acceleration.

So, what am I looking at when scratching WOT? More fuel?

 

[barnett468]

post a photo of the two front plugs again

buy a 1" spacer.

what size are your header tubes?

 

[Casey72]

post a photo of the two front plugs again

buy a 1" spacer.

what size are your header tubes?

I'll need a new air cleaner, too, then. Header primaries are 2", which are big enough to fit the exhaust ports.

The plugs look the same. Electrodes are bare metal with a slight dark tan powdering. Dark tan deposits stronger on the tips. This was after a good 20 minutes of idling followed by 15 minutes of driving with 12.5 AFR vs. 14.0 AFR from yesterday.