[DogMeister]

Been having some issues getting my setup to run satisfactorily and will welcome any advice. At best, it is currently running "okay." Took a while to figure out the acceleration enrichment setting which eliminated the off idle bog, but it's surging on acceleration and cruise but not at idle, and the acceleration is mediocre. It ran like a bat out of hell with the Quadrajet carb.

I looked at the timing today and found that it was advancing to 54 degrees at 3000 rpm with the vacuum advance connected to manifold vacuum. Disconnected and plugged it and it maxed out at 36 degrees with 16 initial. Running a GM HEI distributor with a new vacuum canister. Double checked, it was not plugged into ported vacuum. Not sure what's going on there.

461 long-rod stroker in a '69 400 YB block, #45 small-valve heads, 10:1 cr. Melling SPC-5 cam, 198/208 @ 0.050, .404/.408, (I know, it needs more) 4 degrees advanced. Holley in-tank pump/sending unit. 460lb-ft at the rear wheels with the carb.

AFR at idle 13.5, 14 at cruise, 13 at wot. Fuel pressure 60 psi.
Acceleration enrichment 10.5 lb/hr.

Advice greatly appreciated.

[JLMounce]

I'm assuming this is not running timing control through the Sniper?
When you added the sniper did you make any changes to the ignition system from where it was set with the QJet?
Have you verified 60psi of fuel pressure during WOT application?
Does your Holley in-tank pump sit in a sump, or is it sitting in a tank designed around having a carb with fuel bowls?

I think there's way too much advance in your vacuum can. That should likely be limited to around 12 degrees. Fuel slosh away from your pump (if it's not in an internal sump) would certainly cause surging by way of intermittent fuel starvation.

The cam in this is exceedingly small for the size of the engine and the compression it is running. The smallest cam put in a 455 in the early 70's was the 066 and that was put into engines with advertised compression around 8:1. I don't think you can rule out some detonation being cause for some of the surging either. While a TBI system does have a certain degree of charge temperature cooling, it doesn't have the same effect as a carburetor does on the intake charge temp. The carb may have been working in your favor in that regard.

One thing you could do to test that theory is to put some higher octane fuel in the car. If you can get a couple gallons of 100 or 104 in the tank to test with, you may be able to glean if that's an issue. Given the setup, I'd add some WOT fuel as well. I'd want that closer to 11:1.

If you can get and post a datalog, that would be helpful. I'd want to at least see AFR, Throttle Position, MAP, RPM and Fuel Flow.

[DogMeister]

Originally Posted by JLMounce

I'm assuming this is not running timing control through the Sniper?
When you added the sniper did you make any changes to the ignition system from where it was set with the QJet?
Have you verified 60psi of fuel pressure during WOT application?
Does your Holley in-tank pump sit in a sump, or is it sitting in a tank designed around having a carb with fuel bowls?

I think there's way too much advance in your vacuum can. That should likely be limited to around 12 degrees. Fuel slosh away from your pump (if it's not in an internal sump) would certainly cause surging by way of intermittent fuel starvation.

The cam in this is exceedingly small for the size of the engine and the compression it is running. The smallest cam put in a 455 in the early 70's was the 066 and that was put into engines with advertised compression around 8:1. I don't think you can rule out some detonation being cause for some of the surging either. While a TBI system does have a certain degree of charge temperature cooling, it doesn't have the same effect as a carburetor does on the intake charge temp. The carb may have been working in your favor in that regard.

One thing you could do to test that theory is to put some higher octane fuel in the car. If you can get a couple gallons of 100 or 104 in the tank to test with, you may be able to glean if that's an issue. Given the setup, I'd add some WOT fuel as well. I'd want that closer to 11:1.

If you can get and post a datalog, that would be helpful. I'd want to at least see AFR, Throttle Position, MAP, RPM and Fuel Flow.

Yeah I don't know what's going on with the vacuum advance. The only change from prior operation with the carburetor is the new vacuum can since the old one had a hole in the diaphragm. And, well, obviously, the EFI. There should be no vacuum advance at rpm. The can worked fine when installed. Going to see what the manifold vacuum is at idle vs. rpm and make sure the can is releasing.

Even with the dinky cam it ran flawlessly with the carb. The tank is not baffled, but the surge rate was probably not due to fuel slosh since it was happening on straight line level ground .

On the last test run I turned on data logging but shut the car off before turning logging off so it didn't record. This EFI stuff is new to me...

[DogMeister]

And yes no timing control via the Sniper.

[Lee]

If the efi is getting the tach signal from the HEI, then that is where I would start. LOTS of electrical "noise" at that terminal, which can cause the ECU to think that the actual RPM of the engine is bouncing up and down. The ECU will chase the false signals, causing the system to run poorly. Remember, the ecu is making a bunch of calculations every second.

At the least, use the HEI to trigger a CD box, and let the CD box provide a tach signal to the EFI. Even better is to use the distributor designed for this system. With the ECU controlling fuel & spark, AND providing a very accurate tach signal, the system should perform significantly better.

[DogMeister]

I was hoping to get the throttle body set up before going with a controlled distributor, but variation in the tach signal makes sense as a cause.

[Lee]

Originally Posted by DogMeister

I was hoping to get the throttle body set up before going with a controlled distributor, but variation in the tach signal makes sense as a cause.

I installed my first EFI system about 7 years ago. I started with the HEI (Chinese) providing the tach signal. The system ran horrible! Adding a filter made little improvement. Then I added the distributor - clouds dispersed, birds sang,... I was amazed at how different it ran.

About a year later, I took a 2-day seminar at FAST. This was discussed there in more depth. Tachometers are HEAVILY buffered, so they do not bounce around. But if you look at the actual signal, there are all sorts of extra spikes. The ECU needs to respond QUICKLY, so it can't be buffered - so those spikes throw the fuel calculations WAY off.

Then the O2 starts sending rich signals, and the EFI tries to compensate for that, while still using erroneous RPM readings for calculations.

Once you have the ECU controlling timing and fuel, it will start using the timing to smooth out transition periods (going in/out of drive, compressor kicking on/off, abrupt throttle changes, etc.) The timing changes can occur virtually instantaneously, whereas the IAC and such will lag slightly behind. So the ECU will buffer the changes with timing, then restore the timing as the IAC and such settle into place.

I won't install an EFI system unless the owner agrees to let me install the matching ignition system as well.

Good luck

[DogMeister]

Great input everyone, it looks like a dedicated distributor is the way to go.

What have you had success with:
Holley Dual Sync?
Sniper EFI HyperSpark?
MSD Magnetic?

Out of town for a week and a half so nothing's going to be done for a while.

[Lee]

I mainly use FAST. They've treated me well.

For what you have, the HyperSpark should be a perfect fit. I'm not sure if that one requires a CD box or not. If it does, then I suggest NOT using any of the MSD digital stuff - I've had bad experiences with those. I'd rather use a 30 year old MSD analog box (made in Texas) than a brand new digital version (NOT made in Texas, probably in China).