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Discussion Starter #1
Here is what I am dealing with gentlemen.

fresh 390 with edelbrock heads and the whole msd ready to run dizzy, blaster 2 coil, msd plug wires, and just installed yesterday 6al.

I am running 93 octane

The problem is the car break up under throttle when it wants to. like taking off never getting over 2500 rpms it breaks up under a load but when it gets up in rpms it smooths out and all power comes back.

Also it breaks up every time under full throttle around 4000 rpms and up. It just stops pulling and acts like its trying to find timing or something. I am stumped here.

Please ask any questions and I can answer it. has a 750 edelbrock. total timing is 32. It does have a vacuum advance and taking it off does not change the problem.

Should I change the spring weight in the MSd distributor?? a picture of my progress. Its been a while since I updated on here.



 

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Just an assumption but car wasnt doing this before? What all did you change? Think all the R-T-R stuff needs a full 12v and not ran thru the original resistor/ignition wire. Check that first (needing full 12v to coil) Then maybe someone else will have other ideas....
 

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also.. maybe a lose connection somewere or break in wire...
causing it to cut in&out under load as motor move a little. or short out.??
 

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Discussion Starter #5
So here is what I just did, I changed the springs around and got it to stop breaking up at low rpms under a load. No change in the upper. I then changed the bushing in the distributor and it seems to pull a little better.

After all this I decided to check the plugs and they all looked great and nice and crispy brown, other than the #5 was a little blacker and looked to not be burning as well. I regapped all of them from 35 to 50 since I added all the msd and I could tell a huge difference. She didn't break up half as bad on the upper end.

The car has really done this ever since the new engine build install.

Here is another factor I found I am running an edelbrock fuel pump and edel 750. but its all running through the original 5/16 fuel system. I felt as if no need to change it because the pickup tube in the tank is a 5/16. Well I just replaced the tank with a 66 tank with a 3/8 pickup. Could I be starving the engine of fuel when I get down on it. It seems to pull hard and break up less if I ease through the petal. The real breaking up is if I just slam it to the floor and once it gets in the upper rpm range it breaks up.

I am thinking about just buying the new MSD ATOMIC EFI with timing control and just put it on and forget it.
 

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Discussion Starter #6
also what does floating the valves sound like and feel like. Its not consistent enough for me to think its this but if it is I have another set of heavier dual springs in the shop
 

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Discussion Starter #7
also to answer any questions, all connections are great. Has a solid 12 volts to the msd 6al with a solid state 12 volts positive and negative from the battery. The only thing feeding the coil is the 6AL. I am pretty positive its not connections in the 12 volt system. Could a broken plug wire cause this? I put my timing light on all of them right at the plug boot and raised the rpms and never seen any stop firing.

I am starting to believe its running out of fuel. Also just notice I have a 1/4 in line filter.
 

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It COULD be fuel related, but after reading your answers to the questions and the updates, do you know the rpm it starts to 'break up'. Does it just start missing or is there sound associated with it? Have any idea of what valve springs you are using, age? Or is the break up in the upper rpm range of your engine and what is the rpm there? All kind of needed to help clear it up without just throwing 'fixes' at it....
 

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hmmm...i think there's fuel in bowls at idle.when taking of..??but sounds like carb needs to be tuned also...??
taking off never getting over 2500 rpms it breaks up under a load but when it gets up in rpms it smooths out
 

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Discussion Starter #10
Its starts breaking up around 4000 and up, it will break up then pull a little then keep on over and over. There are no sounds assosiated with this problem that I can hear. I have comp cams roller rockers with comp cams recommended valve springs for my cam and lift, all less than 5000 miles.

The comp cams rollers are a little louder than factory, almost sounds like a loud sewing machine. And I do swear that I hear rockers around 3000 rpms with the windows up but everyone says I am crazy and besides thats not where the rpm range has problems.
 

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Discussion Starter #11
I have adjusted the floats per edelbrocks specs when I first started seeing this. I am going to get some 3/8s line tonight or tomorrow and will see what this does, if nothing happens I am going to sheck into more carb tuning. Is there any adjustments that can be made on the edel to get more fuel at WOT
 

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1) The IGN MOD and IGN COIL should have separate BAT VOLT feeds.

2) You have an EDEL mechanical pump correct? Why is the filter installed before the pump?
 

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Discussion Starter #13
1) The IGN MOD and IGN COIL should have separate BAT VOLT feeds.

2) You have an EDEL mechanical pump correct? Why is the filter installed before the pump?

The IGN COIL is fed by two designated wires off the 6AL now. "Not the Ign from the car battery.

The 6AL and dizzy is the only thing in the MSD system that is getting switched 12 volts from the key

Also I realize the filter is in the wrong place, I will post back up tomorrow how she does, I got some 3/8s line and a new inline filter for after the pump.
 

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The IGN COIL is fed by two designated wires off the 6AL now. "Not the Ign from the car battery.

The 6AL and dizzy is the only thing in the MSD system that is getting switched 12 volts from the key

Also I realize the filter is in the wrong place, I will post back up tomorrow how she does, I got some 3/8s line and a new inline filter for after the pump.
What I should have said is the MSD Module should be fed directly off the BAT through a fused relay circuit. I am surprised MSD did not suggest this.
 

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Ok lets see from rereading the post(s) I gather that the onlymajor change was the 6AL box? Have you tried to run the car with out it?


Also the new 6AL's has a built in rev limiter doesnt it? If so check to see where its "set" at, could be your running it up against the limiter...... PN6420/6425has the limiter PN6200/6201 does not.... I just had the "Better Idea" light bulb come on is the reason i took a left turn when i started to answer.

(The 6420 is discontinued and replaced w/ 6425 same thing with the 6200and 6201 , according to their website..)

Let us know the results of the fuel line change...and if the rev limiter is part of the equation...
 

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What I should have said is the MSD Module should be fed directly off the BAT through a fused relay circuit. I am surprised MSD did not suggest this.
I havent d/led their instruction manual so I am unsure if they do or dont...
 

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Copy and paste from MSDignition.com

REV Limiter Verification
MSD Digital 6AL Ignition Control
PN 6425
The MSD Digital 6AL has an optional built in Rev Limiter Verification feature. When activated, it will display the
unit’s rev limit setting at key-on. This feature is not activated from the factory. To enable this feature, follow the
procedure below.
Note: It is important to note that this feature should not be used with EFI systems. When activated, an rpm
signal is sent to the tachometer. With an aftermarket EFI system, this could activate the injectors causing
a flooding situation.
ENABLE REV LIMIT VERIFICATION
1. With the ignition switch in the off position, ground the Gray tach output wire.
2. With the Gray wire connected to ground, turn the ignition on without starting the engine.
3. Hold the Gray tach output wire to ground for seven seconds. (AT LEAST five seconds.)
4. Release the wire from ground before ten seconds have passed.
5. To confirm the process has worked, cycle turn the key On. The tachometer should sweep to the rpm limit
set on the ignition.
To deactivate the verification feature, repeat the process.
M S D • MSD Ignition • (915) 857-5200 • FAX (915) 857-3344
FRM30943



© 2012 Autotronic Controls Corporation

Created 01/12


Printed in U.S.A.
 

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Ok lets see from rereading the post(s) I gather that the onlymajor change was the 6AL box? Have you tried to run the car with out it?


Also the new 6AL's has a built in rev limiter doesnt it? If so check to see where its "set" at, could be your running it up against the limiter...... PN6420/6425has the limiter PN6200/6201 does not.... I just had the "Better Idea" light bulb come on is the reason i took a left turn when i started to answer.

(The 6420 is discontinued and replaced w/ 6425 same thing with the 6200and 6201 , according to their website..)

Let us know the results of the fuel line change...and if the rev limiter is part of the equation...
GOOD FIND! :tup:
 

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Discussion Starter #19
It was doing this before the 6AL, I was hoping the 6AL would help the problem.

I have the 6Al set to 6000 rpm on the rev limiter. When I installed the MSD dizzy it IS capable of a rev limiter as well but I did NOT set it up. My tach never moves during key on. Its not set, only the 6AL is

So here is what happened when I put the 3/8's line on this morning. It took 90 percent of the higher rpm range break up completely out, Like so much that if you was to ride in it for the first time you would never notice it. I have come to the conclusion most of the problem was the lack of the fuel, And now I feel like it is a matter of better tuning. The plugs still look good but I want this thing perfect. Has anyone seen the MSD ATOMIC efi on an fe yet?????? IF Not would yall like a write up and install of one with pictures when i buy mine????lol
 

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Well am glad that you are sorting it all out, sounds great that progress has been made, and a little fine tuning should sort the rest out.

Well I am not running the atomic and probably never will, carbs for me, but a write up with pics and experiences i am sure would be welcomed....
 
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