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Rickey
10-10-2003, 09:41 AM
High RPM popping

we have a 7AL-3, MSD dis, and coil, 11mm wires, changed plugs several times

saw on talk forum's where several guys are replacing their 7AL-3 with 7AL-2
and selling their 7AL-3's

is there a problem with the 7AL-3's that we should know about?

we have changed coil and dist wires with shielded cable

can tack output connection have any affect? our data recorder shows RPM's bouncing around

msdtech4
10-10-2003, 09:48 AM
Sir,

There is nothing wrong with the 7AL-3, but you do need to make sure the system is good and clean. Here is a number of things that you can look at that can cause problems. Here are several items that you can check, first the only 2 wires that should be physically touching the coil, should be the orange and small black of the MSD unit. Check voltage at higher RPM's it should maintain above 10 Volts, if voltage is falling too much this can cause a miss. The wires that go from the MSD unit to the distributor, make sure these wires are not close to any other power wires, try to isolate these wires away from any other power wire or spark plug wires. If you have already tried isolating these wires, you may want to check spark plug wires for resistance, to much resistance on a wire may cause a lot of RFI noise. When checking the resistance, shake them around and see if there is any resistance change or breaking up. If you have any electrical component like an electric fan or water pump try to shut these items down for testing purposes and see if it clears up. Try reducing the plug gap by .005 increments and see if it improves. These items can cause the engine to miss at higher RPM's.

Thanks,

MSD tech4

Rickey
10-10-2003, 11:34 AM
the wires from the unit to the coil and dis have been replaced with twisted shielded wire.

plans are to replace spark plug wires next, even tho the ones on it are new 11mm

will double check spark plug gap

what should the gap be for the 7AL-3?

msdtech4
10-10-2003, 02:42 PM
Rickey,

We can address both of your questions on this one thread. The problem you are having with the high RPM misfire is causing the problems with the data recorder. The system is picking up noise which is why this is happening. Even though you have changed to the shielded cable that cable must be routed by itself, keep it away from anything carrying current. If it goes through the firewall make sure it goes through it's own hole. Do not zip tie or loom this harness with any other wires. Plug wires are made by people and if a wire is not crimped correctly they will not suppress noise which will cause this problem. Don't buy another set, check the resistance of the wires and get the per foot average. You are looking for a wire that is out of range as far as the per foot average compared to the rest of the wires. It takes one wire to cause problems so make sure you check the coil wire also. Anything electric, like a fan water pump etc., turn off during a pass. These can generate a lot of noise and as they wear will become even noisier. Make sure you are using a resistor type plug also. Double check the grounds from the motor to the battery. If you are relying on a chassis ground for the motor don't. I would recommend running a ground from the battery to the block and then distribute your grounds from this one point. A motor with a poor ground will not only not fire correctly but will be a very noisy (electrically) motor. With out knowing the compression of the motor a normally aspirated motor I would set them around .045 and a motor with some sort of power adder I would recommend about .035.

Thanks,

MSD tech4

Rickey
10-13-2003, 08:23 AM
the coil wire and dist wire is shielded and both go thru seperate holes in fire wall.
the Tach output wires are also shielded
the spark plug wires were MSD changed to Blue Max and back to MSD wires.
I checked both sets, MSD were about 50 ohms per foot and Blue Max 800 ohms per foot, no difference
have new plugs NGK spark plugs ordered

will run a ground cable from battery

problem just started a couple weeks ago

we have taken engine apart to check everything

plans are also to replace the MSD 7AL-3 with a 7AL-2 based on other racers

hope to run again this weekend, if we get all back together

msdtech4
10-13-2003, 09:06 AM
Let me know what happens. Keep in mind that going to a 7220 is really not a valid test, but let me know.

Thanks,

MSD tech4

Rickey
10-15-2003, 06:51 AM
nothing is working, we have tried all the changes, rewired the truck, tore engine down, changed spark plugs, wires, everything.

our engine builder, who is a long time NHRA engine builder says we need to replace Coil and MSD 7AL-3 box


what do we have to do to have them sent back and checked?

it's a lot of money to replace them, only have 13 runs on them

msdtech4
10-15-2003, 09:33 AM
Rickey,

Go ahead and send them in with a note explaining what is going on and we will get them checked out. It is very uncommon to have a problem with a box and it still functions but let us check it out. No you do not have to replace them!!! The address is:
MSD Ignition Attention Repair Department
12120 Esther Lama Dr Dock 5
El Paso, TX 79936
If you would like include a copy of this thread and send it to my attention and I will get it checked out.

Thanks,

MSD tech4

Rickey
10-15-2003, 09:59 AM
plan to remove tonight and Fedex tomorrow,

do I need a RMA number?

msdtech4
10-15-2003, 10:21 AM
Rickey,

None needed just put a copy of this thread in with the box.

Thanks,

MSD tech4

Rickey
10-16-2003, 09:31 AM
thanks


have also included Distrubitor just in case


on another note my son had a dead 6AL so we put it in same box to save on shipping
hope it can be fixed


will be shipped priorty overnight am delivery

msdtech4
10-16-2003, 10:28 AM
Rickey,

Ok, we will get them checked out. The 6 boxs can be repaired with a maximum charge of $55.00 if the unit is out of warranty.

Thanks,

MSD tech4

Rickey
10-20-2003, 06:08 AM
making sure you got my units last Friday?

thanks

Rickey
10-20-2003, 09:31 AM
need back asap

let me know please

if not back by weekend will have to buy new ones
big race

msdtech4
10-20-2003, 11:07 AM
Rickey,

There where logged into the system this morning and are going through repair. Normal turn around on a rush is 8-10 days, we will see if we can get them done in time but do not want to promise you and it not happen. give me a call Thursday morning at 915-855-7123 EXT 186 so I can check on them for over night delivery for Friday.

Thanks,

MSD tech4

Rickey
10-21-2003, 08:36 AM
the MDS 6 box can wait and be shipped at any time as it was just sitting on the shelf

we do need the others back tho, if there is a chance they want get checked out and shipped back this week I need time to replace them


do you know anyone that has them on sale right now?

msdtech4
10-21-2003, 08:54 AM
Rickey,

That's fine, we can ship the 6 box back at a later time if it is not done. We actually do not keep track of who has what on sale, but give us a little time to get the unit checked out. There is no sense in buying another box if we can finish the unit. The vast majority of us either race, have street cars etc., so we know about wanting to make a "show" so we try and get them done when the customer requests it.

Thanks,

MSD tech4

Rickey
10-22-2003, 02:38 PM
any idea where it is in the line to be checked?

my son is bugging the sh?t out of me

will need to know by am Thursday, that gives me time to order new parts over night

msdtech4
10-23-2003, 11:24 AM
Rickey,

I will call you as soon as I have some information.

Thanks,

MSD tech4

Rickey
10-24-2003, 06:51 AM
did all but 6al get shipped ok?

thanks for all your help

will let ya know if the problem goes away

msdtech4
10-24-2003, 09:00 AM
Rickey,

Yes, everything except the 6 box. let me know what happens, at least they found a problem.

Thanks,

MSD tech4

Rickey
10-27-2003, 06:19 AM
don't what fixed our problem as we changed so much stuff but it's fixed

we ran 5.18, 5.16, 5.14, 5.13 and never got a chance to do any tuning

great job , thanks

msdtech4
10-27-2003, 10:09 AM
Rickey,

Great! This was one of those "never" cases that happen. Super uncommon to have a box still function but cause a misfire. Like I had mentioned chances are it would have failed eventually until you took the RPM chip out. But none the less I am glad it fixed the problem!

Thanks,

MSD tech4