Craign74

New Member
Jun 3, 2020
2
0
1
45
Chicopee, MA, USA
Looking for some help or advice. I've just recently rebuilt my 1991 LX with a 408 stroker motor and MSD ignition system, and Aeromotive Fuel System. Here is what has been done so far:

Verified fuel pressure running around 42PSI, and the motor has great compression, problem seems to be with the Ignition System.
So to start I did a wire tuck, and battery relocation to the trunk, to which I was extremely cautious to use the correct gauge wires, and all my grounds I sanded down the locations to make sure they made good contact. I have 12 volts, to the MSD box and when cranking it drops down to around 10 volts. Verified with all the on-line sites I can find that my TFI and PIP are sending a proper signal to the coil but it still wont fire with my MSD 6AL box connected. If I by-pass the 6AL box I can see a spark but it looks weak. I have talked with MSD numerous times, and done there box/coil test and which has me ground the white wire to body ground with key on and I get a GREAT spark. So to me there is definitely a signal missing when cranking to the coil.
I have replaced the MSD 6AL box, coil, and distributor all twice with no difference. Any help would be GREATLY appreciated.
 
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7991LXnSHO

Now I want a 10 year badge
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I think more will
see this if you post it in Fox Tech.
Here is the info you need.
 

giddyup306

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Oct 22, 2002
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Looking for some help or advice. I've just recently rebuilt my 1991 LX with a 408 stroker motor and MSD ignition system, and Aeromotive Fuel System. Here is what has been done so far:

Verified fuel pressure running around 42PSI, and the motor has great compression, problem seems to be with the Ignition System.
So to start I did a wire tuck, and battery relocation to the trunk, to which I was extremely cautious to use the correct gauge wires, and all my grounds I sanded down the locations to make sure they made good contact. I have 12 volts, to the MSD box and when cranking it drops down to around 10 volts. Verified with all the on-line sites I can find that my TFI and PIP are sending a proper signal to the coil but it still wont fire with my MSD 6AL box connected. If I by-pass the 6AL box I can see a spark but it looks weak. I have talked with MSD numerous times, and done there box/coil test and which has me ground the white wire to body ground with key on and I get a GREAT spark. So to me there is definitely a signal missing when cranking to the coil.
I have replaced the MSD 6AL box, coil, and distributor all twice with no difference. Any help would be GREATLY appreciated.
You gave us a whole lot of info we don't need. Did you check with an inline spark tester to see if there is spark (you can also use a regular test light but it can blow out the bulb)? I've heard of brand new crate engines not starting because they had the wrong plugs in them (also check gap). If you don't have spark at the plug, try directly out of the coil. If no check with a test light to see if you have a pulsing signal to the primary of the coil. If no, wiring or the box. Did you inspect the distributor cap? Lots of times you can get a carbon track in there, and will ground through that.

If it's on the fuel side 42PSI may or may not be enough. Check with a mechanics stethoscope to hear in the injectors are working. If not use a noyd light to check for power and ground (but you can use a test light). Ford injector problems is pretty uncommon. Or you can pull the plugs out after cranking and look to see if fuel is being injected. Also how old is the fuel?
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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The no start go to:
Do it step by step, don't skip around
 

Craign74

New Member
Jun 3, 2020
2
0
1
45
Chicopee, MA, USA
Looking for some help or advice. I've just recently rebuilt my 1991 LX with a 408 stroker motor and MSD ignition system, and Aeromotive Fuel System. Here is what has been done so far:

Verified fuel pressure running around 42PSI, and the motor has great compression, problem seems to be with the Ignition System.
So to start I did a wire tuck, and battery relocation to the trunk, to which I was extremely cautious to use the correct gauge wires, and all my grounds I sanded down the locations to make sure they made good contact. I have 12 volts, to the MSD box and when cranking it drops down to around 10 volts. Verified with all the on-line sites I can find that my TFI and PIP are sending a proper signal to the coil but it still wont fire with my MSD 6AL box connected. If I by-pass the 6AL box I can see a spark but it looks weak. I have talked with MSD numerous times, and done there box/coil test and which has me ground the white wire to body ground with key on and I get a GREAT spark. So to me there is definitely a signal missing when cranking to the coil.
I have replaced the MSD 6AL box, coil, and distributor all twice with no difference. I have followed all the steps from link https://www.stangnet.com/mustang-fo...-checklist-for-fuel-injected-mustangs.787471/ and nothing seems to be pointing to the issue, except possibly an ECU issue.
Only last things I can think of is because I moved the battery to the trunk i only used 1 ground for my ECU ground in the wheel well and the original wire also also went to the battery. Or the other suggestion I heard was that it would be a good idea to separate the ECU ground in the wheel well from the MSD ground because the two together could cause an issue. For now I have sent my ECU out for evaluation, so we will see what they find, but any other help would be GREATLY APPRECIATED!!!
 
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