Help!

I put a 1976 390 with duraspark II ignition into my 1975 truck that had a standard ignition 360 engine. I poured over the forum to make sure I was wiring the conversion properly. The newer 390 only has 14000 miles on it and was running great when I pulled it out of the 1976 truck.

After converting the wiring and installing the 390 into my 1975 truck it started right up! I was super proud. BUT, then when I tried to add any fuel to the 390 it advances slightly and then starts backfiring out the exhaust. I've put a new coil (the one with the posts for the duraspark), new fuel pump, rebuilt the Edelbrock 1405 carb, new plugs gapped at .045, new vacuum advance, and installed a new engine control module.

Nothing seems to make a difference. The truck starts and idles nicely. It just won't come above idle without massive backfiring.

I never could find a "pink" wire from my ignition switch to "cut". One thing I did that was a little different from most folks' instructions was to run the red wire that powers my ignition control module to the voltage regulator instead of to the ignition switch.

Can anybody figure out why the engine is backfiring so much and not coming up off of idle?

Thanks!

 

I put the red wire going to the voltage regulator so unless you put it on the wrong wire (I doubt it would start) I'm guessing that's not the issue

Try taking some voltage readings

How much is at the red wire
The white wire during start up
The coil

I assume the "pink" wire is actually the red wire unless you're looking at a different year or something

Then again every diagram I found of those ignitions always had the wires labeled all sorts of weird colors

 

Backfiring when coming off idle can also be a vacuum leak, check for that while it is running.


Also, pull the vac line off of the distributor, plug the end and try it that way too. The distributor will advance as you increase RPM's, that is normal.


What do you have the timing set at?

 

Thanks for your help,

I have around 12 volts at the red wire.

There is also 11-12 at the coil.

I wasn't able to get a reading on the S side of the starter relay. Need my helper!

I still have a brown wire connected to the "I" part of the starter relay and there is 11-12 volts there as well. When I remove that brown wire from the starter relay it has no effect on how the truck starts or runs.

 

You either have a vacuum leak or a timing problem. The brown wire on the I terminal can be cut and used for the retard on start signal to the Duraspark module.

That will allow you to advance the initial timing to 10 degrees or more and it will automatically drop when the starter is engaged. If you are reading a voltage there it is because it is tied to the resistor wire in the ignition circuit (assuming it originally had points).

In the original design the brown wire supplies a full 12 volts to the coil while the engine is starting. It sounds like you tied the red wire into the original ignition circuit, which is why you're reading 12 volts at the I terminal when the brown wire is connected. Disconnect the brown wire and you won't read anything at the I terminal unless the starter is engaged.

 

The coil should be getting 12v only at start, and around 8 or 9 when running

If you had the distributor apart, you may have put the reluctor on backward. I did that a couple of times. Idled fine but wouldn't run above idle

 

I figured you had too much voltage at the coil

Get a ballast resistor at the local auto parts store plumb it in on the hot side of the coil

I don't have much to add except plug wires

 

While that is true for points ignition, it is not true for Duraspark II. It should get 12 volts all the time. Running a constant 12V to points will cause them to fail prematurely. Not a concern with Duraspark. Just need to use the module with the blue strain relief.


And that is essentially a timing problem. If he took the reluctor off and didn't put it back in the same place, then he changed the timing in the distributor.

 

Where to start...

The biggest question I have that may help me trace the problem is: what would make the engine run this way. Is it too much voltage at the coil? I don't think so because I agree that with the duraspark I've read that you'll have 12 volts at the coil all the time.

I live at 7,300 feet elevation and have the initial timing set at 15. I've never taken the reluctor out.

I think 66v8baby may be right about the wiring. I looked at Painless and they have a pricey kit that looks like it might be the way for me to go. Anybody have any experience with that?

Thanks for chiming in everyone!

 

Maybe this will help:
1975-79 DISTRIBUTORS & IGNITION

 

Agreed. DSII....if you have 12 VDC at the coil at any time other than starting, it will burn out the coil. The "I" terminal on the starter solenoid will have 12 VDC only on "START," bypassing the ballast resistor circuit. After that, you should read zero (0) VDC and the ballast resistor bypass circuit kicks in (key in "RUN") limiting the voltage to the coil to 6~8 VDC.

Papa Bear Yuma had this reluctor problem before so he knows of what he speaks when he says it being (possibly) assembled incorrectly. On some DSII models, there are two marks indicating reluctor assembly while other just fit the roll/shear pin in for correct assembly. Worth a peek-see.

Vacuum lines worth checking as well as a breaker plate check to see if it's freely moving and not binding.

 

Great info guys! I'll go over it this weekend when I get a chance. Got to work

I'll post when I get some more questions of info.

Have a great weekend!

 

I've been running Duraspark II with the blue relief on my 69 Mach 1 since 1994. I have tens of thousands of miles on 2 different engines. I've driven from coast to coast. I've raced it on the track at Carolina Motorsports park and the one in Nashville. I bypassed the resistor wire completely and use the brown 262 wire for the retard on start signal to the DII module. I run an MSD blaster II coil (Duraspark compatible) and it has never burned out.

While it's true Ford initially dropped the voltage to the coil with Duraspark I, by the mid 80s the starter solenoid didn't even come with the I terminal. They ran 12v to the coil all the time.

 

I purchased a Painless Duraspark II harness and will be installing it this week. Interesting note: It comes with a ballast resistor but tells you to look at your coil and if your cold has written on it "No Resistor Required" then you don't have to install the resistor and run straight 12 volts to the coil.

 

The MSD blaster II coil has served me well. I first had it on the 351W with a mild performance cam, Autolite 4100 and twisted wedge heads.

I replaced the 351 with a 500 HP roller cammed 408 and thought I should "step up" to a more performance oriented ignition. I tried an MSD 6 when I first installed the 408, but it didn't want to idle very well so the Duraspark II went back in. Problem solved. I've never considered anything else since then.