Dang waggy won't start after swapping injection harnesses

[AwesomeJ10]

I can't figure this one out.

'88 GW AMC 401 TFI ignition TBI injection. GM 8 pin ignition module. Stock dizzy.

It all was working great but I was wanting to swap over to my 'better' junkyard TBI. Everything swapped over great. Problem is it won't start. It won't start because it has no spark. On TBI, you must have spark before the ECM fires the injectors.

I'm getting 12V to both sides of the TFI coil even while cranking the engine. No spark. Here is the catch - I have yet to remove the dizzy and weld the advance. It's not been removed since the engine last ran (4 days ago). ECM is working great. Fuel Pump comes on and I get a green 20 in winald and all sensors are working and reading data.

Why the HECK am I not getting spark? I think the problem is either the 8 pin module or the dizzy, but which one??

[Stuka]

Maybe I am misunderstanding something, but you should only have voltage on one side of the coil. The other side grounds which collapses the magnetic field which creates the voltage needed for the spark.

But if the EFI is looking for spark, I am betting its actually looking for the spark signal, not actual spark. So the coil working or not working should not matter. I would go back to the ignition module and check its voltage supply, and see if it is sending a signal out.


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[AwesomeJ10]

Bingo!

The GM 8 pin ignition module wasn't grounded, so it wasn't working. The funny part is that I actually ran a ground wire to it, but the ground wire wasn't making continuity

But yeah, the TFI coil does get 12V to both terminals (at least it did start up and run with 12 V to both terminals).

Took this pic while it was idling in the garage. Check engine light was on. I'll have to do some more work as the wiring is still a MESS and it didn't turn off when I shut off the key (run on).

[Stuka]

I could have sworn mine had had a + on one side and a - on the other.


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[jsinajeep]

I could have sworn mine had had a + on one side and a - on the other.


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It does, but if you put 12v on the + side the current will go through the coils and out the -.
If he put a test light to the wire that go to the - by itself he should not have 12v.

[AwesomeJ10]

Yes, some of them do.

However

I'm running a stock (from junkyard Ford big block) TFI coil and it's NOT labeled. None of my other junkyard TFI coils actually have a + or - on them. Previous experience and posts from IFSJA indicate that a TFI coil must ground through it's bracket, not the terminals.

[jsinajeep]

The coil works the same as on an old point system. You had the 12v wire to the + side of coil
And the - side went to the point in the dist. everytime the point closed it caused a ground and it
signal the coil to send the current through the coil/dist. wire to the dist.

[REDONE]

Yes, some of them do.

However

I'm running a stock (from junkyard Ford big block) TFI coil and it's NOT labeled. None of my other junkyard TFI coils actually have a + or - on them. Previous experience and posts from IFSJA indicate that a TFI coil must ground through it's bracket, not the terminals.

I don't think so, mine works just fine with the body (the laminated metal frame around the outside) undgrounded. Grounding it through the bracket after testing just made my stereo sound better.

My TFI coil is a new OEM from the parts store and it wasn't labeled either. I had to look at pics of aftermarket ones to figure out which side was positive. I'm with jsinajeep on the voltage thing.

Whatever though, you got the sucker running and that's really all that matters! Nice job at the races the other day by the way!

[Stuka]

Mine is an aftermarket coil with a bracket. If it required a ground through the laminated plates and the bracket, no way my Jeep would be running.


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[REDONE]

Mine is an aftermarket coil with a bracket. If it required a ground through the laminated plates and the bracket, no way my Jeep would be running.


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Yeah, I'm not an electromagnificalogist, but the sheetmetal sammich looks like an RF suppressor type doo-hickey to me. Probably has to do with the hall-effect, which is something I have absolutely no understanding of, but is one of the main causes of problems in my life from what I'm told.

[lindel]

Yes, some of them do.

However

I'm running a stock (from junkyard Ford big block) TFI coil and it's NOT labeled. None of my other junkyard TFI coils actually have a + or - on them. Previous experience and posts from IFSJA indicate that a TFI coil must ground through it's bracket, not the terminals.

You have to look down into the connector, the markings are there.

I can tell you that on the last TFI mod I did, I never grounded the coil. It was held down with tie-wraps, not a bracket and it worked fine.

[fulsizjeep]

I am glad my Truck Avengers need nothing from the wiring harness except for choke power. Just sayin...

[AwesomeJ10]

I am glad my Truck Avengers need nothing from the wiring harness except for choke power. Just sayin...

LOL

Yes, I 100% agree. Holley TA's are simple and work great.

I'm still loving the TBI though. The wiring really isn't that bad. It really isn't. Once you properly install the wiring, you don't have to mess with it again.

The benefits of TBI really outweigh the benefits of any carb, IMHO.

[fulsizjeep]

gotta get me a TBI Trunk Monkey

[BGW]

Hey Blake,

Random question. How does the engine sound with the TBI on it? One of the only redeeming factors of a carb (to me) is that wonderful sound. There's probably some injector noise but I'd imagine TBI would sound better than the MPFI I'll eventually be doing.

[AwesomeJ10]

Hey Blake,

Random question. How does the engine sound with the TBI on it? One of the only redeeming factors of a carb (to me) is that wonderful sound. There's probably some injector noise but I'd imagine TBI would sound better than the MPFI I'll eventually be doing.

Sounds fine. I don't understand how a carb would sound 'better'?

There should be no injector noise.

It does take some tuning to get the IAC to be silent though - especially when it's cold.

[Stuka]

TBI's are near silent as there is no ticking. Its basically a constant stream of fuel, not pulsed.

The only difference in sound that a carb is going to make to the exhaust is maybe some stumbles and misses. Air intake sound should be the same as a GM TBI is very similar to a carb in the way that air passes through it.

BTW: I moved this post to General FSJ.

[BGW]

I think it has to do more with the air intake than the fuel delivery. I was just asking because carbureted engines seem to sound a bit throatier than their FI counterparts. Of course, it could just be the design of engine too.

[Stuka]

I think it has to do more with the air intake than the fuel delivery. I was just asking because carbureted engines seem to sound a bit throatier than their FI counterparts. Of course, it could just be the design of engine too.

Thats due to the air intake design. Most vehicles have air boxes designed to make them quiet. Put on a cold air intake and they get a whole lot louder. Current gen mustangs actually rout a bit of the air intake into the cab to help give them a better in cabin sound.