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post #1 of (permalink) Old 11-30-2002, 10:37 AM
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GM HEI...Please, help me, i feel so frustrated!!!

Hello,
i have a GM HEI dist with a Corvette ignition module to control it threw the GM TBI ECM... I have no spark while cranking, i checked my connections, my timing and fire order, my coil...
The only thing i didn't check is the module, is there anyway to check it???, it is a brand new one!!! [img]images/graemlins/grin.gif[/img]
Thanx



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post #2 of (permalink) Old 11-30-2002, 09:06 PM
 
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Re: GM HEI...

sounds like you got the wrong ignition module you shouldnt have to drill a new hole for it and as far as i know corvette never came with a tbi only tpi
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post #3 of (permalink) Old 11-30-2002, 11:25 PM
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Re: GM HEI...

</font><blockquote><font class="small">In reply to:</font><hr />
sounds like you got the wrong ignition module you shouldnt have to drill a new hole for it

[/ QUOTE ]

Well, i assume that the guy who made it knew what is talking about and if he put a Vette module then...
So, my question is simple: "what can make a GM HEI dist not make any spark?"
If some one can send me a 10 pages post with every thing i could check and do to make it run i would appreciate a lot!!!
Thanx
PS: the guy who made it is Mr CustomEFI so..... [img]images/graemlins/grin.gif[/img]
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post #4 of (permalink) Old 11-30-2002, 11:55 PM
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Re: GM HEI...Please, help me, i feel so frustrated!!!

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post #5 of (permalink) Old 12-01-2002, 07:41 AM
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Re: GM HEI...

Hey Eric,

I can't help, but I sure would like to see some pics of CustomEFI's setup.

Thanks,
Tom
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post #6 of (permalink) Old 12-01-2002, 08:22 AM
 
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Re: GM HEI...Please, help me, i feel so frustrated!!!

The reason to drill the new hole is the dist was made for a 4 terminal module and that's a 7 terminal module.

Ok now I'll try to help the best I can.
The dist. you have there has centrifical and vacuum advance and uses a basic 4 termimal module from the factory. The module you swapped in to it is for a dist that has NO advance to it what so ever those 3 extra terminals are for the computer to control all timing. That is why on those models you set timing at TDC. Some modules with more then 4 terminals have a built in 20* +/- of advance for fail safe mode incase of computer or wiring problems and some don't.

Are you hooking any wires to the 3 extra terminals?
If not that may be your problem that module may need input from the computer to work.

I don't see why you even went to that corvette module it will not give you any performance gain and will even cause problems. The only thing it does is add expense as the 4 terminal modules are much cheaper. If I was you I would just get the RIGHT module for that dist and be done with it.

As to the problems it will cause here you go. If your not using those 3 terminals and lets say it has the built in 20* or even if you are using them and then you have the other advance (centrifical, vacuum) its going to mess up your timing. Think about it most vehicles will have 40-50* of advance at 4-5000 RPM then add 20 more degrees and your at 60-70* total advance. Then if you are using them you will get the 40-50* from the computer and 40-50* from the dist. Both ways give you to much advance. (these are just generic figures but you get the idea)

Also you can bench test these dist by just hooking up 12 volts to them and spin them by hand just make sure your not the easiest path to ground. [img]images/graemlins/smile.gif[/img]
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post #7 of (permalink) Old 12-01-2002, 08:46 AM
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Re: GM HEI...

I don't remember the Corvette module mounting any different,
but I've never tried to put the wrong one in the wrong
housing either.

I hope you are appliying a full direct 12 volts to the HEI
unit, not through a resistor, and it needs a wire size of
at least 12 gauge, preferably 10 ga.

I'm trying to do this from memory:
Start by visually checking the 3 wires up to the coil.
Sometimes they get put on backwards.

Make sure both of the primary wires from the coil eventually
go to the "Tach" terminal and "Batt" or "+" terminals.
The third wire is a ground and should lead to case ground.

If all was well there, disconnect the 2 pickup coil wires
from the module. Connect an analog Voltmeter or Ohmmeter
(meter type, not digital) to the disconnected wires from
the pickup coil. Set the scale to a 10 volt scale or the
low ohms scale. Spin the distributor - this can be done
either installed in the engine or in your hand.

The meter should swing wildly up and down as it spins over
- IF the pickup coil unit is working.

If OK, re-attach those pickup wires, connect full +12 volts
to the "Batt" or "+" terminal. Connect a good ground to the
distributor housing if you are holding it in your hand - a
jumper cable around the shank works fine.

Check to make sure the 12 volts gets up to the upper primary
wires on the coil, both should read 12 volts. If not, find
out why.

Disconnect the 12 volts and reassemble the rotor and cap on
the unit.
Re-connect the 12 volts.
Spin it, it should generate spark, you should be able to hear
it jumping around inside the cap, or put a plug wire on to
ground to see it spark.

If no spark, put your voltmeter on the "Tach" terminal.
You should read 12 volts at that terminal, but when you
turn the distributor it should jump up and down momentarily
as you turn it. That indicates the module is working - it's
switching current to the coil on and off.

Let it sit for a moment. Touch the module carefully with
your finger, it should be warm to the touch - or very hot,
after it's been connected to 12 volts for any length of time.

If it stays cold it's a good indication of a dead module.
It's very important to use the proper heat sink grease under
the module - else it can burn up within minutes from heat.
Use heat sink compound, not the same silicone grease you use
on plug wire ends or on electrical connectors, such as Ford
connectors.
The plug end grease is an insulator, it will fry the module
even though some of the tubes of that crud say you can use
it there. Once the module gets overheated it's dead forever.

One of the holes through the module is ground, make sure
that's a good connection.

Tell us what you find, if it still is a mystery we can did a
little deeper.
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post #8 of (permalink) Old 12-01-2002, 09:02 AM
 
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Re: GM HEI...Please, help me, i feel so frustrated!!!

Another thing I just thought of after reading RRich's post. Do you have the ground strap going to the coil? The coil should have 2 wires coming out plus that middle slot in the cap should have a ground strap going to one of the coil mounting screws.

FYI all modules mount the same and look the same but there is a differance in mounting bolt spacing.
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post #9 of (permalink) Old 12-01-2002, 09:06 AM
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Re: GM HEI...Please, help me, i feel so frustrated!!!

</font><blockquote><font class="small">In reply to:</font><hr />
Well, i assume that the guy who made it knew what is talking about and if he put a Vette module then...

[/ QUOTE ]Sounds like you've fallen prey to some big time American BS. He SAID it was a 'vette module because that's more impressive than if it was a Firebird or Camaro which use the same module or any one of probably a bunch of other engines. I'd never trust someone calling himself MR. CUSTOM EFI without knowing a lot more about him, just sounds like a lot of smoke and mirrors. We don't make them prove that they can live up to the name they've chosen to impress people.

I'm no expert on the subject, but the engine I run in my Jeep is the same basic TPI setup that Corvette used in '85. If memory serves, my module looks like the one you have there. I believe the major differences on the Corvette were aluminum heads, wrinkle finish tube runners and aluminum valve covers.

Another thing that concerns me is that vacuum advance diaphragm in the picture. Doesn't the ECM take care of all the advance. My distributor has no vacuum or centrifugal advance, it's all done in the 'puter.

As to your question, "what can make a GM HEI dist not make any spark?", distributors don't make spark, the coil produces a high voltage which the top part of the distributor "distributes" to the proper spark plug. In the old systems, the lower part of the distributor grounded one side of the coil for the proper amount of time "dwell" through a set of contacts "points" and broke the connection at the correct position "timing" to cause the coil to provide the voltage to the spark plugs. Those days are long gone though.

You seem to have some hybrid system which I couldn't even begin to tell you how it works without knowing what it is, maybe not even much then. But, I suspect that you've got a magnetic rotor and the pick-up module that sends an engine position to the ECM which selects the advance/retard and sends a signal to an ignition module which in turn grounds one side of the coil to provide a voltage to the plugs.

For openers, do you have 12V to the ignition side of the coil, that's also where the distributor module gets it's power? Do you have a good ground to the distributor module? Do you get a pulse signal on the minus side of the coil?

Did you get any schematics with this setup? What does it use for an ECM and spark module? Do they have a website?

Has this system ever run or is this a new install?

I see you've gotten some other responses while I was writing mine.
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post #10 of (permalink) Old 12-01-2002, 09:22 AM
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Re: GM HEI...Please, help me, i feel so frustrated!!!

</font><blockquote><font class="small">In reply to:</font><hr />
I don't see why you even went to that corvette module it will not give you any performance gain and will even cause problems. The only thing it does is add expense as the 4 terminal modules are much cheaper. If I was you I would just get the RIGHT module for that dist and be done with it.

[/ QUOTE ]Doesn't the system need this module to provide a signal to the ECM to fire the injectors?
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