running a GM HEI in my basically stock freshly re-built 1969 396.

When I stomp on it and the RPM starts getting up it starts missing.

I turned the distributor a little bit counter clockwise (looking from the top) and the miss got MUCH better ....BUT after I shut the car down and give it a minute it barely wants to crank over.

Seems like I sacrafice one for the other with no happy medium.

I was think of getting an Aftermarket distributor with the adjustable spark control and rev limiter, and was wondering if this may help my problem.

Other than that the car runs great I do however get a whiff of unburned or raw fuel once in a while.

Any ideas or suggestions?

Thanks guys

How high rpm are we talking 3k or 6k?

How high of an rpm are we talking? I have the pertronix conversion kit on mine it was maybe $80 from summit makes as much power as an msd on my 540 according to the dyno.

a stock distributor should be fine in a stock motor.

Are you running 12 volts to the distributor?

Have you checked the major grounds?

I'm going with the Martyr in this general direction. In addition to letting us know specifically what RPM you're spinning at miss, I'd say you need to check your wiring. Sounds like you've got a weak connection in there somewhere.

Have you tried testing the power lead to the HEI? That's often a source of trouble. Since you're running a '69, I'm going to ask if you replaced the power supply wire to the HEI with a non-resistor wire. That could be an issue.
Put a test light in line between the power lead and the coil. Turn the batt on and it should come on brilliantly. Have someone crank the engine and watch the light. It should stay bright. It should NOT dim a considerable amount. Such a situation would indicate that you're losing power to the coil under a loaded situation.

I had troubles like this once that seemed to appear out of nowhere. Turned out that my power supply wire to the distributor/coil had a bad connection with undue corrosion on it.

Hope this helps.

1)I have not checked any connections so far.


2)Seems to be breaking up around 3-4K but I really didn't look at the tach and will take note tomorrow.

3)It is hooked up for a 12 volt supply but is it getting 12 volts? I will test it. Is there a way to test for 12 volts under load?

4)"I'm going to ask if you replaced the power supply wire to the HEI with a non-resistor wire".

No I did not since swicthing from the point distibutor. Is that a fusable link wire and which one is it, the original one that supplies the 12 volts?

5) "Put a test light in line between the power lead and the coil."

Is this the line that comes off the distributor marked coil? With this test the engine will not fire correct?

Sorry if these are dumb questions I just want to make sure i'm understanding you correctly.

Thanks for your help guys.....

if you are still useing the same power source to the hei as you used at your old coil when you had points you need to change it , there is a resistor in that wire that only allows approx. 7 volts to the coil so you dont burn up your points..you need a good 12 volt source to your hei unit,,, Steve B

Originally posted by ACLineman:
4)"I'm going to ask if you replaced the power supply wire to the HEI with a non-resistor wire".

No I did not since swicthing from the point distibutor. Is that a fusable link wire and which one is it, the original one that supplies the 12 volts?

I think this is something you should address, and it may be the source of your problem. As techman said, it doesn't give you the full 12 volts, and, yes, it is a fusible link wire. It is the one that originally went to the coil hot side and supplied power to the coil. Now it would be the one that is plugged into the "coil" tab on your HEI unit.

To do the static test with the test light, just disconnect the power wire, clip one end of the test light leads to the wire, then clip the other to the "coil" tab on the HEI. Turn the ignition switch to the "run" position (the position it sits at while the engine is running, but the starter is not operating). The light should come on nice and bright. I have never tried it with a meter, but I'm sure the directions with any good meter could tell you how much juice you've got flowing through there.

To do the dynamic test you just turn the key to the "start" position and see if the light dims to a large degree. You know, now that you metion it, I don't recall that it the engine started when I did this test. I can't remember if I disabled it to do this by unplugging the connectors that went to the module, or if it just wouldn't start. I'd have to glance at it again.

Hope you're making progress.

Thanks guys for the in depth info.
I will test this out tomorrow and post my findings.
7 volts or anything under 12 volts to a 12 volt system sounds like this could be the problem. :eek:

Hopefully this will be the finding an an easy fix graemlins/thumbsup.gif

Thanks Again

Ok,
First off my HEI does not have a tab marked "coil". It is marked tach and +Bat.
+Bat is the one I preformed the test on.

First I tested across the battery terminals with a fluke meter and got 12.30 volts.

Then I pulled the heavy gauge red wire from the +Bat tab on the coil and tested with key in the "on" position and got 12.10 volts.

Next I cranked the engine over and it dropped to around 9.70 volts.

Is that acceptable?

Does this simulate "load" conditions only?If so that maybe causing the miss at higher RPM's and how to correct it?
Would voltage come back up to 12.10 volts if the motor was "running".

I unwrapped the tape on the wiring harness and the heavy gauge red wire from +Bat runs from the HEI to the block into the firewall block, from there i'm guessing it goes into the back of the fuse block,correct?
It doesn't appear to have any fuseable link in the line. Wire end was cut off and a new terminal was connected (may have already been removed?)

Just for the heck of it I tried this test with a light also and it dimmed considerably.

Any help here?

Thanks guys, Harry

Harry; 9.7 volts is not adequate.You should actually have around 13.5+ when running,as the alternator usually kicks out 13.8 or more.You need to run a new 14 gauge(or larger) wire from the ignition terminal in the fusebox to the BAT terminal of the HEI.This wire must be hot in start and run only.Just tape the old resistor wire to the harness,in case you ever want to use it for a "correct restoration".That should cure your problem. graemlins/hurray.gif . Steve

Harry, you should have 14v at 1500-1800 rpm. Test it there.

Old wiring harnesses had a 12v source from the starter and that resistance wire to the +coil side. It would get a full 12v at start and then run at 9v for continuous operation ( to keep the coil cooler). Just some background...

Check the volatage at your _bat terminal at 1800 rpm. It should be at the same voltage as the alt puts out. Around 13.8 should do it.

If it checks out OK, replace the module . Also check the timing curve/vacuum advance on the distributor, it could be way far from where you want it.

67CHEVY2 and 427L88, with all due respect, I seem a little confused :confused: .

This test was done with the engine "NOT" running. It seems your talking about the ALT output???

Did you read the thread?
The wire IS large and hot in start and run only , and there IS no resistor that I see,I checked the length of the wire until it enters the firewall.Where else should I check?

If it would get a full 12v at start and then run at 9v for continuous operation ( to keep the coil cooler). wouldn't 9.70 volts in the test I preformed be adaquate??? :confused:

Check the volatage at your _bat terminal at 1800 rpm. It should be at the same voltage as the alt puts out. Around 13.8 should do it.

If it checks out OK, replace the module . Also check the timing curve/vacuum advance on the distributor, it could be way far from where you want it.
How are these two test preformed?

Again no disrepect just want to make sure were on the same page,and that I understand your info correctly.

I did take the car out for a spin and at 5200 RPM is when the break up occurs. I bumped the distributor a TOUCH CC and it ran up to 6100 RPM before shifting and "NO" miss at all.....BUT........a little hard cranking after I shut it down and try to re-start, but not "too" bad.

Thanks again for all your help and anything else you can think of......Harry

9.7 volts is not adequate. check your coil voltage at 1500 rpm, guess you'll have to pigtail it with an hei for the test.

Set the timing with a light then, and also rev it up slowly to check the timing curve. Sounds like you need to bring it back just a bit from where it is now, retard it just a bit.

Run a new wire from your fuse box marked ING and test it again.If still low check your ALT out put
and battery out put.

what rpm is the problum starting at . stock hei's are not very good after 5,500 rpm. 2nd your coil may be starting to brake down . so if its an old coil replace it. 3rd cheak to see if everything inside the distibuter is moving like it should . they get gummed up and wont advance.only other thing is to cheak the gap on the plugs . if they are opend up too much that could be a problum at high rpm's

also . you could be running out of gas at the top end . some chevelles have no baffles in the tank to keep the gas from running away from the pick up. try it with a full tank . just an idea

First, an HEI and the original ignition system are Apples and Oranges. They are DIFFERENT and have DIFFERENT requirements.

In order to make the ignition system reliable in your Chevelle, the factory reduced the voltage under load to the ignition through the use of a "resistance" wire. It looks like every other piece of wire but is made of alloys that make it harder for the power to go through it. Imagine a 1" water line that necks down to 1/2" in the middle. Pressure (voltage), with no load, will be the same at each end. Open the tap, and the pressure at the end (past the 1/2" restriction is reduced.

An HEI distributor was designed not for 9volts, not even for 12 volts, but it was designed to operate correctly with 13.8+volts in order to push enough amperage through it to do a superior job the original points did. Circle track racers who are notorious for trying to run their cars without alternators found that they'd get a highspeed misfire running on battery alone(12.XXV). The HEI MUST have the highest voltage available in your car to operate correctly. Quit looking at the end of the original wire and trying to make it work. Replace it from the fuse panel(ign) to the distributor with a #12 wire.

Miss is occuring around 5100-5300

Greybeard I see where your coming from ,and I'm going to pigtail a wire from the + Bat side of the distibutor and test voltage there, like someone earlier suggested. I'm assuming that I should get the ALT output reading at that point correct?

If the reading is too low I will run a temp "jumper" (wire) from the ING on the fuse block to the distibutor and check it again. If the reading comes up to 13.8 or so I will replace that wire. If not I will check into the ALT I guess.


CHEVELLERACER I see your from Egg Harbor, did you make it to Wildwood this weekend?
What kind and year Chevelle you running?

Thanks guys. Gotta get this ironed out before the guy calls and tells me my new 12 bolt is ready.
Going from an open 10 to a 3.73 12 bolt posi, Can't wait !!! :D

no i didnt go. ill go to the fall wildwood. if you need a hand let me know ill stop over. i have a 72 chevelle ss that im putting a blown 496 in it

i have a 72 chevelle ss that im putting a blown 496 in it :eek:

Guy I used to work with has a 72 with a 502.Wins the burnout contest in Wildwood every year graemlins/hurray.gif

Anyway thanks for the offer. I'm gonna try a couple things and see what I can come up with.
This board is awesome and the guys are really knowledgable and helpful !!

Hopefully it gets straighted out before the rear is done.
Flemings in EHT is having a show next weekend too.I'm gonna try to make that one.

i know the guy your talking about. do you know john with the white 68 camaro. i help him with his car. we have it running 11,40's right now

John who works for the Electric Co?

Yea, I know who he is but can't think of his last name, lives in Egg Harbor also. I think he's in the meter Dept.

I heard that car was a SCREAMER !!