304 randomly cuts off 6 months after cheap HEI install - JeepForum.com
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post #1 of 18 Old 03-06-2020, 11:23 AM Thread Starter
Tim Damnit
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304 randomly cuts off 6 months after cheap HEI install

Hey everyone!

I've been having a very annoying issue with my 304/mc2100/ebay HEI this past few weeks.
This engine has been pretty much trouble free for the past decade but recently she's been cutting off on me and then it can be very hard to restart, very much like it's flooded.
It will cut of randomly sitting at a stop light or even while I'm in 2nd or 3rd gear driving.

I installed a cheap Ebay HEI about 6 months ago and it was running great for the longest time but just recently i've experienced this random shutting off and hard starting.

I cleaned out the top half of the carb, removed and blew out the venturis/idle tubes...the fuel is super clean, new lines, tank and filters about 2 years ago.
I have yet to remove and clean the jets, that's gonna happen after I get out of work today....I had a clogged jet issue many years back on my old 258/MC2100...but this is all new lines and tank so I wouldn't expect it to be too filthy.

When she runs, she runs great but then with no warning she dies, and it will even die as i'm giving it throttle and it's at 2500-3000rpm.
Even when I pour a lil fuel down the carb, she doesn't fire right up but is kinda stubborn...
I've used these cheap Ebay HEI's on my 258's in the past for years without any issue.

Has anyone experienced something like this with their cheap HEI units?

Thanks
Tim

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post #2 of 18 Old 03-06-2020, 01:13 PM
jtec
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this s a carb, SO concentrate on ignition, when the issue arises- is there spark?
is there12v to coil?

Do you have any info on cheap HEI system, wiring diagram or maybe a picture of components and we may be able to figure which system it is?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 18 Old 03-06-2020, 01:46 PM
uptillnow
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^^^^^^ Like that...

I have found many HEI's that after some time the 12 volt power supply connector to the HEI comes loose and makes a bad connection. Also, inside the HEI the connector "tabs" to the grounding at the coil get a loose connection.
Also, sometimes corrosion will get in the connection tabs, and look very clean will cause a weak to bad connection.

UTN
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post #4 of 18 Old 03-06-2020, 02:22 PM
uptillnow
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Here is a picture showing the "tab's" and ground connections.

Also, the pin under the coil, can blow through the rotor cheap plastic to the shaft that is grounded. This is the first place I look anytime.
UTN
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post #5 of 18 Old 03-06-2020, 03:42 PM
chatham
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two things, make sure your have a very good ground. run a dedicated ground to the dist. if necessary. replace the ign module in the HEI with a high quality one. that fixed my issues when i had a intermittent problems.
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post #6 of 18 Old 03-06-2020, 03:52 PM
jtec
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Above is a GM HEI and IIRC there are several modules we can post info on. trying to figure which module

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #7 of 18 Old 03-06-2020, 05:40 PM Thread Starter
Tim Damnit
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right on. thanks guys. definitely some good things to check out! I'll update as I look into it.
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post #8 of 18 Old 03-07-2020, 08:40 AM
keith460
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Also, don't rule out a bad ignition switch on the steering column. Loose or burnt connections will give you the same results you are experiencing. Happened to me last year.

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post #9 of 18 Old 03-07-2020, 09:03 AM Thread Starter
Tim Damnit
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Well I checked the connections to the cap and under cap and everything was clean and tight...so nothing to report there. I took the carb off and blew the main jets out, reinstalled it and experienced the same issue: it would fire up for a second or two and then die, some backfiring out of the carb, can't keep her running etc, so I'm pretty sure I can rule the carb out here.

I got her to run for about 1 min and held her 2500-3000rpm, firing smoothly, then she dies again!! After some more of the same, running for a second and dying, out of NOWHERE it cranks up and runs normally!!
I hate when a problem like this fixes itself!! This is the third time this month that she's done this where it's barely running and cutting out to running normally! So I'm gonna go buy a new module and keep it on hand so when she goes into this failure mode I can swap it quickly and see what happens. Seems like replacing the module makes the most sense for now.


Keith: Very interesting point about the bad ignition switch....I did replace this column with a YJ one about a year ago and I'm not sure if I kept the YJ switch or put on my CJ one on there.... So I'm not sure about the history of the one that is on there. I think it may be worth swapping it out for a new one. But I really want to fail again first so I can get some piece of mind about this!

Thanks everyone!
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post #10 of 18 Old 03-08-2020, 07:34 PM
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Hello,

Mind that I've been out of the game for over 20 years, but, were it one of the hotrods we built with HEI, I'd say it's the ignition module under the rotor. They get hot and break down. Cheap ones go sooner.

Used to be Autozone and others could test those ignition modules. I don't know if they still do; I imagine they would. Have them test them several times to heat it up (and it'll get hot) since that might induce the failure.

When you reinstall it or install a new one, make sure you use heatsink grease.

Regards,
Josh
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post #11 of 18 Old 03-09-2020, 07:59 AM
cJAY904
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A new ignition module looks like it will cost about 50$. I personally would start with that.
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post #12 of 18 Old 03-09-2020, 02:09 PM
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Quote:
Originally Posted by uptillnow View Post
^^^^^^ Like that...

I have found many HEI's that after some time the 12 volt power supply connector to the HEI comes loose and makes a bad connection. Also, inside the HEI the connector "tabs" to the grounding at the coil get a loose connection.
Also, sometimes corrosion will get in the connection tabs, and look very clean will cause a weak to bad connection.

UTN
My '78 K5 Blazer used to do the exact same thing. Pulled the HEI coil, cleaned the carbon build-up off the module and cradle, and it was fine for a little while after that, but quietly crept back into the picture. Once I pulled and replaced the ignition module from inside the dizzy itself, all was good again.

Hope that helps!
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post #13 of 18 Old 03-10-2020, 09:00 PM
SteveMann
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I could be WAY off-base here, but your description was exactly like my Grand Cherokee a couple of years ago. It turned out that the crankshaft position indicator had failed, and there was no OBD code that I could see on my cheap OBD reader. (The dealer did, however and fixed it the same day).

The Jeep would die as if the fuel or ignition was simply squelched. Let it sit for a while and it would start and run like normal.
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post #14 of 18 Old 03-11-2020, 08:22 AM
jd50
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You may want to change the pickup coil. Years ago, I had a Camaro that did the same thing. I put several ignition modules and coils on it, trying to fix the problem. Finally, I put a new pickup coil on it. Problem solved, it never gave me anymore problems.
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post #15 of 18 Old 03-11-2020, 12:26 PM
uptillnow
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Quote:
Originally Posted by jd50 View Post
You may want to change the pickup coil. Years ago, I had a Camaro that did the same thing. I put several ignition modules and coils on it, trying to fix the problem. Finally, I put a new pickup coil on it. Problem solved, it never gave me anymore problems.
Yes, changing the ignition module, the pick-up coil, burning through the rotor's plastic to the shaft ground, after replacing all of this, the high performance HEI distributors start making a lot more sense.
Just sayin....
UTN
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