HEI Distributor problems (I think)
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Mountain Pass
Joined: May 2007
Posts: 223
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HEI Distributor problems (I think)
Quick run down of what is new on the truck. HEI, Offy Dual, hedman header, Summit/FiTech throttle body.
Symptoms: Really rough idle with an intermittent miss on at least one cylinder, but I suspect more than one. Vibration at certain rpms from what seems to be the same miss at idle.
What I have checked: Changed the plugs, checked all of the plug wires, tuned every which way possible but still runs rough. No vacuum leaks, 17 hg at idle. I put a laser temp gauge on the header tubes and one second the temp will read 400 about two inces from the flange, then I go back to it and it reads 130. But it does this on 3 cylinders. Changed those plug wires so I know it isn't a bad wire. Timing is set.
I am at a loss and don't want to start throwing parts at it unless needed. When I hooked power up to the HEI I just found a random ignition source from the old systems wiring and used that. I read that HEI's need at least 12v to run right, should I try hooking the HEI up to the "i" on the starter solenoid? Maybe as the coil is firing it is not getting enough voltage, causing a random miss on certain cylinders? I know these 300s are supposed to run like a sewing maching but I'm worried at times mine is going to break a motor mount.
Symptoms: Really rough idle with an intermittent miss on at least one cylinder, but I suspect more than one. Vibration at certain rpms from what seems to be the same miss at idle.
What I have checked: Changed the plugs, checked all of the plug wires, tuned every which way possible but still runs rough. No vacuum leaks, 17 hg at idle. I put a laser temp gauge on the header tubes and one second the temp will read 400 about two inces from the flange, then I go back to it and it reads 130. But it does this on 3 cylinders. Changed those plug wires so I know it isn't a bad wire. Timing is set.
I am at a loss and don't want to start throwing parts at it unless needed. When I hooked power up to the HEI I just found a random ignition source from the old systems wiring and used that. I read that HEI's need at least 12v to run right, should I try hooking the HEI up to the "i" on the starter solenoid? Maybe as the coil is firing it is not getting enough voltage, causing a random miss on certain cylinders? I know these 300s are supposed to run like a sewing maching but I'm worried at times mine is going to break a motor mount.
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From: Virginia
As an experiment, take your power wire to the HEI and disconnect it from the wire you found, and run it with a scrap piece of wire directly to the battery + terminal. See how it runs then. Of course you can't leave it that way, and to turn the engine off you will have to go out and pull this wire off the battery. But it would be a way to figure out if your power source to the HEI is faulty. If it clears up you know you need to find a better wire.
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Mountain Pass
Joined: May 2007
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Likes: 2
Thanks for your help. So.... This morning I went to hook it up to the solenoid and notice the ignition post was loose. Luckily I had a brand new solenoid on the parts shelf. Swapped it out and for about the first 10 seconds of idle it seemed great. Then it started running rough again. After about 2 minutes I went to shut it off and the truck kept running when I shut the key off. Lmao I can't win. New solenoid bad? Separate issue I guess. The only thing left that I can think of is the HEI distributor? It's only got about 2000 miles on it but I suppose something could have went wrong? Can't imagine internal engine damage as it won't rev high enough to come apart
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Mountain Pass
Joined: May 2007
Posts: 223
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I just got through doing that, weather has been bad. I wired in a relay and am drawing power straight from the battery and it is still running really rough. At this point I think it has to be the distributor? 58 psi on the fuel at the motor so the pump and filters are good. If there is a vacuum leak it is eluding me
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Mountain Pass
Joined: May 2007
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I actually don't! Lol. Biggest regret out of the money I have dumped into it was not just spending $300 more and getting a Holley sniper system. One problem after another with this crappy unit. IAC valve was bad from the factory, took me a while to figure it out. Then summit doesn't list replacement parts so you have to do some deep searching to find out you buy a IAC from an early 90s Chevy and hope it works.
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Mountain Pass
Joined: May 2007
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Forgot. I have thought about throwing a carb on it and might just. I would have to get an in line carb pump and new regulator in order to avoid re-doing the fuel system. Have nylon braided -6 from both tanks to the motor.
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From: Virginia
From both tanks? I guess you have guidance from FITech on how to plumb two different tanks to their system? Have you checked fuel pressure to the system? They have a return line in their fuel system don't they? If they do, you would need the fancier 6 port valve to switch two tanks.
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Joined: Jan 2001
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From: Virginia
Replace one thing at a time. We are sitting on the edge of our seats waiting to see what the problem is. For example, change the dist only first.
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Mountain Pass
Joined: May 2007
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This is about the most disgusted I've been with anything in a while. Did the carb first, still running terrible. Thought ok, it has to be the HEI? Put the DUI on it, still runs rough. Plugs wires and dizzy are all new. Carb is new with no vacuum leaks that I can find. Do I have internal damage?
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Joined: Jan 2001
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From: Virginia
Go get a compression gauge. Try to warm it up a little bit if you can. Pull all the plugs, tie the throttle wide open, and then use the compression gauge install it in each cylinder and record the readings. A good cylinder will usually jump up in about 3 rounds to around 150 psi or so. You are looking for them all to be the same more than the actual numbers. This will test the ring condition and that the valves are closing properly.
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Mountain Pass
Joined: May 2007
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Thanks for the advice! I think tonight before I buy anything I'm going to do one more good look for vacuum leaks. It sounds just like how a 300 runs with a bad vacuum leak. Something free and will give me a chance to clean the rats nest up a bit too.
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Mountain Pass
Joined: May 2007
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Was correct, no vacuum leaks but have at least two lifters that are stuck. Would explain a lot. I knew it had one that wouldn't pump up occasionally but thought I took care of it. Took the valve cover off and it was very apparent. Parts get here Friday so will probably update on Saturday.