I need help diagnosing what's wrong with my engine

[aasukisuki]

I want to start this thread by apologizing in advance.  I'm really a novice when it comes to mechanical issues, but I'm trying to learn.  Unfortunately I don't really have any friends or relatives that are car people, so I'm on my own here.

With that being said, my 302 is running like complete garbage.  About 2 years ago, I had a remanufactured 302 from Mabbco installed into my 73.  The Edelbrock 4 bbl carb, intake, and air cleaner were moved from the old engine onto the reman.  A previous mechanic had also installed an HEI style distributor (I think it is this one: https://www.summitracing.com/parts/sum-850021/overview/).  The motor has a slightly more aggressive grind on the cam, GT40 heads from a fox body mustang, moly rings and flat top pistions.

The car has been running well since the motor was installed.

However, about 2 weeks ago, I decided to have dual exhaust added to the car.  I believe it's 2.5" pipes, connected to the stock manifolds, going back to a set of magnaflows.  After driving the car a couple times after getting it back, I started to wonder if there's an exhaust leak.  I was planning on taking it back into the shop this week.

However, last weekend, I was driving the car when it felt like I lost one of the cylinders.  I was only about 1/4 mile from my house, so i just babied it home.  Once home, I made sure all of the spark plug wires were connected.  When idling it seems like something is missing.  Under load, it really struggles, to the point that it's not really driveable more than just taking it in a loop in my cul-de-sac.  I pulled the plugs, and they don't seem to be covered in carbon, or wet with fuel.  I checked the gaps, and they were wildly inconsistent.  Anywhere from .035 to .050.  I re-gapped everything down to .040 because when I was researching yesterday, I found a few posts saying .035 is good for stock, but some people will go as high as .042 with a hotter coil (which I assume would be the case using an HEI).  That seems to have only made matters worse.  I could barely keep the car running while simply driving it in a loop around the cul-de-sac.  After doing some more research today, I came across [a thread](https://www.jalopyjournal.com/forum/threads/correct-spark-plug-gap-on-ford-302-with-hei.59805/) saying the plugs with an HEI actually need to be opened up even more, somewhere like .044-.050 (one guy even said .060!)  Does anyone have any guidance on this?

I've read that I should check also the carb to make sure it's not dirty, or plugged up, but I really don't know the first thing about carbs.  I plan on watching some youtube videos tonight to get some basic info.

If video/audio of the car running, or photos help, please let me know and i'll be happy to post them.

Thanks for any advice you can provide.

 

[Fabrice]

If the gaps are consistent 0.35 , 0.40, you should not have much diffs to observe while it runs/idles/low rpm. It's when hot and under load that these make a diff.

As you do not describe the way it runs in details, its hard to tell with that little...

if you can post a vid where the sound is not too saturated, that would surely give a better picture of the situation.

 

[73pony]

A video of it running would likely help. Based on the distributer you linked above a .050 gap is about right. Is there play in the distributor shaft. What is timing currently showing at idle with the vac advance detached and capped off? Is the timing steady or does it jump around? I am not familiar at all with Edlebrock carbs so I would not know what to tell you on working on it other look at some youtube videos.

Did the car sit for a long period of time? Is the gas old?

Did you do a compression test across all 8 cylinders?

 

[Carolina_Mountain_Mustangs]

Since this happened after someone was working around the spark plugs I might suspect that they pulled an end off a plug wire or two. You can take a spark plug and hook each wire up to it and put on a metal surface on the engine and see if you get a good spark across the plug gap.

You should also use the electrical grease on all the plug ends and the rubber boots to stop any arching that might try to occur. Permatex and several others make it. Good for any wire connections or light bulbs and sockets also.

Sometimes when pushing the plug boots back on you push the wire up into the boot and not onto the plug.

Always go back to the basics when something happens.

You can also use a pair of insulated pliers and pull each plug wire off one at a time while running and you can tell which wire or cylinder is the issue. You can do at the distributor so it is easier. When you pull the one with a problem there will be no change. When you pull a good one it will miss worse.

Some people just go jerking the wires off you should always pull on the boot not the wire.

My X wife had a grandfather that could pull the wires off and stand there and hold them and smile. Never seemed to shock him. Me I hit my head on the hood and jump off the ground.

It will be something simple for sure.

BTW reving the engine will not fix it do something to fix it.

 

[Jeff73Mach1]

I suspect it is in the ignition wires as well. old 302 firing order and 5.0 firing order are different. My best guess is that either a wire is damaged, or a couple of wires are swapped.

leaking exhaust makes noise, but shouldn't affect driveability enough to be able to tell.

 

[TommyK]

Also check that all vacuum lines are connected and any unused vacuum ports are capped.

Might want to check or change the fuel filter while you are at it.

 

[aasukisuki]

Thanks for all of the suggestions.  I haven't had time to dive into the carb yet, so no updates there.  I did re-gap the plugs to .050, and the car seems to idle better when cold.

Here are a couple of videos I was able to take.  I can re-take them if they aren't helpful

Here is right after I gapped the plugs to .050 and running cold:  https://youtu.be/nZtlHOZzfZ0

I then took the car out for a short drive.  You can hear a noticeable difference in how the car is running around the 2:20 mark.  Shortly after the video cuts out, the car started running so poorly, I was barely able to get it back to my driveway before the engine cut out completely.  I should note that i'm a total jackass, and didn't realize that I had the car in 2 instead of drive, so this is in one gear the whole time. 



73Pony - There is no play in the distributor.  I don't own a timing light (and have never timed a car), so maybe it's time to invest in one.  The gas was fresh, from within the last couple of weeks.  I also have never checked the compression on a cylinder, so I'll need to buy that equipment too.

Carolina - I checked and re-checked that all plug wires were firmly attached, and snapping onto the top of the plugs.  I also used a multimeter to check for continuity on all of the wires, and they are seem to be fine.  I did pull each wire as the car was running, and it seems like cylinder 8 is the one missing.

TommyK - As far as I can tell, all lines are connected or capped (should the distributer be capped or actually connected to something via hose?)  I tried to snag a new fuel filter this morning at AutoZone, but of course the one closest to me was the only one without in stock.

Thanks for all of the help and ideas so far.

 

[73pony]

When you pulled and set gap on the plugs what did the #8 plug look like? Were any of them black and oily?

 

[73pony]

Where in Iowa are you located?

 

[Fabrice]

Not familiar with 302's sound, (my t-bird's 5.0 has same firing order as the cleveland, 1372658, and sounds like one)

aside an exhaust leak, as you did compression tests, check ignition components and all looks fine,

I'd tend to think it's a fuel related issue, too rich. Just before it went bad, you open a bit, say +-2/2.5 rpm and it sounds ok, at least on the video I can't really hear a miss.

It's when it goes back to idle/low 1k's when you brake and take the turn that it's too late.

I'd begin by checking the carb floaters and tune it a bit leaner. Also make sure you have an air filter with enough capacity or make test run without one.

 

[rackerm]

Someone mentioned earlier if you checked for any vacuum leaks. Worn thru or cracked vacuum hose. You may already tried these....Spray carb cleaner around the base of the carb and listen for the engine idle to pick up, if it does you have a vacuum leak at the carb base. Remove the spark plug wires one at a time see if the engine idle drops, if it does plug it back in and try the next one. If it doesn't, check the wire for spark. When cold take the radiator cap off, run the engine and check for gas bubbles coming up in the antifreeze?

 

[Hemikiller]

I'm betting on the distributor is the cause of the problem. Since the problem gradually gets worse the longer the engine runs, it is probably the control module inside the dizzy.

 

[aasukisuki]

When you pulled and set gap on the plugs what did the #8 plug look like? Were any of them black and oily?

These are the plugs from 1 & 2, but I don't remember any of the additional plugs looking much different than these. I can pull 8 again tonight to be sure:

Where in Iowa are you located?

I'm SW of Adel

Fabrice - I'm still planning on digging into the carb once I have a chance to watch a little youtube so I have some idea of what i'm looking for / at.

Rackerm - All of the hoses and vacuum lines were installed brand new about 2 years ago, but I'll go through them more carefully. I can also try the carb cleaner trick. I have checked all of the spark plug wires, tested them for continuity, and visually witnessed spark occurring from the distributor to the wire (not from the wire to the spark plug though). I also pulled wires with the car running, and the only suspect cylinder is 8.

Hemikiller - Is there a control module in these HEI style distributors? Is that something repairable, or am i better of just getting a different electronic distributor?

 

[Fabrice]

Thought you had the vacuum lines checked by now, tho I would expect a constant prob if that was the case, higher idle rpms and hesitation when you'd pressed the pedal.

Even if if the dist may be involved, which would be an easy fix, you will need tune that carb and ensure your air filter is clean/sufficient for the air volume it's supposed to let thru. The plugs are black, as there's rust on the thread, it shows a rich condition over a long period of time. Should be brownish/ dull grey.

@hemikiller

[since the problem gradually gets worse the longer the engine runs]

Could you develop a bit on this? Not familiar with these, but eager to learn, why this module would progressively fail and not right away?

 

[Hemikiller]

The GM HEI system has an internal control module that functions much like the Duraspark control box on Fords. The module is mounted to the distributor base with a thermal compound to transfer excess heat away. One of the failure modes I personally experienced was a misfire on warmer days at sustained operating temperature. Since I usually had a bunch of parts lying about, I simply started swapping one component at a time until the problem was fixed, in this particular case it was the module. To be honest, I have no love for the HEI, but it works well when it's working.

Since the OP's distributor is a Summit, most likely of Chinese origin, every component is suspect. My first thought is the module, as it's the most complex component in the unit. It very well could be the coil or the pickup, or none of the above.

Something to consider before you do anything is you need to double check that you have a solid ground path from Battery (-) -> fender apron -> block. Many aftermarket ground cables do not have the factory lug for the fender apron and it can cause some seriously weird issues. I had a 71 sportsroof that I did an auto to 4 speed swap on, and apparently the tranny cooler lines were the ground path for the engine to body. Some seriously odd issues popped up, lots of head scratching but I finally figured it out. 

You can see the lug crimped in the middle of the cable on the ground cable in this set.

https://www.npdlink.com/product/battery-cable-set-concours-heavy-duty/101975/202869?year=1971

 

[Fabrice]

+1 on that. I have 2 extra braided lines, you can never have enough grounds. Make sure no rust is at the bolts.

thx for the module tech.

 

[aasukisuki]

Regardless if the HEI is the issue or not, it's something that I'd probably like to replace at some point.  Do you have a recommendation on what to replace it with?

 

[73pony]

The two most recommended I have seen are the ford Duraspark upgrade or a stock style distributor with a Pertronix 2 unit. DO NOT USE A PERTRONIX 3!!!!! THEY ARE JUNK.

 

[Ron Tanzi]

Thanks for all of the suggestions.  I haven't had time to dive into the carb yet, so no updates there.  I did re-gap the plugs to .050, and the car seems to idle better when cold.

Here are a couple of videos I was able to take.  I can re-take them if they aren't helpful

Here is right after I gapped the plugs to .050 and running cold:  https://youtu.be/nZtlHOZzfZ0

I then took the car out for a short drive.  You can hear a noticeable difference in how the car is running around the 2:20 mark.  Shortly after the video cuts out, the car started running so poorly, I was barely able to get it back to my driveway before the engine cut out completely.  I should note that i'm a total jackass, and didn't realize that I had the car in 2 instead of drive, so this is in one gear the whole time. 

It sounds to me like the ignition is breaking down possibly due to a failing distributor pick-up. What brand is the HEI unit that you have? I have seen practically new over seas no name distributors fail more than once   Ron