Engine vibes and is underpowered

[FridayGt]

The Background:
Alright folks, I'm a bit at wits end here and am wondering if you can once again, lend me your experience. My '72 road runner has been a massive work ever since I picked her up in September. This is my first classic car and I think the seller pulled nearly every trick in the book on me for my first major learning experience...

Fast foward a few months and I now have a new 727 in her, a mostly stock '69 440HP refreshed and dropped in and a rebuilt Edelbrock 1411 carb in it. The engine has a performer intake manifold on it, Headman 3" headers and Eddie carb. I originally thought this to be a 650cfm carb (as I was told by the shop that dropped it in), but google seems to be pointing me to a refurbished 750CFM carb (1411 2420). There's also a massive load of other work done that doesn't relate to this issue. It has an MSD ignition system, all new plugs and plug wires. Here's a picture or two.

Now, keep in mind that my education level with this stuff extends as far as bolt-on work and minimal maintenance. I bought this car to learn with and when the tranny blew followed by the engine, I realized I bit off more than I could chew and at least needed something mostly working to learn on instead of diving right in to something massive like that. So, most of the work has been done at a transmission/ performance shop.

The Problem:
Now, when I most recently picked her back up from the shop, everything was running like a disgusting dream. I mean, to the point where they put my old shackles back on and air shocks in the back, just so that they could keep some slight dream of traction. Now, within a day or two after picking her up, this performance seems to be lessened significantly. When under a significant load, the engine seems to shake quite a bit with not a whole lot of get up and go when compared to before. The tires won't break loose, just lay about one foot of rubber when I womp on the peddle from a stop and that's it. When I first got it, she'd chirp the tires when shifting! Now, under "normal" driving, she runs like a champ, just not nearly as much power as before with MY "normal" driving.

I have made no changes apart from quite a few tanks of gas, all 93 octane, most recently with octane booster. I checked for a leak with carb cleaner and there was none. I put in a new air filter as the old one was pretty foul. I checked every single spark plug and all had a nice perfect tan, except one was fouled. I replaced it and while my performance MAY have improved a smidge, the issue is still present.

I've called the shop and am dropping her back off tomorrow morning so that they can replace the oil pan gasket as the one they put in is leaking and so that they can take a look at the issue and see if they can find what's up.

Does anyone have any thoughts or suggestions as to where I should look or try next? I'd really love to know for future reference, or maybe even a fix before I go! Just bear in mind, when it comes to this stuff, I'm still coloring with crayons.

 

[70Fish]

Ha, that was funny. Sorry to hear you're running into a bunch of issues with your first old ride. How about checking your carb to make sure you're still getting WOT with the pedal all the way down? Also check out the timing, too. Being that the motor is newly installed maybe one of these wasn't tight enough and is now out of adjustment. Does the "performance" shop have a chassis dyno?

For the vibration part, check out the motor mounts, trans mount, etc to make sure none of those came loose, and that they did in fact tighten those up on the install.

 

[FridayGt]

Ha, that was funny. Sorry to hear you're running into a bunch of issues with your first old ride. How about checking your carb to make sure you're still getting WOT with the pedal all the way down? Also check out the timing, too. Being that the motor is newly installed maybe one of these wasn't tight enough and is now out of adjustment. Does the "performance" shop have a chassis dyno?

For the vibration part, check out the motor mounts, trans mount, etc to make sure none of those came loose, and that they did in fact tighten those up on the install.

Ok, off to the parts store to pick up a timing light. I didn't get one from Santa like I asked for, and I should have one anyway... lol. I did check the throttle cable though, and it is WOT with the pedal on the floor. Also, the motor mounts appear to be fine. When I picked it up, they had to chain the engine down as it kept snapping the mounts. I can't visibly see any breaks in the mounts and the chain is still in place.

Oh, and he doesn't have a dyno. He did, however, tell me that he marked the timing for me.

 

[Meep-Meep]

You said you had one plug that was black or fouled? Seems to me that cylinder isn't firing and that will cause a rhythmic shake or vibration. I'm sure there are a lot of other problems that lead to your poor running engine but we need to start with the basics. Only three things need to make an engine run. Compression, fuel and spark - and all at the right time. Also you need to find out why that cylinder had a fouled plug through simple diagnostics like a compression check or confirm a bad plug wire. Get all the cylinders firing first then talk about carbs and other bolt on parts.

 

[Mopars & Missiles]

....You said you had one plug that was black or fouled? Seems to me that cylinder isn't firing and that will cause a rhythmic shake or vibration..........Get all the cylinders firing first then talk about carbs and other bolt on parts.

I agree 100%. Also, check, and re-check the distributor wiring for correct firing order. This could be the cause of your mis-fire.

 

[Cranky]

It's all about diagnostics. Besides a timing light, also buy a decent vacuum/pressure gauge and check the vacuum of the engine at idle and see if it's steady or not. You can also check the fuel pressure at idle and under load. Tie wrapping a 'live' fuel pressure gauge to the wiper arm is dangerous for a fuel test under load, they do sell a setup that uses an electrical gauge that can be installed inside the car or temp tied to the wiper arm or something else to be able to view it while driving. Get a good repair book for your car too. It has a wealth of info in it and you will probably spend less time reading so much here lol

 

[FridayGt]

Ok, checked the timing and it seems as though the distributor hadn't loosened at all. I wasn't able to retard or advance the timing at all by twisting by hand. It is currently hanging around a hair above 14 BTDC.

You said you had one plug that was black or fouled? Seems to me that cylinder isn't firing and that will cause a rhythmic shake or vibration. I'm sure there are a lot of other problems that lead to your poor running engine but we need to start with the basics. Only three things need to make an engine run. Compression, fuel and spark - and all at the right time. Also you need to find out why that cylinder had a fouled plug through simple diagnostics like a compression check or confirm a bad plug wire. Get all the cylinders firing first then talk about carbs and other bolt on parts.

Yes, there was one plug that I pulled that defenitely appeared to be fouled with what looked to be a blackish scorch mark while the others were perfect. I'll pull the plugs and check again once the engine cools completely to see how that cylinder's plug looks now. Next time I go to the parts store I'll pick up a compression guage as well so that I can check myself in the future. In the meantime, since it's going to the shop tomorrow anyway, I'll ask them to check that cylinder.

Just for my personal knowledge as well, would there be any other indicators of valve or ring issues? The exhaust coming out the pipes seems to be perfect, and it only vibes noticably under a decent load. The oil didn't look the cleanest, but as I didn't put it in, I can't say for certain how it was when it was filled.

 

[FridayGt]

I agree 100%. Also, check, and re-check the distributor wiring for correct firing order. This could be the cause of your mis-fire.

The wiring has not been changed since the last known good configuration. When checked the plugs, I did it one at a time to ensure I didn't plug them back in out of order. Also, if the firing order was off, would I be getting this issue at all times, or only under load as I am currently?

I'll be checking this anyway when I go back to pull the plug as I just don't feel comfortable right now going with the last good configuration from the shop anymore.

 

[67 B-body]

Were those plug wires cut to length, or purchased with ends already on?
Your under load shake and smooth under light load sounds like a break down in the secondary portion of the ignition. This is how a bad rotor, cap, wire or plug reacts when it's "going" bad, "on its way out". I think you have probably already discovered the cyl in question, and with a little more invetigation you'll determin why.

 

[Cranky]

Is the shop you are using good with Mopars? Also, 7 fires right after 5 and are next to each other and it's common to mess them up.

 

[67 B-body]

Is the shop you are using good with Mopars? Also, 7 fires right after 5 and are next to each other and it's common to mess them up.

He should have two bad plugs if the wires were swapped....

 

[Cranky]

He should have two bad plugs if the wires were swapped....

Yup, thought about that after typing it....and no, I wasn't typed when I drunk that....:icon_redface:

 

[Randy73]

Sounds like a loose SP wire, would not be the 1st time or millionth time someone put a plug wire ALMOST on and the then engine vibration makes it separate from the plug.

Also, check the nuts holding the +/- wires on the distributor, done this more than once, tighten them finger tight and forget to tighten all the way.

 

[Altered64]

If you have a multimeter you can check if there is resistance in the plug wire from that one bad cyl.
Or if u or a friend have a spare plug wire throw it on and see if it still shakes!

 

[FridayGt]

Were those plug wires cut to length, or purchased with ends already on?
Your under load shake and smooth under light load sounds like a break down in the secondary portion of the ignition. This is how a bad rotor, cap, wire or plug reacts when it's "going" bad, "on its way out". I think you have probably already discovered the cyl in question, and with a little more invetigation you'll determin why.

The plug wires were cut to length, so I'll check the offending spark plug wire and make sure it's maintaining a good connection.

Yup, thought about that after typing it....and no, I wasn't typed when I drunk that....:icon_redface:

LOL, it happens to the best of us!

If you have a multimeter you can check if there is resistance in the plug wire from that one bad cyl.
Or if u or a friend have a spare plug wire throw it on and see if it still shakes!

Hmmm, I don't really know anyone nearby with spark plug wires sadly, I will however test it with the multi-meter if I have the time tonight.

Thanks again everyone, I'll report back with my findings. Too bad it's raining out, so I won't be able to truly test it for a bit.

 

[FridayGt]

Ok, well I went back and re-checked what I had thought I already checked and you guys told me to check again anyway. I checked the spark plug wire for cylinder #7 that kept fouling and had continuity from one end to another no matter how it was tugged. So, I checked the connector on the plug side, bright and shiny new. Then I checked the connector on the distributor side and this is what I saw;

Here's some of the corroded gunk where it connects on the distributor;

Not only was it badly scorched and corroded, but it appears as though the shop cut the wire a little short and instead of replacing it, tried to make it work. I should have taken a picture of how it was before, but this is after cleaning and reseating, the best I could get it. Since it's so far back in the boot, it took me a lot of cussing and a set of snub nose pliers to get this thing on like this. I can now see why it would have only made an intermittent connection before. The section that engine started to really get up and go, it'd shake that plug loose since the rubber boot was putting so much pressure on it in the wrong direction.

I should be able to really test it tomorrow on the way to the shop. Thoughts? Pending the test drive, do you think that this would explain it, or do you think I may have just found another issue? Thanks again.

 

[Altered64]

Good find that would cause the vibration and loss of power!

Im pretty sure there should be a brass terminal crimped to the wire inside that boot that locks into the dis cap.

I would check all ur terminals make sure no others look like that.
It may be time for a new set of wires!

 

[FridayGt]

Good find that would cause the vibration and loss of power!

Im pretty sure there should be a brass terminal crimped to the wire inside that boot that locks into the dis cap.

I would check all ur terminals make sure no others look like that.
It may be time for a new set of wires!

It used to be brass, and actually all of the others on every other wire is absolutely bright and shiny brand new brass. That one terminal is the only one that's like that.

 

[Meep-Meep]

Good work! With the brass terminal that far up the boot it's possible it was only getting intermittent spark jumping to it (or none at all) and that could cause a misfire. As mentioned, check them all and make sure the carbon conductor is folded over the end of the wire under the brass clip.

If you have headers an easy way to check for a mis is to find the cold pipe.

 

[FridayGt]

Good work! With the brass terminal that far up the boot it's possible it was only getting intermittent spark jumping to it (or none at all) and that could cause a misfire. As mentioned, check them all and make sure the carbon conductor is folded over the end of the wire under the brass clip.

If you have headers an easy way to check for a mis is to find the cold pipe.

I do have headers, thank you Meep-Meep.

And seriously, thanks everyone. I'll let you know how it works after the drive in to work.