Nurdyguy

I installed some MSD wires and it seemed to help a little bit which seems strange. I would have expected it to fix the issue or not fix the issue. The engine is still "shuddering" but they are smaller and quieter. Also, they seem to happen more frequently as the engine warms up.

I noticed that the distributor cap is slightly loose. I can twist it slightly.

I tried your coil test. The first time I tried it the spark went from the top of the coil to the negative post because I still had the ground wire connected there. When I removed the ground wire I could no longer get it to spark. I tried two different wrenches and a couple of different ground points. I even tried just hovering the ground wire about 1.5 inches above the coil but got nothing.

Nurdyguy

New vid of the engine running.

Gun Jam

Well if its jumping out of the coil to the ground wire its probably good...the metal thing you place above the coil needs to have a good ground or it will find something more suitable.

If you remove the round wire from the coil it wont fire because its getting no power.

a slight amount of dizzy cap twist is normal.

If you pull the cap off is the rotor and contacts in good shape? Are they burned and corroded? Replacing them is a common service item perhaps you could look into a new cap and rotor.

From the video alone I cant really make out any misses...its just not high quality enough.

If you take a non contact temp gun and shoot the exhaust headers near the head as the engine warms up are any of them running extra cold? like for example 550, 475, 610, 495, 280,601 499, 513?

Nurdyguy

Sorry, I know the video isn't great. Since replacing the wires it is much harder to hear the shudders but there is one at 4 seconds and one at 6 seconds that you can still make out. In total it happened over 10 times during the video but they are very hard to hear.

Nurdyguy

Here is an interesting pic... An old buddy of mine watched that last video I posted and said he didn't think I was running on all 8 cylinders based on the sound. To me it sounded like it always has. Then I pulled out the plugs to check 'em and guess what?!?! The bet is that my intake manifold gasket is bad. The two clean plugs are the #1 and #6 and they are both on the same runner. I'll do a couple of tests before pulling the manifold off but this may explain a lot, including why the car is so slow.

Gun Jam

this is the part where the non contact temp gun comes into play as described above.

also where the carb cleaner test comes into play...(spray carb cleaner around the intake to head seam) listen for idle change.

and as mentioned initially checking plug color...

Looks like you are on to something!

Before getting too serious (IMPORTANT TEST) see below

Take the plugs that are bright white and place them back in the original plug wire that they were removed from so for example take plug 4 and place it back into plug wire 4 and take plug 7 and place it back into plug wire 7 (assuming 4 and 7 are the bright white ones). what you will need to do is check for spark at those plugs. This can be done by placing the plug into the plug wire boot as it would be if it were installed normally. Then take the plug and rest the threads against a metal engine component...this will provide a ground. Have someone crank the engine over, make sure the coil is connected (but the other plugs can be removed) and watch for the spark to jump the plug gap. it should be a noticeable blue spark.

Dont stand in front of the plug hole in case fuel or something gets spit out from the cylinder. Stand off to the side when you watch for the spark...a darkish room is best.

If you see a good healthily spark then its most likely an intake leak causing a very lean run.

without testing for spark at the plug it will be difficult to make a good decision as what to do next...its a free simple test..let us know what you find.

Nurdyguy

Thanks Gun, those two tests are next on my list.

Nurdyguy

Well, my parents were in town visiting for the last few days so I couldn't work on the car until tonight but here is what happened.

I put the plugs back in and connected the wires. The two white-tipped plugs were the #1 and #6 (they are our of order in the pic). I put everything back except the #6, left it out but connected to the wire so I could test it. When I cranked the engine it wouldn't catch at first, then I gave it some gas and it started but clanked really loudly so I immediately cut the engine.

I went back and checked all of the wires and they were all on securely. I put an old plug in the #6 spot but left the wire out on the fresh plug for testing. I cranked it again and it started ok. It ran extra rough but I saw spark from the plug. Actually, I was dumb enough to pick up the wire and it shocked it a little, oh well. I then tested the #1 the same way and it got spark too.

Next test, with all plugs in and all wires on I started her up. I then sprayed some starter fluid near the ports of the intake manifold just below the valve cover. I did this for both the #1 and #6 cylinders but saw no difference in rev.

So, both tests came out negative?!?! I called a buddy of mine and he said to check oxygen in the carb. With the engine running I opened and closed the choke plate and see how the engine reacts. The natural position of the plate is closed (as closed as it can get anyways). But changing it had zero effect. The only way I could get any reaction from the engine was to close the plate and cover the small gap with my hand and even then there was very little response (only slightly rougher than normal).

Next I opened the plate and sprayed some starter fluid into the barrel. I only did a very quick spurt but that was enough to almost completely stall the engine.

Based on all of this, I guess my next stop is a compression test?

Gun Jam

a compression test is a great idea.

While the same runner feeds 1 and 6 they are on opposite sides of the engine. if it were an intake gasket problem it would be very unlikely for it to occur on both sides of the manifold at the same time. I once forgot to install the exhaust cross over block off plates that come with intake gaskets. my intake does not have X over ports so hot exhaust gas deadheaded against that chunk of bare metal on the intake where the x over would be if it had one. It had no place to go and heated up the gasket. Over time the gasket burned through and exhaust gas ran into cylinder 6 and then a few days later 7. It started to stumble and miss randomly. I noticed my vac gauge had been falling off too. normally its 17 at cruise then it was 15 then 12 then 11 and I was like WTF??? The gasket finally burned all the way through and was blowing out between the head and intake at 6 and 7 and left ash or black marks on the head and I could hear it too like an exhaust leak...and i was like Ah!

Okay so you saw a good spark on plugs 1 and 6?...you are not really suppose to start the engine with them out (yeah it will be super loud if it does start) just place the plug electrode to a soild ground and crank it over for a second...helps to have a buddy at this point to crank the engine over.


SO thats interesting about the choke plate...even at idle closing that plate should have a huge effect on idle rpm once its gets past a certain point. If you take an ink pen and close the choke plate until its closed enough that it leaves a gap equal to the diameter of the ink pen that should be close to cold start choke. If the engine is idling at say 700 RPM in this location and you close the choke further RPM should continue to drop until the engine dies. If the choke if fully closed and the engine is still running you have a MASSIVE vac leak somewhere at the carb or near it.

Try gently spraying the starter fluid all around the carb base at idle see if the engine dies at a certain location.

Nurdyguy

This is my carb and that is as far closed as it goes.



I sprayed some starter fluid around the base and got no response so I think the gasket (which is fairly new) is good.

I tried to run a quick test to see how the different cylinders were firing so I removed the spark plug wires one at a time. On some of them, the car ran noticeably rougher. On one or two it ran just the same, on the #8 it actually sounded like it smoothed out some when I unplugged it!

This weekend I'll run a compression check. I'm more and more convinced that I'm going to need some significant engine work soon and I'm not super happy about it.