Lumpy, ‘rocking’ idle.....

[flagoworld]

1 hour ago, tech71 said:

Not taking that bet.

Not even for TP, BP6ES or even Rays pizza?

 

You sure? I Have a set of BP6ES that I swapped for R plugs during the EFI build...

[sam1904]

Man, there really is a strong vacuum leak contingent on this forum!! I know it is most often the cause of these type of issues but when you have a checked for it 30 times you just have to take it off the list.
 

No, there was no misunderstanding. I stood and we chatted about it for about five minutes. While they were pulling the vacuum hose off with the car running the cylinder suddenly started firing. Prior to that you could put your hand on the exhaust manifold on number four and it would stay cold, when they left the nipple open it now fired, responded when you pull plug number four and the exhaust manifold heated up.

 

They specifically stated that although this would suggest an airflow issue there must be some airflow getting through as the plug would be wet after it running for a while. I believe it does fire to some extent beyond idle although this needs to be confirmed. (I have a hard time believing the car will do 90 mph running on three cylinders although it does seem a little flat getting there.)

 

The next step they suggested on Monday is to pull the carb (That poor thing has been on and off more times than my shorts in the last couple of months) and put a borescope down intake runner #4. 
 

sooooooo...... back to my question ? has anybody ever had any experience with any strange airflow issues causing number four to get starved?

[sam1904]

2 hours ago, tech71 said:

i dunno... If there were a partial obstruction limiting airflow into #4 you could still be getting fuel in there, possibly a lot of it as in way way rich.  "de atomized" fuel could puddle in the runner, any pressure differential could then draw raw fuel into the cyl. The other 3 cylinders would also likely run rich.

Carburetors....Shades of Fred Flintstone.

Heres another reach to throw out... An obstruction in the exhaust side of that cylinder would also seriously affect proper airflow. Saw that once as a young lad working at a car dealer.  A defect in a double wall exhaust pipe. It was a new car.

Thanks for this, I will check into it. I’ve been thinking so much about the engine breathing in I didn’t think about it breathing out! I did put a new Ireland Engineering exhaust manifold on this thing a while ago and honestly cannot remember if it ran better before I did that!?

Edited May 2, 2020 by sam1904

[sam1904]

17 minutes ago, flagoworld said:

 

You sure? I Have a set of BP6ES that I swapped for R plugs during the EFI build...

I will tell everybody it is a vacuum leak if you give me those plugs! Those suckers are going to get hard to find ?

['76mintgrün'02]

11 minutes ago, sam1904 said:

I did put a new Ireland Engineering exhaust manifold on this thing a while ago and honestly cannot remember if it ran better before I did that!?

 

Was it like this one?

 

 

 

[flagoworld]

So many people recently have pulled out their plugs only to realize they are resistor plugs... I feel like the non resistor plugs dont make much difference for normal street applications ?‍♂️ Anyways I am holding on to these in my pile of “reverse EFI” parts. Sowwy.

[racer86]

Hi Sam, 

 

I have the exact same issues. 

 

I removed my intake and exhaust and found no physical obstruction. It's a mystery. Hopefully my manifold comes back on Monday so I can put it back together and try some more stuff. 

 

If it runs with more air, maybe it's over- rich. I'm going to try BP5 plugs so they run hotter and I can run richer. 

 

I have a 4 branch ex manifold and it has been suggested it my be causing scavenging on 3-4 thouh I'm not convinced as I'm on a stock cam...but if you're not could be a factor?

Edited May 2, 2020 by racer86

[sam1904]

This one with a stock cam......

 

https://www.iemotorsport.com/product/race-step-style-header-2002/

Edited May 2, 2020 by sam1904

[sam1904]

Hmmm. I have it on a stock motor.....

back pressure issue on the twistier #3 and 4 runs?

 

“This header was designed for race engines with more than 175HP. Our customers have reported dyno results which show these are absolutely the best performing M10 headers on the market. Photo shows header with optional ceramic coating.”

Edited May 3, 2020 by sam1904

[tech71]

 

5 hours ago, sam1904 said:

 

The next step they suggested on Monday is to pull the carb (That poor thing has been on and off more times than my shorts in the last couple of months) and put a borescope down intake runner #4

 

Excellent plan, hope they get a pic or two.

[sam1904]

5 hours ago, racer86 said:

Hi Sam, 

 

I have the exact same issues. 

 

I removed my intake and exhaust and found no physical obstruction. It's a mystery. Hopefully my manifold comes back on Monday so I can put it back together and try some more stuff. 

 

If it runs with more air, maybe it's over- rich. I'm going to try BP5 plugs so they run hotter and I can run richer. 

 

I have a 4 branch ex manifold and it has been suggested it my be causing scavenging on 3-4 thouh I'm not convinced as I'm on a stock cam...but if you're not could be a factor?

Good thought, it might not be not enough air, it could be way too much fuel in that runner.