Fuel not getting to cylinder?
Thread Starter
Racer
Joined: Dec 2001
Posts: 461
Likes: 184
From: Lachute QC
Fuel not getting to cylinder?
I have my 1970 at the shop to try and find an issue... 350/300hp base engine. Mechanic is running out of ideas. There are 2 cylinders that are not firing (#5 and #8). When he removes the plug wires from the distributor cap on these 2 cylinders, there is no difference in the way the car is running, so the assumption is that it is not firing on those 2. But when you hold the wire near the terminal on the cap, there is spark. When he took the spark plug out of #5, it was not wet, which if it wasn't firing you would expect the plug to be wet... as a side note, the distributor had one of those breakerless conversion kits to convert it to a non-points system.
So he tried a different distributor cap, tried a different coil, tried a different plug wire and a different spark plug... same result, wasn't firing on #5 and #8.
He then decided to convert it back to a points system in the event that the conversion kit was defective. He just finished that earlier, and the car has the same symptoms. But again, the spark plug is dry.
He removed the carb just to check the base gasket to ensure it is sealing properly, and it was good.
Is it possible that there is no gas making it to the cylinder, and if so, any ideas of what can cause that?
Thanks...
So he tried a different distributor cap, tried a different coil, tried a different plug wire and a different spark plug... same result, wasn't firing on #5 and #8.
He then decided to convert it back to a points system in the event that the conversion kit was defective. He just finished that earlier, and the car has the same symptoms. But again, the spark plug is dry.
He removed the carb just to check the base gasket to ensure it is sealing properly, and it was good.
Is it possible that there is no gas making it to the cylinder, and if so, any ideas of what can cause that?
Thanks...
Thread Starter
Racer
Joined: Dec 2001
Posts: 461
Likes: 184
From: Lachute QC
... update... it appears that there is a "major" vacuum leak from inside the motor... when he blocked off the vacuum hoses that go to the power brake booster and others, the engine runs smooth, and #5 and #8 are now firing properly... I was sitting in the car, and he removed the plastic wrench that was blocking and you can feel the car rocking because it's not firing on all cylinders, then when he put the wrench back on, it was so smooth...
He's going to take a look at the intake gasket to ensure a proper seal... so something is preventing enough vacuum to be produced. Anyhow.. I'll wait to see the outcome.
He's going to take a look at the intake gasket to ensure a proper seal... so something is preventing enough vacuum to be produced. Anyhow.. I'll wait to see the outcome.
Race Director
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From: Sunshine Coast, Queensland, Australia
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Sounds like you need a new mechanic! if pinching off vacuum lines clears the problem, your leak is down those lines.
Race Director
Joined: Jul 2015
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From: SW Florida.
agreed. the brake booster blew. 5 and 8 are the back 2 on one plane. and the vacuum fitting is right at the junction where those 2 runners split. tell the mechanic to fix the brake booster instead of running up the tab pulling the intake.
Last edited by derekderek; Jul 8, 2021 at 05:02 PM.
Thread Starter
Racer
Joined: Dec 2001
Posts: 461
Likes: 184
From: Lachute QC
I'm no mechanic by far... but if the brake booster is blown, would that produce a bad brake pedal, or spongy pedal? I've been test driving my car locally over the last month or so, and I didn't see any impact in the braking performance of the car, but this car is "new" to me since the spring, so maybe I simply don't know how it should feel...
So I guess my question is that if the brake booster is blown, would that affect the braking ability?
Drifting
Joined: Aug 2019
Posts: 1,341
Likes: 225
If there was a vacuum leak at the booster, you'd hear it, and your pedal would be hard, I would also think that there would be a great difference in how the engine ran with just the booster hose blocked. Your mechanic needs to do his work, by isolating the leaks, It's shouldn't be that difficult.
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Le Mans Master
Joined: Aug 2005
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From: Temple Terrace Florida
Tell your mechanic to invest about $20 and purchase a vacuum gauge and take the time to learn how to use it. It should be the go to tool for every car owner with engine problems. Jerry
Thread Starter
Racer
Joined: Dec 2001
Posts: 461
Likes: 184
From: Lachute QC
So the problem ended up being the seal between the master brake cylinder and the brake booster... the o-ring that was there didn't seem to be thick enough to provide a proper seal. I'll also need to change the check valve that is on the brake booster as is not working adequately.
But it is running MUCH better obviously now that it is firing on all 8 cylinders...
But it is running MUCH better obviously now that it is firing on all 8 cylinders...