Causes of engine missing?
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Logistics Pro
Joined: Mar 2001
Posts: 4,157
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Causes of engine missing?
Ok, my 78' 400 engine starts and runs pretty good. It does miss a bit-more when cold-and I would like to figure out why. Here is what I have done to it.
New plugs-old ones looked good
New Wires
New cap and rotor
Choke is set properly
Vacuum is about 23-25lbs.
No leaks that I could tell.
Timing is 10dtc-should be 8dtc-have been soaking the distributor with PB Blaster it won't budge.
Anything else I could check for?
New plugs-old ones looked good
New Wires
New cap and rotor
Choke is set properly
Vacuum is about 23-25lbs.
No leaks that I could tell.
Timing is 10dtc-should be 8dtc-have been soaking the distributor with PB Blaster it won't budge.
Anything else I could check for?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
A compression test will identify the cylinder in question and a leak-down test will tell you where the compression is going. Alternatively, while the motor is running you can pull plug wires one at a time. If the motor runs the same, that cylinder is the one causing you problems. Just be careful not to ground yourself on the fender when you're doing this.
Post Fiend
Joined: Apr 2008
Posts: 8,261
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From: Big Sky Country
At idle you should have a pretty rock steady needle without any fluctuation, 21" at sea level is perfect, you'll lose an inch of vacuum for every 1,000 feet in altitude.
Reading your vacuum gauge
Reading your vacuum gauge
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Logistics Pro
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I am at about 150 feet above sea level. From the link you posted it looks like it could be a manifold leak at intake port.
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Post Fiend
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Logistics Pro
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Yes, it's connected to the manifold via the tree. I took off the plug-the tree had one open port. At idle warmed up it reads between 23-24/25is. It bounces between those numbers. I can post a video later.
Would a leak anywhere cause the needle to bounce?
Would a leak anywhere cause the needle to bounce?
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Shanemh
1987 - 1996 F150 & Larger F-Series Trucks
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Apr 27, 2010 03:37 PM