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Old 06-04-2012, 08:27 PM
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Plugs not firing.

Hello all. I have a rebuilt 400 sbc it runs but the # 2 and # 3 cylinders will not fire. I have changed plugs and wires adjusted carb and timing. The valves are adjusted correctly and working properly. The firing order is correct. Still those 2 cylinders do not fire. I was thinking maybe a vacuum leak, but would this not cause misfires on all cylinders? Any help or thoughts will be helpful. Thanks Jason.

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Old 06-04-2012, 08:34 PM
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Have u proved that no spark at the plug exists ? What type of igmition ?
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Old 06-04-2012, 08:46 PM
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Have you checked the distributor cap?

You should be able to check each wire for spark with a screwdriver and gloves grounded to the frame. Or spill for a proper tester from NAPA. How do you know they are not firing?
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Old 06-04-2012, 09:00 PM
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Quote:
Originally Posted by byrddogg65
Hello all. I have a rebuilt 400 sbc it runs but the # 2 and # 3 cylinders will not fire. I have changed plugs and wires adjusted carb and timing. The valves are adjusted correctly and working properly. The firing order is correct. Still those 2 cylinders do not fire. I was thinking maybe a vacuum leak, but would this not cause misfires on all cylinders? Any help or thoughts will be helpful. Thanks Jason.
When you say "will not fire", do you mean that there is no spark at those two plugs or that there is spark but no fuel mixture ignition?
1. If it is a fuel mixture ignition problem, it could be a valve issue on those two cylinders. If the valves are not sealing, during the compression stroke, the fuel is pushed out past the valves and not igniting. You need to perform a compression test on those two cylinders. Without compression, there will be little to no combustion.
2. If there is no spark at those two cylinders and you have changed plugs and wires, check the distributor cap.

Just need more info in order to help better.
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Old 06-04-2012, 09:01 PM
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I have checked the cap it looks brand new. It has a miss and I have pulled all plugs those 2 plugs were black and wet with gas. The other plugs were all a bit on the lean side and a bit white. Also I repainted the headers and the paint on all the cylinders but those two has blistered. I can put my hands on the exhaust coming out of these 2 cylinders while it is running and it is barely warm and the paint looks new??? I can just hear that it is not running on all cylinders. The valves are opening same as all others. Thanks for any info.
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Old 06-04-2012, 09:04 PM
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Ooops I forgot I do have spark coming from the plug wire and when I pull these 2 wires while it is running nothing changes. The heads are brand new aluminum.
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Old 06-04-2012, 09:10 PM
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Does it have a flat tappet cam, Hyd. or Solid? Tell us your method of valve adjustment.
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Old 06-05-2012, 09:32 PM
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It is a hyd. cam and the ign. is a Mallory uni-lite. aluminum heads. Weiand stealth intake. Could this intake poss. be cracked, I noticed the front bolt hole on pass side has a crack all the way around. Not broke but would this cause a vacuum leak?
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Old 06-06-2012, 11:32 AM
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Clean those fouled plugs with Brakleen or something similar, dry them completely and check them for spark, pull the other plug wires off, short the plug to the head and crank it over. If you have juice coming to the plug connector the wire's OK, the plugs are too fouled to fire or defective.
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Old 08-18-2012, 04:39 PM
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OK I think we figured it out, but not sure which way to go. It is a hyd. cam, have spark at plug, but not firing in the cyl. chamber. We then checked valve adjustment and noticed that when the valve was open it would slowly close on it own. So no we believe that the springs are to strong for the hyd. lifters and the high pressure is pushing the plunger back down. No I am wondering if I should replace the springs with weaker ones or should I go with a solid lifter cam. It is probably easier to change springs and get new lifters, but would the cam swap be the better way to go? Any ideas will be greatly appreciated. Thanks Jason.
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Old 08-18-2012, 05:21 PM
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byrddogg65,

Follow these steps and you will find the problem.

Take the spark plugs from cylinders 2 and 3 and swap them with the spark plugs from cylinders 1 and 4
Take the wires from cylinders 2 and 3 and swap them with the wires from cylinders 6 and 7

Here is what we are doing. IF the misses are still in cylinders 2 and 3 then there is something wrong with the cylinders (compression low, exhaust valve staying open, vacuum or distributor cap???)
If the misses move to cylinders 1 and 4 then the spark plugs are bad.
If the misses move to cylinders 6 and 7 then the wires are bad.

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Old 08-18-2012, 07:15 PM
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You can't swap solid lifters into an engine that has a hydraulic lifter cam. You need the cam to also be a solid lifter to use the solids with it. Have you done a compression test on this engine to compare cylinders?
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Old 08-18-2012, 11:32 PM
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Plugs not firing.

What is the brand of aluminum heads and the part numbers? Did you order the heads with a spring change IE. springs for a hyd or mechanical roller cam? It could be the lifters leaking down not the springs. Thats pretty weird four lifters bad. Have you ran this engine at all. Could you explain your cam break-in procedure including the type oil you are using.

Last edited by cdminter59; 08-18-2012 at 11:38 PM.
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Old 08-19-2012, 09:31 AM
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Have done all the above with no luck. Always # 2 & 3 not firing. I have had it running but it will only run on 6 cylinders. I changed the intake with a brand new Edlebrock EPS and when I fired it up it ran perfect. I used Royal purple brake in oil with a bottle of zinc additive. I ran it at 2000 rpm for 25 mins. and thought all was good. I pushed it into the garage and 3 days later I changed the oil to conventional Valvoline 10W 40. and another bottle of zinc additive. When I fired it up it was back to running on 6 cylinders. Tried everything I can think of, but it has not ran correct since. Did a compression check all cylinders are about 170 to 175. I have spark down to the plug on all 8 cylinders. I am on the verge of scraping the entire engine and ordering a crate motor, but I have to much $ in this one. This is my last ditch effort to get this thing runnig. Thanks for any info. Jason.
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Old 08-22-2012, 03:44 PM
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Plugs not firing.

Maybe you are going have to pull the lifters on those two cylinders. Do not get them mix up. Label for which hole they were in. Take the lifters apart searching for dirt or anything to cause leak down. If you don't want to install them back after cleaning, buy 4 new ones same brand. Take the parts from the inside and install in your lifters, this way you less a chance of destroying your camshaft.
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