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1972 Duster 340 #8 cylinder won't fire

Posted By: reno340

1972 Duster 340 #8 cylinder won't fire - 06/03/09 06:29 PM

Help! I have a 1972 Plymouth Duster 340 w/ factory electronic ignition. My # 8 plug won't fire. I replaced it w/ Bosch Platinum plugs, New cap and rotor and a new wire set. I took that plug and switched it w/ #2's plug and #8 cylinder still does not fire. I switched back to the old cap and rotor in case the new one was faulty. I first noticed it when I Put the exhaust back on the open headers (Hooker Comps) and one tail pipe sounded different, that exhaust was nuch cooler and there was more condensation comming out of that pipe (clear water not antifreeze) and you could smell a raw gas like smell comming out of that pipe. I found out it was the one when I squirted each header tube w/ a spray bottle set in stream and #8 did not sizzle off like the others. Can some one help me fix this? I don't have a lot of money to throw at this in parts or tools.


Posted By: 05dakota

Re: 1972 Duster 340 #8 cylinder won't fire - 06/03/09 06:37 PM

LOW or no compression on 8?
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 06/03/09 06:38 PM

BTW. I am no mechanic so you will have to give me more complete instructions than others. Also, no buddies to help me bump it over or other 2 man jobs. I do have hand tools and a timing light but have never used one. (got it for free)

Posted By: goldmember

Re: 1972 Duster 340 #8 cylinder won't fire - 06/03/09 06:57 PM

Remove number 8 plug wire from the plug. Insert a screw driver into the plug wire boot until it's securly touching the metal terminal. Hold the handle of the screw driver with the shaft close to a metal surface on the valve cover,head,etc,non painted surface. Have someone spin the engine over for 10 seconds. You should see get a spark. If so the problem is with something mechanical,I'd lean toward very low compression on the number 8 cylinder. Do a compression test of that cylinder.
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 06/03/09 08:35 PM

Quote:

Remove number 8 plug wire from the plug. Insert a screw driver into the plug wire boot until it's securly touching the metal terminal. Hold the handle of the screw driver with the shaft close to a metal surface on the valve cover,head,etc,non painted surface. Have someone spin the engine over for 10 seconds. You should see get a spark. If so the problem is with something mechanical,I'd lean toward very low compression on the number 8 cylinder. Do a compression test of that cylinder.




What should it read?
Posted By: stumpy

Re: 1972 Duster 340 #8 cylinder won't fire - 06/03/09 08:39 PM

At least 110lbs
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 06/03/09 09:48 PM

How do you do a compression test?
Posted By: goldmember

Re: 1972 Duster 340 #8 cylinder won't fire - 06/03/09 09:55 PM

Compression gauge(availible from Autozone,etc),install in the sparkplug hole,remove all plugs,open the carb wide open and secure it open,remove the coil wire from the dist cap and ground it. Spin the engine over while watching the gauge,it should in 4 or 5 stokes be at it max reading. Do the other cylinders and compare the readings.
Posted By: ph23vo

Re: 1972 Duster 340 #8 cylinder won't fire - 06/03/09 10:16 PM

before you do that swap the 7 and 8 plug wire at the plugs and see if that helps dan
Posted By: JonC

Re: 1972 Duster 340 #8 cylinder won't fire - 06/03/09 11:31 PM

If you have power brakes, make sure the booster hose is attached to the intake nipple or make sure there is no leak there (7 and 8 intake runner is at this point.) BTDT.
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 06/04/09 12:08 AM

I do have spark. I wonder how bad this is gonna get? The guy that sold me the car in 1991 said he rebuilt the engine doing a ring and bearing type of rebuild. I hope that rules out anything in the short block.
Posted By: stumpy

Re: 1972 Duster 340 #8 cylinder won't fire - 06/04/09 02:42 AM

Sounds to me like you need to spend a few buck to have a mechanic check it out. It will be cheaper in the long run.
Posted By: RapidRobert

Re: 1972 Duster 340 #8 cylinder won't fire - 06/04/09 03:48 AM

as said do a compression test
Posted By: aarcuda

Re: 1972 Duster 340 #8 cylinder won't fire - 06/04/09 04:24 AM

Quote:

as said do a compression test

and get rid of those platimum plugs. they are for longevity not performance
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 12:10 AM

Sorry it took a long time to get around this. I did a compression test on the passenger cylinder head and got these results. #2- 110lbs, #4- 125lbs, #6- 130lbs, #8- 120lbs. #8's plug is perfectly clean other than gas. (remember I had tried switching wires, plugs, cap, rotor....) What gives?



Posted By: MoparforLife

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 12:34 AM

You got compression, you got fuel, you got spark. It should fire. Put in a new plug, one that isn't gas fouled. recheck your spark plug wire orientation, make sjure that the right wire is going to the correct plug following the firing order. The firing order is 1-8-4-3-6-5-7-2 clock wise around the cap.
Posted By: ph23vo

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 12:45 AM

5 and 7 are probably crossed double ck dan
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 01:04 AM

Quote:

You got compression, you got fuel, you got spark. It should fire. Put in a new plug, one that isn't gas fouled. recheck your spark plug wire orientation, make sure that the right wire is going to the correct plug following the firing order. The firing order is 1-8-4-3-6-5-7-2 clock wise around the cap.

I kind of already did that:
Quote:

Help! I have a 1972 Plymouth Duster 340 w/ factory electronic ignition. My # 8 plug won't fire. I replaced it w/ Bosch Platinum plugs, New cap and rotor and a new wire set. I took that plug and switched it w/ #2's plug and #8 cylinder still does not fire

I poorly explained I changed the plugs and #8 would not fire so I switched it w/ # 2's plug and it still did not fire but #2 cylinder fired fine. I am not above doing it again. I have double checked the firing order too. I can recheck it again though since I still haven't found the problem.
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 01:16 AM

Quote:

5 and 7 are probably crossed double ck dan

Will that effect #8?
Posted By: ph23vo

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 01:18 AM

if you are using fat white electrode platimum plugs dont! if they have the tiny pin like tip they should be ok dan
Posted By: RobX4406

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 01:19 AM

Pull the valve cover and inspect the rockers/pushrods for #8

Crank it over watching those rockers to make sure they are moving.
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 01:27 AM

Quote:

if you are using fat white electrode platimum plugs dont! if they have the tiny pin like tip they should be ok dan

They have the tiny pin like tip.
Posted By: mopars4ever

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 01:36 AM

are you sure your not getting coolant in that cylinder?
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 02:36 AM

Quote:

are you sure your not getting coolant in that cylinder?

Yeah, pretty sure. Besides, it just is not firing, oil is not milky and there isn't too much pressure in the coolant system. Doesn't the good compression rule that out?
Posted By: buildanother

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 02:48 AM

If it is runnimg good otherwise, off of idle etc, I'd check for vac leak and for pcv or power brake booster prob as mentioned above. The intake runner for that cyl may have the vac port for those two items.
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 03:10 AM

Quote:

If it is runnimg good otherwise, off of idle etc, I'd check for vac leak and for pcv or power brake booster prob as mentioned above. The intake runner for that cyl may have the vac port for those two items.



I found the vacuum advance line was disconnected but it is too late to start it tonight to see if it is the fix. (neighbors ruin everything, lol) I don,t have power brakes and the plug over that port is tight w/ teflon tape added
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 03:29 AM

BTW, do I use the timed or full vacuume advance port for the vacuume advance on the distributer? (timed is passenger side) Just checking to see if it is hooked up rifgt. Currently the distributer is hooked to the timed port and I have the vacuume lines in the stock air cleaner hooked to the full vacuume port.

Posted By: RapidRobert

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 05:11 AM

Quote:

BTW, do I use the timed or full vacuume advance port for the vacuume advance on the distributer? (timed is passenger side) Just checking to see if it is hooked up rifgt. Currently the distributer is hooked to the timed port and I have the vacuume lines in the stock air cleaner hooked to the full vacuume port.


You have both correct
Posted By: moper

Re: 1972 Duster 340 #8 cylinder won't fire - 08/28/09 12:16 PM

Completely swap the #7 and #8 wires see if the skip moves to #7.
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire - 08/29/09 12:08 AM

Any other ideas?
Posted By: Sixpak

Re: 1972 Duster 340 #8 cylinder won't fire - 08/29/09 02:19 AM

Change the plugs to Autolites. Bosch plugs are junk, platinum or not.
Posted By: reno340

Re: 1972 Duster 340 #8 cylinder won't fire **UPDATE** - 02/24/11 05:45 PM

Update
I found a broken valve spring on #8. It is the one right next to the firewall. I have never changed a valve spring. What do I do next?

Posted By: 1972challenger

Re: 1972 Duster 340 #8 cylinder won't fire **UPDATE** - 02/24/11 05:56 PM

You may have sucked the intake gasket in under the intake. Just a thought
Posted By: JohnRR

Re: 1972 Duster 340 #8 cylinder won't fire **UPDATE** - 02/24/11 07:30 PM

Quote:

Update
I found a broken valve spring on #8. It is the one right next to the firewall. I have never changed a valve spring. What do I do next?





Change it,You need to pull the rocker shaft assembly, take out the plug and either hook an air compressor to the spark plug hole or lower the piston to the bottom of the stroke , feed in a piece of rope and slowly bring the piiston to the top till it stops , now you can use one of those on head spring compressors to change the spring .
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