Issue with misfiring and wrong firing order! : MG Midget Forum : The MG Experience

Issue with misfiring and wrong firing order! #1
BenH Ben H Broadstairs, Kent, UK Sign in to contact	Topic Creator (OP) Aug 30, 2016 12:49 PM Joined 7 years ago 6 Posts

Hi there guys, new here so go easy winking smiley

Had a look around but couldn't find anything to help me.

After a regular misfire on cylinder 2 on my MG Midget 79, I took a look at the distributor and noticed spark plugs were wired out of order (3 4 2 1) rather than the order I have seen posted (1 3 4 2). I have attached a picture of the current wiring order required for it to run.

When I wired it up in the "correct" order, the car doesn't even start.

I have isolated the issue to something to do with number 2, as have swapped leads and plugs around and it's always 2.

Thanks in advance for any wisdom you may be able to impart onto me! smiling smiley

IMG_2471.JPG 66.5 KB

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Re: Issue with misfiring and wrong firing order! #2
76lucas Josh L Christiansburg, VA, USA Sign in to contact 1978 MG Midget 1500 1979 MG Midget 1500 "Blue "parts" Car" 2013 Toyota Camry "Boring Daily"	Aug 30, 2016 01:12 PM Joined 8 years ago 1,892 Posts

Have you checked the inside of the cap? If you swapped leads and plugs that would be the next place to look.

If you never try to do it You will never be able to do it

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Re: Issue with misfiring and wrong firing order! #3
BenH Ben H Broadstairs, Kent, UK Sign in to contact	Topic Creator (OP) Aug 30, 2016 01:14 PM Joined 7 years ago 6 Posts

I have - can't see any evidence of tracking. Nothing looks off, but maybe the contacts are worn. Looking at getting a new cap tomorrow.

Still, that doesn't explain why it wouldn't run at all in the proper configuration confused smiley

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Re: Issue with misfiring and wrong firing order! #4
76lucas Josh L Christiansburg, VA, USA Sign in to contact 1978 MG Midget 1500 1979 MG Midget 1500 "Blue "parts" Car" 2013 Toyota Camry "Boring Daily"	Aug 30, 2016 01:24 PM Joined 8 years ago 1,892 Posts

I am not sure I think someone who is a little more experienced is going to have to step in on that one. All I can say is #1 on yours is about 1 off from mine but I have a US spec car.

If you never try to do it You will never be able to do it

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Re: Issue with misfiring and wrong firing order! #5
66jalopy Phillip Jolliffe Lake City, FL, USA Sign in to contact 1956 Morris Minor	Aug 30, 2016 01:25 PM Joined 11 years ago 6,727 Posts

If someone in the past installed the distributor shaft out of timing the plug wires won't mach the proper position. It doesn't really matter, the car should run fine. You have another issue. Maybe cap or rotor, bad plug maybe or low compression on #2 cylinder.

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Re: Issue with misfiring and wrong firing order! #6
ice Larry Ice Lawrenceville, GA, USA Sign in to contact 1971 MG Midget MkIII	Aug 30, 2016 02:36 PM Top Contributor Joined 12 years ago 6,101 Posts

Like Phil says do a compression check........and look at distributor, maybe 180 out.
Change plugs and really examine #2 wire along with rotor button and cap.

Iceman

Atlanta GA

71 MG Midget

62 AH MKII
67 Midget
71 Midget

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Re: Issue with misfiring and wrong firing order! #7
bev sleet Bev S Raunds, Northamptonshire, UK Sign in to contact 1977 MG Midget 1500	Aug 30, 2016 02:38 PM Top Contributor Joined 7 years ago 1,896 Posts

Okay Ben lets start from scratch . remove No 1 plug and insert a screwdriver then turn engine over by hand until it is at the top of cylinder, then check rotor arm
it should be pointing at No 1 cylinder and the timing mark on the bottom pulley should be at 10 degrees on the pointer , the rotor arm pointing at No 1 cylinder
is No 1 plug lead then work around the distributor cap anticlockwise for the other plug leads they shud be 1342 . If the rotor is facing the opposite way to No 1 turn
engine over 180 degrees until it faces No 1.. hope this helps

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Re: Issue with misfiring and wrong firing order! #8
rntanner Roger N. Tanner (Disabled) Oxnard, CA, USA Sign in to contact 1970 MG MGB 1977 MG MGB	Aug 30, 2016 02:55 PM Joined 15 years ago 4,348 Posts

Please read this webpage from many years ago:

http://www.mgexp.com/phorum/read.php?3,1915817

Roger N. Tanner
Professional Engineer, Retired

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Re: Issue with misfiring and wrong firing order! #9
BenH Ben H Broadstairs, Kent, UK Sign in to contact	Topic Creator (OP) Aug 30, 2016 03:42 PM Joined 7 years ago 6 Posts

Hey all,

Thanks for the rapid and thorough responses!

I'll be doing a compression test tomorrow, along with checking the timing. Will post results, fingers crossed! smiling smiley

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Re: Issue with misfiring and wrong firing order! #10
B-racer Jeff Schlemmer Shakopee, MN, USA Sign in to contact 1950 Willys Jeep Pickup "Ratrod" 1964 Land Rover Series IIA 1971 MG MGB	Aug 31, 2016 07:44 AM Top Contributor Joined 17 years ago 20,012 Posts

You didn't change the firing order. The plug wires stayed in the same order. It appears you rotated them each 90 degrees, so you are firing one cylinder off. No, that will never run. Put them back where they were and it should start.
1-3-4-2 = 3-4-2-1 = 2-1-3-4 = 4-2-1-3 Get it? Same order but different start point, different positions on the cap. You need to find #1 cylinder TDC, firing stroke. If on exhaust stroke the rotor will point at #4 (half turn of the cam = 1 turn of the crank.)

jeff@advanceddistributors.com

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Re: Issue with misfiring and wrong firing order! #11
rich wino Richard Ruggiero wallingford, CT, USA Sign in to contact	Aug 31, 2016 10:19 AM Joined 10 years ago 112 Posts

Jeff I was thinking the same thing and was going to post something of the same. It reminds me of the tests we had in school what number comes next in a sequence.

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Re: Issue with misfiring and wrong firing order! #12
BenH Ben H Broadstairs, Kent, UK Sign in to contact	Topic Creator (OP) Sep 1, 2016 05:10 AM Joined 7 years ago 6 Posts

Ah yes Jeff see what you mean about the sequence staying the same.

We found number 1 on the distributor, so it's in the correct order and position. Still misfiring on cylinder 2 at the moment.

We looked at the timing, and it seems to be ~5 degrees out. Haynes workshop manual says it should be 10° Before TDC, whereas mine currently looks to be about 5° BTDC. Would this cause a misfire?

If not I'm going to do a compression and leak test later.

It's quite fun though, first time I've tinkered with a car - it's great having a community like this to discuss things with!

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Re: Issue with misfiring and wrong firing order! #13
jmac Jere McSparran Greenup, IL, USA Sign in to contact 1970 MG Midget "(SOLD)" 1978 MG Midget "Therapy" 1978 MG Midget "(SOLD)"	Sep 1, 2016 06:28 AM Top Contributor Joined 16 years ago 3,269 Posts

Your misfire could be related to carburetion. Maybe a bit of an intake leak. You are correct to do the compression check. You can check for vacuum leaks around your intake and exhaust gasket by spraying some starter fluid around it. If the firing of the engine changes you are sucking the spray in around the gasket. Make sure that you keep the spray from the front of the carburetor because that will cause the engine to change too.

I would be interested to know what the #2 plug looks like compared to the other plugs.

Jere McSparran
JMAC Engine Shop
Website: http://www.jmacengineshop.com
email: jmacengineshop@gmail.com
Phone: 217-232-7303

JMAC Engine Shop jmacengineshop.weebly.com

MG/Triumph engine rebuilding. Specializing in the Midget/Spitfire 1500 engine.

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Re: Issue with misfiring and wrong firing order! #14
BenH Ben H Broadstairs, Kent, UK Sign in to contact	Topic Creator (OP) Sep 1, 2016 11:27 AM Joined 7 years ago 6 Posts

Thanks, will have a look at that too.

Replaced Distributor cap today, no change. Looked at all spark plugs, all looked fine, though I think number 2 looked a little bit... wet? Makes me think it's a problem in the cylinder as opposed to the distributor.

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Re: Issue with misfiring and wrong firing order! #15
66jalopy Phillip Jolliffe Lake City, FL, USA Sign in to contact 1956 Morris Minor	Sep 1, 2016 11:37 AM Joined 11 years ago 6,727 Posts

Put that plug in another cylinder. see if a different plug will fire in #2. It may be shorted.

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