MG Car Repair/77 mgb

Advertisement


Question
QUESTION: hello. have a 77 mgb that Im trying to get running. It has been in storage for nine years. Did all the normal things befor trying to start the engine and discovered I have no spark. Engine cranks good thanks to new starter. have rebuilt webber carbs. new oil and filter. Pulled coil wilre out of distrubuter and forund I had no spark while cranking. I did as the expert advised me and ran a jumper wire from positive side of fuse box to positive terminal on coil. still did not give me any spark except now and then when key was released I would get a spark from coil. When I checked the coil with the ignition on  with a test light the positive side light up. checked the negetive side while cranking and found the test light was so dim you could barely see it and it was not going off and on. checked the voltage at the fuse box 12v at the positeve side for the coil 6.24 and the negative was 1.95. I hope I made some sense and you can give me some advise on what to try next. Thank you for taking the time to help.

ANSWER: Brian:
Sounds like I would try a new or at least a different (but known "good") coil. Coils will work either way you hook them up, but work best when the lead to the distributor matches the ground of the car's electrical system, i.e. Neg or Pos ground. Also check all of your ignition primary (12V) and secondary (from the coil- through the thick coil wire and spark plugs) wires.

You can go to this url to view coil testing proceedures. http://www.youtube.com/watch?v=rJYJ3KvPhhY

Good luck!
Brian

---------- FOLLOW-UP ----------

QUESTION: Brian,

Thanks again for the help.  Since my last post, I have cleaned connections on the starter relay, the ignition relay and the coil.  Still have had no spark at coil when cranking the engine.  Decided to take off the steering column plastic and check wires at the ignition switch.  Found the purple wire on the front of the switch was loose although the phillips head screw that was holding it was tight.  I put pressure on the purple wire hoping this had something to do with the coil not firing and cranked the starter. The engine fired. I started the car and heard the engine run for the first time. sounded good. I then proceded in the next two hours or so the start and run the engine about eight times. Excited to move on to step two off one hundred, Clutch brakes ect. The next morning I went out to start it again for piece of mind, and notheing. Back to no spark at coil. I pulled the coil out and put a meter on it and I had 1.5 when I went from positive side of the coil to the negative.  When I checked the secondary positive side of the coil to center of coil I had 6.5K.  I think from what I read I was to have 11K or better.  Could this be an issue with the coil and should I go ahead and replace both the igition swith and the coil.  If so, do I need to buy a coil that doesn't have an internal resister in it that I could pickup from a local hardware store?  Or do I need a coil that is 1.5 that is externally resisted?  If I buy a internally resisted coil what will I do with the two wires going to the resister that sits next to the coil now?  Thanks again, Brian Cussimanio

ANSWER: Brian:
Will try to give some ideas regarding your issues and questions:
1.) Re-check the connection of the purple wire to your switch. If it is not correct, ie. continues to be "loose" then repair that - as that did start and run the car when you moved it last. I'll assume also that your starter, solenoid, and battery are in good condition. A fully charged battery should be about 12.5V or so. When the car started did the engine turn over well, or was it sluggish?

2.)You should have a ballast resistor in the wiring harness in 1977, as you have noted. This means that when you go to start the car the coil gets a full 12V  through a blue/white wire that goes from one side of the coil to the starter solenoid, but when the ign. switch is to the run position you get a reduced voltage to the coil through the ballast resistor (about 1.5 ohms resistance)while the engine is running. Also check the connections for the blue/white wire.

3.)In a ballasted system your coil resistance should be about 1.5 ohms resistance + or - a bit depending on the temp of the coil when tested. You need a 1.5 ohm  externally ballasted coil should you go to replace it.

4.) A great source of info may be found on Moss TV (on Youtube) at the following url:
http://www.youtube.com/playlist?list=PL203268D84EE9ADD8

Good luck and let me know how it goes.


---------- FOLLOW-UP ----------

QUESTION: hello Brian. I have replaced my coil and still have the same problem. No spark at coil when cranking, even with jumper wire to coil. I have decided to replace the distributor. It is 45de4 I am told not very reliable. What distributor and or coil match would be best for my 77 mgb. What would you recommend so I dont have to do alot of re-wireing not to good at it. thank you for your time

Answer
45DE4
45DE4  
Brian:

O.K. Replacing the distributor with another has some fair amount of considerations, like vacuum advance timing curve, etc. The Lucas 45DE4 Electronic Distributor was unreliable in service though if yours has lasted this long it might be a record. I would suggest keeping the 45DE4 and rebuilding it with a Pertronix, Crane or other similar aftermarket electronic ignition setup. Make sure it matches the ground of your car- which I think was neg. ground by 1977? With new internals you then have no need for the original amplifier so you would not connect its wiring. I don't think you can simply remove it from the side of the dist, but am not sure.

This may be repetitive but to test your coil detach the coil lead to the distributor cap at the cap and the lead from the negative side of the coil. Leave the lead on the positive side of the coil (input). Attach a jumper wire to the negative side of the coil and put it out of the way where it cannot ground on its own. Turn on the ignition switch. Position the coil lead very near but not touching the block or a good clean ground/metal, and quickly touch the jumper lead from the negative terminal of the coil to the block/ground. As the contact between the lead and the block is broken, you should see a spark at the coil high tension lead if the coil is working properly. If you do not see a spark, you need to replace the coil with the proper type. If you do see a spark, you have a distributor problem.

The 45DE4 dist also fits Triumph Spitfire 1500 and MG Midget (and probably others)if you want to find another one but by now most are decades old. Make sure the vacuum advance is not broken off and works.  Also about your coil wiring - There should be two wires that connect to the coil's positive terminal, I believe both are white and/or with a light green tracer. One wire supplies a full 12V during cranking which comes from the starter solenoid - the other supplies the reduced voltage through a resistance wire in the loom once you've let the key back to the run position. Make sure you have both wires. A new electronic system will tell you what coil you need in the instructions that come with it.

Last but probably most importantly -If I were you and before I'd do anything - call "Jeff" at Advanced Distributor and ask him what he suggests or what he can do for you. He has rebuilt distributors for me and does very good work and stands behind that work.  Go to this link: http://www.advanceddistributors.com/index.htm

Good luck!
Brian  

MG Car Repair

All Answers


Answers by Expert:


Ask Experts

Volunteer


Brian Warmuth

Expertise

General questions regarding most MG autos from 1950 through 1980 - primary are the TD, MGB, Midget and MGA.

Experience

Over 30 years of working on and restoration of MGs

Organizations
Ohio Chapter New England MGT Register, AACA

Education/Credentials
BA, and MS, from WVU

Awards and Honors
several local regional awards for restorations

©2016 About.com. All rights reserved.