Ignition & Electrical / Q&A / Tech

Ask Away with Jeff Smith: How Can I Pinpoint and Diagnose Ignition Problems?

I have a 1970 Z/28 Camaro with a strong, small-block Chevy engine that that I’ve owned since it was new. Mostly I autocross race the car and recently I had a problem with an electric fuel pump. After replacing the fuel pump and readjusting the flow levels, I took the car out for a test drive and about 5 miles from my house, the engine died. I’m back after a tow truck ride and the engine has fuel, so it appears that my problem is with the ignition. I cleaned all the terminals and replaced the cap and rotor but it still won’t start. The distributor is an MSD Billet with vacuum advance, and an MSD-6A CD box and matching coil. Is there a way to determine if it is the distributor, the 6A, or the coil? I’m thinking about just buying a new distributor and trying that. Any ideas?

Gerald L. Los Angeles, CA

Jeff Smith: Before you spend any money on new parts, let’s do some simple diagnostics first to determine exactly what failed. Too often, guys just jump to conclusions about what has failed and keep buying parts until the problem is repaired. If you take the time to perform a few simple tests, often you can identify the problem. Let’s get started.

MSD-6201_xlIn your case, the MSD distributor uses a magnetic pickup that triggers the 6A CD box to fire the coil. The best way to do any diagnostics is to eliminate the most obvious issues first. We know that fuel is not your problem, so we can safely assume the engine is not getting any spark. You can check this by removing a spark plug wire and crank the engine over. Assuming no spark, the quickest way to narrow down the variables is by testing the CD box. MSD supplies a white wire from the 6A box that triggers the box when using a points-triggered distributor. In your application, the white wire is not used. Simply remove the coil wire from the distributor and position it so that it will show a spark from the coil wire to ground on the engine. Don’t touch the coil wire during this test or you’ll get a nasty shock. Next turn the ignition to the on position but do not try and start the engine. Now temporarily ground the white wire to the engine. If there is a spark between the coil wire and the engine, then both the 6A box and the coil are working, which means the problem lies with the ignition pickup in the distributor. You can also perform this test by disconnecting the two-prong lead from the MSD distributor to the 6A box. Using a paper clip, jump the two wires (green and violet) coming from the 6A box. If both the coil and 6A box are good, there will be a big healthy spark.

If after double-checking your test, the system does not create a spark, then we’ve narrowed the possibilities to either the 6A box or the coil. The next step is to substitute a known good coil for the one in your car and perform the same test again. If there is a spark, then you know the coil is the culprit. If there still is no spark, then it could be that the 6A box is the source of the problem. But you should check one more item before making that assumption. First you should check to see if there is actually 12 volts on the small red wire from switched ignition to the 6A box with the key on. It’s possible that this wire has failed and that the MSD box is not switched on. If there is 12 volts to the 6A box, then the 6A amplifier is the culprit.

Replacement pickup.

Replacement pickup.

If you think the pickup is at fault, you can quickly test it with an hand-held multimeter. These meters are very inexpensive and will test for voltage, resistance (ohms), continuity, engine rpm, and many other features. Summit Racing offers several that are priced under $50. Set the meter to test for ohms. When you connect the two leads together, the meter should read 0. Now connect the two multi-meter leads to the purple and orange wire that comes from the MSD distributor. The meter should read between 500 and 700 ohms. If the reading is outside of this range, then it’s likely the pickup is bad. A new pickup is available as a replacement piece (and it’s an easy piece to replace.

Running through these tests should get you closer to locating the problem. Often the solution is really simple. For example, a friend brought his carbureted, 302-powered ’68 Mustang over one afternoon complaining of an intermittent issue where the engine would just quit. I discovered the ignition lead from the firewall to the positive side of the coil had four poorly-executed crimp connectors spliced into the wire. I replaced that abused wire with a new one, and the car has run great ever since.

Often, the solution is simple once the problem is clearly identified.

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15 Comments

  1. I Had A box Like Yours Kept Burning The Coil Out. MSD Wouldn’t Help Me !

  2. Yes add me to MSD failures this one right out of the box a Ford ready to run dist. and blaster coil MSD wire set and correct hook up recommended by MSD with all solderd connections total run time about 25 minutes if that. Instead a Pertronix dis. 2 wire hookup turned the key and instant start that’s when I learned what MSD stands for My Spark Died. By the way my MSD dist.and MSD wire set is for sale 25 minutes old make offer.

  3. i have the same problem switched from stock dist with petronix ignition to msd 8595 ready to run hooked it up and have no spark never ran

  4. Gary West says:

    I have 69 Windsor with 6 a l box/coil / dist. etc. has spark and fuel ..when starting it will run for 1-2 seconds an shut off and will continue to do that till battery to low? any suggestions? thanks in advance.

  5. I have a 74 GMC pick up the wire from the coil gets hotAll the way back to the firewall any ideals? Also put the third ignition switch on and still not crank the engine over!

  6. Hi there ftom Western Australia
    I have a digital E curve sbc dizzy thst cuts out after 50 to 100 kilometres then let it sit for 2 minutes and then it goes again Eg : No spark then spark
    Where can i send it to be repaired thank you

    • Jeff Smith says:

      I would contact MSD and ask them what they would recommend. Sometimes electronic devices like this can be affected by poor rotor phasing – meaning there is too much distance between the rotor and the spark plug wire terminal on the cap. If the gap between these two components, the spark must jump this gap – creating an immense amount of electronic noise. This could cause the ignition to shut down. If you look on MSD’s website, they have a video that shows how to measure the rotor phasing. If the rotor is too far away, you may need an adjustable rotor that will bring the phasing in closer. This may solve your problem. We’ve sen this happen before – so it’s not just a theory. Plus, the magnetic pickup used in the distributor is very susceptible to this electronic noise. So this could be your problem. It’s worth checking into before sending yoru box back to have it checked out since it has to travel such a great distance… We’ve also seen where the rev limiter is not very accurate adn can shut of the engien early – so set your rev limiter to 9,990 rpm and see if that helps. I’ve experienced this before as well!

  7. Hi Jeff,
    i have an MSD ready to run distributor in a small block chev. I only drive the car every 2nd or 3rd weekend. Over the last few drives its been getting harder to start for the first time.
    Once im out driving its fine. Eventually it now will not start. I have plenty of fuel but a very weak intermittent spark. I borrowed a working coil and still no spark or a faint arc (not enough to fire a plug). I bpowered the coil from a separate battery to ensure 12v at the coil as i was thinking maybe the starter is drawing too much current. Now i am thinking module in th edizzy? Is there any way of testing these (Ohms test?), it has orange, red and black wires only.
    thank you.

  8. paul bassett says:

    I have a 85 monte carlo..with a lt1 fuel injection engine…12 volts going to the msd box, but no 12 volts coming from it….

  9. Hello Jeff,
    I have a 78 for d bronco, that quit running. I had the factory box and distributor in it with a msd coil.I had spark to the coil, power to the distributor but no spark, Changed the factory box ( replacement from auto zone. installed it and still the same issue, the motor cranks but doesn’t start. Boughgt a new distributor and installed it, still no spark. Decided to by-pass the factory completely. Installed my msd 6a box and distributor into the truck. Double checked all wiring, power to the box, coil fires, ohms from the distributor 0.510 with all of this the motor will not fire. Ground wire to the motor to the frame. Deep cycle optima battery to power the box 2 ga ground wire to the motor, box red and blackfrom the box to the battery, grey for tach, orange and black to the coil, no fire. I am at my wit’s end

  10. Joe Womack says:

    I have a 30 over sbc msd small billet distributor 6LA box! It runs perfect but I have no timing! A little advance it won’t turn over! A little retard it won’t fire! One tiny sweet spot it runs fine!

  11. I just installed a new accel MSD ignition box and a MSD dist and MSD blaster 2 coil onto a 1980 ford 2.3L engine. The engine will not start fully but I noticed with the timing light that the flash jumps around in location, sometimes it hits the cyl one correct degree and then sometimes it’s way off when it flashes. What could be causing this to happened, bad new dist or accel box or coil, all these parts are new.

  12. Anthony Giannotti says:

    well after reading all the cons of MSD units installed in a wide range of vehicles, it no wonder my friends 57 chevy /350cu in.runs well and dies without warning . most of the time it will startup after a few minutes until the next time .he replaced the unit with a new one and for a short time all was well but now it doing the same thing again. my fix, back to stock distributor with points, coil with resister and now it is flawless . solid state trouble . good luck

  13. Hi, my son and I are building his small block ’78 Aspen. He bought a new MSD distributor and 6A digital box. Coil is a msd blaster 2. We are now looking for best place to put the MSD box in engine room. Is it possible these major problems with MSD digital box has something to do with over heating? What do you suggest for a place to attach that box? Firewall? Inner fender? Inside the car under dash? Thanks! -Ari

  14. Raymond Greet says:

    I have a 76 Dodge W-200 Power wagon and I just installed-upgraded my MSD ready to run distributor that was running fine, with the addition of a 6AL Box and now no spark at the plugs. I did all of the trouble shooting, 12 bolts at coil, ground white wire and get a bright blue spark from coil wire but nothing past the distributor cap no spark at the plugs! WTF it was running fine! Trying to help the old girl and this is the thanks I get. Magnetic pick-up ?????Maybe?

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