Popping / Backfiring problem while on MSD6AL

[GerryLP]

Hello everyone,

Some of you may have heard me talk about this on-going problem with my car. I installed an MSD 6AL box, and after hooking everything I started to experience popping / backfiring between 2,800 - 3,200 RPMs.

I have checked the folowing so far:

replaced power valve
installed jet sizes for 4777-7 as stock configuration (this at 5,000' alt is relatively rich)
checked for vacume leaks
adjusted gaps from 0.045" to 0.055" (milage increased but popping remained)
replaced sparkplugs
check idle mixture (approximately 11 HgIn at idle)
checked and adjusted timing (went from 10 initial to 14 initial)
Changed fuel pump (re-installed new OEM type)


checked MSD box connections
Replaced ignition wires
cleaned mechanical weights and springs in distributor
reinstalled HEI module and car functioned fine with no popping, although milage suffered some [it even ran well without popping and the 0.055" sparkplug gap :confused ])

re-attached msd box and checked connections a third time
replaced ingnition wires again (Accel)
drilled holes in rotor cap to vent ionized air
checked MSD box connections (even cleaned tie point at rear frame for negative cables)

refreshed carb while installing a 700 cfm body
checked idle misture (approximately 9.5 HgIn)
After installing the 700 cfm DP and double backfire protection, I returned from test run today because it popped and backfired at 3,000 rpm. AT home I noticed slight wistle at idle and discovered power valve blown.

The car runs strong through 2,800 rpm. At freeway speeds it mantains 70 - 75, but ever so slight load will make it pop (slight grade, strong wind, acceleration).

I need to find out what the engine is doing at 2,800 rpm - 3,200 rpm in fuel pressure and in timing. There is a plastic filter in fuel tank that could be causing problems but I need to find out fuel pressure first before dropping tank. Trying to make no more than one change at a time, so it has consumed the better of 7 weekends so far.

I believe that Jack mentioned that the MSD requires to run rich but how rich and why? How do I check for fuel pressure while under load at 2,800 - 3,200 rpm? (I suspect that I need a long hose, but I am affraid of spills or worst fire while holding fuel pressure gauge in vehicle and going through the motions)...the best guess would be a dyno run???

JohnZ..can you think of any suggestions to resolve this issue?

 

[Chris Kennedy]

I have an '81 4-spd and used the MSD 6 for a number of years until it finally stopped working. I never felt it added much, if anything, to the performance of the car, and it was an extremely complicated device to install and also really screwed-up radio reception and the car alarm, of all things. What I have been told is that these units work best in cars with old fashion point distributors with lower output, and if you have a HEI unit they probably don't do anything, except add another layer of electronics with the potential to stop the entire car if it quits on you (like mine ultimately did) with other side-effects like you are experiencing. My recommendation would be not to waste any more weekends fussing with the thing, and to take it out and get an HEI if you don't already have one. Generally, I have found that these aftermarket "re-engineered" improvements often do not do anything, but even if they improve some aspect of performance it comes at a cost to performance somewhere else.


--Chris Kennedy
Houston, Texas

 

[Ken Anderson]

MSD= May suddenly die. If your problems started after you installed the MSD, why did you change all the other stuff? CK is right, a stock HEI is all you need. If you're using a Holley, then every "backfire" blows out a power valve unless you installed the anti backfire check ball. Good luck!

 

[GerryLP]

MSD= May suddenly die. If your problems started after you installed the MSD, why did you change all the other stuff? CK is right, a stock HEI is all you need. If you're using a Holley, then every "backfire" blows out a power valve unless you installed the anti backfire check ball. Good luck!

The main thing I am searching for is to reduce the loose feel of the engine at 5,000 rpm in the 1/8 mile marker. This loose feel on the pedal has been often attributed to the decay of stock ignitions at high rpm. The engine misses more at high rpm.

The power valve protection is not helping. This carb has one, and in addition to the one it has, I added a Centek-type power valve protection, so I don't know why it's blowing them like soft candy.

I guess giving up could be in the future, but I tend to try figure things out (if not just for the challenge), and what a challenge it's been.

I plan to take the car to the dyno (Dyno Edge) to check fuel pressure and mixture ration under load when the backfire occurs. Does anyone know if a timing light would be damaged while operating under load as well? I suspect that it should work fine, but I like my timing light, and want to keep using it.

 

[SG4206]

Take this to your chassis dyno. Sounds like a total timing issue at certain rpm levels. The MSD will act like this when hooked up backwards with an HEI.

 

[GerryLP]

Take this to your chassis dyno. Sounds like a total timing issue at certain rpm levels. The MSD will act like this when hooked up backwards with an HEI.

SG,

What do you mean by backwards? Do you mean using the trigger in the distributor instead of a crank trigger?

 

[curtis]

Some aftermarket ignitions like DUI can be damaged by using a dialback type timing light. Maybe this is what happened. I run Accel module and coil, in my HEI , no misfires up to 6000 when the valves float.

 

[SG4206]

Sorry- I had a flash back with a MSD 7 and an Accel magnetic trigger distributor , I had wired backwards.
Please disregard my statement.
I believe the wires are indexed to only connect one way ,with your set-up.

 

[Jack]

GerryLP:
Misunderstanding here. Often, circle track carbs will "go rich" at high RPM due to "fuel pullover" ... often this condition requires an MSD box to fire that over rich mixture. Also, race carbs are a bit rich anyway ... again requiring more fire the MSD provides. But it's NOT the other way 'round ... just because you have an MSD does NOT mean you should run rich setting. On a street car, the MSD may ... repeat may burn so efficiently that you may ... repeat may need to richen up. I'm of the opinion that majority of street cars do not need an MSD ... nor the potential problems associated with them or their like. Dunno how your's is hooked up ... but if there's a polarity mismatch between pickup and MSD 6 ... that can cause misfire ... whether using HEI distrib pickup or MSD distrib pickup. In both race car and 71 vette ... I run a gutted early type HEI ... the type that had 4 pin ignition module and both mechanical & vacuum advances and coil in large cap. I remove the module completely and use the HEI pickup to trigger the MSD 6. For the EARLY type HEI, the pickup's WHITE wire is POSITIVE and connects to MSD VIOLET Mag POS wire ... and the pickup's GREEN wire is NEGATIVE and connects to MSD GREEN Mag NEG wire. For most carbureted street cars, a good 4-pin HEI with NO MSD is quite sufficient and very reliable. At some tracks, rules don't permit MSD box ... there I run an early 4-pin HEI with a DUI "DynaMod" ignition module and hot coil ... it's good beyond the physical limits of our expensive crank & rods ... but we do have that over rich problem at about 6500 RPM ... but that's caused by the carb itself ... the dynamod & good coil are good to over 8 grand. All of our close competitors have the same issues and employ the same ignition combos ... although some use an MSD distributor in lieu of gutted HEI ... I don't see real advantage in MSD dist. HEI ignition module (OE or not) runs very hot and needs good contact between its bottom side and pad on distributor base ... uses base as heat-sink. Without this heat transfer, the module can get too hot and will break down.

Simply an educated guess ... but if your wiring is correct and the MSD is relatively fresh ... could it be that the module itself is failing? Bad modules can exhibit problems you describe.

Let me make a distinction regarding the fuel pullover issue. The required carb at most tracks for Late Models and Supertrucks is a Holley 2300 TWO-Barrel (350 / 500 cfm). I dunno, but I suspect the fuel pullover issue is peculiar to the 2300 series ... and probably not much, if any, of an issue with 4-barrel Holleys. We all run the 2300, with the exception of those that run a sealed GMPP "crate circle track" motor ... with those (and their relatively smaller cams), some tracks permit a tiny Holley 390 cfm 4-barrel. Their cams start running out of breath about 5200 RPM anyway.

-edit- you might also try these two things separately: pull the rpm pill/chip out & see if any improvement. Also, disconnect tach connection to MSD. Either circuits inside MSD could be inducing misfire. It has happened, quickly checked.
JACK:gap

 

[GerryLP]

Jack,

Thanks for clarifying this for me. I see what you mean. I am actually using the MSD without the 4-pin module and using the two harnesses (violet/green) that MSD sells.

I will try those easy checks that you recommended. I was also researching my Holly book again, and as a result, I ordered a 7.5 and 8.5 HgIn power valves. The book reminded me that the power valve should have a value of approximately 2 HgIn below the highest manifold vacume attained on the run (I understand that what they mean is a run around a circle track, a 1/4 mile strip, a freeway section, or any segment that typically represent the portion of condition the vehicle is subjected through).

In Auburn, I installed a 6.5, and it did not seem to help, except that it seem I was able to reach 75 mph without hardly any popping. Currently with the 700 cfm I am geting 9.5 HgIn at ilde, but this check should be done on auto tranny-equiped vehicles in drive, and I think I failed to do that, but it looks as if I will be able to use a 7.5 or 8.5 power valve (at 9.5 HgIn, the value is kinda too close to the 8.5, so I am hoping that the 7.5 will do the trick).

 

[GerryLP]

Possible solution to problem

Well folks,

I finally ran out of options with the popping issue, and decided to get MSD to check the box out. Yesterday, I spoke with them, and they told me that it was "bad and not financially advantageous to repair the box." Apparently, there were a number of diodes burnt, and that the board itself shows heat signs of overtemperature. They also told me that usually, welding on a vehicle's frame while the box is connected could cause this problem. That sounds a little weird, for I have not done any welding on the car. Maybe the person who sold me the box on e-bay did. I don't know.

On the other hand, they offered me a cosmetic-return 6AL box with a 1 year warranty for $65 dollars. It comes with all the stuff a new comes with. These are returns that normally exhibit a few scratches or small dent, but the technical departtment has checked out and extended its warranty. So, I took the option. Not even on ebay is easy to find a 6AL MSD box for $65 dollars.

I am glad that I have closure on this issue. Its about time.

 

[Bob Chadwick]

Gerry,

Glad you got this taken care of.

Did you follow the thread on my installation and see that I got everything in. I haven't had a chance to run it but at idle and gunning it everything seemed great.

Bob

 

[GerryLP]

Gerry,

Glad you got this taken care of.

Did you follow the thread on my installation and see that I got everything in. I haven't had a chance to run it but at idle and gunning it everything seemed great.

Bob

Bob,

Yeah! That's great! I am glad you had no problems. I can't wait to try the new box to see the the problem truely gone.

Gerry

 

[GerryLP]

Case Closed

It's official!

Installed new MSD box, and now car accelerates through 4500 rpm on 1st gear (Automatic) very smoothly and no backfiring or hesitation.

Gerry

 

[Bob Chadwick]

That's great Gerry. I've put about 100 miles on mine and like the way it runs. Seems a little smoother at idle and seems to get a little better gas mileage.

I'm about to start on the next project. Replacing the u-joints on the half shafts.

 

[Rowdy1]

Sorry I missed This

Glad you finally contacted the tech guys at MSD. They are the BEST! A while ago I had a problem (posted in here) that drove me nuts. Long story short, it had nothing to do with the box but the coil. They took my box, one year after the warranty was gone, refurbished it FREE and called me twice afterwards to see how I was making out.
Being you bought the box "used", that would have been my first clue and I would have suggested you send it in for the bench test, they don't lie That box is around $200 so you did very well for $65. I wouldn't hesitate to call those guys with a problem, they actually care which is rare in this day and age of buy it from the internet or a catalog.
See Ya' at the "next" Cruisefest!!!

 

[timme69680]

We had the exact same problem, but I am really depressed now, we gave up and removed the darn thing. I am gonna pull the box out and see if it is burnt. Ahh that kills me. Glad to see your up and running again though. Here is the project site www.helptimmebuyahonda.com if you look at this picture you will see the MSD box under the body with all the wires cut.... http://www.helptimmebuyahonda.com/teardown/09202004-04.JPG

 

[Bob Chadwick]

That looks like a tough fit. I ended up putting mine in the nose on the brace for the bumper.

 

[timme69680]

Yeah we had fun getting that thing in there. I had to drill holes in the firewall and stick my hand behind and in front to tighten down the bolts. It took the better part of two hours to get it mounted. I am not going to re-install or buy a new one for this car. I have not decided that MSD really gives you that much for the headache it creates. Well at least in a street car, circle track yes, factory 350 I don't know. Time may change my mind though.

 

[GerryLP]

BobChad,

It did seem as if the gas gauge was moving slower to the left....:L

Rowdy,

I was treated right by the MSD guy's, and you're right -that is rare in today's high performance market. All I need now is a good "blend" by our good buddy Evo...

Timmmmeee!,

I plan to take the car to the dyno and track pretty soon. We'll see if the mushyness on the gas pedal goes away between 1/8 and 1/4 mile segment. The car pulls very strong on the XE274H cam power band, and now the responsiveness is awsome above 3,000 rpm.

Gerry