View Full Version : 6al Misfiring On Mazda B6 Turbo
I've got a Mazda B6T (1.6L DOHC Intercooler Turbo) with a cr of 7.9:1
I just installed my MSD 6A (with tach adapter pn 8910), and now my car seems to be misfiring at pretty much anything above 4,000 rpm (before that it has heaps of balls!).
When we installed the 6A, the car had trouble turning over due to a shift in the timing, so we set that all back to normal, at about 10 deg BTDC. I advanced it some more to try to get rid of the misfire, put it up to around 14 BTDC, and it did help quite a bit, but I can't really advance it anymore for fear of detonation.
I've got Champion 7mm leads which are probably nearly a year old now, but they have no burn marks or anything, and I have newish NGK Iridiums with a heat range of 6 (they don't make colder plugs of this kind for my motor from NGK, I might try Champion) gapped at 1.1mm. I've also got an MSD Blaster 2 Coil and a new distributor cap, and weights and springs. It's running 8-10 PSI of boost off of a VF10 w/ VJ20 exhaust side and custom front pipe. It's also running 98 Octane (BP Ultimate).
Any ideas ?
I was thinking about replacing the leads with some bigger ones.
I checked the earth on the unit and it doesn't look like its as good as the one on the engine so I'm gonna shift that over when I get back from holiday, it's still earthed, is the quality very important, would it cause a miss like this ?
10-02-2003, 02:18 PM
The MSD unit requires a good ground path (earth); by not having a good ground could create misfiring problems as well as other problems. The higher the RPM the more amps the MSD needs, so a 4000 RPMs it is pulling 4 amps, and by not having a good ground can cause misfiring.
I grounded it to the battery and its still misfiring !
I've ordered some colder champion plugs, help!
I put the colder Champion plugs in and it did indeed help a lot, but it's still playing up..
Could my leads be shot from the increase in voltage ? They are almost a year old and are only Champion 7mm's
10-06-2003, 02:13 PM
First, I would suggest dropping the gap down to 0.75mm (0.030in.) and try it again to see if it improves or stays the same. If it improves then I would go ahead and change the wires. MSD suggests using at least an 8mm wire with then MSD Ignition.
I dropped the gaps down to .7mm and it does run a lot better, so now I'm looking at getting some leads.
Any recommendations ?
How decent are the MSD ones, and would you make them for such an engine ?
Cost ? Shipping to NZ ?
10-07-2003, 10:57 PM
MSD Does not make a custom set for your engine. I would recommend using a suppression type wire that is not over 1000 ohms per foot.
I replaced the leads with a set of Magnecor CV8.5 Competition leads, and the problem still remains.
It only does it under high load (pretty much WOT), AND above about 3,500-4,000rpm. It seems to be fine when the engine is hot, but it has been sitting for about 1/2 an hour, it goes quite nicely to redline, still feels a bit faint though.
I've got another two theories.
Maybe the wires I've used aren't a large enough gauge, particularly the earth wire, and maybe it can't carry the current asked of it. Maybe it's fine when the peripherals have been sitting for half an hour because the resistance is lower due to it being allowed to cool down ?
Also, maybe the Tach Adapter I'm using is the wrong kind (8910), would the car function with the 8910, but need the 8920 ? Or are they completely different in design. This also doesnt support the ambient/peripheral temperature factor, so I don't believe its this.
11-04-2003, 12:25 PM
As long as the ground wire is 14 gauge or bigger there should be no problem with the ground wire. The PN 8910 is working fine, this is only used for a tach purpose, and it should not affect the firing on your application.
Try reducing the gap by another .005 to see if it will improve it better, go down to .025. If this helps then the engine is lacking spark energy under full boost pressure. If this is what the engine is requiring you may have to change to a higher current coil. The better coil would be a Blaster SS Coil, PN 8207.
The car doesn't run without the 8910 plumbed in though.
You mean the Blaster2 is not good enough ?!
Ok ill have another look at my earth wire.
I got some chunky wire and redid the earth and joins, and make the connection strong on the battery, still misfiring.
I gapped the plugs right out again to .38" and it misfires lower in the range, which is interesting as I have brand new leads, plugs, dizzy cap.
What else can I check ?
Can you give me a list to go through ?
I'm sure the coil would be able to handle..
11-12-2003, 10:37 AM
If you have replaced the cap, use the old one and make a hole on one of the terminals, so you can check rotor phasing. If rotor phasing is off, this can also cause misfiring.
The following is a link on how to check rotor phasing.
My battery terminal was slightly loose !
It helped a great deal, but still feels weak and misses through the range, although a lot less. I am going to go through all the wiring and redo it again. At least it sort of accelerates now !
I'm going to try my old (better) Iridiums too, although I've heard these MSD units melt any precious metal plugs.
Are there any voltages I should check across the board ? Ie. negative/positive of coil, running/not running, resistance maybe ?
11-14-2003, 12:11 PM
In order to check voltages on the coil, you will need a non-automotive oscilloscope; you will not be able to test with a voltmeter. The MSD Unit provides 460 volts to the primary side of the coil, but it is a pulsating voltage. The only check that can be done is a resistance check to the coil, the primary resistance is .7 ohms and secondary is 4,500 ohms, this will vary depending on temperature.
I checked the rotor phasing and I believe it's out.
I reverted the ignition back to normal and it works fine, but I had to change my timing back again .. it was about 20 degrees out ?!
I think it's pickup in the wrong place .. what can I do to fix this ?
11-19-2003, 01:50 PM
The MSD Unit will only fire when it is told too, so if there is a problem with the pick up, this will just amplify the problem. You will have to see if the pick up has any adjustment, and play with it until you can get the proper phasing.
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