need help with engine misfire-MSD experts

[fredmeister]

I installed an MSD 6AL2 programmable ignition and am having a terrible misfire after the engine has started.

The rotor is the NAPA non resistor rotor and brand new cap. Wires are stock OEM braidied wires and the plugs were gapped at 0.040.

I am able to start the car and it runs fine for the first 1 minute or two then it starts to stumble and misfire. As soon as I touch the gas peddle to rev it up the engine starts to backfire and stall. AF ratio is bouncing all over the place going lean then rich as this is happening.

My max timing was set at 32 degrees BTDC and I have programmed the retards to take out timing to exactly simulate the stock 79 turbo timing curves from the manual. Idle timing is 2 degrees BTDC at 950 rpm.

I have replaced the front fuel pump and all the relays thinking it migh be fuel related. Front pump was making some noise so I installed a Bosch 044 front pump and rewired the fuses to break up the circuit to each relay. --No change.

Fuel pressures are 3.5bar warm CP and SP is 6.4bar all within spec.

I have read on the MSD forums about rotor phasing thinking this might be the cause, but am not sure if I am barking up the wrong tree here.
HAS ANYONE HAD ISSUES WITH ROTOR PHASING WHEN USING THE MSD 6AL2 UNIT? Is this what it sounds like, as I am running out of hair to pull out of my head and need to get this thing running.

Any help is greatly appreciated from you guys this has me stumped now.

Fred

[304065]

Fred,

What are you using to trigger the MSD?

You can either use a crank trigger to trigger the MSD, and have it do the calculations for your advance, and leave the advance mechanism in place in the distributor to properly phase the spark; or

You can use the distributor to trigger the MSD, and zero out the advance in the MSD, relying on the mechanical advance curve to control the timing.

Leave boost retard out of it for the moment.

Which is it? You most certainly cannot do BOTH-- that is, have the distributor/advance trigger the spark and use an advance table in the box.

You didn't lock the advance, did you? I think the consensus is that leads to misfiring-- even the Factory used advance mechanisms in the 3,2 and 3,6 engines to "phase" the distributor rotor for correct orientation even though the Motronic control unit and crank trigger determined the timing.

[rsscotty]

Are you sure the wires to the MSD trigger from your distributor or crank trigger are not backwards?

[fredmeister]

Originally Posted by rsscotty

Are you sure the wires to the MSD trigger from your distributor or crank trigger are not backwards?

Positive they are good.

[fredmeister]

Originally Posted by 304065

Fred,

What are you using to trigger the MSD?

You can either use a crank trigger to trigger the MSD, and have it do the calculations for your advance, and leave the advance mechanism in place in the distributor to properly phase the spark; or

You can use the distributor to trigger the MSD, and zero out the advance in the MSD, relying on the mechanical advance curve to control the timing.

Leave boost retard out of it for the moment.

Which is it? You most certainly cannot do BOTH-- that is, have the distributor/advance trigger the spark and use an advance table in the box.

You didn't lock the advance, did you? I think the consensus is that leads to misfiring-- even the Factory used advance mechanisms in the 3,2 and 3,6 engines to "phase" the distributor rotor for correct orientation even though the Motronic control unit and crank trigger determined the timing.

The distributor was locked out at full advance with the counterweights wired tight. The vacuum pot was left on but the ends are capped so no air gets in or out. With the internal spring inside the pot I dont think it will move the plate inside the dizzy without a vacuum signal and remain stable.

All my timing retard is controlled via the MSD program as I have the distributor timed to 32 degrees BTDC and locked down.

Fred

[Lapkritis]

Try a flat spark table at 15 degrees retard for all RPM. You may be requesting advance that falls off the edge of the rotor onto a neighboring cylinder... causing a misfire which will be indicated on the wideband as air to fuel flying about.

[Daniel930]

I have the same MSD set-up you have. I would check the ohms at your mag pick-up. Quote
“The published specification for the magnetic pulse generator is 600 Ohms +- 100. Our experience has shown that a variation of +- 25 Ohm indicates a need to repair defective connections or to replace the magnetic pulse generator windings.”
I bought a new Mag Pulse Gen and I’m right at 600 Ohms. Also I would check your power supply wire, and ground. BTW mine did the same thing until I figured out the battery was low.

[Steve@Rennsport]

My money is on a rotor phasing problem; especially since you effectively locked the weights. They do more than simply provide part of of centrifugal advance.

You will need a distributor machine (or access to) and a spare cap to see if this is the root of your issues or not.

[fredmeister]

So lets say that I have a rotor phasing issue. What can be done to fix it?

The only way I can think of is to somehow index the rotor tip thru some angle to attempt to center it with the distributor cap post. MSD sells an adjustable rotor for this purpose but no such thing exists for my 930 distributor. OR DOES IT?

What about grinding down the trailing edge of the rotor tip to keep it from jumping to the #5 cylinder when it should be firing on #1 for example. Sort of making a pointed tip on the rotor contact versus a broad tip like it currently has.

With the advance mechanism locked at full advance like I have it I assume the rotor wants to jump to the cylinder one clockwise from the target cylinder with a counterclockwise rotating dizzy is this correct? So for example when its supposed to fire #1 it jumps to #5, and so on. I tried to check for this with a timing light on the #1 plug wire with the engine running and it was very stable and gave no indication of a misfire. This perplexed me.

I dont want to/can't afford to pay someone with a distributor machine for their time and really want to solve this on my own. Any tips appreciated.

thanks for the input so far,
Fred

[Daniel930]

Hi Fred,
On my 930 the dizzy is locked out full advance mechanical/vacuum.
Question
1. Did you tap into your original 6 plug pigtail from the Bosch CDI for your trigger and power.
2. What’s your LED light doing on the MSD when you were able to get it to run.
On my car since I had the engine out, I rebuilt the whole engine wire harness, eliminated the AAR and thermo time switch in the L/H chain cover, my cold start valve has a manual switch I can toggle, anyway there is no more 6 pin plug. I ran the power wire to the starter +, the negative to the ground stud behind the Fuel filter ground point. I ordered 930-602-907-01 for the signal wire into the dizzy, and an extra Bosch electrical connector, so basically the MSD plugs right into the dizzy trigger wire. Nice and clean.

From MSD


To Dizzy

[304065]

Fred,

Unlock the advance mechanism and use a crank trigger to fire the MSD box. This will allow the rotor to be in a better position relative to the cap for each ignition event.

The only thing requiring a bit of fabrication would be a bracket for the sensor, as most solutions (Clewett's, for example) call for removing the distributor.

[LJ851]

Just for fun switch the wires on the mag pickup.

It changes the rotor phasing quite a bit, ask me how i know. My car sounded very similar to what you describe.

[Lapkritis]

Any luck with this? I was educating myself on the MSD for my own application and I see they state small distributor caps should be drilled to allow air to exchange in order to prevent misfire...

[fredmeister]

Originally Posted by Lapkritis

Any luck with this? I was educating myself on the MSD for my own application and I see they state small distributor caps should be drilled to allow air to exchange in order to prevent misfire...

Still working on it.
I replaced the front fuel pump and did tests on flow and voltage drops to the rear pump. Thinking its fuel related.
Fuel flow is above spec and pressure in the CIS system is in spec. Car will not start at all now and I smell fuel so I don't think its a fueling issue.

I found that the voltage decreases to the rear pump terminals from 11.5 volts upon initially running the pumps to a final reading of 10.2 volts after 2 minutes or more. This led me to think i had a battery dropping charge since it is 7 years old.

So I purchased a new battery and am installing it today. Is it possible the battery cannot maintain a steady 12 volts and this is effecting the MSD unit? I have read that the unit is susceptible to voltage drops or inconsistency.

Is it possible the alternator has a bad voltage reg and this is effecting the unit?
I see 13.5-14 volts on my lap top readout when its connected to the MSD and confirmed at the battery posts when the car was running.

I have not tried a flat spark curve yet like you suggested to see if reducing the maximum amount of retard dialed into the curves will fix the problem. Of course this is not the way I want to run the unit, so this is only good at diagnosing its an ignition issue. I will do this next if the new battery does not change anything.
Throwing more parts at the car is not a good way of fixing it, but the battery and front pump were a rational change due to the age of the battery and the noisy front pump.

Keep the ideas coming guys, I will keep updating this thread when I can.
This is a tough one.

Fred

[fredmeister]

Originally Posted by Daniel930

Hi Fred,
On my 930 the dizzy is locked out full advance mechanical/vacuum.
Question
1. Did you tap into your original 6 plug pigtail from the Bosch CDI for your trigger and power.
2. What’s your LED light doing on the MSD when you were able to get it to run.
On my car since I had the engine out, I rebuilt the whole engine wire harness, eliminated the AAR and thermo time switch in the L/H chain cover, my cold start valve has a manual switch I can toggle, anyway there is no more 6 pin plug. I ran the power wire to the starter +, the negative to the ground stud behind the Fuel filter ground point. I ordered 930-602-907-01 for the signal wire into the dizzy, and an extra Bosch electrical connector, so basically the MSD plugs right into the dizzy trigger wire. Nice and clean.

From MSD


To Dizzy

I wanted to answer your questions:
1) Yes i got an adaptor from Permatune and wired into the factory harness for the CDI unit to trigger the MSD and provide a switched power source. The main power and ground ot the MSD is off the starter pos terminal and grounded to the chassis ground used by the tranny ground straps.
2) checked the red light and it blinks as the car is running off the starter motor upon cranking the engine to start it. This means its getting a proper start signal from the dizzy right?
I dont know what the red light does when its actually running, but the lap top readout shows the unit runnign properly. RPM and MAP readings are correct and the retard curves are behaving like programmed.
I ran the car at night to look for arcing in the wires or cap and saw nothing sparking or arcing over.
I dont think the OEM steel braided wires would cause a problem would they? They are compatible with MSD right?

Fred

[Lapkritis]

Braided wires are correct. It's the solid core that are warned against as causing problems.

The arcing would be under the cap hidden from view if you had an electrified air field issue. Moisture, high humidity, dust can all contribute to the effect. That's more of a long shot though... plenty of simpler solutions to consider first.

[Daniel930]

Fred,

The LED light should be steady with the engine running.

One thing after reading your thread, you only locked out the mechanical advance full, not the vacuum. You may be over retarded with your curve.

I would put a timing light on it, at least check your idle settings.

With my dizzy locked out full mech-vac, I’m running about the same stock settings at idle and 4000 RPM with timing light.

You have good power and ground, the only thing left would be your trigger, check your ohms about 600, with engine cold, and after it’s warmed up.

Volts check your battery before start and after you get it running, this thing likes power. MSD says it draws .7 amps per 1000 rpm

MSD Success

[fredmeister]

Hi Dan,
I wanted to correct you in that my post says that the vacuum canister is un connected from all hoses so it sees no input on either the vacuum or boost retard nipples. They are capped with rubber plugs so the canister should not be moving the advance plate at all. It has internal springs which keep it in position so I did not think that the plate would move on its own either so no need to mechanical lock this canister mechanism.
Anyway, I ran more tests today with the flat rpm advance curve at 14 degrees retard total. The car ran fine, so far but starting it against 14 degrees BTDC was not easy and the idle at 14 degrees BTDC is too high at 1250rpm and the throttle screw is damn near closed off.
This would indicate that the rotor is jumping spark to adjacent terminals probably due to the fact that the mechanical advance is locked at full advance and the MSD needs to take out 30 degrees total retard at idle which puts the rotor in a bad position inside the cap.
I am thinking of locking the advance counterwieghts at full retard to reindex the rotor and then going back to the stock curves i had before so i can still get vacuum retard and rpm advance curves to work together. Then I can get 30 degrees retard at idle and have 2-4 degrees BTDC instead of 14-16 like I do now.

Fred

[304065]

Fred,

Locking the advance counterweights at full retard is the same as having them in their current full advance position and rotating the distributor body. A fixed position over the RPM curve is a fixed position over the RPM curve.

[Daniel930]

Good Morning Fred,

Ok you got the engine running, so you can rule out a trigger problem. Based upon the PP forum that I have searched, it’s my understanding that the Centrifugal advance will give you 16 deg. and the Vacuum advance will give you 10 deg. For a total of 26 deg.- advance-. ( I don’t have access to a SUN dizzy machine to verify this, and I’m too cheap to pay anybody).

Based upon your first post, you are telling the MSD box to retard your timing 16 deg until about 1500 RPM and letting it back in full by around 2700-2800 RPM.

Since you only advanced your centrifugal, it should only see 16 deg. hopefully the arm pressure on the pot is not affecting the rotor plate +/-

If you set your engine to TDC number 1, Z1 at pulley to case parting line, drop the dizzy into the engine with the rotor pointing to the hash mark on the dizzy body, fire the engine up, with a timing light (MSD box working correctly) you should see the flash around the Z1 mark at idle, indicating you are firing at 0 TDC. I’m not sure your pulley is marked for the 16 deg. bringing the engine to your 2800 RPM should see the flash from the timing light.

Question: where is your timing light flash in correlation with your MSD run retard curve?