need help with engine misfire-MSD experts

[fredmeister]

Originally Posted by 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?

My California model engine and dizzy should be 16 degrees machancial advance and 18 degrees vacuum advance according to the factory manual. These are the curves I have replicated in the image on my initial post. One of the problems diagnosing the early turbos we own is the existence of several different timing curves and distributors the factory used from 76-89. I am going with the distributor in my car which is the California model with both a vacuum and boost port on the canister.
My engine pulley is marked at 10 degrees ATDC, 5 degrees ATDC, TDC, and 29 degrees BTDC. I added marks at 10 degrees BTDC and 35 degrees BTDC to help me with timing the engine with the MSD unit.
My timing light is adjustable and works fine with the MSD and shows a strong strobe. The timing is fine at 2 dgrees BTDC at idle with the timing curves shown. This is right where it should be with 32 degrees BTDC total timing as I have the dizzy set now. At least it runs this way for a minute or two before it starts to misfire and stall, long enuff to get a reading with the light.
Bear in mind the total retard at high vaccum (idle) and low rpm my curves retard 34 degees total retard, but the MSd unit truncates to 30 degrees maximum retard. Thus 32 degrees Total advance minus 30 gives 2 degrees BTDC at idle.

Fred

[Daniel930]

Fred, any luck with this?

[fredmeister]

I have modified a Echlund EP407 rotor which is a direct replacement to the Bosch but without a resistor by cutting the base and re indexing the tip about 15-20 degrees to position it better in relation to the terminal in the cap. This eliminated any potential for rotor phasing.

This made the car easier to start then before. However my real issue is that the car starts fine when cold and runs well with throttle response and no misfire for about 1-2 minutes as it warms up. Then about 2 minutes into the cycle it starts to misfire and stall and AF ratio goes off scale rich then lean.
If I manage to keep the car running long enuff or just keep restarting it to the point where it gets hot then it will maintain an idle but occasionally a misfire can be seen.
I have replaced the cap again with a new one that I drilled a hole in the base for venting. No improvement.

I have checked the fuel pressures while this is happening and they are rock steady and no oscillations in the fuel pressure or the fuel metering plate. Cold pressure rises steadily from the intial engine start to a warm control pressure of 3.5bar and the car is misfiring the whole time this takes place.

The AF ratio starts about 11.5 when cold starting and runs thru to 12.8 to 1 at WP 3.5bar. This is no different then how the car ran before my rebuild so I know it likes these numbers.

I even adjusted the WP up to 3.7bar and down to 3.2bar to see if that changed anything and no luck.

One other thing that occurs when i manage to take the car out for a drive after it is hot. It runs fine down the road thru the gears but at approximately 0.5bar it falls flat and misfires as if it hit the rev limiter or fuel cutoff. IT is no where near the rev limit I set at 7000rpm. Its as if the spark shuts down.

The only thing I have not changed at this point is the original OEM braided spark plug wires. Plugs are NGK BP8ES.

QUESTION: would bad wires cause this issue as I described?
Car starts and runs fine bone cold after sitting all night, then 1-2 minuntes into the warm up it starts misfiring. Then it also misfires above 0.5bar but below that boost level its fine.

I am out of ideas and patience with this? I dont want to keep throwing parts at this but need t get this thing fixed.

The MSD prgram is replicating the factory timing like mentioned earlier in the post. Idle timing is 2 degrees BTDC total timing 32 degrees BTDC. Timing at 0.5bar boost is approx 26 degrees BTDC.

Thanks guys......
Fred

[fredmeister]

Some more pix of the rotor indexing. Note that I tried this first with a stock rotor with resistor in the photos but have since done the same with a non resistor rotor as required by the MSD.

[fredmeister]

Originally Posted by 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.

I checked the ohms and they are 585 which is within range.

Thanks,
Fred

[Lapkritis]

Go get resistor plugs.

[fredmeister]

Originally Posted by 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?

The red light on the MSD box is steady when its running.

Checked the timing and it is fine and follows the retard curve programmed. I can monitor it with the lap top while the car is running. Which is a nice feature.

I am really wondering if the age of my OEM wires is causing this. they could be original and 34 years old or been replaced at sometime over 8 years ago or more.

Thanks,
Fred

[fredmeister]

Originally Posted by Lapkritis

Go get resistor plugs.

Can you recommend some?

I would like a plug number that is cool enough for the turbo....can you provide a plug number?

Fred

Just checked and NGK BP8ES are resistor plugs. Aren;t they?

[Daniel930]

Fred,
I’m using the Magnecor wires and NGK BP8ES plugs. (1) I would take a heat gun to the dizzy with the engine cold, try to heat the dizzy up and see what happens. Heat will cause the resistance to go up in an electrical component, see if there is any effect on the pickup coil. (2) On my car, I did the green wire Modification, since it was 28 years old. (3) Silly check- when you took the dizzy apart, did you get the rotor trigger wheel back in the right place on the shaft with that little roll pin?
I feel something is happening with the trigger event, why would it start cold then break up after a few min.

[Lapkritis]

The BP8ES comes in both flavors so it's easy to end up with the wrong one. The 2912 version is non-resistor type of the BP8ES.

[Daniel930]

Andrew,
Good catch, I ordered mine from PP, did not even check resistor/non. By the way, if I seen a Skunk-works sticker on the back of a Porsche, I would approach with caution and high boost.

[fredmeister]

Originally Posted by Lapkritis

The BP8ES comes in both flavors so it's easy to end up with the wrong one. The 2912 version is non-resistor type of the BP8ES.

Dammit man! I have a box full of about twenty 2912 number plugs at home here.

Can you give me the correct resistor part number so I can order some? PLEASE-----

Got these from our host and never had a problem with them in the stock CD ignition.

Been running them for years with the old CD in the car.

Thanks
Fred

[fredmeister]

Originally Posted by Daniel930

Fred,
I’m using the Magnecor wires and NGK BP8ES plugs. (1) I would take a heat gun to the dizzy with the engine cold, try to heat the dizzy up and see what happens. Heat will cause the resistance to go up in an electrical component, see if there is any effect on the pickup coil. (2) On my car, I did the green wire Modification, since it was 28 years old. (3) Silly check- when you took the dizzy apart, did you get the rotor trigger wheel back in the right place on the shaft with that little roll pin?
I feel something is happening with the trigger event, why would it start cold then break up after a few min.

Yes I did and the roll pin is in place. I checked the rotor and its locked down on the shaft fine.

Of course I ge ta little play in the shaft from gear backlash and the slop in the parts but its about 4-5 degrees total roatation.....not bad.

Fred

[Lapkritis]

NGK Spark Plugs#739-BP8ES

[WinRice]

Fred,

I've had cars that I could run up to 0.050" gap on a MSD6A, and other cars that would only go 0.035" with out missing because of a breakdown somewhere in the HV system. Those braided covered stock wires could be the issue. Gap your next plugs at 0.035" and see what happens.

Here's a good chart on NGK plugs:

http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf

A resistor plug should be BPR8ES

[rsscotty]

Originally Posted by WinRice

Fred,

I've had cars that I could run up to 0.050" gap on a MSD6A, and other cars that would only go 0.035" with out missing because of a breakdown somewhere in the HV system. Those braided covered stock wires could be the issue. Gap your next plugs at 0.035" and see what happens.

Here's a good chart on NGK plugs:

http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf

A resistor plug should be BPR8ES

I would agree with the chart on this. It is pretty definitive... if it doesn't have an (R) in the long part number it must not be a resistor plug.

[Lapkritis]

NGK has been phasing their inventory records to the retailers to supercede the lettering with a 3-4 digit code. If you go to autozone for example, you may not find the b code as available but the other is. Jegs has these available with resistor. I would be surprised if the host would not also have these available if you phone in.

[Lapkritis]

Originally Posted by Daniel930

By the way, if I seen a Skunk-works sticker on the back of a Porsche, I would approach with caution and high boost.

. And if you spot an old grey Jetta with the same and making funny noises, good luck.

[fredmeister]

Originally Posted by Lapkritis

NGK Spark Plugs#739-BP8ES

Thanks Andrew.

And thanks everyone for their input.

I measured the resistance in my wires yesterday and they ranged between 39.1 to 40.4 kilo-ohms. Dont know if this is good or not and of course this was when they were cold.
Does anyone know what the resistance should be in the OEM braided wires?

Also, took a compression test and cylinders were five at 145psi and one at 150psi....pretty good. so I know its not an issue with sticking valves or dead cylinders.

I gapped the plugs at 34mils down from 40mils when the problem first surfaced so I could try dropping the gap again, but maybe I should wait before i order a set of the proper resistor plugs.

Here is a photo of the plugs removed yesterday:

[fredmeister]

Just wanted to post an update on this problem.

I replaced the OEM braided wires with new Magnecore 8.5mm racing wires. This alone did not make much improvement. Also rerouted the violet and green wiring harness from the distributor and used a new coax green connector instead of tapping into the 6 pin original wiring harness for this connection which used the original green wire. This made a big improvement as i made sure to run the harness away from any other wire source and as far from any spark plug wire as possible to reduce EMF interference.
This fixed 90 percent of the misfire at idle and low load driving. However the car still misfired at high boost.
So I made one last change to replace the plugs with resistor NGK IX iridium plugs gapped at 30mils. I think the original gap I was running of 34mils was blowing out at high boost.
Ran the car with all these changes and it pulls like a train now and no more misfire at high boost.
I still have a misfire when i first start driving the car after a cold start. I cant put much load on the car and can cruise around in low rpm high vacuum until the car warms up after 5-10 miles before I can give it any throttle without a misfire.
Once the car is warmed up it runs without any hesitation. Dont really know what is still causing this but the car's ignition programming is emulating the stock distributor curves with the only modification I made was to set idle timing to 6 degrees BTDC versus 0 stock.
I can live with it for now but would like to get this last thing resolved to make it 100%.

Wanted to thank everyone who contributed info to me to solve this problem.

Hope my post might help anyone else making this switch to MSD programmable ignition.

Fred