Worse... Now CONSISTENTLY running on 6

**dz3774000** · 09-11-2021, 01:48 PM

I've replaced/swapped all the normal potentially related stuff:

New Coils
New O2 sensors
New Plugs
New Plug Wires
New Fuel Pumps
New Fuel Filters
New Distributor Caps/Rotors
New Crank Sensors
New Batteries
Swapped Throttle Motors
Swapped ECU's
Swapped Fuel Regulators

The car sat for 3 years after hitting a deer in my neighborhood. After finally repairing the body and changing all fluids, replacing radiator, brakes/rotors, shocks, I drove the car for a little more than a month with no issues. Then, the car started to drop to 6 cylinders while driving. For several weeks I could "reset" things and return back to 12 by simply lifting off the gas pedal completely for like a full second. Once back on the gas I once again had all 12 cylinders firing.

But now it's progressed to where I only have 6 cylinders, no matter what I do with the gas pedal. I've had it at two "expert" shops only to be stuck with rather large bills and no change. The last shop suggested I look at the relays. But after looking over the lists of relays, I don't see anything that jumps out as a possibility.

Any suggestions welcomed.

**CD05001CIA** · 09-11-2021, 02:08 PM

Originally Posted by dz3774000

I've replaced/swapped all the normal potentially related stuff:

New Coils
New O2 sensors
New Plugs
New Plug Wires
New Fuel Pumps
New Fuel Filters
New Distributor Caps/Rotors
New Crank Sensors
New Batteries
Swapped Throttle Motors
Swapped ECU's
Swapped Fuel Regulators

The car sat for 3 years after hitting a deer in my neighborhood. After finally repairing the body and changing all fluids, replacing radiator, brakes/rotors, shocks, I drove the car for a little more than a month with no issues. Then, the car started to drop to 6 cylinders while driving. For several weeks I could "reset" things and return back to 12 by simply lifting off the gas pedal completely for like a full second. Once back on the gas I once again had all 12 cylinders firing.

But now it's progressed to where I only have 6 cylinders, no matter what I do with the gas pedal. I've had it at two "expert" shops only to be stuck with rather large bills and no change. The last shop suggested I look at the relays. But after looking over the lists of relays, I don't see anything that jumps out as a possibility.

Any suggestions welcomed.

The question is .... are you loosing spark or fuel on the bank that isn't running.

Although is has been quite some time since I have worked on an M70 engine, I would first check the condition of the donut sensors and that they are installed correctly on plug wires 6 and 12. Measure them with a volt ohm meter for resistance and see that they are within specification.
The fact that you have one bank running will allow you to swap one part pair at a time to find the culprit.

How can you confirm that you have steady spark on plug wire #6 and plug wire #12? Let us know here on the message board.

Each DME will shut down the fuel(by dis-abling the injectors) rather quickly on a per bank basis so as not to wet fuel coat the catalytic converters.

**rjjablo** · 09-11-2021, 02:59 PM

Doughnut Sensors are going bad test, Lift off the throttle and back on it works is the classic symptom

Test the Crank Position Sensors at the same time, just because

Maybe the fuel pump relays. Again pull and test, I had one go bad and hit a bump and half the motor would drop

**dragon850** · 09-12-2021, 10:27 AM

I suspect a MAF sensor.

You do also need a proper diagnostics computer otherwise you will continue to replace parts in hopes it will solve your issue.

**ByMW** · 09-13-2021, 04:07 PM

A fault code would be very helpful ("stomp test" or diagnostic computer or even a Peake tool reader).

**petejk** · 09-13-2021, 05:34 PM

Speaking of MAFs, I’ve just sent mine for rebuild to Kevin at Injection Labs, following a recommendation from another thread.

This supposedly one of the best ways of getting a pair back to factory spec.

Sent from my iPhone using Tapatalk

**dz3774000** · 09-13-2021, 09:51 PM

Originally Posted by ByMW

A fault code would be very helpful ("stomp test" or diagnostic computer or even a Peake tool reader).

Stomp Test:

2247 Driver Side (LHD)
1222 Passenger Side

- - - Updated - - -

Originally Posted by dragon850

I suspect a MAF sensor.

You do also need a proper diagnostics computer otherwise you will continue to replace parts in hopes it will solve your issue.

I swapped the MAF sensor with the working side.

- - - Updated - - -

Originally Posted by CD05001CIA

The question is .... are you loosing spark or fuel on the bank that isn't running.

Although is has been quite some time since I have worked on an M70 engine, I would first check the condition of the donut sensors and that they are installed correctly on plug wires 6 and 12. Measure them with a volt ohm meter for resistance and see that they are within specification.
The fact that you have one bank running will allow you to swap one part pair at a time to find the culprit.

How can you confirm that you have steady spark on plug wire #6 and plug wire #12? Let us know here on the message board.

Each DME will shut down the fuel(by dis-abling the injectors) rather quickly on a per bank basis so as not to wet fuel coat the catalytic converters.

I put a timing light on both banks. Running side (passenger) lights with spark activity. Driver's side (non-running side) shows no spark when engine running.

- - - Updated - - -

Originally Posted by rjjablo

Doughnut Sensors are going bad test, Lift off the throttle and back on it works is the classic symptom

Test the Crank Position Sensors at the same time, just because

Maybe the fuel pump relays. Again pull and test, I had one go bad and hit a bump and half the motor would drop

I put new crank position sensors in, plus the last shop that worked on the car replaced as a precaution as well.
I changed all plug wires and donut sensor with new ones. I'm not opposed to changing again if there is a strong possibility that the problem could be there.

**rjjablo** · 09-14-2021, 05:50 AM

Originally Posted by dz3774000

I put new crank position sensors in, plus the last shop that worked on the car replaced as a precaution as well.
I changed all plug wires and donut sensor with new ones. I'm not opposed to changing again if there is a strong possibility that the problem could be there.

Compare the doughnut sensor from the side that is running to the other side. Look at the orientation. Some are very obvious with tabs that should be pointed to the distributor. Others more subtle.

Did you verify that the Cam Position sensor plug wires are going to 6 and 12 Sparkplug?

**ByMW** · 09-14-2021, 09:45 AM

All I can suggest is to find some old (stock - 1K ohm resistance) spark plugs and try them at #6 and #12. Many of the newer plugs (even if they are specified as proper replacements) have higher resistance and will prevent adequate detection in the cylinder ID sensors. Best wishes!

**dz3774000** · 09-14-2021, 08:15 PM

Originally Posted by ByMW

All I can suggest is to find some old (stock - 1K ohm resistance) spark plugs and try them at #6 and #12. Many of the newer plugs (even if they are specified as proper replacements) have higher resistance and will prevent adequate detection in the cylinder ID sensors. Best wishes!

I would think a timing light would still pulse with bad plugs installed. The lack of light pulse I'm experiencing would seem to indicate no spark being delivered to the plug.

**CD05001CIA** · 09-15-2021, 02:08 AM

Originally Posted by dz3774000

Stomp Test:

2247 Driver Side (LHD)
1222 Passenger Side

I put a timing light on both banks. Running side (passenger) lights with spark activity. Driver's side (non-running side) shows no spark when engine running.

OKAY ... this is BIG! Need to solve spark problem FIRST. Do you have a way to check that the driver's side coil is receiving its 12V operation signal voltage. Is the driver's side coil swollen? Are the driver's side coil 12V terminals corroded?

Is the carbon pin and spring behind it, in the distributor cap in good shape. (You do not need to dis-connect the plug wires from the distributor cap) I remove the cap and plug wires as a sub-assembly.

Sometimes when the distributor cap is removed and set on a work bench at a garage, the carbon pin and spring fall out and nobody notices.

**dz3774000** · 09-16-2021, 10:35 PM

Originally Posted by CD05001CIA

OKAY ... this is BIG! Need to solve spark problem FIRST. Do you have a way to check that the driver's side coil is receiving its 12V operation signal voltage. Is the driver's side coil swollen? Are the driver's side coil 12V terminals corroded?

Is the carbon pin and spring behind it, in the distributor cap in good shape. (You do not need to dis-connect the plug wires from the distributor cap) I remove the cap and plug wires as a sub-assembly.

Sometimes when the distributor cap is removed and set on a work bench at a garage, the carbon pin and spring fall out and nobody notices.

Ok, after about 8 months trying to hunt down the issue, I'm back in business. The car is once again running on all 12. The problem was in the donut sensor plug, mounted behind the oil filler. The male/female plug was not making a great connection.

**CD05001CIA** · 09-16-2021, 11:28 PM

Originally Posted by dz3774000

Ok, after about 8 months trying to hunt down the issue, I'm back in business. The car is once again running on all 12. The problem was in the donut sensor plug, mounted behind the oil filler. The male/female plug was not making a great connection.

Good news. Glad you were able to find the source of the problem.