Chrysler Newport 1975 360 - 2 barrel - misfire? running problems

[Johny]

Last year I have bought Chrysler Newport from 1975. Car was starting up but have problem with running. Car was a barn find. Somebody put new Alternator, regulator, NGK Platinum sparks, new mechanical fuel pump. The seller failed to solve the problem and sold the car .
In winter time I made:
- new oil Millers Classic 10w30 with oil filter
- new cooper champion spark plugs rn12yc
- new air filter, Bosch fuel filter
- rebuild carb Holley 2245 - float level about 3/16"
- new choke spring, new electric choke controller
- new ignition distributor because old had problem with a shaft, new NGK wires
Refreshed lot of staff, new gaskets etc .

Car starts cold /hot good. Every 15-30 seconds I have some misfire? It is on cold/hot/idle/while accelerate. Always. What I have checked:
- charging measured on the battery cold: 14.5V, hot up to 15.0V
- ballast resistor cold: upper pins 1.2 Ohm for ignition, lower pins 5,1 Ohm. After few miles ballast resistor is really hot 212F. Voltage before ballast resistor (hot) 14.2v , ignition coil: 8,0V.
- ignition coil cold 1.6 ohm. I have checked cable positive goes to +, negative to - .
- I have add additional ground wire to ignition Control module (5 pin ICM)
- initial timing 6 degrees before tdc - idle 850 RPM.
- vacum 18.5
- spark plugs a little bit lean?
- checked air leaks with a spray - no air leaks -PCV Valve is open when there is vacum, no vacum closed.
I made a video, on 8 seconds there is my problem. Sorry for my english.
Have a nice Sinsay
Johny

 

[66fs]

Check compression on all cylinders, get richer jets for the carb.

 

[George Jets]

Yep, everything except a compression test.

Cylinder #6 on those 360s are known to burn exhaust valves... sunken valves.

☆☆☆☆☆

 

[Dana67Dart]

Hi Johnny,

Welcome to FABO.

I sure wish everyone would start a thread with this much information.

THANK YOU!

And your English is better then many Americans on FABO!

I have a few questions

1. Is the air-conditioning running while it seems to misfire?
2. Does the time between misfires happen sooner as the rpm increases.
3. There are most likely smog control electronics on the engine some of them could be failing.
4. Would you post a close up and clear photo of the ballast resister and see if you can determine where the wires are going
5. Did you double check the firing order?
6. Mymopar.com has wiring diagram and factory service manuals. Might not have your year or car but they are a great resource, a 73 book might be close enough.
7. Classiccarwiring.com sells fully color coded laminated wiring diagrams
8. There is a ForCBodiesOnly.com site many members there are also on here but the site might have some more specific info
9. Google "Chrysler master tech video" + a topic like " ignition" there are many of these videos that explain how many systems work. They are a bit old school but really good.

Thoughts...

1. I would do a compression check but the misfire seems too slow to be a cylinder issue
2. At 800 rpm the same cylinder fires about every 0.15 seconds, the misfire seems to be happening at 10+ second intervals
3. Most of the electronic smog control devices can be disabled or bypassed for testing
4. Remove the gas cap and see if the misfire goes away
5. The car may still have vapor recovery and other smog related lines and devices.
6. With a timing light put it on each cylinder and look for the light to not flash at the same time as the misfire happens. If it happens regardless of the cylinder it's on its most likely electronic, of it happens on just one cylinder then there might be something the look at there.
7. If you have access to an old school engine analyzer oscilloscope that might help rule out things.
8. If you short one cyl at a time, grounded paperclip on a screwdriver between the dist cap boots and the plug wires, the engine rpm should drop an the engine run a bit rough. If all cylinders do the same, it's probably not a single cylinder

What I suspect....

1. If you had a bad cylinder the engine would be running rough and smooth out as rpm increases
2. If it was a vacuum leak the same would happen
3. If it was a fuel delivery issue then it would misfire more as the rpm increases (fuel starvation)
4. To me it feels electronic not mechanical

Good luck to you.

Let us know.

Also watch out for rabbit holes. The cause of the problem is probably less complicated or involved then an engine rebuild.

 

[MOPAROFFICIAL]

Ignition box or a misfire from a cheapo plug wire.

 

[Johny]

Carb:

When I opened my carb to rebuild fuel float was about 1/8 ". First I leave it. After turning on the engine was going to reach, more misfire, smells unburn fuel from exhaust and smoke white.

New electronic distributor set gap 0,008"

Aircondition is off, lights off.
Misfire intervals is 10s, sometimes 30s, cold engine, hot engine. Sometimes there is no during agressive kickdown.
During drive engine sometime dies ( usually low engine speed) . But it starts easy without pumping accelerator.
Fuel is fresh, unleaded , the higher premium.
I have driven today 70 miles. Nothinkg broke. Misfires are as they were without any changes.
Oil clean, engine coolant clean, thermostat new 180F, not overheating, heat inside works.
Ignition box looks fresh. I will check spark wires and make compresssion test.
Charging is to high up to 15v on battery. When there is misfire the voltage drop down for half a second to 12,5V. It looks like something turns off ignition for half second.


Johny

 

[Dana67Dart]

Charging is to high up to 15v on battery. When there is misfire the voltage drop down for half a second to 12,5V. It looks like something turns off ignition for half second

If you can get a analog volt meter (needle) it will show more than a digital will.


But the voltage drop could be from RPM drop or a momentary ignition drop out.

Does it still happen at 1500 to 2000 rpm?

Keep at it.

That the engine sometimes dies at low idle but restarts easily, still feels electronic.

You mentioned the dist was replaced due to a shaft issue. What was the issue?

 

[Johny]

There was a problem with a gap beetween distributor reluctor/sensor. On 5 cylinders gap was ok, other 3 cylinders no-gap and terrible misfires.

During ride misfires are all rmp. Maybe less higher rmp.

I will check also with analog volt meter. Maybe something cut ignition because of to high charging.

 

[Dana67Dart]

I will check also with analog volt meter. Maybe something cut ignition because of to high charging

I don't think your charging voltage is excessive.

 

[Mattax]

The low voltage may be related to the misfire.
Or it may be the result of the engine faltering and the alternator not producing when the engine rpm drops.

A 1975 C-body is very unlikely to be wired the same as a '73, but some general concepts will be the same.
When you voltmeter goes to 12.5, does the ammeter swing to Discharge ?
This would confirm the 12.5 Volts represents the battery powering the car.

Typically the alternator's rotor gets power from the 'ignition run' circuit.
So this misfiring could be an interuption in the ignition circuit. A loose wire or bad connection in that circuit is a possibility. (If the ammeter swings hard to discharge, then its shorting)

 

[Mattax]

Charging is to high up to 15v on battery.

may be a bad connection.
Measure the voltage at the battery, then at the alternator output (Bat terminal), and then at any location(s) you can backprobe in the ignition circuit. Ignition run is almost always dark blue and dark blue with white stripe insulation. Ballast resistor is a convenient location to backprobe.

 

[Bewy]

Post #8. If the reluctor touches the p/up coil, you will get a 'no-spark', a misfire. If some reluctor teeth were touching, but not all of them, that sounds like an out-of-round reluctor, or worn/bent shaft. Make sure the plate the p/up sits has no wear that could change the air gap.
Also, after high mileage, the p/up wires can break if it has vacuum advance, because the vac adv flexes the wires. Check with ohm meter while flexing the wires, should be 120-600 ohms.

If all checks out, I would suspect corrosion in electrical plugs/sockets...or a bad ECU...because of the random nature of the problem.

 

[RustyRatRod]

Raise the hood when it's dark out and start the engine and look for plug wires arcing. Usually a misfire as you describe is secondary ignition. That's easy and free to do and after that, you should run a compression test.

 

[Dana67Dart]

Keep in mind it's not a single cylinder misfire that would be happening every tenth of a second or so. It's a 10 to 30 second misfire.

My dart actually does a similure thing. And you can see the charging ammeter drop at the same moment. That was with a point ignition both dual point and single point. I have Mopar electronic now and don't recall if it still does it.

 

[Johny]

I have found.... cylinder 6 compression.

1. Spark cables are in good condition
2. Alternator:
Bat + 15.3V , Battery Terminals 15,1V
Purple wire: 14.7V
Green wire 9V
3. Distributor ressistance 413 OHM ( engine hot)
4. Voltage from ICM to distributor 0,540v ( ignition on, engine off )
5. Spark cables tested, seems good.

 

[66fs]

Probably a burnt exhaust valve.

 

[CRUZE 418]

There may be another issue waiting in the wings on a car that old, unless it has been overhauled. Nylon timing gear. When I pulled my '78 van 360 apart for overhaul, the timing set , nylon gear, was just ready to shed its teeth. Put a double roller timing set back in it.

 

[Mattax]

I have found.... cylinder 6 compression.

1. Spark cables are in good condition
2. Alternator:
Bat + 15.3V , Battery Terminals 15,1V
Purple wire: 14.7V
Green wire 9V
3. Distributor ressistance 413 OHM ( engine hot)
4. Voltage from ICM to distributor 0,540v ( ignition on, engine off )
5. Spark cables tested, seems good.

I agree. #6 is bad.

AlternatorBat to Battery positive 15.3 to 15.1 Volts = 0.2 Volts drop.
Whether this is good or bad depends on how much current was flowing.

Purple Wire: Show us photo of the wire and where you measured it. I *think* this is the field's feed based on a non-factory diagram.
Green Wire: This is the return from the alternator's rotor. Voltage is always lower after going through a motor or lamp.

14.7 V is the voltage the regulator is seeing. So 0.6 Volts is lost between the alt and the reg.

Distributor resistance. I don't understand this measurement. Resistance should never be measured on a live circuit.

 

[George Jets]

Folks may wonder, how did a person know that it was going to be cylinder #6 the bad cylinder... before the compression test was done?

See post #3 above...

Burnt Exhaust Valve


☆☆☆☆☆

 

[Mattax]

14.7 V is the voltage the regulator is seeing. So 0.6 Volts is lost between the alt and the reg.

IF this diagram is correct, your Newport has a relay for the ignition circuit.
With that, the voltage drop should be very small.
Look at the connections of this relay.

@72RoadRunnerGTX likely knows more about the wiring on your car

 

[Johny]

I made measurment on alternator:
Bat + 15.3V
Purple wire: 14.7V
Green wire 9V

Today I have started with engine. Heads off. Factory head gaskets. On 6 cylinder I made tightness test using fuel with oil. I have a terrible leak on intake valve. Exhaust valve it's supposed to be tight but has big clearance between valve steam/ valve guide and during work it can "cross" loosing tightness.

Cylinder wall looks the best on #6 cylinder.

I have decide to rebuild both heads.

 

[Illahe]

The low voltage may be related to the misfire.
Or it may be the result of the engine faltering and the alternator not producing when the engine rpm drops.

A 1975 C-body is very unlikely to be wired the same as a '73, but some general concepts will be the same.
When you voltmeter goes to 12.5, does the ammeter swing to Discharge ?
This would confirm the 12.5 Volts represents the battery powering the car.

Typically the alternator's rotor gets power from the 'ignition run' circuit.
So this misfiring could be an interuption in the ignition circuit. A loose wire or bad connection in that circuit is a possibility. (If the ammeter swings hard to discharge, then its shorting)

My .02: Bulkhead may be giving you an issue. Run a FUSED wire from the alternator output to the + battery and see if the intermittent miss goes away.

 

[Dana67Dart]

Bat + 15.3V
Purple wire: 14.7V
Green wire 9V

I assume you have a square back isolated ground alternator.

The green wire from the voltage regulator should have lower voltage on it than the purple (blue in A-body world) which should be about battery voltage.

The green wire is a variable ground and depending on the needed charging level will be lower or higher than 9v

So the green wire IMHO is ok. The voltage drop between battery and purple is concerning, 0.6v is a bit much.

Bulkhead connections, ignition switch, ignition switch connector, connector on the VR are all points of bad connection

 

[66fs]

I made measurment on alternator:
Bat + 15.3V
Purple wire: 14.7V
Green wire 9V

Today I have started with engine. Heads off. Factory head gaskets. On 6 cylinder I made tightness test using fuel with oil. I have a terrible leak on intake valve. Exhaust valve it's supposed to be tight but has big clearance between valve steam/ valve guide and during work it can "cross" loosing tightness.

Cylinder wall looks the best on #6 cylinder.

I have decide to rebuild both heads.

Get 8 stainless steel exhaust valves.

 

[CRUZE 418]

My opinion, time for an overhaul. Set of good heads on tired engine.