Posted: Sun Jul 06, 2014 12:48 pm Post subject: HELP M38A1 ignition timing Problem I think
Hi all
I have a M38A1 jeep in the UK, after a year of ownership and very little use, it has started to run rough. I recently replaced the exhaust manifold with a brand new one and new gaskets etc, the rest of the exhaust system was only a year old and has only done about 20 miles !
I thought the rough running was due to old gaskets on the manifold but it still was rough, so I then replaced the coil, distributor cap, rotor arm, CB points, both condensers. The plugs were only a year old and are in good condition. So I cleaned and gapped them. With all this done I reset the ignition timing manually (finger over number 1 plug hole and turning flywheel until mark on pulley line up with the 5 degrees before TDC mark on tab, then slackened distributor and with ignition on turned it anticlockwise until points closed then slowly clockwise until spark was seen , then locked it in place.
When you listen to engine running with head under hood it sounds lovely ticks over with no abnormal noises, the engine starts easily and will idle nicely. But when you apply pressure on the gas pedal you can feel it running lumpy and the exhaust sounds loud and rough like an ancient tractor.
I tried also removing the complete exhaust system off and checked it and there are no holes, and I put new gaskets on the joints.
I am beginning to wonder if the internal baffles in the muffler have failed (can they fail?) as mentioned before I put this exhaust on when I bought the jeep and it's only done about 20 miles and is kept in a dry garage.
I have swapped old plug leads for new ones too , and now just don't know what to try next, does anyone know if perhaps the timing should be done professionally with a strobe? Would this help? I don't have a strobe but can easily buy one and try this.
I even took off the rear bumperette above the exhaust exit in case that was interfering with the flow of air but still the noise remained.
One thing I am unsure about too, is the vacuum pipe from the distributor around the engine and offshoot to wipers,does this make any difference, can they cause a problem?
If I set the engine 5 degrees before TDC on the exhaust stroke in error I guess the engine wouldn't fire and tick over nicely so I assume I did that correctly?
HELP?????
Any advice gratefully received.
Thanks Mark
I have read here that you did a lot of parts replacing but virtually no troubleshooting.
1-What are the cylinder compressions.
2-Where is the timing really at? Get a timing light and confirm it.
3-Is the exhaust system clear of any blockage? Especially broken baffles in the muffler.
4-Is fuel pump delivery pressure correct?
5-Is float height correct?
6-Is the fuel tank vent system clear/un-obstructed?
7-Does the accelerator pump system work correctly?
That tube running from the wiper "T" to the distributor has no affect on timing. Suction in a limited amount (restrictor in the leg of the "T" that goes to that line) is applied to the distributor housing so that air from the air cleaner via the crossover pipe and the short tube to the other side of the distributor housing is sucked through the distributor housing evacuating any residual ionized gasses from the electrical arcing that occurs there. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Posted: Wed Jul 09, 2014 2:11 pm Post subject: thanks - still needing advice ….
Hi Wes, thanks for your advice, with my limited technical knowledge and even more limited technical facilities - I have now set the timing with a strobe and its bang on. It hasn't cured the problem.
I have checked the exhaust and no blockages - the silencer makes no rattly noise to indicate broken baffles when I shake it so I don't think it is broken - but I guess it may be …..would make a noise when I shake it?
I can't check cylinder compressions …..
Fuel pump is working fine - supply to the carb is good - when i disconnect pipe and turn engine on it flows out fast.
Float height was way out - I have re-set this
There is no vent on my fuel tank
With ref to the carb - here I need your advice please
I have overhauled carb as mentioned before - and I was very careful to take 1 bit off at a time so I am pretty sure it all went back together correctly.
The carb is a Carter YS (I have it here on my kitchen table again !) it has 1-897 stamped on the bottom section too.
I am wondering if I have made a mistake - with reference to the metering rod. I set up the assembly and need to check that its all in the right order.
In order of reassembly I have going in first -
The metering rod seat….screwed in until tight …… then
the rod which is held into the diaphragm with a small pin then ..
on the other side of the diaphragm there is a cup type thing with a spring which fits in - and finally the outer cover/plate screws on with 4 screws.
Is this OK - do I have to adjust in any way?
When you overhaul a carb - am I right in thinking its the float level that needs adjusting? Assume everything else just gets screwed together tightly ?
Please excuse my ignorance - this is my first Jeep after 20 odd years of taking Land Rovers apart…(it may be my last too I think!!)
Accelerator pump system - i am assuming that this is the diaphragm and spring opposite the casing to the metering rod? Again all spares are new - I have the shorter of the 2 springs in the accelerator pump - the longer one in the metering rod. Is this right - or should I swap them ?
Part of me thinks it is the silencer on the exhaust …I may order a new one
I have checked the exhaust and no blockages - the silencer makes no rattly noise to indicate broken baffles when I shake it so I don't think it is broken - but I guess it may be …..would make a noise when I shake it?
Exhaust restrictions are not always loose pieces of rattling metal. Disconnect the muffler and run the engine.
I can't check cylinder compressions …..
Actually you can. Leave all the plugs in and while maintaining pressure on the generator belt/belts turn the engine over by hand. You should have four equally resistive compression strokes.
Fuel pump is working fine - supply to the carb is good - when i disconnect pipe and turn engine on it flows out fast.
Float height was way out - I have re-set this
There is no vent on my fuel tank
If there is no vent in your tank then you have found your problem. Stock tanks came with a vent. Several types of gas caps (vented & Non-vented) are out there. If you have an aftermarket tank with no vent and a cap with no vent then shortly after starting your engine it will die.
With ref to the carb - here I need your advice please
I have overhauled carb as mentioned before - and I was very careful to take 1 bit off at a time so I am pretty sure it all went back together correctly.
The carb is a Carter YS (I have it here on my kitchen table again !) it has 1-897 stamped on the bottom section too.
I am wondering if I have made a mistake - with reference to the metering rod. I set up the assembly and need to check that its all in the right order.
In order of reassembly I have going in first -
The metering rod seat….screwed in until tight …… then
the rod which is held into the diaphragm with a small pin then ..
on the other side of the diaphragm there is a cup type thing with a spring which fits in - and finally the outer cover/plate screws on with 4 screws.
Is this OK - do I have to adjust in any way?
When you overhaul a carb - am I right in thinking its the float level that needs adjusting? Assume everything else just gets screwed together tightly ?
Please excuse my ignorance - this is my first Jeep after 20 odd years of taking Land Rovers apart…(it may be my last too I think!!)
Accelerator pump system - i am assuming that this is the diaphragm and spring opposite the casing to the metering rod? Again all spares are new - I have the shorter of the 2 springs in the accelerator pump - the longer one in the metering rod. Is this right - or should I swap them ?
Your carb comments lead me to believe you have rebuilt it without using any manual. The applicable portions of the Carter carb military manual TM 9-1826A are in out downloads section. Be sure to use the correct illustration. The original TM 9-1826A Carter YS illustration had the spring on the wrong side of the diaphragm.
I have a question also i about a timing light adapter it is used to go between the spark plug and the ignition wire so that you may attach a timing light for checking the timing. Is it needed? _________________ Mike ake Tigger
If you wish to use a timing light then you must have a way to attach it to #1 wire. Your choices are: leave the wire stock and buy the adapter, get a used wire and cut a section of the shielding out, or temporarily intsall a civilian wire & plug. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Hi Wes, apologies for delay in replying. Still have same problem where engine idles fine sounds good under bonnet and rough at exhaust. Manifold is new, I even tried a new silencer but no difference. When accelerating engine backfires through exhaust / breaks down under load, sounds like hole in exhaust but there isn't one. Carb has been stripped twice now and float adjusted, if I had not already replaced coil, points , dist cap, rotor arm and plugs I would say it was an ignition system issue. Both condensers are new and coil is one of the shiny foreign (non USA) types, I know they have a poor reputation but it's brand new. At a complete loss now.....could it be valves needing adjusting in the engine? Is it ok to permanently remove the condenser in the small square box on front of the distributor? The fuel cap vent is set to open and fuel tank vent line goes to the air filter housing and they all look clear. Regards Mark
Just a thought. Although I set the timing with a strobe light do I need to set the dwell angle as well. If this is incorrect could it cause the problems I am having. Could someone explain how to do this with the military 24v system. I don't have a military testing meter just a standard 12v auto one.
Thanks again
Mark
Dwell is the time in degrees that the points remain open. It is determined by the setting of the gap. If you set your gap correctly then checking dwell is not necessary. The use of a dwell meter allows the mechanic to quickly and easily check for improper point gap. Except for the old externally adjustable GM distributors if the dwell was too long or too short you have to open the distributor and mechanically adjust the gap.
It may be time to seek a technically competent and properly equipped technician's help. Without performing the basic set of diagnostics and without an experienced ear under the hood you could end up spending hundreds of dollars and still not solve the issue. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
I've just taken off the rocker cover and had the engine running at the same time. Viewing the engine from the exhaust manifold side, push-rods 1, 3 and 4 seem to be operating in the same manor; not only moving up and down, but spinning as they do so.
Push-Rod No.2 is not spinning and to my eye looks to be moving slower (Is this possible?).
Also, with the rocker cover off and when pressing the accelerator with the car in neutral, the raspiness of the exhaust which you could feel through the accelerator peddle seems much reduced.
I probably will end up sending it off to a Garage, in due course, but have you ever come across anything like this before?
Sticking valves, burnt valves and leaking valves are found by doing a compression check. This is a very simple procedure and in view of what you have attempted so far it should be an easy task for you to master.
It is possible that the one intake pushrod you mention being slower in it's movement may be caused by a sticking valve or a rocker that is adjusted too tightly which would not allow that intake valve to close completely.
Removing the head to investigate this properly is probably more then you wish to tackle but I cannot over emphasize the importance of a simple compression test which would reveal and/or confirm this type issue. And a simple leak down test would pinpoint the issue.
Instructions for 80520 Leakdown Tester
1. Run the engine until it is thoroughly warmed up.
2. Remove all of the spark plugs.
3. Rotate the crankshaft until the piston of the cylinder to be tested is at top dead center on the
compression stroke.
4. Install the adapter hose into the spark plug hole.
5. Connect hose to leakdown tester.
6. Connect leakdown tester to a good source of high pressure compressed air (preferably filtered and
water trap-equipped; preferably not oiled).
7. Adjust regulator knob until the left hand gauge indicates at least 10 lbs less pressure than the source
pressure.
8. Read right gauge, subtract it from the left gauge, then look up the difference in the conversion table
below to get the leakdown percentage. We have included tables for 75, 90 and 100lb left gauge
settings.
9. If you get an unrealistically low reading, there may be an obstruction in the small orifice in the coupler
between the gauges. Take the tester apart and remove the obstruction.
Updated 04/30/04
Conversion from gauge difference to percentage of leakage
Left 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Gage
Reads
100# 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85
90# 89 88.2 87.3 86.4 85.5 84.6 83.7 82.8 81.9 81 80.1 79.2 78.2 77.4 76.5
75# 74.2 73.5 72.7 72 71.2 70.5 69.7 69 68.2 67.5 66.7 66 65.2 64.5 63.7
By listening for escaping air at the intake system, exhaust system, radiator and crankcase breather,
the possible sources of a high leakdown rate can be determined.
Crankcase breather ........Defective rings or worn cylinder walls
Exhaust system...............Defective exhaust or valve seat
Intake system..................Defective intake valve or seat
Radiator...........................Leaking head gasket or cracked head/bloc
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