Distributer air gap - Defender Source
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  #1  
Old December 13th, 2006, 02:43 PM
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Scott Yates
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Distributer air gap

Hopefully an easy question. What is the air gap in the distributer supposed to be? I found several references to it on the forums but not the actual value. Still trying to figure out my issue, lol.

Thanks
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  #2  
Old December 13th, 2006, 11:54 PM
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On a related note, if I went with the switch to the Mallory what components do I need? I am trying to weigh the cost vs. the ignition relocation kit as mine has never had it done. I am trying to figure out the poor performance, inconsistent idle, and inability to exceed 3200 rpms. I am thinking either the ignition module or ecm at this point. I am about to give up and just start replacing crap in the hopes of fixing the problem. Wife is already annoyed lol.
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  #3  
Old December 14th, 2006, 01:23 PM
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Jim Ngo
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First check the vacuum advance on the distributor. It may be stuck or not moving as easily as it should.

Myself, I first went with the relocation kit and then decided to spring for the Mallory since the vacuum advance on my old distributor wasn't working well, plus the cap & rotor were 100,000 miles old. So it made sense for me since the cost was incremental. I bought the Mallory without the gear, which requires you to reuse the gear from the old dist. You have to drill a hole for the roll pin in the new dist shaft, which isn't too hard to do (just slip the gear on the shaft, set the gap w/ a feeler, then use the hole in the gear as a drill guide). My truck runs strong now, way past 3200 rpms.

The relocation kit is also easy to install and, BTW, mine is for sale in the parts-for-sale section.

As for the air gap, perhaps you should just set it as close as possible without the parts touching. I can get you the actual air gap spec after I get home from work.
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  #4  
Old December 14th, 2006, 05:01 PM
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Scott Yates
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Thanks Jim for the response. I am think the vacuum advance on mine is much much to hard to move as well. Can you provide any guidence on the Mallory? What I ask for etc. Do I still need an ignition module with it or do they have a better one? Did you also have the high rpm power loss prior to switching to the Mallory? Was it a straight forward install or a pita?

Thanks.
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  #5  
Old December 14th, 2006, 05:41 PM
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Jim Ngo
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The Mallory dist comes complete with its own internal ignition amplifier and cap and rotor. Installation is fairly straightforward swap. Before you remove the old distributor, just make sure that you first turn the crank so that the rotor points to the #1 lead and the timing mark is lined up to TDC. That'll make the static timing setup of the new distributor much easier.

For me, I was trying to fix two problems: a sudden power-loss & failure to idle. The distributor was one of a few things I replaced, (along with relays). I also reset the base idle (previously it wouldn't even run at all if the idle air bypass was plugged). Unlike you, I could get above 3200 RPMs before, but the truck runs a little stronger now.
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Old December 14th, 2006, 05:47 PM
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Great. Now which distributer do I ask for? Is it this one? Any other parts required for the swap?

BTW, Jim, you are bomb!
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  #7  
Old December 14th, 2006, 10:42 PM
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My box says 4768901, which is this one. I didn't need anything else.
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  #8  
Old December 15th, 2006, 02:46 PM
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Per Land Rover D90 work shop Manual airgap for pickup in the distributor is .11-.13"

PICK-UP AIR GAP ADJUSTMENT
20. The air gap between the pick-up limb and
reluctor teeth must be set within the specified
limits, using a non-ferrous feeler gauge.
21. If adjustment is necessary, slacken the two
barrel nuts to set the air gap. See Engine
Tuning Data.
NOTE: When the original pick-up and base plate
assembly has been refitted the air gap should be
checked, and adjusted if necessary.
When renewing the assembly the air gap will
require adjusting to within the specified limits.

Follow-up Post:

Here is some more information on the electrical side of diagnosing your issue

Some has referenced the airgap to about the size of a matchbook cover. It is also a good tool if you don't have brass or plastic feeler guages to check it with. It is set from factory and doesn't change so it shouldn't need adjusting.

More info than you prolly want :D

ELECTRONIC IGNITION - PRELIMINARY CHECKS EXPECTED READINGS
Inspect battery cables and connections to ensure
they are clean and tight. Check battery state of
charge if in doubt as to its condition.
Inspect all LT connections to ensure that they are
clean and tight. Check the HT leads are correctly
positioned and not shorting to earth against any
engine components. The wiring harness and
individual cables should be firmly fastened to prevent
chafing.
V1. More than 11.5 volts
V2. 1 volt max below volts at point 1 in test circuit
V3. 1 volt max below volts at point 1 in test circuit
V4. 0 volt 0.1 volt
PICK-UP AIR GAP
Check air gap with a non-ferrous feeler gauge.
NOTE: The gap is set initially at the factory and
will only require adjusting if tampered with or
when the pick-up module is replaced.
TEST 1:
Check HT Sparking
Remove coil/distributor HT lead from distributor cover
and hold approximately 6 mm from the engine block.
Switch the ignition 'on' and operate the starter.
If regular sparking occurs, proceed to Test 6. If no
sparking proceed to Test 2.
(c) If all readings are correct proceed to Test 3.
(d) Check incorrect reading(s) with chart to
identify area of possible faults, i.e. faults listed
under heading 'Suspect'.
(e) If coil or amplifier is suspected, disconnect LT
lead at coil, repeat V3. If voltage is still
incorrect, fit new coil. If voltage is now correct,
check LT lead, if satisfactory fit new amplifier.
(f) If engine will not start proceed to Test 3.
KEY
OK Expected Voltage.
H Voltage higher than expected.
L Voltage lower than expected.
TEST 3:
Check Amplifier Switching
Connect the voltmeter between battery positive (-ve)
terminal and HT coil negative (- ve) terminal: the
voltmeter should register zero volts.
Switch the ignition 'on' and crank the engine. The
voltmeter reading should increase just above zero, in
which case proceed with Test 5.
TEST 2:
L.T. Voltage
Switch the ignition 'ON'
(a) Connect voltmeter to points in the circuit
indicated by the arrow heads and make a
note of the voltage readings.
(b) Compare voltages obtained with the specified
values listed below:
6 REISSUED: FEB 1993
ELECTRICAL EQUIPMENT
If there is no increase in voltage during cranking
proceed to Test 4.
TEST 5:
Coil HT Sparking
Remove existing coil/distributor HT lead and fit test
HT lead to coil tower. Using suitable insulated pliers,
hold free end about 6 mm from the engine block and
crank the engine. There should be a good HT spark.
If weak or no sparking, fit new coil, repeat test.
HT sparking good, repeat test with original HT lead.
If sparking is good, carry out Test 6.
If weak or no sparking, fit new HT lead, if engine will
not start carry out Test 6
TEST 4:
Pick-Up Coil Resistance.
Disconnect the pick-up leads at the harness
connector. Connect the ohmmeter leads to the two
pick-up leads in the plug.
The ohmmeter should register between 2k and 5k
ohms if pick-up is satisfactory. If the ohmmeter
reading is correct, check all connections between
pick-up and amplifier, if satisfactory, fit new amplifier.
If the engine still does not start carry out Test 5.
Change the pick-up if ohmmeter reading is incorrect.
If the engine still does not start proceed to Test 5.
TEST 6:
Rotor Arm
Remove distributor cover. Disconnect coil HT lead
from cover and using insulated pliers, hold about 3
mm above rotor arm electrode and crank the engine.
There should be no HT sparking between rotor and
HT lead. If satisfactory carry out Test 7.
If HT sparking occurs, an earth fault on the rotor arm
is indicated. Fit new rotor arm.
If engine will not start carry out Test 7.
REISSUED: FEB 1993 7
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