v8 spark plug leads?
Discussion
chopwood said:
I have an esprit V8-GT and one of the cylinders is not firing, i have replaced the plugs and still nothing. Does any body know how to access and change the leads and ignition coil?? Thanks Dave. (CDH@IC24.net)
Dave,
There are two twin-coil packs located in the "V" between the cylinders, hence they are under the intake plenum. To replace them you must remove the plenum.
Are you certain you are having an ignition problem? Do you have a check engine light?
Regards, KM
2000 V8
Dave,
There are only four drive circuits from the ECM to the two twin-coils. This yields an arrangement where each coil section (of which there are four) are driving two cylinders in parallel. So logically, if you have one cylinder with an ignition problem, you have two by default. The only exception to this would be a bad high-tension lead from one of the coil packs to a particular cylinder's spark plug.
I can only suggest that you carefully check the high-tension leads and ensure that you getting spark to all cylinders. Also check to ensure that you do not have a short on one of the high-tension leads which would effectively ground out the spark to one cylinder. Note: you do not need a full short to affect spark, even a slightly damaged wire could arc to the engine block and short out spark to one cylinder.
Regards, KM
2000 V8
There are only four drive circuits from the ECM to the two twin-coils. This yields an arrangement where each coil section (of which there are four) are driving two cylinders in parallel. So logically, if you have one cylinder with an ignition problem, you have two by default. The only exception to this would be a bad high-tension lead from one of the coil packs to a particular cylinder's spark plug.
I can only suggest that you carefully check the high-tension leads and ensure that you getting spark to all cylinders. Also check to ensure that you do not have a short on one of the high-tension leads which would effectively ground out the spark to one cylinder. Note: you do not need a full short to affect spark, even a slightly damaged wire could arc to the engine block and short out spark to one cylinder.
Regards, KM
2000 V8
Dave,
The schematics only identify the coil packs as 1 and 2... each has 3 leads marked as 1, 2, 3. On coil pack1, lead 2 is common and goes to fuse B5 for +12V. Leads 1 and 3 go to the ECM pins 29 and 49 respectively. On coil pack2, lead 2 is common goes to fuse B5. Leads 1 and 3 go to the ECM pins 32 and 52 respectively.
If you have a logic probe or scope you easily monitor the ouputs of the ECM for coil drive. Also note that with the ignition on but the engine not running, you should be able to measure ~ +12 volts at ECM pins 29,49,32,52 as the voltage will pass thru the coil packs. If you don't have voltage on one of the ECM pins you either have a broken wire or an open coil in one of the packs.
Hope this helps....
Regards, KM
2000 V8
The schematics only identify the coil packs as 1 and 2... each has 3 leads marked as 1, 2, 3. On coil pack1, lead 2 is common and goes to fuse B5 for +12V. Leads 1 and 3 go to the ECM pins 29 and 49 respectively. On coil pack2, lead 2 is common goes to fuse B5. Leads 1 and 3 go to the ECM pins 32 and 52 respectively.
If you have a logic probe or scope you easily monitor the ouputs of the ECM for coil drive. Also note that with the ignition on but the engine not running, you should be able to measure ~ +12 volts at ECM pins 29,49,32,52 as the voltage will pass thru the coil packs. If you don't have voltage on one of the ECM pins you either have a broken wire or an open coil in one of the packs.
Hope this helps....
Regards, KM
2000 V8
Thanks again for your help, it's been priceless! To day with the ignition 'on', i'v confirmed +12v at pins 29, 49, 32, 52. Engine running, equal pulse on all of these pins, however still no spark on 2 cylinders. Primary drive seems to be in order and suggests a secondary coil/lead problem. I would have no hesitation in condeming a faulty coil or lead. However when i originaly removed the plenum to inspect the coil/lead i replaced the plugs and manualy fired the coils (using a conventional 12vpointcapacitor ignition discharge system) and it produced a wacking spark?!? As if this was not bad enough the throttle cable has become disconnected at the peddle end. I'v had my head under the footwell and it looks impossible, any tips? Regards.Dave
Hello Dave,
Good news is you have a solid line from the +12V to both coils... I would probably check to ensure that you have current draw on all four ECM drive lines. These are most likely open-collector drives which simply pull the output pin to ground. As a result, the pulsing will always be there if the line is functioning.
There is the possibility that you have some corrosion or oxidation (creating resistance) on one line which still passes 12V to the ECM, but may not allow any significant current draw when the ECM pin goes to ground which would prevent two cylinders from getting spark.
If you can confirm that you have current flow on all 4 drive lines then you can pretty much count on a bad coil section or bad high-tension line(s). As you are now missing spark on two cylinders I would tend to suspect either a bad drive line (from cause above) or one coil section in the coil pack went out. I would not expect two high-tension lines going out together.
As for the throttle cable, should be pretty apparent. It's a "U-shaped" clevis which is pinned to the pedal. At the bottom of the "U" is a cutout which the end of the throttle cable slips into. There is a ball-type end on the throtttle cable which is hidden inside the "U" when normally viewed. It sounds like yours just slipped out.
Regards, KM
2000 V8
Good news is you have a solid line from the +12V to both coils... I would probably check to ensure that you have current draw on all four ECM drive lines. These are most likely open-collector drives which simply pull the output pin to ground. As a result, the pulsing will always be there if the line is functioning.
There is the possibility that you have some corrosion or oxidation (creating resistance) on one line which still passes 12V to the ECM, but may not allow any significant current draw when the ECM pin goes to ground which would prevent two cylinders from getting spark.
If you can confirm that you have current flow on all 4 drive lines then you can pretty much count on a bad coil section or bad high-tension line(s). As you are now missing spark on two cylinders I would tend to suspect either a bad drive line (from cause above) or one coil section in the coil pack went out. I would not expect two high-tension lines going out together.
As for the throttle cable, should be pretty apparent. It's a "U-shaped" clevis which is pinned to the pedal. At the bottom of the "U" is a cutout which the end of the throttle cable slips into. There is a ball-type end on the throtttle cable which is hidden inside the "U" when normally viewed. It sounds like yours just slipped out.
Regards, KM
2000 V8
Today i have removed 88way plug from ECM, with ignition on. I ran a 55w 12v bulb between each drive and 0v. The current through each drive was a little over 4.2A. I hope you can aggree that this seems to prove L.T wiring to be ok. I think the coil must be faulty in some way. Before i order a new one from lotus do you know if it is a part used on any other car, as the V8's seem to use a lot of G.M parts. In trying to reconnect my throttle cable at the pedle end i found myself upside-down with no room to move, would you recomend removing the stearing wheel? Thanks.Dave
Dave,
yes, I would agree that the wiring and coil pack primaries appear good. So, the only other options are:
- bad high-tension leads or corrosion/oxidation at the connection point
- bad secondary winding on the half of the coil pack
- bad grounding of the secondary winding on half of the coil pack... could also be corrosion/oxidation.
Unfortunately, I do not know if this is a GM part.... I know that Marcus at PUK Racing is breaking up a V8 engine and might still have the coil packs and high-tension leads... maybe worth a shot and give him a call.
As for the throttle cable... just kneel outside the door and reach in... I am able to get to all the pedals and adjustments in this manner. You should not have to remove the steering wheel. BTW - I'm only 5'10" so getting in/out of tight spaces is not a problem... your frame size may differ ;-)
Regards, KM
2000 V8
yes, I would agree that the wiring and coil pack primaries appear good. So, the only other options are:
- bad high-tension leads or corrosion/oxidation at the connection point
- bad secondary winding on the half of the coil pack
- bad grounding of the secondary winding on half of the coil pack... could also be corrosion/oxidation.
Unfortunately, I do not know if this is a GM part.... I know that Marcus at PUK Racing is breaking up a V8 engine and might still have the coil packs and high-tension leads... maybe worth a shot and give him a call.
As for the throttle cable... just kneel outside the door and reach in... I am able to get to all the pedals and adjustments in this manner. You should not have to remove the steering wheel. BTW - I'm only 5'10" so getting in/out of tight spaces is not a problem... your frame size may differ ;-)
Regards, KM
2000 V8
Thanks a million for all your help KM!!!!!
I have fitted a new coil pack at the weekend and all is well again with my v8. i'm not sure how the old coil has failed as it is neither open circuit or short circuit and being potted should not suffer from moisture. (being bosh it is probably just another unreliable german car component). Lotus wanted £100+vat for a coil, however i have obtained mine through a lucas agent, which managed to cross-refferance it to a part number DMB410 (vauxhall). The coil pack is about £70 total, so it may be worth adding to this site's parts list. Thanks once again KM. & thanks for the offers from people to buy a coil, i ordered a new one before checking messages. Dave
I have fitted a new coil pack at the weekend and all is well again with my v8. i'm not sure how the old coil has failed as it is neither open circuit or short circuit and being potted should not suffer from moisture. (being bosh it is probably just another unreliable german car component). Lotus wanted £100+vat for a coil, however i have obtained mine through a lucas agent, which managed to cross-refferance it to a part number DMB410 (vauxhall). The coil pack is about £70 total, so it may be worth adding to this site's parts list. Thanks once again KM. & thanks for the offers from people to buy a coil, i ordered a new one before checking messages. Dave
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