Hi guys. My magna TE v6 is misfiring under load. It happens after the engine warms up. When engine is cool, there is no problem. After the engine warms up decently, lets say running for 30 mins or so, the problem is noticed. If I put the gear to neutral or P, the problem is not there. If I stop at a signal with the shift left on "D", the misfire can be felt. It gets worse with time if I continue to drive. Once the engine is hot, if I try to drive very slow, for example trying to reverse slowly, I can feel the misfire every few seconds. during normal driving I cant feel it.

as a history, the problem had started in a terrible magnitude when I got my heater core fixed from a new mechanic. I believe the distributor cap was faulty and hence it was replaced. This reduced the problem greatly but the problem did not go away. I took it back to my regular mechanic who tuned the engine and cleaned the throttle body. The problem went away during idling but in a day or two I realised that it is happening under load. They have now increased the idle speed. Checked the front bank of spark plugs without any problem.

I am obviously reluctant to go over the rear plugs as it is a big job. They were all replaced less than 12 months back.

Any suggestions?

Ignition coil.

Ignition coil.

Thanks madmax. The thought comes to me that there might have been some spillage of coolant onto the dizzy when the heater core had leaked. while the dizzy cap was replaced, it might have been better idea to change the dizzy at that time. Iis there a way to check if the problem is coming from the distributor, without taking it off?

Check the leads from the dizzy side, or could be oil in the plug chambers..?

Check the ignition coil. Also check leads, plugs and distributor for condition.

Ignition coil check:
http://i881.photobucket.com/albums/ac19/rons105/dist1.jpg

Other checks:
http://i881.photobucket.com/albums/ac19/rons105/dist2.jpg

Coil price:
http://www.ebay.com.au/itm/310157964614?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Coil or transistor. The transistor is my best bet but often the simple digital multimeter check won't pick up problems in partially failed components. Note that in the photocopies above the transistor is checked with an analogue meter and they can find partial failures. Instead of the needle being fully to one side it will have a reading of some amount. Also, its best you do the check when the transistor is hot so as to reproduce the same conditions. You can also heat it up in an oven.

Coil or transistor. The transistor is my best bet but often the simple digital multimeter check won't pick up problems in partially failed components. Note that in the photocopies above the transistor is checked with an analogue meter and they can find partial failures. Instead of the needle being fully to one side it will have a reading of some amount. Also, its best you do the check when the transistor is hot so as to reproduce the same conditions. You can also heat it up in an oven.

Yes, low voltage testing at room temperature of a power transistor and ignition coil may not pick up component breakdown that occurs at high voltage and temperature, but it is a start.

You would carry a dist in the boot just in case, wow, not extreme in the least

The dist is what is usually causes this issue in the OP, is not that common but does happen, more when oil leaks have caused oil to soak the internals of the dist. The coil and transistor are the usual suspects, generally I charge $85 for a complete dist and most wreckers will be on the same mark

Thanks a lot to all of you guys for the inputs. As madmagna said, the cost of a used dist seems to be under $100. It is probably best bet to replace the distributor rather than trying to replace components. I already replaced the distributor cap recently when the problem started. Replacing bits at a time may add up to much more.

As madmagna said, atleast in my case there is a good chance of oil seepage inside the dist. I have had repeated oil leaks around that area for many years, which has been finally fixed only last year.

Will let you know how it goes.
cheers

Did this model have plug leads? My TR had this problem, proved to be the leads. Replaced them and good as new.

Replaced all leads 12 mnths back alongwith the plugs. Still checked all leads and the front plugs again.

Could not get time over the weekend. Planning to look at the distributor tomorrow. Will keep updated.

What leads did you use? I had a new set of Bosch leads and they turned out to be crap. It took ages to finally isolate the cause of misfires and poor fuel consumption. I now have Eagle leads and they have not misfired once. Once, I used Topgun leads on my Pajero and they caused massive backfires and all sorts of problems. The only leads I will use are NGK or Eagle now.

To check the leads, get your car into totally dark position, lift the hood and give the engine a rev. If you see any form of discharge it is time to replace the leads. With the Topgun leads, I could see the spark going down the inside of the leads, occasionally jumping ot earth as well. The Bosch leads were jumping to earth on 2 leads only. The NGK and Eagle leads - I can see NOTHING.

Have not been getting the time to get at the distributor. Checking the leads in dark sounds simpler. Will try that this evening.
The leads I used - NGK

By the way, how risky is it to drive the car in current condition? Can I end up damaging something more?

Checked the leads last evening. They all look good. I could not see any sparks.

can anybody comment whether driving the car in the current condition can cause any further damage?

Okay. This is an update for anybody checking the thread in future.
while I would have liked to replace the dizzy, could not get a reliable used one.

Finally the problem was the rotor switch and the ignition coil. I guess the bad rotor spoilt the coil over time. replaced both. Its all good now.
Thanks to all for the inputs.