I have a problem with my TJ AWD that's got me puzzled. Normally, there is no hint of hesitation when accelerating, especially from a standing start. However, if it's been pushed a bit hard, say up a good mountain climb, with lots of alternate acceleration and backing off around corners, the engine can suddenly fail to deliver when the accelerator is pushed past a certain point. It's as if a rev limiter has cut in far too soon, or the ignition is not firing properly.

Has any other AMC member had this problem with their 3rd Gen Magna, and if so, what was the cause? The most alarming thing about it is not having confidence when overtaking on a country road - it's not good to be left spluttering on the wrong side of the road!

I have a problem with my TJ AWD that's got me puzzled. Normally, there is no hint of hesitation when accelerating, especially from a standing start. However, if it's been pushed a bit hard, say up a good mountain climb, with lots of alternate acceleration and backing off around corners, the engine can suddenly fail to deliver when the accelerator is pushed past a certain point. It's as if a rev limiter has cut in far too soon, or the ignition is not firing properly.

Has any other AMC member had this problem with their 3rd Gen Magna, and if so, what was the cause? The most alarming thing about it is not having confidence when overtaking on a country road - it's not good to be left spluttering on the wrong side of the road!

Could be in need of a fuel system service. How about fuel filter? Fuel pump could be on the way out. Is the fuel line flattened? Some AWDs are being used/have been used as 4WD! so have damage underneath to fuel line. When were plugs last done? CAT could be blocked/melted.

Cheers,
Alan

Could be in need of a fuel system service. How about fuel filter? Fuel pump could be on the way out. Is the fuel line flattened? Some AWDs are being used/have been used as 4WD! so have damage underneath to fuel line. When were plugs last done? CAT could be blocked/melted.

Cheers,
Alan

The plugs are still original - it has only done 43,000 km to date. The previous owner practically wrapped it in cotton wool, so I doubt it's been off-roaded! I have the car serviced every 5,000 km by a very good mechanic.

I took it around local roads today, deliberately choosing a couple of steep hills to get it "loaded up", but it performed faultlessly (of course), so I'm worried I won't be able to demonstrate the problem to the mechanic on Friday. It looks like the mis-firing only occurs when the car is hot after a fairly long run and full throttle is applied.

Intermittent faults like this are pigs to diagnose.

Intermittent faults like this are pigs to diagnose.

You're not wrong there. So many times just a bad connector, even seen the same caused by voltage spikes when radiator fan kicked in.

Have the front plugs been changed or filed and regapped? Amasingly some who treat their cars in certain ways are tight in other areas.

Also if the car had previously only done short trips and was babied the injectors may be a bit gummy. Ordinary unleaded has the legal minimum detergent so if the engine was run short distances and turned off there is a lot more chance of tar deposits. Running Premium 95 for a few tanks may fix it if this is the problem. Both 95 and 98 have more or better quality detergents. 95 E10 doesn't as far as I know, but the ethanol cleans a bit anyway.

Cheers,
Alan

hey, i had a honda legend that had a similar problem and a lead had broken down. When are the leads replaced normally if service times are followed? 100,000?

hey mate i have the same problem for about 1.5 months and now i cant' fixed the problem but it gets a lot better. i have done alot of things to fix the problem.
- brand new pulgs front and back
-all new leads
-clean injectors
-clean fuel line
-all electric wires are ok
-new throttle body sensors
-engin oil+fillter change
all things above and i still can t' fixed the problem does anyone known what is happening and my is a TE with 290000 on the clock

Aren't normal plugs (front row) only ideally good for 30,000km or so?

Could be in need of a fuel system service. How about fuel filter? Fuel pump could be on the way out. Is the fuel line flattened? Some AWDs are being used/have been used as 4WD! so have damage underneath to fuel line. When were plugs last done? CAT could be blocked/melted.

Cheers,
Alan

i would have said the same thing... fuel system, maybe the spark plugs,

really is the fuel pump ? do they cost a lot ?

is it possible for you to get your car running on a dyno with a exhaust gas analyser? That would be a good way to find out if it is an under fuelling issue. Might also be a good idea for your mechanic to hook the car up to a scan tool and view the live operation data and compare it with the factory specs.

Thanks for all the suggestions guys.

I do quite frequently use 95 or 98 octane petrol to keep the injectors clean, and after the recent run to Coffs Harbour the car is running particularly well (cobwebs blown out!). However, it was on Thunderbolts Way, about half way between Gloucester and Walcha, that it really played up, coughing and missing every time I pushed a bit harder up hills or during overtaking.

The suggestion about putting the car on a dyno is a good one, because I think the car needs to be loaded hard and running fairly hot before the trouble shows up. I just hope I'm not forced to play the depressing game of replacing everything under the bonnet until the problem goes away.

Update. I took the car to a good mechanic this morning. Needless to say, the car performed perfectly during a brief test drive. He said that it was most likely electrical (I agree with him on that!), particularly when I told him it takes a good heat soak to bring on the mis-firing.

The bottom line: the mechanic didn't want to waste my money "working" on the car with no real clue about what was wrong. If I insisted, he would replace plugs and leads first, but he advised waiting until the problem became more frequent and easier to demonstrate under normal driving conditions. He didn't think the car would fail completely - it could still get home on only 4 or 5 cylinders.

Incidently, there are no "error codes" to be seen because the ECU thinks it has received and sent all signals normally. This at least is a relief, because I understand a replacement ECU is costly.