Magna TF 1997 V6 3.0. 140,000 km.
Sorry for my English in advance. All was good until it started to stumble pretty bad after waiting on a light some day. Hardly managed to get home. The idle is almost fine, just a small sputter every few seconds. It runs ok too if I press on the gas when parked. But when driving it stutters and stumbles really badly as I’m pressing on the gas. Have to use the accelerator very gently to get it rolling at all. Sometimes it "wakes up" and runs very well as it always was in the past.
So what I have done so far:
- timing belt adjusted (the cam seals were leaking anyway and it looked like the belt has jumped a tooth when I checked it before doing the work)
- distributor cap and rotor renewed
- cylinder compression test - ok
- inlet manifold gaskets, plenum chamber and throttle body gaskets renewed
- throttle body cleaned
- fuel filter renewed
- air filter checked

No luck so far.

I tend to think towards the fuel pressure regulator and probably that's what I will try next (crazy dear they are at Mitsubishi dealer, found one on ebay, for Diamante).
I don't have a fuel pressure meter to test the fuel pressure, did a rough test by attaching a clear hose into a bucket to the regulator return end. The flow was ok, it was changing when I was pulling throttle lever (the flow slowed down when I opened the throttle) so it looked like it works fine.
Another thing I noticed - I used to hear the fuel pump noise when turning the ignition key - ignition is on - the pumping sound - start. Now I can't hear it any more. Something wrong with the pump?

So I am stuck at the moment and would appreciate any advice or an idea where to look at next.

id sont really have much clue, but i had almost the same issue in my lowlux turbo, and it turned out the afm was round the wrong way lol so maybe its sumthin to do wif ya air flow meter?
just a stab in the dark?

Plugs/leads. Replace those.

thanks James for the quick reply.

I tried to disconnect the air flow sensor - the engine runs crap then even while idle. I will check the voltages there once this rain is over.

Forgot to mention - I checked ECU fault codes - no errors were "blinked out"

I'll go with Disciple, with the proviso that you check each plug for condition as you go - and keeping in-mind that you suspect it hasd jumped a tooth on the Timing Belt.

Condition of plugs may give a clue about whether you have good/even compression on all cylinders and spark timing for all cylinders.

If it is intermittently strong/normal, then maybe plugs/leads or dizzy cap (tracking) could be cause... rather than something more permanently nasty like a damaged valve if belt had jumped.

Easy way to check if there is any high voltage tracking on leads/plugs/dist cap is to look at the engine running in total darkness.

checked for voltage tracking tonight - no sparks seen, will replace the leads/plugs anyway, will replace the fuel pressure regulator too. will update with the results.

Ive been having the same troubles, and have tracked the problem down to leaking exhaust manifold gasket, and manifold to exhaust pipe gasket, have checked my catalytic converter and the guts have blown out, so Im also suspecting possible restriction in the exhaust pipe and rear muffler as well. Managed to get it running perfectly after tightening the rear exhaust manifold nut that had come loose, but the gasket was already blown at that spot and it soon played up again. Anyway, just a thought.

Hi all well i have been chasing this exact problem for the last 18 months . Started with just stalling after cold starts when the car would pul up after the fisrst corner or T junction. Spluttering , coughing and finalally stalling after pumping the excellorater.
This progressed further to doing it all the time even when it was warm , the pedal seemed to get hard or feel like it was pushing back and then all of a sudden take off like a cut snake.
We changed plugs, leads , battery fuel filter all the easy things to no avail. We then changed the airflow sensor and filter , throttle body was next , stepper motor and even the TPS sender.All the same results still playing up.
We then swapped out the ECU , coolant sensor for ECU had Mitsibushi look at it and check all settings and still no luck , not even any sugestions from the dealer .

The fix finally came in desparation when i had a O2 sensor given to me even though it was a toyota one i decided to change it out .Had to rewire the sensor to the mitsi plug as it had different colors to the toyota ones . When i took the old sensor out i notice it was bunged up with massive amounts of carbon , black soot etc.Started the engine and gave it a couple of revs to blow the excess soot out and there was heaps of it .All back together and thats the problem fixed , hasnt missed a beat since goes like a race car all the time its great to get it back to normal again.
O2 sensors should be changed every 100,000 Klms and are never done im told.

castnet and Hughy69, thanks a lot guys for your replies. I have replaced the fuel pressure regulator this morning (just arrived from US), replaced plugs and leads a week ago - no luck, all the same, bugger. Was thinking towards replacing fuel pump, throttle body and ECU but decided to check the thread. Will check the exhaust system, I replaced the rear muffler a year ago, it was rusted out so there could be something wrong up the pipe too. Will check O2 sensor as well. Will be back with the result.

O2 sensor will not have any bearing on acceleration

I would say 99% your issue is the dist itself, I have done a few of these in the last year or so as the cars get older, is becomming an issue with the exact same symptom you hvae

Have also had similar symptom with faulty MAF as well but less common, either way I have distributors and MAF sensors here

ALso, you can not check a fuel pressure reg with a bit of hose, you need to check it has the appropiate pressure

Got it fixed finally. It was the distributor that caused the problem (Madmagna, you was on the money!). After I replaced it by a used one from ebay and started the car I could hear straight away it made the difference. Got my missus for a test drive - the car is back to normal, hurray!
Thank your guys a lot for your help!!! AMC's the best!!!

After a lot of hair pulling and use of some finer english, seems my problems among many also was in the distributor, took the dizzy off the other motor I have, and it now feels like a v6 should feel. Wasnt that easy to track down, no engine codes were generated, and it was a stab in the dark to swap the dizzy over, thinking maybe its a bad coil or cam sensor problem, would start easy, idle reasonably OK but splutter as soon as I opened the throttle quickly. Thanks Madmagna, your post above got me thinking in that direction.

Can the distributor be dismantled and the coil replaced, or is it basically a matter of the distributor being a throwaway item?

Is not worth the hassle to be honest given how many 3.0 engines are out there in wrecks.

On monday I threw out 4 3.0 engines as they are really worth very little for much at all aside from scrap metal

Are the 3.0 and 3.5 distributors the same? Might go and pick up a spare, you never know. I've had plenty of coil problems with both first and second gen Magnas, and I imagine the third gen is no different.

Just noticed these coils for sale on this site, appears one has to dismantle the distributor and swap them over, $88, not sure if it includes the cam sensor though. http://www.cyberspaceautoparts.com.au/contents/en-uk/p496_Mitsubishi_Ignition_Coil.html
How much are complete distributors worth new?

Just noticed these coils for sale on this site, appears one has to dismantle the distributor and swap them over, $88, not sure if it includes the cam sensor though. http://www.cyberspaceautoparts.com.au/contents/en-uk/p496_Mitsubishi_Ignition_Coil.html
How much are complete distributors worth new?

Well genuine I had a look at MD374448 (supercedes MD327305) same part for 6G72/6G74 and they come up at $690 on http://www.amayama.com/search/?q=MD327305
and $713 in the USA http://www.mitsubishipartscentral.com/ plus freight.

The coil assembly does not show up in the parts breakdown on its own.

Just noticed these coils for sale on this site, appears one has to dismantle the distributor and swap them over, $88, not sure if it includes the cam sensor though. http://www.cyberspaceautoparts.com.au/contents/en-uk/p496_Mitsubishi_Ignition_Coil.html
How much are complete distributors worth new?

Price sounds ok, paid that much for a gen 2 coil years ago. Might be available cheaper from the US of A though.

rockauto.com has the complete distributor for $277

http://www.rockauto.com/catalog/x,carcode,1374397,parttype,7108

Why is it that people seem to just throw a shitload of parts (and money) into finding faults,
To me it sounds like fuel starvation, take it in to a workshop and get it sorted mate, otherwise you will end up throwing something at the car and emptying your wallet.

good luck

Is not worth the hassle to be honest given how many 3.0 engines are out there in wrecks.

On monday I threw out 4 3.0 engines as they are really worth very little for much at all aside from scrap metal

!!!! Next time you feel the urge to toss out any healthy 3.0s, let me know :) I'll grab one as a spare for the Mum mobile