I've had this problem for years now but I always thought it was the gearbox. Now that I have a different gearbox in the car I don't know what the cause is.

Basically, the symptoms are;

When the is car cold (not driven for 8 hours), the engine performance under 3000RPM is sluggish and laboured. If you plant the foot, it struggles to 3000RPM and then suddenly launches like a turbo kicking in. After this first surge, the engine has come alive and feels responsive from idle. There still a power kick at 3000RPM but that pretty normal for the 6G74.

I have no idea whether this is engine management related or an issue with the fuel system.

Anybody else have this problem?

Cheers,
Mons.

I also suffer this problem after the engine has warmed. I have a suspicion it is something to do with an emissions function or even the auto choke. GM engines I know run a secondary air valve which pumps hot air into the inlet of a cold engine in order to warm it up quicker. This is known to cause the engine to be a little 'laggy' while the valve is open. Perhaps there is something similar on our engines?

ive told people once, i'll tell them again.


ninja supercharger install.

ive told people once, i'll tell them again.


ninja supercharger install.

Ahaha. I found your reference. That was ninjas hiding in the transmission. This is more like ninjas "Stealing the peach from the monkey" - At 3K they let go and Monster Inc charges from the blocks.

Others must be facing this same problem - and worked out what it was.

There are a few things I would be looking at here

For startes a proper cold fuel pressure test
Cap and button, I know is an obvious thing but is essential especially with a cold engine
Plugs, again as above
Did also have a car with something similar and it turned out to be the cat was partly blocked, when warm it expanded and was better

Also, these do not have a choke, they like all efi cars get a fast idle from the air bypass valve and use ecu set mixtures to determine the fuel mixture

From here, would really be hit and miss, doubt is temp sensor or 02 sensor as neither will clear after the first rev.

yeah I was thinking towards the air bypass valve process (called secondary air valve by other manufacturers). Mal, from what you said it is actually a very diverse range of possible issues. Definately not temp sensor or O2 sensor, mine is still very economical, even on short runs.

yeah I was thinking towards the air bypass valve process (called secondary air valve by other manufacturers). Mal, from what you said it is actually a very diverse range of possible issues. Definately not temp sensor or O2 sensor, mine is still very economical, even on short runs.

Definently no issue with fuel economy. 10.5L per 100km on the combined cycle.

I've changed the plugs only recently and it made no difference.
When the car hits 115K, I'll be having a look at the leads and dizzy cap/rotor (112K atm)

How do I go about a cold pressure test on the fuel system?

Is there an easy way of checking the Cat convertor without $$ replacing it $$.?

Cybermonkey you refer it to the EGR valve (exahust gas recirculation) helps warm the motor when cold, but sounds like a ISC issue to me personally, it has probably retarded everything due to being cold.

Cybermonkey you refer it to the EGR valve (exahust gas recirculation) helps warm the motor when cold, but sounds like a ISC issue to me personally, it has probably retarded everything due to being cold.


I think EGR is different, since in most applications EGR is open unless there is WOT. Secondary Air Valve shuts as soon as the engine is up to temp and doesn't go off unless it cools down.

I think EGR is different, since in most applications EGR is open unless there is WOT. Secondary Air Valve shuts as soon as the engine is up to temp and doesn't go off unless it cools down.

Thats for old school Carb motors, the EGR in the magna motor open and shuts depending on the vaccum in the Manifold.

Ok,
The air bypass provides more air on a cold start to hold the revs up higher in order to make the engine a/ smoother b/ warm up faster.

The EGR is only open under certian conditions and is not open when cold

The ESC will make absolutely no difference to the running of the engine off idle as is totally redundant off idle. Once that butterfly cracks open, might as well not have the ISC there

In relation to a cold pressure test, you need the proper pressure testing kit like I have here, you would hook it up the night before, leave overnight and then get the car to play up and see if you have an issue with pressure

Another trick to point this out can be to pull the vac hose off the pressure reg and go for a drive and see if the issue differs at all

You state your economy is good, this also then takes away issues with blocked or faulty injectors

Mal wouldnt good economy also take away from possible O2 sensor issues?

Personally, I hate problem solving intermitent issues, you may replace 20 parts and *think* you have it solved, until it comes back a week later.

I've had this problem for years now but I always thought it was the gearbox. Now that I have a different gearbox in the car I don't know what the cause is.

Basically, the symptoms are;

When the is car cold (not driven for 8 hours), the engine performance under 3000RPM is sluggish and laboured. If you plant the foot, it struggles to 3000RPM and then suddenly launches like a turbo kicking in. After this first surge, the engine has come alive and feels responsive from idle. There still a power kick at 3000RPM but that pretty normal for the 6G74.

I have no idea whether this is engine management related or an issue with the fuel system.

Anybody else have this problem?

Cheers,
Mons.

TJ2 3.5L t/tronic

Hi Mons

Check your TPS as it controls the ECU for engine and transmission, and if faulty will play havoc with your auto change points

It must be adjusted precisely using a multimeter

Check EGR by manually raising the EGR valve - it should tend to stall, then recover when released

Have your injectors ultrasonically cleaned - they can still give reasonably good economy on cruise, but fail to deliver enough fuel on high demand

Cheers, Barry

TJ2 3.5L t/tronic

Hi Mons

Check your TPS as it controls the ECU for engine and transmission, and if faulty will play havoc with your auto change points

It must be adjusted precisely using a multimeter

Check EGR by manually raising the EGR valve - it should tend to stall, then recover when released

Have your injectors ultrasonically cleaned - they can still give reasonably good economy on cruise, but fail to deliver enough fuel on high demand

Cheers, Barry

Thanks for the response Barry,
1. Possibly a Cold start, intermittent fault with TPS???? :doubt: But nothing to do with Auto shift points. Shifts fine now I have a new gearbox.
2. Not possible its the EGR - It has been disconnected and sealed from the zorst with the RPW headers
3. hmmm - Injectors seem fine as I have plenty of power once the initial rev is out of the way.

Keep suggestions coming people. I can't have the only magna with this issue.

I have same prob with the KJ AWD.
Worse since being on gas not that that should effect anything as it runs on fuel till at full op temp.
My plugs are all fairly new so can't be that.
Also 02 sensor is new and it made no difference before and after.
Car runs fine at warm temps so injectors seem fine.

Disconnected battery completely yesterday and left it till this morning. Shift points much improved again and no longer seems hesitant with first acceleration with cold engine. Weird!

Anyone had any more luck?
Mine seems to be getting worse.
Another common prob it seems or KJ's.
I've had more small issues with kj's than any other model. Not just engine but quality in general.
What is so different? Mitsub sourcing cheaper parts in some occasions.

I've got a couple of projects on the go but no solutions just yet. I've noticed the issue can happen intermittently now when warm too. Could be injectors.

I had a bad seal between the TB and intake hosing. Reseated it all and it appears to be better.

EGR is only used when the engine has warmed up and is under part throttle.. there is a VSV on the top or the front cyl bank to control it

The engine uses the ISC upto 25% throttle

what you all need to try is a throttle housing and ISC clean

get a can of O2 sensor safe carbie cleaner and a tooth brush and scrub out the throttle body give it a good gout until it is sparkling then fill the ISC port with cleaner and let it sit for a couple of minutes
re assemble and start her up with 50-75% throttle till she starts and then let it idle for a couple of minutes

every time i do a set of rear plugs i like to scrub out the intake manifold, remove the throttle housing and scrub it out and remove the ISC and give it a good go too

also a spray of cleaner every service helps

try it and see... you may be suprised and it could save you a bit in time and money on bad guess work

EGR is only used when the engine has warmed up and is under part throttle.. there is a VSV on the top or the front cyl bank to control it

The engine uses the ISC upto 25% throttle

what you all need to try is a throttle housing and ISC clean

get a can of O2 sensor safe carbie cleaner and a tooth brush and scrub out the throttle body give it a good gout until it is sparkling then fill the ISC port with cleaner and let it sit for a couple of minutes
re assemble and start her up with 50-75% throttle till she starts and then let it idle for a couple of minutes

every time i do a set of rear plugs i like to scrub out the intake manifold, remove the throttle housing and scrub it out and remove the ISC and give it a good go too

also a spray of cleaner every service helps

try it and see... you may be suprised and it could save you a bit in time and money on bad guess work

Probably help with rough idle but will have no impact on power delivery. Be very careful about using carb cleaners around the ISC servo. Solvents are not it's friend. I've finished a complete overhaul and high flowing of a throttle body and Will fit it in next couple of weeks.

Also I'm planning a fuel system clean out over Easter so Hoping this will improve things.

So I have completed the following chasing this issue;

New spark plugs
New Ignition Leads (NGK)
New Distributor Cap and Rotor
Fully Rebuilt the Throttle body (including lip removal to improve low throttle response)
Cleaned out Upper Inlet Manifold
Cleaned out Lower Inlet Manifold
Replaced Fuel Injectors and seals
Replaced Rocker Cover Seals and spark tube seals (They were hard and leaking)
Relaced Fuel Filter
Chucked a $20 bottle of fuel system cleaner in tank

Results...

Good: Some horsepower restored. Overall smoother engine operation. idle smooth when cold ambient temperature (Early morning).

Bad: Power Discontinuity has not gone away. idle still rough when warm ambient temperature (During the day).

So I wonder whether the MAF sensor may be an issue. There are no logged error codes.

Thanks for posting that mate. Saves us witrh the same prob wasting money.

As for rough idle, usually increasingthe idle fixes it. From what i have experienced over time with many rada's is that some are prone to rough idle and like yourself, have spent way to much money trying to fix with no result.
Put it down to different engine tolorances.
A fix is to increase the idle speed. This can only be done properly by pluging into the computer. The air screw on throttle body will do it but only temp until the computer re-adjusts it and brings it back down.
I have done it in my rada's and i have been happy since.

Duplicated Response

Thanks for posting that mate. Saves us witrh the same prob wasting money.

As for rough idle, usually increasingthe idle fixes it. From what i have experienced over time with many rada's is that some are prone to rough idle and like yourself, have spent way to much money trying to fix with no result.
Put it down to different engine tolorances.
A fix is to increase the idle speed. This can only be done properly by pluging into the computer. The air screw on throttle body will do it but only temp until the computer re-adjusts it and brings it back down.
I have done it in my rada's and i have been happy since.

Doesn't address the intermitent power lose issue though.

The hesitation (engine Warm or cold and between 1000-3000RPM) feels like the engine is shaking or pulsing. As soon as you hit 3000RPM it lets loose and you're thrown into your seat. Also doesn't happen if you go WOT from standstill. anything less and it can happen.

Thangs not checked yet:
Fuel Pressure Regulator and/or pump
O2 sensor (Unlikely)
Air Flow Sensor
Crank angle sensor
temperature sensor

This is doing my head in.

I totally agree.
I have the same prob in my KJ AWD.
I have recently put a new 02 sensor in with no difference.
It almost feels like huge flat spots, similar to the feeling of a carboned up motor.
I use to run a fleet of Mazda bravo utes.(current shapes).
They would do 90% of their work just at idle. They use to become very carboned up. It felt like the feeling we are experiencing but the only difference is that these utes did it all the time even when warm/hot.
They had absolutely no power under 3000rpm. It even felt like they were miss firing because there was just nothing.
I use to give them one mighty thrashing when taking them out of the fleet for a service which would help a little but we just had them all carbon fluched/cleaned when in for services and they were like a brand new car. For memory, they use to runn this hard ass stuff/cleaner through the fuel line directly.

One thing is though, there is no way mu KJ AWD could be carboned up. All it does it FWY work every day, good long runs and also i give her a bit every now and then so this makes me think it might not be a carbon issue.

I had the car a Dynamotive this morning,

Turns out that my MAF sensor and Oxygen sensors are both rooted. No codes in the computer because that haven't completely failed.

So I'm sourcing replacements and will have the car redyno'd on Friday. Even with the stuffed sensors, The magna pulled 124kW atw. (Up from 112.8kW - previous tune)
From what Mark at Dynomotive told me, the previous unnamed tuners didn't even bother optimising the tune. An extra 11kW from a 4degree advance in ignition timing isn't bad.

First Change yesterday was the MAF - Instantaneously improved the power delivery. Stumble, hesitation on acceleration are gone. Vehicle is smooth right through rev range. Idle was still as rough as guts.

Then Last night I put the new oxygen sensor in. Idle is now perfectly smooth. Apparently the sensor response was too slow and once off cruising, it was not telling the computer to revert back to the 'rich' fuel map. Thus at idle it was so lean it was about to stall all the time.

All that's left now is to get the unichip retuned and I'll get back to not wasting money on my car......for now.

Cheers,
Mons.

Ps. For others wanting to replace their MAF. Mitsu want $980 each for them. A place called auto computer engineering in Braeside remanufacture our MAF sensors (New hot wire and circuit board) for a third of this. I got mine through R&E auto parts. - My favorite auto parts chain. :)