Flat spot NG Pajero

[awbeattie381]

Ive been putting up with this for a couple of months now.

I have been experiencing a flat spot when accelerating. It occurs usually when ive slowed down and put it into 2nd gear, turn a corner or roundabout, or am in heavy traffic then accelerate (still in second gear).

When i go to accelerate gently the first few mm of accelerator pedal there is nothing, 1mm further depressed the car will lurch forward with a bit of a clunk.

I initailly thought this was the step down motor as this had been messing with my idle. Ive now got a reco idle step down motor (which i think is only a bit better and will probably be repalced) and i still have the problem.

With these electronic engine management systems is there such this as a flat spot or should i be looking more mechanically - driveline, gears, unis?

help would be appreciated!! its becoming frustrating!!

Andrew

[PHIL]

To be honest, the first place I think I would check is the throttle cable itself, to see if it is binding, etc. Its amazing what a small burr on the wire will do...

If it is actually electrically related rather than mechanical, I'd start by pulling the codes. In a GENI it takes 30 seconds to do, and will tell you right away whether everything is A-OK with the FI system or no.

If you've never done this, I've got a modest writeup on 4x4wire to guide you through it:
http://www.4x4wire.com/mitsubishi/tech/ ... eshooting/

But I'd check the linkage on the throttle cable first, right from the pedal to the t-body....

Best Regards,
PHIL

[awbeattie381]

phil, what rims are you running?? are they the standard 15x6?? what size tyres are you running?

btw ill check out that link and have a look at the throttle cable.

just looked at the 4wdwire forum. thanks for your reply to my tyre question.

[PHIL]

phil, what rims are you running?? are they the standard 15x6?? what size tyres are you running?

btw ill check out that link and have a look at the throttle cable.

just looked at the 4wdwire forum. thanks for your reply to my tyre question.

You're welcome. I was running 33x950 BFGs on the 15x6" OE chromies. But this was on my SWB. I now am building up an LWB, using the engine from the shortie. This truck is bigger and heavier (and taller with 2" bodylift) so I am going wider. I now have a set of 8" rims, and I'm gonna run 33x1250s.

AFAIK, BFG is the only manufacturer producing the 33x950, over here anyways.

I ran 31x1050s on the 6inchers for several years with no handiling problems, but I did get some funny wearing on them after 50k clicks or so...

[awbeattie381]

did you experience any problems with the tyres running off the rims when aired down for sand/mud driving?? ive been as low as 12psi (for VERY soft beaches) but the norm would probably be around 18-20psi.

what do you mean by funny wear? inconsistent?

[PHIL]

did you experience any problems with the tyres running off the rims when aired down for sand/mud driving?? ive been as low as 12psi (for VERY soft beaches) but the norm would probably be around 18-20psi.

Not with the 31x1050s on 6" rims. But I did lose 3 beads all at one time last winter with the 33s on 6" rims. I think a 4" difference holds the bead better than 3"... I was running 14 psi at the time, and the temp was -27*C, so that was also a factor...

It was in this rut here (I'm smiling because my jaws are frozen that way! )

what do you mean by funny wear? inconsistent?

What the tire shops call "cupping".. the tire felt "bumpy"...[/img]

[awbeattie381]

nice pic mate - looked very bloody cold.

looks like the 31s are the way to go. cant wait to change them over.

[Noisey]

You have exceptional writing skills Phil - especially for the conditions

[PHIL]

You have exceptional writing skills Phil - especially for the conditions

Heheh.. why thank you! (I think somebody's got too much time on their hands? )

After a few beer I can write a book!

[mkpatrol]

Check your ignition system first. Most problems in fuel injected cars can be cured by a tune up.
Relpace the filters, spark plugs and check the plug leads for resistance and the dissy cap for cracks. If it is a V6, they are notorious for cracking caps and a buggered plug lead can cause a hesitation on acceleration. Check the compression of the engine and for any head gasket leak while you have the spark plugs out. Also clean the throttle body of any carbon buildup.

Stepper motors dont usually cause flat spots.

Next thing to check the injecters. Mitsubishi motors a prone to them blocking up. If the idle is rough as well, clamp off the fuel return hose to the tank. This will increase the fuel pressure in the rail. If the engine runs smoother then the injectors are dirty.

Check these basic things first before you go looking for injection problems as the injection is pretty reliable in these vehicles.

[PHIL]

Check your ignition system first. Most problems in fuel injected cars can be cured by a tune up.
Relpace the filters, spark plugs and check the plug leads for resistance and the dissy cap for cracks. If it is a V6, they are notorious for cracking caps and a buggered plug lead can cause a hesitation on acceleration. Check the compression of the engine and for any head gasket leak while you have the spark plugs out. Also clean the throttle body of any carbon buildup.

Stepper motors dont usually cause flat spots.

Next thing to check the injecters. Mitsubishi motors a prone to them blocking up. If the idle is rough as well, clamp off the fuel return hose to the tank. This will increase the fuel pressure in the rail. If the engine runs smoother then the injectors are dirty.

Check these basic things first before you go looking for injection problems as the injection is pretty reliable in these vehicles.

I agree it sounds ignition related, but to throw parts at it before taking 30 seconds to pull the codes is not the best approach, imho. A simple volt meter will yield results from the computer before you could have the first plug out. If the ECU is not admitting anything, THEN I'd look elsewhere.

[-Scott-]

Retarded timing can cause a flat spot. On the 3l V6 there is a wire which is supposed to be earthed before you manually adjust the timing - on mine I found it made a 5 Deg difference - the timing appears advanced if you don't short the wire, so it is easy to retard the timing too far.

I don't know that 5 Deg would be enough to notice, though.

Cheers,

Scott

[mkpatrol]

Phil, the basics of diagnosing a vehicle is what I have stated here. I don't know if your a mechanic or not but I am. If you are a mechani then I wouls hate to take my car to you bacause you would spend a lot of time looking in the wrong places first.
The golden rule when diagnosing faults is to not forget your basics. It is the first step to correct diagnosis.

[PHIL]

Phil, the basics of diagnosing a vehicle is what I have stated here. The golden rule when diagnosing faults is to not forget your basics. It is the first step to correct diagnosis. I don't know if your a mechanic or not but I am. If you are a mechani then I wouls hate to take my car to you bacause you would spend a lot of time looking in the wrong places first.

Actually, I'm a teacher, and you spelled "you're", "mechanic", "would", and "because" wrong.

No need to take pot shots here, my man - I am not disputing a tuneup, simply saying that pulling the codes from a GenI is so quick and easy that its the first thing I'd do. Hell, if I can do it, anyone can, if your characterization of me is accurate, eh?

[mkpatrol]

As i said I am a mechanic not a teacher. I'll stick to what I know and you do the same.
A bit petty to pick up on my spelling mistakes as I typed that in a hurry this morning.
We don't need to confuse the issue by giving people bad advice.

[awbeattie381]

MKpatrol, ...and your advice is.........

[mkpatrol]

MKpatrol, ...and your advice is.........

Buy a Patrol
No seriously, I have given it already, about half way down this page

[awbeattie381]

oops sorry didnt see that post

the idle has started to become a little rough - not the typical smooth mitsubishi fashion. You feel it thru the gear stick at idle.

might put a bit of spitfire plus stuff in the tank. Put a new thermostat in it yesterday and that helped a lot believe it or not - the car seemed to have more go!! didnt help the idle though.

is cleaning the injectors a $$ process?

[-Scott-]

Mkpatrol

People come here for advice, and anybody asking for free advice must accept there is some risk associated with it - you get what you pay for.

You state that you are a mechanic, and the first thing you want to do is throw parts at it. My grandfather was a mechanic, he ran several different dealership workshops, and he sacked mechanics for throwing parts in before attempting to diagnose a problem.

When you are under pressure to get jobs out the door, a new set of plugs is a cheap way to rule out a problem. When I'm trying to sort out a problem at home, I'll try a few checks before I throw in new parts.

Your advice is appreciated by all who read this board, but don't get upset if someone has an altenative suggestion. Do like I do, and feel quietly superior

Scott

[mkpatrol]

Mkpatrol

People come here for advice, and anybody asking for free advice must accept there is some risk associated with it - you get what you pay for.

You state that you are a mechanic, and the first thing you want to do is throw parts at it. My grandfather was a mechanic, he ran several different dealership workshops, and he sacked mechanics for throwing parts in before attempting to diagnose a problem.

When you are under pressure to get jobs out the door, a new set of plugs is a cheap way to rule out a problem. When I'm trying to sort out a problem at home, I'll try a few checks before I throw in new parts.

Your advice is appreciated by all who read this board, but don't get upset if someone has an altenative suggestion. Do like I do, and feel quietly superior

Scott

OK Point taken Scott. I just reread my post & maybe i need to clarify myself a bit.

To start diagnose process (I am not being a smart arse here):

Test drive to determine problem (already done here).

Pressure test cooling system before removing spark plugs (slight head gasket leaks can cause an engine miss even though there is no overheating evident)

Check condition of air filter (this will tell you a lot about the state of the engine tune. If the filter is clean then the car is generally naintained well, if it is extremely dirty, chances are the engine is not maintained and it will have to be replaced along with the rest of the consumable tune up parts in the engine).

Remove the air tube to the throttle body. Check throttlebody for oil buildup. Clean if required.

Remove spark plugs & check for condition.

Remove EFI fuse so you dont spike the system with a stray spark from the coils (remember the spark plud are removed and the sparks gotta go somewhere).

Wind the engine to check head gasket. No water ok. Water, do not pass go until the leak is repaired.

If the head gasket is ok , then do a compression test. If the compression is ok then continue, if it is not repair as required (Valves or rings ETC).
As the plugs are out you might as well replace them (they are cheap and you may not know the history of the plug, it may have been dropped when it was fitted. I never fit a dropped plug i always throw them away).

Check the condition of the Distributor cap and plug leads. Measure the resistance of each lead through the cap then remove each lead from the cap individually ti check for corrosion build up. If there is any high resistance or corrosion renew the spark plug leads and cap as required. I prefer to replace the leads as a set for reliability reasons. They are all the same age and can become faulty at any time. Check for cracks in the cap. If it is cracke renew it and the rotor button as a set to make sure the air gap remains correct. If the cap is ok then clean the corrosion buildup on the contacts inside the cap before you replace it onto the engine.

Check the fuel filter for dirt. Replace as required.

Once you have finished all these checks. Reset the idle (make sure the throttle body is clean) and the ignition timing.

If i have missed anything I am sorry.

If the problem persists then check the injectors as i stated in my previous post.

If the problem then still persists, then start checking the EFI system. These systems can be quite tricky to diagnose faults on so I would source a Mitsubishi workshop manual if you can as they are vary simple to follow. I rebuilt my first gearbox during my apprenticeship using one of these.

I hope that makes my previous post a bit clearer. I wasn't trying to "just throw parts at it", just trying to direct someone in the right direction.

[mkpatrol]

I did forget something. While you are checking the injectors, theck the fuel pressure. A fuel pressure check can tell you the pressure, flow and if any injectors are leaking down. It also checks the pump to see if its holding line pressure while the ening is stopped.

[-Scott-]

Wow! Is there an FAQ for this to be copied to?

On the subject of spark plug leads - what sort of resistance measurement do you expect? I've never actually measured one, but I vaguely recall that they aren't necessarily a short circuit?

Scott (showing his ignorance again )

[Bitsamissin]

Gee it all sorted itself in the end, no need for me to moderate
Would have been the first blue in the Mitsu thread
Personally I'd be pulling the ECU codes first, takes 5mins with a multi-meter (an analogue meter is better) then going through MKPatrols checklist if there was no fault codes present.
Good result guys.

Cheers, Frank.

[mkpatrol]

Wow! Is there an FAQ for this to be copied to?

On the subject of spark plug leads - what sort of resistance measurement do you expect? I've never actually measured one, but I vaguely recall that they aren't necessarily a short circuit?

Scott (showing his ignorance again )

Rule of thumb - 6-8 thousand ohms per 30cm but they can be all different.

Ahh bitsamissin - What can I say!!!!!!1

[awbeattie381]

some good advice thanks mkpatrol and phil. Have 3 weeks planned and am doing the great ocean road then to adelaide. will start fiddling when i return.

[PHIL]

some good advice thanks mkpatrol and phil. Have 3 weeks planned and am doing the great ocean road then to adelaide. will start fiddling when i return.

Good luck, and keep us posted.

(BTW, MKPatrol, I was kidding about the spelling thing: Hell, I re-read my own post 3 times and found three mistakes before I replied! I was not kidding about the teacher thing, though sometimes I wish I was... )

Cheers!

[mkpatrol]

OK Phil No worries. I still think everbody should buy a patrol This would fix all your probs.

[-Scott-]

OK Phil No worries. I still think everbody should buy a patrol This would fix all your probs.

But MKs are getting harder to find

Scott

[mkpatrol]

OK Phil No worries. I still think everbody should buy a patrol This would fix all your probs.

But MKs are getting harder to find

Scott

Yeah I know. Mines going in the next few weeks to make way for a GQ. I waved a compression gauge over mine as I was going to have my injectors done. 300-330 psi per pot. The manufacturer recommends 375-425 psi. I can clean the injectors until the cows come home & it will still blow smoke. I decided $5000 would be better spent on a newer truck.

If anyone wants a cheap truck I only want a couple of grand for it as it is. It still runs well & is still regoed till may. It just blows smoke & is hard to start in the winter.