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Acceleration flat spot.
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Old 20-01-2018, 12:32 PM
GunMentalGrey GunMentalGrey is offline
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Default Acceleration flat spot.

Ive had a search, and canít quite find a matching fault. My 2007 D40 STX manual (145000km) is getting to almost undriveable stage so itís time to get the spammers out. Not long after I got it I gave it a liquimoly purge which cleaned up the frequent limp mode. Last service I got the mechanic to install new filters, including fuel. Recently the car has been hesitating off the mark once warmed up. Today, it was running really rough between about 1500 and 2300 rpm when trying to accelerate. It seemed to run just fine Ďjust driving alongí. It was worst in 1st and 2nd gear, and a couple of times felt like limp mode, except not running smoothly, so I switched off and on again which seemed to help. Once over the point where the turbo could properly kick in it would run fine and pull strong but it meant racing off from the lights to keep the revs up enough to allow a gear change without dropping back into the dead zone.

Iíve got an EGR plate to fit, I tend to clean out the intercooler and turbo lines and check the suction control valve and replace as required.

Anything else I should be looking at?
Thanks In advance
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Old 20-01-2018, 02:12 PM
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Hey mate,

I'd probably try cleaning the maf sensor too. You can get cleaner for it, just make sure you don't try and wipe it with anything. It is in the intake pipe just after the airbox. Give it a good spray until the wire looks clean, then let it dry out before refitting it.

Normally suction control valve problems show themselves at idle, but it wouldn't hurt to check it. Do you have access to an obd2 scantool or know someone who does? It would be interesting to see the engine load and fuel rail pressure when it is having its moment...
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Old 20-01-2018, 08:39 PM
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Agree with the clean of the MAFS.

I wouldn't discount the boost control solenoid playing up either. Cleaning stuff is always a good thing and can never hurt, but the BCS is uncleanable and once it becomes erratic it just needs to be replaced. Monitoring boost pressures during acceleration would be a good thing. If the BCS is failing, you'll find boost pressures down around 6psi while accelerating until the BCS decides to cooperate.

Another consideration is electrical glitches. Dirty electrical contacts can (and have) caused all sorts of erratic operation. Check and clean the battery terminals and if you've got (or have a mate with) some of the electrical sealer (spray can), give the terminals a quick spritz after they've been cleaned.
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Old 20-01-2018, 11:23 PM
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take the cover off the top of the engine and check all your boost hoses that come and go from the BCS and the turbo actuator. you can also take the pipe off that goes from the BCS to the turbo turbo actuator at the BCS end, and suck on that hose. you should see the actuator arm rise and fall.
i had very similar problems, and it turned out to be perished boost hoses on the drivers side under the plastic cover!
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Old 21-01-2018, 01:25 AM
GunMentalGrey GunMentalGrey is offline
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Thanks all. Got some work to do. I’ve had a look under the bonnet and there is some oil around some of the hoses, I assume turbo hoses but not having played diesel or turbo mechanic much before really need to work out what is what.
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Old 22-01-2018, 01:05 AM
GunMentalGrey GunMentalGrey is offline
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Drove it again yesterday and until it got really warm it wasnt too bad. Being 30+ degree, once it got to full operating temp was near undriveable. Even stalled a few times, once on a roundabout which wasn't fun - isn't the steering heavy without assist? Still, managed to drive it home by keeping the revs up a bit when wanting to accelerate.
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Old 22-01-2018, 11:22 AM
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A faulty BCS won't make the engine stall. Sounds more like the SCV. Is the idle steady, or does it do little surges, like it can't make up its mind how fast it wants to turn over?
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Old 22-01-2018, 12:10 PM
GunMentalGrey GunMentalGrey is offline
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Seems to idle smoothly, most of the time. Also runs smoothly under normal driving conditions. It only seems to play up when I accelerate reasonably hard, like from a standing start keeping up with the other traffic.

Cleaned the MAF tonight, because it’s an easy job, the MAF was quite grimy. then took it around the block with no real improvement. I then came back and grabbed my so , his android phone and installed the torque app and hooked up the obd. Logged another trip around the block and it seemed to improve, but the temp was cooling so not sure if that helped. Boost gauge seemed to show normal, intake pressure seemed ok. It was also the first time using torque app and still learning how that works. Will look at the obd log tomorrow when I’ve got a full size screen to check details.

Last edited by GunMentalGrey; 22-01-2018 at 12:12 PM.
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Old 23-01-2018, 06:51 AM
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Someone had a similar problem years ago and it ended up being dirty earths and connections to the ECU.
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  #10  
Old 28-01-2018, 11:02 AM
GunMentalGrey GunMentalGrey is offline
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Will have a look at earths. I guess it is a possibility.

The test drive while recording with the torque app did t prove anything, the data only recorded gps position for some reason, nothing else. Need to try it again. All the app gauges seemed to be running normally too.

More driving and trying to diagnose and it appears to happen mostly in 1st to 3rd and mostly when I’m not going easy on the accelerator. I can almost avoid the problem by taking off slowly in each gear. Travelling in 4th at 60km/h I can give it a boot full and it appear to accelerate normally.

Still testing...

Last edited by GunMentalGrey; 28-01-2018 at 11:11 AM.
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