Acceleration flat spot.

[GunMentalGrey]

Ive had a search, and can’t quite find a matching fault. My 2007 D40 STX manual (145000km) is getting to almost undriveable stage so it’s 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 ‘just driving along’. 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.

I’ve 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

 

[bods]

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...

 

[Old.Tony]

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.

 

[ericcs]

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!

 

[GunMentalGrey]

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.

 

[GunMentalGrey]

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.

 

[Old.Tony]

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?

 

[GunMentalGrey]

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.

 

[happy john]

Someone had a similar problem years ago and it ended up being dirty earths and connections to the ECU.

 

[GunMentalGrey]

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...

 

[GunMentalGrey]

Took it for a good drive today. Included some off road fun, nothing too far off the beaten path just in case. It played up from time to time, but I was able to ‘drive around it’ mostly.

Then after about and hour of driving we got back onto the main road I gave it a boot full in third to get past the missfiring and it gave a little backfire noise and went into limp mode and would rev again until I pulled over and shut off the engine. Funny thing though, since the ‘backfire’ it’s been back to normal, so seems to be fixed.

Still be interested I working out what went wrong though. Any hints?

The only thing I’ve done in the whole process is clean the MAF and i
nstall the EGR block. Haven’t had time for anything else yet.

 

[Old.Tony]

Still sounding like the SCV. Very typical symptoms. Fuel system cleaner (Liqui Moly) may improve the thing temporarily. It never hurts to use that stuff, chuck the whole can in the tank, you should see some results within 100-200km.

We went through a whole range of things with my car at one point, replaced the throttle body, replaced the throttle control and finally when we replaced the SCV the thing was fixed.

I still doubt it's the BCS because you said your car stalls, which means engine cuts out completely - a dead BCS won't do that, it'll just simply not boost any more, so the worst that will happen with a failing/failed BCS is a complete lack of power and tonnes of black smoke.

I call the SCV on the fuel pump. It's a pair of allen bolts and an electrical connector. If you have a hoist it's easier to get to from underneath.

 

[fitzie]

Someone can definately correct me if I'm wrong, but when the fuel filter is replaced, doesn't the ecu need resetting.

 

[GunMentalGrey]

Someone can definately correct me if I'm wrong, but when the fuel filter is replaced, doesn't the ecu need resetting.

Possibly, but it had been running perfectly after the service for a couple of months.

 

[GunMentalGrey]

Still sounding like the SCV. Very typical symptoms. Fuel system cleaner (Liqui Moly) may improve the thing temporarily. It never hurts to use that stuff, chuck the whole can in the tank, you should see some results within 100-200km.

We went through a whole range of things with my car at one point, replaced the throttle body, replaced the throttle control and finally when we replaced the SCV the thing was fixed.

I still doubt it's the BCS because you said your car stalls, which means engine cuts out completely - a dead BCS won't do that, it'll just simply not boost any more, so the worst that will happen with a failing/failed BCS is a complete lack of power and tonnes of black smoke.

I call the SCV on the fuel pump. It's a pair of allen bolts and an electrical connector. If you have a hoist it's easier to get to from underneath.

Thanks. WHEN it reoccurs I’ll jump straight into the SCV then.

 

[happy john]

Someone can definately correct me if I'm wrong, but when the fuel filter is replaced, doesn't the ecu need resetting.

The ECU ajusts the fuel flow dependent on the restriction of the fuel filter. As the filter gets blocked it works harder to deliver the fuel. Fitting a new filter will see those values change and a reset is a good idea.

 

[bods]

The other thing is, the ecu may throw a high fuel pressure code or go into limp mode from high fuel pressure if the filter is very blocked and the ecu is not reset.

I'd be looking more and more at the scv with the issues you are having too.

 

[GunMentalGrey]

Well, after a while of not making the time to fix the problem properly it’s back. Only now it’s added ‘hard to start’ as well. Winds over well, just takes a little while to kick and start. Day off on Thursday so it’s wrenchin time.

 

[GunMentalGrey]

New SCV is in. This morning I was having a right old time trying to get the nav going. Nearly ran out of battery I wound it over that much. Something extra I noticed was that Welsh’i I went for the fuel prime pump bulb thingy there was moisture on it. Turned out to be fuel and when I got back home to replace the scv found it was dripping - a lot. New one ordered now, maybe there is some air getting into the fuel system that way as well.

 

[bods]

I was going to suggest having a look at the fuel filter. Excessive cranking on a cold start usually points to air getting in somewhere. Hopefully that sorts your problem out. Good luck.

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