Hesitation/judder between 2200-2700 rpm
 

Right, as has been discussed here, I'm experiencing a judder between 2200 and 2700rpm (roughly). It occurs on light throttle and is most noticeable at motorway speeds (70-80 mph).

It feels like the car slows down, then speeds up again slightly and sometimes it judders in waves, which always occurs at about 2500rpm. It still does it when the cruise control is engaged, but not as badly. This is probably due to the ECU counteracting the loss in power by adding more fuel and 'smoothing out' the problem.

It's done nearly 70k miles and has recently had a new turbo fitted (old one went blew a seal and dumped oil out of the exhaust) and the garage who changed the turbo nd fitted a new exhaust, said that they had fitted a new EGR valve, but I'm not 100% sure if this was done. It has also had a custom remap, but this was fine before the turbo went pop.

I've tried cleaning off the MAF, which didn't seem to cure it, but the hesitation feels like a MAF fault, as if it is telling the ECU that there is more air getting in than actually is and less fuel is consequently injected.

Any other suggestions? :mumbles:

reply
 

Hey there. Ive got a 1997 S40 2.0i and ive got a hesitation when the engine's cold. Its almost as if the car has a slight misfire. If you give the car more revs i seems to go through it. Once the car has warmed up the car seems to drive fine. The garage had the computer wired up to it and they couldn't find any problems. The car had a service recently so it's not the spark plugs or leads. Someone suggested it could be a faulty coolant temperature sensor. If you find out what your problem is id like to find out how you cured it. Many thanks Chris

Do you think the fault might be to do with the turbo going from overboost to low boost repeatedly, causing a judder feel? Does it feel like that do you think? Possibly when they fitted the turbo they did not set the wastegate link correctly... seems weird that the problem has occurred since then (so it is not the same problems as before, but has come since all the big work?) So I was trying to think if they messed it up somehow.

Pete

From what you have told us, I would say that your problem is something different, for a start your car is not turbocharged and not a diesel, and your problem only happens when car is cold. It could be worth you changing the coolant sensor, it is quite simple and cheap. Your symptoms could be explained by the ECU believing the engine is warmer than it is. A pity the garage didn't run a real time analysis of the engine temperature as told to the ECU, that might have given more clues. Does it idle a bit duff when cold as well?

Pete

Hessitation
 

Check the plugs and re-adjust the gaps on them as incorrect gaps will cause hessitation. Check coolant sensor also security of plug leads etc.

Charlotte

I'm not sure if your reply was to me or cpiddy, but I don't have any spark plugs!

I'll check the coolant sensor, but I don't think it's that, it's more of a fuel/air delivery issue I think.

It could be, especially since it only happens at a particular rpm and in all gears. I'm not sure if it only happens when the engine is warm and therefore off-choke. I'll have to give that a go and see what happens.
Is it easy to adjust the wastegate link myself or am I best to get a garage to have a look?

I also think it is slightly down on power and up on fuel consumption as well, especially when accelerating. I used to get no less than 15mpg on the instant readout, even when pressing on, but I saw 11 today and I wasn't even using full throttle. :hissyfit:

Yeah Charlotte is replying to cpiddy must be, I wouldn't bother checking the CTS I don't think yours is anything to do with that.

How long have you had it back since they did the work? The ECU might take a while to re-learn the engine so things like intermittent fuel mpg might not be realistic for a bit.

If the wategate linkage is like the T4 then it is easy to adjust. Do you have VADIS? The "check" measurement is documented in there. But I think the thing is just to make sure the wastegate is closed when engine off type thing. To adjust, on my car, you remove the heatshield so you can see the link arm and then you have to slacken the locknut (9mm open ended spanner I think it was), remove the clip and lift the arm carefully off the wastegate and then turn the free end of the arm (grip the other so it doesn't turn) either clockwise to shorten or anti-clock to lengthn. Here's a picture of mine, the arrows were to do with a problem I was having but it gives you an idea of what you are looking at: http://www.volvoclub.org.uk/photopos...500&ppuser=568

Other turbo probs could be the solenoid thing which controls the wastegate boost valve. Again assuming your car is like mine from a turbo perspective.

Pete

I've had it back over 3 weeks now, so it's had a fair old chance to re-adjust!

Yeah, I do have a copy of VADIS, I hadn't even thought of looking at it, to be honest, cheers!

Sounds easy, but I'm sure it's not! Turbos are a new thing to me, but I'm pretty good with mechanical stuff in general if I can get my head round the idea first!

I'll bare that in mind as well, could it be that the escaping air noise as the car is just coming onto boost that I reported way back in April is a badly adjusted or broken wastegate?

I'm also inclined to think you're right about it overboosting as well. I'll speak to the people who did my remap for me and see what they say. It might be worth me going back to get it remapped again now that I have a new turbo.

Andy

No believe me it is easy, try taking off the heatshield so you can see what's involved.

I've gonna go and do same thing to mine too, in a minute when it cools down a bit, maybe I'll send photos.

Why? Well I know it is hot etc. and mine has only done 50 miles since battery last disconnected, but it feels low on boost again poxy thing. I wonder if some of the exhaust nuts might need re-torquing. I hope my "custom wastegate" hasn't fallen off. Probably just me being picky and car trying to learn how I drive it again, we'll see.

Pete