1999 V70 T5 hesitation / Misfire

Help!

My 1999 V70 T5 (160 000 miles) has developed a "hesitation" when cruising between 60-90 MPH. It is most noticable when using cruise control and can be best described as a slight hesitation at very small throttle settings.

The problem has got worse over the last 8000 miles, it now has become noticable on general driving when using mild acceleration. If you hoof it then all is well!

I have changed the fuel filter, no change. The air filter, still no change. and finally the plugs, this caused a marked improvement in the misfire; however, it did not completly cure the problem and it is starting to get worse again. There are no warning lights showing on the dash.

I have got to the stage where I may well have to resort to taking the car to the local main dealer which will be a shock as I have maintained the car for the last 50k miles.

Any advice gratfully accepted!

Cheers

David Harris

Hi David,

When were the HT leads, dizzy cap and rotor last replaced? If they haven't been replaced for some time then it may be worth changing now to see if there's any improvement here.

Regards

Andy

This car has coil packs, so no dizzy cap or rotor. Could be the insulation breaking down in the coil pack. Did you put the right plugs in and is the gap correct?

Adam.

Adam

The last set of plugs were NGK and gapped correctly, the misfire did start during the time these plugs were in the car; however, I have recently changed them for origional Volvo items (gapped correctly according to the Haynes values). This did make a hugh improvement; however, the misfire is stuill there.

If the the misfire was ona normally aspirated car I would diagnose the problem as crap in the carb and a slightly blocked jet.

The only other possible sign is that the black covering tube of the LT leads going to the coil packs is starting to become brittle and break. I have looked closely at the cables inside and they are in good condition.

I cannot think of what else I can do at home without access to a computer diagnostic set up? All suggestions very gratfully accepted.

Cheers

David

[Chris_Rogers]

I take it this is an electronic throttle (fly by wire) car.

Is it a misfire or 'hunting' while cruising.

If it's hunting I would think the problem is worn throttle position tracks in the throttle control module.

If it's done 160k without the throttle module being changed it's done well, they seem to manage only about 50k.

The cure seems to be a new throttle body at about £600, this has to be done at the dealer as a software download is required.

www.bba-reman.com may be able to repair your old one.

Thankd for the advice. You are cottect, it is a "fly by wire" throttle. Is it worth me dismanteling the throttle control module and cleaning it before I shell out the £600+? If so any advice?

Chers

David

[Chris_Rogers]

Well if you want to have a go here's a link to show how:

http://www.rally-photos.co.uk/volvo/tcm/

Chris

Removed the throttle control module, below the inlet manifold. A bit of a pain to get at but not too difficult.

On the inlet side of the butterfly there was a thin layer of what felt like a cross between graphite grease and carbon deposit on the inlet tract. It took some time to clean with petrol and a paint brush.

I also took appart the electronics on the sides of the unit, what a mistake! It took several hours to re solder them back together!

However, happy ending to story, the misfire is cured. In future I will just clean out the inlet tract on the module as this appears to have done the trick and leave the electronics alone!

Thanks again for the help.

Cheers

David

[Chris_Rogers]

Well done!

I've not had to take mine apart yet, (cross fingers).
I'll bear what you say in mind when it comes to it, I'll clean the throttle plate first.

What sort of state were the carbon tracks in, any wear?

I do know my car has had a new throttle body fitted at some point it's now got 102k on it, 15k in the last four months. So I guess I'll be having to do some cleaning soon.

As with everything you learn by your mistakes!

I think it would be possible to remove the plastic inlet pipe that goes to the throttle body and clean it while in situ thereby not having to remove the inlet manifold/injectors etc. All you need to do is to be able to put a small try under the throttle body and slicce the inlet tract out with petrol and a cleaning rag or plastic pan scourer.

Good luck! I have just driven 500 miles any not a single misfire...hurrah!

Cheers

David