Engine: 850 T5/R Hesitation in 4th only.

[andy m]

Hello,

Have a 96 850 T5

A couple of times the following has happened.

When accelerating hard on the motorway in 4th the engine power cuts / misfires at 4000 rpm.

It does not happen in 1st, 2nd or 3rd and I have not been brave enough to try it in 5th (4000rpm in 5th = faster than the speed limit)

The card has been a bit lumpy recently on start up, but this goes after 10 sec.

Have changed the HT lead 20,000 miles ago. No loss of oil or coolant.

I am thinking distributor cap and rotor arm or is there any other possibilities.

Also, why would it only occur in 4th and poss 5th only?

Thanks in advance,

Andy.

[Peteodell]

When was the last time you changed the spark plugs? Does your car run rich at all? The spark plugs could be coking up when you are cruising at motorway speeds and then when you are accelerating hard they are causing the lumpy running until they have burnt off the crap...

You can usually prove this... Next time it happens, slip the car into neutral and rev and hold at 5-6000 rpm for 5 secs or so... then put it in gear again and try again... If it no longer does it, its probably the plugs...

Pete

[andy m]

Hello,

Thanks for the suggestion. Tried that as suggested, but still doing it.

To update. It is now doing it in 3rd as well!!!
I have noticed it only seems to happend when the outside air temp is 1 degree or below.
Also it only happend with the foot right to floor. If I accelerate slowly then no prob and it is as if it is misfireing hard. I get a massive lurch as if the whole engine dies, not just one cylinder being a bit lumpy.

Any ideas.

Thanks,

Andy.

[ovlov25]

A Stage '0' service sorts most things, otherwise it might be worthwhile to check the spark plugs and give Jimanthan on this forum a shout about his injector cleaning service.

My 2 pence worth would be on the spark plugs being past their best.

[andy m]

Thanks for the suggestion. Plugs last done at correct interval. Now coming up to 157000 miles. I can remember if it is every 30000 for plugs or 40000?

Excuse my ignorance, but what is a stage 0 service?

Thanks,

Andy.

[Peteodell]

If you do a search on this forum, you should find a thread on a Stage 0 service explining what has to be done...

I had a very similar problem to yours and carried out a service over the weekend, changing Plugs(Geniune Volvo) oil,air and fuel filter along with an oil change... Upon taking the car out agian the problem had gone and it was pulling better than ever..

Plugs do last longer these days than they use to, but when I took mine out you could see that they were past their best!! Please bear in mind that if you have not owned the car that long, that you cant guarentee that the plugs were changed on a service because they last longer these days people tend to leave them....

I would suggest giving the car a full service as it is pretty easy to do and see what happens... I was amazed at the difference it made....

Pete

[andy m]

Thanks for the replys. I had a look through my service history. (I have had the car since 100000 miles)

Cap rotor and leads were changed on 120K as were the plugs. However my local garage did not replace the plugs at 150K. So I suspect it will be the plugs. Will also have words with the garage!!

Cheers,

Andy.

[Peteodell]

Hope it solves the problem mate.... Let us know how you get on....

[andy m]

Hello all,

Just an update.

The car went to the garage today. The problem appears to be a split in a hose in the turbo causing it to over boost. The car was cutting out as the boost limiter thingy was cutting in. It only seemed to happen when it was cold as the denser air was causing more boost pressure hence the limiter would cut in.

The downside to fixing this is that the car is slower as it is not boosting as high :-(

Thanks for all the suggestions, thought you might like to know the outcome.

Cheers,

Andy.

[Peteodell]

Good to hear that you got it sorted....

Pete