99 Volvo c70- Jolt/buck under heavy acceleration

Dstrongc70 · Post by **Dstrongc70** » 05 Nov 2015, 15:59

Hey guys I am having an issue with my 1999 Volvo c70 convertible and have no clue where to start. I work on cars(3rd year apprentice) but have never worked on a volvo. Any help or advice would be greatly appreciated!

My vehicle
1999 Volvo c70 convertible
2.3l high pressure turbo B52346
m56 manual tranny

Problem:
When pulling hard sometimes in 5th at highways speeds say going from 100-130km very fast to pass pretty much WOT, it will have a sudden jolt which stops almost all acceleration for about half a second it almost feels like a traction control problem but it even happens with STC off. This has always happened in such a fashion until today when i downshifted and tried to take off around a slight bend quick jolt loss of all acceleration and then normal pulling hard. Honestly the way it jolts or bucks for that half a second it makes you lurch forward in your seat, makes me nervous it is going to cause my clutch to explode. I have no idea where to start on this one.

Post by **abscate** » 05 Nov 2015, 16:12

On a 1999 you have coil on plug ignition so the ignition system is simple, but we need to know where the engine is at.

What's the maintenance history on this car? If it's been driven like a Toyota it will have lots of things past service life that can all contribute to a problem like this.

Keywords: it's been running great for three years, now all of a sudden....

Dstrongc70 · Post by **Dstrongc70** » 05 Nov 2015, 16:19

I purchased the car about a month and a half ago. Has 164,000 Kms on it. Has been running perfectly fine except for this issue, as well as a rough fluctuating idle on first start up about once a week it will bounce from about 1200k-2000k for 20 or seconds. Previous owner did the abs module, and did some slight mods like lowering,short shift sway bars and strutbar. I have to do the timing belt, clutch and PCV. already did plugs. Clutch never slips and i have tested the pcv with methods ive read about on here. ive tried to tell you as much as i know please feel free to ask any questions

Alecw81 · Post by **Alecw81** » 05 Nov 2015, 16:21

loose throttle cable?

Dstrongc70 · Post by **Dstrongc70** » 05 Nov 2015, 16:22

It is fly by wire

jcdillin · Post by **jcdillin** » 05 Nov 2015, 16:45

Sounds like an ETM module, has it been replaced?

Dstrongc70 · Post by **Dstrongc70** » 05 Nov 2015, 16:53

No that is on my to do list currently, i live about 20 mins from xemodex tho this was one of the last things i was planning on doing tho

Post by **abscate** » 05 Nov 2015, 17:42

Okay! New car.

It's time to pull out the spark plugs and see what shape they are in. A miss under heavy load is likely an ignition problem, but that rough idle is bad.

The 1999 are electronically flow and tend to be digital. They either run great or ask you for 1000 USD

And before you invest into mods, do a compression test on that engine and make sure it's good

Dstrongc70 · Post by **Dstrongc70** » 17 Nov 2015, 15:32

what is proper compression and allowable compression variance on these vehicles, and are there any special ways of doing it Ive heard that you can mess up the results if not done properly, and i also changed the spark plugs out already. My engine light doesn't blink as if it is a misfire nor does traction control. No engine,ETM, or traction control codes are present. It is literally a millisecond lurch of the car and it is back to normal, would a restriction from the throttle plate suddenly closing under heavy load cause the car to buck like that?

Post by **RussB** » 17 Nov 2015, 19:31

11 bar (159psi) to 13 bar (189psi) , with a 2 bar (29psi) maximum difference between high and low, so says my Haynes manual