96 850 T5 misfire when warm - Urgent

[boosticus]

Hi, symptoms are as follows:

- Car is fine when cold, runs normally, albeit poor MPG
- Car is fine after even 15 - 20 minutes after starting from cold however shortly after this there is a misfire that seems to disappear under hard acceleration.

average mpg is down from about 23 normally to 13/14. It appears to be over fueling, replaced the plugs today and the old ones that are about a year old were badly fouled with sooty deposits.

Does anyone have any ideas what the problem is? There are no codes to be read.

Compression is also good- was tested 4 or 5 months ago for an unrelated issue.

[grnmachine02]

Do you have access to something that can read sensor values? Friend of mine had similar symptoms and his coolant temp sensor was reading in the negative numbers.

[TrickMick]

Originally Posted by grnmachine02

Do you have access to something that can read sensor values? Friend of mine had similar symptoms and his coolant temp sensor was reading in the negative numbers.

^^^^^...have done several *nasty* temp sensors for just the
"symptomology" your car is exhibiting...can't hurt to have a looksee!

[mtd240]

Relevant thread:

http://www.matthewsvolvosite.com/for...hp?f=1&t=50124

[boosticus]

So coolant temperature sensor is likely to be the issue.. Not sure if relevant but in-car temperature gauge appears to act normally? + Seems to start up OK when warm

[grnmachine02]

Originally Posted by boosticus

So coolant temperature sensor is likely to be the issue.. Not sure if relevant but in-car temperature gauge appears to act normally? + Seems to start up OK when warm

I'm not 100% on this so make sure you double check before you start shotgunning parts at the car. Some models actually had 2 sensors. One was for the gauge, and the other actually sent the signal to the ECM. I don't know if this applies to the 850 or not however.

[TrickMick]

Originally Posted by grnmachine02

I'm not 100% on this so make sure you double check before you start shotgunning parts at the car. Some models actually had 2 sensors. One was for the gauge, and the other actually sent the signal to the ECM. I don't know if this applies to the 850 or not however.

I believe that this is a "twofer"...signal from ECU informs the cluster and
processes the info for the fuel management at the same time...

CHECK THE CONNECTOR carefully before you get $pendy....

[Janspeed]

Originally Posted by boosticus

Not sure if relevant but in-car temperature gauge appears to act normally?

never trust Volvo temp gauges. They seem to be designed to stay dead in the middle except when the engine is either ice-cold or red-friggin-cookin'-hot.
Apperantly it's a feature so the gauge doesn't freak out the driver when the engine gets a bit hotter under heavy load.