I have been experiencing harsh downshifting when accelerating to pass. It used to only happen when cruising at 50ish. I took the car in to the local volvo dealer and they did some reprogramming download of the transmission thing. Not sure what it was about but it helped for a while. Now, however, it does the harsh shudder downshift at most high speeds 50, 70, etc.

Is this normal for automatic transmissions?

The car also has a serious backfire problem which 3 different dealers were unable to fix/solve. It used to only do it when stopped (at lights or stop signs mainly) and now it does it when accelerating as well. It is very embarrassing to be sitting in this lovely "fancy luxury" car while it is backfiring and the dealers have no clue.

Any help will be greatly appreciated.

Hi Ralph,

One other item that came to mind is the backfire. Are you sure it is a backfire and not a sudden engine stop? A bad crankshaft sensor can cause the engine to stop running for a split second. When this occurs the entire car will shutter and may feel like a back fire.

Steven---

The car does not shudder at all while backfiring. Only when shifting. The backfire noise is a muffled pop like sound coming from somewhere in the back of the car. Sometimes it is just one, sometimes a series of no more then three. It isn't a violent thing. My wife heard it while outside the car and she thought it sounded like it came from the midsection, not the tail end. Sometimes it sounds like it is on the right side, sometimes the left side. (when two happen, it sounds like that, one right, one left). It used to only happen after coming to a stop, but now it happens when accelerating as well. Sometimes it happens a lot, sometimes not at all during the day. But on most days it does backfire or make that noise at least once.

It is awful annoying though.

Ralph

Hi Ralph,

I am not entirely sure you are having a problem with old fashion backfire. Backfire is caused when the timing is advance too far back (i.e. the spark plug is set off when the exhaust value is opening, hence the explosion occurs in the exhaust manifold). The symptoms are poor acceleration and a backfire when you let your foot off of the gas. You are saying that you are getting backfire both when you are accelerating and de-accelerating and if I read you correctly when sitting at a traffic light.

Here is what I recommend:

When you take your car to the shop tell the Dealer's Service Rep that you are hearing a noise and describe the noise. DO NOT PRE-DIAGNOSE THE PROBLEM. Say nothing of the backfire. Don't even use the work backfire. Say things like bang, bump and so on. Let the technician diagnose the problem. Keep your description vague but let it be known you are having a problem. This will force the technician to look at everything not just the engine. Let them keep the car for a few days so that they can drive it around to see for themselves. If this does not solve your problem ask the dealer to set up an appointment with a Volvo after Market Sale Representative. He/She can help you get this problem fixed. Don't give up!

My feelings on what your problem can be are listed below:

1) Crank Shaft sensor (Volvo calls it an Engine RPM Sensor) not working correctly. I checked over the weekend on where and how this sensor is mounted. Volvo used a good tough designed on this component.

2) Possible wire/connector problem. Electrical issues are a pain to figure out!

3) Stuck open fuel injector causing too much gas being injected into one cylinder. Which can cause unburned gas making it to the exhaust system and hence detonating.

4) Timing belt not aligned. Jumped a tooth. This will cause the timing to be off.

5) Possible broken muffler/tail pipe hanger (made out of rubber). Causing the muffler/tail pipe to hit drive shaft/body.

6) Broken/missing drive train bolt/nut causing the drive train to hit the body.

7) Broken engine mount (upper only) causing the engine to hit the body (this has happen to me twice).

Let me know what happens.

Good Luck,

Steven---

Hi Ralph,

Your problem sounds like the crankshaft sensor could be position incorrectly (shaken lose due to Engine vibration). Or the sensor is going bad.

This sensor is required for the ignition system to work correctly. The crankshaft sensor is use to tell the computer where the engine pistons are located with respect to engine stroke (Power, Exhaust, Intake, Compression) so the engine computer can calculate the spark plug timing. The only time the computer diagnostic system can detect a bad crankshaft sensor is when the sensor misses the timing mark located somewhere on the crankshaft (sometimes the manufacture will locate the crankshaft sensor on the camshaft, I am not yet familiar with Volvo engine sensor locations). If the computer diagnostic system can not detect a fault/bad sensor then it is up the technician to diagnose the problem the old fashion way by gut feel and do some experiments (i.e. replace the sensor and see what happens and so on…).

A bad temperature sensor could cause the timing to go out. The sensor could be telling the engine computer that the engine is cold when the engine is hot. This would make the computer run the engine with a rich gas mixture and could cause a backfire. This would also account for some extra power. An old carbon monoxide commando trick it to install a switch/resistor across the engine temperature sensor telling the computer that the engine is cold when the engine is actually HOT, hence you now have a rich mixture and WHAM an extra 50hp! Burn them tires! Check your gas mileage. If the gas mileage has gone way down then this could be your problem. Also a stuck fuel injector could emulate this problem. A stuck fuel injector is easy to detect.

One only other explanation I can think of at this time is a possible bad wire/connector. I doubt this is a problem. Volvo did a good job on the wiring. However, it should be looked at.

I agree with Eric G. Your Dealer should fix this with no excuses! If the Dealer can not fix the problem then contact Volvo After Market Sales Representative. He/She will get it fixed for you.

And one last note. Driving a car around with this kind of problem can damage the Catalytic Converter! A Catalytic Converter is an expensive item to replace so get this fix as soon as possible. If you need more help let me know some more details and I will see what I can dig up for you.

Good luck!

Steven---

"An old carbon monoxide commando trick it to

> install a switch/resistor across the engine temperature sensor

> telling the computer that the engine is cold when the engine is

> actually HOT, hence you now have a rich mixture and WHAM an extra

> 50hp! Burn them tires!"

Please tell me more... is it really 50hp? I don't plan on doing this to a XC.. maybe an old honda or acura.

Hi Nick,

Yep you are right it should work on an old Honda/Acura. However there are a few items you should know about up front.

1) It will destroy the Catalytic Converter!

2) You will need to improve the engine airflow. Both intake and exhaust.

3) It will suck up gas like there is no tomorrow!

4) It violates EPA regulations for a street car. However if you plan to go to the race track then it is ok.

In my youth (which was many a moon ago) I use to impress the ladies with a Pontiac Grand Prix Hot Rod. You know a Chevy 350 V8 with multi port injection dual exhaust; wide tires built up suspension and so on. One trick when drag racing was to hook up a switch/resistor across the engine temperature sensor. When you were on the street just cruising around you would have the temperature sensor switch in so everything worked as normal. When you were challenged you flip the switch and WHAM! The engine went from 275hp to 325hp. The computer was tricked into thinking that the engine was cold! The computer would then set a rich fuel mixture while the engine was hot. Since I had improved the exhaust (dual glass packs) and added an air dam I could tear a set of tires off the car with out even moving forward 1 inch!! MAN WHAT A FEELING!!!! AND WHAT A SMELL!!!!!!!!! Burned tire rubber WOW!!!!

If you are still interested let me know I will dig up the details.

Steven---

Yes! now I really wanna know more!! hehehe...would this work on a carb too? -Nickl13@aol.com

Yo Nick,

I will dig up the detail this week end. So give me a few days.

And, NO this will not work on a carbed car. Sorry.

Steven---

Thank you,

I have tried 2 dealers in the area, so far the reply was "unable to create sound at this time" so therefore nothing was done. I also got a distinct impression that they thought I was lying, which made me even more upset.

I have already called Volvo customer service to lodge a complaint and they said I should try yet another dealer so I am going to do that next week when I have a chance.

I love the car like crazy, but the customer service I have been getting makes me seriously displeased, as my parents own a Lexus and I see what type of service they get. (free full wash and wax whenever they take it in, etc)

Hopefully the third dealer is a charm.

Thank you again for all the great advice,

Ralph

Ralph,

For your harsh tranny downshifts, there is an actual TSB for this which is a complete transmission oil flush. They did it on mine. Look for a brownish color in your oil as it doesn't have the hydraulic properties anymore. The reprogramming thing will absolutely do nothing in my opinion.

As for the backfire.. I unfortunately have no good answer for such a new car. One thing for sure is that the firing and timing is electronically controlled in your vehicle (no distributor/cap, no rotor, no plug wires) so there may be something wrong with the coil packs (I'm only assuming here). Other than that, I'd start suspecting the fuel injection system. Did your dealer checked for codes? Did they call the tech hotline?

Good luck. Hey, if I were in your shoes and none of the dealers are able to fix my problems, I'd ask a Volvo rep to have a serious look at the XC and give him a reasonable deadline to get everything fixed. Otherwise.. lemon law. This is totally unacceptable on a 2000.

lmao... What kind of gas are you using? bang! bang! lol

We have tried every type and range of gas, no difference, same amount of backfiring if it is supreme or regular octane. Even changed brands (was exxon, tried shell, also chevron, etc...) Gave up logging it whenever it happened cause there was no rhyme or reason.