Reporting you as follows..

I placed an order for timing belt kit for timing belt check up with my mechanic on my car problem.

This morning, only to check and just because it is easy to do, I replaced the AMM on this car with the extra AMM I had. I was not even sure whether this reserve AMM was a good one but I knew for sure that it had a different performance characteristic.

Then something good happened.

- The engine was suddenly making a healthy sound; not as much noisy
- picked up speed normally, quick when I put on accelerator
- Pressing the overdrive button, picked up speed as well

So it seems that the faulty AMM may have been the reason. But I will keep you informed if anything changed. (I will be diligently replacing air box thermostat which might have affected my AMMs on my 240 cars. On my other 240, once in a while problem of car engine stalling disappeared when I replaced AMM.)

Thanks everyone for comments!!

Realizing that there is "more to the story"...

If: Ignition parts are all verifiably clean and in good condition

If: Throttle is clean

If: ECU's are all working equally after swapping between identical happy and not-happy cars...

If: Timing belt proves to be on the correct tooth (I have seen good ones jump one or 2 due to deteriorating timing covers dropping bits into the gears)

I would look at 2 things:

Inlet air hose from Air Mass Meter to throttle body- cracks do develop and sometimes only open up when engine moves around on its mounts (i.e. under acceleration)

Or Fuel pressure regulator. The entire mixture depends on this functioning correctly. Often they make the engine too rich or hard to start but other failure modes are possible. It's 20+ years old. Good replacement part to throw at it. As always, check the vacuum line for gasoline in the line- that would be proof of failure.

--Rob

Did you try swapping the ECU from the car that runs great? The other 91?

Another cause of pinging is a hot running engine. Any overheating?

Thank you everyone for the replies.

This happened when my ECU failed a year ago. Then I went to the junk yard and picked up ECUs (2 of them).

I wanted to confirm that I put in the right ECU. So just now I called the Volvo dealer. Volvo told me that my correct ECU is:

- part number 5003780 if I have EGR
- part number 5003894 if I do not have EGR.

How can I tell whether I have EGR or not?

On the car, my ECU label says:
JETRONIC
91466 P01
Bosch
0 280 000 933
made in spain
AJ AJ

I have one extra
JETRONIC
3501687
Bosch
0 280 000 556
Made in germany
3 501 687

For your information, I also tried to put in fuel injector cleaner but did not change anything.


According to the record, timing belt was changed at 40,000 miles in 2008. I bought the about 2 years ago. Now the car has 65,000 miles.

Thanks again. After checking whether I have a correct ECU, then I plan to take the car to mechanic for timing belt check. Will let you know.

It sure sounds like the Timing is off. That would be from the Belt being off a tooth. The marble sound is Ignition Pinging (knocking).

Did you recently have the Timing Belt changed on this car? It's kind of easy for the Tensioner to take up on the Cam sprocket side and move it a tooth.

I'm not sure the knock sensor would even come in to play if you are running on regular gas and the Timing Belt was on correctly.

--
'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html http://cleanflametrap.com/tony/

If it's making that clattering (marble on floor sound) when you're giving it gas under load, that indicates "pinging". I suspect the timing may be too far advanced (if not ECU controlled), and/or the fuel quality/octaine is too low. You could have dirty fuel injectors, a clogged or failing cat (as suggested already), failing O2 sensor, or your ECU is on the fritz.

To start, I would run some fuel injector cleaner through it and put a good tank of high octane gas as well, see if that changes things.

I would check your cam timing like Art said an if that is ok, look for clogged cat.

Too easy to assume you mean ignition timing. Like Ken's reply guesses, your 91's ignition timing is not intended to be adjusted.

But, valve timing will give you the same result if one cog out of time. I bought a 91 similarly sluggish and found the belt was one tooth off.

The easiest way to check is by pulling the upper timing belt cover and rotating the crank using a 15/16" socket until the cam sprocket mark lines up with the reference. Then look at the timing mark on the crank pulley. If not lined up, you've got some more work to do regardless of the reason.
--
Art Benstein near Baltimore

I'm not into working out. My philosophy: No pain; no pain.

Sometime around the model year of your car (a '91), Volvo changed from a system using the distributor to adjust ignition timing to a system in which the ECU makes all timing decisions (advance or retard) -- along with it, it introduced a new sensor (to tell the ECU the crankshaft's angle) using a magnetic pickup on the bell housing above the flywheel called a CPS (Crankshaft Position Sensor). More explanation at the end of this.

Honestly, I'm not sure which model year it changed -- maybe '90, maybe your '91. If you have the "old-fashioned" distributor, yes, you can adjust your timing (but you should adhere to the instructions using a timing light -- don't advance it by trial and error).

If you have the new system, it's impossible to change your ignition timing. As I wrote above, the timing is entirely under the control of the ECU. Even if you manage to somehow circumvent the stopper that ordinarily keeps your distributor from being rotated (this stopper was added along with the new system), that will not change your timing at all. But then again, your timing can't be wrong, so you'll have to look for another cause of your problem.
___________________________

FYI, the old-fashioned distributor (sometimes) had an air pressure/vacuum diaphragm to use manifold pressure (for load) and centrifugal weights and springs, all to adjust timing based on the need of the engine, as well as (usually) some "hall pickup" to tell the ECU or ignition computer where the crankshaft is. And you could adjust the "basic" ignition timing by loosening a clamp and rotating the distributor body, which would change the timing of the spark in relation to the crankshaft (actually if you want to be a stickler for details, to the intermediate shaft on red-blocks, which are tied to the crankshaft by the timing belt).

But with the new system, the distributor is mostly empty. No vacuum diaphragm, nor any centrifugal weights and springs! Nor are there any "hall pickups" or other devices to convey crankshaft position. Only the rotor remains inside, because the only job left for the distributor is, literally, to direct the spark energy to the right spark plugs. And it's locked in place, so it cannot be rotated.
All of the distributor's old tasks such as deciding the amount of advance or retardation, measuring engine load (based on manifold pressure), and rpm, and even the crankshaft's position, is measured by other sensors, and all of that information goes to the ECU. It alone then decides when to fire each spark plug, based on algorhythms that take all those factors (not to mentions others such as coolant temperature, etc.) into account.
If you did try to turn the distributor's body, all you would wind up doing is interfere with the overlap of the rotor and the distributor cap's electrical contacts.

Hope this explains things.

Good luck.