96 volvo 960 runs perfect for 20 minutes than MAJOR engine vibration

[516volvo]

We came across rather odd problem on our 1996 volvo 960 with only 130k original miles (mileage is accurate we are the only owners).

Vehicle starts and runs perfect (no misfires, no shaking). BUT after EXACTLY 20 minutes, the engine vibration get to the point that the car is impossible to drive. Also the catalytic converter overheats BUT no error code from 02 sensors. I have to time the trip to make stops every 15 minutes. Wait about an hour for the car to "cool down". When start it again everything works perfect for another 20 minutes. OBDII shows 3 codes: p0302, p0304, p0410.

It is worth to note that p0410 has been there for many years, but it never affected car's performance.

We have recently replaced intake manifold gasket. The reason for repair - misfires in cylinder 3 and air leak around intake gasket. Prior to the repair the car did have a rough idle, but it was running fine at higher engine RPMS. Along with the intake gasket we replaced:
- rubber sleeves and clamps
- oil separator and hoses that attach to it
- throttle body gasket

The following parts have also been replaced but did not yield any results:
- ignition module (for odd and even cylinders)
- spark plugs
- MAF sensor

All injectors were tested with multimeter. One injector was replaced due to odd reading.
Engine compression was tested several times. Everything appears to be fine.

Perhaps someone out there can point us in the right direction. While the car is great, it is becoming a money pit & it is not really usable at this point.

Is it possible that the problem is caused by malfunctioning 02 sensor or possibly bad cam shaft position sensor?

[516volvo]

Today we had an unfortunate development. The car was parked overnight, when I tried to start it in the morning it was idling VERY rough. To the point I was afraid to drive it at all. Tried revving up engine a bit - nothing helped. Ended up turning the car off. Trying to figure out the next step.

Surprisingly, only one code showed up this time p0302. But it felt like 2 or more cylinders have been misfiring or "dead".

[thefisch]

My coil plugs are in bad shape and have gotten loose leading to misfires. Have you checked those?

[516volvo]

Purchased 2 new ignition coils (aftermarket). Installed them on cylinder 1&3 (cylinder 3 was coming up as misfiring prior to intake manifold gasket replacement). Had 0 effect.

I did visual inspection of all coils. They seem to be in pretty good shape. Tomorrow will remove coils again and test them with the multimeter. If anyone has instructions on proper way to test these ignition coils - that would be greatly appreciated.

I think, we are down to 4 major suspects:
- defective ignition coil wiring (either a short or a broken wire somewhere in that harness). Not looking forward to this repair.
- crankshaft position sensor and camshaft position sensor. Since I already bought new ones, might as well give it a try.
- oxygen sensor. This requires short drive to the nearest mechanic. So I hope, I can get the car back to running for 20 minutes.
- faulty Engine Control Module.

Can anyone recommend affordable OBDII scanner that can do more than just read and reset codes. I have basic OBDII scanner. It is great for reading and erasing codes, but I have no way to test various vehicle systems. Scanners I saw online say that they work with 1999 and newer vehicles. Not sure, if there is actually a difference between 1999 and 1996 car when it comes to OBDII system.

[516volvo]

To answer coil plug question (sorry forgot): I bought a set of 6 new coil plugs and had a local shop replace all plugs. For some reason, instead of just replacing plastic plug (the piece that comes apart) they spliced into original harness. It is very possible that they screwed up somewhere along the way and now I am paying the price for this.

[jimmy57]

If you have a P0302 code then replace coil on cylinder 2. That code is for cylinder number, not a cylinder count. The engine control module pinpoints the exact cylinder when the misfire occurs continuously on a cylinder for roughly a second. If the system detect irregular misfires that happen randomly then the code is P0300

[516volvo]

Turns out I was freaking out over nothing . The cause of misfires and other problems were indeed in the ignition coil plugs. As I mentioned before, I did purchase new coil plugs from Amazon (obviously made in China). Turns out 3 out 6 were purely assembled. The wire was not crimped properly. As the temp inside the engine compartment got to the certain point, metal expanded plugs expanded and lost contact with the wire. That in turn led to misfires, etc.

The electrician in the local shop was able to fix this in a matter of 20 minutes. He even zipped tied the plugs to the coils to be on the safe side.

If you decide to replace ignition coil plugs, first of all make sure the wire is crimped properly. You can do it at home using regular pliers. This would save you WHOLE LOT of time later on and, possibly, even save you money.

Now I have a new predicament: I need to find a plastic gear shifter. Mine cracked the other day. I looked online. New shifters cost over $120 - 160. This seems insane for a piece of plastic in 28 year old car. If anyone knows where to find this part for a reasonable price, I would appreciate it very much. If you have 960 parts car and can sell me this part PLEASE let me know.

[volvolugnut]

Can you post a photo of the shifter knob? It may be the same as 240/740/940.
volvolugnut

[516volvo]

Here is picture of the shifter on my 960. Volvo part # 6843471

I believe, it is different from 240/740 as those shifters have a button on the top of the shifter. On 960 the button is located in the front (facing the radio).

Later 940 models might have the same shifter. Have not seen too many of these cars.