Model 245GL wagon

Engine: B23F or B230F (according to tag) with an "847" on the timing belt cover.

The engine pings under fairly light acceleration, making it a real pain to drive the car. We have tried different gas, short of the most premium grade. Another 1984 with the same engine we had before had no problems with regular gas with an octane rating of 86.

At first I thought that a mechanical advance system might be to blame until I found out there is no mechanical advance on these particular distributors. If I set the timing at 12 deg BTDC at idle, the engine advances to over what I would guess at 40+ degrees on the crankshaft at highway rpm.

I have checked the wiring back to the ignition control module and the wiring looks good here.

I looked at the vacuum module on the ignition control module and determined it has variable resistance according to the following short table

no vacuum 68 ohms

5" vacuum 93 ohms

10" vacuum 123 ohms (this is the idling value at roughly 7000’ of altitude where we live)

I am wondering what might be next. I have also replaced the knock sensor which now retards when the engine block is tapped above the oil filter boss area while idling. I thought this might fix the problem; it did not.

I have tried power timing the engine but it needs to be adjusted so far that I cannot start the car or keep it runnig when started from a cold engine.

I have looked at my partial set of Volvo manuals and a Haynes manual and I cannot find any other suggestions at this time.

Has anyone else have this problem before and discovered a solution?

So far, nobody has mentioned it so I will...

The EGR system is designed to lower burn temperature to inhibit the formation of oxides of nitrogen (NOx). It allowed manufacturers to program more agressive timing advance curves without detonation on lower octane fuels, ESPECIALLY at lighter loads where EGR has its greatest effect. Take away the cooling effect of the inert (non-combustable exhaust) gas in the cylinder without changing the advance curve (only an option with mechanical distributors) and you have exactly the problem you describe.

I'm not familiar with the exact setup on your 84, but to operate properly, the EGR valve should open partially under light engine load and further as you approach med load. At higher throttle is will start to close. This is NOT engine speed related which means you cannot simply pop the hood and open the throttle to check it - but if you observe the valve and *snap* the throttle open, you should see it move. It should be completely shut at idle.

Apply some sort of vacuum source to the valve while the engine is running and see if the valve holds vacuum and opens. With the valve opened, the engine should be idling VERY rough or die due to mixture dilution. If it doesn't, then it's probabably just the port/tube from the exhaust manifold that's blocked and in need of manual cleaning. A partly clogged passage can fool you into thinking it's clear but not allowing enough exhaust to pass to prevent pinging. Just confirm that opening the valve makes it run terrible at 1200-1500 RPM too.

If the passages seem to be clear then you may have to "tee" in a vacuum guage to the EGR hose and observe the it's getting vacuum while driving and go from there.

One thought if there's no vacuum - make sure the coolant is not running cold since the EGR is inhibited below 125°F coolant temp.

It sounds like you recently bought this car so check the emission certification label and see if it's qualified for high altitude (I call 1.25 miles in the sky high alt). That 10" manifold vacuum sounds awfully low and usually means a mechanical problem, but check with local shops to find out what normal readings are in your area. (This has nothing to do with being a Volvo, it's normally 18" Hg at sea level on ALL gasoline engines.) If it's lacking in power too, then make sure the the timing belt wasn't installed with the camshaft mark one tooth late. Improper engine calibration may actually be part of your problem.

There are a number of factors that can make an engine ping. Unfortunately, our high-compression B23Fs are very easily provoked into doing it. I had a similar knocking problem on my '83 240 B23F, and it was a vacuum leak. Search around every seal, junction, gasket and hose from the AMM to the block, including the fuel injectors and the brake master cylinder/booster junction (ask how I know :) ) using a length of hose placed to your ear.

Also, did you torque your new knock sensor down to 7-8ft-lbs? This figure is critical to the sensitivity of the sensor. Too tight, and you'll be retarding all the time. Too loose, you'll get excessive ping.

The suggestions about carbon build-up are also good. It may also help to run a bottle of Techron or that BG-44K stuff that cleans your injectors, take it out on the highway, and 'burn out the gunk' with some sustained high-rpm blasting. Be sure you change your oil after using one of these products.