1986 740 GLE B230F Ignition Timing Issue

[vegasjetskier]

Another thought is that if your engine has high miles the rings may not be sealing to the cylinder walls all that well, letting some engine oil be consumed and upping your smog readings. A couple ways to counteract that would be to change the oil to a heavyweight like 20W50 or add a can of STP.

[Kmaniac in California USA]

Well, I bit the bullet and bought a rebuilt distributor and, of course, installed it. However, the timing is still advanced!! But at least I have a good spare distributor now.

My next step will be to replace the ISC Valve. It seems that when I slowly disconnect one vacuum tap to this valve, the timing increases until the engine dies. Since this is a vacuum operated device, a leaking vacuum diaphram would most likely cause this condition at idle. I will keep you all posted on the progress.

[Kmaniac in California USA]

It has been a few weeks, but I finally returned my attention to my recalcitrent Volvo. I am embarassed to say that besides the distributor, I replaced the Idle Speed Controller and the Power Stage and still the timing was advanced. At that point, I parked the Volvo out back and moved on to other projects.

So, after a few weeks, I decided to replace the timing belt, which I knew needed replacement. Once I got the timing cover off, I discovered the root cause of my timing issue. With the crankshaft at TDC, both the camshaft and the auxiliary shaft sprockets were advanced by two teeth. It's hard to believe a timing belt would skip in this fashion, especially since all the belt teeth were still intact. I also found, too, that the tensioner pulley spun rough and the contact surface of the pulley looked as rough as a worn bearing. Needless to say, that pulley got replaced, too.

The poor car is not quite all together yet, but I should have it running this afternoon. I will post the final outcome after I finish.

[billofdurham]

Chris,

Thanks for the partial update. Why don't we check the obvious before going off at a tangent. This happened with my 240 many years ago and it completely slipped my mind. For being absent minded, I apologize.

Bill.

[Kmaniac in California USA]

Well, I did check the relative position of the camshaft timing mark previously by setting the crank at TDC and pulling back the upper timing cover enough to see the cam sprocket mark, which appeared normal at that time. Unfortunately, the alignment mark you have to match the cam sprocket to, is inside the timing belt case and I didn't see it the first time I checked. Now, if I had just replaced the timing belt earlier than I did, I could avoided this whole scenario. But hindsight is better than foresite, which I keep proving to myself every day. Hopefully, someone else can learn from my stumbling around.

[Kmaniac in California USA]

We have a saying in California:

"EUREKA, I found it!!!!"

...although it took replacing the timing belt to find the problem.

Kudo's to the previous poster who eluded to my ultimate problem.

I first replaced the timing belt by setting the crank using the timing mark on the pulley and aligning the marks on the cam and auxiliary sprockets with the marks on the timing case. Well, the car would not start!

The only thing I could deduce from this was that something was wrong with the crank pulley. My local Volvo parts store (rprusa) had one in stock. When I compared my crank pulley with a new one, I found the timing mark on my old pulley was 48 degrees advanced of the new pulley. Yep, the vibration dampener had failed and the pulley had shifted relative to the hub. With the new vibration dampener/pulley installed, along with the new timing belt and tensioner, the car runs beautiful, doesn't vibrate as much as it did before and the timing mark is in the right place. In fact, the engine has never run smoother in the four years I have owned the car!

The final test will be the smog inspector's verdict.

I hope this will be a lesson for someone else.

[billofdurham]

We have a saying in California:

"EUREKA, I found it!!!!"

In Greece you have to run naked down the street before you can say that.

Good to know it is not a train at the end of the tunnel but a geuine light.

Fingers now crossed for the smog test.

Bill.

[Kmaniac in California USA]

I need to bring you all up to date with my final update on my 740.

With the new timing belt and all the other new parts I didn't really need, the Volvo failed smog yet again with very high NOx. In fact, it was in the Gross Polluter range. I went so far as to replace the spark plugs and wires, with no change on the smog test #3. Next, I replaced the O2 sensor, which drop the NOx a little on smog test #4, but it was still a gross polluter. People I spoke with recommended changing the catalytic converter.

Now for a little history on my existing cat. When i bought the car in 2004, it had the original cat installed and it passed the last smog test with it. However, it began to rattle as something had come loose inside. So when the smog test was due in 2006, I replaced the original cat with an inexpensive aftermarket unit (to get rid of the rattle) and it passed just fine. So I didn't think I should have an issue with a two year old cat.

I took the Volvo to a local muffler shop to have the cat inspected. They commented that it looked small for the application. They also told me that the State of California was soon going to mandate the installation of replacement catalytic converters that met stricker smog standars starting in 2009. So I had the shop install one of these new cats on the Volvo. This unit was much bigger than the original.

As a back up measure, I replaced my existing AMM with one I retrived from a wrecking yard a couple years ago.

When I took the Volvo in for smog test #5, it passed. In fact, the test recorded "zero" residual O2, "zero" unburned HC, "zero" CO and "zero" NOx at both 15 and 25 mph. That new catalytic converter really made a difference. I must now have the cleanest Volvo in the State of California, if not the World.

Now that all this work has been completed, my Volvo is running the best it has ever run since I bought the car four years ago.

[billofdurham]

Thanks for the update.

Someone once told me that hard work pays off. In your case it has.

Bill.

[volvoman1980]

Hey, I don't know if this has been mentioned in this post(apologies if its covered I just quick browsed). I noticed on page 1 that it was mentioned that the ecu advances/retards the timing. It is the ICU (ignition control module-computer is located when you pull the driverside panel off that hides the accelerator pedal amplifier etc looking up by the brake pedal is a black box smaller usually plastic not metal like the ecu this is the icu computer). It advances/retards the SPARK that henceforth advances/retards the timing accordingly. It also controls the knock sensor and has a "link" to the ecu(fuel computer) that has to do with the coolant sensor etc.
You can adjust the distributor but normally its not the issue unless its been put off mark that will advance/retard timing a bit but be careful. The hall effect can be an issue but normally results in no start from what I was told (not sure on that one)
The knock sensor normally does not go bad(I have over 250k on my old orig sensor) but if its dirty or wires are degraded it will give a false signal, same with coolant sensor (if sensor is bad ecu goes to minus infinite degrees fahrenheit but that's gas related -floods alot). Try checking also the harnesses, especially main engine as they tend to DEGRADE especially 82(maybe earlier) to 1987 (they fixed wiring sometime in 1988 manufacture date). It was an experiment on Bosch's end and was a very bad one at that -liquid tape. Make sure nothing's crossed and test with meter thoroughly each wire for potential shorts. This can cause multiple major issues and safety concerns. I've seen many good volvos at the wreckers with obvious reason they were there (wiring) or replace. If it's fine good but keep an eye like an eagle on them (at least they could fry expensive computers)

Again sorry if these things have been previously covered but I just thought I'd add a few of my own experience tips. Moderators feel free to modify my post as appropriate if needed.

Good luck
Geoff