1986 740 GLE B230F Ignition Timing Issue

[Kmaniac in California USA]

Greetings All:

Hopefully someone else has experienced this same issue and can point me in the right direction.

Today I took my trusty Volvo to the smog test center for California's biannual smog test. The poor thing failed. The biggest reason for failure was that the ignition timing was hovering around 40 degrees BTDC instead of the specified 12 degrees BTDC. I have not touched the distributor in the four years and 35,000 miles the car has been in my stable. It appears that something is telling the distributor to keep the timing advanced. Does anyone have any idea where I should look to find the culprit of this issue. Any advice would be greatly appreciated.

[wojeepster]

the ecu listens to the knock sensor and advances the timing until it hears knock and then backs off 5 degrees, it then slowly advances again until it again hears knock and backs off 2 degrees. It may not do this at idle when the throttle position sensor closes it makes a microswitch. So I would slowly close throttle on throttle body and see if you hear audible click, if not clean throttle body or adjust throttle position sensor until you hear audible click. If this does not help maybe your knock sensor is inoperable.

[Kmaniac in California USA]

OK, I am confused now.

First, I did check the throttle switch and it is still clicking, just like it did the last time a adjusted it.

My Haynes manual has been helpful, but to a point. It refers to a coolant sensor that tells the computer when the engine is cold or hot and advances the timing when the engine is cold. It also talks about the knock sensor. Looking at my engine, I could only find three temperature sensors; one on the radiator that appears to control the cooling fan; one on the head below the intake positioned at #2 cylinder that has a single lead (I think this is the temperature gauge sending unit); and a third on the head below the intake positioned at #3 cylinder that has two leads and locking connection, which I presume is the one that tells the computer to advance the ignition when cold. Looking around though, I can't seem to find the knock sensor. Can anyone tell me where the knock sensor is located??

By the way, the engine is a B230F (no turbo) with ZF automatic. The control unit (behind the right kick panel) is labeled "Jetronic". Any sage words of wisdom or advice would be welcomed.

[billofdurham]

The knock sensor is below the centre of the intake manifold.



Bill.

[Kmaniac in California USA]

Hi Bill:

Thank you for the picture. Unfortunately, it is quite small and I cannot blow it up with enough clarity to read it. Do you have something BIGGER??

[Kmaniac in California USA]

Now I'm even more confused!!!

Instead of taking the smog man's word that the timing was advanced as he said, I put a timing light on it myself. Sure enough, the timing was as advanced as he said. I had to look under the water pump pulley from the passenger side of the car to find the timing mark at idle. When I kicked open the throttle valve, the timing advanced even more, as much as 15 degrees. I did notice, though, that the timing mark would sometimes retard momentarily then move back up, indicating to me that the knock sensor was working. I closed the throttle and the timing returned to its lowest point, which is about 40 degrees BTDC.

What in the world would cause my timing to be so advanced at idle?? Could something have slipped inside the distributor? The distributor housing is NOT loose as I might expect. And I have never heard of a timing belt skipping a tooth or skipping so as to advance the cam timing.

I guess my next step is to adjust the distributor, if possible. Unlike my Big Block MoPar's the distributor on this car is quite hard to reach at the back of the head, next to the firewall. I guess I will have to let it cool down before I proceed.

Any additional tips anyone can offer would be greatly appreciated.

P.S. The car seems to run just fine in this condition.

[MadeInJapan]

Chris the "K MANIAC", just click on what Bill provided and it will blow up in a new window...then click on it again and it will be even BIGGER! These he posts are called "thumb nails." Certainly, though uncommon, your belt could have jumped a couple of teeth. If this happens, it's usually the tensioner to blame, so check it out. If it wasn't changed last belt change, it's worth changing...hey, but what do I know about RWD's...I typically only post about FWD's because that's all I've worked on until recently.

[Kmaniac in California USA]

Hey there, MIJ

Thanks for the input. Greetings from the "Left Coast".

Regarding the timing belt, the records I obtained when I purchased the car four years ago only went back 3 years previous to my purchase. From 168,000 miles then to 237,000 miles now, there is no record of timing belt replacement. I never worried about it since the B230F, as I understand, is a non-interference engine, but given the current circumstance, a new belt and tensioner may be in order. Is there a way to check the timing marks on this thing without tearing the front of the engine down to bare belt??

The pictures here and in my Haynes manual show slotted bolt holes on the distributor, which I presume will allow for distributor rotation and timing adjustment. But with the distributor facing the firewall and little space back there, any pointers on how to do this would be appreciated.

I will delve back into the Volvo in my next spare moments. Until then, any other words of advice from anyone would be helpful.

[MadeInJapan]

Hey there... To be brutally honest, I have no idea, but I need to find out the same thing eventually. I have the same engine in my 240.

[Kmaniac in California USA]

I must say that my frustration has now turned to fastination. I refuse to be outwitted by a machine!!! Besides, there are some valuable lessons to be learned here and whatever I learn I will pass on here for posterity. Still, I welcome any input along my journey.