1986 740 GLE B230F Ignition Timing Issue

wojeepster · Post by **wojeepster** » 26 Sep 2008, 07:32

Your ignition timing is controlled by this ignition module mounted on the fender. You can learn more about it here:

http://www.megamanual.com/ms2/Bosch_124.htm

Perhaps your module is bad, or like you have already said the ecu is feeding it the wrong information. You can search the bosch number on fleabay. I bought a module for mine very reasonably. I think about $20

Post by **billofdurham** » 26 Sep 2008, 11:28

Very interesting article.

I think we can safely assume a typo error and the Volvo 740 2.2I GLE should be the 2.3 but why do they start at 1987? I can't find any difference between the '86 and the '87.

Bill.

Kmaniac in California USA · Post by **Kmaniac in California USA** » 27 Sep 2008, 10:05

There is a like at the end of the tunnel and it is definitely the TRAIN!!

I took my best educated guess and replaced the coolant sensor for the ECU. The old one broke during removal and didn't look that good. I restarted the car and the timing is still advanced, both hot and cold. So it looks like I'm back to square 1.

I guess I need to rethink this a liitle more. Again, any other advice would be appreciated.

Kmaniac in California USA · Post by **Kmaniac in California USA** » 28 Sep 2008, 08:51

I have been thinking about this problem and I am at my wits end.

As Bill stated before, there is no crank or cam sensor that tells the ECU the location of TDC. So it appears that the ECU assumes a relative TDC based on the fixed position of the Halls Effect sensor and the impulse wheel in the distributor. With the distributor is its most retarded adjustment, the timing mark at idle is still 20 to 30 degrees advanced of where it should be. Advancing the distributor only advances the timing mark at idle. When I open the throttle, the timing advances as I think it should for the load and engine speed inputs and retards back to the base timing when the throttle is closed. Unless there is something I missed in the system that is telling the ECU to advance the timing at idle, the only reason I can come up with for this condition is either the Halls Effect sensor is giving a signal too early or the impulse wheel has slipped (advanced) on the distributor shaft. I'm about ready to order an rebuilt distributor for this car, but at $250 USD, I would hate throw money in this direction without being absolutely sure this is the problem.

Can anybody think of something else to check before I go this route??

Post by **vegasjetskier** » 28 Sep 2008, 09:19

Can you lengthen the adjustment slots in the distributor enough to retard the timing 20 degrees?

Kmaniac in California USA · Post by **Kmaniac in California USA** » 28 Sep 2008, 09:55

There is a second adjustment slot on one side of the distributor that would allow for further retardation. But by using this second slot, the distributor is held in by one bolt. Anyway, tried using this second slot and installed the distributor at the full advance end of this slot. However, the engine just sputters a little and will not start with the distributor in this position. Maybe I could knock out the metal in between the two slots, but I would rather correct the real problem than just treat the symptom.

Post by **vegasjetskier** » 28 Sep 2008, 10:05

It might get you past your smog test, though. Then you can reset it to where it was since it was running OK (it was running OK there, right?).

Did they fail you on the smog test because the timing reading was too high? Or did the car produce excessive emissions and the thought is that the emissions were caused by the advanced timing?

Kmaniac in California USA · Post by **Kmaniac in California USA** » 28 Sep 2008, 12:49

The car failed smog for advanced timing AND excessive emissions (HC: measured 140 ppm @ 15 mph & 122 ppm @ 25 mph with maximum allowable of 133 ppm @ 15 mph and 108 ppm @ 25 mph/ NOx: measured 3122 ppm @ 15 mph & 2909 ppm @ 25 mph with maximum allowable of 1125 ppm @ 15 mph & 955 ppm @ 25 mph). I attemped to humor the smog mechanic by saying, "I least I know it's not a bad EGRvalve". The guy looked me straight in the eye and with all seriousness said, "It doesn't have an EGR valve". Well, ...duhhh, I already knew that and clearly he didn't have a sense of humor.

From my perspective, the high emissions are a direct result of the advanced timing. With my renewal just four days away, a temporary quick fix now would help in the short term. Time to get out a rat-tail file and see how much more adjustabiltiy I can add to the distributor.

Post by **vegasjetskier** » 28 Sep 2008, 13:11

Wow. You're really close on HC and way out on Nox.

A trick that someone I know used to use is to run the fuel tank down to about 1/4 full. Go to the drugstore and buy a couple quarts of rubbing alcohol. Try to get 70% alcohol or better. The higher the % the better it will work. Pour the alcohol into the gas tank. Drive around a few minutes to get the alcohol mixed in and up to the injectors, then go straight to the smog test. The alcohol acts as an oxygenator and reduces the emissions. I saw one test on a car (not a Volvo) that had the precats from the downpipes removed (main cat still in place) and it still made a 0% CO and 2 ppm HC.

After you get the test done, go straight to a gas station and fill up with gas to dilute the alcohol back down.

EDIT: Oops, I just read that it is illegal in CA to use any additives, so don't do that.

Post by **vegasjetskier** » 28 Sep 2008, 13:30

Kmaniac, did the mechanic tell you what the timing was supposed to be in order to pass? If so, I'd set it there and no more advanced. As you turn the distributor the rotor will start to line up with the wrong electrode on the cap and will increase the likelihood of a missfire.