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Car Forum / Volvo Cars / May 2006My first time with a timing light, can someone help me interpret?
1987 740 GLE B230F I finally got my hands on a timing light to see if my timing was indeed off and causing my lack of power. I connected the light as per the instructions and let the motor reach operating temperature. At normal idle the light hit about on the 10 -- off to the right of 0. I turned the throttle assembly slowly and the light moved about 2 inches more to the right, then RPMs picked up and the light then went off to the left as RPMs increased. Did I do this right? At idle, where should the light be? PS: I am not sure exactly what angle I need to be looking at the hash-marks. I tried to look from different angles and I am convinced the light is to the right of 0, nearest to the 10. Thanks! Here are the photos of the timing light. You can see the 10 mark farthest on the right. Haynes says 12 degrees BTDC at 750rpm, which I guess is Before Tap Dead Center. I am not sure what to make of this: http://www.flickr.com/photo_zoom.gne?id=153341427&size=l http://www.flickr.com/photo_zoom.gne?id=153341433&size=l http://www.flickr.com/photo_zoom.gne?id=153341432&size=l http://www.flickr.com/photo_zoom.gne?id=153341428&size=l > Here are the photos of the timing light. You can see the 10 mark > farthest on the right. Haynes says 12 degrees BTDC at 750rpm, which I [quoted text clipped - 7 lines] > > http://www.flickr.com/photo_zoom.gne?id=153341428&size=l At idle it should be about where you see it. When you accelerate the motor from idle it should back up to about 5*BTDC then advance to about 30 something by 3000 RPM. If you remove the top cover section and shine the light on the cam timing mark the dot on the cam should be a few teeth to the left facing the motor.One tooth at idle, three plus teeth at full advance. If the motor really bogs when you put your foot in it off the line, and takes throttle better when you let off or press the throttle gently to accelerate, you've probably got a restricted catalytic converter or something else restricting the exhaust. I forget why you had the motor redone (and it looks like the guy did a very nice job) but if it was spewing antifreeze, or oil, or raw fuel into the exhaust it doesn't take long to trash an old converter. Now as I said yesterday if you set the mark you're looking at in the pictures to the zero mark on the outer timing cover and look down inside the lower section at the crank pulley, the index marks inside there should be aligned and the cam shaft pulley dot will either be aligned with the top inner cover mark (#1 firing) or 180* away (#4 firing). If it's on #4 then turn the motor through 360* one time and check the marks again. If they don't align you've found the problem. Either the belt has slipped, the roll pin in the cam has broken and the pulley has slipped on the cam shaft, or the outer sheaves have turned on the crankshaft hub. Bob  SignatureThe goal when driving is to miss the maximum number of objects. What I may do is cut the exhaust just before the cat with my hacksaw, run the engine and see what that does. I can always use the same aluminum tape to put the pipe back together until I get a new muffler. > What I may do is cut the exhaust just before the cat with my hacksaw, > run the engine and see what that does. > > I can always use the same aluminum tape to put the pipe back together > until I get a new muffler. A really quick and dirty (no fooling!) test is to loosen the collector between the exhaust manifold and the exhaust pipe, then put your face to the tail pipe and exhale hard. You should feel very little restriction. If you feel back-pressure doing that your engine will certainly feel the same sort of restrictions. My limited experience with blocked exhaust is that the effect is more obvious at full throttle; not much seems to happen between 1/2 throttle and full throttle. Mike I went home at lunch and unbolted the catalytic converter and ran the engine - it still hesitates and stalls when I pump the pedal. I guess the catalytic converter can be ruled out. I need to maybe revisit the AMM. I unplugged it and it started and then stalled when I gave it gas. I really don't know how to test it besides trying another AMM. I guess I'll still have the full timing check performed next week. I am rethinking the AMM and leaning away from it. When the car is idling, I can easily rev the engine to high RPMS and hold it there. The car starts fine The car idles fine Once I get into 3rd gear I can easily accelerate smoothly up to 75+ mph and the car runs like a charm. But, when I "bump" the accelerator at an idle, just a hair each time, it stalls for a second or two in park or neutral. I can easily accelerate "through" the stall and work the engine back up, but that first 1/4 turn of the accelerator causes a dip, sometimes a sputter and small backfire. So, when I shift into drive, no power until around 3rd gear when I am up to about 40 mph, then the engine starts to run just fine. > 1987 740 GLE > B230F [quoted text clipped - 15 lines] > > Thanks! Looks about right. On my '93 240 the ignition timing spec in the Bentley manual says 12 +/- 2 deg. BTC. When I checked my car it was at about 10 at idle just like yours. You might be able to run a touch more advance, but certainly your pictures don't show anything which would explain poor running. John Just curious, but is that 10 degrees advance, or 10 degrees retarded? IOW, is there a 0 to the left of it, or a 20 (obscured, can't tell). Thanks all! The original mechanic insured me he carefully aligned all of the gears and I guess after I pay a guy $130, he'll tell me if the marks are still aligned. BUT, the exhaust is in bad shape. The muffler broke off, so I taped it back together at the pipe with aluminum tape. It shot black rusted metal out when I patched it - but was quiet. Yes, it used to spew oil splatters before I had the engine work done. It still has an oil drip from the rear main seal after driving it, but doesn't seem to do it in the driveway BEFORE driving. Is there a way I can check to see if it's the catalytic converter? I guess remove it? Will it have to be cut off? Thanks! > Thanks all! > [quoted text clipped - 15 lines] > > Thanks! Besides the quick and dirty test I mentioned before, the Haynes manual for my daughter's Honda has a slick test using a manifold vacuum guage. Warm up the engine and note the idle reading on the guage. Rev the engine to about 2000 rpm and let it stabilize, then watch the guage when you release the throttle. If the guage drops quickly and returns to the idle reading within 2 seconds, the exhaust is clear. If the guage appears to hang for a moment or very gradually returns to the idle reading it indicates blockage. Mike Ahhh -- I guess the logic in that is that by revving up the engine you are creating a pressure against the exhaust restriction, and when you let off, if there is an obstruction, the pressure will gradually decrease as trapped air escapes. If there is no blockage, there is no resistance and the air escapes instantly. hmmmm -- I have no gauge and not sure who in this little town would. They might. I may have to opt for the exhaust disconnect test. Thanks! |
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