Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - 97 Camry 2.2L -- timing belt set right?

Paul Milenkovic · 07-04-2015, 11:07 AM

My 1997 Camry has 160,000 miles, and I had a shop replace the timing belt. Taking it home, it started downshifting on hills where it didn't before, and the idle fuel flow on my Scan Gauge was reading .4-.5 GPH where it was reading a solid .3 GPH before.

Took the top timing belt cover off, set the notch on the outside-the-bottom-cover crankshaft pulley ("harmonic balancer") to the 0-deg mark, and the cam pulley was back from its mark. Took the car back, but they claimed that "harmonic balancer mark is not the right crankshaft mark" so they would not change anything.

I checked the harmonic balancer mark as OK two ways -- a timing light showed the same idle advance of 5-7 deg as the Scan Gauge, and I pulled the spark plugs out and put plastic rods down the holes to find the #1 cylinder TDC aligned with the harmonic balancer mark. Next, I advanced the cam pulley 2 full belt notches to align with its mark, and I followed the procedure for resetting the belt tension and turning the crank a full 2 turns before rechecking.

The car has more power, and the idle fuel is back at .3 GPH. But something has changed on the car. I don't have a lot of tank fills to be certain, but it appears though that the Scan Gauge tank-fill correction has changed from -11% down to -4.5% (In other words, with the -11% correction and my change to the timing belt, the Scan Gauge was giving optimistic MPGs, and changing to -4.5% gives more realistic, lower MPGs).

The idle manifold pressure, transmission in neutral, reads 4.1 PSI at 700 RPM on the Scan Gauge, and a "steam gauge" vacuum reading is 21" Hg. With the transmission in Drive, the MAP is 5.1 at 650 RPM. I tested the compression and got 185, 190, 187, 185 PSI where the factory spec is 178.

I have a theory that a another shop that changed the camshaft timing belt, at 85,000 miles and 13 years ago when I bought the car used, set the belt back one notch, accounting for the -11% correction. After my second timing belt change, it was set it back another notch (each notch is 15 crankshaft deg so the valves were a full 30 crankshaft-deg back). I wish I had written down more Scan Gauge readings, but I am thinking the Scan Gauge was being pessimistic about gas mileage because the power-robbing retarded intake valve was reducing manifold vacuum but reducing pumping losses? Shop #1 having the belt back one notch had the Scan Gauge somewhat less pessimistic but still requiring the -11% adjustment (meaning the tank fill is 11 percent below what the uncorrected Scan Gauge thinks). And now that I set the cam to the factor spec, I am getting low MAP, high vacuum at idle?

I don't have enough tank fills to be certain, but it seems that I am trading power for gas mileage, and maybe I want to try 1 notch back for more MPGs? The thing that is unexpected is that I can vary the cam timing over a 30-deg range on this car without making it hard-to-start, throwing a code, or cause and alarming symptoms in the engine.

Do people have experience that the cam timing can be varied through a full 2 belt notches (30 deg) without doing anything crazy to the car? Any thoughts about the different Scan Gauge tank-fill calibrations at what are 3 cam settings -- how does the Scan Gauge calculate MPG? Doesn't it work from the fuel injector on-time, and why would the cam change that calibration? Anyone experiment with cam timing?

07-04-2015, 11:07 AM	#1 (permalink)
Paul Milenkovic EcoModding Lurker Join Date: Jul 2015 Location: Madison, WI Posts: 6 Thanks: 1 Thanked 0 Times in 0 Posts	97 Camry 2.2L -- timing belt set right? My 1997 Camry has 160,000 miles, and I had a shop replace the timing belt. Taking it home, it started downshifting on hills where it didn't before, and the idle fuel flow on my Scan Gauge was reading .4-.5 GPH where it was reading a solid .3 GPH before. Took the top timing belt cover off, set the notch on the outside-the-bottom-cover crankshaft pulley ("harmonic balancer") to the 0-deg mark, and the cam pulley was back from its mark. Took the car back, but they claimed that "harmonic balancer mark is not the right crankshaft mark" so they would not change anything. I checked the harmonic balancer mark as OK two ways -- a timing light showed the same idle advance of 5-7 deg as the Scan Gauge, and I pulled the spark plugs out and put plastic rods down the holes to find the #1 cylinder TDC aligned with the harmonic balancer mark. Next, I advanced the cam pulley 2 full belt notches to align with its mark, and I followed the procedure for resetting the belt tension and turning the crank a full 2 turns before rechecking. The car has more power, and the idle fuel is back at .3 GPH. But something has changed on the car. I don't have a lot of tank fills to be certain, but it appears though that the Scan Gauge tank-fill correction has changed from -11% down to -4.5% (In other words, with the -11% correction and my change to the timing belt, the Scan Gauge was giving optimistic MPGs, and changing to -4.5% gives more realistic, lower MPGs). The idle manifold pressure, transmission in neutral, reads 4.1 PSI at 700 RPM on the Scan Gauge, and a "steam gauge" vacuum reading is 21" Hg. With the transmission in Drive, the MAP is 5.1 at 650 RPM. I tested the compression and got 185, 190, 187, 185 PSI where the factory spec is 178. I have a theory that a another shop that changed the camshaft timing belt, at 85,000 miles and 13 years ago when I bought the car used, set the belt back one notch, accounting for the -11% correction. After my second timing belt change, it was set it back another notch (each notch is 15 crankshaft deg so the valves were a full 30 crankshaft-deg back). I wish I had written down more Scan Gauge readings, but I am thinking the Scan Gauge was being pessimistic about gas mileage because the power-robbing retarded intake valve was reducing manifold vacuum but reducing pumping losses? Shop #1 having the belt back one notch had the Scan Gauge somewhat less pessimistic but still requiring the -11% adjustment (meaning the tank fill is 11 percent below what the uncorrected Scan Gauge thinks). And now that I set the cam to the factor spec, I am getting low MAP, high vacuum at idle? I don't have enough tank fills to be certain, but it seems that I am trading power for gas mileage, and maybe I want to try 1 notch back for more MPGs? The thing that is unexpected is that I can vary the cam timing over a 30-deg range on this car without making it hard-to-start, throwing a code, or cause and alarming symptoms in the engine. Do people have experience that the cam timing can be varied through a full 2 belt notches (30 deg) without doing anything crazy to the car? Any thoughts about the different Scan Gauge tank-fill calibrations at what are 3 cam settings -- how does the Scan Gauge calculate MPG? Doesn't it work from the fuel injector on-time, and why would the cam change that calibration? Anyone experiment with cam timing?