SC300 Timing - Misfire vs. Engine Stall!!
06-28-13, 02:13 PM
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SC300 Timing - Misfire vs. Engine Stall!!
Boy, do I regret not coming here first! 
I'm going to copy/paste the background of my issue, then wrap it up more concisely.
- I did not detect any coolant in the oil when I checked the dipstick, the color and consistency seemed fine.
- Timing hasn't been checked with a timing light, the alignment was done by manually rotating the timing gears so the white lines matched up with the grooves on the cover. The mark on the distributor gear is aligned with the one the body, sort of clicking into place. It was rotated back slightly so that when it was reinserted, it turned back to that original position. Could the tooth be off by less than one groove and have this issue? Should the gear tooth be pointed directly at the magnetic contact when inserted, or should it be slightly off? Also, if the timing were off even more drastically, would the engine even start?
- I manually rotated the engine to get it to TDC again, but stopped the lines just a little early to narrow down the issue. The car fires up, but the misfire from earlier is back, as well as the Check Engine Light. The throttle response has returned, though, but only while the timing is off like this. I am unsure why the opposite of my first problem occurs when I line up the timing marks properly.
Long story short, I had a misfiring cylinder and Check Engine Light. Replacing some parts and aligning the distributor/timing gears with the marks got rid of the Check Engine Light and the rough misfire, but the engine idles at extremely low RPM and stalls unless the throttle is pressed (still with no increase in RPM).
I hope someone can shed some light on this issue, I will be forever in your debt!
I'm going to copy/paste the background of my issue, then wrap it up more concisely.
I drive a 1996 SC300. The problem began one night when I was driving home and the Check Engine Light turned on. I felt a sudden surge then decrease in RPM. The engine began to shake pretty intensely, so I pulled over to check it out. I heard what I thought was a misfiring cylinder, so I drove it the rest of the way home very slowly. I took it to a Sears Auto Center to have it diagnosed, where they confirmed that I was misfiring on cylinder #2, but also gave me a laundry list of other supposed problems that required fixes.
I was told that coolant was mixing with my oil, which was what they thought was the main culprit. I changed the spark plugs and wiring; the old ones were wet. I replaced the distributor rotor and cap, and did a cursory cleaning of the butterfly valve in the throttle body. I reassembled everything and started the car successfully, but I still heard misfiring and the engine shut itself off while I coasted to a stop.
I suspected that I had misaligned the distributor rotor, so I had it towed to a different service station where the tech told me he thought it was either misaligned or broken, and to try adjusting that before anything else. He also said he didn't notice any coolant in the oil.
I manually cranked the engine to TDC by aligning the white lines on the timing gears with the notches on the top of the case, and now am able to start the car consistently with no Check Engine Light. However, the engine shudders and idles at around 500 RPM or less, and stalls very quickly. When I put the pedal all the way down, the engine manages to stay alive, but it does not rev whatsoever and the RPMs remain the same.
Manually pulling the lever under the hood DOES rotate the valve in the throttle body, but produces no additional power.
Country: United States
Make: Lexus
Model: SC300
Year: 1996
Already Tried:
-Replace spark plugs
-Replace spark plug wires
-Replace distributor cap
-Replace distributor rotor ...
I was told that coolant was mixing with my oil, which was what they thought was the main culprit. I changed the spark plugs and wiring; the old ones were wet. I replaced the distributor rotor and cap, and did a cursory cleaning of the butterfly valve in the throttle body. I reassembled everything and started the car successfully, but I still heard misfiring and the engine shut itself off while I coasted to a stop.
I suspected that I had misaligned the distributor rotor, so I had it towed to a different service station where the tech told me he thought it was either misaligned or broken, and to try adjusting that before anything else. He also said he didn't notice any coolant in the oil.
I manually cranked the engine to TDC by aligning the white lines on the timing gears with the notches on the top of the case, and now am able to start the car consistently with no Check Engine Light. However, the engine shudders and idles at around 500 RPM or less, and stalls very quickly. When I put the pedal all the way down, the engine manages to stay alive, but it does not rev whatsoever and the RPMs remain the same.
Manually pulling the lever under the hood DOES rotate the valve in the throttle body, but produces no additional power.
Country: United States
Make: Lexus
Model: SC300
Year: 1996
Already Tried:
-Replace spark plugs
-Replace spark plug wires
-Replace distributor cap
-Replace distributor rotor ...
- Timing hasn't been checked with a timing light, the alignment was done by manually rotating the timing gears so the white lines matched up with the grooves on the cover. The mark on the distributor gear is aligned with the one the body, sort of clicking into place. It was rotated back slightly so that when it was reinserted, it turned back to that original position. Could the tooth be off by less than one groove and have this issue? Should the gear tooth be pointed directly at the magnetic contact when inserted, or should it be slightly off? Also, if the timing were off even more drastically, would the engine even start?
- I manually rotated the engine to get it to TDC again, but stopped the lines just a little early to narrow down the issue. The car fires up, but the misfire from earlier is back, as well as the Check Engine Light. The throttle response has returned, though, but only while the timing is off like this. I am unsure why the opposite of my first problem occurs when I line up the timing marks properly.
Long story short, I had a misfiring cylinder and Check Engine Light. Replacing some parts and aligning the distributor/timing gears with the marks got rid of the Check Engine Light and the rough misfire, but the engine idles at extremely low RPM and stalls unless the throttle is pressed (still with no increase in RPM).
I hope someone can shed some light on this issue, I will be forever in your debt!
07-01-13, 04:15 PM
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Sorry for the delayed response, and thank you for the advice! I jumped the pins for the Fuel Pump ECU, and I got slightly better response when holding down the pedal, but I'm still pretty sure no additional fuel was being delivered.
I am going to test it again today with a better jumper, then I'll move on to checking the pump itself. The confusing part to me is that the fuel delivery/throttle response seems to be fine when the timing is off!
I'll be sure to keep you guys updated as I make progress.
I am going to test it again today with a better jumper, then I'll move on to checking the pump itself. The confusing part to me is that the fuel delivery/throttle response seems to be fine when the timing is off!
I'll be sure to keep you guys updated as I make progress.
07-01-13, 04:52 PM
#4
you need to set the timing with a light, its pretty hard to just guess at it once the distributor is out even when you line it up sometimes it needs to be turned a bit back, sometimes that doesn't work, the light is the only way to know what the timing is. you can get a cheapo one off of amazon that will do the job or other places online.
2nd, pull the code for the check engine light, you will probably need to borrow a scanner since you are 96.
2nd, pull the code for the check engine light, you will probably need to borrow a scanner since you are 96.
07-01-13, 05:07 PM
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Thanks Ali, I'm picking one up soon to get precise with the timing.
The CEL is not up now, but I can borrow a scanner to see if any codes are stored.
The CEL is not up now, but I can borrow a scanner to see if any codes are stored.
07-02-13, 08:18 AM
#6
also make sure when you have 0 on the crank that the notches on the cam gear are pointing up at the notches on the cover. If the notches aren't lining up, turn the crank around one more time till it reads 0 again, and then the notches on the cam gear should point straight up at the notches on the cover.
once you verify this is right we can move on to cure the problem, wouldn't even bother diagnosing anything with the timing out, and yes the car can start with the timing off but will usually not run well after it starts or immediately stall out.
once you verify this is right we can move on to cure the problem, wouldn't even bother diagnosing anything with the timing out, and yes the car can start with the timing off but will usually not run well after it starts or immediately stall out.
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