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New to forums in general so take it easy on me lol, i have looked all over and have not found a problem like mine that hasnt involved timing, so bought a 91 ls400 with 189k miles, the lady told me it was an fpr problem and come to find out it was a spun cam bearing, snapped sprocket bolt and a destroyed distributor. Okay so new intake cam on passenger head, check. Fixed bearing, check. New sprocket and new complete dizzy, check check and check. Did timing belt, used a nice new gates belt, timing was correct, tensioner was tight, cranked her up, boom ran fine, revved it up, boom backfire 🤦🏻♂️. Checked timing, was off a tooth on cam, took it back apart retimed it, double checked, triple checked, ran it, checked timing again, perfect, started it up, revved it, boom fire from my intake followed by backfire and pings, cut it off, starts desieling, i almost cried. Engine finally shut off after about 10-15 seconds of running backwards on its own with no electrical power. How is this even possible, i pulled codes, all i got is code 28 main o2 sensor, that shouldnt cause this, im completely stumped, my engine is perfectly in time, im running 93 premium, barely any error codes, super clean maf sensor and new parts all over the place, this car is killing me, someone help please, never dealt with something this strange
Strong engine though, was still running somehow with a dislodged hanging sprocket and only 2 cylinders firing, it never made this backfire before i put her back together 😭🙄
New to forums in general so take it easy on me lol, i have looked all over and have not found a problem like mine that hasnt involved timing, so bought a 91 ls400 with 189k miles, the lady told me it was an fpr problem and come to find out it was a spun cam bearing, snapped sprocket bolt and a destroyed distributor. Okay so new intake cam on passenger head, check. Fixed bearing, check. New sprocket and new complete dizzy, check check and check. Did timing belt, used a nice new gates belt, timing was correct, tensioner was tight, cranked her up, boom ran fine, revved it up, boom backfire 🤦🏻♂️. Checked timing, was off a tooth on cam, took it back apart retimed it, double checked, triple checked, ran it, checked timing again, perfect, started it up, revved it, boom fire from my intake followed by backfire and pings, cut it off, starts desieling, i almost cried. Engine finally shut off after about 10-15 seconds of running backwards on its own with no electrical power. How is this even possible, i pulled codes, all i got is code 28 main o2 sensor, that shouldnt cause this, im completely stumped, my engine is perfectly in time, im running 93 premium, barely any error codes, super clean maf sensor and new parts all over the place, this car is killing me, someone help please, never dealt with something this strange
maf sensor is new from the looks of it, did not clean it, spark plug wires aint the best but doing a test by unplugging each one or unplugging different sides doesnt make any change accept make it misfire un the unplugged cylinders, so every cylinder is firing apparently, im not sure what you mean by separate bearings, if you mean the little cap bearings like the crankshaft has where they slide out then no its just caps with oil journals, i smooth and polished the spun bearing instead of replacing the head and its perfect, havent had any scrapes scratches or oil spewwing.
The cam gears should have what looks like a groove for a woodruff key where the rotor button would slide into. If the new rotor button didn't have any way to dictate the orientation, it could be off 180°. The car would then have wonky timing and cause fire/combustion to be escaping through the intake valves. Everything is still working, hence the misfires when unplugging plug wires, but in the wrong order.
This wouldn't explain how it ran well initially but it's something to check.
The cam gears should have what looks like a groove for a woodruff key where the rotor button would slide into. If the new rotor button didn't have any way to dictate the orientation, it could be off 180°. The car would then have wonky timing and cause fire/combustion to be escaping through the intake valves. Everything is still working, hence the misfires when unplugging plug wires, but in the wrong order.
This wouldn't explain how it ran well initially but it's something to check.
i was thinking that too but when i timed it the second time i made sure to key the rotors, ive seen the notch, i do not understand how someone would possibly put them in backwards, i feel like the tilt of the rotor would shred it and the cap apart, id like to think i mistimed the scissor gear on the cam to the exhaust cam but i made sure that was timing when installing the cam, didnt wanna take it back apart lol, only explanation i could have is leaking injector, passenger side exhaust pours visible gas vapors from the exhaust and at the manifold, its running rich, misfires, backfires, knock sensor senses this and retards the hell out of the timing and when the engine comes to a stop it fires and sets off a chain of events that will start the motor backwards and run until gas vapors in the exhaust are completely depleted, this is my theory on it so far, idk how to explain the constant timed backfire unless a valve is burnt or not seating right. Does this make any sense? 😕
This has been a three week project and i was offered what i initially paid for the car, if i dont fix it today i may sell it tomorrow, i love lexus’s dont get me wrong but money is tight and i need a vehicle that will run, may invest the money in my gsxr750
I've seen a few rotor buttons from China that had zero orientation...
it does make sense but I couldn't see that being your issue. I'd assume that if there were runaway fumes, there would be more valve issues than just a couple not seating. I've never seen this issue with anything other than timing. I've had a timing belt be 1 tooth short, run perfect, then do the same thing you're experiencing. Had to sit and count teeth on the belt to make sure. It was a gates belt. Exact part number I needed but one tooth shy of perfect. Went back to get another one, counted the teeth, and it was how it needed to be. Same part number for the two belts and for the same car.
Sell it. If you can (almost) break even on it, why not? It's getting warmer so the bike will be way more fun!
Had to sit and count teeth on the belt to make sure. It was a gates belt. Exact part number I needed but one tooth shy of perfect.
I counted the teeth on a Gates belt a bought for my 93, just for the hell of it. ( I was feeling good that night) 😎 Good thing I did, one short. I brought it back to Advance Auto and the guy says "it's supposed to be like that for when it stretches." ?????? WHAT?????? Who the hell gave this guy a job at a parts store? Had to return it for store credit which I gave to the kid next door. I never went back there.
Did you check the cam sensors? If ya had that much damage maybe something clipped the cam sensor wires.
05-09-20, 12:02 AM
Backfiring and dieseling, please help!
