rbtconsultants
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We've been working on the 2002 liberty 3.7l for a bit now, since it dropped a valve seat. In summary, engine was pulled, a couple pistons replaced, new timing set installed, heads were replaced with remanned heads. The engine is now back in.
When we first put the engine back in, we fired it. Basically ran it off battery for a few seconds. Had no alternator or belt on it, no cats or o2 sensors, bare bones. Exhaust was loud but It ran, but the fuel rail was leaking. After a few seconds of running I tried to rev it, it backfired through the intake, and wouldn't start after that. I chalked that up to going lean from low fuel pressure from the leaking fuel rail.
A few days later installed the new fuel rail. It behaved exactly the same way. It fired up, ran for probably 10 seconds. Turned it off, restarted it for another 10 seconds. Then tried to rev it, big backfire through the intake, wouldn't start anymore.
Started to think it was electrical. Battery was low and we were starting off of a power booster. Decided to charge the battery. That was Wednesday.
Today, Saturday, tried again with charged battery, no booster. Fired immediately, idled ok, revved it fine. Seemed all good, turned it off. Spent the rest of the day reassembling everything, alternator, belt, cats, everything plugged in and back together, except air cleaner assembly.
Then, tried to fire it again. Immediate single big backfire through intake, then no start. Tried a bunch. Sounded like it wanted to fire a few times, but no joy. Left it with the battery disconnected and charging. Trying to figure out what is next. I would not be surprised to get back to it tomorrow and fire immediately, or not at all. Confusing.
There are no codes. I actually disconnected the cam sensor at one point just to see if would code. It did. Tried the same with the crank sensor but it did not throw a code. I don't know if that is because it wasn't running, or if it should tell me something
So, timing? Intake backfire would point that way, but the timing was set dead on when the new chains/tensioners were put in. Plus, would it start sometimes and not others if timing? Could a cam sprocket be off just a tooth and cause all this? I guess I can pull the valve covers and see if something looks off.
Compression? Didn't do a compression test with a gauge but pulled plugs and did confirm compression. Plus it did start/run several times. Maybe need to test with a gauge, was going to but have misplaced my gauge somewhere. Have to buy a new one I guess.
Electrical? I did pull one coil/plug today and there was spark, didn't seem particularly bright. Thinking about a new battery. Low voltage could make the computer act weird I suppose, cause backfires, no start, weak spark, whatever.
Fuel? I can hear the pump priming. Popped the quick connect on the fuel rail and fuel coming out when the motor is turning over. Maybe I need to get a fuel pressure tester. Maybe an injector problem? Old fuel? Fuel was very low and probably 6 months old. Added a couple gallons of fresh but no change. I didn't pull the plugs to see if they were wet.
Anybody have any thoughts? What would you check first? The weird part to me is three times now it has run, then backfired and wouldn't start anymore until I let it sit for a day or two. Just odd.
Thanks
Bob
When we first put the engine back in, we fired it. Basically ran it off battery for a few seconds. Had no alternator or belt on it, no cats or o2 sensors, bare bones. Exhaust was loud but It ran, but the fuel rail was leaking. After a few seconds of running I tried to rev it, it backfired through the intake, and wouldn't start after that. I chalked that up to going lean from low fuel pressure from the leaking fuel rail.
A few days later installed the new fuel rail. It behaved exactly the same way. It fired up, ran for probably 10 seconds. Turned it off, restarted it for another 10 seconds. Then tried to rev it, big backfire through the intake, wouldn't start anymore.
Started to think it was electrical. Battery was low and we were starting off of a power booster. Decided to charge the battery. That was Wednesday.
Today, Saturday, tried again with charged battery, no booster. Fired immediately, idled ok, revved it fine. Seemed all good, turned it off. Spent the rest of the day reassembling everything, alternator, belt, cats, everything plugged in and back together, except air cleaner assembly.
Then, tried to fire it again. Immediate single big backfire through intake, then no start. Tried a bunch. Sounded like it wanted to fire a few times, but no joy. Left it with the battery disconnected and charging. Trying to figure out what is next. I would not be surprised to get back to it tomorrow and fire immediately, or not at all. Confusing.
There are no codes. I actually disconnected the cam sensor at one point just to see if would code. It did. Tried the same with the crank sensor but it did not throw a code. I don't know if that is because it wasn't running, or if it should tell me something
So, timing? Intake backfire would point that way, but the timing was set dead on when the new chains/tensioners were put in. Plus, would it start sometimes and not others if timing? Could a cam sprocket be off just a tooth and cause all this? I guess I can pull the valve covers and see if something looks off.
Compression? Didn't do a compression test with a gauge but pulled plugs and did confirm compression. Plus it did start/run several times. Maybe need to test with a gauge, was going to but have misplaced my gauge somewhere. Have to buy a new one I guess.
Electrical? I did pull one coil/plug today and there was spark, didn't seem particularly bright. Thinking about a new battery. Low voltage could make the computer act weird I suppose, cause backfires, no start, weak spark, whatever.
Fuel? I can hear the pump priming. Popped the quick connect on the fuel rail and fuel coming out when the motor is turning over. Maybe I need to get a fuel pressure tester. Maybe an injector problem? Old fuel? Fuel was very low and probably 6 months old. Added a couple gallons of fresh but no change. I didn't pull the plugs to see if they were wet.
Anybody have any thoughts? What would you check first? The weird part to me is three times now it has run, then backfired and wouldn't start anymore until I let it sit for a day or two. Just odd.
Thanks
Bob