MG ZS 2.5 V6 won't rev past 5500rpm
Discussion
Brief history. I bought this car from a scrap yard, it needed a new engine. I managed to pick up a new engine and put it in myself. The car starts and drive ok, but it won't rev past 5500rpm when driving, and 6000rpm when stationary. The red-line starts at 7000rpm!!
When driving it's definitely down on power, but for general driving is fine.
I've fitted a new fuel filter, replaced all six spark plugs and swapped all six coil packs with a spare set I have.
These engines also have a variable manifold, and I've confirmed that both the power and balance motors are working as the should be, and the internals of the manifold are fine.
The ECU isn't showing any errors.
I disconnected the exhaust after the pre-cat and and the issue was still there, I did this to rule out a blocked exhaust. It's been suggested that the pre-cat could be partially blocked, but a mechanic friend says there's plenty of pressure being generated by the exhaust and doesn't suspect it's blocked. Although I'm not ruling it out.
I've tried diagnosing this myself as much as I can, but I can't seem to figure it out so I'm asking if anyone else has any other suggestions before I hand the car to my mechanic for him to figure out.
The only things I can think it could be are a partially blocked cat, fuel pump, and maybe timing? I didn't touch the timing and just presumed it would be timed up properly. I would check the timing, but it's a fairly time consuming task on these engines and time is something I'm short of at the minute.
When driving it's definitely down on power, but for general driving is fine.
I've fitted a new fuel filter, replaced all six spark plugs and swapped all six coil packs with a spare set I have.
These engines also have a variable manifold, and I've confirmed that both the power and balance motors are working as the should be, and the internals of the manifold are fine.
The ECU isn't showing any errors.
I disconnected the exhaust after the pre-cat and and the issue was still there, I did this to rule out a blocked exhaust. It's been suggested that the pre-cat could be partially blocked, but a mechanic friend says there's plenty of pressure being generated by the exhaust and doesn't suspect it's blocked. Although I'm not ruling it out.
I've tried diagnosing this myself as much as I can, but I can't seem to figure it out so I'm asking if anyone else has any other suggestions before I hand the car to my mechanic for him to figure out.
The only things I can think it could be are a partially blocked cat, fuel pump, and maybe timing? I didn't touch the timing and just presumed it would be timed up properly. I would check the timing, but it's a fairly time consuming task on these engines and time is something I'm short of at the minute.
Hmmm, a tricky one.
I would expect the car to rev round to 7000 rpm when there is no load on it even if the fuel pump is playing up or the cat is blocked as you would need very little power to achieve this.
As much as you dont want to hear it I think the timing has jumped slightly. I had a ZR that did exactly the same would only rev to about 5500rpm and after trying everything I discovered the tensioner had failed and the belt had jumped about 10 teeth.
I do sympathise as its a ballache of a job, maybe you might get the confirmation you are after by looking at the 2 smaller belts by comparing there positions compared to the crank position
Good Luck!!
I would expect the car to rev round to 7000 rpm when there is no load on it even if the fuel pump is playing up or the cat is blocked as you would need very little power to achieve this.
As much as you dont want to hear it I think the timing has jumped slightly. I had a ZR that did exactly the same would only rev to about 5500rpm and after trying everything I discovered the tensioner had failed and the belt had jumped about 10 teeth.
I do sympathise as its a ballache of a job, maybe you might get the confirmation you are after by looking at the 2 smaller belts by comparing there positions compared to the crank position
Good Luck!!
If it helps, here's a video of my attempting to thrash the car
http://www.youtube.com/watch?v=y_uWzph2Dkg
http://www.youtube.com/watch?v=y_uWzph2Dkg
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