I've recently picked up a 2003 D2 to wrench on, and it's got a very frustrating misfire on cylinder #8. It only misfires at high RPM under heavy load. (kickdown while climbing an offramp, for example) I can drive around for a week or more, as long as I keep it to about half throttle at max, no CEL or misfire code.
The only code I ever see is P0308.
Naturally, I suspected the usual plug/wire issue, so I put in Champion copper plugs & Kingsborne wires. Good practice for a new purchase anyway. No change. Old plugs all looked similar, darkish grey color, basically what I would expect for a used plug. I also took the time to use a borescope and compare cylinders. Nothing special about cylinder #8, no contact marks on the piston, no evidence of coolant or oil leaking into cylinder.
Next step was to do a compression test, since I noticed that the headgaskets seem to be original (~140k). 155-150-150-160 down the passenger side head - cold, closed throttle. Looks pretty good.
Then I swapped the coils to see if the issue moved. No change. Then, for the hell of it, I swapped in a new spare coil I had. No change.
Then I swapped in a known good MAF I had. No change.
Then I pulled the injectors, cleaned them, installed new o-rings, and swapped all injectors from passenger to driver side. No change.
Next, I used a vacuum gauge to determine whether it could be an exhaust restriction or sticking valve. Cold idle registered 18mmHg, dipped and spiked appropriately with a snap of the throttle plate. Held steady at 2500rpm. Only questionable thing about vacuum reading was a continuous vibration of the needle (max 1mmHg fluctuation) at any speed, though I suspect this is because I'm using an unfiltered gauge directly off the manifold.
I'm starting to think it may be a valvetrain issue. Next on the agenda is to measure rocker arm lift and compare to cam specs/other cylinders to see if I've got a worn cam lobe. I'll also be looking for a broken rocker shaft or valve spring, if the rocker arm movement checks out. Barring that, what else could it be? Collapsed lifter? I feel like I'm starting to look for pretty obscure causes.
Is there anything else that I should be looking for while I've got the valve cover/intake off? The odd thing is that this engine is extremely quiet. It's the quietest Rover engine I've ever owned. No ticking/tapping/knocking, nothing.
Thanks in advance for any suggestions.
The only code I ever see is P0308.
Naturally, I suspected the usual plug/wire issue, so I put in Champion copper plugs & Kingsborne wires. Good practice for a new purchase anyway. No change. Old plugs all looked similar, darkish grey color, basically what I would expect for a used plug. I also took the time to use a borescope and compare cylinders. Nothing special about cylinder #8, no contact marks on the piston, no evidence of coolant or oil leaking into cylinder.
Next step was to do a compression test, since I noticed that the headgaskets seem to be original (~140k). 155-150-150-160 down the passenger side head - cold, closed throttle. Looks pretty good.
Then I swapped the coils to see if the issue moved. No change. Then, for the hell of it, I swapped in a new spare coil I had. No change.
Then I swapped in a known good MAF I had. No change.
Then I pulled the injectors, cleaned them, installed new o-rings, and swapped all injectors from passenger to driver side. No change.
Next, I used a vacuum gauge to determine whether it could be an exhaust restriction or sticking valve. Cold idle registered 18mmHg, dipped and spiked appropriately with a snap of the throttle plate. Held steady at 2500rpm. Only questionable thing about vacuum reading was a continuous vibration of the needle (max 1mmHg fluctuation) at any speed, though I suspect this is because I'm using an unfiltered gauge directly off the manifold.
I'm starting to think it may be a valvetrain issue. Next on the agenda is to measure rocker arm lift and compare to cam specs/other cylinders to see if I've got a worn cam lobe. I'll also be looking for a broken rocker shaft or valve spring, if the rocker arm movement checks out. Barring that, what else could it be? Collapsed lifter? I feel like I'm starting to look for pretty obscure causes.
Is there anything else that I should be looking for while I've got the valve cover/intake off? The odd thing is that this engine is extremely quiet. It's the quietest Rover engine I've ever owned. No ticking/tapping/knocking, nothing.
Thanks in advance for any suggestions.