Diagnosing drivability; what say you?
This may turn into a chronicle of fixing myriad small problems with my '91 318is, or it may be short and sweet if I find the crucial part or someone gives me a really good tip. Here goes!
Bought the car last February with 182k or so miles on it. About 1k miles and 30 days later, the idler sprocket lost its bearings, the timing chain slipped, and all the intake valves bent. FredK hipped me to another engine the next state over and I've been running another M42 with about 145k miles.
I've had some minor drivability problems that didn't really change when I put the new motor in (at which time I also replaced a slew of parts at the same time; pretty much every rubber or plastic coolant or vacuum part is now new). I've also been living with a hard start that's noticeable when it's warm out and much worse when it's cold; the engine'll crank and crank before finally firing up. Once running and warm, it feels pretty good, but has a stumble off idle. It also smells like it's running rich after it's started.
So, wind the clock back a couple of weeks. The car starts running *horribly*, check-engine light points to the AFM. Turns out I'd left the PCV hose disconnected. :crazy: I started reading Charles Probst's Bosch fuel injection book published by Bentley, realized this stuff isn't that complicated, and dove in.
My AFM has dodgy resistance readings. My analog multimeter shows non-linear resistance when moving the vane from closed to open, and at fully open, the resistance dances quite a bit. I bought another AFM, and that one doesn't change resistance AT ALL. The car runs with both of 'em, the new one has bodged studs for the air box cover, so I went back to my old one. I'm trying to get a couple of folks to give me the readings from their M42 AFMs; if you'd like to contribute, please do! The AFM could be the reason for the stumble off idle, if it's not telling the computer that more air is flowing (or if there's a mismatch with the throttle position sensor).
I've tested the throttle position and engine temperature sensors; both look normal. I haven't plotted the temp sensor resistance against temperature, however, so it's possible it's not working correctly, but at 70°F or so, it looks right according to the E36 Bentley manual.
Today I decided to take a look at the injectors, thinking maybe they're dirty or leaking or something. As I was disassembling the intake, I noticed that the gasket between the upper and lower halves of the intake were wet, and I'm pretty sure it was gasoline. There intake just behind the throttle body was also wet. And the gaskets between the lower intake and the head were also a little wet, mainly on cylinders 2 and 3.
It also appeared that zero fuel came out of the return line when I disconnected it from the fuel rail. This makes me think the fuel pressure regulator is blocked and not allowing ANY fuel to return, but it's possible that it could have just drained back to the tank (the inside of the line looked dry, however). I finally managed to pry the injectors out of the intake and the fuel rail. That was a complete pain in the ass and I'm hoping I didn't break any of them (one I'm not so sure about). They look fine, but I'd like to hook them up to check the spray pattern and look for leaks.
Tonight I borrowed a fuel pressure gauge. Since the intake and fuel rail are completely disassembled, I can't check the pressure of the system (tomorrow morning, hopefully), but I did do a static test with the gauge on the high pressure line to the fuel rail. I think my pump is bad: even after pumping for 20 seconds, it barely gets to 40 psi. The pressure does not build quickly and linearly to the spec of 43.5 psi. And after about 15 minutes it's already lost more than 7 psi. And the pump's kinda noisy. I'm going to look into pulling the pump tomorrow to check for a clogged pickup. The lines between the tank and the hard fuel lines look original; hopefully none of them are restricting the pressure, but I'd only expect them to restrict the flow. I replaced the hard fuel lines a couple of months ago. I need to return the fuel pressure gauge by Monday evening, so I'll have to wrap up my pressure testing soon.
Please let me know if you've got any thoughts on what I've reported here. I'm particularly interested to know why the intake seems to wet. I was thinking that if the fuel pressure regulator weren't working and the pressure was building too high that I could be getting excess fuel in the intake. Could still be happening if the injectors or their seals are leaking…
Bought the car last February with 182k or so miles on it. About 1k miles and 30 days later, the idler sprocket lost its bearings, the timing chain slipped, and all the intake valves bent. FredK hipped me to another engine the next state over and I've been running another M42 with about 145k miles.
I've had some minor drivability problems that didn't really change when I put the new motor in (at which time I also replaced a slew of parts at the same time; pretty much every rubber or plastic coolant or vacuum part is now new). I've also been living with a hard start that's noticeable when it's warm out and much worse when it's cold; the engine'll crank and crank before finally firing up. Once running and warm, it feels pretty good, but has a stumble off idle. It also smells like it's running rich after it's started.
So, wind the clock back a couple of weeks. The car starts running *horribly*, check-engine light points to the AFM. Turns out I'd left the PCV hose disconnected. :crazy: I started reading Charles Probst's Bosch fuel injection book published by Bentley, realized this stuff isn't that complicated, and dove in.
My AFM has dodgy resistance readings. My analog multimeter shows non-linear resistance when moving the vane from closed to open, and at fully open, the resistance dances quite a bit. I bought another AFM, and that one doesn't change resistance AT ALL. The car runs with both of 'em, the new one has bodged studs for the air box cover, so I went back to my old one. I'm trying to get a couple of folks to give me the readings from their M42 AFMs; if you'd like to contribute, please do! The AFM could be the reason for the stumble off idle, if it's not telling the computer that more air is flowing (or if there's a mismatch with the throttle position sensor).
I've tested the throttle position and engine temperature sensors; both look normal. I haven't plotted the temp sensor resistance against temperature, however, so it's possible it's not working correctly, but at 70°F or so, it looks right according to the E36 Bentley manual.
Today I decided to take a look at the injectors, thinking maybe they're dirty or leaking or something. As I was disassembling the intake, I noticed that the gasket between the upper and lower halves of the intake were wet, and I'm pretty sure it was gasoline. There intake just behind the throttle body was also wet. And the gaskets between the lower intake and the head were also a little wet, mainly on cylinders 2 and 3.
It also appeared that zero fuel came out of the return line when I disconnected it from the fuel rail. This makes me think the fuel pressure regulator is blocked and not allowing ANY fuel to return, but it's possible that it could have just drained back to the tank (the inside of the line looked dry, however). I finally managed to pry the injectors out of the intake and the fuel rail. That was a complete pain in the ass and I'm hoping I didn't break any of them (one I'm not so sure about). They look fine, but I'd like to hook them up to check the spray pattern and look for leaks.Tonight I borrowed a fuel pressure gauge. Since the intake and fuel rail are completely disassembled, I can't check the pressure of the system (tomorrow morning, hopefully), but I did do a static test with the gauge on the high pressure line to the fuel rail. I think my pump is bad: even after pumping for 20 seconds, it barely gets to 40 psi. The pressure does not build quickly and linearly to the spec of 43.5 psi. And after about 15 minutes it's already lost more than 7 psi. And the pump's kinda noisy. I'm going to look into pulling the pump tomorrow to check for a clogged pickup. The lines between the tank and the hard fuel lines look original; hopefully none of them are restricting the pressure, but I'd only expect them to restrict the flow. I replaced the hard fuel lines a couple of months ago. I need to return the fuel pressure gauge by Monday evening, so I'll have to wrap up my pressure testing soon.
Please let me know if you've got any thoughts on what I've reported here. I'm particularly interested to know why the intake seems to wet. I was thinking that if the fuel pressure regulator weren't working and the pressure was building too high that I could be getting excess fuel in the intake. Could still be happening if the injectors or their seals are leaking…