M42 cranks but won't start

[roguetoaster]

Sounds like a vacuum leak. I'd pull the intake boot off and check for tears/cracks. Might also try unplugging the O2 sensor and see if it changes anything. Do the same with the AFM.

Also, don't set the idle with the throttle body screw or the throttle cable. This will not allow the ECU to go into closed loop and you will have worse idling problems. The screw on the throttle body is a stop, not an idle adjustment.

While it might be, I don't think it's a simple vac leak. I say that partly due to the no start initially and the condition of the plug he showed, but mostly due to the idle staying stable despite being at a lower than spec'd RPM.

Yes, the screw is the throttle stop, but can be used for the purpose I suggested. I'm not saying you should leave the throttle open/adjusted to compensate permanently with the adjustement I suggested, but rather just as a diagnostic tool. To be sure, you don't want to leave the throttle open 100% of the time.

Still very worth checking for vacuum leaks.

[AndrewBird]

Sounds like a vacuum leak. I'd pull the intake boot off and check for tears/cracks. Might also try unplugging the O2 sensor and see if it changes anything. Do the same with the AFM.

Also, don't set the idle with the throttle body screw or the throttle cable. This will not allow the ECU to go into closed loop and you will have worse idling problems. The screw on the throttle body is a stop, not an idle adjustment.

[roguetoaster]

I'd start by raising the idle to spec with either the throttle screw or the twist adjustment on the cable just to see where that takes you.

Then if it's not exhibiting any change in operation, but the idle does stay up I'd check timing. Frankly, the odd bucking when you apply throttle seems like a timing issue.

[Mohit]

Cleaned the ICV, and idling doesn't seem to irradiate now. It's a bit steadier but still pretty rough. When I apply throttle, it's very hesitant to increase RPM, and does so slowly, and once you let off, it drops slowly and almost to 400 RPM, where it wants to die. It also still smells like gas in the exhaust, and I see some droplets blowing out the muffler.

Here's a video of the current idle, I dunno if it will help.

https://www.youtube.com/watch?v=P8XaeMoexog

[Mohit]

I verified spark on each plug, and I tried a stomp test and no codes came up. I'll try cleaning to ICV next.

[Mohit]

Well, if it truly started out of the blue it should to be an ignition issue, either bad a bad coil (did you verify spark on all 4?) or an ECU issue. It could still be a coincidental vacuum leak, but this would probably not be an issue at operating speeds.

As to the catalytic converter being empty it won't impact engine operation, but will make the exhaust smell more of gasoline.

It may be worth checking the vibration dampener/crank wheel. Some time ago mine separated without failing completely (the trigger wheel rotated on the vibration dampener) and would still start and run for a very short time before stalling, but was 100% undriveable.

I only checked spark on one of the the plugs. I don't know about the vibration dampener/crank wheels, it doesn't seem to stall.

[roguetoaster]

Well, if it truly started out of the blue it should to be an ignition issue, either bad a bad coil (did you verify spark on all 4?) or an ECU issue. It could still be a coincidental vacuum leak, but this would probably not be an issue at operating speeds.

As to the catalytic converter being empty it won't impact engine operation, but will make the exhaust smell more of gasoline.

It may be worth checking the vibration dampener/crank wheel. Some time ago mine separated without failing completely (the trigger wheel rotated on the vibration dampener) and would still start and run for a very short time before stalling, but was 100% undriveable.

[Mohit]

If it's running rich, or running at all, you should not need to replace the fuel pump relay.

Is it only running poorly when warm? If so, it may be the oxygen sensor. Bad idle from start up? Probably vacuum leaks or ICV in need of cleaning.

Beyond that it could be any number of things, from the catalytic converter to the air flow meter. Be sure that the wire on the passenger side under the plastic cover (the one that covers the 3 relays) in unplugged. After that I'd check the position of the throttle at 0% input to make sure it's seated.

It's a rough throttle at start up, not really even driveable right now. I am about 70% sure my catalytic converter is empty, according to the muffler guy. He said that it was basically hollow, and this was about four or five months ago. That wire you're talking about is unplugged, I had that hot start problem when I first bought the car a year ago. I also had a smoke test done when I bought the car and everything checked out, but I guess that could be bad now.

Thanks.

[roguetoaster]

If it's running rich, or running at all, you should not need to replace the fuel pump relay.

Is it only running poorly when warm? If so, it may be the oxygen sensor. Bad idle from start up? Probably vacuum leaks or ICV in need of cleaning.

Beyond that it could be any number of things, from the catalytic converter to the air flow meter. Be sure that the wire on the passenger side under the plastic cover (the one that covers the 3 relays) in unplugged. After that I'd check the position of the throttle at 0% input to make sure it's seated.

[Mohit]

I changed the valve cover gasket and replaced the spark plugs, and it starts fine now but has a rough idle. It smells like gas, so it's running rich for sure. I guess I'll start with the fuel pump relay.

[noypi2]

I have the same problem. I replace the fuel pump relay and it works. I have a M10.

[d_elson0]

Mine did the same thing. My battery seemed fine, would crank all day and lights would all work. Threw some cables on it and jumped after a minute or so of being hooked up. My 2cents

[Mohit]

belts loose!

Any belt you think in particular?

[Dj Buttchug]

belts loose!

[Mohit]

those need to be changed. Are you sure the engine is getting fuel? I think your fuel pump might be crapped out conveniently when you started working on the car.

Okay, I'll buy some new ones. I tried turning it on while WOT to clear out fuel because this guy said so, and let the plugs dry. It started after cranking for ~8 seconds, with a super rough idle. After letting idle for about a minute I revved it about 1.5k RPM and started squealing really loud. It's squealed like this before in the morning when it was around 50F outside.

https://www.youtube.com/watch?v=gkP5CfhbS34