Would either a bad knock sensor or a broken MAF cause a no start condition?

I replaced my waterpump today and when I buttoned it up, the motor would turn over and would also display spark (so I am assuming that the OPTI is not broken) but would not start.

Any suggestions?

Scott

 

You can unplug the MAF and the engine will start and I doubt the knock sensor will prevent starting the engine. Engines need spark (and at the right time), air , and fuel to start and run. You need to check the spark timing with your timing light, then measure the fuel pressure on the fuel rail, then put a small 12v lamp on the fuel injector wiring harness plug to see if it is being pulsed when cranking the engine. Remove the flexible horn on the MAF to ensure air is getting to the engine. One or more of air, fuel, spark is missing.

 

Neither sensor failure would cause the engine to not start. What are the symptoms.

1.)Is it turning over at full speed? Battery or starter.

2.)Does it try an fire or backfire at all? Opti, coil, wires

3.)What do you mean by it displays spark? Pull the wires and ground a spark plug to see if it arcs.

My room mate killed his opti by hooking the vaccum lines up wrong, you might check those. Also, since you replaced you water-pump I am assuming your old one failed, this tends to kill optis.

 

It does turn over at normal speed.

It does not fire (attempt to run) at all when turning over but does somewhat backfire when I stop cranking the motor.

As far as ignition. The coil wire (via my timing light) is "firing". Have not checked at the spark plugs. Will have to figure out some way of checking that. Need to buy a friend.

The water pump did not fail. I had to replace most of the rest of the cooling system (radiator, thermostat...) so I was pre-empting by replacing this also.

I have pulled the MAF and had the same indications.

The knock sensor was a big question as I attempted to pull it (passenger side), the part of the housing that has the nut rotated but the sensor housing did not (I was attempting to drain the block). I then re-attached the connector and left well enough alone. So the question on this is, if I damaged it, might the ECM possibly be getting erroneous knock information, be pulling back the timing to far which will not allow the car to start. Finally, can I check this by pulling the sensor lead?

I'll keep investigating, but any help is appreciated.

Scott

 

No, the knock sensor won't pull enough timing to make it not start, you can try disconnecting the connector and trying to start it, but I can almost guarantee it won't make a difference.

To test for spark at the plugs, pull a wire off, put a spark plug in it(can be an old one), touch the threaded part to a ground(the engine works well), and then have someone turn the car over, you should clearly see the arc in the spark plug.