Will a bad VSS prevent starting?

**czjeeper** · 02-08-2010, 08:22 PM

My brother's jeep again...
We finished plumbing in the front drop for his OBA.
Went to start it (it had been running minutes before), and it just cranks, no start.
The fuel pump is energizing and building pressure at the rail.
We have spark at the plugs.
Checked all fuses (engine and dash).
I pulled the codes 12, 33, and 15.
I'm kind of at a loss here.

Mark05059 · 02-08-2010, 08:27 PM

you sure you didnt get 12 33 and 55 ??

**czjeeper** · 02-08-2010, 08:44 PM

Well, I did get 55 after 15. 55 is end of codes right?

540i · 02-09-2010, 10:07 AM

Missing VSS shouldn't cause any problems starting.. I'd say cam sensor

**czjeeper** · 02-09-2010, 10:18 AM

Would a cam sensor failure trip a code?

Mark05059 · 02-09-2010, 10:48 AM

cam sensor wont trip a code always.

**czjeeper** · 02-09-2010, 11:27 AM

So, I pulled the crank sensor and tested it for resistance.
It appears that it is open. I'm going to try a new one of those.
Can someone give me more info on the CAM sensor?

Mark05059 · 02-09-2010, 12:04 PM

90% of the time it will be your crank position sensor OR wiring...then I would move onto the PMC/computer.

1. Check the 8-volt power supply to the Cam Angle Sensor (CMP) and Crank Angle Sensor (CKP).

2. Unplug them (cam and crank) and the Vehicle Speed Sensor (VSS) and then turn the key on.

3. If 8 volts is now present, start plugging each of the sensors in again, to see which one is shorted out.

Potential Causes:
Crank Angle Sensor (CKP)
Cam Angle Sensor (CMP)
Vehicle Speed Sensor (VSS)
Powertrain Control Module (PCM)
Wiring

A PCM shut-down, due to a short to ground on the 8 volt power supply. The sensor may not come back to life, after removing the short, unless the key is cycled off and then on.

Also, The Automatic Shut Down (ASD) relay is powered up when the Powertrain Control Module (PCM) sees the signal from the CKP sensor toggling.

Another check:
1. Check the 8-volt power supply to the Camshaft Position (CMP) sensor and Crankshaft Position (CKP) sensor.

2. If OK, check the Grey/Black wire at the CKP sensor for a 0-5 volt square wave signal when cranking.

3. If not a 0-5 volt square wave signal, the CKP sensor is faulty.

**UltimatE** · 02-09-2010, 12:38 PM

VSS will only trigger your CEL -- I've been driving without it for a while.

**czjeeper** · 02-09-2010, 12:49 PM

Well, I can't figure out the 8 volt thing...could be my crappy Harbor Freight multi meter.
I don't get why the CKS, or CMS aren't showing a code if they are bad.

**Que89YJ** · 02-09-2010, 01:38 PM

If the cam goes the engine will turn but you wont get spark, but you will have power to the coil, asd, fuel pump, etc. which is the indication of the bad crank sensor. Vss can stop the vehicle from starting on a short. It will take down refrence voltage.

**czjeeper** · 02-09-2010, 02:49 PM

Okay, I think I figured out the voltage thing.
I've got 9 volts at the VSS, CKS, and CMS plugs.
I tried a brand new CKS, and no start.
Sooo, I'm back at square 1.
I'm familiar with the 4.0 motors, but after cranking a few seconds, it smells of gas almost like it's flooded. No leaks anywhere.
Also, it won't start on starting fluid.
I pulled the codes again today, and it's still 12, 33, and 15.

**czjeeper** · 02-09-2010, 05:46 PM

Well, I replaced the VSS just now, and still no start.
I didn't think the VSS would make any difference, but it was bad and we wanted a speedo again when it runs again.
So, the only other thing is the ECU?

**czjeeper** · 02-09-2010, 06:23 PM

Well, as I do more reading on failing ECU's, it sounds like I shouldn't be getting spark and or fuel pump priming. Is this true? If so, I have both spark and fuel.
What is the ECU doing to keep it from starting?

**czjeeper** · 02-09-2010, 06:43 PM

Just for fun I just tried the NEW CKS with the NEW VSS, and still no go.
At least I can take that back and get my $60 refund.