Crankshaft position sensor questions

[gforce1108]

Sorry - just realized that I posted in the Defender area instead of the Discovery section... duh

I've done a bunch of searching and have posted on a couple LR sites but haven't quite found the answer to a question.

I believe I am dealing with a bad crankshaft position sensor but I have conflicting evidence...

I have little to no spark (slight spark at first that seems to fade). Not a fueling issue. I have the factory service manual and it states that a bad crank position sensor will result in no tach reading. Using and OBDII scanner, I can monitor the RPMs while cranking and the ECU is showing 145RPM or so.

If the sensor is bad, would I be able to read RPM? Also, the CEL turns off while cranking after one or two revolutions. I think I read that this is a symptom?

Background info:
1999 LR Discovery II 4.0 210k miles that belongs to a friend. Developed an intermittent miss a month or so ago which got progressively worse. Had codes for multi and cyls1,4&7 misfire. Same codes came back after clearing. Would go back and forth between running perfect one day, stalling the next. Since 1,4&7 are all on one coil pack I had him order one. I installed it yesterday, cleared the codes and it ran perfect all the way back to his house (5 miles or so). He later went out to start it and it fired, stumbled and then stalled. No codes stored. No fire on carb cleaner.

I pulled the intake again to make sure I didn't pinch anything (all good). I held my hand over one intake port and I can feel good vacuum. Pulled battery connection, armed disarmed alarm (plus lock/unlock door 4x) after reading about alarm problems, although the owner believes that it would not turn over if that was the case.

If money were no object, we'd have already ordered the sensor. The owner is very tight for cash and wants to be sure before ordering. Any help would be appreciated.

 

[Disco Mike]

any other fault codes?
with that sort of mileage a crank sensor could very easily be the issue.

 

[gforce1108]

I can't remember the code right now, but the only other one was ABS related (it has the 'three amigos' more often than not). Currently, there are no codes. I did find that odd since I was attempting to start it with the TPS, IAC, coil packs (checking 12v) disconnected with the whole upper intake removed. I guess since it never detected that it was running, it ignored it all.

So far everything I've read has pointed to the crankshaft sensor except for the RPM feedback on my scanner... But there has been no evidence that anything else would cause this either. Thanks for the feedback.

 

[Disco Mike]

Wish you hadn't torn the engine down, makes it hard to help you.

 

[gforce1108]

Wish you hadn't torn the engine down, makes it hard to help you.

I tore it down to change the coil pack based on the original misfire codes/stumbling/stalling, reassembled it (ran perfect / later no start), tore it apart a second time to verify my work and then reassembled it again. Currently - everything is as it should be. Well... other than it not starting!

 

[Disco Mike]

My money is on the crank sensor.

 

[gforce1108]

Owner of the truck picked one up today... I'll update when I have a day off to install. At the very least I'll have more data for people troubleshooting in the future.

 

[gforce1108]

Started the replacement late last night... Autozone/Duralast which happens to be an actual Bosch part (very surprised when I opened the box and found the Bosch stampings). Finished up the install this morning (had to grab more tools) - no change... Guess the answer to my question about being able to read the RPMs through a OBDII scanner shows it was working. Hopefully this will help someone out in the future.

More troubleshooting... Found fuel pump is not running. Jumper fuel pump relay and the pump runs, but truck will still not start (not exactly a surprise since it wouldn't fire on carb cleaner). It has switched 12v to energize relay, but 6ish volts floating on the ground. If I ground it, the pump comes on with the key (still no start). Reading through the manual, the ECU will switch the pump on with the key, but turn it off if the car is not started within 30 seconds. I still have 12v long after 30 seconds. It appears that the ECU switches the ground to turn off the relay?

Still no spark. Wondering if I have an ECU problem? No codes stored.

 

[Disco Mike]

No fuel, no spark, that is a classic CPS. Are you sure you reinstalled the new one correctly, sensor to the block, space then nuts?

 

[gforce1108]

No fuel, no spark, that is a classic CPS. Are you sure you reinstalled the new one correctly, sensor to the block, space then nuts?

Yeah - install went smoothly. I made sure the connector was fully seated, nuts tight and even installed the cover before testing. The part that still make me skeptical of the sensor was that I can read the engine RPMs while cranking using my scanner. The manual says that there wont be any tach signal. Gotta dig through the wiring diagrams to see where I'm loosing a signal.

Any chance of it being the ignition switch? I get 12v while cranking but I noticed it doesn't always spring back from the start position. I fixed a VW Jetta a while ago that had a bad contact with similar symptoms.