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Discussion Starter · #1 ·
Another crank-no start issue...
I've done a bunch of searching regarding a no start problem but have a question regarding the symptoms and the behaviour of the crank position sensor. 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. 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).
 

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I had a bad fuel pump...but when I tested a plug while cranking I had maybe one spark, seemed kinda weak. Once I replaced the crank position sensor, I had a lot of spark.

I didn't think the ECU would register RPM's below 300. Might be the "no tach reading" the RAVE mentions.

Positive you have good fuel pressure at the rail?
 

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Discussion Starter · #3 ·
I don't know for sure that there is good fuel pressure, but I shot carb cleaner into the throttle body and then later straight into the open intake. Not a single sign of firing.

There is no movement on the tach but the OBDII scanner does record 0 before cranking and then upwards of 150 while cranking. All other parameters (temps/TPS, etc.) look normal.

Thanks for the input - it's very appreciated!
 

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Sounds more like crank sensor. They aren't the most fun thing to replace. Watch when you remove the sensor that you don't lose the barrel spacers, one on each bolt. I had to tie a piece of wire (slip knot) and loop it around the sensor once removed. That way I had the ability to pull on the sensor while trying to disconnect the connector with the other hand. No room for 2 arms up there. Probably easier with 2 people. Some have to remove the exhaust manifold.

Fuel pressure, there is a test port located between the intake manifold and firewall on drivers side of center. I popped the wire loom out that rests below the wipers to give a little more room. The port is tough to reach. Unscrew the cap and depress the valve while cranking, fuel should squirt for a couple seconds then stop. If you only have a few drops, that isn't normal. Don't put your head over it while testing or you'll get fuel in the face...
 

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Discussion Starter · #5 ·
Thanks for those hints! I climbed under to locate the sensor but didn't really inspect what was needed to replace. It died in a dirt driveway but fortunately right in front of the garage door. We are going to have to push it inside for me to get to the sensor.

I guess it isn't a bad idea to check fuel pressure as well - could be weak spark and no fuel caused by the same component. I have pushed the inertia switch, just in case.
 

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Sensor is located on the bell housing. I crawled from behind the drivers tire head first towards front of truck. Sensor cover is located above the exhaust manifold, probably covered in crud. Remove the 2 bolts holding the cover on. The connector is mounted to a bracket further up the engine, and there is zero play in the wiring. Connector needs to be pushed up (from below) and slid off bracket. Remove the sensor, (2 more bolts and spacers), make sure they go back on the same order. Then disconnect connector.
There is a heat shield by the brake fluid reservoir that you might want to remove to better get at the connector from above.
 

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Discussion Starter · #7 ·
Sensor is located on the bell housing. I crawled from behind the drivers tire head first towards front of truck. Sensor cover is located above the exhaust manifold, probably covered in crud. Remove the 2 bolts holding the cover on. The connector is mounted to a bracket further up the engine, and there is zero play in the wiring. Connector needs to be pushed up (from below) and slid off bracket. Remove the sensor, (2 more bolts and spacers), make sure they go back on the same order. Then disconnect connector.
There is a heat shield by the brake fluid reservoir that you might want to remove to better get at the connector from above.
It's definitely covered in crud! 210k miles and everything leaked when he first brought it to me. I've done head gaskets on it, repaired multiple coolant leaks (and bypassed throttle body coolant loop to stop a leak), and installed an oversized oil drain plug - last 'mechanic' RTV'd it in after stripping it. I had it leak free for nearly a year, but old age is catching up to it. Valve covers are leaking again along with the radiator.

The suspension hasn't worked right in years - slowly from intermittently dropping down to now only occasionally working. Been trying to convince him to let me put springs in it. Overall, it's pretty hurting but he seems to love it. I am impressed with that 4.0... very nice motor!
 

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Tighten valve cover bolts every oil change, only outboard bolts (2) are accessible. 8mm 12 pt I believe.
Springs are a good alternative to the airbags (SLS). If airbags are removed pull the relay in engine compartment fuse box and fuses for SLS. Even after that I've had my compressor kick on a time or two. It should be turned off, disabled in the BCU for complete "removal".
That v8 is a 1960's Buick design...
 

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Easiest test for the crank position sensor: when it stalls hot, spit water down the driverside rear of the engine, over the CPS shield. The water will cool it, and it will start right up once cooled. It will get you home in a pinch and conclusively diagnose a dying CPS. Not the easiest part to access but its less than an hour job. I did it in my D2 99, and a month later in the wifeys ML500 (much harder to get to). The water trick worked on both.

Oil leaks around valve cover gasketts- The outer valve cover bolts can be replaced with standard ace hardware stainless 1/4-20 x 2" bolts, that use a standard hex wrench vs the dang 12pts. Makes it a heck lot easier to tighten, and while there put a stainless split-washer underneath the bolt head, and no more tightening neccessary. Not to say it wont ever leak oil again, but keeping those bolts tight does help stop/control it.
 

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Discussion Starter · #11 ·
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.
 

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Discussion Starter · #12 ·
I did more testing today. I ohmed out the ground signal for the fuel pump relay from the ECU to the relay - tests good. Also checked grounds to the ECU since it sends switched grounds to the relay and coil packs. I can see that someone has had the ECU removed at one point (current owner has owned it for 10 years). I'm about out of ideas other than swapping in another ECU.
 

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When say you have 12v after 30 secs, is that at the pump or the relay? I seem to recall having 12v at the pump regardless...but don't quote me. My pump was sounding faintly like it was running, more of an electrical hum rather than the sound of a pump...The crank position sensor goes on the studs first, then spacers, then nuts. Just making sure it was put back in correct order...

I know when a BCU is replaced, the ECU and dash cluster have to be replaced all at once from the same donor vehicle, or else it has to be flashed by someone with the right computer, Testbook/T4, nanocom etc. Not sure if same is true for the ECU replacement.
 

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From the RAVE...might want to check crank sensor at the ECM. Sensors have been known to be bad from the get go.

Input/Output
Because of the nature of its operation the CKP sensor does not require any electrical input source. The CKP sensor
is a 3 pin variable reluctance sensor generating its own electrical output. The 2 output sources from the sensor are
earthed via pin 46 of connector C0636 of the ECM and sensor output is via pin 32 of connector C0636 of the ECM.
This output is in the form of an ac voltage waveform. The 3rd pin is used by the ECM as an earth screen, this screen
protects the integrity of the CKP sensor signal to ensure that outside electrical interference is eliminated, it is
controlled via pin 45 of connector C0636 of the ECM. The ac voltage generated from the CKP sensor is relative to
engine speed.
 

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Discussion Starter · #15 ·
I installed the sensor the way you mentioned. Wasn't too bad other than needing to run back to my garage to get a 7mm socket for the cover.

12v at the relay. Looking through the schematics that appears to be normal. The ECU switches the ground to control the relay (12v direct from ignition). I had not been able to confirm the operation when I posted above.

I'm 99% sure that the crank sensor signal is making it to the ECU. I can monitor the RPMs while cranking (around 140 depending on the battery charge). That really was my original question. I have the actual print service manual but also downloaded the RAVE manual. This is why I think it's working:

In the event of a CKP sensor signal failure any of the following symptoms may be observed:
l Engine cranks but fails to start.
l MIL remains on at all times.
l Engine misfires (CKP sensor incorrectly fitted).
l Engine runs roughly or even stalls (CKP sensor incorrectly fitted).
l Tachometer fails to work.
l Flywheel adaption reset – ferrous contamination

The other thing I am wondering... What if the crank sensor can not detect TDC? The sensor would read RPMs, but the ECU would not know what position the engine is in. If I read it correctly, if the ECU forgets that position, it should learn it after 1 complete revolution. My CEL does turn off while cranking at about that time.... Something to think about.
 

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Just for grins... try and bypass the inertia switch. Disconnect the connector for the switch and jump the outside pin slots. If it does start, don't let the owner drive it that way with no fuel cut off... it would be your butt if something happened.

Still no spark. Wondering if I have an ECU problem? No codes stored
Did you pull a plug and check for spark? Did it look the same/better/worse than before CKP was replaced?
 

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Discussion Starter · #17 ·
Just for grins... try and bypass the inertia switch. Disconnect the connector for the switch and jump the outside pin slots. If it does start, don't let the owner drive it that way with no fuel cut off... it would be your butt if something happened.

Did you pull a plug and check for spark? Did it look the same/better/worse than before CKP was replaced?
I didn't bypass the inertia switch, but I did accidentally leave it unplugged once while ohming it out. Learned that the truck turns on the 4way flashers when the switch isn't made and an attempt is made to start it. Thought that was pretty cool actually.

I pulled one spark plug wire - didn't see any spark at all, but I did have a fairly bright light on. Hard to say if it was the same or worse - but definitely not any better!
 

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Bypass the inertia switch. See if that allows it to start or impacts the lack of spark. Rule out the easy/cheap crap first before replacing the ECU. My switch appeared to be functioning correctly, flashers on when disconnected and tried to start. Truck would not start when switch was connected, only when bypassed.
 

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Discussion Starter · #19 ·
Bypass the inertia switch. See if that allows it to start or impacts the lack of spark. Rule out the easy/cheap crap first before replacing the ECU. My switch appeared to be functioning correctly, flashers on when disconnected and tried to start. Truck would not start when switch was connected, only when bypassed.

Very interesting..... I almost tried it, but thought we had eliminated it when the flashers indicated the switch was open. I will certainly give it a shot!
 
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