Testbook Question

jt_armstrong · Nov 27, 2011

hi guys,
Looking for some advice from those of you with diagnostics kit. IFor the past few weeks the wife's '99 4.6 has had an intermittent starting problem. When it happens the engine spins as normal but will not start. To begin with I thought it was a failed engine temp sensor. I changed that (twice to be sure) but no difference.
I took it to the local Indy who has the full land rover diagnostics who gave, me a list of the codes stored in the various computers. Few appeared relevent (to him at least) He cleared them and they stayed cleared. As expected the car started every time when it was plugged in.

A few days later and the same no start problem. Took it back and there are no faults logged. I would have thought that failing to start would have recorded something - would you guys agree? I thought I was being clever by getting the faults read rather than throwing parts at it but at 50 quid a pop on the test book I am not so sure.

dougdotcom · Nov 27, 2011

What do you get on the dash display when it wont start or is it the same as when it dose start?, have you checked fo corrosion on connectors to the Becm. ECU. and the underside of the fuse box?

Rick-the-Pick · Nov 28, 2011

Diagnostics are only useful in the right hands.

If you can manage to extract fault codes, you then have to distinguish between the genuine & false codes.
A good engineer will use these codes to determine where the fault lies.

Now, with no faults logged & from your history i'd replace the crank sensor & see if that cures it.

jt_armstrong · Nov 28, 2011

dougdotcom said:
What do you get on the dash display when it wont start or is it the same as when it dose start?, have you checked fo corrosion on connectors to the Becm. ECU. and the underside of the fuse box?

Hi Doug
Everything on the dash appears to be the same. The only anomaly I did see was the engine light flashing as the engine was turning over. This does not happen all the time.
I have checked the ECU and Becm and the connectors on both are dry and clean.

jt_armstrong · Nov 28, 2011

Rick-the-Pick said:
Diagnostics are only useful in the right hands.

If you can manage to extract fault codes, you then have to distinguish between the genuine & false codes.
A good engineer will use these codes to determine where the fault lies.

Now, with no faults logged & from your history i'd replace the crank sensor & see if that cures it.

Hi Rick

Changing out the crank sensor was my original plan after the ECT sensor failed to cure the problem. But I thought that a dodgy crank sensor would at least score a fault on the computer. Could it be that she logs a fault when she fails to start and then clears the error when she does start?
I have already cleaned the sensor disconnect at the back of the engine with no luck. Maybe better to spend the 50 quid on a new sensor than on another diagnostics episode

Irishrover · Nov 28, 2011

The crank sensor output trace can be checked with a scope if needs be

996TURBO · Nov 28, 2011

jt_armstrong said:
hi guys,
Looking for some advice from those of you with diagnostics kit. IFor the past few weeks the wife's '99 4.6 has had an intermittent starting problem. When it happens the engine spins as normal but will not start. To begin with I thought it was a failed engine temp sensor. I changed that (twice to be sure) but no difference.
I took it to the local Indy who has the full land rover diagnostics who gave, me a list of the codes stored in the various computers. Few appeared relevent (to him at least) He cleared them and they stayed cleared. As expected the car started every time when it was plugged in. A few days later and the same no start problem. Took it back and there are no faults logged. I would have thought that failing to start would have recorded something - would you guys agree? I thought I was being clever by getting the faults read rather than throwing parts at it but at 50 quid a pop on the test book I am not so sure.

Check your battery first.
At 12,1v engine spins as normal but doesn't start first time
At 12,6v engines starts immediately.

I have a Testbook T1 and it's very cool being able to work on my own car when i want but i doesn't find all the issues because it can take a long time for the ECM to register a fault

jt_armstrong · Nov 28, 2011

Irishrover said:
The crank sensor output trace can be checked with a scope if needs be

Any idea how the crank sensor fails? It doesn't appear to require power and it has no moving parts so what can go wrong with it?

jt_armstrong · Dec 3, 2011

Not 100% sure if fault is fixed but so far she has started everytime since I swapped out the crank position sensor. The old one is bent. Not sure if that would cause intermittent starting issues but can't see how it would help.

Rick-the-Pick · Dec 4, 2011

Crank sensor failure can be open or short circuit.
It rarely kicks up a logged fault.

Intermitent starting/running is a feature of the sensor failing.

I used to scope them up when suspected, but now when i suspect they're the culprit i just change them.

wammers · Dec 4, 2011

jt_armstrong said:
Not 100% sure if fault is fixed but so far she has started everytime since I swapped out the crank position sensor. The old one is bent. Not sure if that would cause intermittent starting issues but can't see how it would help.

Think you can rest easy now, that was the problem.

jt_armstrong · Dec 4, 2011

wammers said:
Think you can rest easy now, that was the problem.

So far so good. A few cold starts and hot starts since and she has started everytime. The wife was even happy to take it Tescos this morning which is saying something...

eightinavee · Dec 4, 2011

What would worry me is why it got bent,something must have attacked it.You say your car is a 99 - is it Bosch injected with the banana manifold or Gems with 4.6 on top of the plenum ?
Bosch flywheels have a cast iron milled ring for the sensor to read,Gems have a steel plate with rivetted tangs instead.The Gems ones can and do fall apart/bend.
I cant remember if the ecu will log a fault if the crank sensor fails to work on cranking,I dont think it does log anything until its running fast enough to look for other sensor outputs,ie - when its getting away from the starter at 4-500 rpm.If it then gave an implausible value you should get a crank/cam synch fault logged and the engine will run open loop ans not fire the injectors sequentially.
Sorry to dribble on,but removing the sensor again and checking for damage may be a good idea.(Plus checking the crank for excess end float)

jt_armstrong · Dec 4, 2011

Definitely a Bosch job with the bananas. My theory is that it might have been damaged when the starter motor failed a few months back. The first replacement got stuck in the flywheel. Maybe some part of the starter broke loose.

I know I am clutching at straws with this explanation but is all I could come with.

eightinavee · Dec 4, 2011

Ok,thats good in one way,bad in another....
Good that its got the cast flywheel,bad that the alloy sump covers the lower back half of the sump - Gems engines had a plate you could take off with 3 bolts.
I'd still advise looking back in there if you can,a dropped bolt/nut/washer etc could do it all again.

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