P38 4.6 lpg 2000 hard starting when cold

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andymalham

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After a couple of weeks trouble free on the new Turner motor the beast has started playing up. It's a complete bitch to start from cold. The only way it will fire up from cold is if I floor the pedal until it struggles into life and then just tease the throttle for a few seconds. It then runs perfectly. Warm and hot starts are not a problem. A cold start would qualify as the car being stood for two hours or more.
So.....I hooked up my mates OBD tester and got a P0112 code for IAT low. The data showed a reading of -40 degrees and this stays at this reading no matter what the circumstances. The MAF readings are changing when the car is driven so that part is probably OK. When I disconnect the 5 wire plug from the MAF the car seems to run OK but I haven't really tested this out. With the plug disconnected I still get -40 on the IAT and no readings from the MAF (no surprise).
So, here's my theory. The IAT has failed and needs to be replaced or there is a wiring issue. My plan is to meter out the IAT wiring to the ECU and see if there is a short or break. We have just changed the engine so that is quite possible.
 
+1
Mine will die as soon as i pull the plug on the MAF. When my old failed MAF was unplugged the engine would still run as it was running on default settings.
 
hi andy , I have a couple of spare maffs if you want to try swapping them over to see if yours is ok ???? I know from previous occasions that sometimes when you have changed things for whatever reason , I,e, engine , heads ,etc etc ,,then your original maf goes into default ,and soon as you swap it the engines fine ,,!!!!! im happy to post them f.o.c. and you can send them back to me when finished ,, just pm me with your address and il'l put them in the post ,,, its worth a try cos as I said its happened to many people before ,,,ok cheers mozz
 
Thanks for the offer Mozz. I am going to meter the wires out this morning and see if I have a short or a break and will get back in touch. Ref disconnecting the MAF. If you do this with the motor running it will immediately cut out but will restart OK. I think the car is running in default mode as it does seem down on power. Last night I did 25 miles with the OBD tester plugged in and the IAT temp never shifted off -40F. Also, the fault happened quite suddenly on Friday which points to a component failure rather than a short or break which usually start off as intermittent. The P0112 code can be cleared but it comes back as soon as the engine is started.
 
Well that's a funny thing. Left the Rangie in our workshop overnight and it started up a treat this morning! Admittedly it's a lot milder today and the workshop is warmer than outside (marginally) so that could make a difference. Did notice that this problem only started when the weather turned cooler last week.
But, the important thing is this, I put the OBD tester back on and the IAT and MAF readings are good. IAT reads ambient temp of about 57F and varies slightly when I rev the motor. Cleared the code (P0112) and this did not come back. This might have fixed itself. Had a long conversation with Mozz yesterday and got the impression that this can happen. I am going to take it out for a blast now to see if it is running normally again.
 
Well, that seemed OK. Did notice one tiny thing. I decided to start the car on petrol because it sometimes doesn't start cleanly on gas when the car isn't properly warm. There is a switch on the dash to turn the gas on or off so I turned it off. The car started cleanly on petrol but I noticed the previously good IAT reading had gone back to -40F. Oh bugger. Let it warm up for a minute and then manually switched the gas on. It switched over cleanly and I noticed that the IAT reading immediately changed to a good reading on gas. Switched the gas off again and the IAT reading stayed correct. Switched back to gas, all good. Test drive was all good. Plenty of power, smooth tickover, pickup and acceleration. IAT temp reading maxed out at +88F in light traffic. Don't know if this is correct?
 
andymalham said:
Well, that seemed OK. Did notice one tiny thing. I decided to start the car on petrol because it sometimes doesn't start cleanly on gas when the car isn't properly warm. There is a switch on the dash to turn the gas on or off so I turned it off. The car started cleanly on petrol but I noticed the previously good IAT reading had gone back to -40F. Oh bugger. Let it warm up for a minute and then manually switched the gas on. It switched over cleanly and I noticed that the IAT reading immediately changed to a good reading on gas. Switched the gas off again and the IAT reading stayed correct. Switched back to gas, all good. Test drive was all good. Plenty of power, smooth tickover, pickup and acceleration. IAT temp reading maxed out at +88F in light traffic. Don't know if this is correct?
Click to expand...

IAT should be the same as ambient air temperature give or take a few degrees. It is the air temp measured as it goes through the MAF sensor on the Motronic engine. IAT sensor on the Gems was in the filter box. +88 f does not sound correct unless you are having a warm spell in your area. Or it is sucking air in from the engine bay. ;);):D:D
 
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mozz smith said:
hi andy , I have a couple of spare maffs if you want to try swapping them over to see if yours is ok ???? I know from previous occasions that sometimes when you have changed things for whatever reason , I,e, engine , heads ,etc etc ,,then your original maf goes into default ,and soon as you swap it the engines fine ,,!!!!! im happy to post them f.o.c. and you can send them back to me when finished ,, just pm me with your address and il'l put them in the post ,,, its worth a try cos as I said its happened to many people before ,,,ok cheers mozz
Click to expand...
Hi Mozz. The MAFs arrived this morning thanks. Will have a session on Monday with the replacements. The car was working correctly on Thursday but it went back to playing silly buggers yesterday. This is good in a way as it proves that the ambient temp has no influence on the fault, i.e. the hard starting occurred at air temps of -2C and +14C just the same.
 
wammers said:
IAT should be the same as ambient air temperature give or take a few degrees. It is the air temp measured as it goes through the MAF sensor on the Motronic engine. IAT sensor on the Gems was in the filter box. +88 f does not sound correct unless you are having a warm spell in your area. Or it is sucking air in from the engine bay. ;);):D:D
Click to expand...
The test drive was done in light traffic so the motor would be pulling in warmer air than it does on the motorway. I did notice that as soon as the car started moving forwards the IAT temp came down. We are having a mild spell here. +15C was normal this week. I now have the MAFs from Mozz so I will have a play around with them on Monday.
The airbox installation and pipework all look good and are unmodified.
 
andymalham said:
Hi Mozz. The MAFs arrived this morning thanks. Will have a session on Monday with the replacements. The car was working correctly on Thursday but it went back to playing silly buggers yesterday. This is good in a way as it proves that the ambient temp has no influence on the fault, i.e. the hard starting occurred at air temps of -2C and +14C just the same.
Click to expand...

ECU temp sensor maybe the cause of that.
 
wammers said:
ECU temp sensor maybe the cause of that.
Click to expand...
So, I got the three combined MAF and IAT units off Mozz. To get the ball rolling I left my old unit installed, and plugged in my generic OBD tester. I will call my original IAT/MAF unit # zero. I noticed that there were fault codes for the IAT and MAF but the car seemed to start and run OK. I cleared the codes and noticed that the IAT and MAF readings were correct I.e. +55F IAT (ambient temp) and about 1.0 lb/min MAF. Did a quick test run and the IAT came up to about 73F with the MAF settling down to about 0.7 to 0.8. No fault codes.
Tried the first replacement unit which I will call unit # one. Started and ran OK and after a brief warm up run was getting 75F to 78F IAT and MAF of 0.7 to 0.8 at idle.
Tried the next one which I will call unit # two. Car seemed to idle much sweeter and ran nicer as well. After a brief run the IAT settled down to between 79F and 86F and the MAF was 0.7 to 0.8.
Moved on to Unit # three. Not so good. Struggled to start and ran like a bag of ****e. Ran it round the block and it just wasn't happy. Felt like it was going to pack up. Strangely enough the IAT showed 75F with a MAF of 0.6 at a steady warm idle.
NO FAULT CODES WITH ANY OF THESE UNITS.
So it seems # two is the clear winner despite giving very similar readings to the two slightly inferior units (#zero and #one) and the obviously dodgy unit (#three).
I will investigate this further but I am getting the impression that the IAT/MAF units may give OK readings and the car may still not run right. Like I said, units zero and one seemed to be OK. It was only when I fitted unit two that I noticed that unit two gave me a much sweeter car than the others. Unit three, on the face of it isn't faulty, but the car still runs like a dog.
P.S. The 3 units I got from Mozz were all Bosch. The original one I started with has no manufacturers markings.
 
yes their all bosch , I try not to buy second hand or cheaper brit-part stuff ,you only get what you pay for !!!!!!! lets hope its sorted for you ,cheers mozz
 
Well it's nearly winter again and we are getting some pretty frosty mornings and the poor old bus struggles to start from cold so I decided to have another go at this fault. Figured that a water temp sender is cheap and fairly straightforward to fit so ordered one from Island 4 X 4 in Kent. I got the Britpart version of the MEK100160L. Ordered at 13:30 tuesday, arrived 08:30 wednesday. £16 inc vat and shipping. You can't beat that for value and service. Took about an hour to fit as you have to take off the fan, serpentine belt, A/C pump, steering pump and bracket etc and........................ bugger me! It works!
So, Lesson to be Learned. Just because the temp sensor gives a good reading to the gauge, doesn't mean the sensor is working correctly. If you have an option which is cheap and easy, take it, regardless of conflicting evidence pointing you in the another direction.
ALSO. I was so tied up with the idea that I had a MAF/IAT fault that I completely ignored Wammers comments. The fact that the temp gauge worked correctly convinced me that the sender was OK.
Wammers, please accept my sincerest and most grovelling apology? Please keep up the good work even if you sometimes get ignored.
 
andymalham said:
Well it's nearly winter again and we are getting some pretty frosty mornings and the poor old bus struggles to start from cold so I decided to have another go at this fault. Figured that a water temp sender is cheap and fairly straightforward to fit so ordered one from Island 4 X 4 in Kent. I got the Britpart version of the MEK100160L. Ordered at 13:30 tuesday, arrived 08:30 wednesday. £16 inc vat and shipping. You can't beat that for value and service. Took about an hour to fit as you have to take off the fan, serpentine belt, A/C pump, steering pump and bracket etc and........................ bugger me! It works!
So, Lesson to be Learned. Just because the temp sensor gives a good reading to the gauge, doesn't mean the sensor is working correctly. If you have an option which is cheap and easy, take it, regardless of conflicting evidence pointing you in the another direction.
ALSO. I was so tied up with the idea that I had a MAF/IAT fault that I completely ignored Wammers comments. The fact that the temp gauge worked correctly convinced me that the sender was OK.
Wammers, please accept my sincerest and most grovelling apology? Please keep up the good work even if you sometimes get ignored.
Click to expand...

No problem. The ECU temp sensor is the one that controls whether or not cold start conditions are set. The gauge has nothing to do with it and is separate. The IAT temp sensor in the MAF whilst it is used for fuel trimming, it's main function is to tell the ECU air temp so that it knows how much airflow there actually is. Cold air will cool the hot wire better than hot air will so the ECU needs to know the temp of the air flowing in to adjust airflow readings according to ambient air. This gives the correct flow rate.;);)
 
Two days later and the old girl is as sweet as anything. My mpg has improved drammatically from 11-12mpg to 14-15mpg at commuting speeds, which is crawling rather than sprinting! Also noticed that the idle has dropped to 600 rpm when warm compared to 900 rpm in the fault condition. This makes driving in traffic much smoother.
I had almost resigned myself to booking the car in at our local LR independant dealer for diagnosis but I'm pretty sure their Diagnostic S/W would not have shown the temp sensor as faulty, as it was neither short circuit or open circuit.
My day job includes diagnosing faults on Harleys and Victory motorcycles and very often the Diagnostic S/W shows no faults despite the bikes running like a bag of crap.
 
andymalham said:
Two days later and the old girl is as sweet as anything. My mpg has improved drammatically from 11-12mpg to 14-15mpg at commuting speeds, which is crawling rather than sprinting! Also noticed that the idle has dropped to 600 rpm when warm compared to 900 rpm in the fault condition. This makes driving in traffic much smoother.
I had almost resigned myself to booking the car in at our local LR independant dealer for diagnosis but I'm pretty sure their Diagnostic S/W would not have shown the temp sensor as faulty, as it was neither short circuit or open circuit.
My day job includes diagnosing faults on Harleys and Victory motorcycles and very often the Diagnostic S/W shows no faults despite the bikes running like a bag of crap.
Click to expand...

It does not matter whether the engine is diesel (if the glow plugs are sound) or petrol, on any electronically controlled fuel injected engine that suffers from bad cold starting the ECU temp sensor is the first port of call.
 
wammers said:
It does not matter whether the engine is diesel (if the glow plugs are sound) or petrol, on any electronically controlled fuel injected engine that suffers from bad cold starting the ECU temp sensor is the first port of call.
Click to expand...
Just 2peneth I had a problem with my car at the time on gas during a cold snap, the software that came with the system indicated that the temp was short so I insulated all the pipes, started on petrol and when temp up over to gas it sorted it.
 
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