Bungle
Member Since: 07 Apr 2015
Location: Wanborough
Posts: 254
  
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| V8 scared of the cold.... |
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Dylan the Discovery has developed a problem. When the temperature gets low the engine cranks fine and will often fire up, then die. Normally giving it another go it will crank for a while then reluctantly fire up. Once it has been running 10 seconds or so, it is fine. I have had a similar problem since I got the vehicle which occurs if I do a really short run, when I go to restart it will take a lot of cranking before it finally splutters into life.
With this really cold weather it has got to the stage where it can take several crank cycles to get it to go, and then I have to hold the revs up for a minute or so otherwise it will die, but once it is past that stage it is all fine. No error codes on the engine.
Any ideas?
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 2nd Mar 2018 11:24 pm |
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Batfink
Member Since: 31 May 2017
Location: Isle of Sheppey
Posts: 1510
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No expert on these but general petrol engines but it sounds like a fuelling issue. I'm sure someone with more ideas will be along soon  2006 TdV6 HSE.
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| 2nd Mar 2018 11:50 pm |
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pjm-84
Member Since: 04 Oct 2016
Location: Hampshire
Posts: 2439
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Mine will start on the button and run at about 1250rpm and then slowly die back to 700 rpm. This duration is longer when its colder. Maybe 30seconds or so.
It seems your "cold start" is not working.
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| 3rd Mar 2018 12:38 am |
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Bungle
Member Since: 07 Apr 2015
Location: Wanborough
Posts: 254
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Yep, once running mine does the same (i.e. falls back to under 1000rpm), but to get it going you need to hold the revs at about 2500, try and hold them at the usual fast idle and it will splutter and die.
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| 3rd Mar 2018 2:11 am |
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Globetrotter448
Member Since: 21 Mar 2017
Location: Londonderry NSW
Posts: 1783
 
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On cold starts, it should have a control function (like a choke on older system) that puts more fuel into the engine so that the revs are held at around 1200 for a few minutes before backing off. It sounds like this is not happening or insufficient fuel. Make sure you have more than a quarter of a tank of fuel.
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| 3rd Mar 2018 2:22 am |
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SafariDave
Member Since: 19 Nov 2011
Location: NYC & LA
Posts: 775
 
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we have 2 V8's that never this issue in cold weather.
Dave D3 2005 V8 SE Bonatti Grey "The Rhino" (our NYC D3)
De-tangoed Headlights, D4 2016 Style Black Pack Grille, D4 19" Wheels/ Bridgestone Alenza
D3 2005 V8 SE Bonatti Grey, D4 2016 Style Black Pack Grille (our LA D3)
D2 1999 V8 SD7 Chawton White (our Caribbean Beach truck)
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| 3rd Mar 2018 3:58 am |
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Bungle
Member Since: 07 Apr 2015
Location: Wanborough
Posts: 254
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Globetrotter448 wrote:On cold starts, it should have a control function (like a choke on older system) that puts more fuel into the engine so that the revs are held at around 1200 for a few minutes before backing off. It sounds like this is not happening or insufficient fuel. Make sure you have more than a quarter of a tank of fuel.
Yep, as above, it is trying to do this, but at 1200 the engine just won't run properly when it is stone cold, coughs misses and splutters until it eventually gives up. If you manually hold it at 2500 it clears and is fine.
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| 3rd Mar 2018 7:23 pm |
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Bungle
Member Since: 07 Apr 2015
Location: Wanborough
Posts: 254
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SafariDave wrote:we have 2 V8's that never this issue in cold weather.
Dave
Mine didn't until recently. Though it has always had issues if you do a very short run and then try and restart it.
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| 3rd Mar 2018 7:24 pm |
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cleland72
Member Since: 16 Sep 2016
Location: Cambridge
Posts: 79
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I've not had a chance to look at the fuel system on the AJ V8 yet but on my old Rover V8s, both Lucas and Megasquirt injected, there's an idle air valve (IAV) that bypasses the throttle plate and lets more air in to the engine when it's cold - the MAF/MAP sensors detect the extra air flow and add more fuel; on top of this the ECU will enrich the fuelling when coolant temperature is below normal running temp. Assuming the AJ V8 has an IAV, that would be the first place to look.
Scrub that, just found http://www.jagrepair.com/images/Training%2...9-5-01.pdf - throttle is electronically controlled so the ECU just opens the throttle a bit more, no IAV.
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| 3rd Mar 2018 8:21 pm |
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Charliecloud
Member Since: 31 Jul 2014
Location: Tonbridge
Posts: 980
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pjm-84 wrote:Mine will start on the button and run at about 1250rpm and then slowly die back to 700 rpm. This duration is longer when its colder. Maybe 30seconds or so.
It seems your "cold start" is not working.
Same as mine - starts first turn of the key.
OP - have you had the MAF cleaned and the throttle body ? If you have no codes I would start with the simply and easiest first and then progress to the harder and more expensive
Let us know how you get on
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| 3rd Mar 2018 10:14 pm |
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Globetrotter448
Member Since: 21 Mar 2017
Location: Londonderry NSW
Posts: 1783
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A simple no cost check, the V8's have a "coil per plug" I would disconnect each one, individually and see what happens, it could be a fouled plug or bad coil/connector, I am still favouring fuel though or sticky throttle (does not move until it is exercised, holding at 2500 rpm)
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| 3rd Mar 2018 10:26 pm |
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pjm-84
Member Since: 04 Oct 2016
Location: Hampshire
Posts: 2439
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Just reading the workshop manual.
MAF and Engine Coolant Temparture sensor.
Quote:ECT
The sensor is located at the front of the engine in the water pipe below the throttle body. The ECT sensor is a thermistor used to monitor the engine coolant temperature. The engine coolant temperature sensor is vital to the correct running of the engine as a richer mixture is required at lower block temperatures for good quality starts and smooth running, leaning off as the temperature rises to maintain emissions and performance.
The sensor has an operating temperature range of -30 Degrees Celsius to 125 Degrees Celsius. When a defective coolant sensor is detected, the ECM uses the oil temperature sensor value.
This sensor is fairly quick to change.
I changed all 3 sensors (2 more by the oil filter housing (oil and fuel )) on mine when I lost the temperature gauge one day whilst idling for a while. No errors were recorded.
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| 3rd Mar 2018 10:35 pm |
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Bungle
Member Since: 07 Apr 2015
Location: Wanborough
Posts: 254
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Globetrotter448 wrote:A simple no cost check, the V8's have a "coil per plug" I would disconnect each one, individually and see what happens, it could be a fouled plug or bad coil/connector, I am still favouring fuel though or sticky throttle (does not move until it is exercised, holding at 2500 rpm)
Can't see that it would be a dodgy coil, they tend to play up when hot rather than cold.
Even if I take the revs up to 2500, unless I have held them there for a bit, it still won't idle at 1200, so don't think it is that. Also that wouldn't explain why it struggles to start with the same symptoms when lukewarm.
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| 6th Mar 2018 2:06 pm |
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Bungle
Member Since: 07 Apr 2015
Location: Wanborough
Posts: 254
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Charliecloud wrote:pjm-84 wrote:Mine will start on the button and run at about 1250rpm and then slowly die back to 700 rpm. This duration is longer when its colder. Maybe 30seconds or so.
It seems your "cold start" is not working.
Same as mine - starts first turn of the key.
OP - have you had the MAF cleaned and the throttle body ? If you have no codes I would start with the simply and easiest first and then progress to the harder and more expensive
Let us know how you get on
Did do the MAF some time ago, no big deal to whip them off and check them over but I doubt they would only affect starting from cold/lukewarm. I'll add it to the things to try....
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| 6th Mar 2018 2:08 pm |
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Bungle
Member Since: 07 Apr 2015
Location: Wanborough
Posts: 254
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pjm-84 wrote:Just reading the workshop manual.
MAF and Engine Coolant Temparture sensor.
Quote:ECT
The sensor is located at the front of the engine in the water pipe below the throttle body. The ECT sensor is a thermistor used to monitor the engine coolant temperature. The engine coolant temperature sensor is vital to the correct running of the engine as a richer mixture is required at lower block temperatures for good quality starts and smooth running, leaning off as the temperature rises to maintain emissions and performance.
The sensor has an operating temperature range of -30 Degrees Celsius to 125 Degrees Celsius. When a defective coolant sensor is detected, the ECM uses the oil temperature sensor value.
This sensor is fairly quick to change.
I changed all 3 sensors (2 more by the oil filter housing (oil and fuel )) on mine when I lost the temperature gauge one day whilst idling for a while. No errors were recorded.
Temp gauge is working fine, but I will check the value showing on IID to make sure the extreme cold end isn't an invalid number - good shout.
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| 6th Mar 2018 2:09 pm |
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