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Cold Start Issues: Vacuum and Sensors?

 
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Aaron



Joined: 28 Jan 2010
Posts: 56
Location: Surrey

PostPosted: Wed Mar 16, 2016 10:56 am    Post subject: Cold Start Issues: Vacuum and Sensors? Reply with quote

I have finally finished ski holidaying and it's time to find my cold start issue! (Also sending the Speedo off to Cluster Repairs....time to get all these jobs done!).

The engine starts up no problem. Jumps to 1500rpm and sits there (my TVR -Rover V8- does the same, but quickly normalises to 900-1000rpm within minutes). The Defender just stays there, no matter how long you leave it or drive it from cold. Only when you turn off and restart when it's warm/hot will it start and then sit correctly at 900-1000rpm. So something is at fault.

I searched on here, and have read various posts. The stepper valve and hole has been cleaned, as I've had the same before on my TVR (no change). I replaced the stepper (no change). There was also mention of vacuum leaks, but seems pipes are okay, unless I'm missing a pipe connection or two.

- Does anyone have a good diagram showing the vacuum pipes to check?

- The air intake pipe (being so long thought maybe split) seems okay (btw, anyone know where you can get a replacement if needed? seems to be obsolete now).

- Failing that, does this sounds like a failed sensor somewhere? Not sure which ones to check.

Maybe vacuum pipes are not sealing correctly until things get hot and expand, then the hot restart is all okay.

Appreciate any pointers or ideas, suggestions. A process of elimination I think Confused
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101FC



Joined: 06 Sep 2009
Posts: 227
Location: South Gippsland (VICTORIA)

PostPosted: Fri Mar 18, 2016 9:24 pm    Post subject: Reply with quote

Sounds like a temperature sensor issue to me (probably coolant). IIRC the 50th has 4 temperature senders. One is coolant temp for the dash gauge only, one for the ECU coolant temperature. The other two are the air intake temperature and fuel rail temperature. Both coolant temperature senders are on the front left of the engine, I cant remember which is which but they are inexpensive. The air intake temperature sender is mounted next to the MAF and is critical to the correct operation of the MAF. Fuel rail temperature I doubt would cause these kind of symptoms as I think its only used for starting.

From RAVE:

Engine coolant temperature (ECT) sensor
The coolant temperature sensor measures the temperature of the engine coolant fluid. The signal from the coolant sensor is used by the ECM to adjust the fuelling mixture. The engine requires a richer mixture at lower temperatures.
The sensor relies on a temperature dependent resistive metal strip. The resistance of the metal strip varies considerably with temperature and is immersed in the engine coolant fluid.
If the sensor fails, the ECM assumes and engine coolant figure of 80C. The fault could be noticeable during the engine warm up period.

Intake air temperature (IAT) sensor
The IAT sensor, by measuring the temperature of induction air, enables the ECM to determine the density, and hence, the oxygen content of the air being burned in the engine. As air temperature increases, it expands, and its density (Mass/Unit of Volume) decreases.
The basis of the IAT sensor is a temperature dependent resistive metal strip. The resistance of the metal strip varies considerably with temperature. When an inlet temperature of 55 C or higher is detected, the ECM retards the ignition timing . If the sensor fails, the ECM assumes an inlet temperature of 50 C.

Engine Fuel Temperature (EFT) sensor
The fuel temperature sensor measures the temperature of the fuel rail. The signal from the sensor gives the ECM a warning of fuel vaporization and the possibility of bubbles forming in the injectors, which may cause poor hot starting. If the ECM receives a high fuel temperature signal during starting, the fuel injector opening period is increased to
clear any vaporization bubbles from the injectors and correct the fuelling. When the engine is running, fuel circulation from the fuel tank keeps the fuel rail cool.
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Aaron



Joined: 28 Jan 2010
Posts: 56
Location: Surrey

PostPosted: Sat Mar 19, 2016 11:34 am    Post subject: Reply with quote

That is great. Thanks for the details on this, and the information on the sensors. Hopefully that is the fault. I will see how I get on and replace a sensor.
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101FC



Joined: 06 Sep 2009
Posts: 227
Location: South Gippsland (VICTORIA)

PostPosted: Sun Mar 20, 2016 3:35 am    Post subject: Reply with quote

Good luck with it, mine stalled at every junction when the weather was below 15ish degrees and hunted at idle. I never got to the bottom of it and eventually I junked the engine and went with some modern GM power.
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Aaron



Joined: 28 Jan 2010
Posts: 56
Location: Surrey

PostPosted: Sat Nov 05, 2016 9:33 am    Post subject: Reply with quote

Issue now resolved. Thermostat was jammed open. Now replaced with a 74.

Also mapping fixed, which may have had an impact too. However, it wasn't an issue before and became intermittent, until it happened at every cold start up. Seems most likely that was the issue - coolant temp sensor and stepper had already been replaced.
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50Def



Joined: 15 Jan 2016
Posts: 19

PostPosted: Mon Nov 07, 2016 8:26 am    Post subject: Reply with quote

I use thermostat ETC4765. Is that an 88Degree or 74Degree. If not what is the part number for 74Degree and what is the advantage of a lower thermostat? Also what temperature is the engine designed to run at and is it an issue to run it at a lower temperature?

I understand that the engine will run cooler but is this an advantage as surely LR did some tests to determine what is the optimum running temperature?
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Aaron



Joined: 28 Jan 2010
Posts: 56
Location: Surrey

PostPosted: Mon Nov 07, 2016 9:44 am    Post subject: Reply with quote

I must admit I have no idea on your questions. As mine was broken (jammed open) I just went with the replacement recommendation from RPI. They know their stuff, and it seems to running great now.

I believe the 88 is fitted usually for Cold Climates and the 74 is for Hot Climates. So the range is down to preference and running choice.

Someone else might be along with some deeper knowledge on these questions.
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