Thread: Weak Td5

@sierraferry: Yes, I replaced the small (and unreasonably expensive) filter under the FPR, and also the fuel filter behind the wheel, which I change regularly. The tires are not oversized, and I have checked and lubricated the wastegate actuator arm which indeed was stuck and I thought I'd found the problem but no difference. The new fuelpump is not a VDO, but today I connected a pressure monitor to where the fuel temperature sensor sits in the FPR and the pressure is well above 4 bars, almost 5 even when driving at high load uphills, no decrease at all in the pressure monitoring. BUT: strangest thing, with the pressure monitor connected It was performing wonderful, could even accelerate uphills! So, I put the fuel temp sensor back and the problem was back... disconnected the contact from the sensor and Voila! Perfect preformance!!
Bad sensor or something corrupt in the ECU. I am suspecting the ECU since I also found an error message from the gearbox: "P1884 CAN MESSAGE MD_IND INVALID" (no other errors), and strange Engine temp data from gearbox:

enginetemp.jpg

It never goes above 53 degrees...

So now I'm contemplating how to proceed? New temp sensor? New ECU? Other Ideas? Are there any negative effects driving without the temp sensor connected?

So you disconnect the fuel temp sender, and it goes good.
Reconnect the fuel temp sender and it goes bad.
But you're getting engine temperature values from the gearbox temp sender?

Is this an OBDII tool you're using to get this data, or the nanocom?(looks like nanocom, but need to ask question).

I'd say drive with the fuel temp sender disconnected for a while and see how you go.
But before you condemn the ECU, pull some stuff off around it and triple check the wiring loom to the ECU for damaged parts or shorts.

My brother's TD5 had an issue a while back and I thought it was ECU related. So when searching on the issue I found that damaged ECU looms are not so uncommon.
Maybe the wire from the fuel temp sender is cross contacting with another wire before it gets to the ECU and therefore the ECU gets corrupted or scrambled data.

Alternatively: when you changed the fuel pressure regulator, did you change the entire assembly or did you rebuild your old one with some new parts(eg. regulator/o-rings/gaskets etc) and keep the body of the assembly including the temp sender?
I think many people assume that when you do the FPR, you buy the new assembly in it's entirety, which means an entirely new body, hoses .. ie. an entirely new part, which includes the temp sender.
If you used your old fuel temp sender to rebuild your FPR, maybe the sender is dead, giving a high reading on the fuel temp and confusing the ECU?

Red herring first - the temperature reported in nanocom for engine temp from the gearbox is rubbish. I have *no* idea where it comes from but it is never the actual engine temp. There is also no temperature sensor on the gearbox.

The error message on the box I see quite often on most of the D2s I've hooked my nanocom to, it usually indicates a low voltage at some point - I swear the box can log a fault during cranking....

It sounds like you have the fault found though, check the fuel temperature in the TD5 engine section of nanocom, I'm guessing it is reading high and so the ECU is reducing the fuel being fed in because of the perceived temperature. Disconnected the ECU just assumes a default value.

Ditto eng temp from gearbox values, its just a reference value.
You can swap eng temp sensor with the fuel temp sensor to eliminate that ( clean first :-)

I read values with Nanocom Evolution. From what I've found, the Engine temperature reported from gearbox is received from the engine ECU and is used by the gearbox to determine if it's warm enough to engage lockup.
My fuel temperature sensor seems to give correct values?:

fueltemp.jpg

...and the coolant temperature follows the same curve. When disconnected the fuel temp value defaults to 60 degrees.
I'll have a closer look at the cables

The temp senders don't normally fail outright, they tend to flatten off with age reporting values lower than reality, typically 10-20C less. At least when using Bosch parts.

For the coolant sensor this normally manifests as increased fuel consumption.

I've not had a problem with the fuel sender yet, but would imagine it would not retard performance in this failure mode (on a manual at least!) - looking forward to seeing the outcome of this investigation though as I'm not sure how/if the auto ECU uses the fuel temp information and whether this is actually a wiring issue.

If you've got a multimeter to hand you can test the sensor by setting it to resistance (~20kohm) and referring to this datasheet to approximate temperature from the output -> http://www.bosch-motorsport.com/medi...2569739pdf.pdf

If you believe your problem is the ecm, replace all of the power feed and earth wires running to the ecm. You don't need a loom, just replace them individually. I haven't had it on a Td5, but too many times to count on trucks.

@BennehBoy

I think you are right. According to the Nanocom manual, fuel temp should be about 10 degrees below coolant temp, mine measures approx. 30 degrees below. The fuel temp is used by the ECU to calculate fuelling so this might be it! I have ordered a new sensor, not so expensive and since I've replaced everything else....
Will update when I've replaced it.