Have you ever seen..

[wolf_walker]

Ambient temp effect an injection pump?

I keep telling myself it can't be, and that on a well warmed up motor even airflow through the engine bay ought not to effect the thing, but darned if I don't keep coming to this conclusion from observation.

As an example, I took the interstate to work this morning since my usual back road is covered in icy crap.  I started with a block heater so it was well warmed in the five miles to the interstate.  I cruise fifteen miles at a leasurly 65mph with the CC on, pull off my exit and down-shift to 4th and some light throttle and it's clattering like hell.  JUST like it does when it's cold.  Op temps are steady, no smoke, etc.  The only thing I can figure is cold air in the engine bay had cooled the heck out of the pump and/or lines.  It had started to clear up and quiet down by the time I got to work a few minutes later.

Yes this pump is tired, I've been having some less than ideal running with it over the winter, it is SO sensitive to temp.  Ran great in the summer, I can tell a marked diff in how it runs and sounds with a 12-15 degree drop in temp though, easy.  Another piece of data is if it's fairly warm and I sit at idle for awhile, it runs great directly after, till some road time and it cools off again.  How the heck can air temp underhood effect the thing so much?  I can't think of anything other than expansion/contraction and the thing being worn out.  I don't believe fuel viscosity would be effected THAT much at the rate these things return fuel to the tank under light load.  Thoughts?

I have another pump to reseal if I can get myself out in the shop and do it, looking forward to contrasting the two.  Assuming I get it done before winter.

[rallydiesel]

I don't know about ambient temp but fuel temp definitely affects timing.

[Vincent Waldon]

On TDIs there is a fuel temp sensor built into the IP and the ECU directly mods the timing in real-time based on fuel temp... that's how important it can be.

One thought... do you still have the temperature-sensitive fuel tee in your fuel filter??  Do you have a different one you could swap in as a test?

[wolf_walker]

No temp switch on the filter that I've ever seen on these, this one has the screw on canister filter.  It's either been gone long as I remember or never had one.

Well, I guess my pump temp theory may well apply to fuel, as the pump is full of it, eh?
If it IS fuel temp, it has to be changing during the time it's in the pump.  It's like clockwork that I can sit at lunch for 30 minutes with it at idle and when I drive off it will run nearly as well as it does in the summer, for a brief time, till things cool off.

Now I want to stick a remote temp sensor on the thing.. 

[745 turbogreasel]

Or your filter restricts when cold?

[wolf_walker]

Or your filter restricts when cold?

Dunno, replaced it three times in the last 15K/ less than year. 

[R.O.R-2.0]

what brand of filter do you run? bosch filters work good.

[wolf_walker]

Yeah I sell euro parts for a living, no junk on my cars.

[rabbitman]

I noticed some of that too. Another thing I've noticed is that in the summer the IP is hot after running and in the winter it is ice cold..........

I've read that these pumps are cooled by the fuel so if the fuel is -20F there's no way the IP will warm the whole tank up, so the IP will be down to -20F.

A local guy with a eco diesel installed a little thing in the fat coolant hose leaving the head for the fuel to circulate through. It's rather hard to explain, it's just a short plastic hose for the coolant to flow through with a coil inside for fuel to flow through so it heats it up.

He gets it started with a master heater and says it runs just like in the summer.

[wolf_walker]

That's interesting.  Weren't there fuel heaters on some diesels?  I know the wvo guys run all sorts of fuel heaters. 
I can remember years ago when I used to make long continuous interstate drives that after six or eight straight hours even in the winter these things would run better than usual, maybe long enough to warm the fuel in the tank.

[rallydiesel]

The newer tdi's have fuel coolers. Just a finned heat exchanger on the underbody.

[rabbitman]

I saw an older diesel truck that had coolant hoses running through the fuel tanks. It had saddle tanks.

[maxfax]

That's interesting.  Weren't there fuel heaters on some diesels?  I know the wvo guys run all sorts of fuel heaters. 

Older Ford diesels had em.. SO did a lot of the Isuzu cab over trucks..  It's funny that you bring up the wvo thing..  This is the first winter in about 10 years that I have NOT been running wvo other than in sub zero temps of past winters.. It hasn't been as peppy either... I was blaming it on air leaks, fuel filter, timing, sitting for a few months, etc..  I covered all those bases and just figured that it's finally getting worn out..  Although it hasn't really been run more than a few thousand miles since last winter..  Now you all have me wondering..  Maybe I'll try putting the fuel filter warmer on the diesel filter and see what happens..

[wolf_walker]

I'm pretty curious too.  I have another pump or two that are likely in better shape than mine if I can get my act together and stick em on, but for the sake of experimenting I'd be willing to try warming the fuel/pump up some and see how it reacts.  Wonder if a filter warmer would be enough?

[745 turbogreasel]

A small battery heating mat tied around the fuel filter works pretty well.