Engine revs slow to drop down

[killerme]

Hi - can anyone suggest a possible explanation for this? I have a turbo diesel 1600 1988 T25 (the engine was changed to diesel sometime in Germany before importation). After about 15 mins of driving, when I change gear there seems to be no drop in revs, perhaps even an increase, possibly, hard to judge. When I brake the revs seem to drop down normally. Perhaps they are slow to drop down so when I change gear there isn't time to drop so it feels like its racing. I have ruled out the cable after cleaning it up really well and besides this only happens after 15 mins, ie after the engine is warmed up sufficiently. I'm no great mechanic but if it was a petrol engine I would think it was a carburetor issue but I don't even know if diesels have carburetors.

Diesel engine slow to drop down its revs after 15 mins of driving. Feels like it is racing when I change gear.

Any suggestions, if anyone is kind enough to think about it?

chris

[HarryMann]

Firstly are you abs. sure throttle cable isn't sticky or lever failing to return fully.

Is the cold start lever active or ignored / bypassed?

This isn't uncommon... and annoying/dangerous.

First check those things and add a light elastic to lever ensuring it comes back fully as a trial.
If pump's been apart or messed with then coiled spring not enough turns..

Finally there is idle stop up the side of some pumps other than the basic lever stop.

Basically its overfuelling or overadvanced pump timing when hot. Make sure cold start isn't gummed up and set right back.. when hot & idling fast, move c/s lever on pump fully back (off)

[HarryMann]

Oh and your aircleaner is clean and new?
And you haven't excessive oil mist from the breather getting into inlet.

[HarryMann]

If you don't know what you're looking at give location so maybe near someone who does...

[HarryMann]

Oj just thought.. do you know where the cold start lever flap is im the cab.. just below and to left of steering wheel. Is it connected.. get someone to watch pump when operating.
Assuming a JX 1.6 TD is fitted as per original specs. Not a lashup in othet words

[Oldiebut goodie]

Going by the clue that it happens after 15 mins it certainly sounds like it has got the cold start permanently on - maybe someone has tweaked the cold start stop or clamped the cable too short...?

[killerme]

thanks chums. brilliant response. I'm just up on the north coast in NIreland for a few days (I live just outside belfast) and will try some of those things asap. Will try the elastic on the return. Will post in a few days. ta guys really appreciated.

[tommin]

HarryMann, I seem to be having same issue, posted earlier and on my oil pressure post. I recently changed the pumps injector housing seal with pump still attached, seemed easily enough to do and van started no problem, just now and then this high revs business.

What do you mean "If pump's been apart or messed with then coiled spring not enough turns.." what and where is this? Any advice or help is greatly appreciated.
Regards
Tom

[HarryMann]

You mean... throttle lever seal under the coiled spring?
I mean... the original registration of the lever on the splines is a factory set position.
There are usually definite alignment marks on shaft and lever. If that registration is lost or the return spring is a turn or half a turn short of a requirement.... you may get these symptoms.

[tommin]

Okay I can see what your saying.
When i replaced the pump seal i only pulled out the injector head less than half inch to replace the seal, could/would that have upset anything internally? I found several articles on the web and some videos showing how to do it, all explained not to pull head to far or you can upset some internals. I only opened enough to see seal, so do not believe i did anything untoward but cannot be 100% sure coz here we are with this little issue which i never had before? I am at loss at the moment, am i looking at pump rebuild?

[HarryMann]

Did you remove the throttle lever?
Don't think the pump head could do this but if didn't close up same amount maybe you need to defuel a little.
Do you know the main fuelling screw locked off with a 13mm I think. Very sensitive so watcj carefully... about 1/4 turn at a time. Out I think...
If main fuelling is higher can increase idle. May be capped off for emissions.

Are you certain idle stop posn for lever is right back.

[tommin]

Yes marked the position prior to take off and that was a while back, no problem apart from almost finger amputation as spring tried to to take it off
Okay so if i screw out the main fuel screw like you say, out reduces in increases. Does it need to be done engine running or off? will try that tomorrow

[HarryMann]

Def. Not running or I've never considered leaning that far over a running engine.

[Oldiebut goodie]

I have done it with the engine running but it is difficult holding the screwdriver in the slot unless you have a very even tickover. (You must have very short arms! )

[tommin]

Well being over 6 foot helps, did it with engine idling, but no change. Turned it 1/4 and did that twice, if anything it seemed to smoke bluish a little more. If i inadvertently cocked the screw up when i took it out last time, how can it be reset to factory setting?
Another thought came to mind after the seal repair to the hydraulic head. When i tried to loosen off an injector the whole valve holder came out with it (turned out the somebody prior did something and cross threaded the injector into the valve holder) and when i put it all back in place (valve contents) noticed the shim at back of spring would not sit right in holder, it would not go all the way in (i think it was over sized as i could see where it had been worked on around the edge). It may have fitted when the clown before did it, but since it came out when i undid everything there is a possibility it did not go back in the same. I dunno i am just chucking queries in the air at the moment, but if this did not sit proper could it cause this rpm surge???????

Oh old age don't come alone or without it's complications, am just about ready to chuck in the towel on this old girl......