Surging on acceleration

My 96 2.5DSE P38 has a strange accelartion, especially when cold. It doesnt accelerate cleanly through the auto box changes, from about 50mph up to 70 mph the revs vary up and down by approx 200 rpm.
The hotter it gets the better it gets. But like all it seems to run very cold on the temp gauge.
MPG is great still 28MPG at cruising speeds.
Is this a problem with the Auto box? I suspect its more to do with the Intercooler. As it just has a feeling of being starved of air or fuel.
Or could it be the fuel filter wanting changing.
Any help appreciated.

Hi Dave.
If you rev the engine up with no load on it does it present the same problem at the same rpm?
You will have to take the revs up to were the problem is and kind of " mess about " as the weight of the flywheel will hide any small hiccups when there is no load on the engine. I have not had a diesel 38 but have had diesel Discovery's (200/300 Tdi) and am assuming its turbo assisted? If you manually change gear at the same revs that the auto box changes gear does the problem get better or worse and is it definatly better when hot. Also has it always done it or has the problem " appeared " with the colder weather? I have seen other posts about these diesels and their operating temp and would just say that both my Discoverys sat in the middle of the gauge but i couldnt tell you what that temp was (i'll see if my manual tells us). And i think that i also saw that cleaning with white spirit (intercooler) was acceptable.

Cheers, Nick.

Hi Nick
If I free rev the engine it runs clean at all rev levels, I dont get any sign of the problem. It only appears under load. Not tried manual shifting so will give it a go.
The problem is certainly less when it has warmed up a bit. When pulling under load it feels restricted, that is why I think its intercooler.

Dave

Hi Nick,
Just to say i tried manual shifting today, 1st 2nd 3rd great no sign. pulls cleanely. when in drive then at about 3k rpm its surgging about 200 rpm, almost as if its trying to continue but cant get enough breath. Also happens when cold on cruise control. Speed where it occurs is 55mph to 65mph. Kick down is a little slow to come in, tried it whilst running at 2000 rpm in top, kicked down and nothing, then suddenly it dropped almost 2 gears and shot to 4000 rpm. Pulled like mad then.

Hi Dave.
Having read the manwell it seems to me (tho i could be completly wrong) that if the gear box works ok when you manually shift that it could be the control unit but i have heard stories of loose wires causing these faults, so it wouldnt hurt to check the connections under the seat. Does it also work ok in lo box?

Cheers Nick.

Hi Nick, Not tried low box, but will. I will have a check at the connections.

Just to say I tried it in low range. Didnt have the same problem. pulled cleanly through all gears in drive.

Strangely this morning it pulled much better only the slightest hint of a hestitation as I pulled out onto the motorway. Outside temp was reading 7deg.

Dave

just wondered if you ever managed to cure this dave?

i have a 96 disco 300tdi Auto, and have been pulling my hair out with exactly the same problem, though never really noticed it change with temperature.

When i boot it up hill, on the motorway, and more noticebly when i'm towing and making the engine really work, it gasps for something and if i keep my foot flat the speedo is like a pendulum bu approx 200rpm as you say.

i've checked/replaced the intercooler hoses/fuel filter/sedimenter under tank/air filter/cleaned air flow sensor.......etc.........etc.......to no avail.

now considering injection pump and or injectors but we're talking serious money now.

over the last 6 months this problem has remained and is gradually getting worse.

please tell me you found a simple easy fix for the problem.

Albert

HI Albert, sorry to say I have gone through all the same as you, and mine hasnt improoved.
My thoughts are that as the turbo kicks in you get a boost, it then maybe the waste gate is opening and dropping the boost, only way I get around it is to keep my foot hard down and let the kick down come in.
One other thought I had is I have a performance chip added, I wondered if that was foolling the system.

i too have a performance chip fitted, but when i disconnect it and revert to normal the surging continues though not as severe (obviously because there is less power).

mine i fine really when driving normally, but when i boot it uphill or when i am towing the caravan its really quite bad and speed gradually drops of due to the surging.

just bought a recon injection pump at the right price so i'm now in the dilemma of whether to tackle the job of changing it or not.

if i thought i could take it somewhere and they could diagnose the problem correctly at a cost of a couple of hours labour i would, but i'm not convinced they could.