Fault code P0638

does the engine run ok, then you rev it, then, when it returns to tick over it surges???
 
When you first start it the tickover is smooth until the engine gets slightly warm if it starts hunting on tick over you can rev it and sometimes it will drop back to a smooth tickover but then it will slowly start to hunt again. Drives well under load and acceleration but again when it drops back to tick over it will hunt over fifty percent of the time. Hoping a change of the dpf controller and some dpf cleaner will give it a hand.
 
Changed the dpf control valve and checked there was vacuum getting to it when the engine is running. Engine starts and is fine for two or three minutes then starts to hunt on tick over, if you slowly open the throttle it chugs until you reach about 1500 rpm. Have yet to give her a good run and hopefully early next week can do ten to fifteen miles at 2500 to 3000 rpm if that sounds about right. Really do want to get this sorted now as not happy about long trips until she sounds right. Sorry to keep popping up but kind of loosing confidence in the van at the moment.
 

Attachments

  • IMG_2670.mov
    20.7 MB
tidewatcher said:
Changed the dpf control valve and checked there was vacuum getting to it when the engine is running. Engine starts and is fine for two or three minutes then starts to hunt on tick over, if you slowly open the throttle it chugs until you reach about 1500 rpm. Have yet to give her a good run and hopefully early next week can do ten to fifteen miles at 2500 to 3000 rpm if that sounds about right. Really do want to get this sorted now as not happy about long trips until she sounds right. Sorry to keep popping up but kind of loosing confidence in the van at the moment.
Click to expand...
Don’t worry about keeping us informed. That’s what we (me) want.

You did check your EGR whilst TB off? Did you apply vacuum and test EGR again?

You say the DPF control valve is that what you mean?
 
About a year ago I had the exact issues you describe. The local mechanic had a look and told me he had reset the throttle parameters and the motorhome has been fine since then but he also said if he had to point a finger it would be the EGR valve messing about.

Subscribers  do not see these advertisements

 
I would remove and clean the egr of the engine, ( Mr muscle oven foam cleaner) and the pipe that feeds the air to the intake, from EGR. Your manifold is a little choked by soot. No way any additives will help you with that. Proper of the engine manifold of, degreaser and sweat.
I had in the past a vx combo hunting to the point that the engine vibration destroyed the rear engine mount. Upon lots of inspection, cleaning this and that, scanning all parameters ok, I took the air valve ( throttle body) off to clean, revealing the sooted choked manifold. The only thing that sorted the hunting and improved power, was to take the bull by the horns: remove the manifold, soak in a container with petrol, then brake fluid to help cleaning it and finally mr muscle to give it a shine like new. My wife drove it after I finished with it, her words: it goes like shit of a shovel now at roundabouts when you need it most.
Do not try to clean it in situ, you will ram lots of solid soot on top of the valves down the air ways; really bad and a head out to rectify.
 
Landy Andy said:
Don’t worry about keeping us informed. That’s what we (me) want.

You did check your EGR whilst TB off? Did you apply vacuum and test EGR again?

You say the DPF control valve is that what you mean?
Click to expand...
While the throttle body was off I tested the egr valve using a vacuum gauge which showed no vacuum leaks. I changed the electro pneumatic controller which sits above the engine centrally and has the two vacuum pipes, one from the servo vacuum side and one to the egr valve itself. I have checked there is a vacuum reaching it and also that the pipe to the egr valve is not blocked.
The odd thing is that when first starting the engine the tick over is as before, about 800 rpm and steady. After a few minutes it suddenly starts to hunt and then if you slowly increase the revs it has a hesitation but if you blip the throttle it is clean. Driving the van will pull cleanly if you floor the throttle even from quite low revs in a higher gear putting load on.
Never had a dpf fault code, the only one that came up was the P0638 throttle body.
 
tidewatcher said:
Changed the dpf control valve and checked there was vacuum getting to it when the engine is running. Engine starts and is fine for two or three minutes then starts to hunt on tick over, if you slowly open the throttle it chugs until you reach about 1500 rpm. Have yet to give her a good run and hopefully early next week can do ten to fifteen miles at 2500 to 3000 rpm if that sounds about right. Really do want to get this sorted now as not happy about long trips until she sounds right. Sorry to keep popping up but kind of loosing confidence in the van at the moment.
Click to expand...
Keep us updated ,I feel your pain as i am having similar issues at the moment and it sounds like plenty people have had the same. Keep your chin up it will get sorted it s all good information for us
and as usual loads of info and help from the funsters 😁. I have someone coming to go over mine in a week or so will see what happens.
Cheers Cris 🍻.
 
Todays update! Wondered if the new throttle body needed pairing with the management system so a googling I did go. As usual you can pick your answer, however there were a number of sensible looking posts which suggested it should be and they gave two ways of achieving it. First was the good old removed the starter battery earth strap for twenty minutes and the other was to turn on the ignition for two minutes but not start the engine a few times. Took the easy option of suggestion number two. Then started the van and maybe a slight improvement on the tickover but headed out and gave the van a fairly heavy pasting but only for about five miles as time was pressing. Some white smoke from the exhaust and the engine did get well up to temperature. The result was an improvement though not yet perfect. Very little sign of lumpy tick over, engine revved freely and pulled cleanly and well. No management light on.
Sooo…..
Hope to give her a good ten mile plus run up the motorway now it seems it will keep going, as I said not perfect but a big improvement which makes me think the fault is (was) ninety per cent EGR and ten percent confusion in the management system.
We will see. Thinking of selling the film rights as I reckon it would make a good mini series on Dave.
 
Have you looked at the actual and expected flow rates of the air mass sensor?
If this is faulty the revs will go up and down (hunting) on tickover.

Subscribers  do not see these advertisements

 
tidewatcher said:
How can I do that?
Click to expand...
You need the proper software. Is your van a ducato or peugeot?
Some other software will read the values. I have a peugeot and the cloned manufactures software.
A cheap £10 reader does my wifes Mokka readings. Select live data on the reader
 
Thanks will check my reader and have a look.
 
A failed/sticking EGR, a gummed up MAP sensor, can also cause incorrect MAF sensor readings.

Subscribers  do not see these advertisements

 
Landy Andy said:
A failed/sticking EGR, a gummed up MAP sensor, can also cause incorrect MAF sensor readings.
Click to expand...
Will run diagnostics tomorrow using a garage friends better kit. Still think it’s a sticking egr but hoping a thrash with a good dose of cleaner helps. In honesty with the faulty throttle body I was driving very gently to get home from France which wouldn’t have helped.
 
tidewatcher said:
Will run diagnostics tomorrow using a garage friends better kit. Still think it’s a sticking egr but hoping a thrash with a good dose of cleaner helps. In honesty with the faulty throttle body I was driving very gently to get home from France which wouldn’t have helped.
Click to expand...
A good few drives will be a good start in your diagnostics as they can require a few drive cycles so set its parameters.

Incorrect MAF readings was one of the indicators of my failed (open) EGR. No warning lights, just incorrect readings.
 
I found this

In addition, after fitting a new solenoid or throttle body it is advisable
to run a procedure using a diagnostic device 'Re-learn self-learned functions' so that new items can be recognised and adjustments that have been made automatically will be reset.
 
I saw that and also the one which suggested turning ignition on for two minutes but not starting the engine for a few times which I did. The alternative was disconnect the battery for twenty minutes which I assume clears the memory on the management system so it sets off afresh as they say. Plan to give it a few good drives and see if it continues improving and if not will then head down the more advanced OBD path. Every days a school day.
 
Another bulletin on the palace gates…. Took her for a twenty mile round trip on the motorway keeping in fourth and fifth at 3000rpm or just above when traffic permitted. Slight change in that when the lumpy tickover starts a quick throttle blip seems to cure it for a while. If the engine is on idle and the lumpy tickover starts if you open the throttle very slowly the lumpiness gets worse until about 1500 rpm then clears. It’s very hard to tell if it is the low revs or the throttle position causing it, I think I favour throttle opening position as you could just feel a unevenness in higher gears and that sort of rev range or a shade higher.

Will put it on a better grade obd reader tomorrow to see if there is anything there although the management light never came on.

Onwards and upwards.

Subscribers  do not see these advertisements

 
tidewatcher said:
Another bulletin on the palace gates…. Took her for a twenty mile round trip on the motorway keeping in fourth and fifth at 3000rpm or just above when traffic permitted. Slight change in that when the lumpy tickover starts a quick throttle blip seems to cure it for a while. If the engine is on idle and the lumpy tickover starts if you open the throttle very slowly the lumpiness gets worse until about 1500 rpm then clears. It’s very hard to tell if it is the low revs or the throttle position causing it, I think I favour throttle opening position as you could just feel a unevenness in higher gears and that sort of rev range or a shade higher.

Will put it on a better grade obd reader tomorrow to see if there is anything there although the management light never came on.

Onwards and upwards.
Click to expand...
Remember that your throttle pedal, has no connection to the throttle body (unlike a petrol engine). You throttle pedal, is controlling via electronics how much diesel is injected into the cylinders. It doesn’t alter the air flow, or control the flap inside the TB. The TB is only operated when the EGR is operated, and when you shut the engine off.
 
Landy Andy said:
Remember that your throttle pedal, has no connection to the throttle body (unlike a petrol engine). You throttle pedal, is controlling via electronics how much diesel is injected into the cylinders. It doesn’t alter the air flow, or control the flap inside the TB. The TB is only operated when the EGR is operated, and when you shut the engine off.
Click to expand...
So would that tie in with clean pick up when you floor it as assuming TB wide open and lumpy at low revs when either it’s too open or too closed? Have a feeling the egr is looming. Thanks for taking the interest.
 
The TB doesn’t really do too open or too closed. It’s either open or closed on old basic stuff like ours. Modern stuff different.
On tick over the TB should be fully open. If you then gave it a BIG rev (TB still fully open), stop reving, then the EGR would open, and the TB closed, all this happens fairly quickly and then this remains for 3 mins (from memory). This is so the engine can use the fuel you potentially just shoved out the exhaust, and the TB is there to stop the clean air, so engine sucks via EGR cooler. The TB then returns to fully open, assuming all is work as it should.

Lumpy tick can be a sign of failed EGR.

Only other thoughts.

Have you looked at your injector /cylinder balance figures?

It reads like you have a cylinder that is missing, and a few higher revs are carrying a weak cylinder (one that isn’t getting the correct air fuel mix). But I’m only going on what I’m reading.

Can your reader do cylinder or injector balance?

Just thoughts.
 
Landy Andy said:
The TB doesn’t really do too open or too closed. It’s either open or closed on old basic stuff like ours. Modern stuff different.
On tick over the TB should be fully open. If you then gave it a BIG rev (TB still fully open), stop reving, then the EGR would open, and the TB closed, all this happens fairly quickly and then this remains for 3 mins (from memory). This is so the engine can use the fuel you potentially just shoved out the exhaust, and the TB is there to stop the clean air, so engine sucks via EGR cooler. The TB then returns to fully open, assuming all is work as it should.

Lumpy tick can be a sign of failed EGR.

Only other thoughts.

Have you looked at your injector /cylinder balance figures?

It reads like you have a cylinder that is missing, and a few higher revs are carrying a weak cylinder (one that isn’t getting the correct air fuel mix). But I’m only going on what I’m reading.

Can your reader do cylinder or injector balance?

Just thoughts.
Click to expand...
To be honest my own reader doesn’t but heading Friday to a friend who runs a repair shop with better kit than mine. Will let you know.
 
So obd reading postponed until Friday, however I decided to take the intake pipe off the TB again and then started the engine leaving it on tick over. Butterfly wide open and steady tick over then after a couple of minutes the tick over started “hunting” again and lo and behold the butterfly was partially closing and opening in time with the variation in revs. Guess there’s no ducking it, dpf valve must be stuck. Clean or replace as it’s a bit of a fiddle to remove by the look of it.

Subscribers  do not see these advertisements

 
Do you have the ability to turn off /clear fault codes?

If you do, try disconnecting the TB, and see how it runs. This will bring on a fault code so you need the ability to clear it.

If the TB is closing at the wrong times you need to know why? Because it wants close it, or is it because something is faulty.

How bothered are you about keeping vehicle standard, and keeping the emissions stuff?
 
Landy Andy said:
Do you have the ability to turn off /clear fault codes?

If you do, try disconnecting the TB, and see how it runs. This will bring on a fault code so you need the ability to clear it.

If the TB is closing at the wrong times you need to know why? Because it wants close it, or is it because something is faulty.

How bothered are you about keeping vehicle standard, and keeping the emissions stuff?
Click to expand...
I assumed that if the dpf valve was stuck then the butterfly was being told to do something about it but that may be a bit simplistic. My friend has the kit to cancel codes so can try disconnecting. As for the blanking path my only concern is the emission test on the MoT. Having seen industrial areas of China compared to the amount of miles I do yearly……..
 
Two things this morning which are relevant. Firstly the code reader only showed one code P2A00 O2 sensor 1/1 circuit performance.i would assume this is due to the EGR not doing its stuff. Nothing else. Then disconnected the egr vacuum valve electrically and the engine ran ok on tickover but threw a warning light P0403 EGR valve which I would expect. Then reconnected the vacuum valve and the engine began hunting again. For some reason I then put my finger over the small vent that sits at the bottom of the valve and then the engine ran smoothly, took my finger off and lumpy again. It really does point towards the EGR valve being clogged or stuck. Perhaps, and this is speculation, the throttle body fault was brought on by trying to overcome the EGR valve sticking. I then drove incredible gently for about four hundred miles, keeping revs low and not using big throttle openings which in all likelihood made the condition far worse. Anyway looking like a change or clean of the EGR valve and associated pipe work. Will let you know how it evolves.
 
now getting confused. When the surging tick over happens the butterfly in the throttle body goes from fully open to three quarters closed in time with the hunting occurs. Where does the signal come from? If I close the small breather at the bottom of the electro pneumatic valve just under the scuttle with my finger the tick over stabilises. So is that valve telling the egr valve to open and close? If so is it also telling the throttle body butterfly to fluctuate.

I have now changed the throttle body, the electro pneumatic valve, the maf sensor. I have run the engine at over three thousand revs for twenty miles with dpf cleaner and top grade diesel.

I still have the tick over problem and if you very slowly open the throttle then it becomes a heavier miss fire until about fifteen hundred rpm then clears.

Anyone had this and cured it?
 
On my 2007 2.3 Ducato, there is 2 rubber pipes going to the valve under the scuttle of which you write. It is very easy apparently, according to others, to put these the wrong way round and even if correct, it is advised to replace this valve at the same time as the TB because, it has been working overtime try to rectify faults on the old TB + check there is no holes or leaks on the 2 rubber pipes.

I have, so far, had no problems with my old TB but have been carrying a new one around for the past 5yrs just in case?

The advice in the first paragraph, is advice I've read from MMM magazine experts, not from personal experience.

Good Luck! 👍

Subscribers  do not see these advertisements

 

Join us or log in to post a reply.

To join in you must be a member of MotorhomeFun

Join MotorhomeFun

Join us, it quick and easy!

Join us

Log in

Already a member? Log in here.

Latest journal entries

Back
Top