Misfire when cold, on throttle semi-cold

pdtdiarl · May 8, 2018

Greets,

I have a good question for you guys.

After a swap from a tdi vp 110 to a ARL pd150 on my G4, and I don't think there isnt anything wrong with the swap but an engine problem.

The engine starts ok, amb temp around here is 10°C so no glow plugs needed, but on the first minute, misfires at idle,

After the first minute runs ok at idle and only misfire if I step the throttle.

When the engine gets a little bit warm, around 40°C, it runs perfect, pulls very well, absolute 100%.

Picking up codes, I only get fuel pump relay, but because the lift pump is wired directly from the fuse box, and i'm getting 3l/min of diesel flow.

Checked the pressure on tandem pump, at the side port, i get pressure 15psi at idle and around 50psi at 1500rpms.

Change 4 injectores but the injectores aren't new, so not sure if they're ok.

I cant figure out wich cylinder misfires because all the injectors deviation go wild when misfires, and when they are stable, they all are bellow 1.00 mg/r dev.

To me, it feels like fuel starvation, smokes white just a little bit when cold.

Fuel filter is not that old, installed clear fuel lines, no air and no oil, I get a stream of bubbles, about the size of an inch when it starts, but appart from that diesel comes and goes nicely.

Last week I removed the sump to check the rods, all of them are nice and straight.

Haven't done a compression test yet, and didnt measure the return flow of tandem pump (how important is that diagnosis?)

Camshaft looks ok, sounds ok, but I hear a tapping, more when I rotate the engine by hand and then start it, which could indicate a lifter needing a replace.

Any more ideas to find the problem?

Carlos_TJ · May 8, 2018

-What does the white smoke smell like? Diesel?
-Is the ARL a PD engine ? If yes, what is the crank/cam torsion value?
- Do you have a working clean EGR?

pdtdiarl · May 8, 2018

Torsion value is set 0.0/0.6.
ARL is PD engine, yes.
Smells like diesel, yes.
EGR/Shutdown valve is off the manifold now, does the same.

Carlos_TJ · May 8, 2018

If white smoke has strong diesel smell, it could be worn injectors or low compression.
Can you provide injector balance data from VCDS?

pdtdiarl · May 8, 2018

@26.1ºC:
-0.05 -0.89 0.33 0.59

@52.2°C
0.24 -0.71 0.16 0.28

The 2nd injector went for testing and it's ok.

Wouldnt low compression cause hard start?

Im still waiting for the compression tester kit to arrive ...

pdtdiarl · May 9, 2018

Measured the return Flow just now, engine off, lift pump always on, I get 50ml/min, is my tandem pump dead?

pdtdiarl · May 9, 2018

It seems that if I run longer the lift pump, its starts better and missfires less.

About the return flow, I installed a check valve on the return line to try to hold the fuel.

Also checked some values on VCDS

Carlos_TJ · May 9, 2018

^^^ that 1.60 value on cyl#2 injector balance is too high.
You said injector is fine. How about cam lobe for #2?

Franko6 · May 9, 2018

I'd call those injectors 'all over the place.' Because of the expense of the injectors, you have to root out what is bad. You say the second injector tested ok... compared to what? The others? I somehow doubt it. The simplest test is to switch 2 injectors. I'd move the two most imbalanced set, #2 and #3.

You must use a new hold down bolt, and check to make sure there is no burr in the injector bore to damage your injector seals. We often find a burr in the injector bore that is caused by the hold down block pushing the injector against the bore, where it vibrates, where it often raises a burr. As a matter of fact, if you didn't check for a burr before installing this set, that may be exactly what you have done, cut the lower black seal, which will allow the higher pressure going to the nozzle to leak back to the return galley.

If the misread follows the injector, the injector is the problem. If the misread follows the cylinder, you have to figure out what is wrong with you engine.

Also, if you are testing nozzles, don't put more than 78 in pounds, +1/4 turn and you will be able to get your values figured out, without ruining another bolt. The injector hold down bolts are expensive and cannot be reliably reused. If you try, it's very likely you will snap the bolt off even or below the bolt hole.

pdtdiarl · May 10, 2018

Thanks for the reply.

After changing the set of injectors, I pulled the 2nd injector for rebuild with one injector of the old set. The figures before were these:

So it seems the worst cylinder is always #2, already check the con rods and they are straight. Still waiting for that compression tester kit to arrive.

The cam lobes seems shiny, didnt measure the lobes yet, but I can see that I have some dished lifters. O dont have that popping noise of a worn cam.

About flow return of the tandem pump, I installed a check valve at the return avoid returning fuel back to the tank, because yesterday I noticed that if I keep lift pump working a minute or 2 before starting, it misfires less.

I've already had some tdi pds with bigger deviations, and never misfired ...

Franko6 · May 10, 2018

If you can see that the lifters are dished, you have to install a good set of cam and lifters. There is no sense trying to get injectors to balance if the engine's cam will not allow enough air into the engine to burn the fuel. A difference of .004" (.1mm) is enough to make the engine's idle balance come into play. A bad lifter can easily reduce the lift .020"(.5mm) or more.

I said to switch the two most imbalanced. With the injectors you had in there, you have a known deviation. By using a different injector, you just throw another variable into the works.

But, that being said, changing out that one injector seems to move the scale across the board in the right direction. Switch what you now see as the most imbalanced... #2 and #4. Once again, if the deviation follows the injector, it's the injector. If it follows the cylinder, then the first thing I would do is check compression and change out the cam/ lifters.

If you can see that the lifters are dished, you have to install a good set of cam and lifters. There is no sense trying to get injectors to balance if the engine's cam will not allow enough air into the engine to burn the fuel. A difference of .004" (.1mm) is enough to make the engine's idle balance come into play. A bad lifter can easily reduce the lift .020"(.5mm) or more.

You mention changing out some of the lifters. That will not work. The cam is more worn than the lifters and you will damage the new lifters very quickly. Cam and lifters wear in together and wear out together. Replace cam and lifter as a set.

Beware, there are a lot of CRAP cams and cam followers on the market that are cheaper and you get what you pay for. There are also cams that claim 'billet' and charge more, when there are few, if any cams that are anything else but billet. Don't pay more for fancy marketing that actually gets you the same thing.

An occasional misfire under load is an indication of under-fueling. The most common cause is a bad lift pump or a clogged fuel filter. We have been ultrasonically cleaning lift pumps that will hum, but will not spin. After as short as 1/2 hr, we found many have sand and grit that came out of the pump and they go back to working normally.

pdtdiarl · May 10, 2018

Franko6 said:
If you can see that the lifters are dished, you have to install a good set of cam and lifters. There is no sense trying to get injectors to balance if the engine's cam will not allow enough air into the engine to burn the fuel. A difference of .004" (.1mm) is enough to make the engine's idle balance come into play. A bad lifter can easily reduce the lift .020"(.5mm) or more.

I said to switch the two most imbalanced. With the injectors you had in there, you have a known deviation. By using a different injector, you just throw another variable into the works.

But, that being said, changing out that one injector seems to move the scale across the board in the right direction. Switch what you now see as the most imbalanced... #2 and #4. Once again, if the deviation follows the injector, it's the injector. If it follows the cylinder, then the first thing I would do is check compression and change out the cam/ lifters.

If you can see that the lifters are dished, you have to install a good set of cam and lifters. There is no sense trying to get injectors to balance if the engine's cam will not allow enough air into the engine to burn the fuel. A difference of .004" (.1mm) is enough to make the engine's idle balance come into play. A bad lifter can easily reduce the lift .020"(.5mm) or more.

You mention changing out some of the lifters. That will not work. The cam is more worn than the lifters and you will damage the new lifters very quickly. Cam and lifters wear in together and wear out together. Replace cam and lifter as a set.

Beware, there are a lot of CRAP cams and cam followers on the market that are cheaper and you get what you pay for. There are also cams that claim 'billet' and charge more, when there are few, if any cams that are anything else but billet. Don't pay more for fancy marketing that actually gets you the same thing.

An occasional misfire under load is an indication of under-fueling. The most common cause is a bad lift pump or a clogged fuel filter. We have been ultrasonically cleaning lift pumps that will hum, but will not spin. After as short as 1/2 hr, we found many have sand and grit that came out of the pump and they go back to working normally.

Thanks for the detailed reply, I'm aware that I have to replace the cam and lifters. Second job, the first and most important is the underfueling.

About the lift pump, it gives 3l/min so it seems ok. But while the engine is off, lift pump on, it drops 50ml per minute at the return line, is that normal?

pdtdiarl · May 12, 2018

Got another read, after sitting for 4 hours, just before usually starts to misfire.
Engine @36.9°C

Got my hands on a nice deal while searching for the tandem pump.... tandem pump, injecor loom and black lifters, and the rest goes for resell.

Going to replace the tandem pump next week and hope it gets running fine.

By the way, when I get negative values, does it mean the ECU is cutting back some fuel that is beeing injected? thats what always happens on #2.

pdtdiarl · May 14, 2018

To make things interesting, I give you these readings, haven't done anything yet, haven't replace the tandem pump yet or the injector loom. Still not getting any codes.

Is the injected quantity supposed to be this high on the first minutes of idle?

Im getting no replies for the last 2 posts but I feel I can help someone with this issue in the future. Replies to give me tips to solve the problem are welcome, but I feel I'm getting to the final solution.

KLXD · May 14, 2018

Normal for IQ to be high on a cold engine. If you use the graphing feature it has a warning about low temp.

On AHU's you only got three numbers which I understand were referenced to the fourth. ALH's and later report four values. Not sure what the reference is, maybe the average but yeah the neg indicates less fuel.

You seem to be ignoring the best advice you're likely to get here. You can't say that the cam is #2 when you are trying to solve a problem it may be causing.

People tend to get tired of helping when their input is ignored.

I suppose you could use a dial gauge to measure the valve follower travel. Then you could say "see the valve lift is ok in spite of the worn followers so we can ignore the cam for now" but you haven't done that.

pdtdiarl · May 14, 2018

KLXD said:
Normal for IQ to be high on a cold engine. If you use the graphing feature it has a warning about low temp.

On AHU's you only got three numbers which I understand were referenced to the fourth. ALH's and later report four values. Not sure what the reference is, maybe the average but yeah the neg indicates less fuel.

You seem to be ignoring the best advice you're likely to get here. You can't say that the cam is #2 when you are trying to solve a problem it may be causing.

People tend to get tired of helping when their input is ignored.

I suppose you could use a dial gauge to measure the valve follower travel. Then you could say "see the valve lift is ok in spite of the worn followers so we can ignore the cam for now" but you haven't done that.

Any input is appreciated, i'm not ignoring it..

The reason I'm leaving the camshaft/lifters for #2 is that I found a dished lifter in just one cylinder, don't even remember which one, the camshaft doesn't have significant wear on it, doesn't make the popping noise and the injector deviation appears at all cylinders, randomly.

Today if I have the time, I'm going to replace tandem pump and injector loom, if it doesn't solve, camshaft will be next for sure. Already have the ina black lifters, just need to buy a camshaft and the timing belt kit.

pdtdiarl · May 15, 2018

Changed Tandem Pump, didn't solve.

Changed injector loom, didn't solve

Finally my compression tester arrived. I'll bring you the readings tomorrow.

If compression is ok in all cylinders, its time to get a new camshaft and lifters.

Any suggestions for a well built camshaft? Already have the ina lifters.

Today I started the engine @35ºC, sitted after 7 hours, didn't misfire. Inj readings were:
+2.5 #1
-2.5 #2
-0.2 #3
0.1 #4
approximately

When I stepped on the acelerator to about 2000rpms, started misfire and the cyl #4 rose to 2.99 instantly, and stayed misfiring, restarted the engine, no misfire, cyl #4 started with correct values again, just like that, just by restarting it ...

Since I'm getting the problem only at cold temperatures/after sitting for more than 5 hours, should I still do the compression test with hot engine?

pdtdiarl · May 26, 2018

Greetings.

Had the rest of the injectors tested, so all of them are tested, all good, new seals, all tight with 12nm+270. Lash is set to 180°, all by the book.

The problem still remains. Injector deviations are still on the same cylinders.

One thing I noticed was, it's not because it's warm or cold, it's because it stays off for more than 5/6 hours.

Yesterday when I reinstalled the injectors, I had to prime the fuel line, that took me some work with the lift pump and some engine revs with no fuel as usual ... the weird thing is it started perfectly, revved to 2000rpms, no misfires.

This morning, started, kept misfiring, white smoke, as I touch the throttle and had to wait a while to drive it.

So it seems the engine has to do some revolutions first, with or without fuel, to work correctly.

Could be a lifter busted, losing pressure and gain up again after some revs?

Could be a problem with the injector bore + injector, or even cracked head, not sealing properly and dropping fuel to the combustion chamber, and with some revs clean it? Or because I sucked all the fuel on the combustion chamber when I was replacing the injectors?

Should I just replace camshaft + lifters or maybe its best to take the head off?

Any suggestion how I check if the combustion chamber is getting fuel while the engine is off for a long time?

pdtdiarl · Jul 2, 2018

Ok

Just to update, had a busted lifter on cyl #4, the one that used to rose to 2.99 when I stepped the throttle, replaced camshaft (steel) and lifters (black), that's solved now, no more misfire when stepping the throttle.

I start the car and I can step the throttle and it doesn't misfire. Thanks for you suggestions.

But still isn't 100%. When I start the engine, cold, after sitting, I still get a bit o juddering and white smoke.

Right after starting the engine I get:

It only judders and smokes on the first 5-10 seconds

2 mins after, I get:
0.64mg/str -0.33mg/str -0.16mg/str -0.16mg/str

And when warm:
-0.05mg/str -0.09mg/str 0.19mg/str -0.07mg/str

Before replacing the camshaft, I already had that high values on cyl #1 and low values on cyl #2.

I'm still going to swap injectores #1 and #2 to make sure the deviations don't move.

Do you have any suggestions?

Compression test shows:

#1 410
#2 478
#3 450
#4 465

Could it be the gap between compression #1 and #2?

It's possible that there is a problem with the new camshaft or lifters? If it were would I still get so perfect values on readings when warm?

Misfire when cold, on throttle semi-cold

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