Sudden MPG Drop 2002 ALH Golf w/ 0M1

Fair enough. Got another car for him while you drive this one for a tank?

...aaaand I'm back.

There has been no improvement in MPG since I last posted in this thread. Still getting 22-24 mpg. Car has been parked a lot recently (my son had to have his ACL/meniscus replaced/repaired on his right knee). I did get out VCDS the other day and took the following readings:

IQ: hovers around 4-4.5

Injector Balance at idle:
1) -.64
2) .28
3) .16
4) .16

Timing: Still directly between the blue and green lines (i.e. "slightly" advanced).

All readings taken with engine at op temp (after a 20 minute "spirited" drive in the country).

I replaced the EGR valve and cleared related code (before the drive). No more cel.

VCDS shows no errors when I scan (well, I get a "no communication" error for the radio, but that's it).

So for my next step I'm going to pull the valve cover and re-check the static timing AND (after reading ANut's "TDI Timing Revisited" thread) retard the static timing down to the blue line.

Other Observations:

I reset and re-programmed my trusty scan-gauge for this car. In years past I noticed that the MPG reading would shoot all the way up to 9999 when coasting downhill. Now it will max out at 44-45 mpg when coasting. I also spent a bit of time in the car running vcds while the car idled. The exhaust smells very rich (to use the gasser term). I'm of the opinion that the car is overfueling somehow. What systems to I check for that?

Overfueling will display as white smoke (when cold) accompanied by a raw diesel smell. When warm, overfueling will display as sooty exhaust. If it was doing this and able to just idle, smoothly or not, there would have to be an air restriction somewhere in the intake tract.

In what shape is the intake manifold?

Seems to me it should show the 9999 when coasting since the ECU sets fueling to zero under that condition.

"Overfueling" at idle would result in higher idle speed which the ECU would respond to by decreasing fuel. To me smelly exhaust might indicate a bad cat.

Maybe the thermostat is stuck open. Has it been checked?

That small amount of change to the timing won't affect fuel economy that much. I've read here that running it advanced was supposed to improve economy, anyway.

What about brakes? Brake drag is likely contributing to this situation.

EGR, maf, and boost readings? I would run a couple logs and see what the boost is doing. If the vehicle thinks it's getting air that it's not is there only way it can over fuel at idle.
Fuel, air, heat/compression. To much fuel is generally a lack of another.

The part where this correlates to a TB change might just be coincidence, however, physical timing and boost leaks are highly common after one.

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I need someone to splain to me how a Diesel can overfuel at idle without the idle speed increasing. Idle speed is determined by the amount of fuel injected. Too much fuel, too much idle speed which the ECU would compensate for.

Unless there's some kind of load on the engine. But then it wouldn't be overfueling and the one could see that with a high IQ number.

KLXD said:

I need someone to splain to me how a Diesel can overfuel at idle without the idle speed increasing. Idle speed is determined by the amount of fuel injected. Too much fuel, too much idle speed which the ECU would compensate for.

Unless there's some kind of load on the engine. But then it wouldn't be overfueling and the one could see that with a high IQ number.

Click to expand...

The only way for this to happen is for there to be a lack of air, or combustion. If there's not enough air then the fuel doesn't combust completely and exhaust smells rich.
Fuel, air, compression are the three factors that cause a diesel to run and all three are factors in combustion performance.

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If there were enough of a restriction to affect the idle like that the thing would run like ... poorly when driving.

KLXD said:

If there were enough of a restriction to affect the idle like that the thing would run like ... poorly when driving.

Click to expand...

Not if it's actually the sensors lying to the ECU.

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eddieleephd said:

Not if it's actually the sensors lying to the ECU.

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Click to expand...

I don't follow. How could you have an intake restriction causing overfueling at idle yet normal running on the road due to bad sensors?

Quick answers:

I get a little white smoke at start up (when cold) and some white smoke when I give it the ol' Italian Tune up... I've never seen any black smoke.

Intake was swapped out for a cleaned one (at the same time I did the TB).

I had a dragging caliper... passenger rear. Replaced it. No other dragging brakes that I can identify (by pointing my laser thermometer at the discs after a drive). No change in the MPGs.

MAF was replaced 3 years (30,000 miles) ago with a new Bosch unit... I'd like to think that's not the issue, but I can't rule it out.

The thermostat is a little over 5 years (70,000 miles) old... definite possibility there.

I'll have to run some logs and post back.

Merry Christmas, all!

Here's a log with groups 003, 011, and 004. Do y'all see anything out of order?

https://www.dropbox.com/s/cv0qzb5ofd1rn4m/LOG-01-003-011-004.csv?dl=0

FWIW, it popped a P0102 code while driving:

1 Fault Found:
16486 - Mass Air Flow Sensor (G70)
P0102 - 35-00 - Signal too Low

An UltraGauge or ScanGuarge is an excellent aid to have in these cars. You would be able to get a better idea of how the car is driven by looking at Ave MPH. This would tell you if it's idling a lot. FYI - I run mostly highway miles and my average MPH is roughly 41 (one would think it would be higher, but that's pretty much what it is and I have averaged right about 51mpg over the course of 75k miles of owning my car).


Nothing jumps out at me with the logging other than the MAF seems a tad bit weak, though it does seem to manage to reach the higher ranges. Tripping a code is something that ought to be addressed: perhaps the MAF is just starting to become marginal. My experience is that a bad MAF doesn't have a huge affect on FE.


I like to use the logging instructions provided on Malone Tuning's web site. It's nothing specific to them and their tunes.



Did you look at the injector balance as suggested in the link you posted (frank06 suggesting checking at 1,500 rpm)?


To have FE this slammed it's like there is a big fuel loss happening. Something fundamental is horribly amiss. I have only ever seen one other instance in which someone got FE that was this horrible: and, sadly, I don't recall what the cause was. Do you smell any excess fuel?


Is the trans being left in drive (youngster isn't manually holding gears)?



Can anyone speak to how an improperly timed cam might play into something like this? (clearly, one can only be so far off here before it becomes extremely obvious that it's off! [bent valves etc.])

It certainly sounds like an air issue, I don't know anything else that would cause white smoke while hot. Assuming it's a lack or air causing lower compression. It sounds like a reach unless you have some bad fuel but can diesel be "bad"

Or the other possibility is low injection pressures maybe...not generating enough pressure to make a good combustion cycle?

If the cam timing were off, the intake valves would open early and close early but would it be enough to cause this?

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Check compression if you can. Air, compression, fuel is a diesels need.

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You had the intake manifold cleaned,..
was it clogged bad?
I've been working on a TDI that has what I concider mild carbon buildup in the intake manifold.

,.. and crazy carbon buildup in the head's intake ports.
I had to chip it off, couldn't even see the valve stems.

Answers are in red below:

UhOh said:

An UltraGauge or ScanGuarge is an excellent aid to have in these cars. You would be able to get a better idea of how the car is driven by looking at Ave MPH. This would tell you if it's idling a lot. FYI - I run mostly highway miles and my average MPH is roughly 41 (one would think it would be higher, but that's pretty much what it is and I have averaged right about 51mpg over the course of 75k miles of owning my car).
The Avg MPG on the scan gauge sits in the lower 20's... teens on acceleration and 45 when coating downhill.
Prior to the TB change (when I was driving it full time) it would average 42 mpg and that's over 6 years and 85,000+ miles. But my son started driving it at the same time I did the TB.
Nothing jumps out at me with the logging other than the MAF seems a tad bit weak, though it does seem to manage to reach the higher ranges. Tripping a code is something that ought to be addressed: perhaps the MAF is just starting to become marginal. My experience is that a bad MAF doesn't have a huge affect on FE.
I like to use the logging instructions provided on Malone Tuning's web site. It's nothing specific to them and their tunes.
Will Do!
Did you look at the injector balance as suggested in the link you posted (frank06 suggesting checking at 1,500 rpm)?
I didn't Note it down specifically, but I'll run it again to double check.
To have FE this slammed it's like there is a big fuel loss happening. Something fundamental is horribly amiss. I have only ever seen one other instance in which someone got FE that was this horrible: and, sadly, I don't recall what the cause was. Do you smell any excess fuel?
At idle, it does smell heavy with unburned diesel. It's not smoky though. I get a little bit of white smoke at cold startup and a puff of smoke when I floor it. No smoke otherwise.
No smell (or any sign of fuel leaking) when she's not running.
Is the trans being left in drive (youngster isn't manually holding gears)?
It's an 0M1 automatic (and he hasn't driven it in three months... only me).
Can anyone speak to how an improperly timed cam might play into something like this? (clearly, one can only be so far off here before it becomes extremely obvious that it's off! [bent valves etc.])

Click to expand...

fatmobile said:

You had the intake manifold cleaned,..
was it clogged bad?
I've been working on a TDI that has what I concider mild carbon buildup in the intake manifold.

,.. and crazy carbon buildup in the head's intake ports.
I had to chip it off, couldn't even see the valve stems.

Click to expand...

The buildup had restricted the intake input down to about 3/4 of an inch diameter. The intake ports on the head had very little buildup... maybe 1/16th of an inch?