Author Topic: AHU issues (Read 3990 times)

MichaelBuck · « **on:** January 25, 2008, 11:24:57 pm »

I've been reading and watching here for a while and now, in my first post, need a little help. I have an AHU that had 120k on it when I bought it to swap into my vanagon. I had the head rebuilt, bought a k03 'stage 2' hybrid turbo, 4BT IP, pp520s and an AWIC. The block was honed but I may not have gotten accurate info from the shop on the overall dimensions of the cylinders. I assembled with new rings, bearings, and gaskets. Now that it is up and running I'm sorely disappointed in several ways. Power/torque is very low compared to what I expected. I recently drove the van from Oregon to Texas and found that the van would run at a ok to meager speed on the flats but ANY incline immediately begins to slow the engine/vehicle down. Most times I would have to downshift and drag my way up the hills. Oil consumtion seems quite high - about a quart/3-400 miles. I don't see any oil leaks aside from a very slight weep from between the turbo halves. Very little smoke except for the last few days when I was seeing a bit of oil smoke at start up. Boost seems a bit lower than I expected based on the info I gave to the turbo builder that did the hybridization. I spoke to him today and he explained that they designed the turbo to flow more freely (larger turbine and compressor) giving the benefit of more air with out the increased temperature that comes with increased pressure. Essentially he was saying that it's all about volume of flow and not pressure developed. Don't know much about turbos,yet, but they are very reputable shop that came very highly recommended so I'm 'willing' to follow along with that for now (until that theory is shot down). Fuel economy is about 3/4 of what others with similar setups are getting.

I've received a bit of input from others that say the rings may not have seated causing low compression and excessive blowby. I haven't had a chance to do a compression test yet but it is slated for the next couple days. I pulled he breather hose (engine running) and there did not seem to be too much from the breather. I did notice when I pulled the breather hose (engine running) that there seemed to be as much pressure coming back into the air cleaner hose from the turbo as was coming from the crankcase breather. I assumed that with the breather hose pulled from the air cleaner hose (engine running) I would feel some suction at that opening. Others say the turbo is maldesigned. Like I said, I'm not buying that until I deal with these other symptoms.

Been working with the yahoo group to figure this out but thought I'd pick ya'lls brains a bit to see if we can come to some conclusions before I tear it back apart.

TIA
Michael

Quantum TD · « **Reply #1 on:** January 26, 2008, 12:03:31 am »

Hmm. This can go many ways. I will say a few things:

1) How bad were the cylinders before the hone? I've seen these AHU blocks, and they hold up surprisingly well when run on synthetic. I've got the head off an AHU with 114k on it (similar to yours), and the walls look like factory with the original cross-hatching still clearly visible. If the motor was running before, chances are the rings weren't that bad.

Also, the crankcase pressure you descibe is not that bad, and since there is not a ton of white smoke while running, then the oil scraper rings probably seated properly. I'd do the compression test. You can get cheapy compression testers from Harbor Freight tools or on ebay. That will tell you the condition of the ring seating.

The oil consumption is quite high for that motor. You should see something on the order of about 1/2-1 qt every 10k if you're running synthetic.

2) The turbo setup you have may be an issue. The K03 is a good mate from what I understand: giving good boost at low RPMs. But the modifications may have sent you backwards a bit. Obviously, a boost gauge would help if you don't already have one.

3) What gears do you have in your transmission? Was this a gasser with a diesel conversion, or a 1.6D to 1.9 TDI conversion? Finding the right transmission match is key to unlocking the power of the diesel motor. Too low a final drive and you're at a loss for torque, too high and you're taching out at low speeds. Check and see what others are running for gear spreads and final drive anc compare with what you've got.

4) Is this a full TDI conversion (all electronics), or an M-TDI conversion (little to no electronics)? Not sure if you mentioned that (I'm not up on all the TDI upgrade lingo yet). If it's full TDI, then you can monitor basic engine parameters with your VAG-COM to see what its doing under certain conditions. There are several tests you can run that will help you diagnose it's lack of power.

If it's an M-TDI, then the problem lies in the compression, the turbo or the injection.

In all, I'd look to the compression first.

Just out of curiosity, what condition was the motor when you got it? Running motor? Overheat? Basket-case? Accident?

MichaelBuck · « **Reply #2 on:** January 26, 2008, 12:31:20 am »

The engine was running when I got it although very carbon filled. Driven by a young girl who did not drive in the appropriate rpm range to clean things out. I fell in love with the mechanical idea and so am m-TDI. 1,2, and 3 were in great shape but #4 had a leak around the injector and was quite gunky and the cylinder wall was a bit pitted. I brought it home from the machine shop hone and gave #4 just a bit more to clean up the pitting. That brought the ring end gap right to the limit but I think it was still within reason. Not 100% on that but.... I'm seeing 15-16 max on the boost gauge but the IP builder says I should have 20 to run right with the amount of fuel the 12mm pump and pp520s are pushing. The turbo builder wasn't afraid of the combination - holding to his theory of more unrestricted (lower pressure) flow. Gearing is setup properly together with 235 tires. I had the tranny build for the swap.

jimfoo · « **Reply #3 on:** January 26, 2008, 01:37:40 am »

Quote from: "MichaelBuck"

I did notice when I pulled the breather hose (engine running) that there seemed to be as much pressure coming back into the air cleaner hose from the turbo as was coming from the crankcase breather. I assumed that with the breather hose pulled from the air cleaner hose (engine running) I would feel some suction at that opening. Others say the turbo is maldesigned. Like I said, I'm not buying that until I deal with these other symptoms.
Michael

Turbo working or not, I really don't think you should be getting air coming OUT the air cleaner hose. Is the EGR hooked up? Did the 4BT pump get modified any? If not, the governor is set way lower than your engine needs.

MichaelBuck · « **Reply #4 on:** January 26, 2008, 02:16:59 am »

What would the 'backflow' indicate?

4bt pump has all the necessary internals to make it VW worthy, including 4500 rpm governor.

No EGR

jimfoo · « **Reply #5 on:** January 26, 2008, 09:50:47 am »

I'm not sure as I've never seen it on any of my vehicles. The only thing I can think of would be bad valve to head sealing. If you slowly turn it over by hand, can you hear any air escaping out the intake? Maybe he made you a turbo that sucks air out of the engine.

:lol: :lol: :lol: