jhoeppel

So help me understand what's going on here. A view of measuring block 032 on my wife's 1.8T ('01 Passat) shows fuel trim at idle Ok at +/-1% while trim at partial throttle is sitting around +16%. Way too high. Suspecting a bad MAF, I do some WOT runs in 2nd and 3rd gear logging block 002 but find the air mass peaking as expected around 125-132 g/sec, what you'd expect from a 170hp version of our engine (170x0.8=136).

Curious and befuddled, I check <b>my own TT</b>'s ('01 180) block 032 and find a similar situation with trim at idle Ok +/-1% but trim at partial throttle sitting around 11%. WOT runs also find the air mass peaks looking normal.

Some have suspected a vacuum leak, but wouldn't that throw off idle trim (value1) not part throttle trim (value2)?

I'm confused... if the MAFs are Ok, what's likely to be happening here with these readings?

~john

Rocky-in-Connecticut

remove and replace MAF . case closed

jhoeppel

and the block 032 fuel trim numbers when running without the MAF in the equation are:
. idle trim= -7.1%
. part load trim= 7%

I'm also wondering about a potential vacuum leak, because of a suspiciously dirty/oily hose.

~john

Rocky-in-Connecticut

..to fuel pressure regulator first. These will fail soon if they have not already. period. Be sure wet lines are not due to leaking cam adjuster seals or valve gaskets.

jhoeppel

I will check or replace the vacuum lines you suggest.

On the Passat, the wet "line" is more of a fitting (see yellow arrow). And the stuff around it isn't oily so I'm thinking fitting itself might be leaking. It's sort of a shaped rubber bit with two branches... here's a pic:
<img src="http://www.neiu.edu/~jrhoeppe/whatsthis.jpg">

Thanks,
~john

DasTT

The one called idle is an additive trim value. Having this value close to zero means you don't have a constant correction needed. The partial value is a multiplicative one. It means that a factor is applied to the injector time to compensate at all loads.

Your cars are running lean and the engine management is trying to compensate by applying a factor. Usually means something like a vacuum leak or a clogged injector.

Your fuel could just be poor quality. Try a few tanks of a high detergent high quality fuel first. Since you see the same result in two different cars, I'd go with what's common between the cars - fuel. Those fill-ups might clear out your clogged injector.

jhoeppel

we do tend to refuel at the same place (Costco) but it claims to use BP 93-octane, which should be decent stuff. I occasionally run Techron through mine. OTOH, both are 2001 model cars, so maybe they've both got small vacuum leaks as the hoses are all the same age (but with 89k miles on the Passat, only 55k miles on my TT).

DasTT

has no additive package. Depends where you live of course but the general rule on gasoline distribution works this way...

What goes in the pipeline at one end is *immediately* taken out at the other end. That is the gasoline delvered is not the gasoline sent. All this really means is that in a region, *all* gasoline is the same. The only difference is the brand additive package that is mixed in the distribution terminal. Costco, grocery and quick-mart stores get fuel with no additives. Chevron/Texaco adds techron, Mobil/Exxon adds their detergent, etc.

Costco also suffers from a volume problem which causes many deliveries to be made stirring up the sediment in the underground tank. The industry rule is to delay retail delivery 2 hours. Have you ever seen the tanker at Costco at the same time cars are fillng up? I'm sure you have. Have some gunk with that fuel.

Really the only way to see if injectors are dirty is to take them out and do a spray test. I'd try some good fuel for a while to attempt to clean things up.

One other thought... there is a poor design 180 degree hose on the left side under the intake on 225 cars. Many have reported cracks that are not visible on this hose. That could also be a quick fix item, but wouldn't explain the motor in the VW. Vacuum leaks should me measureable with a gauge. You could try that as well.

This group loves to blame MAFs and they are proven bad, but you have shown yours is OK.

I'm still convinced it is fuel delivery. Filter, pump, regulator, injectors.

jhoeppel

in fact, my wife's car has a suspiciously dirty/oily hose fitting ("suction pump") which is way dirtier than any of the surrounding bits... methinks it's leaking. And word on vortex and PassatWorld is that these are known trouble spots. I think it's the VW world's equivalent to the TT hose of which you speak. See the pic in my post below

BTW, while the guys at the Costco where I go (Chgo suburbs) claim their fuel comes from from a contract with BP, I still run Techron concentrate through the tank every few months as insurance.<ul><li><a href="https://forums.audiworld.com/tt/msgs/1667414.phtml">&lt; pic of suspicious VW "suction pump" fitting &gt;</a></li></ul>