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Re: [T3] Carberators or FI

On 5 Aug 2006 at 11:18, shalom@ucla.edu wrote:

> I was wondering if anyone had any ideas on what the pros and cons of 
> Carberators and Fuel Injection.

The FI vs. carbs debate has been played out here many times. I'm one 
of the FI defenders. In my opinion, there's nothing to be gained, and 
a lot to be lost, in converting a stock engine from FI to carbs. A 
stock FI setup runs better and has better driveablitiy than almost 
any conversion.

Carbs have the edge once you get into radical engine modifications, 
like displacement increases over 10-20%, or large cams. But carb 
conversions need to be chosen carefully (not all conversions which 
are on the market will actually work well) and you have to expect to 
re-jet them after you install them. There is a rather long learning 
curve; they are NOT just "plug and play." 

> I've been wanting to rebuild my engine(1600 FI) and I'm a little
> worried about the reliability of the FI system(being 30 some years
> old).  Would you change over or stay.  I'm working on my graduate
> degree in "Controls", so I like the idea of the feedback control
> loop(as in the FI system), but this system is pretty old.  I've looked
> at a new FI system kit by Weber Redline, but this kit 2600 dollars(a
> little much on my student budget).  

As old as it is, the Bosch D-Jetronic FI has been extremely reliable. 
The main problem with it is that you are very unlikely to find a 
mechanic who is actually familiar with it. You need to learn about it 
and do your own work. That said, it has a few quirks, but all the 
help you might ever need is available for free on this email list.

One bit of advice: Don't ever start out by GUESSING where your 
trouble might be. Replacing parts by guesswork is the least 
successful, most time consuming, and most expensive way to proceed. 
There are ways to test almost every component in the system, so if 
you're having trouble of some kind, the best way to proceed is to 
post your symptoms here FIRST, and wait for some insight into the 
cheap, quick fix that you really need.

For example, we've seen numerous cases of people who have leaky 
injectors. They often go out and buy 4 new injectors and replace all 
4 on the theory that all the injectors are equally old and should all 
be replaced together. This costs hundreds of dollars, while the 
actual problem (leaking gas) can usually be repaired for less than $5 
by just replacing the short pieces of hose on the injectors.  

The second most common "FI problem" turns out to be running 
excessively rich with poor fuel economy. This almost always turns out 
to be a bad voltage regulator which is producing low system voltage. 
The VR can be replaced rather cheaply, but owners and mechanics who 
are not familiar with the quirks of the D-Jetronic system often 
replace hundreds of dollars of perfectly good FI parts in an 
unsuccessful attempt to fix this charging system problem.  

In the end, your best solution is to get familiar with your system 
yourself, get a Bentley manual, and post your problems here first, so 
that you can benefit from the abundance of experience available to 
you for free, BEFORE you start spending your money.

As for aftermarket FI systems, I have no experience with them, but 
others on this list may. I suspect, however, that they have nothing 
to offer over the stock system unless you do major increases in the 
engine displacement. This can all be done successfully, but it's not 
cheap, and if done properly the extra cost of the aftermarket FI 
system will only be a minor part of the total.

Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA

List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org

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