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Wed Nov 15, 2006
18:53
Older VWs like to keep you busy, and my Digifant Golf has been no exception lately. I posted some time ago about replacing the knock sensor, and she just ran fantastic after that... for about a week. The next gremlin was a cold starting issue that got so bad I nearly gave up on getting the car started after work one day. The car would run fine after warming up, but would run rough for the first minute or so after a cold start (if it even started, that is). In the process of troubleshooting, I tested the fuel pressure by hooking up a fuel pressure guage to the fitting on the end of the factory fuel rail. The pressure was 44 psi - quite a bit higher than it should have been, which indicates a bad fuel pressure regulator. I replaced the fuel pressure regulator (pretty easy chore, it's quite accessible), but it was not related to my cold starting issue. I eventually had it narrowed down to either the coolant temperature sensor or the ECU itself. The ECU uses the signal from the coolant temperature sensor to determine how far to advance the ignition timing under certain conditions, so it's pretty critical that the sensor operates correctly. I really didn't suspect the coolant temperature sensor because I had replaced it a couple summers ago, but when I tested it I found the signal was way out of whack when the coolant temperature was cold. As the coolant warmed up, the signal from the sensor quickly pulled back into it's correct range. The sensor is an easy and inexpensive fix, so I was happy. With the sensor replaced, my cold start issues were gone and the Golf ran real nice immediately after cold starts - no more rough running.

With the Golf really straightened out, I thought it would be a good time to install a Digifast 2 performance chip from vw_pilot (if you're on the vortex, look him up if you need a digifant 2 chip). It was $42 including shipping; however, I never received it. After about a month it was looking like the post office had just lost it or something. The seller was great about it, though - he sent out another one, at no charge, via usps priority mail so we could track it. The chip arrived this evening, so I installed it and took the Golf for a quick test drive. I am definitely happy with it. There's some extra pull at low RPMs under heavy load. I didn't really wind it out, so I have no idea how it affected the top end under full throttle yet. My favorite thing about it, though, is the fuel cutoff when the throttle closes. The fuel shuts off completely when you let off the throttle, until the RPMs reach idle speed. That may not sound like anything, but it's a huge difference in "fun factor" as it really increases the engine braking. The Digifant II cars are fairly high compression (high enough so that they use a knock sensing system), so there's some pretty decent engine braking when the fuel is cut off. Not only that, the RPMs drop quicker between shifts, which means you can shift that much quicker without trashing your syncros. In fact, the RPMs drop so quick that most of the time I end up double clutching when up-shifting in order to bring the RPMs back up to where they should be for the next gear.

Here are pics of the new chip - one before installation, and one after installation (click for larger view):
Digifast 2 Digifant performance chip installation
Digifast 2 Digifant performance chip installation


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Date: 11/15/06, 22:57:53 PST
From: Vince
Comments: Yeah, I just put the same chip in my '92 Jetta and you're right... not really convinced there's a lot more power but the compression braking is fun... I double-clutch as well. I was a bit surprised that the chip was shipped in plain styrofoam... I see you have the ECU o[en on conductive foam so you know what I mean... oh well... it works.

Date: 11/16/06, 07:04:10 PST
From: max
Comments: Yeah, I know what you mean. As long as it works, I'm okay with it I guess. Building PCs is one of my (many) hobbies, so I have lots of anti-static bags and board-safe foam lying around. That reminds me - I have a "computer stuff" section on this site that I need to update some day. I have a bunch of pictures of our various machines and my projects to post up, as well as software stuff I've done. There are a million and one things I need to do to this site, but I don't get much time to work on it. Perhaps this winter, when it's too cold to go outside.
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