Issues with replacement FPCU.

[mattd1979]

I recently had an intermittent problem with the FPCU on my Q and had to short the ground terminal to body ground. At one time I did remove the control unit and added more solder to the board. When the FPCU was working, you couldn't here the fuel pump unless you opened the trunk and put your ear close to the fuel tank. When I jumped it to body ground, I did hear it but only if I turned off the A/C and was sitting at a light. I had a spare that was supposedly good and I was going to swap it in but first I had removed the bottom cover and added a piece of wire to the ground terminal to help reinforce the connection. This morning I tried it but it didn't work. So, I had to reconnect the ground wire to body ground temporarily. I then removed the old FPCU and removed the bottom cover to inspect the internal connection which looks good. So I figured that there must be another issue with the pump controller. Anyways, what I was wanting to know is if there is a way for me to be able to test the two controllers two determine what is wrong with each. I figured that maybe I can swap good parts from one to make the other work. What I noticed between the two is that the newer one on the right in the photo has an additional capacitor that is connected parallel with the other capacitor as compared to the older one that only has the one capacitor. Do you think that the reason the older one doesn't work with my fuel pump is because of the lack of the additional capacitor? The car that the newer fuel pump and the newer controller came out of was a 1995 Q and had somewhere around 60,000 miles on it. I have some pictures of the controllers that I am attaching.

Matt











Modified by mattd1979 at 4:42 PM 1/11/2010

Modified by mattd1979 at 4:45 PM 1/11/2010
Modified by mattd1979 at 6:45 PM 1/11/2010

[Q451990]

I don't think the addition of the second capacitor on the new board is the reason it works or doesn't. Just a rolling revision...

In my experience these controllers either fail at the ground connection - or at the transistors (the 4 three lead parts that are screwed to the side of the case to disapate heat) - perhaps beefing up the ground caused the other weak link to fail. Their solder joints look like they've been hot - but it's hard to tell from a picture.

So you replaced the controller and left the fuel pump in that caused the failure of the old one because it isn't noisy?

Heath
Modified by Q451990 at 5:01 PM 1/11/2010

[mattd1979]

The FPCU and the fuel pump were installed as a pair from a 1995 Q that had around 60K on it. At one time the car hesitated and stalled on me and I popped the trunk to check the connector and noticed that the connector for the ground terminal appeared to not fit snug on the spade terminal and so I reshaped the spade clip so that it fit tighter. I also removed the controller to check the solder joint inside and noticed that it seemed to be missing some of the solder. I re-soldered the joint, reconnected everything, and the car has run fine for about a year. The fuel pump had not been making any of the noticeable whine sounds as one would here from a dying fuel pump. The reason I pulled the two units from the 1995 was because I did have a bad fuel pump and it was making a lot of noise. The one I put in was practically silent and has been the same since I installed it. I had a spare that was supposed to be good. I took it apart and added an additional wire to the trace to help spread the current load on the circuit. I did this after reading a post on here about the joint possibly not being robust enough for the long term. When I put the replacement in and turned the key, there was no sound of the fuel pump running. When I tried to start it, it ran until it stumbled and stalled. I then reconnected the jumper and it started fine. So I take it that this fuel pump is bad also.
Modified by mattd1979 at 11:20 PM 1/11/2010

[Q451990]

Sounds that way. I wouldn't be surprised if we start seeing new failure modes for the fuel pumps as the quality of fuel continues to deteriorate...

Heath

[mattd1979]

Is there anyone here that knows how to test transistors? Here is a link to the datasheet for a particular transistor that I want to test. It is a NEC K591.http://pdf1.alldatasheet.com/d....html

Here is a link to a page that describes how to test the transistor.http://www.kilowattclassroom.c...7.pdf

It says that I need to know if it is a PNP or an NPN transistor. I also need to know which is the collector, the base, and the emitter. It says to refer to the data sheet for the transistor to find out which it is. When I look at the datasheet, it says gate, drain, and source for the 3 pins. Anyone have any ideas which is which?

Matt

[Q45tech]

These things are taught in BSEE or ASEE even military mos schools.

As a MSEE, efficiency is name of game and as such I've collected half a dozen FPCU from junkers over the years. Don't waste time with repairs!But as a packrat I save them just in case when used are no longer available.

Don't confuse Bipolar [base, emitter, collector] and MOSFET transistors [gate, source, drain].