Fuel pump relay not working

milosch01 · Post by **milosch01** » Sat May 06, 2006 1:50 pm

I verified that that signal from the cpu to Q3 is being switched on for 2 seconds like it should be, but the fuel pump relay never energizes. The voltage at the base of Q3 actually stays around 8V no matter what. If I short the collector to ground the relay clicks on, so I guess my boards are wired and cabled correctly. I thought for sure it was a bad transistor. I swapped it with Q5 since I am not using FIDLE currently and it behaved the same. The relays I have are the Omron variety. I wonder if this 2N2222 just can't handle driving this relay? What's silly is that the relay did click on and off in the past due to incorrect configuration.

Dr.Fiero · Post by **Dr.Fiero** » Sat May 06, 2006 9:19 pm

Have you broken the feed line to the relay and measured exactly what current it's drawing?

I'm sure someone else can chime in with what the 2222 can deliver, faster than I can thumb through my ECG book. ;)

milosch01 · Post by **milosch01** » Sun May 07, 2006 3:43 am

I wonder if a TIP31 (Available from RadioShack - locally) would work as a replacement. Seems right.

milosch01 · Post by **milosch01** » Sun May 07, 2006 10:02 am

By the way, I replaced Q3 with a TIP31 and now the relay works as it should.