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Software Logic inside the ECU Computer?[200/1987] posted by Mr. Tool on
Wednesday, 2 December 1998, at 8:00 a.m.
Hi all: I have a 1987 245 DL. B230F engine. LH 2.2 Jetronic. I'm try to get a handle on what specific signals (inputs and outputs) are involved in both the Ignition Control Unit and the ECU computer. I'm having intermintant problems with the main fuel pump relay (system relay) being energized to turn on the main fuel pump. Yes, I have check all the basics, such as a new relay, grounds, etc. I have put some of Don Fosters home made test equipment on the car (neon bulbs to monitor spark and a test light at the main fuel pump power connections), and I'm currently monitoring these. Here is what occurs. You will get into the car and it won't start, but it's cranking. During this condition there is no power (12vdc) at the main fuel pump. The system relay is not being pulled in (energized). This relay is activated by an output from the ECU computer. However, other inputs to this ECU computer AND THE LOGIC programmed into it will determine if the computer will provide this signal to the relay. My understanding that there needs to be an "engine running" (cranking) signal as well to this ECU in order for the ECU to activate the relay. This signal I belive comes from Ignition Control Unit, which come from a pick up (Hall Sensor??). I'm trying to monitor the various signals that are all needed to make this relay turn on. If I don't know the internal logic to both units it will be more difficult. I suspect that I have bad wire, connection, or sensor, that causes this. This "not starting" condition happens only once every 1 to 2 weeks. Then the car will start fine after a while. The Air Mass Meter (AMM) is good. That's why I put the monitor lights on the car. That's how I noticed that the main fuel pump wasn't getting power during this condition.....HELP...Thanks for the help in advance.....Mr. Tool.......
--Mr. Tool
Re: Software Logic inside the ECU Computer?[200/1983] posted by Elliott Freis on
Wednesday, 2 December 1998, at 5:00 p.m.
I think I have much the same problem in my car. Apparently, the Comp wasn't supplying the ground I needed to energize the relay and therefor start the pump. I don't know why as of yet and it still sometimes does it. When the engine is running, occasionally I will hear the fuel pump relay "click" followed by an engine rev immediatly. Seems like the comp could be not getting the "engine is turning over" signal. Alternaly, the red power line might be faulty (although that harness just got replaced a few years back!!) When this happenes to you, try jumping the red power line to the fuel pump power and start her up. For some reason, when I do this (to manually start the fuel pumps) all runs fine.
-Ell
Re: Software Logic inside the ECU Computer?[200/1983] posted by abe crombie on
Wednesday, 2 December 1998, at 9:04 p.m.
The LH CM comes to life when you turn on key. It grounds the main relay power supply section at this time by outputting a ground through a transistor on board in LH CM. The control unit goes to work once it gets a digital signal from Ignition CM. By going to work I mean it begins to calculate and ground all injectors once per crank revolution for a time period that is appropriate to deliver correct amount of fuel and to continuously supply a ground to the fuel pump section of main relay again by a transistor on the LH CM circuit board. If you have injector pulses at the time when pump doesn't run (relay is not grounded) then the LH CM is getting the ignition pulses and the likely culprit is the fuel pump relay grounding transistor. This can be fixed on some control units with a kit that is made by one of the aftermarket Volvo parts companies. A good independent will likely be able to put you in touch with this company (Metrix is the comapny I think).