I am writing to inform everyone what the ultimate solution was to my problem with the fuel pump relay. Frankly, it is a bit imbarassing because the solution was so basic. I missed it for a number of reasons, but primarily because it presented itself as somewhat of an intermittant problem. That is, the fuel relay seemed like the only problem. Okay, so here it is.

The #4 ground wire from my battery to the engine block was actually completely severed. I believe it was still making some contact, but it was severed. Yes, the engine was grounded through the braided wires from the firewall to the top of the engine near the distributor. Regardless, it was obviously a terrible connection if there was one. I overlooked it as when I checked the resistance from my negative terminal to the engine block, the resistance was zero ohms.

For your sake, I will also mentioned that I was having a problem for over a year with the alternator output voltage. It was never more than 12.45 volts. No matter what the engine speed an no matter what the load.

While I had noted over time, that sometimes when I cranked the engine it cranked like a diesel engine in Alaska, this was easily corrected by turning the key off of start and then trying to crank it again. 99% of the time this cured the problem. I attributed it the problem to a bad solenoid which was not making a good contact every now and then.

I got put on the right track to my problem while working on the car at night. I had been playing with the thought of the engine voltage dropping sufficiently during cranking that it was affecting the fuel pump relay working. I felt this had something to do with the ECU and the proper grounding of the 86/2 pin on the relay. (I was still suspicious of the "black box.") Anyway I found that by using a jumper from another vehicle, my Volvo would start properly and once started would always continue to run. Since I could not carry the other car around with me, I kept playing around. I was jumping the engine block to the negative terminal with the engine running. When I connected the ground to the engine block I saw a spark. Well, dumb though I may be, I recognized a problem here.

Well, I waited until the next day when I had some light and managed to find where the wire connected to the engine block. Not a friendly location. Nonetheless, what I found was that the wire looked like it was still connected, but as I said it was completely severed. The last six inches of the wire was very rigid. I cut off the last eight inches of the ground wire, put on a new lug and reconnected it. The car now starts every time and the output voltage of the alternator is now 13.0 volts.

I want to sincerely thank you for replying to my post. I hope that my lesson learned is useful to you sometime. FYI I am posting this same message to everyone else who sent me a response.

Scott,

Thank you for responding. Your logic is very good. My "engine turning" sensor is a Hall Effect transitor in the distributor. I thought of the low voltage due to cranking drain. I put a meter on it and it dropped to 11.24 volts during cranking and I believe this would be withing the normal range so I dropped that idea. (You would have thought that I would have mentioned that in my long post, but I probably was putting myself to sleep when I was writing it.)

One small error in your read of my post, it that the fuel pump relay does not come on when I turn on the key. There are two relays inside the fuel pump relay box. One for the fuel pump and one for the general ECU system (my interpretation). The general system relay activates when the key is turned on. The fuel pump relay comes on for about a second, but this happens when I turn the key off, not when I turn it on.

I don't think I need to test the fuel pump by jumping the 30 pin to the 87/2 pin as by grounding the 86/2 pin I actuate the fuel pump relay which in effect connects the 30 pin to the 87/2 pin and the pump runs.

I have thought about puttin on an auxillary ground wire onto the 86/2 wire to use during cranking. I would put in a spring loaded push button so that it would open after I took my finger off of it once the engine started. This would eliminate the saftety concern regarding the pump running on in the event of an accident. This should work in my case as the relay works fine while the engine is running.

There is another resonse to my post by lucid, and I have read through it quickly. It seems to be an impressive post. Unfortunately, he makes reference to a couple of items I am not familiar with so I need a little time to digest it, which I do not have at the moment as I have to run off to work. When my problem is resolved, I will post what the solution was. Thanks again.

Bruce,

I see you are on line right now, so I will try to ask you a couple quick questions regarding your response. First, thank you. You give me great hope.

First, I have started tried starting the car with the 86/2 grounded. I have had some mixed results, but think that if I stuck with it the results would not have been mixed.

I am thinking that there may be some sort of check valve in the fuel line to prevent the rail from depresureizing when the engine is turned off, the purpose of which would be to enable quick starts. If there is such a puppy in my 740 and it failed, it would explain why I have to repressurize the rail by running the pump before I can get it to start. (I described elsewhere how I would turn the key on and off repeatedly to take advantage of the short approximately 1 second pump runs after the key is turned off.) Someone posted elsewhere about a 240 that had such a check valve, but nothing re 740 especially where it might be if there is one.

My Bosch Jetronic ECU part number ends is 0 280 000 544.

1. Is the ICU integral to the ECU? I mean, is located inside of the ECU box. If not, where is it?

2.a) I am getting spark to the plugs. I checked this early on. I had to contrive a way to place a plug on my windshield so I could crank the engine myself from the driver seaat. At first it did not appear to have a spark. I then tried to improve my ground and I did see the plug spark and shortly afterward the engine began running on three cylanders. Would not the fact that the engine does run once I get it started, also eliminate this from being the problem? Granted, my problem seems to pertain to the cranking phase.

At this point I see this as a fuel supply problem vice ignition problem as I am seeing the fuel pump off during cranking and I can get the engine to run. I checked my cranking voltange and it dropped to 11.24 volts during cranking.

FYI I do not have a Mitchell manual. I do have a Haynes manual, which I have never been all the pleased with.

I don't know if this is related at all, but one other system I have been having lately is decreasing mileage per gallon along with signs of running rich, like black plug and black soot inside of tail pipe. Performance is notebly off. Highway mpg is down to about 16.5mpg whereas it was 20 to 21 the last few years. I used to get 26 mpg highway about 10 years ago. New air filter and plugs did not help. Have not done wires recently. I am only tossing this in for general background regarding the other problem. Seems unrelaated to me, but maybe you see something.

I want to sincerely thank you for your help. I will study your comments and let you know how I make out.

I am writing to inform everyone what the ultimate solution was to my problem with the fuel pump relay. Frankly, it is a bit imbarassing because the solution was so basic. I missed it for a number of reasons, but primarily because it presented itself as somewhat of an intermittant problem. That is, the fuel relay seemed like the only problem. Okay, so here it is.

The #4 ground wire from my battery to the engine block was actually completely severed. I believe it was still making some contact, but it was severed. Yes, the engine was grounded through the braided wires from the firewall to the top of the engine near the distributor. Regardless, it was obviously a terrible connection if there was one. I overlooked it as when I checked the resistance from my negative terminal to the engine block, the resistance was zero ohms.

For your sake, I will also mentioned that I was having a problem for over a year with the alternator output voltage. It was never more than 12.45 volts. No matter what the engine speed an no matter what the load.

While I had noted over time, that sometimes when I cranked the engine it cranked like a diesel engine in Alaska, this was easily corrected by turning the key off of start and then trying to crank it again. 99% of the time this cured the problem. I attributed it the problem to a bad solenoid which was not making a good contact every now and then.

I got put on the right track to my problem while working on the car at night. I had been playing with the thought of the engine voltage dropping sufficiently during cranking that it was affecting the fuel pump relay working. I felt this had something to do with the ECU and the proper grounding of the 86/2 pin on the relay. (I was still suspicious of the "black box.") Anyway I found that by using a jumper from another vehicle, my Volvo would start properly and once started would always continue to run. Since I could not carry the other car around with me, I kept playing around. I was jumping the engine block to the negative terminal with the engine running. When I connected the ground to the engine block I saw a spark. Well, dumb though I may be, I recognized a problem here.

Well, I waited until the next day when I had some light and managed to find where the wire connected to the engine block. Not a friendly location. Nonetheless, what I found was that the wire looked like it was still connected, but as I said it was completely severed. The last six inches of the wire was very rigid. I cut off the last eight inches of the ground wire, put on a new lug and reconnected it. The car now starts every time and the output voltage of the alternator is now 13.0 volts.

I want to sincerely thank you for replying to my post. I hope that my lesson learned is useful to you sometime. FYI I am posting this same message to everyone else who sent me a response.

Hey, Mike,

Thanks for replying and providing your insight. Yeah, my initial message was a bit long and I was concerned it might be a problem.

I have already bought a new relay, but it acts exactly the same. My fuel pump runs fine. My problem is that the relay is that the 86/2 pin is not grounding out when I am cranking the engine. It is grounding and working properly when 1) the engine is running 2) when I turn the key off and it runs for that one second (approximately) interval afterwards.

I was thining about this this morning. I have been thinking tht the problem is in the ECU as I am assuming that either the ground relay is either in the ECU else the message to effect the ground flows through the ECU. I can imagine many ways this message could be initiated, but I am wondering if it might have to do with the key when it is in the crank position, but this is simply speculation. I am wondering now if the relay for the in tank fuel pump relay somehow plays a role in completing this grounding circuit for this main pump relay during the cranking phase.

What I am really looking for is someone who knows this fuel pump relay grounding circuit (i.e., 86/2 pin) and how it is supposed to work, particularly when cranking the engine.

Carl 1987 740 non turbo