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Just signed up to the forum. I have been gathering information for a while off of here, and others, and thought I may join and ask my questions. I was gifted a 1991 740GL with the Regina system last year, and have been doing all that I can with my limited time and resources to get it running correctly. This car had been sitting in the parking lot at work for at least 6 years before I got it. First thing I needed to do was replace the fuel pump which had gone faulty. The car ran pretty well, but it started like an old carbureted engine with a bad choke. I would have to put my foot on the pedal just a bit for it to start, and I would have to keep it in that position until it warmed up a bit. After that it would idle without dying, but the idle was very rough. Acceleration was a bit sluggish, but it drove well. I read that the rough idle could be caused by a dirty throttle body, so I removed that and cleaned it thoroughly. No luck in diminishing the rough idle. I also read that the the idle control valve could cause this. While running the diagnostics check from pin 2 in the OBD I was able to visually see the valve opening, so I crossed that off of the list. In the mean time, the car started to lose power and stall. I found that the crank position sensor had gone bad, and replaced that. At this point the car was back to a hard start, and having to keep my foot on the gas until warm up. I bench tested the intake air temp sensor, and found that it is working. Just for grins I disconnected the vacuum line to the MAP and found that the car would idle without stalling, and would start m,ore quickly. While I had it running I put my finger over the vacuum port, and the car car still idled without stalling. It does a lot of fluctuation in RPMs with the MAP disconnected, but I expected that. I replaces the vacuum hose with a length of fish tank tubing, and that didn't help. Given that the ID is bigger than the stock line I thought that I would pay it little mind.
Now that my long winded explanation is over, is there an easy way to bench test the MAP sensor? Does it sound like a sensor issue, or was it just a fluke that taking the vacuum line off helped? I got this car for my daughter, she will be getting her license in a few months, so I need to get it running correctly. Any guidance will be appreciated.
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Sounds to me like a fuel pressure regulator problem. Can you check the vacuum line for the FPR for the presence of fuel? Can you check fuel pressure?
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Art Benstein near Baltimore
"Don't add too much water," said Tom with great concentration.
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I have played with the vacuum line from the fuel pressure regulator, but I do not remember any fuel in it. As of this moment I have no way of checking the fuel pressure. I will look into that, though.
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If it turns out that you need a MAP sensor, there are some GM cars that use the same one - like a late 80's Chevy Cavalier. It might make a junk yard search a bit more fruitful.
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)
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I was able to test the MAP this weekend, and it showed to be working properly. I'm still looking for a way to test my fuel pressure. I did find that the knock sensor shows an open circuit when I put my leads across the two pins, but I'm not sure that you can test these this way. I was also told by a friend that knows Volvos well that I shoud test my coolant temp sensor. I will try to get to that this week. Any other ideas?
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Thank you so much for the information. I will look it all over several times, I'm sure. I have run the diagnostic tests with the OBD. No codes in socket 6, and two codes in socket 2. One code for the intake air temp sensor, one code for the MAP sensor. Both came about due to my disconnecting both sensors for test purposes. I will replace the knock sensor. I'm assuming that there should be continuity across the pins by your response. I will also look into the coolant temp sensor, as my buddy keeps nagging me to check it.
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The knock sensor is a ceramic crystal microphone. You can't check it with an ohmmeter. You can replace it, of course, but they aren't cheap and I think you will find it doesn't help a thing in your car to replace it.
Checking the temp sensor is a good idea, but best checked by observing the voltage at the ECU plug, not by physically accessing it under the manifold. There are some hints in the 7/9 FAQ to help shortcut the process, but the basic idea is to watch the voltage fall from its cold reading to fully warmed up. Here's a plot of the voltage as a function sensor resistance, along with a plot of resistance as a function of temperature. The graph is for LH2.4, but the sensor is monitored by the same current by the Rex and Regina computers.
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Art Benstein near Baltimore
Reassembly is the reverse of disassembly. Except the profanity. You don't take that back; you just keep adding to it.
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Ran a fuel pressure test this weekend. I was getting all of 20 psi at the rail. I swapped out the FPR and nothing changed. After pulling the fuel pump out I saw that the rubber fittings around what I assume is the check valve are rotted out. I am going to remove the valve for testing purposes to see if there was fuel leaking around that area causing the lack of pressure. I should be able to make some new fittings if I cannot find any replacements online. One question I have at this point is if I have the correct pump. My 740 has the Rex Regina system. If this pump is for the Bosch system would it have less pressure? Or, are the pumps the same for both systems?
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You seem to be describing the pump's pulse damper rather than a check valve, as there's no need for a check valve in Regina's single in tank pump system. Could be the rubber is leaking the pressure back into the tank.
Bosch used a lift pump in the tank to bring the fuel to a pressure pump external, about where your fuel filter lives. The rest of the world went the other way, putting the pump in the tank like yours is.
Notes on Replacing a Regina Fuel PUmp and Why
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Art Benstein near Baltimore
Two atoms were walking down the street one day, when one of them exclaimed, "Oh no - I've lost an electron!" "Are you sure?" the other one asked. "Yes," replied the first one, "I'm positive."
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I put the pump back in last night. It took a minute for the car to start, but once it did it ran well. It stayed at idle without dying, and seemed to have pretty good throttle response. I need to finish the pump assembly installation tonight so that I can take it around the block a few times. I did notice that the pressure went up, but only to about 25-30 psi. The test gauge I'm using is a cheapo from Harbor Freight, so I'm not sure how much I can trust it. The pump that I purchased off of E-bay said that it works with the Volvo 740, but it is really for a Corvette. That should still work, right? I know very little about fuel injection systems as my mechanical specialty is vintage motorcycles. Not a lot of fuel pumps there.
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Several of my Volvo-owning friends enjoy the vintage motorcycle hobby. I too have vintage cycle experience, but the experience is vintage and the motorcycles were fairly current at the time. :)
The pump should be OK, but the thing with fuel injection is the rail pressure needs to be precise, not just "in the ball park." The reason is the mixture that results is directly proportioned knowing just what the difference in pressure is between the inlet and outlet of the injectors, i.e. rail pressure minus manifold pressure. That's the only way EFI knows how much fuel is being delivered.
Could be a gauge problem, or more likely, a gauge connection problem. How do you deal with the clearance below that Schrader fitting; does HF give you a right-angle adapter? Or do you even get to use a Schrader on the '91?
The pump only need supply the rail pressure with head room above the 3-bar regulator setpoint, which is returned to the tank. If that connection between your pump outlet and the fuel line is leaking back into the tank, it is likely you never reach the regulator setpoint pressure needed in the fuel line. Hard to tell which is the trouble if you can't trust your pressure measurement. Have another car?
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Art Benstein near Baltimore
“He who is not contented with what he has, would not be contented with what he would like to have.” -Socrates
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After fully re-assembling the pump unit the car went right back to the way it was running previously. I am going to pull the pump back out and recheck all of the electrical connections. I am also going to look inside the tank for any obstructions, as the pump worked well when the unit was sitting loosely inside the mounting hole, but worked poorly after it was fully seated. I did a quick run through the fuel lines and saw no indication of leaks within the lines, so I am thinking that it is all pump related at this point. I am so glad that I don't have to drop the tank to get to the pump, but that access hole could be a little larger. I keep cutting my hands on the sheet metal when playing with all of the hoses that attach to the pump assembly.
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Pulled the pump assembly and replaced the terminal at the motor. The car is running much better now. I even had a chance to fix the fuel level unit while I had the pump out. It's amazing how much trouble some bad solder joints can give. The idle still has some tremolo going on, but nothing to drastic. It's time for new plugs and what not, so maybe that all will help. I'm sure it wouldn't hurt. Thank you all for the help and input.
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"It's amazing how much trouble some bad solder joints can give."
Amen.
Not only joins made nearly 30 years ago, but fresh ones botched at the factory, as is this one on a 240's aftermarket in-tank fuel pump radio suppression choke.
(From http://cleanflametrap.com/transferPump.htm )
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Art Benstein near Baltimore
A dyslexic man walks into a bra.
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