stalling at low idle only 1991, 740 GL 164,000

Post by **jonesg** » 28 Apr 2008, 22:30

The HAynes manual says lacking a fuel pressure guage leaves you in a hit or miss position as far as diagnosis, the manual is right.
I pumped a cupfull of gas in no time but the fuel pump was still no good.
And the only way I found out was by buying a new pump, my Regina pump costs a lot more than the Bosch.

But I guess you haven't eliminated the pump relay as yet, have you pulled the ashtray and the pocket above it? Pry off plastic bezel around the cig lighter to find 2 screws, remove those and the pocket will come out for relay access. Put your finger on the pump relay , it clicks for a second as the pump primes the line. If it clicks on and off when the engine runs rough its no good but can be resoldered, heat distorts the board and cracks the solder, so after a hot run the engine (pump) goes intermittent. They only last so long.

Did you swap the relays on the coolant bottle bracket?

The in tank pump is a beeeach to replace, I wouldn't consider looking at the in tank sock filter without replacing the pump, its way too much work only to possibly leave the problem in place. Mine took 8 hrs ( in a snowstorm). Its also recommended to replace both pumps at the same time on the bosch system. Getting the pump out is ez, its getting the new one back in thats tricky. It required a dremel with a grinder cutting disk to cut off the old rusted hose clamps, but theres a way around that if you don't have one. Cut the hoses (not the fuel pickup hose though) and do it on the bench. A cutoff disk in a drill or carefull hacksawing.

If its not the relays (pump and injector) and you have good spark then I think I would seriously consider the pumps.
The proceedure is covered in the faq and must be followed to a T to get the new pump back into place, its a ship in a bottle routine with string.
I cut my old pump open , the brushes were toast, everything fell apart, the brush spring was the only thing contacting the stator, the wiring was burnt, the terminal post on the motor was melted. No wonder it ran poor.

Ron Richison · Post by **Ron Richison** » 30 Apr 2008, 07:56

does the plug on the top of the fp/sending unit in the tank unplug? Mine will not. Not sure if it fried and welded shut or it just wasn't suppossed to come off?? Any way, I have a plug that needs to resolder, 2 wires to the sending unit and 1 (red) to the pump motor. But, if it should be a "plug and unplug" set up, I should get a new one because it won't unplug.
did I royally screw this thing up? I will attempt a picture.

Post by **jonesg** » 30 Apr 2008, 10:31

Look at these pics,
http://cleanflametrap.com/ReginaFuelPump/

All the pumps are different but they'll all work, depends on which mfger you bought, mine was made in china, if yours is AC Delco its probably original volvo. I soldered mine, heat shrink , not tape on the wires.

On reassembly use grease on everything, inside and outside of the tank seal and inside the lip of the tank, you need to be able to rotate the cap after its seated in the tank. Find the marks on the cap and the marks on the tank at 3 o clock and 9 o clock, they have to match up.

Check the internal condition of your old pump.

Ron Richison · Post by **Ron Richison** » 04 May 2008, 20:00

well, I am sorry to report that after a very successful fuel pump (and sock) replacement, and a new throttle position sensor, my 740 still stumbles around at low idle!
Can I make my own fuel pressure gauge set up? where would I attach it to get a reading? intake on the fuel rail, or return?
I checked spark best I know how and all seems fine, but could one of the wires be faulty? how about timing? O2 sensor? bad octane gas?
I won't blame you if you're ready to give up, I'm $750.00 into this with no results and am running low on patience myself.
Ron

Post by **jonesg** » 05 May 2008, 06:12

Timing is computer controlled and it can compensate very well even for a bad runner.

Heres a couple of ways to make your own pressure tester for the fuel rail, if you have a valve on the rail a cheap tire pressure guage will work, then throw it away.
http://www.brickboard.com/FAQ/700-900/S ... reTestTool

Do you only have 1 fuel pump ?
If your car Regina ignition or Bosch?

Ron Richison · Post by **Ron Richison** » 05 May 2008, 08:09

I have 2 pumps. I had the main pump out when I changed the fuel filter. It seemed to run fine (before and) after I hooked everything back up. But, I did not change it. The fuel coming out of the filter was very clean. After replacing the low pressure tank pump, I had my dad tear into it and he said it looked fine. And it was running before I changed it. I have no regrets for changing it though.
I've also verified fp and injector relays.
aside from physically looking at plugs and wire and cap and rotor, and pulling wires one by one for the audible, is there any other way to verify ignition?
I will read that link and make the fuel pressure tester.
I know anythings possible, but how likely that the main pump, although running, could be the cause?

Ron Richison · Post by **Ron Richison** » 05 May 2008, 17:48

one more thing. my "brake light out" idiot light comes on when I put on the brakes. my brake lights function fine. this same idiot light comes on and stays on when my head lights are on (brakes or not)
any chance this could be short circuiting something else? anything that could affect my idling? how can I chase this down to fix it?I know it's a long shot but I'm running out of ideas

Post by **jonesg** » 05 May 2008, 18:19

They recommend both pumps be changed at the same time.
Although I think you ought to test the fuel pressure first if you can.

The bulb out light is just a bad bulb or dirty bulb sockets at the back, I had that on every socket, front and rear, bought some spray elec cleaner for it.

Review the lost of odle symptoms, which one best describes yours?

http://www.brickboard.com/FAQ/700-900/E ... mptoms.htm

Post by **jonesg** » 09 May 2008, 16:44

Any luck yet?