i have a 91 740 and one day out of the blue it wouldn't start(it still cranks) after trying to start it multiple times i finally got it to start, but it sounded a little rough though. after turning it off i was able to start it three times in a row then after that it wouldn't start.(if i leave it alone for a day it will start then die in exactly one second then it wont start again)

so i started inspecting the usual suspects, so far i have replaced the spark plugs,spark plug wires, then i realized that when the car normally worked i could hear the fuel pump engage for about two seconds when i'd turn the key to the second position(right before cranking it) but now i don't hear it at all so i replaced the fuel pump relay(and the 25a fuse) but still won't start. i feel like its the fuel pump it self(i think mine only has one pump which is in the tank, i looked under the car and couldn't find a second one).

any way someone said it might be the part inside the distributor cap that sends the spark to the plugs might be bad. is there a way to test wither the spark plugs are getting spark and wither the fuel pump is actually working?

 

Have you checked the codes yet? It may point you in the right direction. Two obvious fails could be the fuel pump relay or the crank position sensor. If you have no spark to the plugs, I'd suspect the CPS.
Unless you have a 16 valve motor, most likely your car has the Rex Regina set up. When you turn the key to on, you should here the fuel pump(s) run for 3 seconds or so. If it's a Regina, you only have one pump, in the tank and it is often hard to hear. With a helper turning the key and the gas cap removed you can generally hear it cycle on with your ear near the filler. Often it is the pump relay that is intermittently failing. It's behind the ashtray and behind the fuse board.
relay3.gif picture by swiftjustice44 - Photobucket
It is possible to remove the relay and power the pump manually by using a jumper wire. Try to use 12 gauge wire as the circuit pulls a lot of juice. There are two rows of 3 sockets side by side. Jumper between the left hand socket nearest you to the middle one on the right hand row. This will provide power continuously to the fuel pump, regardless of key position. It's not a fix, but is a simple way to check. I've been known to limp home using the wire but it isn't a safe thing to do. Best case scenario is you forget to unplug it and run your battery down. Worst case, you get rear ended and knocked unconscious while the pump spews gasoline all over. So...test purposes only. The simplest way to see if the plugs are getting spark is to have someone crank the engine while you remove the plug wire and hang on to it. If it shocks the crap out of you, you have spark. Barring that, you can use a thick rag and remove the boot from the plug and hold it close to the block while they crank it. You should see a fat juicy spark leap from the lead to the block.

 

i actually replaced the fuel pump relay with a brand new one and i can hear it click when i turn the key(i also hear a second click which i assume is another relay) and to make sure i wasn't missing the fuel pump sound i went in the hatch of my wagon and removed the black inspection plate that covers the opening to the in tank pump and i had a friend turn the key, but i still couldn't hear the pump.

when the car was working i could hear the fuel pump while in the drivers seat, but now nothing. i'll try the jumper wire technique , but if it is the pump how do i remove the white collar that's around the pump because it's extremely tight and large.

 

You mean the roughly 6" plastic collar that seals the tank? Giant channel locks work wonders. I know many folks do the entire job through the access panel but I prefer to do the swap from under the car except for the wiring. As I recall, you can get a pretty good grip on it by hand from underneath. I'm spoiled living in Texas as our gas tanks don't grow together with salt and rust. Still, yours is all plastic so should not be too bad. Worst case scenario is to use a wood drift and a hammer and get the lock collar started. It's good form to always replace the rubber tank gasket but in practice on my personal cars, I only replace it if it has flattened out.

 

awesome, i have a big pair of those i can use, thanks for all your help.
i have one last question, i heard that the fuel tank is under pressure, how do i release that pressure and when i'm done swapping the pump how do i re-apply that pressure?

 

Think about it. If the fuel tank were pressurized, every time you refueled there would be a huge whoosh every time the cap was released. It is the fuel line from the pump to the fuel injectors that is pressurized. It is the fuel pump that provides the pressure; if it has failed, there will be little or no pressure. That would be why the car does not run. When a working pump is present, it pressurizes the line when the pump runs.

 

forgive my ignorance, but this was my first major repair that dealt with something that is so dangerous(gasoline) so i didn't want to make any assumptions with that part of the car.

anyway it was the pump after all(i think the one that was in there may have been the original one when it first came off the lot). Once i put the new one in it started as if nothing had ever happened(i could also hear the pump engage once again).

thanks for all of your help swiftjustice44, it was much needed and much appreciated.

 

Woohoo! I love it when a plan comes together! I think everyone with a brain freaks out a little the first time they work on gas tanks. I still have an illogical concern about wiring carrying electricity being submerged in gasoline; the heck with physics, it just seems so wrong! But, do it correctly, take your time as it sounds like you have and it should provide you years of service.