Matt Hohmann

heres a new one for me (old disabled mechanic =Oldsheimers !!) on my 1988 olds cutlass supreme FWD car -my new - electric fuel pump will work fine -when key is just turned on=pressurises fuel system fine -then shuts down -signal from ecm is fine in that mode .Then car wont start-fuel pump will not run-staying on as needed to get fuel to the injection.The compression , spark =is great -its a fuel problem. Whats happening? There are no codes showing ever!!. Help please.
Any one also have a good electrical skematic on this car ?/

2blu442

I can't answer your questions, but to the top so more people might see your post!



John

White_Knuckles

Typical diags would include pressure testing at fuel line tap points i.e. schrader valves. When pressure is reached the pump would normally shut down if it has no flow. With all these systems, there are many variables to where it may be failing from control & monitoring devices to safety interlocks.

Do you have the proper tools, system diagrams and the known pressure specifications? A scope monitor may be needed to see if the injector signals are firing? That's probably where a shop would start poking around. Solving for the pump shutting down may be not even be electrically related. It may be delivering pressure then shutting down as the injectors aren't pulsing?

Modern cars are tricky devils. The more I try and speculate what's wrong the quicker I get pros to verify before I throw needless parts at 'em.

Matt Hohmann

Thank you - the car was operating fine- running good =then just quit!.I have 44psi min. @ the only schrader valve port- all pressureized. I cannot believe it has a thing to do with any injectors. I have no scope -not a high teck sort of guy. Id just like to know what electrical circuit or part in the circuit simply powers the fuel pump after ECM " initially" starts fuel pump operating ( a 2-3 sec. operation)- what makes pump keep working after this-? Like when cranking / running? what is actual power flow to the pump. For what these shops are charging hourly now -a person on limited retirement income cant afford the costs on an older car -just not worth it. There has to be an Olds guy somewhere that has had this exact problem as i do -got to be a simple thing to fix.

garys 68

I'll take a shot, although I'm more familiar with current efi systems.
When you initially turn the key to run, I'm guessing you hear the fuel pump run and you measure good pressure. That pressure should maintain a while. The engine should fire and run a few seconds even if the ecu doesn't trigger the fuel pump during running. Sounds like yours does not fire at all. Does the car crank when you try to start?
You need to confirm spark ($3 spark checker) and injectors (noid lights available for rent at Autozone).
Also, does your car have an anti-theft syatem built in? They were using keys with chips (resistors) and an in-dash 30 or 50hz generator around that time.

Matt Hohmann

Yes -when key is just turned to ="ON"=fuel pump will run & pressureise system. the spark i have checked -all 6 hot & bright -engine has good compression - yet wont run/ as fuel pump wont run after initial "ON " circuit powers it.like when trying to start the car . The car has NO =antitheft- cranks just fine and i did allso replace the crank sensor - had a mechanic do the as i dont have a lift .Hard to get to. Im just sure that what ever is powering the ful pump on the start & run circuit is the problem -yet i do not know what that is??

garys 68

like I said earlier, the engine should fire momentarily with the pressure built up when the key was initially turned. Check the injectors, see if they're firing.

White_Knuckles

Sorry, I meant a diagnostic monitoring tool when I said "scope". Not sure what was available in '88 for analyzing? Was that pre OBDI?

Example: The ECU may shut off the injectors due to lack of crank position input from the crank sensor. My point is, sensors commonly play into no-start conditions where the fuel pump may not be the problem.

Matt Hohmann

Yes -This car is an=OBD-1--- only code ever ive had was a year back =O2 sensor- i then replaced that. I did have a fuel pump go bad - replaced that also=now as i tested the old pump - works fine still- so may have had the starting of the problem then.?? Around 2 years back-the car ran just fine =always -then would die- & on roadside - after a few mins- of trying to start=it would fire & run fine - for many months=many!! Then do the same again. Finallt got so bad it would start run a few feet & die & never start. again =NO Codes!! I finally figured it was the crankshaft sensor - had it towed to a shop & sensor replaced. Mechanic said & showed me the sensor - in pieces & definately bad. Car started & ran fine-for mechanic & next day i picked it uo & drove home = around 30 miles -im in country area. Next day= drove 6 miles & died= towed home & discovered fuel pump wouldnt stay on after initial "key on" & system was preseruised. Tested fuel pressure @ schrader port = 42++ & stayed pressureised. no quick -bleed down. Checked spark - excellent in all 6 plug wires=with a visual spark tester. I even removed the top intake area to find all good & no leaks & all kooked good. I was intended to replace the fuel pail & all injectors @ that time as i have an exact spare set from another 2.8 engine-car was damaged so i keep for parts . was a great car till hit in pass side.actually drove it home after the accident. So, I know all is good on that for parts .Im just at a loss on this pump thing & dont understand what powers the pump on the run circuit -although i do know it is the ECM -although must have several fail safe senders somewhere .? I did find the oil pressure sender was 1 of the circuits?? and checked the power to the sender -all ok there . Im in process now of putting the top intake back on & retrying all. Im also curious as to a fuel pump relay being bad ?? where its located & what it looks like . Still @ a loss on this car's problem.

White_Knuckles

The crystal ball say's you may again have a crank sensor output issue. Some knock-off sensors (read Chinese) are notorious for leaving the party within a few months of operation and also sensors should never come out "in pieces"! Just because it was replaced doesn't mean it's currently working.

You had a no-start situation then and you have one now. Having no codes is not a shocker, OBDI is crude at best. Snap-on and others have hand-held, OBDI "readers" that can see what's functioning. Sensor outputs, fuel, spark and timing data is displayed. Without a scanner, you're flying blind.

One of my friends chased no-start for days. Turned out, a fuel shut-off feature was built into his front and rear bumpers . When you get hit, the system shuts down the pump to save you from a flaming experience. Very simple circuit that had a defective, hidden bumper switch. He had never been whacked so it didn't make sense.

Recommend - stop with the pump control or fuel issue. Bleed some fuel and see if the pump comes back on if you must but the thing won't cycle until there's a fuel/pressure demand. If the car is not starting or running, there is no demand where the line is pressurized and the pump will shut down - as normal. When the injectors start spraying, fuel demand and delivery will be restored.

Good luck!!

Edit: most members up here simply don't have your vintage car. You could try posting on a more general site covering your 80's generation GM not Cutlass or Old's specific.