'91 Lumina electrical ? Prob

[Bearwulf]

Car will not start or run with fuel pump connected, but elevate rear of car about 12", disconnect fuel pump, car will start. It idles very rich, and as throtte is openedit leans out but carries a miss through power range. If car is lowered, it will die and not restart until rear is raised again.

[16th hippy]

odd one. sounds as if there is a power issue with pump. with pump connected, can you hear the pump run for the 2-3 seconds prime? what is fuel pressure at rail also?

[cf1]

Originally Posted by 16th hippy

odd one. sounds as if there is a power issue with pump. with pump connected, can you hear the pump run for the 2-3 seconds prime? what is fuel pressure at rail also?

sounds like its shorting out, or theres crud in the tank that the screen is cloged.. new pump time..

[Bearwulf]

Tried new pump this morn., no help. Tank is clean. New:ecm, tps, ckp, fuel pres. reg., ign. ctrl. mod. also.
Anyone know a place online to get under-dash wiring diag's.for this car?
Have traced wire prob. to under dash, 1 of 4 wires dissapears from group @ this point.

[jeffcoslacker]

Injectors sould not even be able to open without fuel pressure, much less allow the motor to run. I don't see how it's possible for it to run with it disconnected.

Are you sure it's the pump you are disconnecting? (dumb question I know but this is really odd)

[Bearwulf]

Yes, I'm sure. Am unplugging the 4 wire loom that comes directly out of the sending unit in the fuel tank.

[jeffcoslacker]

OK we better define this some more. Which motor? How long will it run like that? Indefinitely? How much gas is in the tank?

[cf1]

Originally Posted by Bearwulf

Yes, I'm sure. Am unplugging the 4 wire loom that comes directly out of the sending unit in the fuel tank.

did you change the fuel filter? my 87 did the same thing ,would idle rough, i couldnt give it any gas it would stall. i think its only runing after you disconnect the fuel pump. because the fuel thats in the thotle body and engine.. is there i fuel pump regulater on that car?

[Bearwulf]

Thereis no fuel pump reg. that I can find, but there is a fuel pres. reg. The filter has been replaced new. This one, if step on throttle engine will wind right up in rpm. It will continue to run as long the key is in run pos. & the tank is elevated approximately 8-12 inches above normal. If rear of car is lowered engine will die.
this happens whether fuel cap is on or off tank.

[cf1]

[quote=Bearwulf]Thereis no fuel pump reg. that I can find, but there is a fuel pres. reg. The filter has been replaced new. This one, if step on throttle engine will wind right up in rpm. It will continue to run as long the key is in run pos. & the tank is elevated approximately 8-12 inches above normal. If rear of car is lowered engine will die.
this happens whether fuel cap is on or off tank.[/QUOT let car down, spray starting fluid or gas into throttle body,, if engines runs its not electrical..

[Bearwulf]

3.1 engine. Will run for more than 5 min. or until fuel pump is plugged in again.Then takes 2-3 secs. to die.

[Blue Bowtie]

A '91 189 (3.1L) runs with the fuel pump unplugged, but won't run with the pump connected? As you well know, that engine is a multi-port injected type, normally requiring fuel pressure and injector pulses to administer fuel.

Given the symptoms, I'd suspect a significant fuel leak in the system, either via a stuck/blown FPR or static injectors. Raising the rear of the vehicle may provide sufficient gravity flow to allow fuel to feed to either the static service injectors or backward through the FPR, allowing the engine to run, albeit richly. Connecting the pump would likely provide far too much fuel to start and run the engine.

Raise the rear of the vehicle, stand on one foot, close one eye, or do whatever you have to do to get the engine running. While running, disconnect the injector electrical connectors one at a time, and keep them disconnected. See if it still runs. While the injectors are unplugged, test each injector solenoid coil resistance. If any of them are below 9.8 ohms, do not reconnect those. If any are shorted to ground, do not reconnect those.

If the engine stops while you are unplugging injectors, the last one unplugged may be shorted. Reconnect the fuel pump to establish injector pressure, and try it again. If the engine does run on the remaining good injectors with the fuel pump running, replace the faulty injectors.

If the engine will still not run with the fuel pump running, and all the injectors check good, there may be a major fuel leak in the FPR and/or fuel return line. To test this theory, you can pinch the fuel return line closed in the engine compartment while the engine is running and judge by the result.

[Bearwulf]

Will it run with the upper plenium off the engine? That is the only way to test individual inj.
All inj. show power to both hot & grnd. when connected even one @ a time. When all are unplugged the system shows power to one side & grnd. to other.

I will dig out the ohm meter.

[j cAT]

Originally Posted by Bearwulf

Will it run with the upper plenium off the engine? That is the only way to test individual inj.
All inj. show power to both hot & grnd. when connected even one @ a time. When all are unplugged the system shows power to one side & grnd. to other.

12volts is always on one side of injector always... the ecm/pcm is grounding the other side so as engine runs the ground side pulses from 12volts to 0 volts understand. now if you have a shorted injector this will mess up the other injectors so you must disconnect one at a time to determine this or buy a meter and check resistance......of each injector....

[Bearwulf]

Sorry taking so long getting back, had other jobs in meantime.
Lowest resistance on any inj. was 11.9 ohms. Am putting in used working set to check system with. Crossing fingers & PRAYING real hard for positive results.
Thanks people, so far has been sensible and pertinent advice.
Will be back to let you know how it turns out.