1991 lesabre
04-07-2021, 12:46 AM
#21
Senior Member
True Car Nut
This depends on the original fuel pressure and power demand placed on the engine.
Sounds like uncontrolled combustion upstream of the intake valves. Could be lean misfires. Could also be running rich.
These will flash engine codes with the check engine light.
You can test towards the pump by testing at the fuel pump fuse. It'* not exactly "at" the pump, but if the pump is receiving power at all it is probably receiving the same amount of voltage as measured here. Worst case, drop the fuel tank and backprobe into the wiring such that you can measure there while it is running.
You can test towards the pump by testing at the fuel pump fuse. It'* not exactly "at" the pump, but if the pump is receiving power at all it is probably receiving the same amount of voltage as measured here. Worst case, drop the fuel tank and backprobe into the wiring such that you can measure there while it is running.
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1985 supra (04-07-2021)
04-07-2021, 12:53 AM
#22
Senior Member
True Car Nut
I did another rev it up test after I switched relays. Let it run for ten mins with a screwdriver stuck behind the linkage by the motor to get it to rev up some. Ran perfect for ten mins. took out the screwdriver idled good. Drove it ahead down the driveway, put in reverse ran like crap. Could barely keep it running to get it back to where I started. Almost does not seem like a fuel problem.
There is almost no fuel or spark needed on an engine revving or idling. Different story with the transmission in gear.
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1985 supra (04-07-2021)
04-07-2021, 01:06 AM
#23
Senior Member
True Car Nut
What are you confused about. You asked me where I am reading the pressure. Most cars at least every Buick I have has a spot right on top of the engine on the fuel rail near the fuel pressure regulator. You simple screw the tester part into that. End of story. You can also take a different attachments and screw it into the fuel filter in between the filter and the fuel line and screw the tester into it there. Don't know how to say that any easier.
As for what the brand was, it was some off brand by someone on ebay. I do not know what the brand was called. I am sure it was not the ones whoever mentioned.
Or did you not understand when I said I put a different relay, from the horn, into the fuel pump spot and it did not help.
Or are you confused when I say when I start it up and drive it around the yard it runs like crap within a couple mins. If I simple let it sit and bring the idle up a decent amount and just sit and wait it will continue to run perfect. And I mean perfect. No misses no backfiring just a nice purring engine sound. And it will continue to run good for as long as I keep it going. Tomorrow perhaps I will let it run like that for 20 minutes and see if it continues to run 100% perfect.
Yes I am confused why it runs like crap almost right away when moving or if kept on a low idle but when the idle it increased a decent amount it runs perfect for any amount of time. Probably if I kept putting gas in it would run non stop till July.
So I would say that pretty much rules out the pump, unless pumps can run perfect at certain speeds and bad at other speeds.
Which the guy who said the oil pressure could cause a problem is making some sense. Perhaps keeping the idle higher keeps a better oil pressure. Which keeps the pump running. As it goes to the low idle the oil pressure drops. Never heard of such a thing happening.
As for what the brand was, it was some off brand by someone on ebay. I do not know what the brand was called. I am sure it was not the ones whoever mentioned.
Or did you not understand when I said I put a different relay, from the horn, into the fuel pump spot and it did not help.
Or are you confused when I say when I start it up and drive it around the yard it runs like crap within a couple mins. If I simple let it sit and bring the idle up a decent amount and just sit and wait it will continue to run perfect. And I mean perfect. No misses no backfiring just a nice purring engine sound. And it will continue to run good for as long as I keep it going. Tomorrow perhaps I will let it run like that for 20 minutes and see if it continues to run 100% perfect.
Yes I am confused why it runs like crap almost right away when moving or if kept on a low idle but when the idle it increased a decent amount it runs perfect for any amount of time. Probably if I kept putting gas in it would run non stop till July.
So I would say that pretty much rules out the pump, unless pumps can run perfect at certain speeds and bad at other speeds.
Which the guy who said the oil pressure could cause a problem is making some sense. Perhaps keeping the idle higher keeps a better oil pressure. Which keeps the pump running. As it goes to the low idle the oil pressure drops. Never heard of such a thing happening.
There are two paths to fuel pump activation:
1. Fuel pump relay and circuits
2. Power supplied by oil pressure
Now if the fuel pump relay fails in the middle of driving in L.A. traffic on the 405 freeway, the car doesn't stall, a pileup doesn't happen behind it, there are no related freeway shootings, riots, beatings etc. This leads to reduced necessity for suing the manufacturer for building a car that fails due to a $10.00 electronic part that lives in environmental misery all its life. In order for low oil pressure to stop the fuel pump, the relay would have to fail at the same time. If the fuel pump runs before starting the car then this is unlikely. Relays tend to fail completely, and not just when warm or dirty or sad or etc.
04-07-2021, 03:31 AM
#24
Senior Member
Posts like a Turbo
I'm still trying to sort this all out in my head. LOL, my manual has many pages on the fuel system and how it works. 10 pages on troubleshooting.
CathedralCub, thanks for correcting me. I always thought if oil pressure got too low the pcm would see this and shut fuel pressure relay off to save engine. but I couldn't find any reference to it in the manual. So thanks for that, I learned something. And it did say the fuel pressure sw would run the fuel pump it the relay failed.
I'll follow this thread, and if I can add anything I will, but for now I'm stumped. but I do agree with Carfixer007 that it sounds like a fuel pump. but I would check the wiring etc before buying another pump.
Good Luck
CathedralCub, thanks for correcting me. I always thought if oil pressure got too low the pcm would see this and shut fuel pressure relay off to save engine. but I couldn't find any reference to it in the manual. So thanks for that, I learned something. And it did say the fuel pressure sw would run the fuel pump it the relay failed.
I'll follow this thread, and if I can add anything I will, but for now I'm stumped. but I do agree with Carfixer007 that it sounds like a fuel pump. but I would check the wiring etc before buying another pump.
Good Luck
04-07-2021, 10:14 AM
#25
Member
Posts like a V-Tak
Thread Starter
Check the wiring do you mean check for 12 volts? Is there a way to check it without dropping the tank and testing by the connection. I would like to test it while its running to see if it drops after running a while.
04-07-2021, 11:24 AM
#27
Member
Posts like a V-Tak
Thread Starter
I can try cleaning up the IAC valve. Perhaps the throttle body also. Watching a video after CathedralCub mentioned this it did state it would run worst in reverse, and the car is the hardest to move while in reverse.
04-07-2021, 12:39 PM
#29
Senior Member
True Car Nut
If I am understanding everything right....
Car runs fine, fuel pressure is fine, everything is great.
After a few minutes, fuel pressure starts progressively dropping (with symptoms as such, verified by a gauge at the fuel rail) until the engine fuel starves and dies.
In an attempt to resolve this issue, you have already replaced the fuel pump and filter, and have not had any change in the problem.
If the above is true, I would agree with checking voltages in line to the fuel pump to see if there is a correlation. Also, and please verify this in the manual/in person, there is an electrical connector that hangs loose in the passenger fender next to the horn. This I believe connects to the fuel pump, post relay. It'* purpose is to facilitate putting power to the fuel pump for a fuel tank pump out, and it may be used to aid in diagnosis. I have never tried it, but it sounds good anyway.
Car runs fine, fuel pressure is fine, everything is great.
After a few minutes, fuel pressure starts progressively dropping (with symptoms as such, verified by a gauge at the fuel rail) until the engine fuel starves and dies.
In an attempt to resolve this issue, you have already replaced the fuel pump and filter, and have not had any change in the problem.
If the above is true, I would agree with checking voltages in line to the fuel pump to see if there is a correlation. Also, and please verify this in the manual/in person, there is an electrical connector that hangs loose in the passenger fender next to the horn. This I believe connects to the fuel pump, post relay. It'* purpose is to facilitate putting power to the fuel pump for a fuel tank pump out, and it may be used to aid in diagnosis. I have never tried it, but it sounds good anyway.
04-07-2021, 02:33 PM
#30
Senior Member
True Car Nut
It'* possible you have a high resistance short that is getting hot and as it gets hot it drops more and more voltage and the pump will slow as a result. It would likely be at a splice or other connection. If the wiring going back has been messed with in the past and not properly fastened back and has rubbed through it could cause this kind of problems but it would more likely blow a fuse. I still think you have a bum pump.