The Oldsmobile Connection

[Collette Nagy]

The car runs smooth whenever the mechanic takes it for a test drive. Often it runs smooth for me, too. But sometimes it seems like it will die. I thought it was a bad tank of gas, but apparently not. I wondered if the transmission was slipping, as it will just start hesitating, almost bucking, while I am going up hills. But then it started doing it on flat ground and downhill. It always idles smooth. At this point, I figured I'd just drive it until it misbehaves all the time so that the machanic is sure to get a live demonstration. However, I'd rather not get stranded from ignoring the problem.

Do you have any ideas?

Collette

[91parkave]

have you performed a full tune-up on the car recently?

[silverlegend]

I've got a 1992 Eighty-Eight Royale LS which just had the fuel pump die a few months ago. Your problem sounds a lot like the symptoms I had, especially if you consider that when you go uphill the gas goes to the back of the tank and the fuel pump has to work harder (while going downhill makes it easier on the pump). Do you notice the problem getting worse when the gas tank is down around 1/4? It'll almost stall out when the fuel is low, if the pump is dying.

Hope that helps!

[andrewk]

The thing to determine is "What am I losing under load". Bad plugs and/or wires could give you a load miss, a plugged fuel filter could mimic what silverlegend mentioned.

I would start with the basics, like making sure all your regular maintenance is done, and go from there.

Andrew

[91parkave]

silverlegend wrote: I've got a 1992 Eighty-Eight Royale LS which just had the fuel pump die a few months ago. Your problem sounds a lot like the symptoms I had, especially if you consider that when you go uphill the gas goes to the back of the tank and the fuel pump has to work harder (while going downhill makes it easier on the pump). Do you notice the problem getting worse when the gas tank is down around 1/4? It'll almost stall out when the fuel is low, if the pump is dying.

Hope that helps!

if your low 1/4 tank of gas and it starts to cut out on you, that isnt a fuel pump problem at all, Its the tank baffle design around the pump and due to the fact its hard for the pump to pickup any gas if the gas has "sloshed" beyond the pickup of the fuel pump. Driving like this ( on E or close to it)will cause pre-mature fuel pump failure because air will enter instead of fuel causing it to burn itself out and over heat.

[88 Coupe]

Hi Collette Nagy,

Welcome to TOC.

Quote: ........ Do you have any ideas?
Check the first post at the following link: http://www.oldsconnection.com/forum/viewtopic.php?t=2894
It would have been an interesting read, if it had not been trashed by our resident "V6 expert".

If you think it matches your symptoms, have your mechanic test the coil pack, as shown at this link.

Norm

[88 Coupe]

silverlegend wrote: ........ Your problem sounds a lot like the symptoms I had ........
"Sounds a lot like" does not sound a lot like something that can be used for an informed diagnosis.

silverlegend wrote: ........ when you go uphill the gas goes to the back of the tank and the fuel pump has to work harder ........
How much harder (in PSI) does it have to work?

silverlegend wrote: ........ It'll almost stall out when the fuel is low, if the pump is dying ........
How is the quantity of fuel related to the the efficiency of the pump?

Norm

[88 Coupe]

91buickman wrote: ........ Its the tank baffle design around the pump ........
Of course it is. It was designed that way, in order to promote the sale of replacement pumps.

91buickman wrote: ........ will cause pre-mature fuel pump failure because air will enter instead of fuel causing it to burn itself out and over heat.
Using your own logic: Pumping air would eliminate the normal stress of pumping liquid. The lighter load on the motor, would cause it to run cooler, which would extend its life.

Norm

[91parkave]

88 Coupe wrote: 91buickman wrote: ........ Its the tank baffle design around the pump ........
Of course it is. It was designed that way, in order to promote the sale of replacement pumps.

91buickman wrote: ........ will cause pre-mature fuel pump failure because air will enter instead of fuel causing it to burn itself out and over heat.
Using your own logic: Pumping air would eliminate the normal stress of pumping liquid. The lighter load on the motor, would cause it to run cooler, which would extend its life.

Norm

Again,
a Fuel pump is designed to pump fuel not air the fluid moving through it, keeps it at its designed RPM's , and also keeps the pump cooler because the fluid also takes the thermal energy created away. pumping air will cause it to spin faster with no way to cool itself in the process.

think of it like this would you run your cooling system to where its almost 1/4 empty, or worse, Then see how long your engine lasts?? i dont think so, same goes for the fuel system.

[88 Coupe]

91buickman wrote: ........ pumping air will cause it to spin faster with no way to cool itself ........
Again: No load = no work = no heat.

91buickman wrote: ........ would you run your cooling system to where its almost 1/4 empty ........
1. Another of your bogus analogies: Unlike the cooling system, the efficiency of a fuel pump is no different at 100%, or 1% of the capacity of the tank. 2. Fuel level was never mentioned as a symptom. Norm

[91parkave]

so lets get this clarified-----youre saying a fuel pump with no fuel while driving has no load? so whenever theres no fuel the pump magicly shuts off? no load means the pump stops spinning? crack must be good out there were you are.

now try to keep up, 88 coupe wrote: 2. Fuel level was never mentioned as a symptom.
read whats actually posted and not what you think was there.

[88 Coupe]

91buickman wrote: ........ crack must be good out there were you are ........
Grow up.

[andrewk]

Quote: youre saying a fuel pump with no fuel while driving has no load?

I'd say that's an accurate statement. I don't think you'd be driving very far with no fuel, but there is certainly no load on the pump.

Quote: so whenever theres no fuel the pump magicly shuts off?

No fuel pump runs all the time- That is why it is wired with a relay. EG, when you turn the ignition on, you will hear the pump cycle, then stop when appropriate fuel pressure has been built.

91parkave wrote: no load means the pump stops spinning?

When the duty cycle of the pump has been reached, you bet it does.

Andrew

[91parkave]

andrewk wrote: Quote: youre saying a fuel pump with no fuel while driving has no load?

I'd say that's an accurate statement. I don't think you'd be driving very far with no fuel, but there is certainly no load on the pump.

Quote: so whenever theres no fuel the pump magicly shuts off?

No fuel pump runs all the time- That is why it is wired with a relay. EG, when you turn the ignition on, you will hear the pump cycle, then stop when appropriate fuel pressure has been built.

91parkave wrote: no load means the pump stops spinning?

When the duty cycle of the pump has been reached, you bet it does.

Andrew

Lets examine that andrew...
andrewk wrote: No fuel pump runs all the time- That is why it is wired with a relay. EG, when you turn the ignition on, you will hear the pump cycle, then stop when appropriate fuel pressure has been built.
If you go back and read this was about when the car is being driven...meaning the ignition is....on...meaning theres 12v+ being applied to the fuel pump...meaning its operating.....meaning its spinning, The PCM generaly controls this procedure, cycle on to build fuel pressure before the car has been started, but after its been started, the circut stays open until its shut off, so while driving the pump will not shut off, so if fuel gets sloshed around the pickup of the fuel pump, it will ingest air instead causing the above problem. If you want to back your friend up thats fine but both of you are wrong...

[andrewk]

91parkave wrote: so if fuel gets sloshed around the pickup of the fuel pump, it will ingest air instead causing the above problem.

This is the crux of the argument. The problem, as described by you.

91parkave wrote: Driving like this ( on E or close to it)will cause pre-mature fuel pump failure because air will enter instead of fuel causing it to burn itself out and over heat.

And this is Norm's response, using your logic.

88Coupe wrote: Using your own logic: Pumping air would eliminate the normal stress of pumping liquid. The lighter load on the motor, would cause it to run cooler, which would extend its life.

Now, any electrical item works in the parameters of Ohm's law, which is I=V/R, where I= Current, measured in Amps, V=Volts, and R= resistance, measured in Ohms. Let's look at how this applies to the fuel pump.

The volts in the case of the pump are, for the purposes of this discussion, constant. We know what the voltage to the pump is 12 volts.

Now, we have a constant figure of 12 volts. Pumping fuel generates pressure, which puts a load on the fuel pump. A greater physical resistance results in greater electrical resistance, which means in order to keep our 12 volt constant, Amps have to go up. More resistance=more heat, because we are putting more current, or electromotive force through that fuel pump. This is another law called the ideal gas law. It states that when volume is constant (in this case the size of the wires and windings is our "volume") An increase in pressure, (in this case, amperage, or electromotive force) will result in an increase in temperature. When there is no fuel to be pumped, resistance goes down, and so does amp draw because we still have 12 volts of electricity to the pump. Less resistance=less amperage=less heat generated by the pump.

Dry running a pump numerous times can cause the pumping mechanism to fail, but not because it overheated.

I believe this was the point that 88Coupe was trying to make.

Now, I don't think this necessarily pertains to Collette's problem, since fuel level wasn't a given symptom.

Collette, One thing you may try when it is bucking uphill is putting the transmission in neutral, and see if the engine is still missing when you apply throttle. If we can determine that the problem is load based, and not position based, we can further hone in the possibilities of what may be causing the problem. Hopefully by now you have found the good parts of the other 'hesitation' thread, and know whether or not you need to test the coil packs.

Andrew