93 Drivability, Stalling,what are normal Fuel Pressures ?

[MKMike]

My Bonnie has begun stalling when turning or coming to a stop, as well as nearly dying at times when trying to accelerate from a stop.
There are no vacuum leaks and the computer is not registering any codes.
I have already changed the fuel filter, some old vacuum hoses plus the TPS, IAC and MAF sensors in an attempt to solve the problem without having to drop the fuel tank
I have a fuel pressure gauge and it reads 36-38 psi at idle and is the same if I increase the RPMs to about 1500 in park.
Any other tests to perform to narrow it down?
Is that normal for a 93 SE or is it very likely the fuel pump is going?
How can you tell whether it's the fuel pump or if the fuel pressure regulator is bad when the fuel pressure is low?
Any brand fuel pumps to avoid?
My local Parts Authority carries Airtex and Delphi.

I should add that I have an Actron scan tool, so would LTFT and STFT readings be useful to take note of? (In browsing past threads it looks like it may be a good indicator of fuel pump issues.)

Also, how does one determine if the fuel tank baffles are broken? Replace the fuel pump and see if the car still stalls?

[J Wikoff]

Your pressure is several pounds low. Pull the vacuum line off the FPR right after you turn the car off. If the vac line smells like fuel, the regulator is shot. If it's original, it's probably worth replacing anyway. In my experience, a new FPR helped some, but it was tank droppin time.

I always use ACDelco when it comes to fuel delivery.

[MKMike]

Thanks, J Wikoff.

Perhaps I should have mentioned that the pressure reading is not steady but is constantly varying from 36 to 38.

Does the stalling while turning mean the pump is failing to pick up enough fuel?

I do have an Actron scan tool but without knowing what readings are normal, it's used as a code reader.

[J Wikoff]

While turning, it could be a few things. Clogged strainer, MIA strainer, undersized 92 carry over strainer, broken tank baffles...

[MKMike]

How would I recognize broken baffles?
I'm guessing the only way is to have a look inside the tank but I'm not sure what exactly to look for.......

[RJolly87]

Broken baffles usually give you the most problems at 3/8 of a tank or below. You will also notice a lot of movement on the fuel gauge too when driving. If baffles are the issue, you will usually be unable to duplicate it with a full tank.

[MKMike]

My thanks to both of you.
I like the car and will hopefully be able to work on it more this weekend.

Baffles will cause significant fuel gauge movement above 3/8 of a tank also or will they not?

[RJolly87]

They can. My fuel gauge can vary by 1/8 of a tank higher or lower (1/4 tank total) depending on the angle the car is at. It should however have no affect on fuel pressure on level ground.

[shenandoah_walker]

My second Olds is a 1992 88 Royale. It had the same issue. Stalled while turning and that was made worse at lower tank levels. Running with less than 1/4 tank was not advised at all.

Dropped the tank and found white plastic baffles to be broken with pieces here and there. The baffle apparently is a stilling well that holds a small volume of gas near the pump. There's a hole at the bottom of this well with close tolerance gap between it and the bottom of the tank. At low level, this stilling well will slowly fill and drain via the bottom hole. A crack in the side of it allows fuel to drain quickly as you turn, and then the pump is starved.

I bought a replacement aftermarket tank at O'Reilly. Its baffle is metal, but in every other way the tank was the same and it fit well.

The issue was resolved with the tank replacement.

I just replaced my fuel pump on the 1996 Olds 88 LS. The baffle appeared to be the same white plastic, but it was not broken. I'm not sure why there would be any difference, but maybe fuel quality or different additives affect the plastic.

[J Wikoff]

In my 92, the baffles were cracked a bit, but a new pump with a larger strainer cured my turn stalling

[MKMike]

Thank you.

The more replies I receive and the more I read past threads, the more I suspect the baffles are very likely also a part of the problem.
If they aren't yet, I'll probably play it safe and change the tank, while I'm at it.

I had noticed the fuel gauge dip from 1/4 tank to empty on a sharp turn and that was when the stalling and severe hesitation/stumbling began.
I just dusted off a Chilton manual that I forgot I had and found that the fuel pressure should be between 40-47 psi--confirming what J Wikoff said about 36-38 being lower than normal.
I revved the engine to 2500 RPM and the fuel pressure actually went down to 32.
It appears that the relatively expensive fuel pressure regulator is presently working, since the fuel pressure increases by 10 psi when the vacuum lead is removed from it.
Please correct me if I'm wrong in concluding that the pressure regulator is OK--and let me know what testing should be done, instead


I'll follow up here if the baffles are broken. I've read here that I should get genuine GM gaskets to seal the pump and the sensor.
Am I wrong in thinking that it's probably best when changing the tank and fuel pump to also change the fuel level sensor--or do those seldom go bad?
Dropping the tank isn't a task that I'll want to repeat anytime soon, I'm sure.

J Wikoff, did you use a Delphi fuel strainer or does GM sell a larger strainer now?
I just want to change whatever's needed until I can be reasonably certain that it won't leave me or another family member stranded someplace.

[shenandoah_walker]

I wouldn't worry too much about your fuel pressure at 36 to 38 psig. Check my post on P0300, 305, and 171 codes. My new restored pressure is 38, but it was as low as 25 psig. As long as the engine was relatively cool, it ran fine even at that low pressure. I suspect the injector spray pattern might have been affected, but fuel delivery to each cylinder is apparently handled adequately by the ECM. I have no running problems at 38 psig that I can tell. Of course, pressure in the upper 30s is needed to put the regulator in a controlling position so that gas flows through the rail back to the tank as the regulator controls the pressure. If feasible, pressure within spec is always a good idea, but a new pump and regulator have put mine at 38 and it doesn't seem to be an issue.

[J Wikoff]

38 is low. 32 under some load is WWAAYAYYY too low. It seems like the FPR is fine, so it's gotta be the pump. When I did my pump (ACDelco) it came with a new strainer that was properly sized. I think it came with a new o-ring too. Unless your fuel gage is erratic or really imprecise, I'd leave the sender alone and just replace the pump.

[Jrs3800]

L27's should run at 41-47 Psi, if you are dropping to 32 psi at any time its too low... 38 at dead idle would be ok as long as the pressure gets near 50 when you blip the throttle.. I would expect to see 45-50 Psi with a good regulator and pump with the regulator vac line disconnected..



@shenandoah_walker

If you are referring to your 96, 36-38 Psi is way low... are you sure your pressure tester is functioning properly?

These series II's from 95-99 run at 48-55 Psi, By the time you get to 30-32 Psi the car will hardly run and it'll ping quite a bit as the computer can't compensate for pressure that low..

[shenandoah_walker]

Jrs3800

Thanks for the comments. I don't understand how all of our apparent facts fit together. The gage was a new loaner tool. See my other post for details. In the end, the new fuel pump made the difference, and that was a 13 psig increase measured as 25 to 38 psig. Runs great now. Spec is 40 to 47 psig.

[MKMike]

Finally got enough time and cooperative weather to drop the fuel tank.
Not surprisingly, every aspect of the work was as bad as I've read about-----complete with straps that had to be cut and fuel lines that were frozen into the quick-connect fittings.
I don't see damage to the inner baffles of the fuel tank but the widely swinging fuel gauge which corresponded to the apparent fuel starvation episodes makes me believe that the damage is there and that I just didn't see it.
Maybe there are cracks that aren't obvious but with the weight of the shifting fuel, the cracks widen and the fuel suddenly fuel flows away from the pump....
In any case, I'm also going to replace the o rings in the quick connectors before reinstalling the tank. The parts store had closed by the time I got to that part. S
The fuel lines were completely frozen into the fittings, so much so that I had to use WD40 just to dissolve enough rust to make their release possible.
(I researched first and found that wd40 is safe to use on the quick connectors and o rings.)
Honestly, I had never imagined that the lines could rust beyond the o rings inside the connectors, but they actually did---which was why they were impossible to remove by the usual methods.
The fuel pump appears to have been the original.
The replacement pump has the sending unit already attached--for my convenience-- and I heeded the forum advice, so I installed a new sending unit o ring from GM.
Needless to say, all of the helpful advice and browsing of past posts has helped immensely.
My gratitude goes out to all who've chimed in to assist me.
If all goes well, my son and I will be driving around in the Bonnie tomorrow!

[MKMike]

Finally got it done!
No more stalling and no more hesitation/stumbling
Thanks again to all who replied!
Now I can move on to fixing everything else that doesn't work properly.......