I got a 1990 4 door auto LX and It has a strange stumble/stalling problem.

Whenever I come to an sudden stop and I am on the brakes fairly good the car will stumble very low to the point of stalling sometimes, now the strange thing is that it only doesit when there is less then half a tank, and it does it more often the less gas there is in it. Now I originaly thought brake booster and checked out the booster line and they look good, checked the fuel pump and it has good power. I also got it to stall with the meter hooked up and it slowly dropped as the idle worsened but voltage was at about 9.8 Volts when the car finaly died, so I figure the pump is sstill pumping, but without any kind of fuel Pressure gauge or something I cant tell for sure.

CEL is throwing 2 codes, 15, and 41 I figure the code 15 goes off when the car finaly cuts out and code 41 is just something I need to replace but I dont think it has anythign to do with the problem at hand.

Any ideas or things I should test out next would help me out a lot.

I got a trouble tree for code 15 and I am going to run through it tomorrow.

THanks in advance

 

did you ever think of checking your IAC?

 

Look for indications the gas tank botton has been displaced upward (curbing strike).
It sounds like the fuel pickup is being uncovered under heavy stopping loads.
You can sometimes duplicate this condition by raising the rear of the car. Ramps MAY get you high enough to get a reaction. We had the advantage of a twin post lift.

If the car has had a prior Master Cylinder failure, you may (still) have an issue with the brake booster.
If you hear a louder than normal Hiss under the dash when you apply the brakes or you can make the engine stall from pumping the pedal quickly several times; you've got a leak in the diaphram.
Another test: with the engine OFF, you should get (at a minimum) two fully assisted brake applications b4 the pedal gets hard. Anything less, you've a vacuum leak in the booster.

P

 

fuel pump may be on it's way out as well....

 

I originaly thought the pump was going out to but it seems like it is fine. Is there any test other then voltage I can run on the pump without actually going to buy a fuel pressure set?


As for the brake booster, my sister had her master replaced and pads rotors done up and and she said this problem only started after the guy did everything. But the thing is I cant find anything wrong with the braking system

When I pulled the booster hose off initialy it realeased all the vaccum it had with a giant hiss which would indicate that it had, and was holding pressure for several minutes, checked the check vavle and it seems like it was installed correctly with the 'E ->' pointing towards the engine. Hoses have no sign of slits or holes.

The car is bogging out either lean or rich I cant tell. When it is stumbling at a stop I found that dropping it into neutral doesnt help anything ruling out anything with the tranny holding it in gear, letting up on the brakes completely after stopping doesnt help anything, pumping the gas brings it up then it drops back down to really low 100RPM or it dies.

I dont think the fuel pump is over heating cause I let it sit for a good 2 hours last night, started it up and did a sudden stop and the car stumbled and died. which leads me to believe it didnt even have enough time to heat it self up to the point of dieing.

P, would you be able to tell me a little more on what to do about the pickup?
Should I just jack the rear up and see if the car will start? if not then something is def. wrong inside the tank itself?

 

put a fuel pressuer guage on it and measure at less than 1/2 tank and then againa at full tank........

 

'90 4dr lx
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by skaterjunky8 &raquo;</TD></TR><TR><TD CLASS="quote">P, would you be able to tell me a little more on what to do about the pickup?
Should I just jack the rear up and see if the car will start? if not then something is def. wrong inside the tank itself?</TD></TR></TABLE>

The interior of the fuel tank is much like the much maligned Titanic with it's open watertight doors. It is internally partitioned with bulkheads that have holes positioned on the bottom which allows gasoline to flow (in a controlled manner) and equalize between compartments. This set up is done specifically to control the effect you describe. It's called Fuel Sloshing where a lateral g-force (stopping / turning) would force the fuel to one side of the tank - uncovering the fuel pickup.
They construct a 'surround' in which the fuel pump/pickup is oriented. This allows for a consistent supply of fuel for the pump (#25). With tank impacts, this system is disturbed. In some cases I've seen, the floor is pushed up (momentarily), bending the pump pickup off the floor of the tank (where it belongs) where it starts picking up fuel 3-4" off the floor bottom. Drop the fuel level enough and you start sucking air.

Raising the vehicles rear duplicates the condition (fuel sloshes forward)



Another thing I'd suggest looking at will be the Idle Air Control Valve and the throttle body. I've seen cases where crud build-up at the Throttle Plate caused stumbling off idle. A dirty or lazy IACV can be responsible for searching idle and stalling too.

P

 

Thanks for the info on the tank I will check that out in a minute here and get back to you on what I have found.

 

if the problem start to happen after they did the work,, I want you to try something,,, remove the brake master cylinder nuts from the booster .. you might be able to pull it far enough to chk and see if it is double gasketed or the rubber gasket at back of master cylinder is missing ,,if you cannot pull it far enough to chk, remove the brake master totally,, you have to bleed brakes afterwards ..

it all could be a coincidence that it started to act up after the work was done ,, but it might be worth a shot ..