Fuel related?

[nkmhockey]

I have a 1997 Buick Lesabre Custom with 108,000 miles on it.

There are two issues I am experiencing. However, there is a story behind these problems.

Originally, the car was having trouble starting; I would have to crank the car for around 5-7 seconds before it started. That was if it started, occasionally it would fail to start on the first try.

I suspected the fuel pump, and my mechanic confirmed my suspicion. He replaced the fuel pump and all seemed well.

The other issue that I experienced before the new pump was that going up gradual hills, the car would "miss". Now when I say miss, I mean that during smooth acceleration, right around 1500 rpm, the tach would drop to 0, and I am forced to drop the pedal almost to the floor to continue accelerating. This issue never occurred on flat land or steep hills.

This issue still remained after the fuel pump was replaced. The car ran great, but there was an incident on the way home from a wedding. The car stalled 3 times, once on local roads, and twice on the highway, and after the third time, the car failed to start again.

The gauge showed I had over 1/4 of a tank left, but it turns out I was out of gas. After that incident I now ignore the gas gauge completely.

The next week, I was driving down a small hill, slowing to stop at a stop sign. Again, the car stalled. I was very angry, because I had been watching the odometer and I still had around 45 miles to go before I filled the tank.

I drifted the car to a flat spot, and it started up in a few tries. I drove straight to a gas station to fill up, and to my amazement I still had 3 gallons of gas in the tank.

I am stumped, I think that it may be the fuel sending unit or the fuel pressure regulator, but I have no means to test either of these. Is there anything else that may be causing these problems?

So far I have replaced:
spark plugs
spark plug wires
air filter
fuel filter (broke the fuel line in the process, used a repair kit from NAPA to repair)
battery
fuel pump

I have also tried using Seafoam to clean out the fuel system. That was done before I replaced the fuel pump. Also of note, before the new fuel pump I got about 16 MPG city and 21 MPG highway. After the change my mileage dropped to 18 MPG highway and 13 MPG city. All of these numbers are far below the EPA 17/27 estimates.

Any help in this matter is greatly appreciated!

[maxwedge]

Welcome to AF. So you never know how much gas you really have, it is possible on a steep hill, the fuel could uncover the pump. It seems you only have issues when low? Many things can cause both issues, you may have a bad ICM, crank sensor, the throttle body could need cleaning, the egr sticking can cause stalling. There is no way from here to pin this down.

[nkmhockey]

I never know exactly how much gas I have, but by using estimates based on below-average gas mileage I can always fill it before it gets anywhere near empty.

The gauge tends to go crazy sometimes and jump between full and 1/4 left when it gets low.

Also, the "missing" issue happens on small-grade hills and happens no matter how much gas I have left.

The stalling also happens on small, mild-grade hills, and 3 gallons seems like a lot of gas for the fuel pump to get uncovered, especially on such a small hill.

[Smith1000]

I have two Lesabres. The delayed starting issue that you fixed by replacing the fuel pump sounds similar to what I am currently experiencing with one of the Buicks currently. The car has 200,000 miles on it and the fuel pressure bleeds off rapidly after shut off. It is either the check valve in the pump or possibly the fuel injectors, but I believe it is probably the pump. I have a pump to install, but have not got to it yet.

The stalling situation sounds like a similar issue I have experienced with my wife's Lesabre. You did not mention if the check engine light came on or not. If so, there could be codes to help. Our stalling issue did not result in any codes. I replaced the cam and crank sensors because they are known for stalling and no start situations. The culprit though, was the MAF sensor. If it stalls, I clean the MAF sensor with the MAF sensor cleaner spray. This stops the stalling completely for many months. Eventually, the stalling returns and I immediately clean the sensor. I should replace the sensor, but for now, the cleaning works. This was a difficult issue to resolve and I thought I had it fixed several times. I had swapped many parts between both cars to pin point the problem. There never has been a check engine light to help identify the issue.

It generally stalled on downhill, gradual grades. I could see the tach drop, it would cut out and not always die, but would often die. It would always restart immediately for us. I checked out many different items and replaced several parts. Someone on this board suggested the MAF sensor. I can't say this will reslove your stalling issue for sure, but it might be one thing you can take a look at.

I have occasionally experienced a cylinder miss and usually get a code to go along with it to indicate the miss.

I have experienced fuel gauge issue before. The sending unit in the tank had to be replaced. It is a variable resistor that reads between 0 and 240 ohms. Sometimes, when the tanks gets very low, the gauge will read completely full. I have also had to replace the gauge units in both cars with salvaged units (in the dash). The gauges would act up. The tach would jump from 0 to 600 RPMs. The speedometer would jump around from 0 to 50 when idling.

[nkmhockey]

Thanks for the tips, I will have to look into the MAF sensor. The check engine light always stays off.

The car used to throw codes for random mis-fires and system too lean bank 1 but these issues were fixed by replacing the fuel pump and the spark plugs/wires.

Are there any ways to test and see if the MAF sensor is the problem? I read something about tapping it with a hammer while the car is idling, but it never stalls.

I only ask because I need to buy a special wrench to remove the MAF sensor on this vehicle due to the screws it uses.

Thanks again for the suggestions, I will have to start poking around some more.

[Jrs3800]

First... If you are still having a hard time starting the car you may need to check the fuel pressure and see if it bleeds off... These cars are known to have issues with the fuel pressure regulator..

Also with the stalling going down hill, its possible that the Baffle in the tank may have been broken or dislodged allowing the fuel to run away from the fuel pump...

Keep in mind you have an 18 Gallon fuel tank... Running the tank low on fuel is very hard on the pump as the fuel is both the coolant and lubricant for the pump.... and if you have even a split second of dry run time on the pump the damage can be done..

Is it the Tach that drops to 0, or the speedo or both?

Honestly I think you may have a couple of different problems happening at the same time..

[HotZ28]

Originally Posted by Jrs3800

Keep in mind you have an 18 Gallon fuel tank... Running the tank low on fuel is very hard on the pump as the fuel is both the coolant and lubricant for the pump.... and if you have even a split second of dry run time on the pump the damage can be done.

I agree, and it does not cost anymore to keep the tank full than it does to run it empty! I always fill up at no less than 1/2 tank!

[nkmhockey]

During the "missing" issue, only the tach drops to zero. The speedo reads my speed correctly, but it does drop because I am going up the hill with no acceleration. I slow until I drop the gas pedal to the floor, allowing the car to accelerate again.

I have no problem filling the tank with plenty of gas left, as a precaution, I just have one concern. I read that gas is heavy, and as you get closer to an empty tank your mileage improves. I am always looking for ways to improve my gas mileage since it is already so poor.

I already fill the tank very early during the winter months due to the risk of getting stuck.

With the pump getting uncovered, I see your point, but 3 gallons still seems like a LOT of gas for the pump to be exposed and cause a stall. I am no professional, but 3 gallons seems to be plenty to cover the bottom of the fuel tank.

My only concern is that by running the car until it ran completely out of gas; did I cause permanent damage to the brand new fuel pump? I have no problems starting it, and when the pump was installed my mechanic said all of the pressures checked out normal. I mean it did stall 3 times before I ran out of gas totally, does that cause damage?

The starting issue disappeared with the new fuel pump, and I have since had zero problems starting the car. I am just lost as to where to turn next. The issues appear to be so intermittent that no mechanic would ever be able to diagnose them properly.

Thanks for all the suggestions!

[Jrs3800]

I still think you have more than one issue..

On the Fuel Pump... Yes any dry run time will harm the pump in a hurry..

As for the Stalling and the Tach dropping to 0... If the tach will drop to 0, and then come back as you are still rolling, like a mini stall and then it goes again without you starting the car.... You may consider trying another Ignition Control Module....

My Question tho is, Does this problem only happen after the car has warmed up?

I can't say for certain the ICM is the issue but its worth a shot..

Also any 1993- Current 3800 ICM should work for you

[Blue Bowtie]

The ICM grounding is always a suspect in these cases. The mounting plate upon which the ICM resides can corrode badly before there is any external evidence of it.

[BNaylor]

Originally Posted by maxwedge

Welcome to AF. So you never know how much gas you really have, it is possible on a steep hill, the fuel could uncover the pump. It seems you only have issues when low? Many things can cause both issues, you may have a bad ICM, crank sensor, the throttle body could need cleaning, the egr sticking can cause stalling. There is no way from here to pin this down.

I agree with Shep. Classic crank position sensor problem.

[nkmhockey]

I agree completely with everyone, this is two separate issues.

As for the fuel issue, I will just keep at least 1/4 tank of gas in the car at ALL times, and pray that I did no damage to the new fuel pump.

For the "missing" issue, I will check into the CPS and ICM. If I take it to my mechanic, is there anything he can do to diagnose these parts? There are some junkyards around, but for parts such as those I find it hard to justify randomly swapping parts, especially when I would prefer to buy new for reliability.

Just some updates on the symptoms. So far, I have noticed that the "missing" occurs on any flat ground, or hill less than about 30 degrees. I can get the car to do it almost every time, all I have to do is accelerate slowly across the 1500 - 2000 RPM range. The tach does NOT drop to zero; it actually drops to just over 1000.

When the car "misses", the engine shudders very harshly, and it normally lasts only a few seconds. After that, you can tell the engine is vibrating more than usual, but not as harshly. The tach drops to the 800-1100 RPM range, and as I push the pedal towards the floor, the RPM's don't change. When I get the pedal close to where the RPM's would normally be over 2000, the tach jumps up over to 2200-2700 RPM's and the shuddering disappears.

Still sound like the ICM or CPS?

Thanks for all the suggestions!

[BNaylor]

Ah so the tac doesn't drop to zero rpms. That might change things in the diagnosis. In addition to the misfire condition are you still getting any stalling?

Did your mechanic run a scan with a full function odb-ii scan tool or a GM Tech 2? Weird not to have any random or fixed misfire DTCs along with a SES/CEL light if the missing is that bad.

Last question is did you look into a possible MAF sensor issue as suggested earlier? Try disconnecting it, the electrical connector and then see what it does just to rule it out. You can run with the MAF disconnected for troubleshooting purposes. The two screws that hold the MAF to the throttle body are Torx T20 tamper proof screws. You can get the tamper proof bits at any auto parts store.

[nkmhockey]

I am not getting any stalling, but I am still on a fairly full tank of gas. That leads me to believe that the stalling is related to the new fuel pump, and I just have to keep over 1/4 tank of gas constantly. I will let you know if anything happens as I get closer to an empty tank.

My mechanic ran a scan before he diagnosed the fuel pump problem, but I cannot say for sure what kind of equipment he used. I will have to ask and get back to you.

In the past when I got the P0171 (system to lean) and P0300 (random misfire) I would just do the lend-a-tool at Advance and clear the codes. Nothing else would ever come up as being a problem, and I have not gotten either of those codes since the repairs. However, my mechanic did find it strange that there were times that my CEL was NOT on, but upon hooking up the scanner there was a P0171 code.

I will double check and make sure my CEL light is working the next time I am in the car, because I already have a burned out Brake idiot light.

I will also disconnect the MAF sensor and let you know what the results are. I can buy the tool to change it, if needed, but since it passed the "tap it with a screwdriver end" test I never bothered to buy the tool and try to clean it.

Thanks!

[nkmhockey]

Just an update, I just tried driving the car with the MAF sensor unplugged...

The car starts right up, but immediately feels as though it wants to stall. While idling after first starting it, the engine shudders uncontrollably. Without touching the gas, the tach jumps up and down between 500-1500 RPM's. I drove it around twice, normal conditions, and it drove relatively normal once I got it out of park. At stop signs etc. the idle seems normal, no excessive shuddering like when it first started. The "missing" issue was still there, no changes.

I have since plugged the MAF sensor back in, but I am completely stumped as to what all this means. The issue with the tach jumping up and down between 500-1500 RPM's reminds me of situations before the fuel pump was replaced.

Before the new pump, the fuel system would lose pressure the longer it sat, and the pump could not provide the necessary pressure right of the bat when starting. There were many times, especially in the heat when the A/C was on, that I would barely get the car started. The tach would "jump" one time, then settle back down to a normal idle. Then I would drive it and everything would be fine. There were very rare situations where the "jumping" would continue even when I drove it, and was most irritating when in reverse. The jumping would go away after I pressed firmly on the gas pedal and floored it.

The CEL is on, but I have to stop at Advance and borrow the code reader to check the code. I will post an update, but my car has an interesting habit of clearing CEL codes on its own.

Suggestions?