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Old 10-03-2021, 02:17 PM   #21
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

In freeze frame data I have this.
STFT= -56.3 (I assume the down arrow next to the value means subtract)
LTFT = +21.1 (up arrow)
RPM = 2024
MAP = 72
Speed = 47.8 mph
TP = 18
ECT = 183

After getting it up to temperature.
Live data at idle.
STFT = average -40 ~ -43 bounces around a lot.
LTFT = +21.1

Live data at about 2000 rpm.
STFT = average -42 ~ -46 bounces around a lot.
LTFT = +21.1
...
When I was younger I drove a lifted 4x4 truck with over sized tires. Needed a ladder to get into it. Now in my 60's I drive an SL2 and need a ladder to get out.
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Old 10-05-2021, 02:21 PM   #22
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

I replaced the filter today, no change. Fuel pressure still measures just over 10 lbs. I used the old filter to make an adapter for my pressure gauge and connected it to the fuel line that would normally go into the filter (see pic). Turned on the ignition (not the engine), heard the fuel pump run for those few seconds and could not get any pressure at the gauge. No matter how many times I turn the key on and off so as to try and build pressure. I suppose this means the pump is shot. But then why would my STFT be so negative? As if it's getting too much fuel.

Takes 3 to 4 tries to start or more, warm or cold. Once warmed up the car idles perfectly fine. Step on the gas and it sputters and almost dies sometimes until it gets to higher rpm like over 1500. At that RPM it also runs fine. I can rev it smoothly over 2000 rpm and up. These are the same symptoms I can remember when the MAP sensor was bad on a different Saturn. I wish the local parts stores didn't sell those things for 2 to 3 times I can order on line. I would just throw one in to get that thought out of my mind.

I also found that the TP sensor doesn't react when first opening the throttle plate under the hood. It turns a few maybe 3 to 4 degrees before showing any change on my obd2 scanner. After that the data seems to rise smooth. I should replace that too.
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When I was younger I drove a lifted 4x4 truck with over sized tires. Needed a ladder to get into it. Now in my 60's I drive an SL2 and need a ladder to get out.
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Old 10-05-2021, 03:29 PM   #23
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

It seems impossible that you got no pressure connecting a gauge to the pump, yet the engine can still run with that pump.

There are two fuel lines coming forward from the tank area. If you disconnect both from the filter/regulator and turn the pump on, is there no flow (and pressure from either of those two lines? If key-on gives no joy, try jumpering the fuel pump relay socket (30 and 87?) to force the pump on for more than 2 seconds at a time.

I would not get too focused on the fuel trims, for now. Yes, the STFT is negative, but the LTFT is quite positive. Trying to make sense of those trims requires correlating them to O2 sensor readings; a lot of freeze-frame data points to create a data log/graph for us to review. It is not worth the bother to do that as long as fuel pressure is suspicious.

Why is there any wonderment about the MAP sensor? Since you have live-data, checking/calibrating that is a trivial task. Do it and get it "out of the equation". Likewise, be sure to check system voltage, both actual measured with a meter and what the PCM reports via live-data. I think your gen3 has high-Z injectors, for which fueling is more sensitive to voltage than the earlier low-Z ones.

Although the TP sensor should be replaced if it seems to be flaky, I would not expect the off-idle "laziness" you describe to cause the symptoms you are describing
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Old 10-05-2021, 06:24 PM   #24
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Quote:
Originally Posted by billr View Post
It seems impossible that you got no pressure connecting a gauge to the pump
Yeah I know. I was more worried my adapter would blow off and spray gas all over the driveway. Yes there are 2 lines going into the filter. From what I understand the smaller 5/16" line is the return and the larger 3/8" is the fuel supply. Does that sound right? I think I confirmed it when I got the filter off the car and drained the gas out of it. The gas that came out of the 3/8" inlet was dirty gray/black so I assume that was the dirty side of the filter (the fuel in). I made my adapter with the 3/8" tube and left the 5/16" line connected to the filter during my testing. I can do what you suggest by disconnecting both fuel lines and turn on the pump but not today anymore.

I wanted to do some testing of my fuel gauge on my Caravan but it does not have the typical schrader valve on the fuel rail. I gotta disconnect a fuel line under the hood and get some special T adapter that goes between the lines and goes to the gauge. Don't have that.

As far as live data my scanner seems to be very basic. It gives me limited data. The MAP data in only in psi.
...
When I was younger I drove a lifted 4x4 truck with over sized tires. Needed a ladder to get into it. Now in my 60's I drive an SL2 and need a ladder to get out.

Last edited by dj1111; 10-05-2021 at 06:37 PM.
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Old 10-05-2021, 08:57 PM   #25
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

I'm thinking the 3/8 is the return and the 5/16 is the pressure.

Any units for MAP would be fine for testing the sensor. Where did you get the freeze-frame posted in your reply #21? That shows MAP as being "72", which I assume is in kPa (kilo Pascals).
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Old 10-05-2021, 10:27 PM   #26
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Quote:
Originally Posted by billr View Post
I'm thinking the 3/8 is the return and the 5/16 is the pressure.

Any units for MAP would be fine for testing the sensor. Where did you get the freeze-frame posted in your reply #21? That shows MAP as being "72", which I assume is in kPa (kilo Pascals).
The filter I purchased said it has a 5/16" return line in the specs. I also found a Purolator filter that says Inlet/Outlet: 0.38 and Vapor Return: 0.31. I will make another adapter with the 5/16" tube from the filter and do some more experimenting.

The freeze frame data does say 72 for MAP. But live data displays psi. It's a scanner from Harbor Freight. I bought it because it includes ABS and was on sale and I used a 25% coupon LOL. Was having ABS problems with my Caravan. Saved me a ton of money.
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When I was younger I drove a lifted 4x4 truck with over sized tires. Needed a ladder to get into it. Now in my 60's I drive an SL2 and need a ladder to get out.
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Old 10-05-2021, 11:23 PM   #27
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Wonderful, the scanner displays data in different units for different functions. the MAP sure won't be 72 psi (won't mater if that is psig or psia or psid, none are possible with a stock S-series engine...) I am guessing it is 72 kPa because that is the only one that I think is possible. Anybody know of some other common units that the 72 MAP could be?

Back to the real point... have you checked the MAP sensor at various pressure levels to se if readings are reasonable; or checked it against a separate gauge?
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Old 10-08-2021, 03:39 PM   #28
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

I ordered a new MAP and TP sensor. I didn't spend a lot of money so no harm done. The car does run better but it is definitely not fixed. I actually took it for a ride and it did not stall, forcing me to push it home. But it still hesitates during low rpm acceleration and between shifts.

Another thing I learned is all those fuel trims I thought were negative are actually positive/adding fuel. While watching the scanner's live data and revving the engine I saw a minus go in front of the values as it decelerated. The down arrow on the screen means something else. So it is always adding fuel. But that's another thing I noticed. The short term trims are not as high as they were before. At idle it's pretty steady at around 17 to 18 now.

I never did replace the coolant temp sensor seeing as the numbers on the scanner seem reasonable. But I do have one laying around from the older Saturn that should be good. As soon as the thing cools down I'll swap it.

So after all this if it is the fuel pump that is failing does anyone have any theories why it runs the way it does. Does it have enough fuel it idle and running at higher rpms but acceleration it does not? But that does not make sense as I can accelerate at pretty much open throttle with no problems as long as the rpms remain high. Get it down to 1200 rpm and step on the gas and it almost stalls if I don't play with the peddle to get the rpms up.
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When I was younger I drove a lifted 4x4 truck with over sized tires. Needed a ladder to get into it. Now in my 60's I drive an SL2 and need a ladder to get out.
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Old 10-08-2021, 05:51 PM   #29
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

I'm not sure what your current question is. Are you asking why it can run OK at idle and cruise the highway, but not when accelerating? A bad pump could cause that by supplying low fuel pressure. Accel generally puts the most load (highest MAP) on an engine and requires the most fuel pressure. No mystery there.

So, have you got a reliable fuel pressure reading at the rail now???
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Old 10-08-2021, 07:15 PM   #30
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

No the fuel pressure at the rail has remained just over 10 lbs. When I was in the car before I noticed the fuel pump has gotten quieter. I used to hear it run for a few seconds after turning the car off. And it used to be louder. Also when it's struggling to run the exhaust smells like when older cars used to diesel after turning them off. Is that the smell of too lean on fuel?

After taking it for a successful ride, then cutting the grass (2 hours), I tried to start it to put it back in the garage. It would not start. Just sputtered and coughed. We had to push it in.

I don't know what to test anymore. And I'm getting frustrated. Even though I've done a ton of auto repairs over the years I am not a mechanic and only learn about stuff when it breaks. Is there anything I should know about changing the fuel pump? Any surprises in store for me? The only gas tanks I've ever had to remove and replace were on a 1964 Chrysler New Yorker (in 1975) and a 1985 Chevy Celebrity (About 25 years ago). The only fuel pump I ever replaced (several times) was in that Celebrity and it was mechanical on the engine. The good old days.
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When I was younger I drove a lifted 4x4 truck with over sized tires. Needed a ladder to get into it. Now in my 60's I drive an SL2 and need a ladder to get out.
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Old 10-08-2021, 10:03 PM   #31
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

We seem to be wandering in circles here...

If you can get 10 psi at the rail, then you should be able to get at least 10 psi at one of those lines coming from the pump/tank; no matter what the problem is. The last I read, you can't get any pressure on those lines, so something about your equipment or procedure must be bad. No definitive test of the pump has been done yet, so throwing a pump at it may not do any good.

My understanding is that changing the pump is fairly simple, but the tank has to be dropped down. That seems to intimidate some folks, never done it myself.
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Old 10-09-2021, 02:33 PM   #32
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Thank you billr for all your help, really!!! Yeah not much more to talk about.

Even when I get 10 lbs at the rail it is not instant. When I first turn the key on, and the initial pump cycle runs, I get no pressure and the car does not start. The second time the car sputters but still no pressure at the gauge. The third or forth time, if it starts, the pressure goes up to 10 lbs quite slowly. Once the engine is running the pump is running constantly, or at least cycling on and off as needed, the pressure stays around 10 lbs. It stands to reason, (in my mind anyway, based on above) with my test for pressure straight from the pump it only ran its initial startup cycle then shuts off so there's no time for it to build up pressure and keep it up. And remember as soon as the pump stops the pressure drops to zero instantly. I found 4 different sources that said the 3/8" fuel line is the supply so I'm sure I had the right line. I did not do the test to remove both the lines from the filter to see if I get flow. I may do that yet.

I read the procedure and looked under the car today to see what it would take to remove the tank. I only have ramps and even with them, as low as these cars are, there isn't a lot of room underneath especially with the tank being more in the middle of the car. Not like the olden days when the tanks were behind the rear axle. I'm going to think about it over the weekend and maybe throw up the white flag and get it to a mechanic. I have one that I trust. Plus the tank has a lot of gas in it.
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When I was younger I drove a lifted 4x4 truck with over sized tires. Needed a ladder to get into it. Now in my 60's I drive an SL2 and need a ladder to get out.
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Old 10-09-2021, 02:43 PM   #33
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Did you miss this?

" If key-on gives no joy, try jumpering the fuel pump relay socket (30 and 87?) to force the pump on for more than 2 seconds at a time."

If you force the pump on, you can verify it is bad; and use it to drain the tank.
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Old 10-09-2021, 03:06 PM   #34
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

No I didn't miss that. Saw you had a question mark (30 and 87?) by the numbers and was scared to try. Is that relay a simple single pole guy where you only have to jumper 2 sockets? A no brainer?
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When I was younger I drove a lifted 4x4 truck with over sized tires. Needed a ladder to get into it. Now in my 60's I drive an SL2 and need a ladder to get out.
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Old 10-09-2021, 06:21 PM   #35
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Yes, a simple SP relay. #30 is the armature contact, #87 is NO, and if you have a #87A it will be NC. #30 is "always hot", connected to battery, and #87 goes to pump. #85 and 86 are coil, one getting 12V from the PCM to turn on and the other coil term is "always grounded".
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Old 10-09-2021, 07:20 PM   #36
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

And those numbers are on the relay socket after you remove the relay. I don't have a wiring diagram for this car. Wish I did. My manual has other years diagrams but none for a 2000. I suppose other years may be close.
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When I was younger I drove a lifted 4x4 truck with over sized tires. Needed a ladder to get into it. Now in my 60's I drive an SL2 and need a ladder to get out.
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Old 10-09-2021, 08:02 PM   #37
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

I don't know about the socket, but the numbers are usually on the relay base (pin area) and on a diagram on the side of the relay. Or, just do a 'net search for "auto relay wiring" => images.
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Old 11-20-2021, 11:18 PM   #38
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Update. It was the fuel pump. It was replaced weeks ago and the car is running fine now.
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When I was younger I drove a lifted 4x4 truck with over sized tires. Needed a ladder to get into it. Now in my 60's I drive an SL2 and need a ladder to get out.
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