2000 Saturn Other • 6 cylinder 2WD Automatic • 130 miles

2000 Saturn LS2 3.0L Vin "R"- Vehicle loses power under heavy acceleration. Say, you're at a stop sign, you begin to accelerate away and you're doing just fine. If you Floor the accelerator pedal, RPM's will jump to 4 grand and remain there. Vehicle speed seems to remain steady (no speed loss or gain) and the transmission doesn't shift, period. That is. Until you release the accelerator pedal maybe 1/4 - Then all is back to normal again.
Fuel Pressure - Key on, Engine Off - 0 PSI! Yes, 0 PSI.
During cranking & running, however, it goes up to 42 PSI
With a fuel pressure gauge attached to the fuel pressure test port DURING a test drive, the fuel pressure is still normal (NEVER drops below 40 PSI) even when this issue occurs. Perhaps ruling out the jet valve on the pump module.

Tried: Cleaning the throttle bore & "reprogramming" the throttle body with alldata procedures.
Cleaned MAF sensor w/MAF sensor cleaner (purchased at auto parts store)
Replaced Fuel Filter (old was definitely clogged)
Flushed fuel injectors with Wynn's Fuel Injection Power Flush system

I'm contemplating replacing the fuel pump, but at $250.00 new-aftermarket, I don't want to spend it if I don't have to.

There are NO DTC's in the OBDII System, period.
March 18, 2011.

When it gets hot and wont shift till you let off the gas go have the exhaust back pressure tested sounds like you have a bad cat that is restricting the exhaust. Let me know what you find.

Mar 18, 2011.
Could be an intermitent issue with the fuel pump relay.
Check the wires to it and make sure they are not loose. If you listen closely, you can hear them, "Prime", the sytem right after the ignition key is turned. If the fuel pressure has been tested under load, it is probably fine. It should jump about 10 PSI when you floor it. However, the issuse with the speed could be several things;

The first is that the fuel pressure should be around 30-40PSI, before you even start it and certainly 40PSI when running. There is a fuel pressure controller that is generaly vacuum controlled and should increase pressure under full throttle and with vacuum removed at idle.
The fuel pressure regulator could be at fault and it can be a faulty regulator or even a bad ECU signal.

The Vehicle Speed Sensor could be bad abd sending a faulty signal to the ECu, but I am leaning towards the fuel pressure regulator. It may be incorporated into the fuel pump whcih I found at Summit for $250.00. It is a dropp in and if it can be replaced by removing the rear seat, it is not too hard a job.
Here is the link for the pump assembly;
Ask the tech at Summit about the regulator as the details on this are not given and I do not have a Factory manual for that car.

The irratic fuel pressure is worrysome as a lean condition under load can cause an engine to damge cam shafts, valves or even fail.

Sometimes Maf sensors can fail and even when cleaned needed to be replaced and the reproggammed by the dealership.

How did you get a 2000 with such low mileage?
I ask because this could help in diagnosing the problem.

Let me know the above information and I will keep an eye on this post for your replay and respond ASAP.

I have seen a lot of L model saturns with plugged cats and a lot of then will just not shift untill you let off the gas thats when I check the exhaust for excesive back pressure. Thats what I would be checking.

Mar 18, 2011.
Regardless of the temperature of the vehicle, this issue occurs whenever you get on the accelerator too hard. It can be just started in the mornings, floor it & you'll get up to 20 MPH or so - RPM's at 4 grand and no trans shifting. Operating temperature - same deal. Higher speeds, same deal. The vehicle was purchased at auction by a used car dealership, & I bought it from them kind of cheap. I'm pretty sure you're right about "priming" the system - W/my fuel gauge attached to the test port - Turning the key "ON" and not cranking/starting the engine - I have 0 PSI fuel pressure. I've depressed the release valve during this test just to make sure my gauge wasn't just inaccurate (it's brand new) and no fuel flow comes at all UNTIL I start cranking the engine.

According to alldata - This system should let the pump run for 2 seconds when you turn the key on and fuel pressure, key on engine off should be approx. 39-44 PSI. I've replaced the fuel pump relay in the left instrument panel fuse box to no avail.

Shouldn't this generate some sort of trouble code? Even if it was the cat, wouldnt' a p0420 set?

Mar 18, 2011.
Stech is refferring to the cats getting to hot, (if I am right and I am sorry if I am speaking out of turn ), he is the Saturn expert and has seen these in and out and knows them all to well.
The excessive back pressure does not allow the hydrocarbons to escape and there is probably a safety shut off for the fuel so as to not overheat the cats.
STech, is this on the right track? What do you think about the 0 PSI fuel pressure at igniton? Would a cat back exhaust alleviate the problem?
Thanks for helping out.I was concerned about the affect of the low and/or flucuating fuel pressure on the engine.

Here is the deal with the key on engine off it doesn't know the cat is restricted.I have never heard of or seen the fuel pump get shut down because of a bad pump. Also gleak said while he is driving and it's acting the fuel pressure remains at least at 40psi. So there could be two different problems the fuel pressure he discovered when doing his testing for the losing power and not shifting. My question is this will the car start right up?Or do you have to have to keep cranking it to start it. Also when you get the 40psi plus pressure and turn the car off does it bleed back down to zero right away?It really sound's like a bad cat think about he said it wouldn't shift until he let off the gas. If the cat was really clogged up the engine would tell the computer it was under a greater load then it really was and not shift up to the next higher gear.I have seen a lot of plugged cat's on the v6 and the 4cyl L model's saturns and when they get clogged bad enough they don't shift up to the next higher gear When I see that and the lack of power he describes the first thing I check is for code's then the exhaust back pressure. As far as code p0420 code I have seen plugged cat's ton's of times without any code's. Check the back pressure to rule a plugged cat in or out make sure they screw the tester into the exhaust manifold's to check it.

Mar 18, 2011.
The fuel pressure, when running - should (according to alldata) never drop below 39 PSI. It never does. Therefore, I don't believe fuel pressure is a cause of the powerloss. However, the 0 fuel pressure, key on, engine off worries me that the pump May in fact still have an issue. Why else wouldn't it run when the ignition is turned on? Alldata says it should run for 2 seconds when the key is on. The fuel pressure does not bleed off completely. When you shut the vehicle down, f. Pressure drops to about 38, then goes back to 40 which I thought was very odd. I don't believe the fuel pressure regulator is to blame here.

I'll have to bring the car back in on monday to the tech working on it and have him check the backpressure (I'm unsure how to go about checking the backpressure - is it the gauge that screws into an o2 sensor port?)
Plugged cat does make sense. But it drives fine if it's not put under extreme heavy load. This problem only occurs when you floor the accelerator pedal. I'll have the backpressure checked & post back w/the findings! Thanks for the help guys

The vehicle needs to crank for maybe a second or two longer than I believe it should, but it does fire right up pretty quick.

Mar 20, 2011.
I am not sure why the fuel pressure prime signal is not working.
Saturn Tech would know best as to what part of the circuit could be causing this. However, if he did not say it was an issue to worry over, I think your okay.
Pressure takes some time to bleed off after running, so no worries there.
I am not certain how to measure back pressure. It will probably be a test on the Cat.

I will watch for your reply.

As far as the pump not running for 2 seconds when you first turn the key to the run position that isn't going to be a bad fuel pump because it operates like it should otherwise.I have never seen it not prime when turning the key to run and then work fine the rest of the time.I have only seen the pump not work at all or work like it supposed to. As far as checking back pressure that's easy they sell a back pressure gauge set for that you unscrew the o2 sensor screw in the adapter just like if you were checking your oil or transmission fluid pressure. Same kind of set up except your checking the exhaust pressure the gauge set's are pretty cheap.I have posted below how you test back pressure.

A slight pressure in the exhaust system is normal, but excessive exhaust back pressure seriously affects engine operation. Causes of high exhaust back pressure are dents or obstructions in the exhaust pipe, a plugged three way catalytic converter or muffler.
Test method (Vehicle Parked): 1. Remove the oxygen sensor.
2. Insert exhaust back pressure adaptor (SA9306E) into the exhaust manifold. The thread designation is M18 x 1.50.
3. Connect the gage bar kit SA9127E, 0 - 15 kPa gage (0 - 60 inch H2O) to the back pressure adaptor.
4. With the engine at normal operating temperature, observe the exhaust back pressure at 4000 rpm.
5. The exhaust back pressure must be less than 5.0 kPa (20.13 inch H2O). Test method (Performed During Road Test): 1. Remove the oxygen sensor.
2. Install exhaust back pressure adapter (SA9306E) into the exhaust manifold. The thread designation is M18 x 1.50.

NOTICE: Do not use the 0 - 60 inch H2O gage when performing this test, as it will be permanently damaged due to the high back pressure during accelerations. Use the 0 - 690 kPa (0 - 100 psi) gage and appropriate hoses in service gage bar kit SA9127E.

3. Connect the gage bar kit SA9127E, 0 - 861 kPa (0 - 100 psi) gage.
4. With the engine at normal operating temperature, perform a 15 mph road test. Automatic transaxles should be in "D" and manual transaxles in "3rd" gear. Maximum exhaust back pressure readings are taken during short wide open throttle accelerations.
5. The maximum exhaust back pressure during wide open throttle accelerations must be less than 50 kPa (7.25 psi).

IMPORTANT: If the exhaust pressure exceeds the specification, inspect for a dented or collapsed exhaust pipe. It may be necessary to disconnect the exhaust pipe before or behind the converter and repeat Step 4. If removing the muffler does not lower the back pressure, disconnect the resonator pipe from the down pipe and repeat the test.

6. Replace any part of the exhaust system found to be damaged.
7. Install anti-seize on the oxygen sensor's threads and install the sensor. It may be necessary to disconnect the negative battery terminal in order to clear any codes set while operating the engine with the oxygen sensor removed or disconnected.

Mar 21, 2011.
Well the tech who is working on my car says he will not have an opportunity to check it out again until Wednesday. Provided that I can buy an adapter kit at the auto parts store or in a tool specialty shop, I'll run the tests myself & post w/the results. Otherwise, I ll have to wait until the tech can get me in.

Mar 22, 2011.