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Old 06-11-2008, 02:39 AM   #1
cuff
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Default SL2 bucking, hesitation, jerking, problem solved.

I've been a lurker since I bought my 1999 SL2 a couple months ago. There's a lot of info here from other posters so I thought I'd share my experience and solution to a problem that many seem to have. Hopefully it will help someone, it was driving me nuts for a over a week.

First off, my car has 100k+ miles so after buying it, I did some routine and preventative maintience. Changed the plugs, wires, thermostat, water pump, alternator, PCV valve, etc. I also cleaned the caked up carbon out of the throttle body and off the TPS and IAC because the throttle would stick. So, I counted all those out with my troubleshooting. A month after doing all that, it started to develop a hesitation and jerking as I would pull away from a light or stop sign. I'd have to almost floor it to get it to move. Even then, the engine would bog down badly but, it would finally get moving after a few jerks and chugging. It had no consistency or specific RPM and would happen in any gear. I would get a P0171 code off and on also. After searching this site, I changed the ECTS, cleaned and tried unplugging the EGR valve, it still bucked. I replaced the fuel filter (Purolator P65501) and no change. I had platinum plugs in so I replaced those with copper AC Delcos, same bucking. I went back through all the sensor connections and made sure they were tight and not corroded. The problem persisted. The other night I found a thread about the MAP sensor, so I figured I'd give it a try. I changed it out with a known good one off another car and it still bucked. I'm at my wits end at this point. Finally, I stuck a coat hanger down the MAP sensor hole. A little carbon was on it but not much, so I sprayed some carb cleaner down the hole and let it sit and evaporate. I put the MAP sensor back on and went for a drive and the bucking and hesitation was completely gone. I guess after seeing how much carbon had built up on the throttle body, I should have figured it must be clogging up the MAP side too. A cheap and simple solution to a frustrating, annoying problem. I'd suggest anyone having the same symptoms to try cleaning out that passage before throwing parts on the car.

CLIFF NOTES: Car would buck from a light. Removed MAP and sprayed carb cleaner into MAP passage. Bucking gone.
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Old 06-11-2008, 12:11 PM   #2
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

good info on this problem isnt it always the littlest frikin things that we dont think of it could be..... i will have to clean out the passage on my MAP now
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Old 06-11-2008, 06:40 PM   #3
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Thats a good idea, I am going to clean out that MAP sensor port hole
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Old 08-04-2008, 07:34 PM   #4
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Where is the hole? I'm having similiar symptoms and have a P0171 code right now as well.

Rob
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Old 08-04-2008, 08:58 PM   #5
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1998 SC2
Default Re: SL2 bucking, hesitation, jerking, problem solved.

Quote:
Originally Posted by RobsSL2 View Post
Where is the hole? I'm having similiar symptoms and have a P0171 code right now as well.

Rob

Remove the MAP sensor. The port is the round hole it plugs into. Hold throttle open and blow it out with compressed air. Look at the rubber seal on the MAP sensor, it should be in good condition and then look to be sure the little port into the sensor is not plugged. Its a lot like your ear, be very careful if you have to clean it out, it can be broke easy.

Next throttle body cleaning look into the manifold and see how much crud is in there.
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Old 07-02-2021, 10:19 PM   #6
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Thank you for resolving a problem that has had me scratching my head for awhile.
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Old 09-28-2021, 02:14 PM   #7
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

I know this is a really old thread but it seems appropriate for my problem. My son had to use my 2000 SL2 (5 spd) for a few days because his vehicle was in the shop. Mind you I put very few miles on the Saturn since retiring in 2019 so it sits in the garage for weeks at a time. We do have a more comfortable and roomy Caravan to drive. The car runs and drive great with no noticeable problems, until today. He was on his way to work (about 15 miles) when the check engine light came on and the car started to run poorly and stalled. He got it started again but it ran like this title describes, bucking, hesitation, jerking. I drove out to his work and the car started, after a longer than normal crank, but seemed to run ok. The code is P0171. So I limped home with the car using the back roads. It only runs poorly just above idle, and wants to stall when starting out and between shifts. When you get it up to speed (over 2000 rpms) it runs fine. I could do 55~60 no problems in 5th gear. I found this thread so I pulled the MAP sensor. The little hole was very crusted up. I used carb cleaner to clean it out but the first try didn't solve the problem. I also cleaned the throttle body while it was off. I tried cleaning the MAP sensor again and no matter how many times I sprayed carb cleaner in the hole it always came out dirty. I must have squirted cleaner in the little hole 6 times and let it soak each time before the cleaner came out clean. Put it all back together and it seems to run even worse now. In fact I took it for a test drive and it stalled and would not restart. Had to push it about 2 blocks home. Grrrr. When I got it in the driveway it started. Double Grrrr. So what do you think? I have had MAP sensors fail in 2 other vehicles including a 1995 SC2 and an old Dodge Caravan. The symptoms were similar to my SL2's. Do you think I may simply have a bad MAP sensor?
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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 09-28-2021, 04:24 PM   #8
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Have you checked/changed the ECT sensor? After that, I would be checking fuel pressure with a gauge, and using live-data to check ECT, MAP, CKP, IAT, and TP sensor circuits.
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Old 09-28-2021, 04:44 PM   #9
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2000 SL2
Default Re: SL2 bucking, hesitation, jerking, problem solved.

I do have an ECT sensor from the old 1995 SC2. Should still be good. I changed it when I was trying to diagnose a similar starting problem on the SC2 which eventually led to the MAP sensor being bad. I'll change it and see what happens.
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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 09-28-2021, 08:19 PM   #10
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

I checked some live data.

The ECT rose to 185 degrees while mostly idling in the driveway. That seems pretty normal.

The IAT was 69 most of the time with the hood open. Jumped to 71 once. The outside temperature was 64.

MAP at idle was moving between 3.9 to 4.2 psi. Engine off 14.4 psi. Current barometric pressure at my house is 30 in hg (14.7 psi).

Throttle position sensor looks to be working fine.

I have an old fuel pressure tester (22 years old) and it seems to not be working. It only creeped up to 10 psi. Could I drive down the highway at 60 mph with that fuel pressure? The short term fuel trim is always on the negative side so it's subtracting delivered fuel. Doesn't seem to go with low fuel pressure.

Again, once I can get it started it idles fine at around 850 rpm. And at high speed/rpm it runs fine. It's just accelerating from lower rpm and shifting (rpm drops) when it jerks and hesitates.
...
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 09-28-2021, 10:34 PM   #11
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

60 mph on a level road is hardly any more engine load than idle. Compare the MAP readings at both conditions.

However, I also kind of doubt your FP is only 10 psi. Try to calibrate your FP gauge against some other, we really have to have some confidence in what the FP is.
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Old 09-29-2021, 10:46 AM   #12
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

My fuel pressure gauge has the adapter for typical (car tire type) schrader valves. So I connected it to one of my van tires. It read 34 lbs. It looks like the gauge is accurate. I'll retest the fuel pressure later and make sure I bleed out all the air. Crap, I was hoping it wasn't the fuel pump. But before I do that I'll change the fuel filter. As far as I know it has not been replaced since I bought the car in 2005. The fuel pump was replaced many years ago.
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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 09-29-2021, 12:56 PM   #13
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Air in the fuel line will have no effect on the pressure reading, and any that may get in will quickly be purged if the pump is OK.
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Old 09-29-2021, 01:16 PM   #14
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Thanks billr for all your help. I did some more investigating.

With the pressure gauge connected I turned on the ignition without starting the car. The fuel pump should start and pressurize the system. It does not. Pressure stayed at zero for a good 30 seconds. Tried starting it while watching the gauge the pressure stayed at 0 for about 5 seconds then it started to slowly rise and when it got to about 10 lbs the engine sputtered a bit then started. It seemed to run fine. While the engine was running it started to sputter a bit and the gauge started to show less than 10 lbs. The needle started to bounce up and down a little. I hit the throttle and it ran fine and the pressure was up a little over 10 lbs again. And even more big news. When I turn off the engine I hear the pump running for a few seconds (nothing new) but as soon as the pump turns off the pressure goes to zero. It should hold pressure for a while.

What I don't know are the differences between the pump failing or the filter/regulator going bad. What are the symptoms?
...
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; 09-29-2021 at 01:22 PM.
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Old 09-29-2021, 03:10 PM   #15
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

Disconnect the fuel line from the pump to the filter and check for pressure directly from the pump. Pressure should go up toward 100 psi, at key-on, with the regulator out of the equation like that. Anything under your specified fuel pressure + about 20 psi is probably insufficient.

I would not pay any attention to how fast the pressure bleeds down when doing that pressure test direct from the pump. Bleed-down is irrelevant except to hint at leaking injectors (also out of the equation during the test) or for "bragging rights" about how quickly your engine will fire up.
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Old 09-29-2021, 05:56 PM   #16
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2000 SL2
Default Re: SL2 bucking, hesitation, jerking, problem solved.

Thanks. I will do that. I think I have some custom made plumbing that allowed connections of the gauge directly to rubber hose. Will have to see if I can find it. Been a long time since I had to test fuel pressure.
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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 09-29-2021, 08:12 PM   #17
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2000 SL2
Default Re: SL2 bucking, hesitation, jerking, problem solved.

Any advice on how I can adapt my pressure gauge (has 2 different size schrader valve fittings) to the quick connect fittings on my car. I think I found adapters for this but I'd have to order one. Looking under the car there is a very short harder plastic hose that comes down from the top of the gas tank and goes right into the filter.
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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 09-29-2021, 10:15 PM   #18
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Default Re: SL2 bucking, hesitation, jerking, problem solved.

You could get a new filter and throw that at it. That may solve the problem. If not, then cut the fittings needed to make adapters off of the old filter.
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Old 09-30-2021, 11:16 AM   #19
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2000 SL2
Default Re: SL2 bucking, hesitation, jerking, problem solved.

Yeah I mentioned a new filter earlier. I'll replace it. There are a lot of discussions here of cheap filters that don't last long. I've searched for the WIX filter and found that almost all sites no longer sell it or is out of stock. Even the WIX website does not show they offer it anymore. I can buy a cheap one $19.99 from an Autozone 20 miles north of me. Or order a Baldwin brand from RockAuto for twice that. Considering the age of the car I'm thinking of invest as little as possible in the bigger interest of diagnosing my problem. A "new" filter should give me different (hopefully higher) fuel pressures and also hopefully prove my pump is ok.
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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 10-02-2021, 02:39 PM   #20
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2000 SL2
Default Re: SL2 bucking, hesitation, jerking, problem solved.

Do you have the freeze frame data?

What is the STFT and LTFT at idle and around 2K rpm?
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