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Old 04-10-2017, 01:20 PM   #1
SaturnStick
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2000 SL2
Default 2000 SL2 - MPG and power dropped. A lot.

I'm having a weird problem and am going to post symptoms, non-symptoms, and any extra I think may be involved (things that started happening at the same time).

I have a few suggestions from friends, but I don't want to start throwing parts at it without doing some form of troubleshooting.

SYMPTOMS - (MAIN problem is the mpg/power)

Operation: 25% drop in mpg & drop in power overall. Happened over the course of about 2-3 weeks. Other than that, seems to run fine.

Fuel Burn: A friend, looking at one of the plugs for me, noted "I smell unburned gas. You're not getting a good burn"

Starting: It always turns over, but sometimes it'll take me 2 sets of cycles to start. Then it seems fine.
Starting: OH, and I generally have to press the gas a little. I put the key in, press a little on the gas, turn it over and it starts.

Idling: ONCE WARM (temp gauge is way), when I stop at an intersection, the idle will drop as usual, but not stop at ~800, instead will get VERY low, even stalling sometimes. But, weirdly, pretty much only when gauge is way.

Accelerator: When the engine is warm ( way), the gas peddle doesn't smoothly press. I start to press and it doesn't move, but then it gives. Once 'released' (and when the engine isn't too warm), the accelerator is smooth.


Recent actions -

I swapped spark plugs and spark wires, mainly because they're old and why not do it with the oil change, right?
The plugs look OK, no fouling, they look like plugs should look.
I have bypassed the IAT sensor with a 500 ohm resistor as, when it's connected, the car will turn over, but starting can take a number of tries.
I will be ordering a new ECT when I order the IAT. The IAT has the plastic cover, so I'm pretty sure the ECT will as well.


Suggestions by friends and thoughts of my own -

1 - Get a new set of coils. The coils could be degrading, which would weaken the burn, so you lose mpg and power & the spark would smell.
I put this in because the person who suggested it is no dummy. I really don't recall if coils degrade. Is there a way to test them?
2 - Check the fuel pressure. The sending unit may be on its way out. Low pressure means poor burn, means lower mpg and power.
I think I can get a gauge at Harbor Freight, and this one makes some sense to me.
3 - Replace the injectors.
This is prefereable to the fuel sending unit only because they appear not too difficult to replace. I've worked on cars for AGES,
so I figure I can probably handle that.. but would rather not.

So, yeah.. what could be causing the drop in mpg and power or at least suggestions for how to start and what direction to go.


Thanks! :-)

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Old 04-10-2017, 01:52 PM   #2
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

You list some potential causes, but I would be in no hurry to replace the injectors - they rarely fail. Fuel pressure is an important parameter to measure. Coils can a do go bad, along with the Ignition Control Module underneath. You will usually get an SES light with this type of failure.

Sounds like your throttle body could use a good cleaning if the gas pedal is sticky.

You should also check for a clogged catalytic converter. To do this, remove the front O2 sensor and go for a drive. If performance is restored with the "new" escape route for exhaust gas, then there is a restriction in the exhaust.

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Old 04-10-2017, 02:05 PM   #3
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Wow, I never would have considered that.. maybe my catalytic has gone.
I'll give the o2 sensor removal a shot!

I'm guessing I should actually pull it out AND disconnect it, I mean, if it's exposed to oxygen, it'll report that to the ECM and that'll respond, right?

As to the throttle body, yeah, I gave it a quick "still in place" cleaning but maybe not enough. :-)

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Old 04-10-2017, 02:14 PM   #4
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

Yes, disconnect it before removing. You may get the SES light while driving with it removed - that will go away once you reinstall and connect.

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Old 04-13-2017, 09:37 AM   #5
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

OK, I've completed the catalytic converter test and learned a couple of things.

First - exhaust gases shooting straight out your manifold will melt a portion of your fan cowling. Oops. Not a huge deal. The fan still works and I just have to sand a small spot smooth.

Second - it looks like my catalytic may be going sometime, but I'd say it's not bad now. I still had low power, I'm still down at 23mpg (went 150 miles and used 6 gallons), and when the engine's warm, stopping (intersections, etc) becomes a game of watching the RPMs and if they drop too low, holding a little pressure on the gas pedal.

So, I'm figuring coils, injectors, and/or fuel sending unit.
Fuel Sending/Regulating - I think I can get a loaner pressure checker from Auto Zone and test the fuel pressure. If I have to buy one, they're not super expensive.

Ignition Coils - My only concern on this is the wide price range I see. I know a lot of SaturnFans people have strong feelings about which IAT/ECTS to get (avoid the plastic cap). Is there any such concern with the coils?

Sound like a plan?



The injectors don't look too difficult to replace

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Old 04-13-2017, 09:54 AM   #6
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

Sounds like a decent plan of attack. Autozone should be able to rent you a fuel pressure gauge. Test port is on the fuel rail very close to the brake booster. You should see 46-51 psi with key on, engine off and the same when the engine is started. When the engine is shut off, pressure bleed off should be a slow process (10 minutes or more).

The fuel pressure regulator is integral with the fuel filter. It is rather pricey.

There is a general feeling from site members that OEM (junkyard) is the the way to go for coils and ICM. While I could support that years back, at this point, the youngest OEM ICM is at least 15 years old. Personally, I'm not going to the pick and pull for old electronic parts. I'm running Chinese coils and a BWD aftermarket (made in USA) ICM. They work fine.

I don't remember if you mentioned the coolant temperature sensor. This should be replaced first if it never has before. The original ones fail, leaving the engine running very rich.

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Old 04-13-2017, 12:34 PM   #7
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

SaturnStick, with many posts and never mentioning it, did you ever check or remove the coolant sensor at all? Poor fuel mileage can be attributed to many things but the top item on a list is the faulty original coolant sensor in every S-series engine from '91-'01. See post#5 in this link; http://www.saturnfans.com/forums/sho...62#post2238562 The iat sensor doesn't fail exposed to air but fails in the cooling system. Another issue may be your bypass resistor. This needs to be removed and iat sensor plugged back in. Meddling with sensors and not having more than casual knowledge of EFI systems tends to make you the beta tester to deal with unanticipated situations affecting existing problems.

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Old 04-13-2017, 01:07 PM   #8
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Wow, thanks to both, I'll replace the IAT this weekend, just in case.
I'm having trouble finding info on that bypass resistor. Will it be in my Haynes?

I did a forum search for bypass resistor and "bypass resistor" and get either TONS of results about bypass or resistor or I get no results at all.

I see lots of info for replacing the ECTS, but not about the bypass resistor.

Thanks, both, for that heads-up on the ECTS. I recall reading about getting the brass-tipped one, but not about them affecting mileage or the bypass resistor.

OH, and FWIW - when the O2 sensor was unplugged, we definitely smelled fuel in the exhaust that was coming out. Oddly, I don't seem to smell it coming out of the muffler....

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Old 04-13-2017, 01:13 PM   #9
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

I believe fdryer is referring to the resistor you state is currently bypassing your IAT sensor when using the term "bypass resistor".

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Old 04-13-2017, 01:43 PM   #10
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

Now THAT is a 'duh' moment..... :-)
OH, and to be clear: the engine does this regardless of the bypass resistor on the air intake.
I'll be replacing both the IAT and ECT sensors as they aren't expensive and have likely been in the car since 2000.

Last edited by SaturnStick; 04-13-2017 at 01:47 PM.. Reason: Minor Clarification about the bypass resistor.

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Old 04-13-2017, 01:53 PM   #11
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

Quote:
Originally Posted by SaturnStick View Post

OH, and FWIW - when the O2 sensor was unplugged, we definitely smelled fuel in the exhaust that was coming out. Oddly, I don't seem to smell it coming out of the muffler....
Raw exhaust is nasty - that's why we all have catalytic converters now. The smelly exhaust coming out the O2 sensor hole in the manifold is what we all used to spew into the air 50 years ago!

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Old 04-14-2017, 10:31 AM   #12
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

I never considered that the catalytic was helping the smell. I do I recall those days. Also the noise - In the mid 2000s, I walked to work along a generally empty road. It was funny realizing that I heard the cars because of the tires on the road before the engine sounds.

Anyway, the new ECTS and IATS are in. I learned one thing: if you don't connect the ECTS before you start the car, it's convinced you're in the Sahara and turns on the cooling fan. It also won't stay started and won't restart. It sounded like what I was facing that started all of this. :-)

I've driven around a small bit and one symptom seems the same: It will idle, but the RPMs still like to drop down as if all is well, then simply not stop and get way down. If it gets low, sometimes it recovers, sometimes it doesn't.

I've only driven a couple of miles, and no hills or freeways, so I don't know about mpg or power, yet.

So, it looks like I'm headed toward the coils.... I saw specific mention to Chinese coils and BWD ICM. I've been using NAPA and have heard RockAuto is good. Any suggestions?

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Old 04-14-2017, 10:58 AM   #13
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

Before throwing more parts at the problem, you might do a little more diagnosis. You have yet to measure the fuel pressure - worth doing. You should also drive a bit more and see if the most recent repairs have made a performance impact.

If you find that the engine now runs better, but still has a wonky idle, that would point to a need to properly clean the throttle body and possibly replace the idle air control valve.

Coil and ICM failures are typically accompanied by misfiring, which will turn on the SES light with a P0300 or similar code. You have not mentioned your SES light being on, so I presume it is not.

Rock Auto is a good online parts source, and NAPA generally sells good stuff. I was in panic mode and bought my coils and ICM from O'Reilly's. Turns out they were not the source of my problem at the time.

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Old 04-14-2017, 12:38 PM   #14
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

The throttle body cleaning makes sense. I did one a while back, but with the problems I'm having now, I didn't think to do it again. In fact, I'll probably do a throttle body clean this weekend. The weather's supposed to be good.
The Idle Air Control valve is less than a year old, but I wonder if I simply removed (unplugged?) it, would that keep the hole open and provide info.

I was out for a test drive and recalled that I hadn't checked the fuel pressure. So I did.

Key on: 48psi
Started: 48psi
Throttled: 48psi (I simply reached to the throttle body and rotated)
Idle: 48psi

So, I'm figuring I have a rock-solid fuel pump. :-)

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Old 04-14-2017, 01:14 PM   #15
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

Unless you're completely familiar with EFI systems, disconnecting sensors can have unintended consequences leading to misinterpreting symptoms and "throw you out into left field". Think about it. Every sensor is needed to serve a specific purpose. A dead, faulty or disconnected sensor will create new problems. If you have problems but don't know where its coming from and disconnect something, how can you prove the disconnect is causing the problem, even if nothing changes? This may add additional problems or mask present problems by layering over it. Guessing is easy, understanding EFI systems and how each sensor operates and how it affects an EFI system when it fails is more difficult and a reason mechanics and techs are ASE certified. They're trained to be skilled while adding experience and practice to their knowledge for more expertise than diyers without this combination. I can speak from experience from electronics.

There were circumstances when several so called technicians were all over a problem but couldn't figure out why. It was determined later, based on their bungling, old style ribbon cables without keyed mating allowed someone to invert these connectors and create more problems. Simply back tracking their feeble attempts at repairs (they threw parts at the problem) and reversing ribbon cables solved several issues all at once. Experience with equipment and the peculiar attitude of people allowed a timely repair to restore expensive electronics.

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Old 04-14-2017, 01:23 PM   #16
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

Further to the good advice above, the proper way to DIY diagnose the IACV is to remove the air intake snorkel with the engine running at idle. With your thumb, cover the hole at the bottom of the throttle body, just in front of the throttle plate. Idle should drop to 450-500 rpm. Remove your thumb and the idle will jump up higher than normal and quickly settle back to normal. If this behavior is observed, chances are pretty good that the IACV is working properly.

And yes, your fuel pressure is healthy.

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Old 04-14-2017, 01:34 PM   #17
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

@fdryer - yes, those concerns are why I talk about it in the forum. I have a decent grasp of what a lot of the sensors and controls do, but how they work together? Yeahhhh.... no. :-)

@BV22 - Duh.. one MORE thing I didn't think of that makes complete and utter sense and I didn't think of! Interesting that it'd go down to 450-500rpm. When my idle does it's "I'll drop like normal, then just kinda keep going past ~800 rpm" it usually pauses right around 450-500rpm and, if it survives that, will go back up. If it doesn't, then it drops until stall.

As to IAC operation and the "go up way high", I've noticed that, sometimes when I get gas, I'll start the engine back up and WOAH, what's IN that gas? I'm up at 3000rpm! It drops back, but now I am wondering about the IAC valve.

Since I'm doing a throttle body clean tomorrow, I'll start with that quick IAC test first. Then after, as well maybe. :-)

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Old 04-14-2017, 10:48 PM   #18
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

As an addition to the good advice you've already received, I'd like to point out that the coils, if they are original, over time can accumulate road grime between the metal laminated core, and the coil. Many of the OEM coils had a gap between the core and the coil. This can cause intermittent shorts which can lead to misfirings, leading to reduced power. Rust can also impact performance by decreasing the spark energy.

I would think that you'd get a misfire code if it happened often enough, but at least check them for rust and little pieces of metal bridging the gap between the coil and the core. And or oil-ish road grime. I found that on my '01 SL1 with the OEM coils, along with rust, and replaced them with coils that had moulded cases to prevent that problem in future.

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Old 04-14-2017, 11:30 PM   #19
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Default Re: 2000 SL2 - MPG and power dropped. A lot.

Quote:
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@fdryer - yes, those concerns are why I talk about it in the forum. I have a decent grasp of what a lot of the sensors and controls do, but how they work together? Yeahhhh.... no. :-)....
Ahh, you're onto something now. The integrated EFI system can be troublesome to anyone not familiar with basic 4-stroke principles and adding electronic engine management - the sensors needed to provide the engine computer what it needs to turn on the fuel pump, run the ignition system to provide precise spark timing and pulse injectors at the appropriate time. Since electronics runs the EFI system, the fuel pump is one of two mechanical things, the other is the engine timing chain to synchronize crankshaft timing to the overhead valves or cams to operate the intake and exhaust valves via a timing chain. These two mechanical devices haven't changed but the ignition/spark and fuel injection systems require computer programming. Sensors help the pcm determine when to generate spark and injectors. When things go wrong, not having advanced knowledge of EFI systems can overwhelm anyone.

Don't spend money until its proven beyond doubt that a part or parts have failed or acting intermittently. While throwing parts at a problem may be one way with money not an issue, there's no guarantee of a solution with parts swapping when you're buying. Swap parts if they're free.

If the ignition system falters, there are usually error codes starting with P0300 and ending around P0341. No error codes usually means this isn't an ignition system problem.

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Old 04-15-2017, 10:43 AM   #20
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2000 SL2
Default Re: 2000 SL2 - MPG and power dropped. A lot.

@ Jim@HiTek - Until that guy at work said, "Maybe it's your coils..." I would never have considered such a thing. One of the main reasons I work on my own car is that I learn a lot by doing so. :-)

@fdryer - yes, exactly. Too much 'invisible' stuff. I was almost hoping the fuel pressure wouldn't be good!
I'd LOVE to get a signal analyzer, hook up to all the sensors and controls, and watch what they do. I've seen a number of things for monitoring the OBD-II system, even apps for the phone, but I haven't looked close enough to tell if any offer to monitor ALL sensors, etc. :-)

Today's actions -
So, I cleaned out the throttle body, cleaned the tip of the IACV, and cleaned the spark plugs, and my test drive was free of idle problems. Then again, I've not gotten it up to full heat (cool morning), so we'll see.

Since I replaced the IATS and the ECTS (yesterday) it seems to fire right up, but I haven't gone a full tank, so I don't know about mpg and I'm still not sure about power. I will say that the engine temp doesn't appear to be any different than before, but we'll see.

I'll give it the next 2 days, by then I should have used the rest of the tank and have a grasp of the mpg and maybe even the power. On the plus side, I couldn't smell any unburned gas on the plugs.

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