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I now have two co-workers that drive the same distance as I do and have Saturn SC's. I would like to print tips and mods for their cars. One is an automatic, the other is a 5 speed.
Any proven recommendations would be appreciated! I have been recommending the Scangauge.

I finally convinced the 5-speed driver to sssslllooowww down. He kept it below 2000 rpm, and coasted every chance he got for the last tank. He got 45 mpg which topped his previous best of 42 mpg.

Hi Msirach:

___We had better let Larry get in deep with the Saturn’s as there is nobody better at pushing one then he is!

___I can see your stick driving owner with some 50’s in a matter of months if he is willing to take it easy out on the Interstates and throw the book at her around town after he is SG-II equipped :D

___Good Luck

___Wayne

Hi Msirach:

___We had better let Larry get in deep with the Saturn’s as there is nobody better at pushing one then he is!

___I can see your stick driving owner with some 50’s in a matter of months if he is willing to take it easy out on the Interstates and throw the book at her around town after he is SG-II equipped :D

___Good Luck

___Wayne

I would be willing to drive there if it's not too far.:) I'm still working on the P&G speed range but I think I could get them close to 50. If they would be willing to do some FAS when they have learned enough to be ready for it, mid 50's are possible; if their route was as rural as mine. Also, I heard some things about Saturn automatics that could be pretty encouraging as well. I hear that with some creative footwork that the torque converter can be made to lockup even as low as 2nd gear. Couple that with an injector kill-switch and some aggressive FAS ing when they have enough experience and I bet consistent low 50's would be possible. Let me know how I can help.

I have a 1999 Saturn SL1. I have been reading a bout hypermiling for about a month now and have implemented a few ideas (coasting, slow acceleration, etc.).

I have reached as high as 47mpg on single tanks and have averaged 41mpg over the last month.

I just put on 4 new struts, 2 front tires (aligned & balanced + K&N air filter).

I don't have a kill switch (doesn't popping the clutch cause extra wear?) or SGII.


What else can I do to get into the 50s like you mentioned?

I have a 1999 Saturn SL1. I have been reading a bout hypermiling for about a month now and have implemented a few ideas (coasting, slow acceleration, etc.).

I have reached as high as 47mpg on single tanks and have averaged 41mpg over the last month.

I just put on 4 new struts, 2 front tires (aligned & balanced + K&N air filter).

I don't have a kill switch (doesn't popping the clutch cause extra wear?) or SGII.


What else can I do to get into the 50s like you mentioned?
The easiest thing I can mention that should get you better mpg would be to consider pumping up the tires to the maximum on the tire's sidewall. This will help considerably. I might suggest that if you choose to do this, you may want to go only a few psi at a time to get used to the stiffer ride a little at a time.

As for extra clutch wear during restart, it would be minimal if not nonexistent if done properly. By properly I mean smoothly and without jerking. I had people ride with me that didn't even know I was doing a bump start.

Over time I got really smooth doing the bumpstarts on my Saturn Sl. I was wondering if this is because the engine is older ?

diamondlarry - what gear do you usually bump start in? I have tried it a few times but the car jerks pretty bad. Even when doing it in 3rd gear I felt a jerk when the engine sprung to life.

I noticed an average drop in mileage of at least 5mpg when I rebuilt my Saturn DOHC engine. Would boring the pistons out by 0.020" cause that dramatic of a change in FE? If not, I suspect I could have a different problem.

I bump-start in 5th, or 4th below 15mph. No jerk at all. Do a quick up-down pulse on the clutch, then select your gear and go.

"boring the pistons" means fresh compression ? (my favourite 5speed's engine bumps-smoother/turns-easier because it has nearly 1/2million kms ... original engine)

The pulse down (or double clutching) smooths out your restart as the engine spools up and tucks smoothly beneath your chosen gear on clutch-release. For more rapid spool-ups I found that high-test reduces 'bump-effect' to turn it over (the engine's rpms are alive much quicker to meet your transmission's shaft-speed of the appropriate gear)

Thanks, I haven't tried 5th gear yet for bump starting. I think I tried 4th gear but I was going 30 or 35 mph. And I didn't do a quick "up/down" with the clutch pedal. Just let off the clutch and kept it in that gear. I will try your method.

When the pistons were bored, the compression was brought up to stock levels. Probably a little over stock since the head was milled a small amount to clean up the surface. I think my main problem could be with my crank shaft. I think it is still slightly bent after the machine shop tried to staighten it after they welded it. I should never have trusted those hackers. I don't think they were used to working on an aluminum 4 cyl engine.

Ok ... I just tried bump starting the car in 5th gear, going around 30 or 35 mph .... Wow! Worked so well I didn't know the car had started. I let off on the clutch real quick, not quite the full travel of the clutch pedal, then pushed the clutch back in. Worked great. No jerkiness at all! I liked it so much I tried it 2 more times in a 1.5 mile stretch. I never thought I would implement FAS because I thought it was rough on the crank bearings, but I changed my mind after feeling how smooth it was when done right. Thanks guys!!

:D Ain't it grand?! Glad to help.

Might get a '93 SC2. Concerned the DOHC engine might suck down a lot of gas. What mpg might I be able to get driving mostly freeway and rural without doing FAS and minimal P&G. I do have some hills involved. For the record I've been getting about 24 mpg lately out of a Mazda B2600i 4x4. Hoping to get at least 40 out of the SC2. Doable?

Might get a '93 SC2. Concerned the DOHC engine might suck down a lot of gas. What mpg might I be able to get driving mostly freeway and rural without doing FAS and minimal P&G. I do have some hills involved. For the record I've been getting about 24 mpg lately out of a Mazda B2600i 4x4. Hoping to get at least 40 out of the SC2. Doable?

Keep your speed down, be easy on the trottle, NICE-on coasting, P&G, adjust tire pressure and maybe add hot air intake, 40's are definately doable. :D

Keep your speed down, be easy on the trottle, NICE-on coasting, P&G, adjust tire pressure and maybe add hot air intake, 40's are definately doable. :D

Thanks for the tips.

Concerned about NICE-on coasting as (this) SC2 idles at ~1500 until speed drops (to ~5 mph?) Maybe something needs adjusting?

I already take it easy on the throttle. Don't do much P&G as I don't like to hold up traffic too much. Already ordered parts for opengauge so I can get the instant feedback. Not sure how that works for figuring benefit of P&G. What's involved with adding hot air intake? How does it help mpg?

Edmunds http://www.edmunds.com/advice/fueleconomy/articles/106842/article.html disputes importance of tire pressure. But I keep 'em close to maximum anyway.

Current owner first (ad) reported 20-30 and then 18-25. Don't know what her driving habits are (she's in CA, her dad is selling the car here in OR). New EPA is 21-32.

Will keep 4x4 for errands so wanted to save enough with SC2 (or another rig) to defray keeping 4x4 insured and registered and get some payback besides. Guess just using less gas and less wear on other vehicles is some payback. Interestingly, SC2 has more hp (124) than the B2600i 4x4 (121).

Have you tried cleaning the throttle body. I had the same problem, also a slightly sticky throttle. Cleaning solved both problems.
I can get upper thirties and low 40's with DWL and very limited to no P&G(NICE-on coast) in my SL2. :woot:

What's involved with adding hot air intake? How does it help mpg?

Missed this earlier. If your engine compartment is set up like mine it is easy. Remove the black tank that sets behind the radiator and connects to where your air filter is. I put a piece of PVC pipe (with a 90 on the end) from the whole left in filter box to in front of my manifold. I then taped off the normal air entrance. No major mods so if it does not work you can go back stock.
As far as MPG I am still experimenting, so I can not say for sure. It looks to have got me about a 10% increase. But I am not done tinkering with the sent up yet. The biggest increase seems to come from FAS as much as possible. 47 and 44 mpg on my last 2 tanks.

Have you tried cleaning the throttle body. I had the same problem, also a slightly sticky throttle. Cleaning solved both problems.
I can get upper thirties and low 40's with DWL and very limited to no P&G(NICE-on coast) in my SL2. :woot:

I had this problem as well when i first got my SC2 and it started acting similar to that again two weeks ago when (I believe) my O2 sensor started to act up. Of course it didnt throw a code until today. Everything is back to normal now and hopefully my numbers will start climbing again. As far as HAI, I currently have a warm air intake that I turned so it sits right above the exhaust manifold. I also have a 150ohm resistor taking the place of the iat sensor.

I had this problem as well when i first got my SC2 and it started acting similar to that again two weeks ago when (I believe) my O2 sensor started to act up. Of course it didnt throw a code until today. Everything is back to normal now and hopefully my numbers will start climbing again. As far as HAI, I currently have a warm air intake that I turned so it sits right above the exhaust manifold. I also have a 150ohm resistor taking the place of the iat sensor.

IAT hack I tried but could not see much difference. However I had added the HAI at the same time. After the next tank I will be adding it back so I can look at it in isolation.

I also have a 150ohm resistor taking the place of the iat sensor.

Have you checked with a scan tool to see what the PCM is reading for Intake Air Temperature?
IIRC, high resistance reads as cold temperature, in which case the PCM would be enrichening the mixture wouldn't it? I would think that shorting it together would get you a higher temp to lean out the mixture

Have you checked with a scan tool to see what the PCM is reading for Intake Air Temperature?
IIRC, high resistance reads as cold temperature, in which case the PCM would be enrichening the mixture wouldn't it? I would think that shorting it together would get you a higher temp to lean out the mixture
I checked my Saturn with the 110 ohm setup and the SG said 247F for intake air temp. Shorting the wires won't work because it throws a code. In fact the bottom limit is somewhere between 110 and higher than 105 ohms to avoid the CEL(check engine light).

I checked my Saturn with the 110 ohm setup and the SG said 247F for intake air temp. Shorting the wires won't work because it throws a code. In fact the bottom limit is somewhere between 110 and higher than 105 ohms to avoid the CEL(check engine light).

Larry, is there any sign the car is running too lean? That is my greatest fear with this and is why I went with a 220 ohms before.

What does one have to do to get 45 mpg in a SC2 ('93) 5 speed (the 124 hp DOHC engine)? (I might buy one as they tend to be less than any other car promising good mpg.)

Somewhere else on here suggested that the sweet spot for Saturns was 40 mph. I was hoping for a sweet spot of more like 55-60 mph. This is probably the wrong place to ask what cars might provide that but any suggestions are welcome at this point BEFORE I buy something.

What does one have to do to get 45 mpg in a SC2 ('93) 5 speed (the 124 hp DOHC engine)? (I might buy one as they tend to be less than any other car promising good mpg.)

Somewhere else on here suggested that the sweet spot for Saturns was 40 mph. I was hoping for a sweet spot of more like 55-60 mph. This is probably the wrong place to ask what cars might provide that but any suggestions are welcome at this point BEFORE I buy something.

HAI, P&G nice/off (as often as possible), basically follow the techniques in "Beating the EPA - the Why's and How to Hypermile (http://www.cleanmpg.com/forums/showthread.php?t=1510)" I am still learning but my last 3 tanks average 44.84.

reedy71: Before I knew anything about hypermiling I was getting between 30 - 35 mpg in my 96 DOHC. Then I rebuilt the engine and lost about 8 - 10 mpg. (I have to rebuild it again) I am back up to 30 mpg with only city driving, by coasting in neutral (or clutch pressed in), acclerating slowly, I don't use the AC, and I have an HAI. The rpm's on my car stay high (1500) till the car just about comes to a stop. I disconnected the IAC valve and the problem went away. The car runs fine without it but if you turn on the AC it will idle so low that it nearly stalls. Also, it will idle lower than normal at startup. That wasn't an issue for me, though. Possibly in the winter it would be.

Below is a pic of my HAI. The silver duct off the side is 3" aluminium dryer vent hose with insulation and aluminium tape wrapped around it. The duct sits along side the exhaust manifold. It has holes in the side of it right next to the manifold. Also, a 3" hole at the bottom. I capped off the other end of the airbox with cardboard, hotglue and packaging tape. I also moved the IAT to the middle of the box to get hotter readings. I have a digital thermometer installed on my dash to read the temp in the box. It is usually around 130 F when driving around 40mph or higher. It takes at least 10 minutes to get to 130 F. It will get to 150 F or a little higher when driving slow in stop and go traffic. I need to wrap some aluminium foil around the whole exhaust manifold to trap the heat better. As Jamtee stated, 40's is doable.

http://i69.photobucket.com/albums/i77/tommyT5/HAIforSaturn.jpg

PS: I hope my wife doesn't mind me posting a giant picture of her on the internet!

Thanks for all the encouraging words.

Still deciding on the '93 SC2. Got codes 22, 27, 45, and 53. Replacing the TPS may take care of all that and it may then get decent mpg (about 25 now.) Then again there may be some other problems. Not sure what to make of code 53. It also needs coolant flush and seems to have a cooling fan problem (the cause of code 27?) and needs a tune up and...

The rpm's on my car stay high (1500) till the car just about comes to a stop. I disconnected the IAC valve and the problem went away. The car runs fine without it but if you turn on the AC it will idle so low that it nearly stalls. Also, it will idle lower than normal at startup. That wasn't an issue for me, though. Possibly in the winter it would be.



Do other Saturn owners experience the same high rpm issue? (The SC2 I've been looking at did 1600 rpm until stopped then dropped to 1250. If running real warm then it went to 900. But it has a TPS problem.)

If so, is disconnecting IAC valve the best solution?

It seems to be something designed into the software. Disconnecting the IAC seems to be the only fix.:( It does cause some minor issues in the cold IN winters on start-up but I have found it easy to deal with. When first starting the car in the morning or after sitting all day at work, I just put light pressure on the gas pedal while starting and for the first few seconds after it starts. After it runs for a bit it smooths out.

Jamtee, I never noticed any signs of running too lean with the 110 ohm setup. The sparkplugs never showed any signs of excessive heat like you would expect form a too lean condition.

This brings up another point I wanted to make. Running an engine too lean doesn't necessarily mean that it will run hot. In fact, running lean will cause the engine to run cooler. This is because there isn't as much fuel to produce the heat; in most cases. The only time the engine will start running hot when lean is when it's under a heavy load such as full throttle or climbing huge hills. If a hypermiler is behind the wheel though, neither one of those conditions should be an issue.:p

I agree with DiamondLarry about disconnecting the IAC. Startup does require a little rev. when cold to get it to idle smoothly. Also, running the AC caused the rpms to go so low that it got a little rough at idle. The nice thing about doing this is that the rpms drop much quicker inbetween shifts, so you can match your rpms to your transmission speed easier when shifting quickly. When I run with the IAC connected I always pause a little inbetween shifts to let the rpms drop enough to match the transmission speed for a smooth shift. I think the Saturn engineers did this on purpose. Probably better that way for people that are new to 5 speeds and tend to shift a little slower anyways. The higher idle while the car is moving is tied into the vehicle speed sensor (VSS). I don't know why they did it that way. Maybe just to keep the rpms up for smoother shifting and to prevent bogging when going to the next gear.

I'll give another vote to the rpm fluctuation when coasting in Neutral at speed.
I just re-ringed my DOHC engine in my wagon about 1,000 miles ago, (about 100 miles after I bought the car) because it was burning oil (as per previous owner 1qt/600miles) and my first couple of tanks were less than impressive. My theory is that Saturns burn oil because oil rings stick in the piston, reducing drag on the pistons. With new rings and honed cylinders, I got alot more drag in the engine till the new rings cut in. My mileage has steadily improved-almost daily. I started to P&G a little on this tank and with about 150 miles, my SG2 is showing 44.1mpg for this tank.

Update on '93 SC2:
1st tank: 26 mpg, some Lucas and a tune-up
2nd tank: 30 mpg
3rd tank: wiped stuff off of IATS, changed ECTS, 37 mpg
Given that I did the ECTS about 1/2 way thru tank 3, tank 4 could be 40+
Car is working out. About the only other things to check are IAC and EGR.

Someone posted a question about substituting a resistor for the IATS and possible engine damage. Haven't seen a reply so I'll ask it. Basically the resistor is telling the PCM that the air is hotter than it really is and thus less dense than it really is (less O2). That would probably cause the engine to run a bit lean - obviously lean enough to save fuel or one wouldn't do it. Doesn't running lean hurt the engine in the long term? If not, why not?

That only works for a little while. The exhaust oxygen sensors will quickly pick up the lean condition, and the ECU will feed more fuel to restore the ratio.

You could make a hot air intake like I did. It definately helped me to get about a 3 mpg improvement. Plus you are not leaning out the AFR, you are adding less air and less fuel but the AFR is still the same.

If you run consistently too lean from the resistor trick (or other tricks) you will get a higher average temperture in the combustion chamber which could lead to burned valves, pistons, etc. The problem is the flame speed slows down which requires you to advance the timing. If that is not done, the combustion event will not be complete when the exhaust valve opens and you end up with a higher average combustion chamber temperature. To be safe, you could fool your ECU to advance the timing, or make changes to the combustion chamber to speed up flame speed. I think you would be fine at AFR's below 16-17. Above that, I would start to get worried. As DiamondLarry said, when hypermiling you have less of a chance of issues with heat because you have low load and low rpm's. With a slower flame speed it is imperative to keep from reving the engine real high. And low load will also keep the heat down. Once you get around 20 AFR you should start to get some misfiring, so that would be your first clue you are too lean.

I put a wideband oxygen sensor on my car recently. I am amazed that the average AFR is well above 14.7. I need to do some datalogging but it looks like the average AFR during light driving is around 15.5. I should re-calibrate just to make sure, but the first time I calibrated the sensor, it came back good. I have been trying to lean out the mixture a little at a time, with the wideband. I got up to 15.6 so far with room to go (obviously). When I put the wideband in, it caused the car to run richer than normal (about 14.6:1). So I have been slowly adjusting it leaner to get were i am now. Which is right about where the factory sensor is at. I thought I would get a pretty good gain on FE with the wideband but now I'm thinking it is already pretty good. There is one thing I would like to try, though. I am going to try and lean out the mixture just during light cruising in order to get the AFR up to about 17 or 18 at that time. It is a little risky, but I am willing to give it a try. From what I understand, Honda used to make a civic that ran lean during light cruising that ran lean for better mileage. I think that was a good idea. I just wish I had some control over the timing.

Anyone know if any of the sensors have direct control over the timing on a Saturn?

Just an update: I lost my datalog info from my narrowband (NB) sensor so I will have to redo that to find the average AFR. I managed to hook up a micro-switch on the throttle plate lever so that I can automagically switch between the wideband sensor and the NB sensor depending on how far I press the gas pedal. The default sensor is the wideband. The car doesn't switch over to the NB sensor until the TPS reads 33 on my Scangauge (or 1.5 volts on my wideband software). My first test was this morning. Everything worked beautifully. The car was running around 16.5-17 AFR (still need to look at the datalog). Then when I hit the gas a little harder, the AFR would go down when the NB sensor kicked in. I am going to turn the NB on a little sooner and lean out the wideband portion a little more. No issues with driveability so far. Water temps look good, too. No mpg results yet, but I hope to get some results in a week or so.

Well, I did some more playing around with my wideband. I tried to lean it out a little further and turn on the NB sensor a little sooner. Around an 18 AFR I am getting some missing and severly decreased power. I was getting missing even when cruising at 40-50 mph. I dialed the AFR back to around 16.2-16.5. Seems to be running fine. I also adjusted the NB to kick in a little later (like I had before). I would like to be able to cruise at around 70mph and not have the NB sensor kick in. Hopefully, I can do that now. Before, my top speed before the NB sensor kicked in was around 50 mph. I am going to get some mpg readings and see how much improvement there is. I would also like to go back to the NB sensor only for a short time and monitor what happens when you do the resistor trick on the Intake Air Temp sensor. I think that would shed some light on why some people are seeing gains.

Anyone know if any of the sensors have direct control over the timing on a Saturn?

From the research I've done, the timing isn't directly controlled by any one sensor. The Saturns use a crank angle sensor to know when to fire the coils. The ignition is a solid-state, wasted spark setup. This amounts to two cylinders getting spark whenever a coil is fired. It's used to save money on parts and tends to be just as effective as ignitions with coils for each cylinder.

The resistor trick has the potential to advance the timing, but as you stated it really shouldn't be considered as a long-term solution.

We basically have 2 options when it comes to controlling the timing. The first and most challenging would be to hack the PCM by finding and altering the timing maps. The second option is a method that has been pioneered by others and it amounts to using the Ford EDIS system with an ignition controller like MegaJolt. Of course, we could always try to look for other options, but something like the MegaJolt Lite Jr. system isn't all that expensive compared to most other options and would give quite a bit of control over the ignition.

As DBN mentioned, no single sensor has complete control but several can influence it. I know that the MAP sensor can be used to tweak the timing as well. I think that the coolant temp sensor may have some influence on timing as well but I would have to do some checking to verify that one.

That only works for a little while. The exhaust oxygen sensors will quickly pick up the lean condition, and the ECU will feed more fuel to restore the ratio.
There is a device called an EFIE that can alter what the O2 sensors see to keep that from happening.