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Discussion Starter · #1 ·
I have spent many hours seaching the forum for improvements I can make to my 96 RMW that will improve both performance and fuel mileage.Wagon has 117,000 miles,2.56 gears,AIR delete, with new platinum plugs,PCV,EGR,MAP sensor,IAT sensor,cleaned MAF. Mobil 1 oil used since new.
The mods I have made so far are TB bypass and CAI .Plug wires and optispark are original but do not have any indication of deterioration.[When I replaced the original plugs at 115,000 miles,they looked as good as new.] To the best of my knowledge do not have any vacuum leaks,motor idles smooth and runs strong.On a recent trip of 196 miles with 25%city and 75% highway [60-70 mph] averaged 17.17 MPG,which I think is on the low side with 2.56 gears.
Am thinking of eliminating some exhaust restriction by replacing the pipes from cats to mufflers with a 2.5" pypes X pipe,which would eliminate the "D" on drivers side and the X would provide better flow to mufflers,since exhaust gases from each cylinder now would flow into 2 muflers instead of 1.
Now my questions are: 1. Has anyone only installed a 2.5" X pipe with the rest of system stock,and if so what are results.
2. In addition to the the X pipe would installing Walker 17749 or Dynomax Ultraflow mufflers be cost effective to increase efficiency?
3. For a daily driver am I correct in thinking that there would be no benefit to replacing the over axle pipes and resonators.
Any input would be appreciated.
 
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Discussion Starter · #2 ·
Suggestions for improved economy:

Engine
- Replace spark plug wires (yeah its a PITA)
- Consider replacing front O2 sensors
- With 2.56 gears, you should already have dual electric radiator fans (no towing package)... if you have the mechanical and electric fan combo, consider changing over dual electric fans.

Exhaust
On an LT1 wagon, the mufflers, then the over-the-axles pipes are your biggest restrictions. Just replacing the stock muflers with more performance 2-1/4" mufflers will increase performance (and probably economy if you can keep your foot out of it). Doing the intermediate pipes will not yield a significant result until the other two are taken care of. Cats are not a factor on a relatively stock LT1.

PCM Tune
Get your PCM custom tuned for 87 octane performance. Regular economy will increase too (if you can keep your foot out of it). Your choice of whether you stick with OBD-II or do an OBD-I conversion.

Tires
If you are running 235/70R-15 tires, consider 225/75R-15 tires.

Transmission
If you have never serviced the transmission, change the filter and just replace the lost fluid; do not flush.

Driving
- Keep your foot out of it.
- At least one member found that driving over 70 mph had a drastic decrease in fuel economy.

YMMV.
 
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Discussion Starter · #3 ·
1. Replace your mufflers. Almost anything is better than the stockers.
2. Strongly consider getting reprogramming from someone like PCM4Less.com.
3. EDIT - REPLACE THE PLUG WIRES. I guarrantee they're tired at this age/miles.
4. EDIT - agreed on the higher speed. My 2.93 roadmasters seem to like 78-80mph. Possibly higher.
 
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Discussion Starter · #4 ·
Will just swapping out the mufflers alone make a NOTICABLE increase in fuel milage? Mine are rotten anyway......
17749's gonna be loud on a totally stock exhaust?
 
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Discussion Starter · #5 ·
Originally posted by Deadman:
Will just swapping out the mufflers alone make a NOTICABLE increase in fuel milage? Mine are rotten anyway......
17749's gonna be loud on a totally stock exhaust?
My thinking when I did mine was that
- my mufflers were rotting out
- I didn't have the $$$ to do a whole system in 2.5"
- I wanted the quietest performance muffler
- I didn't have a lot of $$$ and didn't want to invest a lot in a 2.25" system that was going to be thrown away in a year or two.

I went with Summit Turbos. They were very cheap and sound pretty good. I am very happy with the decision.

As far as gas mileage, I cannot say how much. I have other issues that I am working out (when I time which is very little lately). SOTP feel says that there is more power and it is more responsive.
 
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Discussion Starter · #6 ·
The AIR pump removal doesn't really effect much, but removing the EGR valve should be helpful. EGR provides more favorable emissions but degrades performance and economy. If you are in there slicin' and dicin' then the EGR valve should find a new home in the trash bin.
 
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Discussion Starter · #7 ·
The EGR is an inert-gas mixture dilution system that reduces both emissions and pumping losses during cruising at part-throttle. I would not delete it for economy's sake.
 
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Discussion Starter · #8 ·
Originally posted by Agent Smith:
but removing the EGR valve should be helpful. EGR provides more favorable emissions but degrades performance and economy.
?????????????????????????????????
 
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Discussion Starter · #9 ·
I would NOT recommend removing the EGR either. It adds inert gas to the combustion chamber, which allows the computer to advance timing. It also cools the combustion chamber.

I don't know about LT1 cars, but if you remove the EGR on a TBI car it will throw a code and give you an SES light after about 20 minutes of driving. If you reprogram I guess you could delete the EGR, but I don't see any real benefit to economy.
 
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Discussion Starter · #10 ·
The walker mufflers have a low rumble- not loud at all. I have stock resonators and tailpipes with a simple H crossover. The performance seem to increase. My foot is too heavy to notice any MPG increase.

Jon
 
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Discussion Starter · #11 ·
if you know somebody who's bored, have them check the actual readings from your MAF to make sure they're accurate. the MAF on my caprice was not reading accurately, even after a cleaning; it was telling the computer to dump fuel in as though it was at WOT, resulting in horrible mileage, one dead cat, and really fouled O2 sensors, but it was not reading inaccurate enough to throw the CES light.

one thing you could try, again just to check on the MAF, is to unplug it and see if mileage improves. it will throw a code, but if mileage improves you would have identified a gas guzzling part
 
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Discussion Starter · #12 ·
With about 3/4 tank left, dump a can of seafoam fuel system cleaner in. Drive down as close to empty as you're comfortable (somewhere around the orange bar is good) and fill the car back up. Then change the fuel filter.

Change the rear end fluid to a full synthetic.

Agreed on replacing the O2 sensors (front only - the rears don't require any accuracy, so leave them until you get a code).

Consider doing the whole exhaust, or at least the mufflers. Summit turbos are cheap and not really even noticeable under "normal" driving conditions - WOT makes a little noise, but still not obnoxious. Ultraflows and Magnaflows are a little louder, but still not at all unreasonable - and are available in "won't rust out" stainless. My Summit turbos had rusted through the body in under a year....
 
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Discussion Starter · #13 ·
I would NOT be deleting any polution control devices since you live in FL, since FL is adopting CA Emissions as early as mid 2008. You are just gonna have to put them all back on to pass the new emmission controls.

A very through tune up (including O2 sensors) and maybe exhaust is all that you will need to achieve what your looking for, for mainly fuel mileage, and some (read very little) preformance gains. After all, were talking about station wagons, not performance cars. :D

Larry
 
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Discussion Starter · #14 ·
I put a new coil on my 95 after about 120K = +3MPG, but it was on it's way out.

96 coil is supposed to be better to start with, tho.
 
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Discussion Starter · #15 ·
I replaced the O2 sensors, fuel filter, PCV valve, air filter and EGR valve, cleaned the MAF and got 24 mpg highway on a trip to Cincinnati driving 65-70mph.

Be sure to get an O.E.M. EGR from Dal! I got an aftermarket EGR and the car ran like crap. Dal told me the tolerances for those items were exacting.

I have not replaced the plug wires because the car is running very good now as is and after closely looking at the wires, I really dread attempting to replace them.

I have not calculated the mileage on a long trip since I put the Magnaflows on but I think it is a little better than before.
Stock gears, towing package.

Originaly rated at 26 mpg highway when it was new I think.

My milegage went up 2-3 mpg with the O2 sensor change alone.

[ 07-30-2007, 05:29 PM: Message edited by: Larkwagon ]
 
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Discussion Starter · #16 ·
Originally posted by PHANTOM 309:
</font><blockquote>quote:</font><hr />Originally posted by Agent Smith:
but removing the EGR valve should be helpful. EGR provides more favorable emissions but degrades performance and economy.
????????????????????????????????? </font>[/QUOTE]The one thing an engine does is convert energy from a chemical reaction into mechanical energy. EGR does nothing to improve or optimize this chemical reaction, it only deadens it. From a performance or economy standpoint, deadening the combustion process is not a help.

Sure, you can run more timing when you are pumping the chamber full of used-up air. You are weakening the burn, so it can tolerate more timing without knock. You're also losing power output in the process.

EGR helps to reduce emissions. It does so in the same manner that eating your own crap would help to prevent indigestion. However, since emissions are a legitimate concern, removing the EGR system is frowned upon.
 
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