New Plugs - Worse Gas Mileage ???

[PewterPower]

I have a 2003 H2 Lux with 84000 miles. I changed my plugs from the Factory Plugs to the Bosch Platinum Fusion plugs (4509). My gas mileage went from about 9.8 avg to 7.5...... Why would this happen ? I did not change the plugs for any other reason than I thought it was time (past time). I have an Airraid filter in the stock air box.

Any ideas ?

[H2 Doberman]

I'm no mechanic but it may take the computer a few miles to adjust to the change.

[IRA51]

Bosch plugs blow,use NGK or AC Delco. and always change the spark plug wires at EVERY plug change . also change the plugs with a cold engine never remove a plug from a hot or warm engine with aluminum heads and also use anti seize compound on the plugs and dielitric grease in the wires and any eletric conection under the hood . you may have f*cked up a plug wire when you removed it .check the summit or jegs catologe for some MSD 8.5 mm wires they do a nice job and have a very low resistance and are priced less than what the dealer has .

[mdoyle]

Ditto on Bosch bringing the "suck" when it comes to plugs. I had a similar experience in my old Tahoe with them and went back to AC Delco.

Same heat range, ect- Bosch performed poorly.

[Carbine]

Ira51 Quoted:

always change the spark plug wires at EVERY plug change

Why? Test them with a multimeter and save yourself the money.

[QUOTE.check the summit or jegs catologe for some MSD 8.5 mm wires they do a nice job and have a very low resistance and are priced less than what the dealer has [/quote]
Again Why? I am not trying to comdemn or play devil's advocate but if the wires are designed to carry the load in the first place go ahead and check them with a multimeter. If you suspect weak glow plugs and blame them on the wires stop snap diagnosing and verify power Volts direct current and Amps with a multimeter during the glow plug cycle at cold start. Check resistance at the glow plug and check each of them to see if they vary. They might vary from manufacturer to manufacturer, bad lots ect... Watch for load/current drop at the volt guage and that will give you a general idea if in fact if the glow system is working.

[IRA51]

GLOW PLUGS ? You must be drinking too much Diesel . you should not expect the plug wires to last more than 3 or 4 years .plugs will last 70000 to 100000 miles and you should change the wires at each plug change .as they get older they get dryed out and are not as good wet as new ones and the resistance goes up putting strain on your coils as well. In Arizona the wires get dry and brittle in 2 or 3 years the high heat takes it's toll . if you want optimom preformance and fule milage and prefer not being stranded due to wet wires that cause a miss or won't even start change them at EVERY plug change. also you have a 50/50 chance that you will damage them changeing the plugs .they get stuck and you pull harder and you know what happens.spend mega bucks on a Hummer and cheap out on reuseing old wires I don't think so . Glow plugs indeed ,you must be on something bro. you don't know $hit from shineola. so when you shower you don't change your underwear too.

[jmsspratlin]

Originally Posted by Carbine

Ira51 Quoted:
Why? Test them with a multimeter and save yourself the money.


Again Why? I am not trying to comdemn or play devil's advocate but if the wires are designed to carry the load in the first place go ahead and check them with a multimeter. If you suspect weak glow plugs and blame them on the wires stop snap diagnosing and verify power Volts direct current and Amps with a multimeter during the glow plug cycle at cold start. Check resistance at the glow plug and check each of them to see if they vary. They might vary from manufacturer to manufacturer, bad lots ect... Watch for load/current drop at the volt guage and that will give you a general idea if in fact if the glow system is working.

Glow plugs?....is your Hummer a diesel?

[HUMMERcustoms.com/TAZ]

If You want to change wires go to Taylor wires and You should not ever have to change them again. Nothing against MSD as i like there products. MSD hired HPTUNERS.com to do the programs for MSD Superchips programmer and HPTUNERS.com assist the Superchips racing team with there specialty tuning so that tells me MSD wants to do things right.

Due to old school I ran all Accel ignition parts back in the 70's on my 68 Mustang Coupe with 289 high perf. twin 700 Holy double pumpers on a tunnel ram. Accel was just real popular at that time and they functioned to perfection for me.

Go to most performance shops and they will recommend Taylor wires especially in the southern USA. Taylor is highly thought of in pro drag racing. I have a set on a 99 Silverado that has everything done to it to make it run except no forced induction and I have a set of Taylors that are 7 years old used under extreme load and extreme heat situations daily and still read the same with a meter as when they were new.

I changed to Taylor wires on H2 as soon as i bought my first handheld programmer knowing I was going to get better spark and next I will change to MSD coil pacs on H2.

TAZ

[PewterPower]

Thanks to you all for your help....I have new wires and NGK plugs waiting for my attention !!! I hope to have this problem fixed soon.....

[obzidian]

man, i thought it was me but i think i felt a change in mileage with the plugs, but not much.

I get an average of 12mpg around town and with the new plugs, they are also bosch, im now under like 11.5 or 11mpg. Might be nothing but still, annoying when you sike yourself if you installed the plugs, wires right, etc.

Taz is right, get the taylors and for get about it. Nice, hi-temp wires and less resistance per inch. MSD suck. Also, some will say that ngk plugs suck as well. Some use the ac delco stuff instead in race ls1 applications. If you want some interesting, i read about these wires, nology i think, they have a built in ground/capacitor, that yields a higher spark. Interesting, if they work!!

Anyone wanta try a set?!

[Captain of the Titanic]

Originally Posted by HUMMERcustoms.com/TAZ

Due to old school I ran all Accel ignition parts back in the 70's on my 68 Mustang Coupe with 289 high perf. twin 700 Holy double pumpers on a tunnel ram. TAZ

TAZ - twin 700 holley double pumpers??? Not on a 289 you didn't. Unless you managed to bore it out to 390 or 427.

You wouldn't even be able to START a 289 with two holley 700s...

I trust you on Hummer completely, but that comment about the Mustang doesn't make sense....

I guess the 60s (and 70s) must have been good to you

By the way, I'm running an 289 with a Edlebrock 750 4 barrell, through aluminum heads, Ported and Polished Block, bored .030 over, Edlebrock headers, Edlebrock cam, and electronic ignition on my '68 Mustang Convertible. I am also running a 4.11 (Strange Gears) positraction rear end. Due to the fact that it's tuned to be streetable.
it puts out somewhere in the 350 hp range. Which of course with a light unibody means it goes like hell, but isn't going to kill you!

[IRA51]

FYI the MSD super conductor wires guarentee 50 ohms or less per ft .also many who race the LS1's favor the NGK plugs ,I ran them in my 2000 Z28 6 speed car that had a 382 stroker with 450 rwh (dynoed) 12.36 in the 1/4 mile ON STREET TIRES .I ran the copper Tr6 (a colder than stock plug) with great results .I would use the correct heat range and the platinum plated plugs in a H2,or the AC Delco's. the best bang for the buck in wires are the Summit wires $54.95 8.5 mm made by taylor part #SUM-887830 .40 TO 50 OHMS PER FT SPIRAL WOUND COPPER .VERY NICE FOR THE MONEY.

[HUMMERcustoms.com/TAZ]

I was running 1 of the last 2 289 high performance complete crate engine setups that was made just as Gapp and Rousch left Ford. A local guy I knew found out about them still in warehouse and He made a deal for both knowing I was buying on engine. It was not a streetable motor but we tamed it down a little making adjustments so it would barely run on street. I had a bolt on hood scoop to hide the tunnel ram when taking it on the street but, at the track it came off and a snout scoop would be mounted right on the carbs with all of it sticking out of open hood hole. It helped the heat ecscape better also with scoop off. At track it got a make over running a fuel line ice bucket and few more things. It was a beast and I ran wheelie bars on track as it pulled front wheels with the T-10 top loader in 3 gears if I let it. Had to of course beef up the complete drive train. Ran i think 4.56 Detroit lockers. Had to chain the engine block down as it would not keep motor mounts in it not even solid ones and would break out the tranny mounts. It was not a comfortable riding car at all as i ran Gabriel air shocks so we could raise it up at track to put the wide Mickey Thompson wrinkle walls under it. But, to me it was worth it and i had a blast. My Mom fussed at me because I had spent enough money on the car to have paid for college without having to race to help pay the bills. She was right but, it was more fun my way. I had pearl white paint with the red long C I called them on the side going around the fake side air scoops.

I did make a mistake on carbs after talking to a high school and college buddy who helped work on the ride, well he rode in it mostly but, was the only person that would strap in with me. The carbs were 650 double pumpers. I had run a single larger double pumper on an eldebrock intake before going to tunnel ram. I was getting close to adding a blower. I had the heads reworked and oversize chevy valves used in them. I forget the spring pressure as with my illness i forget many things for now. Doc says it will get better though. But, anyway when we put valve springs on with roller rockers etc. we all just sort of squenched our eyes waiting to see which ever one of us who was compressing springs waiting to see if the springs blew up on the guy. The heads ran double springs as if i did not the valves would float. No one else could drive it just me. Mostly because i was crazy enough I did not care. I figured if i died driving the rig and no one else was harmed it was the way i would want to go it meant so much to me. One reason i never lost i guess was i pushed it to win or blow up. First race at KC Int. it was an 1/8th mile track but, I had to run a Z28 Camaro with a blown 454 on open night for grudge races. If it had been a 1/4 mile i think He may have run me down but, with the small block short stroke I jumped him out of the hole so bad He could not catch me. I always would drive with gas pedal on the floor and never lifted it. I had a quick foot on the clutch and just stabbed it and yanked the Mr. Gasket inline shifter with line lock through the gears.

A motor is just an air pump that we add fuel and spark to, so if You open the motor up to push more air then You can add more fuel to it adjust timing and let it do it's thing then just hang on is the way i always approached power and speed. The same with a waverunner or motorcycle i could not just leave them alone. Just in my blood i guess.

We had allot of fun with that car. Driving through Sonic I would just let it lope at idle and chirp the tires on each lobe of the cam. The heads were the only things we improved as Ford had this motor every part blueprinted and everything that could be polished polished race ready. In 1976 the final total invested in the motor was right at $10,000. Convert to todays dollars? The car was T boned on the street one of the few times i drove it since I loved it so much that i drove a 1970 VW Bus to keep it parked. Anyway, the body was not worth keeping and i was getting married. A guy in town who ran a 69 Mustang fastback came to me and made an offer for the engine out of
"The Iron Horse" as it was nicknamed for never being beat in a race. Over a week time we talked and He finally paid me $13,000 and let me keep the rest of car to part out. The 68 coupe started out with a 302 3 speed and it was just never going to do what i wanted it to do.

I raced regularly in Olathe, Kansas in an abandoned housing development paying my way through college. I happened to work for Keystone Manufacturing during college and when they learned of the car they became a sponsor. In the summer they would haul it along with their rail car. The farthest i ever went was i think Bee Line Dragway in Arizona. Spent most of my racing KC Int. Raceway to hold expenses down for Keystone. It was a better local statement for them.

I have forgotten way more than i can remember about most details. I know I went through a T-10 top loader every other month it seems when racing. Had to keep a scatter blanket over bell housing and tranny at all times.

Well enough of reminecing of the good old days. But, allot of what I have in mind for the H2 comes from the old days of pushing motors up till just before they broke. Anyone can do it know doubt but, it is an area where even in this technology experience of doing it allot helps You to feel what a motor will take over what others think it can do. To get the most You have to have no fear of pushing the motor and drivetrain for all it has then starting over if you mess up.

I like Your setup Captain as it seems You have gotten allot out of what You have had to work with. But, in a small block Ford there has not been and maybe never will be a motor that could do what the original 289HP motor could do. If I had a Stang with original 289 in it I most likley could not make myself to risk destroying it in these days.

Good Luck with Your Stang Captain and I hope You get to enjoy it for a long time. I wish all the time I could get that crate motor back I had my hands on.

TAZ

[f5fstop]

Originally Posted by Captain of the Titanic

You wouldn't even be able to START a 289 with two holley 700s...

I won't get into a debate on whether or not the 289 could or could not run with this setup, since I was a Chrysler dude in my younger days. However, please explain the statement above. Since I'm positive the engine will start, but when the pedal is pressed against the metal, it might stall.

I say many people slap tri-power setups on stock small Chrysler engines, and they started and idled fine; half-throttle they died.

[obzidian]

to much air, not enough fuel maybe?!

IRA51: nice!! Who built your 382ci? Are ya on the ls1tech boards? Im also obzidian on there... have a 408ci in my vert. getting some low c.r. pistons now for boost!

[IRA51]

MTI in Housten TX,sold it in march .it was set up for road raceing not Drag raceing so with slicks and skinny's up front it would have easyly got into the low 11's .if you know anything about the rear end in the Z28 (Thorsen) you know that it won't stand up to slicks and 450 RWH. Once I drove my friends 2006 Corvette the love affair with the Camaro was over .I a'm going to get a Vette one way or another B4 the end of the year .

[obzidian]

yeah, stock 10 bolt is a joke! I have currently a strange 12 bolt which will see anywhere from 600rwhp-900rwhp. Lets hope she hold huh?

I like vettes also, you could get a c5 right now for a good price and drop in a 408ci, you'll make more than the c6 z06, thats for sure.

[IRA51]

Yes but the C6 is so sexy.

[obzidian]

true, and that ls2 is a only a stroke away from a 402ci!!!

[mdoyle]

A small engine can run on large twin 4 barrel carbs since they're not flowing at full CFM at idle. Where things go South is when they open and begin to flow, the port velocity drops off and so does low end torque.

Right about the same time, the velocity drops off, the fuel and air begin to separate and you end up with a poor burn rate during the combustion cycle. In extreme examples it will foul the plugs to the point the everything stops.

I learned this very important lesson when I was about 16 and tried to run a set of Isky Caliopie Stacked Injectors on the street that I bought at a local speed shop (Dale Welch Auto Sales in KCK). The look I got from my girlfriend's Dad when I jumped out with a bottle to prime them as we were leaving her house was worth it (almost).

For all you would be tuners out there; you're not running a *real* cam profile unless you need a vacuum reservoir to keep the brakes going