New Plugs - Worse Gas Mileage ???

[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.....

[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!