Problems With Vortec 454 '96 C3500

[KENNHON]

truck never gave me any trouble[other than fuel pump] now at 130,000 miles it back fires, and 'misses'[NOT ign!] when light throttle at 50mph, or above... when U give it gas, it is ok to redline!. Fuel press. is only 40 psi[Pump is 2 yrs old-a premium Carter pump], and it starts DROPPING when you shut off engine[which COULD be a leaky inj, or fuel leak-could not find any].the vacuum is low[to me] at 17 inches, but staedy as a rock..... EGR valve has 5 volts at harness conn's, and valve has inf. ohms on valve itself... plunger works ok[i have valve off truck]

 

ANY HELP would be Appreciated!! this truck is like new always babied, lowered,wheels etc. Duallie

[pennzoil29]

Welcome aboard Have you replaced plugs, wires, etc?

[mattjulien]

sounds like the cats might be plugged up

[L29er]

17"is good for vacuum, mine runs 18", but 40 psi is much to low for fuel, should be 55-60, although mine runs fine at 52psi. how much volume does the pump put out? should be 1 pint in 30sec. I would first consider replacing the FIlter, then pressure regulator if that doesn`t fix it. I don`t have my manuals to say whether the ohms is correct for your EGR but 5v refrence sounds correct to me. I would also ask how new your cap and rotor are, its amaizing how quickly they get corroded in the contacts, just pulled mine from 6 months ago replacement and it was already showing some crud. I would also try cleaning you MAF sensor. Are there any codes?

[knnhon]

17"is good for vacuum, mine runs 18", but 40 psi is much to low for fuel, should be 55-60, although mine runs fine at 52psi. how much volume does the pump put out? should be 1 pint in 30sec. I would first consider replacing the FIlter, then pressure regulator if that doesn`t fix it. I don`t have my manuals to say whether the ohms is correct for your EGR but 5v refrence sounds correct to me. I would also ask how new your cap and rotor are, its amaizing how quickly they get corroded in the contacts, just pulled mine from 6 months ago replacement and it was already showing some crud. I would also try cleaning you MAF sensor. Are there any codes?

[knnhon]

17"is good for vacuum, mine runs 18", but 40 psi is much to low for fuel, should be 55-60, although mine runs fine at 52psi. how much volume does the pump put out? should be 1 pint in 30sec. I would first consider replacing the FIlter, then pressure regulator if that doesn`t fix it. I don`t have my manuals to say whether the ohms is correct for your EGR but 5v refrence sounds correct to me. I would also ask how new your cap and rotor are, its amaizing how quickly they get corroded in the contacts, just pulled mine from 6 months ago replacement and it was already showing some crud. I would also try cleaning you MAF sensor. Are there any codes?

 

THANKS!!!! my pump, and AC Filter i changed less than 10,000 miles, BUT I am SUSPICIOUS of gasoline down here in Florida[spent most of truck's life at Lake of the Ozarks... The water table is so high down here, U see tanks being replaced at stations all the time!!! i will change filter... I'm worried about pressure[i COULD have leaky inj, and/or a leaking line SOMEWHERE[but no fuel on grd.]. when i change filter, i will check for 1 pt. in 30 sec.[THANKS]. there were NO codes thrown.... except when i disconn. EGR plug. truck ran fine when unplugged. I bought new wires[MSD, and replaced cap/rotor]. they have been fine.... i ckd shaft when i changed cap... no slop obseved.... a new EGR is 156 bucks, so i don't wanna buy that.... i have cut out panel in my P/U bed, so i can change my fuel pump without taking down the tank.

[DofD]

Hi there and welcome to GM Trucks!

[knnhon]

Welcome aboard Have you replaced plugs, wires, etc?

 

 

I never thought of the 'Cats'!!!!! thanks, SHEEEZ... i have Doug Thorley Tri-Wye headers on and NO mufflers[what can i say?]... MSD 6AL box, MSD wires, Denso iridium plugs[from RockAuto]; all installed one year ago... NEVER had ANY trouble until this COLD snap here[i heard rumors that oil companies weren't refining gas as well as before the drop in prices[???].

Anyway, i always use the same BP station[10% Ethanol down here]. i didn't go 1 mile until, at steady speed [50+] with light throttle, there was ALL manner of popping, and back-firing! I had to go to Sebring[140 miles], and, at 75 miles, i filled up just to see [bP premium;at this particular station, they didn't haveta use ethanol]; but no change.

 

After race, it was still bad, but if i alternated my foot on,and off gas pedal, it was better.

Next day i started 'fiddlin'[DUMB]... found that if i pulled EGR harness from egr motor it cured problem, but, of course, the 'check eng' light came on. i checked for vacuum leak with spray from WD-40, but no idle speed up. so is it safe to assume that there are no vacuum leaks.[some use propane, to ck,but i'm 'chicken' to use that...]

 

I sure appreciate all the advice!!!; and U can bet, i'll be checkin' those 'Cats' tomorrow, thanks again!

[knnhon]

Welcome aboard Have you replaced plugs, wires, etc?

 

 

I never thought of the 'Cats'!!!!! thanks, SHEEEZ... i have Doug Thorley Tri-Wye headers on and NO mufflers[what can i say?]... MSD 6AL box, MSD wires, Denso iridium plugs[from RockAuto]; all installed one year ago... NEVER had ANY trouble until this COLD snap here[i heard rumors that oil companies weren't refining gas as well as before the drop in prices[???].

Anyway, i always use the same BP station[10% Ethanol down here]. i didn't go 1 mile until, at steady speed [50+] with light throttle, there was ALL manner of popping, and back-firing! I had to go to Sebring[140 miles], and, at 75 miles, i filled up just to see [bP premium;at this particular station, they didn't haveta use ethanol]; but no change.

 

After race, it was still bad, but if i alternated my foot on,and off gas pedal, it was better.

Next day i started 'fiddlin'[DUMB]... found that if i pulled EGR harness from egr motor it cured problem, but, of course, the 'check eng' light came on. i checked for vacuum leak with spray from WD-40, but no idle speed up. so is it safe to assume that there are no vacuum leaks.[some use propane, to ck,but i'm 'chicken' to use that...]

 

I sure appreciate all the advice!!!; and U can bet, i'll be checkin' those 'Cats' tomorrow, thanks again!

 

Well, i ckd 'Cats'-they were ok... the code was vacuum leak; i changed EGR valve, Evaporative Cannister module... everything is fine now... but i still wanna know why vacuum is only 17"? every engine i've built, ones with wild cams had that much.

BUT, i'm gonna track down why fuel pressure is only 40 psi... s/b 60 psi... filter might be culprit----it's under da truck for me!

[L29er]

like i said mine runs 18", buddy of mines with more miles runs 17" there probly isn`t any reason for concern.

[knnhon]

like i said mine runs 18", buddy of mines with more miles runs 17" there probly isn`t any reason for concern.

Thanks for the 'article' on whipple supercharger!!!!!!!!!!!!!! do they still offer that? i went to Stillen.com, but nothing on Whipples for GM older eng's... Magnacharger has one for the "LS series" of eng's[5.3-6.2]. they have one with a bottom intercooler that wouldn't be hard to adapt to lower half intake of '96-'99 B/B...

Changed filter today, no change....it still stumbles like crazy when starting cold, or hot, if ya let uit stand 2 minutes or more....then it's fine... gonna buy a Super chips tuner, and go from there... i checked fuel delivery i do get over a pint in a minute... need to test pressure before filter.

 

 

BUT.....HOW'S THAT RASCAL of yours runnin'!!!??? i'll go to your post and see

[L29er]

They no longer offer whipple setups for the GMT 400 trucks, stopped like 4-5 years ago or so, only luck is to get a good used one (like i did)

 

Yeah got the truck running today, no issues, other than i don`t have a throttle cable and couldn`t drive it!! OMG it broke my heart not to be able to go for a rip!!! Freakin goosbumps!