need some gearhead advise!!!

Hey guys... i got a mechanical issue, and i need some imput from some of the gear heads in here.

got a 97 3500, 454 vortec.

about a year and a half ago, i bought the truck in a sweet deal from a repo lot, drug it home, put a lot of work (and too much money in it), and now am just getting around to being able to drive it...

it actually wouldnt run when i first brought it home, but after a new iginition coil, it fired right up... idles strong, no clatters, good oil pressure, and sounds real good.

the problem is: when i drive down the road, the engine stumbles and falls flat on its face around 2500-3000 rpms..

anything above that seems to smooth out, and everything below those rpms seem ok.... however, the problem is that it trips some codes and the check engine light is constantly on..


first one is the camshaft position code.

it also throws a cranks position code.

ive already replaced the cam position sensor, and it changed nothing.

also replaced the fuel pump, filter, plugs etc still nothin....

also, we pulled the distribtor out, and the gear on the bottom of the disributor was pratically knife-edged. replaced it with another one from another vortec motor we had layin around. motor still has the same problems...

also... after driving it for a lil bit and killing it, it takes forever to start it again.. it just spins over again and again...

my mechanic has exhausted all ideas, short of tearing into the motor to look for internal problems like a main bearing.

any suggesstions?

sorry to hear your having issues man. well, im by all means not a master tech mechanic but ill throw out my opinion. could it be your computer all outta whack ? ecu/ ecm , that sorta thing. im sure that didnt help ya man haha my bad. i tried. well, im sure you will get some great advice/pointers from richard aka someotherguy. he knows his shit. good luck man

thabks big bear. the computer issue has definitley not been ruled out yet, but like you, im hopin richard will pop in here and share his words of wisdom.

Are your cats plugged? On my 2000, I had one that the insides broke apart and actually plugged off the outlet and made it run like snot and threw some weird codes. Just a shot in the dark, but ya never know.

Are these the only codes it is throwing? And can you give me the code numbers. I can put this on my tech line and see what I can come up with.

Brian

The hard restarts when warm is almost always leaking injectors / bad fuel pressure regulator. Very common problems on the Vortec 7.4's. There's some discussion here about upgrading to some Bosch injectors that are a better design. Best to replace the regulator while you're in there too. You'll be laying out nearly $400 in parts once you include the plenum and throttle body gaskets and crap but hey, ya want it to run right, yeah?

Should have replaced the distributor gear with a brand new one, melonized (anyway that's GM's name for their hardening process), the roller cam in the Vortec engines requires a hardened distributor gear or it will eat it up as you saw - there were some improperly treated gears used by the factory for several years.

The top bushing in the distributor may be toast, too; take the cap off and try moving the rotor from side to side, also twist it a little bit and try again, fiddle around with it a bit and see if you can make it move side to side. If so then the distributor is toast. Buy a new one. Some have bought the Cardone brand "new" distributor for around $125-$150 but others say it's complete garbage; it's hard to know what brand to buy anymore. Richporter Technologies sounds fancy and all but it's also cheap chinese garbage just like the Cardone.

Setting the distributor correctly in the Vortec engine requires (I'll say it again before anyone argues, REQUIRES) you to have a scan tool that can read the cam retard number. Since you had yours out it may already be set incorrectly. Even when the distributor is reinstalled using 2 marks (body and rotor position) you still need to fine-tune the cam retard with the scanner; hold RPM's at least 1,000 and adjust distributor until you get within 2 degrees +/- of zero for the cam retard.

The crank sensor sometimes needs to be shimmed due to main bearing wear. If your old crank sensor looks like the crank has been kissing it, you need to shim the new one. Your new one may have come with a couple of very thin washers; the last one I did gave a combined spacing of about .030" with both washers, which if I recall is the suggested air gap. Since mine had very slight rub marks on it, I went with both washers and hoped for the best.

I won't lie to you, these f'ing Vortec engines can be a PITA to get them running right again once they start messing up.

Richard

New Bosch injectors and FPR in place on the fuel rail


In place on the intake


Those are Comp Caps roller tip rockers used with conversion studs to make them adjustable, btw. Kind of a mixed bag and takes some dicking around to get that setup right, but if your old nonadjustables are way worn, it's an option.

Richard

guys...thanks a bunch for the quick repsonses.

richard... the leaky injectors is something i've suspected. definitely gonna look into that...

i guess i also better pony up the cash for the new distributor, since i dont really know the history of the one that we replaced the original with.

i'll keep yall posted, so in the event somebody else has the same issues they can have some more insight.

thanks again!

good luck man...

hey guys.

just an update..

finally made some progress on this hoopty of a truck... took richard's advice, and replaced some leaky injectors causing a hard-start issue. he was right on the money there. thanks man!

also tried some of yalls other suggestions. borrowed a ECU from an identical truck to see of was the computer, and no luck. ran new wires from the ecu to crank position sensor, and found no difference.

on a whim, we pulled out the crank position sensor out, and noticed that the bracket that holds the sensor was tweaked juuussssst a little bit; straightened it out with some pliars, and put it back in, and damned if it didnt alter the problem! it moved the RPM fluctuations from 25-3000 revs to around 4-4500! it aint fixed yet, but i think we've nailed the problem down to a specific area.

the theory is: whoever was in this engine before i got ahold of it must've pulled the reluctor ring off the crank, and didnt replace it with a new one.
(according to Mitchell, whenever you remove one, you MUST replace it)

long story short, i think the sensor is getting an erratic signal from the reluctor ring, because the reluctor ring may be tweaked just a bit, causing the wild RPMs in a certain range...

solution: replace the reluctor ring, and go from there.

i'll get on here and rant and rave if/when this works.

just wanted to share with yall, either way, in case someone else runs into this scenario in the future....