hello everyone.i'm new to the diesel place.i could use some help..i have a 1994 gmc 3500hd tow truck(car carrier)with the 6.5 turbo..i just installed a k&n filter and am still looking for more add ons to get a little more pulling power..i also dont want to spend too much money..and now i'm having trouble with the engine.runs kinda rough,if i have been sitting at idle for a few minutes then start to drive the motor bucks like crazy...stops after i let off the pedal for a few seconds then runs ok after that..sometimes it stalls after start up and is hard to get started again..fuel milege could be better too.also the oil pressure is pretty low.dont know how many kilometers(im in canada)are on the motor..got it used about a year ago..if anyone could give me some help with the problems i have listed i would be greatful...thanks.

Lack of power? start by checking for vac at the WG(waste gate). If you have vac, look for leaks in the vac lines(tipical senerio). Unplug the WG solenoid and see if it bleeds vac(it shouldn't).make sure the vac line to the WG is coming off the rear most side of the solenoid. Does your lift pump come on when you start the truck? lack of fuel pressure at the IP will make it studder and stall. When everything is running right this truck doesn't stall or hesitate, but when I got my '94 L65 it had the same problems you describe. I encorage you to read more posts that are already here, as this topic is recurent.Edited by: quantum mechanic

thanks...ill check that..after i figure out whats going on with the way it runs do you have any suggestions on what i can or should add to get a little more pulling power???

Towman,


Look into a larger (3" to 3-1/2") straight through exhaust system that comes with the large crossover pipe. It'll add some power, and keep the turbo cooler. Kennedy Diesel http://www.kennedydiesel.com/ in Wisconsin sells fitted systems and has a good rep for service.


I've started to see some rust on the tailpipe and am considering it for my '93.

King;


You have gotten some good advice so far, I'll just thow my .02 in.


Intake work, filter, airbox ect, and exhaust the down pipe replacement is a MUST. Gages and chip and if you want to solve boost problems for now and the future get a manual boost controller. Also if you have over 100,000 mile on the injectors you maybe do a change.

First lets find out why the truck is not running well. You say you think the oil pressure is low. If it is low you may be switching the fuel pump on and off and causing the ruff running at idle and hard restarts.


Tap into the gray wire coming off the oil pressure switch and feed either an analog volt meter or small light bulb the you can monitor in the cab. If the light ever goes out, or flickers while driving or the volt meter drops your oil pressure is too low to maintain power to the fuel pump and the pump is shutting down.Edited by: HowieE

thanks guys..i started checking for vac leaks but havent found anything yet but ill keep looking..ill be ordering a set of downpipes as soon as i get a chance..and HowieE its funny you should mention the oil presure switch...i was just starting to notice that the truck did run a little better when the presure was higher and ran more like crap while it was lower..gonna try the volt meter thing first thing in the morning..ill let you know how it goes..what could be causing the low pressure?.could it be a sensor or a switch?? i really hope the motor isnt worn out.cant afford to have the truck parked until i have the motor redone or while i try to find a decent used one put in..oh well wish me luck..lol.thanks again..

Right Howie lets get to the bottom of the problem first. Towman you should also pull the codes to see if you get any help there. Take a paper clip under the steering colum under the dash there is a plug in for a code reader if you jump between the first two upper holes with a parer clip key on NO start you will get flashes on the SES light one flash and then 2 is code 12 which is default everything okay. If you have others it will flash two sets off numbers like 3 5 three times and move to the next at the end it will start with your first code again. To clear codes key off step on brake and Full on gas peddle then turn key it will cycle throught the codes again but when you shut down and and do it again they will be cleared.


What grade oil are you running?Edited by: 16gaSxS

The OPS is doomed in the current configuration. The lift pump draws 4 amps and the OPS is rated for 1 amp. HowieE told me how to bypass it with a relay, and it's been a good fix.


Don't be surprised to see web casting in the intake snorkel, and a little plastic tube that restricts air in the fenderwell. if you see oil around your turbo, upper intake or the six bolts on top of it, your loosing boost in these areas. Gaskets and gasket sealer do the trick, I seal the torbo intake housing to the centersection also.


http://www.dieselplace.com/forum/uploads/218_exhaust2.jpg


This is my Idea of an exhaust system. costs about $200, and sounds great, lots of whine and roar. I really enjoy the boost control I made. It really improves bottom end torque.Edited by: quantum mechanic

so i checked for any codes and all was normal.but today for some reason my oil pressure was better.but the engine seemed to be holding back.just felt very lazy.not alot of bucking either..i'm still going to hook up a volt meter to my pressure switch to see what happens.right now i'm using 15/40 oil.i was thinking of going to something thicker or even full synthetic.just want to check the pros and cons first..Quantum mechanic,the hose in the fender and the web casting in the snorkel.should i check if these are clogged or modify them to take in more air??..when i installed the k&n filter i noticed some oil in the rubber tube between the filter and the turbo.ill take a closer look for any oil in the places you mentioned.i'm gonna order all of the down pipes soon and have the rest custom built..i havent seen any kits for my type of truck to accomidate my long wheelbase..if i do upgrade my exhaust system is it going to be much louder??..guy from other towing companies around here keep telling me to sell my truck and buy a ford.i like my heavy chevy and i have put too much time and money to give up on the old girl now..i hope all she needs are some minor adjustments and a good kick in the butt..

The web castings in the snorkel have to be cut out(if you have them) and the plastic tube in the fenderwell can be pulled out with a little work. When I refer to sealing the rest of the intake, I'm talking about the aluminum housing on the turbo, between the upper intake(snorkel) and the lower intake(spiderhttp://www.dieselplace.com/forum/uploads/5EB_96l65.jpg The upper intake on the lower.


Yes, a straight pipe with no muffler is louder, but I personally like the sound. I bought a 3" down pipe for a '93 6.5(no catalytic flange) and then went to the local muffler shop, bought a joint of 3" stock, had it expanded at one end to slip over the down pipe, and a 15 deg. bend in the other end. the downpipe was $180, and the rest was $25. do you have a manny tranny or auto? Edited by: quantum mechanic

Towman;


Hmmm I'm not sure if this works on the 6.5, some engines have a pressure relief valve that can be accessed. Sometimes the spring gets weak and allows oil pressure to fall off. If the 6.5 has such a thing or even if it's accessable you maybe able to change the spring. I have never been that far into one of these engines. Just a thunk.


Edited by: 16gaSxS

the Crankcase pressure relief valve (cprv) is the brass colored can that has the plastic line coming off it to the front of the turbo.

quantum..i have a manual tranny.low +4..i havent had time to do more checking on the problems ive been having..i now have a wiring situation under the bed someplace..now i get to lay under the truck and fish through the big mess of wires to find the problem..oh yeahh.fun fun fun...lol..it was running pretty good today though..

hey quantum..if i unplug the w/g solenoid how do i know if it leaks vac or not??..if any of my vac lines are leaking will i hear any sounds???..and do i really have to remove the intake in order to remove the fsd??i have an extra one sitting here and i was thinking of plugging it in to see if she runs any better..i think i have an extra pump too..

www.dieselplace.com/forum/forum_posts.asp?TID=3808&PN=1 (http://www.dieselplace.com/forum/forum_posts.asp?TID=3808&PN=1)


This previous post shows the Repair manuel's WG procedure. I start with the vac line to the WG. Pull it out of the WG with the truck running and see if it has vac by feeling it with the back of your hand. It should pull enough vac to suck your skin a little. now unplug the wire connector to the solenoid, and all vac should stop. if both of these things don't happen, there's a problem. I've had this solenoid pass both of these tests, not give the code 78 WG fault and still be faulty, so that's not set in stone.


When ever I see black exhaust, the vac lines and solenoid are where i look. you might want to completely remove the vac lines and blow through them, or make your own vac(with your mouth), to see if they leak. also check to make sure they plug in tight to their rubber fittings as these can leak too. the WG solenoid is a $30 part unless you get dicsounts( I ask for them Like I'm supposed to get them). and with two trucks to put them on, I have spares, just in case.


you should also be able to feel a strong vac with the other line disconnected from the solenoid(going to the vac pump) or else you might need to get a new vacpump.


Also, I don't think the chip helps the manny tranny as much as the auto, because your controlling the shift points. their are other benifeits, but is it worth th $300 to get a new chip. I would think the programming in your HD3500 would be sufficient once you open the restrictions up.


I was driving behind my dad's truck yesterday with the windows down and it didn't seem as loud. All i could hear was the turbo as he accelerated away.


Did you read my DIY boost control post? I have enjoyed having this modification and I encourage you to make your own.


I like removing the intake at least once. It's not that hard, just be careful what goes into the block when you have it off. I like to wire brush all mating surfaces(on the lower intake and heads) port and polish the intake runners and the "bowl" of the lower area. and this is a great time to look for the cast web in the upper intake(snorkel).Final step is a fresh gasket and a thin coat of rv sealer. Edited by: quantum mechanic

Open the water drain valve with engine idling - lift pump will force fuel\water out.


No drain, lift pump is not functional - close immediately to prevent inj pump evacuating fuel filter, drawing air.


Lift pump operation can be checked on ALDL pin G - Pin A is ground.


If OPS is functional at idle, DVM should read steady battery voltage. Test light should not flicker.


Air filter has been replaced - what about fuel filter?


Plugged fuel filter will give same symptoms as non-functional lift pump - low power, bucking, rough running.


Measured vacuum at wastegate should be 15" at idle.


Measured vacuum at pump should be greater than 20" at idle, usually around 24-26".

here is the upper intake(snorkel) with zero web casting.


http://www.dieselplace.com/forum/uploads/B44_96intake2.jpg

This is the restriction behind the airbox.


http://www.dieselplace.com/forum/uploads/DFZ_restrict.jpg


There's a 1/4 in. screw behind the battery holding it in place.


It's not easy to get it started, but it does come out.








http://www.dieselplace.com/forum/uploads/EAE_restrict2.jpg Que Restriction!

http://www.dieselplace.com/forum/uploads/317_downpipes.jpg


Look at the difference between the factory exhaust and a 3" down pipe and enough length to get past the cab.


http://www.dieselplace.com/forum/uploads/938_exhausts.jpg


The downpipe is evidence that GM stands for goofy and mickey, because they goofed and mickey moused us on this one. I couldn't see daylight through the catalytic and over all, it was twice as long and ten times bent. I wouldn't feel right about the stock exhaust being on my truck.


Edited by: quantum mechanic