I have a 6.5 that some times stalls at low speeds. When i get it up to freeway speed it seems ok. It does buck sometimes at say 55 mph but if i let off the gas then it runs fine. I have replaced the fuel filter and the air filter. I pulled the codes down......but the service engine light has been on for 100,000 mileshttp://www.dieselplace.com/forum/smileys/Cry.gif and i got many codes. Seems like every possible code for the EGR plus some others. I even replaced the gas cap thinking it might not be venting. What should i do next? I can post all of the codes if neccesary. I hate to take it to the dealer.....I think they like selling pumps at 1500 a crack, and they don't seem to know these engines all that well. Thanks in advance for any help.

Pull the battery cables and reset the computer. Leave cables disconnected for 10 - 15 minutes. Then take it for a ride. When the SES light comes on, do the paperclip trick and pull the codes. Post back here with the code(s) and people will help you.

Hard to diagnose multiple faults, is it shutting down or just "fishbiting" a term I first encountered over at TDP, where when driving steady speed the truck starts bucking like a gasser truck missing, or jerk/tug you feel on end of a fishing pole when a fish first hitting the bait.


If fish biting is what you are feeling , I'd check into fuel lift pump function(pressure/flow/& OPS), the truck can run without lift pump IP will pull it's own fuel on moderate load, but task it to pull hard or accel fast with weak or non functional lift pump and it will stumble, also a partially blocked fuel filt will give same symptom. I pulled a bad load of fuel one time the "new" filt only 5K mi on it was partially blocked, I now have a frame mounted 20 mic filt to get the "chunks" out of the fuel before trapping all to the on engine 10 mic filt.


It's prior to the lift pump so I'm protecting the lift pump from trash/tank rust/water as well.


Reset codes use search feature for lift pump several posts how to check it also look for OPS then holler back & let us know what you find.

I reset the codes and took it for a little spin. As soon as I started the engine the ses light came on. When i got back i check the codes and get DTC35 my book chilton book says "injection pulse width error (responce time short)" what does this mean?

Oh it was running good today too.

Uh oh. That's not a nice code. Did you verify that the codes were erased before taking it for a spin? After clearing the codes by leaving the batteries disconnected for a while, before you start it up use the paperclip trick to check for codes. If all you get is a code 12, then you are starting with a clean slate. If you do get codes other than a 12, then you need to leave the battery disconnected longer.


Does it say "Diesel Only" on your gas cap?Edited by: w_huisman

The 20 other codes were cleared. I left the battery disconnected for 20 mins. I'm quite confident they were reset. Not a nice code??? or should that be $$$ ?

It did say diesel only but i replaced it the other day.

DO NOT USE ANY CAP OTHER THAN STRAIGHT FROM GM, AND MAKE SURE IT SAYS "DIESEL ONLY" ON IT. $6 from the dealer.


I can't tell you much from the code 36 alone. By itself, that code points at the IP or PMD. If other codes come up that point you towards some other problem, it's been my experience that fixing whatever causes the other codes can make the code 36 just go away.


So I guess if I were you, I'd drive it around some more as long as it's running well, and check for additional codes from time to time.Edited by: w_huisman

Its a code 35.

35...36... they're both "pulse width" codes. One's too long, one's too short. Both suck.

Ok thanks, I'll go get the other cap and drive the truck and check it for any more codes this after noon.

Is your truck an "S" EGR controled L56 or the "F" engine.
You're getting codes(32,33)for the EGR curcuit.
look on page 4-11 fig. 35 in your chilton's vs. fig 36.Edited by: quantum mechanic

Just got back from a drive to the neighboring town pulled down the error codes. I got a 32, 33, 35, 36, and a 78. And it was acting up again. Fish biting i guess i'd call it that. I did notice too that when its acting up it seems to smoke a little. The lift pump functions. Its a year old and i oppened the petcock the other day (checking for water or sediment) and it did not stall, and flowed real well and clean too. Think that EGR valve could be the problem? what's a 78 code, my chilton doesn't list that one?

Code 78 is the wastegate code. Check for leaks in vacuum lines that run from wastegate solenoid to wasetgate actuator by unhooking these lines at the solenoid, plug the end of the line with your finger, and try to move the actuator arm on the turbo. If the arm doesn't move then the black line is good. If it does, you'll hear a hissing sound that should lead you to the leak.


I think to check the orange (or red, I'm color blind), unhook the connection to the wastegate solenoid again, this time with truck running, and check for suction at the at the solenoid end of the line. If it creates noticeable suction on your finger tip, it's not leaking. If there's no suction then your vacuum pump isn't working. If you hear a hissing (highly doubt it over the sound of the motor), then there's a leak in the line.


If all the lines check out to be leak-free, then it's possible that the wastegate solenoid itself is shot. It's prone to failure and is very possibly part of your problems. $20 at the dealer will buy you a new one, and they only take 2 minutes to replace. It's located on the driver's side cylinder head close to the firewall.


If the problem is the vacuum pump not working (also a part that's prone to failure), then you have a decision to make. Replace pump for several hundred dollars, or remove pump and install a TurboMaster spring loaded wastegate controller.


I just went thru this myself. Ended up making my own wastegate controller, copying the TurboMaster design. Cost me $4. But then I also installed a boost gage to help me monitor the boost and correctly set my new home-made controller. You can buy the TurboMaster for about what I spent on building my own and buying/installing my boost gage, but this way I came out of it with a gage too.


Once you get this accomplished, reset the codes and take her for a ride again. One thing at a time....


I'm still a diesel newbie myself, so some of you other guys with more experience feel free to speak up or disagree if you feel the urge. You won't hurt my feelings any.


Man, I bored here at work today. Sometimes engineering just sucks.Edited by: w_huisman

Your EGR could be the problem. A DTC 35 refers to fuel solenoid driver module on the side of the injection pump. There is a Gm Bulletin for this code #77-63-06A. For a intermittent stall condition to replace the driver module. I don't know about the 78 code but it could be setting because of the driver module fault. Always look at lowest number codes first, looks like you might have mulitple problems.

Always look at lowest number codes first, looks like you might have mulitple problems.


Why do you say that? Is that just a common knowledge thing among auto mechanics?http://www.dieselplace.com/forum/smileys/Big Smile.gif


I don't know squat about the EGR systems cuz I don't have any EGR stuff on my truck. http://www.dieselplace.com/forum/smileys/Clap.gif

should I remove the EGR and vaccumm test it? to see if i need to replace it or would this be a suitable time to bypass the EGR?

well you have to to look at what causes the dtc to set and the condition for running the dtc's. Because if certain dtc sets it could possilbly cause another one to set and lead you to miss diagnosis.

Hmm. Learn something new everyday. What does DTC stand for? And are you saying that codes are tripped like a dominoe effect, from low to high?

Woah slow down too much too soon and we mis diagnose, shotgun trouble shooting not the way to go, also some of the codeds are sympathetic normally 1st out is the one to go with but not always.


You are certain fuel delivery to IP is good, fuel filter is clean, & no stalling when drain is open, Yes??


Air filt is clean Yes???


Looks from that many codes vac system is suspect start at the vac pump with a gauge how much vac do you have, then hand over hand rest of vac plumbing make sure we don't have any vac leaks or solenoid problems. As far as the EGR itself if you want remove it put a hose on the diphraghm draw a vac on it if plunger opens probably it's doing it's thing, it gives no feedback to the PCM , position of EGR is determined by EGR vac supplied vs EGR vent thru firewall baro sensor.


I suspect no vac from pump, EGR sol, EGR vent sol, or firewall baro/vent sensor. I 'm guessing as I haver no OBDI personal experience feel free to set me straight.


A IP is a high $$$ guess if we get it wrong, lets go to the normal mechanical stuff 1st then maybe TDG can give us some good troubleshooting to verify a problem in the IP or not

diagnostic trouble code.


yes some codes can trip like a dominoe effect.

...Looks from that many codes vac system is suspect start at the vac pump with a gauge how much vac do you have, then hand over hand rest of vac plumbing make sure we don't have any vac leaks or solenoid problems...


That's what I meant to say...http://www.dieselplace.com/forum/smileys/Clap.gif


...A IP is a high $$$ guess if we get it wrong, lets go to the normal mechanical stuff 1st then maybe TDG can give us some good troubleshooting to verify a problem in the IP or not.


Ditto...I wouldn't go getting a new car cuz I ran it out of gas either. http://www.dieselplace.com/forum/smileys/HiHi.gif

Fuel supply is good. air cleaner and fuel filter are new about a week ago ie less than 1000 miles or just over, due to a long freeway drive. Was gonna look at the vaccumm lines and play with them but its still pretty hot hate getting those burns on my arms.

Wus no pain no gainhttp://www.dieselplace.com/forum/smileys/Big Smile.gifhttp://www.dieselplace.com/forum/smileys/Big Smile.gifhttp://www.dieselplace.com/forum/smileys/Big Smile.gif a real Diesel guy would bristle up and tough it out, check it out let us know what you find when things cool off; of course I'm set back a little, a steam turbine guy ought to have pretty thick hide, that a little Diesel engine heat would not bother.Edited by: Turbine Doc

I just got done checking for vaccumm. I disconnected the vaccum line going to the wastegate solenoid at the actuator. The actuator moves and when i put my finger over the actuator it locks up pretty good. The line seems to have good vaccumm as well.... it sucks pretty hard on my finger tip. I think this part of the vaccumm system is functioning normally. What next??

I don't think thumb check is sufficient for our purposes, what I have been advising on is for a L56 or letter code S in 8th digit of VIN is that your configuration with 3 solenoids as I named above, you said you checked the WG act on turbo what about EGR valve under the intake cover, the vent sol and the firewall baro.


20-25" vac at pump is norm, 15+" at solenoid outlet as they start modulating, if one is venting /stuck it will pull down supplied vac I don't think finger tip check would catch that. Need to put a vac gage on it I think.

I just happenned to stop and pick up a vaccumm guage. Gonna check it in the morning. I'll let you all know what i find.

I found vaccumm to be 15 - 20 at the turbo and about 5 at the egr valve both at idle.

Thinking about blocking off the egr valve with a shim. Take it right out of the picture. Wouldn't hurt anything. It stalled again today, while driving slow intown.

any recommendations?

It's one or more of your three EGR solenoids..

for the diagnostic effort go ahead & blank off the EGR with a shim to see if driveability improves. 5 " at solenoid is low, try some WD-40 in the solenoid to try to revive them, in your solenoid bank replumb it to WG/turbo sol only put a tee in the line and read vac while driving if you don't have 15+ vac on that sol alone while modulating problem is with that sol, EGR codes will be active as they won't function, what we are trying to do is isolate which sol might be causing the problem. The blank off plate will eliminate dump of egr as the cause, & plumb to the WG/turbo only will eliminate that plus it is most common one to go bad.Edited by: Turbine Doc

well, it looks like the vacuum/EGR/Wastegate problems have been pretty much been covered. but as for your two unrelated codes (35/36), its not looking good for the home team I'm afraid. For some reason when anyone suspects a problem related to the fuel solenoid, they immediately point to the driver module. While the two pieces are closely related, they dont cause the same problems and a PMD is an expensive piece to misdiagnose. The PMD is nothing but an amplifier, it can cause a stalling/no start problem. A bad PMD will not set codes 35/36*. If your closure time is erratic (long/short) your fuel solenoid has become worn/scarred/broken internally and your pump needs to be rebuilt.


*- Just because I know someone on here is going to say something, let me clarify. A bad PMD CAN cause a long closure time if its output is weakened due to internal problems or the IPs wiring harness, but it CAN NOT cause long AND short CT condition. Long CT due to a 'weak PMD/harness' however, is highly unlikely and extremely rare and if it is the case you probably wont notice until it deteriorates to the point where you have a stalling problem or the PMD fails completely. Stanadyne has released a service bulletin on the wiring harnesses, and now if you buy a new PMD it comes with a new harness and heat dispersing pad for pump mounting.Edited by: Texas Diesel Guy

Sounds like a pricey trip to the chevy garage. thanks for all your help guys. Think i might take some advice from the sight to get a touch more power out of her..... maybe get the intake breathin better and out with the catalytic and muffler (I'm on a tight budget, but aren't we all?). Love the sight....