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Stumble/Surge

Bernie

Bernie

Amateur Radio Operator - KJ4VOV
Messages
303
Reaction score
12
Location
Fredericksburg, VA
For the past month or two my 1999 GMC C3500 has had me thinking I was going to be rebuilding the diff soon. The typical scenario was, at first, driving at low speed, make a turn and it would "buck" a little. Not every time, more like just once every few days. I started trying to save some money at that point, figuring if I had to rebuild the diff I'd stick a Detroit Locker in it but, with the holidays getting closer, I haven't made much progress with that.

Then it seemed to get "better", and I didn't have a problem at all for a few weeks. (Figured I dodged a bullet there, and had a little more time to save some cash before the diff went)

Then, Monday, it did it again, HARD, almost like someone bumped me. Except the truck wasn't being driven. It was parked and idling in my driveway. Then it happened again, and the next day it did it again. Then it started happening at stop lights, with the truck very briefly "surging" against the brakes.

I'm thinking the problem is a leaky injector, but I'm not sure. It could also be a bad throttle I suppose.

History of the truck:

1999 GMC C3500, 6.5TD, 4L80E

The truck was a service truck from a county down in Florida, and seems to have spent most of its life parked in the garage. When I bought it in '08 it barely had 68K on the clock. Looking back over its service history though, I see the IP was replaced twice, at around 28K, and a history of fuel and/or fuel delivery issues. Since I've owned it I have had some issues, and replaced the PMD (with a remote unit) at 75K, the starter right after that, mater cylinder in '09, and the hydroboost this past spring. Currently the truck has just shy of 95K on it. I regularly use either PS or Howe's at every fillup, the fuel filter was changed last fall, and this current problem has been happening through at least four fillups from two different stations.

Also, from day one since I've owned it the truck would sometimes "surge" a little in reverse. Typically the way it happens is when I'm coming home and trying to back up my driveway (driveway has a 30 degree slope). I'll turn in to my neighbor's driveway across the street at an angle, put the truck in reverse, cut the wheels and start backing up mine, slowly. Just as the back starts to climb the hill the engine will surge a little, as if I lightly tapped the accelerator. This will typically happen once or twice a month.

So, any thoughts on this? Throttle? Injectors? IP? Any help at all will be appreciated.
 
I think what you are describing could be called fishbiting. Various causes, air in lines, clogged filters/pickup in tank,pmd and or the connector.
 
Check the fuel delivery out, that could be your problem on the slopes. Maybe you have air in the system. I don't know about the diff. problems, maybe an inspection is due.
 
NVW said:
Check the fuel delivery out, that could be your problem on the slopes. Maybe you have air in the system. I don't know about the diff. problems, maybe an inspection is due.
Click to expand...

I think the diff "problem" wasn't a diff problem at all, just the first signs of the current problem, which seems fuel related. I'm inclined (excuse the pun) to rule out the driveway slope as a contributing factor, simply because I never let either tank get below 1/2 full, precisely for that same reason, to prevent problems with fuel not being at the pickup due to the slope.

I think I'll start with a filter replacement and go from there, since I'll be bleeding air from the system after that anyway. I'll report back on how that works out.
 
Put a piece of clear tubing on the return line coming out of the IP. This will let you see any air in the system. You can leave it on and have it there for future use
 
Didn't get a chance to change the filter yet but things got a little weird on me today. Drove about 40 miles with a trailer to pick up something at a friends place. Truck ran fine all the way there, no problems at all. Stayed and talked for about an hour, got back in the truck, started up and went to leave and it was as if my throttle would suddenly go wide open, then just as suddenly seem like there was no power at all. Any touch of the accelerator seemed to instantly cause WOT, with more power than I've ever felt with that truck, then either drop to the point where it felt about to stall, or just back to normal. Trying to maintain 45mph proved impossible for the first 10 miles. It would either not have enough power to get over 40, or try to take off like a 9,500lb dragster. Then, after about 10 miles it just settled down to "normal", though it felt a bit weak, as if it didn't quite have the power it usually does.

Now, to find a filter... The NAPA around the corner closed last year and the only other place close is in a huge shopping mall that's packed today.
 
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Starting to smell a lot like PMD to me... that sudden surge and throttle issue is a characteristic symptom, usually after a period of fishbiting.

Do you have a scanner? Can you check for hidden history codes?
 
JiFaire said:
Starting to smell a lot like PMD to me... that sudden surge and throttle issue is a characteristic symptom, usually after a period of fishbiting.

Do you have a scanner? Can you check for hidden history codes?
Click to expand...

No scanner, and the PMD was changed out for a new remote mount almost exactly 20,000 miles ago. I do remember what it felt like when the old PMD died though, and this is distinctly different. I just ran out to get a fuel filter and air filter and, on the way to the store, coming to a red light the engine surged for about 2 seconds, hitting 3,500 rpm as I was braking from about 45 mph. It made stopping a tad difficult. And no, my foot was off the throttle and the throttle was not hung up on anything.

Right now, sitting in the driveway after changing the air filter (which needed it) I was getting very brief (1/2 second or less) surges at idle with no one in the truck.

I'll go check the links Turbine Doc gave and do a little reading.
 
Based on the episodes of WOT I've been getting I'm starting to suspect a bad TPS, or a problem with the wiring to it. I just ordered a new TPS, and I'll spend some time tomorrow carefully checking the wiring and connections for any damage.
 
Forget my last... I'm an idiot. :rolleyes5:

After a bit of online research I'm going to have to agree with JiFaire... failing PMD. Even though this PMD is a pretty new SSD-006 from SSDiesel Supply (installed in January of last year and now has 20,000 miles on it) the symptoms are pointing towards either the PMD or the fuel solenoid on the IP Since the SSD-006 has a two year warranty I'll be contacting SSDiesel tomorrow to see what their tech support folks think, and to file a warranty claim if they agree with me.
 
I'll 99% say its the PMD especialy if its a older flight systems. I had actually quit selling them until that problem was fixed and it is now, but they had a run of them that would do exactly what yours is doing.
If you can't find the newest release PMD let me know I am stocking them. Also have the Stanadyne PMD they have been very good.
 
ak diesel driver said:
good luck with that he'll probably try to weasel out of that as per my exp
Click to expand...

How right you are... :mad2:

I'm being told it had a one year warranty, not two year (despite it saying two years on the web site) and that I probably caused the failure (if there is a failure - which they won't admit to) by not retorquing the screws holding it to their heat sink, as per their instructions, even though that's not even mentioned in the instructions that came with it, and even though I specifically bought the pre-mounted kit so I wouldn't have to worry about getting the initial torque right.

Sheesh... When I purchased the unit I thought I was dealing with a reputable company. Judging from your comment they have a reputation all right, but that does not equal "reputable". Guess what company I won't be dealing with again...
 
It's black (of course)... And good old Walt at SSDiesel just chewed me a new one via email because I didn't retorque the screws as I supposedly should have. I don't recall that being in the instructions shipped with the unit, and the instructions he sent with his email aren't specific about when the screws should be retorqued. All it says is "periodically" after the first 3,000mi He goes on to claim that it's not the "grade 8 stainless steel screws" (stainless uses a different grading scale AFAIK) loosening, it's the screw heads sinking into the plastic of the module that causes the loosening, so a thread lock compound is useless. Well duh... how about using a washer under the screw head then, so the heads don't do that?

Bottom line, I'm done with SSDiesel Supply from here on out. There are other companies out there who don't (quite literally in this case) screw their customers this way.
 
I dont know what his warranty is, but the FS PMD is one year from the factory. If you have it in writing he said two years then you "might" have a case with your credit card co (its a long shot).

Let me know if I can help with a new one.
 
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