98 3500HD 6.5 auto stumbling under load

[Coghlin]

I just picked up a 98 3500HD (15000lb gvw) with a 6.5, auto, dana 4.63 rearend chassis cab. I have owned a '97 and an '03 gm diesel so I am pretty familiar around diesels. I currently own an '06 Duramax but wanted a good work truck to take some pressure off the Duramax.

My first question is why does it have a GM-4 turbo. Someone replaced it with that or could have it came with that from the factory? The motor has been replaced but I checked the casting and it is a 97 and later block.

Second question is more involved.



Problem: Stumbles on mild to hard acceleration, it seems mostly between 2100 and 2400rpm, no significant smoke, seems like it is running out of fuel.

Demographics: -10 to -20 *C, clear and mostly flat highway driving

- Year: 1998
- Truck model and class (ie: c2500) C3500 HD (15,000 GVW)
- Automatic
- Mileage: 452,000kms
- Replaced parts and mods: OPS, starter, vacuum pump, motor apporx 200,000kms ago, no mods, mostly stock.
- What fuel are you using? (#1 Diesel,)
- What fuel additives are you using? Added a winter additive recently in case it was water causing the problem
- Where are you located? Ontario, Canada

General maintenance: inspect and evaluate the condition of each. When were they last changed?
- Air filter - relatively new
- Fuel filter - just changed
- CDR Valve? - don't know when changed last
- Coolant – last flushed/replaced at - no idea
- Oil – synthetic/regular, changed at - no idea
- Batteries – state of charge, (matched set) replaced at - recently
- Glow Plugs - how many miles on them? don't know but look newer
- Injectors - last changed at - no idea but have been changed at some point
- no codes

Diagnostics:
2] Fuel Issues (if not running):
2a] Can you hear your lift pump working? Yes
2b] Do you get a steady flow of fuel from the water drain (T-handle) ? I live in Canada and it is salted and seized
2c] Loosen the inlet line from the IP – is fuel coming out (Lift Pump on)? Yes
2d] Loosen an injector line and crank the engine - does fuel come out? Yes
2e] Do you hear a vacuum (hiss) when you remove the fuel cap? No

3] PMD / IP Issues
3a] Location of PMD (on pump, on intake, remote mounted) on pump
3b] Condition of Extension harness (if used) Vendor or Homemade? None
3c] Condition of grounds / ground wires to IP / PMD. Check Harness. - not checked
3d] PMD Make: Stock
3e] PMD Age: Unknown

4] Stalling Issues
4a] Do you experience stalling only when hot? No
4b] Does it stall under particular circumstances? (ie hit bump, or on accel) Everything is a bump with this truck. Very rough ride. Under acceleration it stalls but never quits.
4c] Does pouring cool water over the IP seem to help with restarting? Re-starts are not a problem
4d] Is stalling momentary (engine recovers)? Yes
4e] Does SES light come on when engine hiccups? No
4f] Does cruise control quit working when engine hiccups? No
4g] Does re-starting seem to reset engine, restoring cruise and power? Doesn't usually completely quit.
4h] Changes to dash lights or instruments during stalling events? None

List and describe any other factors which are not addressed in this checklist. We can’t see, hear, smell, or touch your truck, so the more descriptive information you can give, the more likely it is that somebody can assist you.

I changed the OPS (figured it was a cheap part and relatively easy to replace in case it was an intermittent failure) but the new one I got had three terminals inside the connector where the old one only had one. Now the gauge reads way too high. Anyone know what this sensor I got is. Must be the wrong one. The fuel filter housing was in rough shape. When I changed the filter I noticed the original was leaking. It had started to come apart and was installed incorrectly (not seated). I solved that. Then when changing the OPS I noticed the lines on the bottom of the filter were leaking. Fixed that. I test lighted the pump and you can feel it running and sometimes hear it. Could it be quitting while driving and the truck is starving for more fuel? I don't have a gauge to hook up for fuel pressure while driving. It could be a PMD issue but I doubt it due to it being so cold here. I know I got to get the right OPS but this one at least works for sure as the pump is running. This truck is rather violent to drive unloaded. The suspension is very hard. I have been keeping the tank relatively full to avoid and air in the fuel lines and I added some winter fuel additive in case their was water or gelling issues. The truck was bought from a guy that purchased the truck only 6 months ago and lost interest in his project. He has put a few new parts on the truck but was unfamiliar with diesels and prefers his 383 stroker. He was familiar with the truck's history as his friend did the servicing on it since new. The motor was replaced a while ago but I am unsure why it has a GM-4 turbo and not a GM-8.

I know I should do the PMD harness and heat sink. I will also likely add a relay to the OPS circuit. I am also pretty sure it will be getting the A-team turbo as I need all the pulling power and reliability as it will be pulling my 15,000lb gooseneck daily. But right now I want it to run correctly before upgrading and fixing all the little gremlins. Is it possible the lift pump is too weak to supply enough fuel? It mostly stumbles when climbing a hill. I haven't had it on the trailer yet as it just a 10 day permit to get it safetied and e-tested.

Thanks in advance and sorry for the long post but I wanted as many details as possible as it doesn't seem to be a straightforward lift pump issue. Also I really like this site. I have been a member of the other boards for almost 10 years now and I am annoyed with their attitudes lately. This site is much nicer.

 

[buddy]

Edit: WELCOME! Youre in the right place and it seems you have already done a good amount of educating yourself.

Its probably your wastegate vacuum solenoid, operating your crappy GM-4 turbo, man that was dumb, and the PO's buddy he bought it from must have been a fool.

Could also be an air leak into the fuel. With all the fuel leaks you mentions I'd be raplacing every hose you can find, including the one that goes to the IP and the one to the t-valve drain. Check all the metal lines by the tank and make sure LP connections are tight, and they have an O-ring on them.

If the PMD was fried ever before if could be faulty even when cold. I'd get a remote kit with new Dtech type PMD right away anyway.

If you keep the fuel tank full youll have little to no vacuum hiss when you open it. Is your fuel cap for diesels, says diesel on it?

 

[Turbine Doc]

Before jumping through hoops looking for air leaks, could be that, but you need to do full lift pump diagnostics http://dieseltowingresource.com/showthread.php?t=6872 as a pump can purr and still not deliver fuel to volume required, as for your valve rusted shut, any valve capable of 20 psi can be used to replace it max you'll see will be about 6 psi with a GM lift pump anyway, for reading pressure you can disconnect the inlet to the valve and put a test gauge there, you should be able to remove and repair that valve, not much to it.

 

[Coghlin]

I doubt the wastegate solenoid as it doesn't really smoke when stumbling. I can also hear the turbo whistling. Pissed off about the GM-4 find but at least the block is a newer one. I believe it was actually a GM crate motor as the valve cover says "New 6.5" with the GM Logo.

I also suspect some type of air leak or electrical connection. But I think I have cured the air leaks so now I am not sure. I went through the harnesses. They are a bit rough. I cleaned up some connections. I may also order a fuel pressure gauge as that would also tell me for sure if the fuel supply was lacking.

I am going to have to spend the money and get a new PMD I think.

I think I will also replace the fuel tank cap as it looks a bit suspicious as well. It doesn't click very well and looks pretty beat.

THanks for the reply and I will keep troubleshooting. Damn cold here though -25*C this morning.

 

[packratt]

For fuel presure it doesn't need to be fancy or permanent. Something like this will work.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93547

You can even extend the line and tape to your windshield wiper to do a road test.

 

[Coghlin]

Thanks TD. I didn't know about the lift pump sock in the tank. WIth almost 500,000kms and an original tank I think that should be investigated. Truck is very heavy duty so it only gets about 10mpg. Thats a lot of fuel going through that sock. I suppose the dealer is the only place to get a new one. I am pretty sure it is a fuel supply issue so I will get a gauge today to help troubleshooting. If I replace the fuel pump it will be a Walbro as this truck will be upgraded in power someday. Or maybe do as you have done with a duel pump switchable. Do you have a check valve to ensure no back flow through the non-running pump?

 

[Turbine Doc]

Check is built into the OEM pump, originally thought I mite need an additional one, but since Walbro is same op pressure as the GM decided to run without, so far so good. I run the Walbro as the primary on mine all time, if IP is sucking it won't have chance to backflow, also way my setup is installed even if possible to backflow it just goes back to suction side of the OEM pump. Presure taking path of least resistance, ie suction of the IP, backflow should be a low probability event.

 

[Turbine Doc]

For fuel presure it doesn't need to be fancy or permanent. Something like this will work.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93547

You can even extend the line and tape to your windshield wiper to do a road test.

No get really long line and bring it inside the cab, did the tape thing once, and it came loose at highway go fast speed, , beat the crap outta the truck until I got it slowed down, thought I was gonna crack the windshield.

 

[Coghlin]

Update. The fuel filler neck had a crack and leak and also had a gas cap not a diesel. Now I get a woosh when opening the cap. Truck is also running much better. Pulled the trailer for the first time last night (15k gooseneck - probably grossing combo at 15-16k). I think the system could not purge itself of air. It always ran worse when cold (fuel thicker). Although it still doesn't run perfect, probably had some damage done to the injection pump. Talked to the previous guy and he could never get it running correctly and that is why he got rid of it. He had spent quite a bit of money on new parts (brand new B&W turnover ball, brake controller, starter, batteries, glow plugs, vacuum pump, harmonic balancer) and I couldn't figure out why he was getting rid of it(he only owned it for 6 months). I assumed it had a problem. A lot of fuel leaks though. He is going to be pissed when I tell him it cost me about $50 to fix.

 

[Coghlin]

Update. Running bad this morning. Put a fuel pressure gauge on teed into the inlet on the injection pump and it reads 7.5psi and doesn't drop below 4 psi. When the engine stutters the pressure goes up so the problem is likely the PMD. That will be my next step.

 

[buddy]

Getting the remote setup is a must anyway. Did you check all the lines from the tank to the filter assembly? Making sure LP fittings are tight.

It sounds like you dont have much of a demand on the lift pump, or you have a really good lift pump.

No codes?

 

[ak diesel driver]

Haven't seen any mention of a new pmd yet. Still could be that.

 

[Coghlin]

PMD is next but it will take a week to get it. Unless I can find someone local that doesn't want to rip me off. Might hot wire the fuel shutoff solenoid on the injection pump in the meantime in case that might be an issue. It just cuts out, no smoke nothing and fires back up or doesn't completely die and goes again. I have gone through the harness, cleaned some grounds and connectors but haven't found anything real significant. I have eliminated everything I can think of so I guess it's time for a PMD. Should do it anyhow. Got the pump number 5521.

 

[Turbine Doc]

PMD is next but it will take a week to get it. . Might hot wire the fuel shutoff solenoid on the injection pump in the meantime in case that might be an issue. It just cuts out, no smoke nothing and fires back up or doesn't completely die and goes again. I have gone through the harness, cleaned some grounds and connectors but haven't found anything real significant. I have eliminated everything I can think of so I guess it's time for a PMD. Should do it anyhow. Got the pump number 5521.

No need to hot wire the the shutoff, they either work or don't, You are seeing classic PMD death warning signs & is most likely candidate form troubleshooting done thus far, but very well could be ignition switch, what gnds did you clean OPS or lift will not cause complete shutdown of engine, stumble at power yes, but your lift checks have pretty much ruled that out. Cracked filler neck and wrong cap will not cause shutdown.

 

[Coghlin]

Update. Truck is dead. I understand that all the things found do not make it stall or quit they just don't help. Found that the lift pump was also faulty. It was not always working so it has been replaced now as well. The new OPS switch I had bought did not work and it was replaced. New one works now. But after doing all this now the truck won't start at all. I cracked an injector line and no fuel there. The fuel system is all leak free with a pump that doesn't work intermittently but now I think the PMD has totally died. Problem is I am 200kms from home with my trailer and I don't know of any retailer in Ontario that would have an extension cable and to change the PMD on the pump involves removing the intake.

 

[Sunshine]

Problem is I am 200kms from home with my trailer and I don't know of any retailer in Ontario that would have an extension cable and to change the PMD on the pump involves removing the intake.

I have removed the PMD with out removing the intake I tried to see if it was possible after I put the new one on from Heath Diesel...

You file down a 3mm Allen Key to about 1- 2mm at the smallest end tape a long piece of string or fishing line from the middle to the end so as you don't loss it down in the Valley..

As your far from home maybe this not much help..

Sorry to hear about this...Good Luck...

 

[buddy]

You dont need an extension cable if you mount the PMD on any heatsink relatively close to the IP. I have a spare that I plug in about 6 inches from the intake, that I just put a flattened L brackets from the intake bolts over to the heatsink. That would get you home no problem. Just cut and extend the ground wire and run it back to the IP.

Although I have had that condition and the PMD didnt fix it, it took an IP replacement.

Did you try unplugging the Optical Sensor and seeing if it would fire up in limp mode?

 

[Coghlin]

Just some more information from an injection shop I called. They said you can test the output of the PMD. I took the harness from the PMD to the pressure side of the pump and tapped into the two wires. Put your meter on AC and you should see 1.5 to 3.0 V on the output when cranking. Mine read zero. Didn't even blink. I am going to get a Dipaco PMD, extension harness and heatsink. I am thinking of locating it in the fender where the snorkel for the air intake was or grille/bumper like everyone else.

 

[Turbine Doc]

Needs a good heat sink, what are your plans with the truck, for longevity nothing better than the Heath setup, and if not going that route several of our vendors sell Dipacos, support those here that keep the site free of fees by buying from a vendor

 

[Coghlin]

Put in a remote mount D-tech PMD with cooler last night. Works great. I got a #9 resistor with it. I swear it had more power now but I didn't think the it would relearn the new resistor this soon. What is the procedure for learning the new resistor? I know it probably doesn't have more power but it sure is nice to have it running again. Got a lot of little things fixed on it though in the process. That is the trouble with getting used. Someone else's problem. Everything on the truck was butchered, from the filter housing to wrong oil pressure switch, to intermittent lift pump even when wired direct, to leaking fuel lines, wrong fuel tank cap, and cracked filler neck hose. Oh well, I can check that stuff off my list for now and start focussing on the rear-end, A/C, and hopefully soon a A-Team turbo as the turbo is leaking oil like crazy although it builds good pressure. It spikes to 10psi and maintains 6.5psi when pulling after the wastegate tells it where to be.