Rough Start after oil change.

[ctjkelley]

Hello all! I am a newbie to this site and diesels....so here goes. Recently bought a 1994 Chevy 3500 flatbed 4x4 with the 6.5 TD. Initially I had some battery and alternator issues, I got those worked by replacing the alt and 2 new batteries. So I decided to change the oil, after the oil change I started the truck up fine, idle was fine. The truck died, ever since the truck had a rough start up, it will turn over and over and over then it will hit. The initial idle is rough for 1-2 seconds the idle is smooth. It seems to have a little bit of power loss since the oil change as well. Once the truck is started its fine, the dying has just stopped, once it's up to temp I can shut the truck off and it's still hard to start. I have replaced the fuel pump and pmd with no changes. Any help would be greatly appreciated.

I went and got the codes checked today and this is what was found.
1. DTC 27, PEDAL POSITION 2 IN RANGE FAULT.
2. DTC 26 PEDAL POSITION 2 LOW INPUT
3. DTC 45 EGR VENT OUTPUT FAILED
4. DTC 44 EGR PULSE WIDTH OUTPUT FAILED
5. DTC 87 HIGH RATIO.
Does any of these make sense of my initial posting? What are the fixes for these codes.

[DmaxMaverick]

Welcome to the Forums!

First, it sounds like the lift pump isn't working (OPS circuit related), and/or it's getting air into the fuel system (leak). It may also have issues with glow plugs and/or the GP controller.

The DTC's you are seeing indicate you have the wrong PCM in the truck, probably intended to accommodate the (also wrong) injection pump. This is unique to 1994 HD models (2500HD/3500). The pedal position faults will cause reduced power and some default conditions that can cause other issues. Look for poor connections and wires before replacing the APP module, but don't rule it out. The failure of one more APP circuit (it has 3 independent circuits) will force limp mode, and failure of all 3 will prevent the engine from starting/running. If the instrument panel has a "Service Throttle Soon" lamp, it should stay on until the DTC is no longer triggering.

[ctjkelley]

The service throttle soon light is not on.
Also I'm new to this if could elaborate on what the APP is and also what the PCM is...I assume that the PCM is the computer??
Thanks for the reply.

[DmaxMaverick]

PCM = Powertrain Control Module (the main computer).
APP = Accelerator Pedal Position module (throttle pedal module).
OPS = Oil Pressure Switch (powers lift pump).
DTC = Diagnostic Trouble Code.

The HD models (8600 GVWR+, GMT-400 trucks like your 3500) do/should not have EGR. If you are getting EGR codes, it has the wrong PCM. The 1994 HD models are OEM with a specific PCM, and require a specific injection pump, unique to only that PCM. These pumps are less common (but can be bought retail), and the PCM will not accept any other IP. It is not uncommon for owners to replace the PCM with a LD model, so the more common Light Duty IP, and later model IP's can be used. The drawback is the EGR codes (absent a custom chip to accommodate the issue), but they don't affect running quality. Most folks just ignore the SES lamp, anyway.

Most DTC's will clear automatically after a few starts, and/or warm-up cycles, once the condition is corrected. Your OBD-I system allows you to retrieve any codes with the use of a paper clip and the ign. key. The procedure and a list of codes is HERE (http://www.thedieselpage.com/members/trblcode.htm).

[ctjkelley]

Awesome info!! Ok now this, say it is the wrong pmc why did it just start this issue? It ran fine before with no codes. But once I changed the alt and batteries things just seem to be piling up.

I need to add that when I put the new alt on I discovered some wiring issues. The po had the wrong alt plug attached it was jerry rigged to the alt and the wires were in the wrong place, I had the new alt tested and replaced the alt plug with the correct plug. There were only 2 wires to tie into the plug a white and brown, since I replaced with the correct plug my voltage meter began to work along with the tach.

[DmaxMaverick]

I don't know why the PO did what he did. If he was trying to make use of the wrong alternator and had to rewire it, what you saw is no surprise. Your tach is driven by the alternator, so make sure you have the correct size pulley or it will not be accurate. One really bad electrical hack may be an indicator of deeper problems, caused by other bad hacks.

You should not be seeing EGR codes, at all. The correct PCM (and correct calibration chip) should not have the ability to monitor EGR status, much less complain about it. If your DTC's are correct, something in the programming is wrong. Verify the DTC's, using the paper-clip method. Simple OBD-I code readers are not completely reliable with the Diesel models. Verify and re-verify (it's free, and only takes a little time). Do the same for the APP codes, being that the STS lamp is not on (it should be, or you don't have that lamp, for whatever reason).

It's entirely possible you have a Heinz-57 truck, unless you know the full history of it. Unless you know what's been modified or replaced with non-OEM, you don't know what you don't know. This is not uncommon with older trucks, and nothing surprises me anymore.

[ctjkelley]

The sts lamp does work, it's on with everything else when the switch is initially turned on.

[DmaxMaverick]

It's possible the APP codes were a one-off error, or maybe caused by voltage issues. Your previous alternator condition may be an indicator of that. If the STS lamp isn't currently on, the codes may only be in history.

[ctjkelley]

Very good point, so I really should be focused on OPS Or a faulty ground?

[DmaxMaverick]

If the lift pump isn't getting steady battery voltage, the OPS circuit is a good place to start. Cleaning grounds and replacing old wires/cables is never a bad idea on these trucks. Grounds are critical with any electronic controlled vehicle, and especially on early models of a series. 1994 was the first model year for the EFI GM Diesel.

[ctjkelley]

How do I check to see if the loft pimp is getting steady voltage? I can crack the vent on the fuel filter and the only time any fuel will squirt out is for a moment when I'm turning the truck over to crank it. With just the switch on the pump should lift and squirt fuel right? And should fuel squirt from the filter vent when the truck is running/idling?

[DmaxMaverick]

I don't recall how/if the 94's power the lift pump, pre-running (prime stage). Once running, the OPS provides power to the LP, as long as it has minimal oil pressure (DOT required fail-safe). While cranking the engine, oil pressure will develop, the OPS circuit closes, and power should be supplied to the LP. A very good upgrade to this system is to relay power from the OPS, so it only carries the current required to power the relay. The OPS is a common-fail component, due to overloading to the power demands of the LP. Simple solutions can be done DIY and inexpensive, or a ready-made LP controller kit can be had from Kennedy (http://www.kennedydiesel.com). 95 models power the LP before a start via a relay, and once running, powered by the OPS. OBD II systems are PCM-relay controlled, but are still backed by the OPS (which less commonly fail).

To test the lift pump while running, open the water drain valve (T-valve at the thermostat housing, route the hose to a container). It should flow well and the engine should not stall. If no fuel flows and the engine stalls, the LP is not pumping fuel.

Unless you generate oil pressure artificially (there's a way, but not at all practical on a fully assembled/installed engine), you can't fully test the OPS circuit without running the engine. Generally, the OPS is just replaced. Use ONLY the OEM replacement. Aftermarket switches are junk. All of them.

[ctjkelley]

ok i tried the t valve and she is as dry as a bone, when i open it up nothing happens at all not even a little drop.

[ctjkelley]

here is a link to youtube. this is my truck on the rough start and brief rough idle.

http://youtu.be/h8a02UGvPcY

[ctjkelley]

Also here is a link to the video showing the open t-valve while at idle.
https://youtu.be/_0-65_74Uig

[DmaxMaverick]

OK, good vids. Your rough start sounds like it may have a little air in the system, or weak/underpowered or bad glow plugs. A bit slow to start, but it didn't sound all that bad and it smoothed out pretty quick.

I don't think the filter water drain is connected to the T-valve, or the valve has failed. It should have either flowed fuel or stalled. Check the other end of the hose that is connected and you may find it dumps open below, and the line from the filter to the valve has been defeated at some point. It's been a while since I've been under a 6.5 hood, but IIRC, the filter line should connect to the lower nipple, and exit the side nipple. You should be able to pull the drain line from the valve up and out (such as to route it to a container). I don't recall ever having to pull the line up from below the valve, and that would defeat the functional design of a needle valve (a whole bunch of them would be leaking, predictably, at the gland packing, which I've not heard of). I suspect the valve isn't connected to the fuel system.

Repeat the fuel flow test, only this time, open the bleed valve on top of the fuel manager. The results will tell you the same thing, but it's more messy.

[ctjkelley]

Ok I figured out the fuel lines on the drain valve, new line installed etc. the fuel line in wasn't attached it had a plug in it for some reason, anyway all is fixed with that and when the drain is opened fuel is draining, only while the truck is trying to start. While the truck is at idle the fuel stops coming from the drain line. I will post a video shortly of the what comes out of the exhaust on start up and a shot of the drain valve that is fixed.


Here is the video.

http://youtu.be/8IlFViAxrQ4

[ctjkelley]

Update on the issue, today i replaced the OPS, the only results i got from replacing the OPS was constant fuel flow through the T-valve and the vent on the fuel filter canister. Still a sluggish start. Next i replace the short fuel line on from the injector pump to the hard line that feed the injectors with a clear line to check for air, i do have an air bubble that shows up in the clear line. I bled the injectors on the driver side and the front one on the passenger side, i cannot figure out how to get to the other 3 injectors with out removing the turbo. Thoughts??

[a5150nut]

go through right fender well. remove rubber mud cover and right wheel.

[DmaxMaverick]

Update on the issue, today i replaced the OPS, the only results i got from replacing the OPS was constant fuel flow through the T-valve and the vent on the fuel filter canister.

That's not nothing. That's a problem diagnosed and eliminated. One step at a time. Fix what IS broken, then move on.


Still a sluggish start. Next i replace the short fuel line on from the injector pump to the hard line that feed the injectors with a clear line to check for air, i do have an air bubble that shows up in the clear line. I bled the injectors on the driver side and the front one on the passenger side, i cannot figure out how to get to the other 3 injectors with out removing the turbo. Thoughts??

Don't worry about the remaining injectors. They will bleed themselves once you get the other issues ironed out. That isn't the problem, anyway. A symptom perhaps, but not the cause.

Test all the glowplugs, and watch the cycle time. If you have AC60G plugs, you may have to extend the glow cycle, one way or another, or replace them with faster plugs.

If you are getting air into the system, the lift pump is working, and you have no external fuel leaks, the air may be leaking in, between the tank and lift pump.