Possible fuel issue

[Erik Unyielding]

While I'm waiting for my 700R4 to be ready to swap in, I'm working the bugs out of my m1008 (stock 6.2L Detroit). The previous owner reported that the main fuel filter is new but the inline fuel filter that's been installed before the lift pump might be an issue if I experience power loss. On the 30 minute drive home, everything was great at first and then it seemed like I was getting some power loss. By the time I'd reached home, putting the truck in reverse resulted in a stall. It restarted fine but stalled immediately if I revved the engine and then quickly let off.
My question is, does this sound like a clogged filter or a fuel pressure regulator or injector issue?I don't know much about Detroits so I don't know where the IPR is or how to check it. I've collected the parts to do an electric pump and spin-on filter conversion but I'd like to make sure if it's an IPR or tank vacuum issue or similar that I'm addressing it first.

 

[Barrman]

Since the truck is new to you. You want to replace all of the fuel and air filters yourself so you know they are new and correct. Use the directions in the Technical Manual to change the fuel filters in such a way as to make it start right back up again. See if the problem still exist. If it does, follow the steps in the TM to diagnose it.

 

[Erik Unyielding]

Since the truck is new to you. You want to replace all of the fuel and air filters yourself so you know they are new and correct. Use the directions in the Technical Manual to change the fuel filters in such a way as to make it start right back up again. See if the problem still exist. If it does, follow the steps in the TM to diagnose it.

I have a new filter set ready to go on before I do the spin-on swap. I'm just trying to get a jump on diagnosis. The truck fired up great today, idled beautifully, revved just fine and returned to idle with no issue. This doesn't feel like a filtration issue to me.

 

[Keith_J]

Hot stall can be inadequate fuel return from the injection pump. The governor cage and weights spin at half crank speed, submerged in diesel which acts as an effective heater if fuel return is blocked. More importantly, if case pressure rises due to a blockage in fuel return, this will prevent the plungers from filling.

Synthesis of your symptoms could point to a collapsed fuel return hose. This should flow 3 fluid ounces per minute at idle. Case pressure should be 8 to 12 PSIG at warm idle.

Another possible cause of warm stall is failed thermal compensator at the top of the governor fork. It is a bimetallic strip which increases governor spring force when warm. It is between the governor spring and the governor fork at the front of the guide rod assembly.

The IP is a volume metered device, energy is based on mass so when fuel is heated, its density decreases which would decrease idle speed. This compensator slightly increases injected volume when warm.

 

[Erik Unyielding]

Hot stall can be inadequate fuel return from the injection pump. The governor cage and weights spin at half crank speed, submerged in diesel which acts as an effective heater if fuel return is blocked. More importantly, if case pressure rises due to a blockage in fuel return, this will prevent the plungers from filling.

Synthesis of your symptoms could point to a collapsed fuel return hose. This should flow 3 fluid ounces per minute at idle. Case pressure should be 8 to 12 PSIG at warm idle.

Another possible cause of warm stall is failed thermal compensator at the top of the governor fork. It is a bimetallic strip which increases governor spring force when warm. It is between the governor spring and the governor fork at the front of the guide rod assembly.

The IP is a volume metered device, energy is based on mass so when fuel is heated, its density decreases which would decrease idle speed. This compensator slightly increases injected volume when warm.

Excellent, thank you for the info! I'll look into those and try and rule them out.

 

[Keith_J]

Stanadyne DB2 Injection Pump - Diesel Engine - Diesel Power Magazine

Read about Diesel Power Magazine's close up look at how the Stanadyne DB2 Injection Pump works (previously known as the Roosa Master).

www.motortrend.com

"Retention of heat is a critical factor in fuel thinning after a high-ambient heat soak. As the hotter, thinner fuel passes through the pump, internal leakage increases and reduces fuel output. To compensate for this loss, a bimetallic temperature compensator strip was added to the governor arm to increase the metering valve opening. This provides a compensated idle speed curve and corrects engine idle speed at elevated ambient temperature."

Good info here. The thermal compensation device is attached to the governor arm. Trying to find a picture. Should be visible with top cover removed.

Part number is 23461, this is a Stanadyne part number. As pictured below the bimetallic strip is riveted to the arm with two rivets. When it heats, it curves away from the steel arm, pushing on the low speed governor spring which slightly opens the metering valve. Springs follow Hooks Law, meaning displacement is proportional to load. This thermal device increases displacement which increases load required by the centrifugal weights for balance. The centrifugal force is on the forked end of the arm. Pivot point is the cone in the middle.

 

[Erik Unyielding]

Thank you for that. I just ordered one because at $35, even if it turns out not to be the issue, it's probably a good part to have on the shelf.

 

[nyoffroad]

Thank you for that. I just ordered one because at $35, even if it turns out not to be the issue, it's probably a good part to have on the shelf.

LOL, so true but just try to find it when you need it! If you're like me, you'll give up looking and order another one and eventually find it when you need something else!

 

[Mullaney]

LOL, so true but just try to find it when you need it! If you're like me, you'll give up looking and order another one and eventually find it when you need something else!

.
YES Sir! Haven't we all...

I've got one around here somewhere!

 

[Erik Unyielding]

On the subject of collecting fuel parts: I'm looking for an adjustable fuel pressure regulator but most I've found are ridiculously priced or the adjustment range is too high for what I need. Any links?

 

[Keith_J]

Thank you for that. I just ordered one because at $35, even if it turns out not to be the issue, it's probably a good part to have on the shelf.

The part is easy to inspect, only removing the IP cover required..you will lose about 25 cents worth of diesel . A tight fitting screwdriver plus a tap with a hammer helps, seen more than one screw snap off.

The thermal compensator only moves off the governor arm by about 0.003" at 150°F. Other possibilities include warm idle speed setting with respect to the cold idle speed solenoid.

 

[Erik Unyielding]

The part is easy to inspect, only removing the IP cover required..you will lose about 25 cents worth of diesel . A tight fitting screwdriver plus a tap with a hammer helps, seen more than one screw snap off.

The thermal compensator only moves off the governor arm by about 0.003" at 150°F. Other possibilities include warm idle speed setting with respect to the cold idle speed solenoid.

Excellent, thanks. As far as inspection goes, what am i looking for? I'm just guessing by the video but there shouldn't be any play? Do I check it hot or cold?

 

[Keith_J]

Excellent, thanks. As far as inspection goes, what am i looking for? I'm just guessing by the video but there shouldn't be any play? Do I check it hot or cold?

Check cold, the riveted part on the arm must be tight and the spring should be up against it. The rivets can loosen, reducing the effectiveness of the temperature compensator. When the fuel heats, the compensator bends slightly towards the spring.
The type of governor here is a minimum-maximum type, meaning there is a weak spring which sets minimum speed or idle and a very stiff spring which allows the governor weights to close the metering valve. At the low speed, the governor weights also close the metering valve to reduce idle speed, meaning there must be a tiny bit of spring force when the pump is not turning. The force from the spinning governor weights overcomes the idle spring force, closing the metering valve when idle speed is over 650 RPM.

I would first start with a good tach reading at warm engine idle to see if a little adjustment on the external idle speed is needed. This sets the idle spring force. No tach? A digital voltmeter with frequency measurement can be used on the tach signal post of either alternator. Should be 215 Hz.

Important warning is to never try to cool the hydraulic head, that is the steel portion of the pump where the high pressure lines connect, all the way to the aluminum body. This can cause rotor seizing which ruins the pump. This means never wash a running and hot engine.

 

[Erik Unyielding]

Great information, thank you. I've been a mechanic of one kind or another for many years but only started learning about diesel engines in the last 5 years so all of this is really helpful for me. I snagged a complete turbo setup from a 6.5 today but before I even think about slapping that stuff on, I want to make sure my fuel delivery, filtration, etc. is all on-point. Part of that is collecting egt, boost trans temp, and most importantly a tach. I'll bump the tach up the list of parts to buy next and take a look at my warm idle speed.

 

[Erik Unyielding]

Went for a short ride earlier, probably about 20 minutes. No hesitation, no power loss, no stalling. I'm going to take it for a longer drive tonight and see what it does before I open up the IP.

 

[Erik Unyielding]

Ok, so I just drove from Charlestown to Weymouth, about an hour in 83 degree heat and stop and go traffic, driving a sick truck. What a miserable ride.
Anyway, this is my report: the first 10 to 15 minutes were ok but then I noticed the RPMS starting to fall off when I let off the accelerator. Things got progressively worse in traffic and had to keep my foot on the throttle to avoid a stall while braking. Hills were very bad, no acceleration or real RPM increase unless I floored it and the tranny downshifted but even then, it was really struggling to get up and over. The situation seemed to get progressively worse; lots of surging, power loss, stalled once, and the RPMs were hunting. I also noticed it was momentarily coughing smoke when I let off the throttle, when I floored it, and when the engine was hunting. I finally made it to my exit, completely lost power, and thankfully coasted into the grocery store parking lot where I now sit. That was about 15 minutes ago so I'm going to sit here another 15 minutes and try to make it the 4 minutes home.
So what do you gurus think? Does this sound like the governor arm assembly? I'm hoping to pull the IP cover off when I get home but let me know if you all think I should look at anything else.

 

[Keith_J]

Before you tear into the IP, find out which calibration spec the pump was last built. The ID tag is on the drivers side body, stamped in metal.

The pump is a DB2829-nnnn. The nnnn is the calibration spec. If an early model, it could have a flex ring governor coupling, these degrade and plug the fuel return causing this problem. All models can have sticking metering valve from FAME deposits as this fuel additive can coat machined surfaces, causing sticking. Diesel Mechanic in a Bottle works well here.

When it cools, wipe the three decades of gunk off the ID plate and record calibration spec so I can more easily diagnose the warm running problem.

 

[Erik Unyielding]

Before you tear into the IP, find out which calibration spec the pump was last built. The ID tag is on the drivers side body, stamped in metal.

The pump is a DB2829-nnnn. The nnnn is the calibration spec. If an early model, it could have a flex ring governor coupling, these degrade and plug the fuel return causing this problem. All models can have sticking metering valve from FAME deposits as this fuel additive can coat machined surfaces, causing sticking. Diesel Mechanic in a Bottle works well here.

When it cools, wipe the three decades of gunk off the ID plate and record calibration spec so I can more easily diagnose the warm running problem.

Is this the plate you're referring to?

 

[Keith_J]

Is this the plate you're referring to?

Ohh, a 4544. This is a 1986 year model HD pump with 54 mm^3 per stroke max fuel..range is 49.5 to 54 mm^3. Uses the 28370 governor cage so no flex drive ring to cause problems.
Get some Diesel Mechanic in a Bottle, remove governor cover, drain as much diesel as possible and inspect the governor arm as stated earlier. Replace removed fuel with Diesel Mechanic in a Bottle and reinstall cover. Drop cover on in a forward position, then slide it toward the firewall so the ESO arm contacts with spring tension. Install the 3 screws, let it sit overnight.

 

[Erik Unyielding]

They didn't have Diesel Mechanic in a Bottle in either store I went to but they did have Stanadyne injector cleaner. While not the same, I'm sure it'll help. Here's what I found under the cover:

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Forgot to mention, the fuel is still warm in the video. Probably about 99 degrees F