Engine Performance Diminishing

[rustyk]

Engine details in sig.

I've been experiencing declining boost and diminishing power for several months. Initially, I suspected issues with the turbo, but now, I'm not so sure.

Symptoms:

At first, straight and level, boost @ 60mph was usually ~2.5psi, EGT, 525-550°. I noticed boost on one trip dropped to 1.5psi and EGT 575-600°. I changed the air filter, no change. The turbo also seemed sluggish off the line. Engine power over time has diminshed.

I replaced the fuel filter (twice) and the lift pump, dropped the tank and changed the sock, and checked the turbo intake for obstructions. The turbo impeller turned freely. No change.

On hills, I had a self-imposed boost limit of 5psi in OD, 8psi in 3rd, and 12psi in 2nd. EGT rarely exceeded 750° (850-900° on long grades). The 4L80E would downshift OD-3rd @ 50mph. I couldn't get more than 7psi boost,

On this last trip, modest hills cause downshift @ 60mph, and 5psi boost seemed to be the limit. Engine coolant ran warmer than usual.

There is visible smoke when the throttle is nearly floored, but more gray, and certainly not volumes of black.

I have suspected the turbo, obstructed exhaust (collapsed baffle in the muffler?), and the IP.

Any suggestions?

[Dvldog8793]

Howdy
I would suspect the IP...?
Did it blow black smoke when it was running right?
If you are running hi-pop injectors, has the IP ever been reworked?

[DmaxMaverick]

Decreased boost and increased EGT indicates all the fuel is there, but coming up short on O2. With a good/new air filter, it sounds like a charge-air-circuit issue. Check for leaks, and wastegate health/operation. Could also be an eroded turbine.

[rustyk]

The turbo has ~85K miles; turbo impeller appeared intact (Non wastegated). I'll check again for leaks; none detected, and the gage tubing has no visible leaks.

Never smoked after warmup before; they are hi-pop injectors with original IP (~95K miles).

BTW, always used a lubricity additive when fuelling.

[rustyk]

I contacted Peninsular, which built the engine, and they suspect the timing has changed. If not, it's time for a new IP. I'll have the tech check when I next take it in.

[rustyk]

Semi-update:

I had the coach serviced for an upcoming trip; 1/2 mile from home, the engine quit. I suspected the oil pressure sender, which I'd had replaced during the service. When I disconnected the wires, the sender came apart. A new sender got it running.

A 700 mile trip in OCT went smoothly, even with the performance issues.

My mechanic, on Peninsular's advice, adjusted the IP timing 1/16". There was no change.

Throttle response off the line is fine, but power flattens on increased throttle.

Talking today to Matt of Peninsular Engines, we concluded that the IP is worn out, and a new one is on order.

Two symptoms led to this: First, I had a lift pump die in the past, but the IP's internal kept things running. Second, the flat throttle response also pointed to an IP issue.

More as the mystery evolves.

Matt at Peninsular has been very generous with his help!

[Warren96]

Lets see, hotter than usual, good boost, no black smoke. My 94 did that when the timing was retarded. Is your 94 an electronic or mechanical pump?

[rustyk]

Mechanical DB2. The on-order replacement is a significantly upgraded DB2. Boost is significantly degraded.

[rustyk]

After a few more trips, the performance continued to decline. 2-3psi max boost. On the last trip in December '15, couldn't even get 1 psi boost on the last 350 miles, although it would run at 65 mph, but no power on hills.

After many delays (from Stanadyne), the new IP finally arrived. I had the shop install it, along with a new turbo and muffler. Performance seems to be at least mostly restored. More black smoke than usual on acceleration from a stop, but it dissipates after a few seconds. Part of that may be because idle is a bit low, which I'll adjust soon.

[rustyk]

Update: Increasing the idle (from around 300 RPM) to ~750 RPM solved the smoke problem; engine now runs like it should.

[rustyk]

With the new IP and turbo, power was restored, but gradually declined.

As part of the suspicion fuel flow was the reason, I had the sock removed from the tank and replaced it with an inline filter upstream from the pump. Stupidly, I used a 5 micron. Replaced it in kind, and same symptoms gradually reappeared.

Belatedly, it occurred to me that 5 microns was far too fine for the lift pump to cope with, so I replaced it with a 100 micron cartridge from Summit. Now I have plenty of power.

I had 2 lift pumps fail after the original ordeal; I think they were overworked (not enough fuel to cool adequately while drawing more current trying to pump).

[JeepSJ]

IMHO, 100 micron isn't fine enough especially if it is your only filter. I have a 10 between the lift pump and tank, then a 2 between the lift pump and IP.

[a5150nut]

Captain Doom have you considered Kennedy's lift pumps?

[JeepSJ]

Captain Doom have you considered Kennedy's lift pumps?

I do really like the look of the lift pump control harness that he has. I'm seriously considering one since I never ran my lift pump through any type of safety control so it runs all the time that the key is on.

[DmaxMaverick]

Said it before (many times), I'll say it again.....

The cross-sectional flow capacity of the in-tank sock is many times that of the tubing inlet. If the sock is a factor with fuel flow, the problem is NOT the sock. The problem is fuel quality. If fuel flow capacity is reduced to a point it effects engine performance, the problem is still not the sock. If the sock is restricting fuel flow, removing it is only allowing the questionable-quality fuel to flow further into the system. A 100 micron filter will "filter" better than the sock, and may flow better, initially, but it will only be effective until the surface area is overcome by the same condition that plugged the sock. Moving a contaminate restriction from before the sock to after does not alter the flow capacity of the system. Removing the sock (leaving only an open tube for the inlet) alters the velocity of the fuel entering the system. Also, higher fuel inlet velocity allows larger/heavier contaminants into the system. The sock does not "filter" the fuel, in as much as it reduces the velocity of the fuel at the initial inlet.

The front-engine motor home is a unique application. A fuel system designed for a pickup truck will not perform the same if the distance from tank to IP is greatly increased (the only significant difference between the two applications). Several factors come into play. Distance (lift) and fuel line friction. Lift is a function of moving fuel from the fuel storage surface level to the destination (IP). I suspect the fuel system may not be up to the task, for any of several reasons. An OEM fuel lift pump designed for a pickup truck may (likely) be insufficient for the motor home application, all else being equal. Or more simply, the fuel line cross-sectional area, throughout the system, may be insufficient. A new pump may perform satisfactorily, but operational time may cause the pump to fall behind well before it would have within the designed environment. The only solution to this condition is to either design a system that will allow the pump to operate within its designed environment, or install a pump that is designed to operate within the current environment. Moving a progressive restriction condition from before the pump to after does nothing to address the original condition. Changing the method and/or location of fuel filtration does nothing to address the original condition.

[a5150nut]

I do really like the look of the lift pump control harness that he has. I'm seriously considering one since I never ran my lift pump through any type of safety control so it runs all the time that the key is on.

I was thinking more of the pumps he offers for the Duramax application. Run single or in pairs.

[rustyk]

IMHO, 100 micron isn't fine enough especially if it is your only filter. I have a 10 between the lift pump and tank, then a 2 between the lift pump and IP.

The stock GM filter is still in place.

[rustyk]

Said it before (many times), I'll say it again.....

A 100 micron filter will "filter" better than the sock, and may flow better, initially, but it will only be effective until the surface area is overcome by the same condition that plugged the sock

The front-engine motor home is a unique application.pump to after does nothing to address the original condition. Changing the method and/or location of fuel filtration does nothing to address the original condition.

I located the 100 micron filter (actually a screen) where it can easily be flushed in about 5 minutes.

Mine's a rear-engine. I moved the LP about 6 lineal feet because I installed a fuel tank for the gaso genset, and the tank covered the LP's prior location on a cross member. That arrangement has worked fine for 80K miles, but I did take the precaution of replacing the suction side with new, HD lines.

Lift pump issues started when, as a preventive measure, I had the oil sender replaced. It failed after 15 miles (on my way home from the shop), and came apart in my hand...the replacement pumps (2 of them) were El Cheapos. The latest is a (claimed) HD pump.

I already have a relay (powered by IGN) and fuse block in a rear compartment for accessories, fed by a 10 ga. wire. I can install a new relay to power the LP directly with the IGN on. Because mine's a pusher, the risk of fuel flow after an accident is infinitesimal.

[arveetek]

I can install a new relay to power the LP directly with the IGN on. Because mine's a pusher, the risk of fuel flow after an accident is infinitesimal.

I just wanted to throw out here that I installed Kennedy's lift pump harness on my Tahoe over 10 years ago, and it has worked flawlessly since. Powers up the LP for a few seconds when the ignition is turned on, then waits for oil pressure to continue pumping. I feel much safer having this installed, instead of like my old '81 6.2L conversion that had a LP powered by ignition full time. Another plus is the handy button to manually engage the LP, which makes for easy filter changes!

Casey

[rustyk]

I'm thinking that I'll install a separate relay, but I haven't decided whether to engage it from the OP switch (which is convenient to the compartment) or the IGN.