6.2 in an RV Low on Power

[Bigshankhank]

I've been fettling with this RV for a few years now as a long term project. Took a while but I've finally chased down and removed/replaced all of the broken bolts in the accessory brackets (5 total between the alternator and power steering pump) and the engine starts & revs fine. I have been running it around in my neighborhood the past couple of weekends now that I have the belts all aligned and tightened properly but the problem is, it won't accelerate over 35mph. I'm not trying to push it very hard but it just won't go any faster. Engine continues to rev, doesn't have any hanging idles or flat spots. Transmission fluid is still clean and red and is above the Fill line. Shifts are rough but they were rough in my other 6.2l RV and that got over 60mph.
Couple cromulent facts;
-33,000 miles on the engine
-Its got a Stanadyne fuel filter assembly up on top of the intake which is a hell of an upgrade from my original RV with the OEM setup
-Currently doesn't have an air filter, housing is there I just haven't bothered to put one in since I'm still troubleshooting the long list of electrical gremlins and not going anywhere in it yet
-Has a momentary switch for the GPs, sometimes it works sometimes it doesn't but either way the engine starts within seconds of cranking
-Exhaust is clear, no smoke whatsoever
-While working on the accessories I removed the fan and fan clutch and on the bench the fan spins ok but it feels a little "gummy". I can give it a twirl and it will spin around once but no further
-By the time I'm up to 30mph the trans has already shifted to 3rd. I seem to recall on my earlier RV the shift points were 15-18mph into 2nd then around 40mph into 3rd so this seems like its shifting way early

I am going to bring an infrared thermometer with me next time I drive it because while it brakes OK I want to check on the hubs and maybe I've got a brake that is dragging. I have Vol's I & II of the TDP maintenance & troubleshooting books but irritatingly I cannot find them.

Thanks for the help.

[DmaxMaverick]

What chassis, model year, weight class, gear ratio, and tire/wheel size?

(In no specific order)

Verify your fuel supply to the IP (get a pressure gage on it, between the fuel filter and IP). It should be about 4 PSI at idle, and not fall below zero, under any condition or load. Low or restricted fuel supply will not only reduce power, but also causes early, harsh auto trans shifts. It should produce at least a little black/gray smoke while throttling. If it doesn't, it isn't getting enough fuel, or the timing is retarded. Too retarded produces white smoke. Verify free fuel flow of the return to the tank, and the tank is properly vented ("Diesel Only" fuel cap, or other venting system). A restricted return can retard timing significantly. Ignition rattle should be sharp, not dull. Advance the timing so the rattle is at the early edge of sharp. Too advanced will increase EGT.

Verify fuel quality (not contaminated with something else, like water, gasoline, or a bio, pull a sample at the filter water drain into a glass jar and let it sit for an hour), and that it has no leaks ahead of the lift pump (small leaks after the pump make a mess, but don't usually effect running). Any air in the system reduces fuel volume and retards timing. The label on the fuel filter means nothing if it isn't allowing good fuel flow, for whatever reason.

Verify the vacuum pump is producing at least 20" hg, as well as a properly routed throttle vacuum valve, and working trans vacuum modulator. I don't think this is your immediate problem. If it's able to accelerate to 35 MPH, it should be able to accelerate further in 3rd, unless power is decreased, for whatever reason.

The fan clutch sounds normal. Make sure it's a HD model with the bi-metal coil on the front. If it isn't, it may not be able to keep up under heavy use. Either way, not your immediate problem.

To check for dragging brakes, jack the wheels and give them a spin by hand after pumping the brakes hard a few times. You should be able to feel any significant drag. If you can spin them by hand, there's not enough drag to slow it down under power. If it has a shaft brake (hand brake), make sure it's working and releasing.

[Bigshankhank]

1984 G30 chassis with dually rear end, not sure about the gearing
https://i.ibb.co/3sx6Z3f/D53-BA368-E1-A7-4314-9-C25-575-A26-BC240-A.jpg (https://ibb.co/DbBc2JG)
According to the info decal inside the GVW is in the 11,000lb range
Tires are 8.75 x 16.5
When I say the exhaust is not smoking, it’s not smoking a cloud but upon throttle up there is a faint white cloud.
Lord knows the age of the fuel that’s left in the tank, I’ve had it in my driveway for 3 years, and bought it from a former member here who told me he hadn’t run the RV in 5-6 years prior to selling it.
Fuel cap doesn’t indicate the Diesel Only
https://i.ibb.co/714MBH2/2-F66-BBC0-C043-455-E-9-DCD-CE3476-AA6-A27.jpg (https://ibb.co/z4J9C1G)
https://i.ibb.co/PcpNHDm/EF302-A91-8474-4452-AC85-7-C90485-A9-D01.jpg (https://ibb.co/QPBfwDb)

[DmaxMaverick]

That leaves a lot of variables. White smoke indicates cold or choked combustion. Since your intake is wide open, that leaves cold (too little heat for complete combustion). Poor fuel quality, restricted fuel supply, and/or retarded timing can cause that. I would start with flushing the fuel supply with fresh fuel, and make sure fresh, uncontaminated fuel is supplied. Change the fuel filter once you're pumping clean fuel. If you find black or very dark goo or chunks in the fuel (algae), add a biological cleaning and treatment. You'll need several fuel filter changes if the tank isn't cleaned and lines thoroughly flushed. Leave the fuel cap slightly loose until you can replace it with a properly vented, Diesel cap.

If you would like to upload photos, go to Community/Albums at the top of the page and create a photo album. You can link them into posts anywhere in the forums.

[Bigshankhank]

Grrr apparently I set my photos to auto delete on the hosting site, I’ll fix them and repost.

[JohnC]

Poor fuel quality, restricted fuel supply, and/or retarded timing can cause that...

Or bad spray pattern...

[DmaxMaverick]

Or bad spray pattern...

Certainly possible, but the first indication is usually difficult starts. He says it starts and runs fine, just doesn't make power. It sounds more like what and/or when it's spraying (or not), rather than how.

[Bigshankhank]

Photos restored.

I've been holding off putting new fuel in the tank because I want to drop it and get it flushed anyway, no sense doing that with more weight than necessary. Plus, the fuel gauge is pinned past Full so I want to clean and service the sending unit and hopefully find and eliminate the short in the circuit.

[DmaxMaverick]

If you are planning on cleaning the tank, I suggest doing nothing else with the running issue until that's complete. If the fuel is contaminated, you really don't want to push it around the system. Also, after the fuel tank and fuel is clean, run the return line into another container until it flows that clean fuel. If you don't, you risk flushing the dirty system right back to the clean tank.

If the fuel gage is off, and cleaning/replacing the sender doesn't help, the gage itself has a resistor on the back of it. When that fails, the gage goes wonky. The resistor is an easy replacement, though. I don't recall the resistor value (I'll bet google does).

If you fixed your pics, you'll need to edit your original post with updated image links, or just post them again.

[Bigshankhank]

If you are planning on cleaning the tank, I suggest doing nothing else with the running issue until that's complete. If the fuel is contaminated, you really don't want to push it around the system. Also, after the fuel tank and fuel is clean, run the return line into another container until it flows that clean fuel. If you don't, you risk flushing the dirty system right back to the clean tank.

If the fuel gage is off, and cleaning/replacing the sender doesn't help, the gage itself has a resistor on the back of it. When that fails, the gage goes wonky. The resistor is an easy replacement, though. I don't recall the resistor value (I'll bet google does).

If you fixed your pics, you'll need to edit your original post with updated image links, or just post them again.

All good info, I have no real need to run it anymore now that I've sorted a couple of electrical drains and the broken bolts. I started trying to take the gauge cluster out a few weeks ago to see if the problem might be easier to get to but I couldn't get enough slack in the speedo cable so I shifted focus back to the engine once and for all.
The images show up again in Post #3 on my screen, if they aren't working on your end I'll have to go back in and edit it if I still can.

[DmaxMaverick]

They may be showing on your system, but this is what I see:

6245

If the links don't work, try uploading your pics directly to the post using the image link at the top of the post editor. You can upload directly from your computer or phone.

[JohnC]

Contaminated fuel could account for you poor performance and the problems with the fuel gauge. I'd deal with that next.

Ditto on the pictures.

[Bigshankhank]

OK, gonna try and upload them again,
Rear differential, no markings as to the gearing inside. Again, 1-ton chassis with the dually rear
https://i.ibb.co/8YRRVWM/4258-C94-B-F87-B-4-E2-B-9-E46-8-F47-F5129034.jpg (https://ibb.co/CPXXFkB)
Fuel cap, no markings for Diesel Only
https://i.ibb.co/v3YTmMX/9-F96217-C-4-B67-4442-BB33-6-D159-CD7827-C.jpg (https://ibb.co/ByNQjYn)

[Bigshankhank]

Since I'm not going to run it for a while until I can flush the tank, I have moved on to deciphering the non-functioning gauges on the dash. I realize that this is a forum specific to the 6.2l Diesel engine so if I need to post these questions elsewhere let me know and I'll continue to focus this thread on the power issue.
On my dash, 3 gauges are pinned past the max; Fuel, Water Temp and Oil Pressure. I removed the cluster and pinged the circuit mat on the back of it, everything is making good connection. I wiped it down with some cleaner anyway and put it back together. I got lucky and found that the female spade terminal on the wire to the oil pressure switch was damaged so I replaced that terminal and now I have a working gauge again. I would like to put a mechanical switch & gauge in there but maybe another time. The Fuel gauge will likely be something back toward the tank sending unit so I'll address that when I drop the tank. But the water temp switch has me stuck. I popped the wire off the sensor in the back of the radiator and couldn't find a pin in the back of the plug behind the gauge cluster that made connection. Tracing the circuit mat pointed me toward the prongs that should be either making contact with the sensor or the ground. Should be the green wire (next to the open space) in this photo
https://i.ibb.co/vV0rCFk/B5-F9-BC19-61-C8-49-A6-8-ED7-4611-F692-B237.jpg (https://ibb.co/NtckgvK)
However with everything plugged in and the ignition switch in the On position, jumping this wire directly to the sensor did nothing. However jumping the sensor to the terminal on the back of the cluster highlighted in this photo
https://i.ibb.co/QJSWx8p/072-ABEA4-FC4-D-4109-8-BFF-5-E8-E008593-D4.jpg (https://ibb.co/CwCjSJm)
brought the gauge to life. Except, that terminal doesn't connect to anything on the circuit mat so my thought is for some reason there is a wire separate from the main harness plug that has a ring terminal that is connected to this stud. The wire on the sensor at the radiator is black w/ green stripe and I can trace it all the way to the firewall, but from there I cannot find it under the dash. I've been going through wiring diagrams online because I cannot find the thumb-drive where I already downloaded all of this stuff to keep things simple, but I'm wondering if anyone here is familiar with these vans and the instrument panel wiring and can help me out.

[DmaxMaverick]

The sender in the radiator is for the coolant level (Low Coolant Lamp). If you have a time when the coolant is low, for whatever reason, take it out and clean it. It can build up with crud and either not work, or indicate low all the time. The temp sender is in the head or coolant outlet (thermostat housing). I'm not much help without a diagram, as I only have them for the trucks. It's anyone's guess without one with the chassis upfitters.

That filler cap is way overdue. Just replace it, they're cheap.

[Bigshankhank]

So yeah it dawned on me last night that that was the low coolant sensor so I feel pretty damn smart having spent hours trying to figure out why it wasn’t working on my temp gauge.
Anyway, may not get a chance to wrench on this for the next few days but I’ll seek out the actual temp sensor and go from there. I actually have a wiring diagram for the RV house and I have one on a thumb drive somewhere for the chassis, but since so was barking up the wrong tree hopefully it’ll be more clear when I am linking the right parts together.
Thank you for your help.

[Bigshankhank]

Did sneak down to the garage for a bit to continue sorting the temp sensor. Found the actual sensor in front of the driver's side exhaust manifold and sure enough it has a dark green wire same as the back of the gauge cluster plug. Snapped the terminal off the end of the sensor and it has continuity back to the green wire on the plug and doesn't indicate a ground. Tested the sensor prong (not the threaded body) itself and it is not grounded, either. I jumped a new wire from the sensor to the backside of the plug and it still pegs past max. So either I've got a bad gauge, or I am missing something obvious. Is there another sensor on the other head?

Oh and a correction to my original post here, I have a Racor aftermarket fuel filter, not a Stanadyne.

[DmaxMaverick]

It doesn't matter what sensor you're talking to, if the connector has continuity back to the gage. That's the one. The 1984 (truck/SUV) glow plug system has its own coolant temp switch and separate relay (usually installed at the rear of the head), unless it's been upgraded to the 85+ (integrated switch/relay box, installed on top of the engine, near the rear, driver side valve cover).

It's possible the gage and/or sensor is bad. Pegged full hot is a closed switch, while open (or disconnected) is full cold, assuming the gage is working correctly. Somewhere on the interwebs is a resistance chart to verify what the sensor should be indicating. Read the resistance at a known temp, then change that temp (hot and cold water, for example), and read again. The value should change accordingly. If it doesn't change, or is reading a dead short or open (infinite), the sensor is bad. The fuse block should have a fuse for the instruments, so check that (doubtfully failed, with the readings you're seeing).

[Robyn]

The sluggish ...no power issue is likely due to a lack of fuel to the IP (volume)

The transfer pump on these were a mechanical pump on the RH front of the engine.

The fuel filter can also be a culprit.

As has been mentioned....cleaning the system is a good thing.
A clean fuel system, fresh fuel, fresh filter and if it were me I would stuff in a fresh fuel pump too....

A failed transfer pump can result in minimal fuel to the engine and exactly what you are seeing.....

At an idle there should be about 5 psi of pressure to the IP or at the filter inlet......

With the engine idling ....open the bleeder port on the filter.....Fuel should squirt out....if there is no pressure and the engine dies, then the transfer pump (On the engine) is not working.....

[DmaxMaverick]

Terminology: a bit of clarification to (hopefully) prevent confusion and keep us on the same page.

Fuel Lift Pump -the mechanical pump located at the lower/front/right side of the engine block, ahead of the starter (in this case). If the chassis has an electric fuel lift pump, there will be (should be) no mechanical lift pump. GM spec. is 4 PSI at idle, and greater than zero at any engine power level. This pump only moves fuel from the tank to the injection pump transfer pump. It is a simple, traditional, diaphragm-type pump, operated by a lobe on the cam, not unlike previous GM V-8 engines.

Transfer Pump -The INTERNAL injection pump transfer pump, not independently replaceable or serviceable. This pump simply moves fuel from the IP inlet to the High Pressure distributor pump inside the IP. This pump is capable of drawing fuel from the tank (all else being healthy) however, engine power will be reduced in the absence of a positive-pressure fuel supply (such as a failed fuel lift pump or significant restriction) at the IP inlet.

[Bigshankhank]

Determined that the low power issue was in fact the driver side rear brake was locked up due to a stuck parking brake actuator. While I was in there I rebuilt the rear brakes on both sides and bled new brake fluid.
Now, when I try to crank the engine it won't turn over enough to start. Batteries are holding 12.35v, turn the key switch on it drops to 12.28v-12.3v, but turn it all the way to start and it drops below 4v. Up until just a few weeks ago when I started it last it cranked right up.
Thoughts?

[Yukon6.2]

How old are the Batteries?
Sometimes batteries will show a high surface charge,but as soon as you hit them with a load they drop voltage to basically nothing.
I would load test them after being charged after 8 hours.
Or a bad connection.

[JohnC]

12.35 Volts is not that good for lead acid batteries, about 60% charged. Closer to 12. 7 is better. Are you measuring the voltage at the batteries, or somewhere else? Two reasons batteries will drop that low. First is that at least one of the batteries is bad. The second is the starter is drawing 2 butt loads of current. This can be caused by a bad starter motor, or a seized engine.

What happens if you turn the headlights on instead of the starter?

[Bigshankhank]

Batteries are about 3 years old. I am measuring voltage on both batteries, right at the ends of the terminals. Original cables so it wouldn’t completely surprise me if the cables are at the end of their lifespan, either. Engine spins once or twice then barely chugs so it’s not locked up. It feels like too much resistance in the starter circuit, but it was getting dark and the dog needed to be walked so I couldn’t check on the connections at the starter, that’s my next area of interest.

[JohnC]

Put the voltage probes right on the edges of the lead pads coming out of the side of the battery and recheck.

Are any of the connections getting hot?

[Bigshankhank]

I've checked voltage at the posts and at the terminal pads on the upper battery (lower one is too hard to get to), same reading.
Pulled the hot lead off the starter and cleaned it up, resistance across that wire back to the battery is near 0. I put it on the 2A charger to warm up overnight and will check again when I get home from work tomorrow. If I can get the batteries to hold 12.7v I pull the starter and have it tested.
Dumb question, but I have the rear end sitting on stands, meaning the rear wheels aren't on the ground. Any chance there just isn't enough rubber touching the ground?

[DmaxMaverick]

....Any chance there just isn't enough rubber touching the ground?

Not a factor. You could have the entire chassis sitting on the ground, and it wouldn't make any difference. Sounds more like at least one failed battery, if you're seeing the voltage drop at the battery posts. A starter load enough to drop the voltage to 4V with healthy batteries would smoke the cables and/or connections in a few seconds. Continuous or repeated cranking with bad battery(ies) can damage the starter.

[Bigshankhank]

I wouldn’t have thought so but again, prior to putting it on stands to rebuild the rear brakes it was starting fine, now it’s not.
I also noticed last night that, despite my voltmeter showing 12.3ish volts at the batteries, the dash voltage gauge isn’t showing anything, which it was working before. I had removed the gauge cluster last year to clean up contacts and see if the fuel & water temp gauge were faulty, and pretty much just plugged it back in just before working on the brakes two weekends ago.

[DmaxMaverick]

Causation vs. corelation. The engine cranked fine and started before, but not after jacking the rear end and messing with some electrical (corelation). Something changed (causation), but jacking the rear wasn't it. Messing with the IPC wasn't it. So, it must be something else.

When you turn the key to Start, does the starter solenoid engage? Can you hear the starter hit the ring gear? Does it hit, then stop? Can you rotate the engine by hand (put a socket/breaker on the damper bolt, and "tighten" it)?

[JohnC]

despite my voltmeter showing 12.3ish volts at the batteries, the dash voltage gauge isn’t showing anything...

You've got a couple of conflicting bits of information in the batteries drop to 4 volts on start attempt, and the dash gauge doesn't show any voltage ever.

[Bigshankhank]

Causation vs. corelation. The engine cranked fine and started before, but not after jacking the rear end and messing with some electrical (corelation). Something changed (causation), but jacking the rear wasn't it. Messing with the IPC wasn't it. So, it must be something else.

When you turn the key to Start, does the starter solenoid engage? Can you hear the starter hit the ring gear? Does it hit, then stop? Can you rotate the engine by hand (put a socket/breaker on the damper bolt, and "tighten" it)?

The starter spins the engine briefly, somewhere between 1/2 & a full rotation before the voltage drops off.
Checked the charger off the batteries this evening, about 22 hours overall. Voltage reading was just a shade over 13v but I'll check it again in the morning to ensure I'm not reading a surface charge.

[Bigshankhank]

You've got a couple of conflicting bits of information in the batteries drop to 4 volts on start attempt, and the dash gauge doesn't show any voltage ever.

How do you mean? My voltmeter shows voltage, the gauge on the dash doesn't. For some reason voltage is no longer making it to the gauge when it was working fine before. That being said, other gauges still function and the dash lights still work so its not a matter of no power is getting to cluster.

[JohnC]

All I'm saying is that if the voltage gauge isn't showing voltage, what else may not be seeing voltage as well? That said, if it cranks briefly, then grinds to a halt, sure sounds like bad batteries to me. Put the headlights on for a few seconds to draw off any surface charge. If I were you, I'd take the batteries to a parts store that can test them for you. Charge them first, individually (remove the ground from at least one to isolate them) and test them individually. One bad battery can quickly kill the other.

[Robyn]

Any more....a 3 year old battery is suspect.
I jumped in our Avalanche a few weeks ago....Fired right up...drove to town, came home... next morning deader than a post......

Battery was bought new 28 months ago....

Dropped in a fresh battery. all good to go...

Batteries do not last like they did a few years ago...The Red Top Optima Glass mat batteries used to go 6 years easy and many times 8 or more....Not now... Get 3 years and ya better be watching your 6......

I would suspect the batteries.....Charge them up and get a draw test done on each one.....

If one is bad....replace both...

[Bigshankhank]

Was super busy this weekend and a day slipped by me without me noticing.
Saturday morning the batteries were still holding 12.65v so I tripled checked my main engine grounds (major pain considering one is beneath the doghouse) and the one of the driver side accessory bracket was a little loose so I cranked down on that one a tad, hopped up in the cab and it fired up. Actually it was spying fine but took a little bit to catch due to the relative cold weather, as luck would have it the PO had put a momentary switch on the GPs so once I warmed them up it fired up.
FWIW I have only driven this rig twice previously as we bought it in non-running condition. First time was right after replacing the broken alternator bracket but it was leaking fuel & coolant so it was just up the street and back, the 2nd time (after fixing the leaks) was around the block till I noticed the brakes dragging. Now that I have the brakes sorted I was actually bold enough to take this up on the local highway and open it up. Its not fast, took every bit of a 1/4 mile to get to 50mph at which point I had reached the other entrance to our neighborhood and started slowing. But the engine was still pulling when I hit the brakes so all in all it was good exercise for it. Thanks for all of the help in this thread. I'm sure the batteries will need replacement as will the tires (nearing 5 years old) before too much longer but for the time being its be fine for local trips to the state park about 30 miles from here.

[DmaxMaverick]

That's great. Always a wiseguy in the works. Notice the long conversation about something so stupid-simple. Happens to all of us, from time to time.

[Bigshankhank]

That's great. Always a wiseguy in the works. Notice the long conversation about something so stupid-simple. Happens to all of us, from time to time.
Well there’s nothing worse than someone starting a “Help Me” thread and then not closing the loop as to how/if the problem got solved.
Honestly I think I would enjoy working on this thing more if it wasn’t in a van, that makes everything such a chore.

[Robyn]

Vans have some great points.....But working on them is NOT one of them....

Glad you got things sorted out....

[Bigshankhank]

Kind of spoke too soon, but to a good end. Long story short the alternator fuse was bad. However...
Daughter decided rather than taking it for a local test drive, she drove it a couple hundred miles over a weekend. Had some charging problems, so she had her boyfriend replace the alternator, but they made it there and back so yay, successful test run. Then one week later they decided to take an 800 miles road trip and it was still not charging, so they figured maybe the new alt belt was too loose and levered the alternator enough to cause the belt to snap 1/2 way through their trip. She called me, I theorized it was the alternator fuse and I checked the Autozone near them and they had a replacement fuse for $5, just pop over there and replace the old one. Their solution? Just don't shut ever off the engine, don't drive after dark and recharge the batteries on a generator when they stopped for the night. Overall they drove over 500miles with no alternator in service. I mean, I'm impressed with this engine.

[Robyn]

WOW...
That is definitely doing it the hard way....

Glad you got it fixed