loss of power in hot ambient temperatures

[oldmansax]

This is an intermittant problem driving me nuts, which, BTW, is a short trip! I have '99 6.5 turbo, dually 3500, 4x4, auto, 198,000 miles, all synthetic lubes, properly maintained, all stock except new FSD & cooler from Kennedy about 5 months ago. It looses power when ambient temp is REALLY hot. Engine temp is always OK. No smoke, just no power. Example: long trip over the weekend. Truck running perfectly. Outside temp about 89 to 92. Made a pit stop for soda & bath room. Left the truck running for A/C (about 15 minutes). Engine temp at 205 when I returned. got back on the highway & had NO power. Ran like a sick 6.2. Ran that way all the way home (about 2 1/2 hours) When I got in it this morning, it ran fine. It has run fine all day. This has happened all summer. Does the FSD reduce fuel when it (the FSD) get real hot? I can provide more info if anyone wants it. Unfortunately, I only have stock gauges. I hard wired the waste gate once just to check for boost problems. Didn't make any difference. Could the cat converter be swelling closed when it gets real hot? I had that problem with a gas engine once. I'm open to any suggestions unless they involve money...LOL & thanks!

[rustypig]

Don't quote me but, I believe that the computer will cut back on boost pressure when it notices things getting hot. An engine temp of 205 shouldn't make much difference (many believe that 205 is just about the optimum temp a diesel should run at anyway).
My money say's it's more boost related. The turbo creates some very HOT air as it is. Combine that with very high ambient temp and it can drag performance way down if it's not producing ENOUGH boost. Kind of weird that it seems to be intermitant, which is why I'd start looking at boost related items first....boost selenoid, vac pump (like how many hg it's pulling), lines to selenoid and back to wastgate actuator etc.
I'm assuming the engine temp dropped as soon as you got moving again right....fan clutch not engaged continually?

[oldmansax]

Temp dropped back to 195 (normal) as soon as I got back on the road. Fan cycles on & off & temp never runs above 200 unless I'm pulling a trailer in the mountains. That does not happen very often because most of my trips are East Coast flat. I thought boost was the problem too so I had the waste gate physically closed (open?) with a piece of copper wire on this last trip so I could bypass all the computer controls. Unless there is some way to stop the turbo, I don't think boost was the problem. It runs perfectly until I stop somewhere & leave it idleing when the outside temp is hot (80+). I can run all day, no matter how hot, as long as I don't stop, or, if I turn off the A/C when I stop so the temp does not run up. Thanks for the reply though. At least soomeone else is thinking in the same direction as I.......

[JCM5]

Your not alone on this one.

I have the gauge package, and when the XX gets hot. Not the coolant but some device under the hood. It does kick back the boost level. I run normally at 13psi at full load. When my fan start to come on, my boost will drop to 9 at full load. Even after the engine temp drops back to 190 gauge.

Something in the computer im convinced. but dont know how to reset it. Time with the engine off seems to do it.

By the way I never leave the engine running at idle on a hot day. Mine start every time for the last 135K, regardless of temp. I have replaced 1 PMD, but beleive it or not it failed when it was 40F outside and rainy.

[dslpwr]

I WAS READING A OLD POST FROM BILL HEATH ABOUT THE SAME THING.
HE WAS REMOVING AIR INTAKE SENSER SO THAT COMPUTOR DID NOT SEE HOT AIR FROM TURBO AND SHUTTING FUEL OFF.
HE WAS LEAVING IT WIRED UP BUT RUNNING SENSER IN HEATER HOSE .
MY TRUCK DID THE SAME THING UNTIL I INSTALL INTERCOOLER.
JUST MY THOUGHT ON THE MATTER, I HAVE NOT DONE THIS.

[charliepeterson]

dslpwr is right. The small sensor in the intake manifold is looking at Intake temps. When it thinks the air is too hot it will cut back on power.

[oldmansax]

I thought it must be something in the computer controls! I will move the sensor & see what happens. I have been using GM diesels since the '70s (remember the 5.7?) but this is the first electronic one I've had. It appears that newer is not always better. I will be making a couple of trips w/trailer to Ohio & one to Florida next month. I'll post the results. Many thanks to all!

[Cowracer]

Log me as a victim of this one too. I have the turbomaster so the computer is not controlling boost. on cool days, I get 1 -2 lbs at idle, 7-9 cruising and 12 max. On hot days, I get nothing till about 1500 rpm then a couple of lbs at crusing and maybe 9 tops.

On the good days, it feel bitchin, on the bad days it feels like a bitch.

I tried just disconnecting the plug to the IAT sensor. No codes, no improvemnt on hot days.

I'd like to know if removing the IAT and keeping it plugged in will help.

Thanks,

Tim

[dslpwr]

YOU MIGHT CALL BILL HEATH, HE SEEMS TO KNOW WHAT GOING ON.
I BELIEVE YOU LEAVE IT WIRED UP TO THE SENSER AND PLUG THE HOLE.

[Jim P]

This is just a thought but maybe the computer is sensing that the fuel is too hot. It would stand to reason that the pump would probably get hotter while the truck is just setting idling, especially with the air on. I know there is a thermistor inside the pump that senses the fuel temp. When I hook up a scan tool to mine it tells me the fuel temp. I don't know for sure but after the computer senses the fuel is too hot, it probably cuts back on fuel and boost. Even after it cools, it probably won't reset the proper fuel and boost until you restart it. Again this all just speculation.

Here is a link to a site that tells all about how a ds4 pump works. I thought maybe some of you would be interested.

http://www.geocities.com/MotorCity/Show/3753/6_5_litre.htm


Jim P.

[ChevyDooley]

I dont know if its a good idea to start removing temp sensors unless you have at least an intercooler. At least try and make it right. My truck provides 14#'s of boost even whens it overheating. ;) I get 1/2 of boost at idle.

Youch!