99 K3500 454 overheats under throttle

[stutaeng]

I figured my cats were clogged also, climbed underneath the other day only to realize I don’t have any cats either…………or downstream o2s. Somebody ran dual exhaust into a dual in/dual out muffler. Technically speaking in Pa a 1 to. Doesn’t need emissions. No visual, no test. Nothing. But I just want it to run the way it’s supposed to.

I think you need a special tune to delete the lower O2s from the ECM? I think that's what my brother said based on a quick search. Maybe Blackbear?

Or just go find yourself some used ones from a parted out truck. I don't know if junkyards have them? I've read here they are not allowed to sell them because of some EPA regulation or something? Don't know.

Or get yourself some new ones?

Or there's a way to "fool" them? I've seen that on a forum here. Not sure if that applies to the 7.4.

 

[99BB3500]

It hasn’t thrown an SES light at all so maybe it’s already done? The existing exhaust is old and getting ready to fall apart so it’ll get replaced also

 

[GoToGuy]

In the situation of not knowing alot of history with your dually, and overheating. The items I checked on a new purchase used truck. Radiator cap correct type and condition, seal and pressure and tested. Water mix condition. Looking in radiator tank tube condition, still has 3 or 4 tube core. Big block radiator is 2 inches taller. When flushing coolant pull hoses off Heat from heater works? Dash temp indication, confirmed.

 

[GoToGuy]

Thats pull hoses off heater core so you can garden hose backflush, coolant does not move as fast therefore it can act as a "settling/ sediment pond" reducing heat transfer. I have a air blow nozzle removed the rubber metal tip. Replaced with a piece of 18 inch metal brake tubing. For 4 or 5 dollars at Oreally's I picked up 48 inch brake line male fittings flared blah blah. Cut one 18 inch put a 90 bend in an inch or two from tbe end. Get another cheap blow handle stick the 30 inch in it with a 90 bend near the tip. You now have a speacial tool. With these you can keep all that crap and debris from piling up in that area at the bottom of fender when you open the door or up around the hood hinge area. The long one if you decide to fab it, works well to back blow the radiator. Have looked at the fins lately? My wife said" there's a weird smell in front of tahoe". Ok ( i just finished oil change ) I'll look. I should have taken a photo. A big ass pigeon is cooked to condenser radiator area. Feathers all over the front of condenser. So how hell....pull all the front grill and...wait. So necessity became the airblow tool. Feathers, feathers everywhere. It can be amazing who much crap gets stuck in radiator. Grass, flowers, big ass dragonflies, small rocks, piece of gasket(?) Just big air screen catching anything too big to through. So when you have an overheating problem add radiator/ condenser area plugged/ occluded to your trouble shoot. Thats my usual and " you won't believe this".

 

[GoToGuy]

As to the in front of cat convert sensor and aft of convert sensor. The sensor in front of or before the convertor is for the ECM to monitor control mixture. The sensor behind, aft or aftercat is decated to monitor catalytic converter health. As the rolling exhaust rules got tougher like a rolling snowball, two cats and smarter ecm watching mix closely, eyeing converters. There have devices to plug in replacing aft cat sensor to bluff the ecm for those whom have removed the cats. And I'm sure i read or somebody's got a device to change the ecm setting. But California no can do. Good luck!

 

[99BB3500]

Ok so I think I found the issue. From what I’ve read the fuel pressure should be 60 psi with the key on engine off (?). When I turn the key on the fuel pressure goes to 45psi and stays there. Start it up and it stays at 45. Easily hitting the pedal the pressure will go up to 52 but no higher. If the pump is bad the overheating would make sense because it would be running lean. Am I right in this assumption?

 

[99BB3500]

Drove it long enuff to almost hit normal operating temp. Fuel pressure stayed between 45-49psi. At wide open throttle it hit max 52psi until 2k but abs then dropped to 50psi all the way to 4K. Pedal was on the floor. I’m starting to get frustrated.

 

[Schurkey]

Several possible issues related to low fuel pressure.
1. Partially-plugged fuel pump "filter sock"
2. Failing fuel pump
3. Hose between pump and "hanger" leaking
4. High resistance in the fuel tank internal wire harness
5. High resistance in the fuel pump wire harness outside the tank; including high resistance in the fuel pump relay contacts, or anywhere between battery and fuel tank
6. Partially-plugged fuel filter, and
7. Failing fuel pressure regulator

If you have the ability to plug or pinch the fuel system return hose, while running the pump KOEO using the bypass wire, you could test fuel pressure with zero fuel flow. If it can't make above-spec pressure then, it's pump or wiring, but probably not the regulator, or the filters.

 

[99BB3500]

What is the fuel pressure supposed to be? I did change the filter thinking that might be an issue but got the same results. I’m leaning toward the pump starting to go out

 

[Schurkey]

What is the fuel pressure supposed to be?

My '97 service manual says it's supposed to be between 56--62 psi.

I assume your '99 is similar.

I’m leaning toward the pump starting to go out

Don't "lean toward" anything. At least test and verify the power supply voltage as close to the pump as you can get--the most-rearward harness connector should be OK; and verify that the pump ground is OK, too. Perform the voltage testing WITH THE PUMP RUNNING. Use a voltmeter, and a length of wire so that you can connect to the battery negative terminal rather than a chassis ground.

That still doesn't verify the final couple of feet of wire outside the tank, or the harness in the tank; but if you install a pump, install a fresh in-tank harness at the same time.