View Full Version : 03 cummins - backfiring

June 15th, 2011, 12:22 PM
So my truck has started backfiring through the exhaust. It's an '03 HO with a six speed, 130k miles and is equipped with a tst box, pac brake, and a 4 inch exhaust. I changed the fuel filter and the fuel pump was already tsb'd before I bought truck.

What causes this? Low fuel pressure? It is not consistent. Sometimes it will happen when pulling the camper and sometimes with no load. I don't have anyh issues with cold or hot start.


Chris Halvorson
June 15th, 2011, 04:35 PM
This could be several things:

Any codes?

First try disconnecting all your power mods and set the TST back to factory program.

Still have problem...

Could be the injectors, ecm or a combo of the two. Are you comfortable with a millimeter? If you are, you can ohm out the drivers on each injector. Anything over 1 ohm..it is toast.
Check that and we can go from there.

Do you have a rail pressure gauge?

Chris Halvorson
June 15th, 2011, 05:55 PM
I shouldn't assume....so make sure you disconnect the injector leads before you ohm the drivers. If your injectors are good, next would be check wiring on the two bank harness to see if your shorting out somewhere.

Have you ever changed out your Fuel control actuator?

You stated this happens intermittently right?

June 15th, 2011, 09:29 PM
I have never changed out the FCA, but I understand they can develop a leak and start bleeding off fuel pressure. I don't have a way to test rail pressure.

The TST will cause an occasional CEL. Apparently this is a common issue and has something to do with the CPS. The CEL will go away on it's own after a few start cycles. I am tempted to bypass the TST (I have a bypass harness) but I don't know if that will solve the issue since the TST harness will still be in place. The TST is a box that wires inline between the ECU and engine harness. There's no program to reset on it.

it is intermittent. It will do it under moderate to heavy throttle from empty weight to have the toy hauler hooked to it. There's nothing unusual with the EGTs (I don't let it exceed 1200F) and boost seems to be normal (max I ever see is 25psi).

I will have to find a spare moment and ohm the injectors and see if they are OK. I suspect they are since the truck runs and starts fine otherwise. I don't think it's ever had a valve adjustment so its probably due for this. I have read that a valve not in adjustment can cause the backfire as well.

Chris Halvorson
June 16th, 2011, 02:31 AM
I thought you had the TST powermax CR like the smarty. I would bypass it and see if that is your problem.
Valves could be an issue. While you are checking the injectors, might as well do the valves. Makes sure you have a cold block..010 intake, .020 exhaust. I had several out of adjustment on my 3rd gen at half the mileage your at. My 2nd gen had four valves out at 100k.
If the truck is running smooth, no white smoke at operating temp...I would think the injectors are fine....but don't rule them out. Easy to check the drivers.
You actually "use" your truck, so I would think the injectors are not all coked up.
I am interested in what the fix is. Hopefully it is a cheap one (like time only).

Chris Halvorson
June 24th, 2011, 01:29 PM
Any updates?

June 24th, 2011, 03:53 PM
Not yet. I am planning on poking around on it this weekend. It's not my daily drivers.