98 vortec backfiring

[Keith Brower]

I have a 98 chevy 3500 with the 3.7 vortec and as it gets colder here in Nevada when we try to start it, it will run super rough and sometimes backfires in the cad. If you slowly add throttle till you can get it up to 2k rpm and hold it there for a while, 2 minutes, it will then idle down and run great. We took it to a shop and the parts bombed it with new distributor wires plugs MAP MAF and new o2 sensors and a new drivers side cad. We got it back 3k later and it still does it. So I changed the Tps and idle air cleaned the throttle body, and replaced the spider under the intake manifold. Still doesn't run good at the beginning of the day but then runs great all day after the initial start up issues. Any ideas on where I go from here? Is it an ECU issue? Please help and I thank you all for any input you can give me. Oh yeah, I changed the fuel pump too to get me at 60psi
Thanks again

 

[movietvet]

Just curious, what does it do when you unplug the coolant temp sensor?

 

[movietvet]

Forgot, welcome to the forum from Oregon.

 

[Nad_Yvalhosert]

I have a 98 chevy 3500 with the 3.7 vortec

That's a funny engine size...

and as it gets colder here in Nevada

Yup. Cold in New Yuck too.

when we try to start it, it will run super rough and sometimes backfires in the cad.

Back fires where? What is a cad?
Cab? Cabin?
Cat? Catalytic converter?

I took an architecture course in school, we used CAD. Computer Aided Design.
I've been patching some holes in the floor of my field truck using CAD. Cardboard Aided Design.

If you slowly add throttle till you can get it up to 2k rpm and hold it there for a while, 2 minutes, it will then idle down and run great.

You rev it at 2000 for 2 minutes? That's wasteful. Youre gonna shorten the life of every fluid under the hood.

We took it to a shop and the parts bombed it with new distributor wires plugs MAP MAF and new o2 sensors and a new drivers side cad.

Again: wasteful and expensive. I hope you didnt pay them. Sounds like they misdiagnosed the problem.
Did they set the Distributor angle?

We got it back 3k later and it still does it.

They put 3000 miles on it?
Shyt. I'd sue 'em.

So I changed the Tps and idle air cleaned the throttle body, and replaced the spider under the intake manifold.

Ahhh. Try-agnostics. Bad idea.
Why keep changing parts? What are the MIL codes?
Did you properly set the TPS via a scan tool to 0.5V?

Still doesn't run good at the beginning of the day but then runs great all day after the initial start up issues.

There's a clue. It runs poorly in open loop.
What does the temp sensor read on the datastream?

Oh yeah, I changed the fuel pump too to get me at 60psi
Thanks again

Only 60? That's a little low. Should be 66psi key on.
Did you replace the fuel filter too?

 

[movietvet]

That's a funny engine size...



Yup. Cold in New Yuck too.



Back fires where? What is a cad?
Cab? Cabin?
Cat? Catalytic converter?

I took an architecture course in school, we used CAD. Computer Aided Design.
I've been patching some holes in the floor of my field truck using CAD. Cardboard Aided Design.



You rev it at 2000 for 2 minutes? That's wasteful. Youre gonna shorten the life of every fluid under the hood.



Again: wasteful and expensive. I hope you didnt pay them. Sounds like they misdiagnosed the problem.
Did they set the Distributor angle?



They put 3000 miles on it?
Shyt. I'd sue 'em.



Ahhh. Try-agnostics. Bad idea.
Why keep changing parts? What are the MIL codes?
Did you properly set the TPS via a scan tool to 0.5V?



There's a clue. It runs poorly in open loop.
What does the temp sensor read on the datastream?



Only 60? That's a little low. Should be 66psi key on.
Did you replace the fuel filter too?

I thought I picked posts apart but you are on a whole other level....I am not worthy...!!!

 

[Nad_Yvalhosert]

I thought I picked posts apart but you are on a whole other level....I am not worthy...!!!

Well, it was challenging to read through a wall of text and O.P. gave a lot of info, very few solutions, no testing process, and confusing abbreviations.
I had no choice!

 

[movietvet]

Well, it was challenging to read through a wall of text and O.P. gave a lot of info, very few solutions, no testing process, and confusing abbreviations.
I had no choice!

Not doubting the need at all. So many times the "parts cannon" is shot at a problem with no good results. At least he/she listed everything they tried and how a shop did not listen to his list of concerns and not "throw" a CTS at it, for s*h*i*t*s and giggles, is beyond me. Unplugging it and starting it does not ring up anything at the cash register.

 

[Keith Brower]

Just curious, what does it do when you unplug the coolant temp sensor?

I replaced that as well. Was thinking the same thing

 

[Keith Brower]

That's a funny engine size...



Yup. Cold in New Yuck too.



Back fires where? What is a cad?
Cab? Cabin?
Cat? Catalytic converter?

I took an architecture course in school, we used CAD. Computer Aided Design.
I've been patching some holes in the floor of my field truck using CAD. Cardboard Aided Design.



You rev it at 2000 for 2 minutes? That's wasteful. Youre gonna shorten the life of every fluid under the hood.



Again: wasteful and expensive. I hope you didnt pay them. Sounds like they misdiagnosed the problem.
Did they set the Distributor angle?



They put 3000 miles on it?
Shyt. I'd sue 'em.



Ahhh. Try-agnostics. Bad idea.
Why keep changing parts? What are the MIL codes?
Did you properly set the TPS via a scan tool to 0.5V?



There's a clue. It runs poorly in open loop.
What does the temp sensor read on the datastream?



Only 60? That's a little low. Should be 66psi key on.
Did you replace the fuel filter too?

Replaced fuel filter too, yes I used a tool to set the TPS to.5 volts, it is a 5.7, mis typed..no codes at all come up. Every once in a while I get a lean code bank 2

 

[Keith Brower]

Replaced fuel filter too, yes I used a tool to set the TPS to.5 volts, it is a 5.7, mis typed..no codes at all come up. Every once in a while I get a lean code bank 2

And in the cat. Auto correct sucks