98 vortec backfiring

[Schurkey]

Stuff was getting posted as I was typing this. Some edits follow.

98 chevy 3500 with the 3.7 vortec

5.7L, I presume.

as it gets colder here in Nevada when we try to start it, it will run super rough and sometimes backfires in the cad.

Exhaust backfires indicate misfire--the cylinder-load of air-fuel goes out the exhaust valve, is ignited by the hot exhaust of another cylinder, or the heat of the catalyst.

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.

Seems to be primarily an open-loop problem. I'm not familiar with the computers on these, even though I own one. Do they have a PROM or similar "chip" that could be re-seated to potentially correct open-loop issues? (Kinda thinking "no".)

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.

Punctuation is important and around here it was taught in elementary school.

There's a big difference between "new distributor, wires, plugs..." and "new distributor wires, plugs..."

Did this thing get a new distributor, or new distributor wires? New cap 'n' rotor? Very common on Vortec engines to have a failed distributor cap, especially cheap ones. #3 is the "typical" failure, I'm told--and that would affect the "driver's side" catalyst.

We got it back 3k later

$3K? That's a heap of money for what you've described as work performed. If it didn't fix the problem, I'd be considering legal action to recover at least some of that. OTOH, given info posted after I originally typed this, a new catalyst could run significant money. Some of these parts may well have been past their service life, or--like the cat--damaged by the backfires. Any chance they gave you the old parts to examine?

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.

I assume you mean the spider injection system INSIDE the intake manifold, not the spider that holds the roller-lifter dogbones 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?

Connect a scan tool, verify EVERY sensor and computer output. Check fuel trims. Check misfire counts for each cylinder while it's cold and running bad.

I changed the fuel pump too to get me at 60psi

Did you actually test the fuel pressure?

I've been patching some holes in the floor of my field truck using CAD. Cardboard Aided Design.

I hope you didnt pay them. Sounds like they misdiagnosed the problem.
Did they set the Distributor angle?

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?

Wonderful. I would like to steal "Cardboard Aided Design" and "Try-agnostics" from you.

 

[Nad_Yvalhosert]

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

Low fuel pressure is a symptom of a lean code, as are vacuum leaks. Even though those would affect both banks of cyls, they cant be ruled out.

Have you done any additional testing?
Do you have an assistant to drive while you watch the scan data?

 

[Keith Brower]

Ok they did install a new distributor, new wires, new cap and rotor. All is new. I didn't get the parts back to check them, but it did have a new engine and new distributor put in it 8 months ago too. I did actually check fuel pressure, originally it had 50 and would drop to 40 when I throttled it up. With a new pump I sit at 62. And yes it was the spider injection system that I replaced

 

[Dud1f3r]

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

I can't tell if this is sarcasm or not. I sure hope it is.

 

[Moofus02]

I had a simular problem with a 98 g30 van. Water dripped onto the computer and corroded the case. It split and let moisture in and would do that until it warmed up and evaporated the moisture. Drove me nuts. Don't think that is an issue with the trucks but I would inspect the computer case to rule it out and that inspection is free

 

[Keith Brower]

I had a simular problem with a 98 g30 van. Water dripped onto the computer and corroded the case. It split and let moisture in and would do that until it warmed up and evaporated the moisture. Drove me nuts. Don't think that is an issue with the trucks but I would inspect the computer case to rule it out and that inspection is free

Ah, that makes perfect sense. Thank you