Why would changing from v6 to v8 cause this?

Asked by Feb 15, 2016 at 05:45 PM about the 1994 Chevrolet C/K 1500 Silverado Stepside RWD

Question type: Maintenance & Repair

I just put a v8 motor in my truck, going from a
v6.I'm now having problems with the truck idling
when first started then runs fine after a few
seconds.Also shuts off by itself like it just runs out
of gas, but starts right back up.Smokes when I
first start it and smells like its burning
rich.Changed distributor cap, rotor, plugs, wires,
map sensor, coolant temp sensor, tps, computer,

29 Answers

Also forgot to mention that it boggs down when going down the highway when I mash on the accelerator.Timed the motor, so idk what would be causing it


Could be a fuel problem? Did you check that out?


Bogging could be a plugged up cat.

Changed the filter and changing the injectors tomorrow.No change with the filter

No cat on the exhaust pipes now


WHEN U want to change parts in ur vehicle you have to make sure if it is perfect with your engine >>>like ur pumps for 8 cylinder it is not the same in 6 cylinder its more powerful >>i think ur problem in injection system >>tell me more am almost engineer

Best Answer Mark helpful

I have the original throttle body that came with the engine also

Didn't use the throttle body off of the v6

My v6 was a 93 and the v8 is a 94 350 stock engine

Took the egr off and put the blockoff plate.No help really

Changed the pick up coil on the distributor and engine runs great now but still having problems with the truck dying on me.Also changed the fuel pump and filter.Any ideas what would cause it to die?

I was told the transmission could cause this.When I put it in drive, it takes a second to lock in.What would the trans have to do with it dying?


Don't know if you got this going, but an idea would be to check the fuel pressure to make sure you have the 9 to 13 lbs pressure. I'm thinking that its possible the fuel regulator in the TBI may need to be rebuilt. The spring in there goes weak. Check by blocking, pinching off the return line with a fuel pressure gauge hooked in the main line, the fuel pressure should increase up to 20 to 26 lbs. They make a rebuild kit for the TBI. Just my 2¢

Haven't got it lined out yet, but have replaced the fuel pump, filter, and had it hooked up to a diagnostic computer.The guy told me I might try changing the steering column out.Do you think this could also possibly fix my problem?

The guy who hooked it up said it had something to do with the ignition control and the map sensor was getting to high voltage

Forgot to mention the tranny shifts hard and takes longer than usual to shift.Have to wait a second for it to lock in from reverse to drive.The guy who did the diagnostic is a tranny specialist and said it wasn't the tranny


I seen you had changed the fuel pump and filter. Still could be a fuel issue along with other things. Unless 12V is not present at the coil when it shuts down, changing the steering column is not going to do anything. If there were anything wrong with the steering column then yes, but otherwise the electrical components can be change if there were a problem. I see you changed out the computer, so did you install the one for the 5.7L? Is the EGR system hooked back up? It should be, make sure the EGR valve works properly, closes all the way, & the diafram holds pressure. The 02 sensor is a must. So when you had it scanned what are the code numbers?

Have you checked the Idle Air Control Valve? I had the same problem with my 94', we replaced just about every sensor, distributor, cap, rotor, spark plugs & wires and kept having the same problem. Once we changed the IAC, problem was solved.

The egr is not hooked up now because on the v6 it was electronic only with a different hookup wire than the on for the solenoid on the v8

I have a blockoff plate where the egr goes.Is there any way to bypass the computer?

Also I'm using the harness that was used on the v6.The egr wire is the only difference


Not that I know of. Why is it not hooked up? You need the ECU and wiring harness for that motor. Was this done?

I changed the ecu but not the wiring harness

I was told the wiring harness would work, but unfortunately I guess it doesn't


Well you know it is different if you can't hook up the EGR valve.


Looks like you fixed things that needed to be, the wiring harness gets changed when switching the ECU. This may be some of the problem you are having, I was always told be good people to change the harness. I don't know if it is different or not, but if the connectors are not the same I'd say it would have to be changed out. I think you are still gonna have some problems to diagnose but that will come easy enough at this stage of the game.

I appreciate the help from you guys.Looks like ill be looking into changing this out.Keep you all updated

I appreciate the help from you guys.Looks like ill be looking into changing this out.Keep you all updated

Did you ever figure out what is was? I'm having the same issue with mine..

Your Answer:

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