hello..im having a problem with my 1990 gmc sierra 5.7L..i just threw on a set of headers that has no o2 bung the truck runs good but breaks up,surges.If i was too drop it from dead stop it will bog then pick up,if i let off the gas after alittle bit of throttle it will surge.Even before the headers ive been having problems like this.It also sounds like it knocks after mid thorttle.So far ive replaced.fuel filter,plugs,wires,coil,cap,rotor,ign module,tps,iac,map,injectors,newer TB,pcv,magnaflow cat..The timing set at 8.let me know what you guys think...maybe i could crossed the plug wires?i understand that having no o2 makes the truck run alittle bit richer.im thinking the timing needs to be advanced alittle bit.. but you guys are pretty good from the past threads ive read..Thanks.The truck always ran a tade bit on the rougher side.I was told the motor was rebuilt but i think they just dropped in a lower mileage one.

 

you need the o2 sensor,buy a bung and have it welded in.
timing connector behind the plastic cover on pass side just above valve cover ,small single wire connector,brown with black stripe wire,must be unplugged to set timing.must be set to 0.

i have the same truck 4x4. headers, chip, msd etc.

 

Things to check..
Fuel pressure, should be 9-13psi.
Timing, stock at 0, should advance when you rev it.
Engine vacuum, should have 17.5"or higher at hot idle, smooth needle not bouncy.
Do a compression test.
Make sure the EGR system is working right, the egr valve shouldn't be open at idle.
Check the grounds, there are some on the back of the engine (heads) that are hard to get to, they are the ground to the ecm.

 

i was just outside messing with it,was checking out the dis to make sure the plug wires were all correct,until i came across the number 5 and 3 cylinder plugs where hand lose.tighten them up started it up,runs fine idles great.now i have to figure out this header leak.What type off gaskets do you guys recommend i got paper on there and i knew i should have gotten fel-pro.

 

Earl's Dead Soft - the best gaskets out there. Thick aluminum or copper (they sell either), that gets mashed when tightening the bolts, seals all leaks. No need to even try anything else.