LS1Silverado98

iTrader: (8)

I just recently picked up a 69 Chevy C-10 truck, with a Ls1/4L60 that was swapped into it about 5 years ago. The truck has a pretty bad hesitation or misfire when accelerating. Seems to be worse when the engine is fully warmed up.

I borrowed a scanner tool from a friend of mine and its not detecting any thrown codes or misfires...

At this point I dont really know what to try next. My friend who did the swap about 5 years ago told me that the injectors were gummed up pretty bad and he had to soak them in cleaner. I dont know if its an injector problem or if its a tuning issue, or coils, etc...

Any help or suggestions would be greatly appreciated.

Grimes

iTrader: (3)

Does the motor have egr still installed? Could be a bad egr valve

Grimes

iTrader: (3)

Either way check the basics firsr...plugs, wires, fuel pump, ground straps

Vexzer

iTrader: (1)

Stock computer most likely to pick up an idle or steady cruise misfire, picks it up by the crank sensor [erratic motor speed].
Has it been misfiring for all 5 years [original biuld issue]? Or did it start after sitting a while [injectors/bad gas]? Misfire at WOT or mild acceleration [fuel pump/plugs/electrical]? What the plugs look like? Fuel filter changed lately? Dead kittens in the airbox?

LS1Silverado98

iTrader: (8)

No EGR, there are block off plates installed on the exhaust.

I just pulled all 8 plugs. They seemed to look pretty normal, a couple were a little oily around the threads.

The guy who did the install told me that shortly after the swap, the owner called him telling him there was some type of misfire. So, yes. I think it has been like this for years.

LOL, no dead kittens in the airbox. I will change out the fuel filter next. Pump was new when they put the engine in.

LS1Silverado98

iTrader: (8)

Here is what the plugs looked like. They are Champion plugs. Do you think I should change them?

It has Packard brand plug wires, which must have been changed out. The motor only has approx 35,000 miles on it.



I checked the grounds, & it is grounded from the engine to the firewall, and from the firewall to the chassis.

Vexzer

iTrader: (1)

Often when motor swaps use the stock lines they are just inadequate with a stock type pump. For fuel pressure test, connect a pressure gauge to a fuel rail, lay the gauge on the wiper cowl where you can see it and drive around to see if pressure maintains under load and WOT. Hell it looks cool so permanently mount it there.
Again on the fuel subject: Go to a local performance shop [call around first] and make sure they have a fuel injector test bench and really test and rebuild injectors. You would be surprised what a before and after injector spray looks like and how much improvement available. Pour-in injector cleaner cannot clean debris from inside an injector.
Those plugs look good [Iridium?], but a perfect looking plug can still be fouled, especially if operated with old fuel, replace them with cheapo's for process of elimination troubleshooting. You can always put the good one's back in. Wires can also look good and be bad.
Not part of your problem, but move the air filter out of the hot radiator air. The IAT's will drop 40 degrees and it'll run better and be happier. It will make noticeably more power, especially on a warm day. Oreilly's sells intake tubing in the retail aisle [I forget the mfg name], stuff works good & not too expensive, looks nice too.

LS1Silverado98

iTrader: (8)

Thanks a lot, this should keep me busy through the weekend. My buddy said the fuel lines were all replaced, and they used a corvette style fuel filter w/ built in regulator. I may replace this over the weekend just b/c its been 5 years.

Just ordered a set of new wires. Also picked up some AC Delco plugs. But I am now wondering if they are the correct part #? Autozone gave me 41-110 / 12621258 irridium plugs.

Agree with you on the intake. Once I get the misfire fixed, that will be my next project.