Twisted46

Been driving the swap LM4 around for a couple of months now, probably 150 on evening a weekend cruises. Running on a terminator X, and the same transmission (T5) and diff (R200) as before the swap. Previously had 355 SBC and did not have the below issue.

Car idles and cruises great, also runs amazing at WOT pulls through all gears. The problem comes in when I give it part throttle while cruising (mild acceleration). 3rd, 4th, or 5th between 2000 and 3500 rpm if I give it say 25% throttle the whole car starts to shake like crazy. The engine does not sound unhappy by any means and data logs show timing and fuel are at 36 and ~15 respectively which are the target values. That seems a little lean but not enough to cause this kind of event. If lay in to the throttle it clears up and takes off right away.

I did have to use a slightly longer driveshaft from fast shafts but it came balanced and this is not speed dependent.

Does this sound like a drivetrain or tuning issue to you guys? everything feels tight in the driveline.

33willys

iTrader: (1)

I'm running an LM4 in my '39 and had an ongoing lean condition problem that eventually was traced to the injector size. Turns out the LM4 uses a much smaller injector than other 5.3 engines. Mind did not shake like you describe and I doubt that a lean condition would cause that. Where I would look is the angle between the engine/trans and the rear end. Also check the universals on both ends of the driveshaft. I once did have a failing joint cause a shake that I could feel.

G Atsma

Not true. Your engine uses 25.2 #/hr. injectors, just like most other Gen III 5.3's.
The exception is the L59 flex fuel engine which uses 33 or 36.6# injectors depending on the year.