Looking for someone who knows lt1s well in Raleigh nc. Not sure if mine is getting full throttle or running on all cylinders. I mean it goes when I get one it, but sounds like absolute trash during idle.
Also someone who knows transmissions too haha. It shifts at 35mph into second. Not sure sire exactly why.
Thnx for the info.
Don't know anyone down there, but maybe we can help here?
Common issues: plugged vent line for Optispark (or if its pre-95, it doesn't have one which is its own problem). Leaking gasket on the plate on top of the TB. Dirty TB. Cracked rotor on optispark. Bad FPR.
Tell me more about the transmission shifting. 35 is not abnormal for second under most driving conditions. Heck, mine shifts to second at 10, but that's because I have a 4.10 rear. If it always shifts to second at 35 regardless of your foot position, its likely a communication issue; wiring, MLP, PCM.
His is an lt1 with a th400. So trans control is independent.
Full throttle is easy enough to check. Pull air filter, and with engine off, have a helper stuff the gas. Look at throttle plate with flashlight.
curtis73 wrote: Don't know anyone down there, but maybe we can help here? Common issues: plugged vent line for Optispark (or if its pre-95, it doesn't have one which is its own problem). Leaking gasket on the plate on top of the TB. Dirty TB. Cracked rotor on optispark. Bad FPR. Tell me more about the transmission shifting. 35 is not abnormal for second under most driving conditions. Heck, mine shifts to second at 10, but that's because I have a 4.10 rear. If it always shifts to second at 35 regardless of your foot position, its likely a communication issue; wiring, MLP, PCM.
Yea it shifts at the same point all the time. Its a hard shift, vehicle punches forward. Near shift the rpms just seem too high, engine screaming pretty loud. It seems to get worse as I drive it more 30+ minutes. Needs more throttle to shift, sometimes feels like it doesn't actually kickdown into first at traffic lights.
I don't think the LT1 ever had a TH400 behind it factory, so make sure all that was done right to begin with (kickdown cable and vac modulator hookup).
EDIT: Missing cylinder is easy to find, the exhaust manifold will be cool(er) on that port, laser thermometer is great for that.
Did you ever check for that vacuum line you said you were going to check?
Chadeux wrote: Did you ever check for that vacuum line you said you were going to check?
Have not. Its been wet as hell in Raleigh all week and have no garage.
I had a Th400 act like that before, turned out the governor was stuck. Shop that built it replaced the governor and it worked fine then. Just something else to check.
Dads old gto would shift into third buy the end of the driveway with a perfectly fine th400 and 4.11 gears. Also shifted real hard because the shift kit.
As for running right, you wanted an older american v8, time to tinker with it
Get a significant other to smash the throttle (engine off of course) with you looking at the throttle without the filter on to check wot. That and spark plugs and wires and whatever the smarter dudes here say about optispark stuff i have had very limited experience with lt1's but plenty with smallblock chevys in general.
Wait great idea, offer beer and pizza to grm'ers in your area to mess with your truck for a night, you could get a lot done for a case or two of beer and a few pizzas.
Yeah, all those old 3 speeds were factory calibrated to shift pretty early (being behind engines that had the torque curve start to plateau before 2000rpm), the stock WOT shift point is only 4000-4500.
Given how tight the undercarriage is, I could see it being pretty beneficial to get crafty with some thermal tyoe foil around exhaust and on transmission pan. Mhbe exhaust heats the E36 M3 out of the transmission.
Unlikely, i mean ive had problems with headers heating up starters too much but i doubt your nukeing the trans with exhaust...does it have a cooler on it? Is it still slipping or just shifting out early
Edit: disregard mph shift points cause its not electronic. What RPM does it shift at normal driving and wot on flat ground.
TH400s only have a vacuum modulator and a kickdown switch. Sounds to me that the vacuum modulator is toast or it isn't getting vacuum.
Runs like crap at idle but good under heavy load is usually a vacuum leak. LT1s that have been in and out of cars are really bad for the EGR valve getting bent, at which point it sticks open. With the engine cold, disconnect the EGR valve's hose. Let it idle for a bit, then reach back and feel the EGR valve. If it's hot, it is passing exhaust gases and it's therefore bad.
Carolina auto masters has been doing LT1s for many years, and they're semi local.
http://www.carolinaautomasters.com/
Henry at Peake Auto in Apex may know enough about the LT1. Good guy.
Carolina Auto Masters has already been mentioned.
RPM Motorsports in Garner may also be good, but I think they shifted their focus to newer stuff.
Yea RPM motorsports was friendly on the phone but I got the vibe it was out of their wheelhouse now.
I'll check out Carolina automaster.
Great now my gas pedal is dead..
You'll need to log in to post.
