Thread: Lt1 Problems Please Read Kinda Long

Tweet

ok heres the list of problems i have been having over the past 2 months and i cant solve it and noone on camaroz28.com wants to help it seems like. ive listed them in order that i posted them on camaroz28.com. please help if you can.


1/20/05
ok guys heres the problem.

i have a 94 z28 and ill will be crusing at 50-55 mph and the tach is at around 1700 rpm and ill give it a little gas to bump it up to 60 mph and the car stars shaking and stuttering. is my opti going bad? also my lights interrior and exterior will start flashing and my volt gauge will jump from around 14-15v to 18v and down to around 10v i think my alt is going bad but checked the voltage from the alt and it stays constant at 13.5 volts someone said my batt. is bad but if that was the case wouldnt it die fast if i have my radio on without the car running?

any help is appreciated. thanks

-----------------------------------------------------------------------------------------------------the problem stoped for a day -----------------------------------------------------------------------------------------------------------------------
1/22/05
Well guys the problem stoped for a day and i figured all was good. But thats what i get for thinking. Took the car to hilton head isl sc to used a friends scaner and no codes were in the ecu and to say the least the prob. is back. this time much worse . the car stutters under a load again but there are times i cant get over 50 mph. I thought it might be the fuel filter so i replaced it and it needed it the fuel that came out of the tank side of it looked like used oil. so i droopped the tank and cleaned it out and i thgought this would fix the prob. well after finishing up around 8 tonight its still "bogging" or "stuttering" under load. Im hoping its the cats when i check them tomorrow. the voltage is still fluxuating <sp>. we tested the alt and bat. and there both good i checked the voltage at the alt and bat. and there fine but if i check from a accessory like the cig lighter or a tail light its still juming from 16.3v to 10.1 volts. i checked it at a relay under the hood and its fluxauating just like on the inside. i checked all the grounds on the enging and body that were under the hood. is there susposed to be a ground going to the tranny? if there is i couldnt find it..

any ideas on what to check next if the getting rid of the cats doesnt work?
and anyidea what could be causing the voltage spike/drop?


----------------------------------------------------------------------------------------------------the problem stoped for a few days so i took it to the local track---------------------------------------------------------------------------------------------------------------------------------------


2/06/05
Well I went to the dragstrip tonight for the first time this year and my first run i redlighted but cut a 14.326 @ 96.43 mph and the second run the lights drop befor i am fully staged. 3rd run i do my burnout and stage and when i leave the line all is fine but i get a lil wheelhop and then the car bogs bad. so bad that the car wont go over 50 mph. i cut a 27.395@49.26mph. i was afraid to try it again so we packed up and left. any one have anyidea what this could be the car ran fine almost all the way home . it did this one more time maby 500 ft out of the dragstrip drive way. i got down on it to see if it would do it and it stayed below 50 again. but if i dont get down on it and ease into the throttle the car is fine. if i ease on it runs great and if im over 50 and i get down on it its fine but if im under 50 and get down on it then i cant get over 50. please help. my mods include descreened maf. and k&n airfilter and thats it. the car has new plugs , wires, fuel filter, and a new opti (replaced 2 months ago) im lost guys so any help will be appreciated


2/15/05
the other week i put a new opti in and replaced plugs and wires again. to say the least i still have the problem. while the plugs were out we did a compression tes and the numbers came up 190, 190, 190, 210,200, 185, 190, 190. with that being ok. i started tracing wires to see if there were any brooken/frayed/damaged wires. Guess what i found 1 that was broken. it was a black wire on the drivers side just above the opti where there are 2 white wires that are grounded to the block. so i fixed that and i also replaced the ground strap thats in the same spot with some 8gauge power wire. and i replaced the rest of the grounds with the 8 gauge power wire. i then took it for a drive and to my dissapointment it was still stuttering/shaking. So with a new opti, plugs , wires, grounds, i decided to check the injectors to see if they were firing. I did this with a noid light. all of them are firing throughout the rpm range. so i checked the fuel ressure and with the vacume line pluged up its at 37 psi and with it unplugged its at 43 psi. so that was fine. I then checked the tranny fluid and it was dark brown with some matter floting in it. so i have came to the conclusion that it is the tranny causing the stuttering/shaking. but what makes no sense to me is why would it not let me go over 3k rpm under a load. if the clutch packs are shot then wouldnt it slip instead of bogging the motor?

Edit: the new grounds fixed the fluxuating voltage.

-----------------------------------------------------------------------------------------------------the problem stoped for a few weeks and then returned---------------------------------------------------------------------------------------------

3/23/05
Ok guys so far I have replaced the opti, the coil, the plugs and wires. I have removed the cats and replaced them with straight pipes. I also replaced all of the grounds with 0 gauge wire, and the car is still bogging once it warms up. I can drive it to the store and it will run fine aslong as its cold, but once it warms up it boggs bad. Sometime to the point where it stalls out. It will crank right up, and once you put it in drive and start moving it boggs again. I have tried resetting the ecu several times thinking maby that would fix it and it hasnt. So i have a few questions .

1. How do i test the ignition module?

2. Could the opti be bad already? i just replaced it a month ago.

3. I did a compression test on it when it was cold and got good numbers. 190, 190, 190, 210,200, 185, 190, 190 I was told that when it warms up the compression will drop some due to expansion of the metal and could it expand enough so that most of the compression was gone and it cause the problems that i am experienceing?\

4. Could this problem be sensor related? its not throwing any codes and when i scan it it doesnt have any stored.

thanks for the help guys.

where did you come up with those fuel pressure #s? dont sound like enough to me. i dont have a way to look it up right now but i think that 37 might be low. you need to drive it and watch the pressure to.

is the lt1 tuned port injected if so lt1s10 may have something with the low fuel pressure. maybe your e.g.r but usually you would get engine light and code. good luck on the ecu quest

My truck had this problem that when i sustained rpms above 2500 or so it would bog up stutter even stall, or when i punch it around the same 2500-3500 mark it would do the same. After messing with the ignition to no end, i went through like 4 coils, i figured out that after it got real bad, my timeing chain was stretched and i guess the certain forces in that rpm range caused it to do funky ass things.

I"m no expert but what you describe seems to be almost the same thing, i dont have a lt1 but they both have timeing chains so you might wana check that.

Another interesting thing was that sometimes it would run perfect but you could literally turn it off go buy a soda and come back 45 seconds later, turn it on and it would barely go down the road.

WHEN YOU DESCREENED MAF YOU PROBABLY GOT DIRT ON SENSORS!!!! DO NOT GET ANY CLEANERS OR ANY LIQUID ON SENSORS CLEAN WITH ACID BRUSH OR OTHER SOFT C L E A N BRUSH THE TWO TEMP SENSORS INSIDE MEASURE GALLONS OF AIRFLOW INTO THE ENGINE SO 1 SPECK OF DIRT ON ONE OF THE PICKUPS CONFUSES THE ECM SO IT DOESNT KNOW HOW MUCH FUEL TO DELIVER ALSO LT1 SHOULD HAVE 45-50PSI AT IDLE WITH REG DISCONNECTED AND MAF WILL NOT SET CODES FOR DIRTY PICKUPS