Hi all,

Im new to the boards and glad to be a part finally after just reading all the posts. So i have my own problem to post hopefully i can get some help and get this out of the way.

Ive got a 350 engine that has tbi injection on top. i originally had a 305. its an 89 firebird base coupe model (whatever its called) I have an open element on it. The engine is a truck engine from an 87 model (i guess LO5 is the code)

I get this problem where the car drives good until i go faster than 45 mph. It feels like it starts to retard/pull timing and then it chugs and hesitates badly like a misfire or somethin. Its only when im at partial throttle, for example giving it a tiny bit of gas, but if i accelerate hard then it runs fine. I have replaced tons of things: fuel pump, knock sensor, esc, fuel lines seem good, new 55# injectors, new wires, new plugs

Someone told me it might be the coil. What would be a good unit to replace it with, because I need it to be relocated somehow so my air cleaner doesnt hit it.

Fuel seems to be delivered good. I bought a TBIchips.com part for my computer and ive had 2 burns on it so far. i was thinking it was the chip because when i put the old chip in it runs semi ok (at least on the highway but crappy on the street in general). Maybe too lean?

Should i consider vacuum leaks? O2?

Any thoughts are greatly appreciated and i look forward to being a member of this awesome community
thanks

Ben

 

Funny the only part that you changed that made the stumble go away was the chip. I'd look there first, people have had good and bad luck with mail order chips. Looks like your not having good luck. I'd have him burn you one for a stock L05 and try that, if it doesn't fix it get one from GM.

 

I had him burn a LO5 chip from the start. Ive heard bad stories of mail order but after 2 burns for my basically stock setup i figure it should be pretty close. Im trying to make my own datalog cable and send him the data.

I wanted to consider other things though. O2 sensor? Vacuum leaks? What can i look for and test to narrow this down more? I noticed that after I replaced the knock sensor its been getting better, as in it seems to run smoother. When i let off the gas it sometimes pulls back and hesistates as if changing the timing. Then it starts to chug. Only when i nail certain patterns, for example light throttle...brake...let off...light throttle...

I wish i could take a video and attach a good microphone so it would be easily heard what it is doing. Words seem useless

 

Sounds like a possible lean issue with highway mode. Above 50 or so, the learn capability is disabled and the ecm runs at a leaner AFR with additional timing. Doesnt work half bad but if the engine is running lean already it can possibly cause lean misfiring and other issues, and even detonation.

 

i've gotten chip from tbi but i log him data and hes a great person to work with.i had a similiar proble and it has that seens i have longtubes i needed a 3 wire o2.so with a regular one it get cold and not send info to the ecm

 

This is exactly why alot of us on the boards harp on DIY prom tuning. You just don't get to really hear and feel a motor when it's 3,000 miles away.

Get your data loging cable up and running and go from there. No use just swaping parts and shooting in the dark when a 10$ cable will tell you what your ecm is doing for sure.

 

TA vid. would definatly help.

Id almost be willing to bet on it being an issue with highway mode. Almost...

ALL the f-body ecms had highway mode (lean cruise) enabled, and it not only adds spark, but pulls fuel as well. This would fully account for what your seeing. Once you give the car some gas, it enters PE and your problems vanish.

The only way to verify this is to disable HW mode. But, alot of the def. files dont have the necesary HW mode params (min temp, speed, AFR, etc.) defined so your 'tuner' probably wouldnt be able to properly disable it. IIRC, there is some gotcha with the HW mode params. Something like the min temperature used for HW mode enable being also used for a closed loop parameter. Ill have to take a look at it. If you can burn your own proms, a simple manual change to the bin would be all thats needed to quickly check whether the HW mode is at fault.