So i have an lt1 in my 59 impala. Just got the car running and it has died on my a couple of times already. Fuel pressure is normal when it happens, maf is good. Today i put a my scan tool on it and i can see the short term fuel readings start at 128 in open loop and begin to fall and the car stumbles and dies.. So I decided to unplug the sensors and it runs excellent, as soon as i plug them in it will drive for like minute or two and begins to stumble and die. NO codes.


I have a tune done by madz28.com so it has no egr,air, all emissions are deleted.. Is it possible that these BRAND NEW delphi sensors are no good?

 

Check the range of the sensors. They should fluctuate wildly from low mv to high mv. 0-9xx

 

from what i remember they go up to like 400 mV but they do fluctuate..

I know that the 128 fuel trim is stock trim.. why is the car leaning itself out till it dies is the question..

the exhaust does not smell rich when the sensors are plugged in.. if i unplug them it smells like my buddies Lt1 camaro..

 

You need to data log the engine and post it here. Something has to be wrong if it will not idle when you only plug in sensors(force it to go closed loop), but idle fine in open. Do you think you have a false lean condition? Maybe a intake leak or another?

Might even be a good idea to contact madz28 and have him look at the log.

Do you still have your old sensors? Maybe swap them back in to see what happens. The MV should go up and down on the sensor all over the range.

 

The short terms always stay at 128 in open loop. They will not start moving until the PCM senses the O2 sensors are hot enough to be working, the engine coolant is hot enough, and the timer has timed out. When it enters closed loop, it intentionally switches the short terms back and forth from slightly rich to slightly lean because that what the cat needs to work correctly.

If the short terms start to drop when the PCM goes into closed loop, something is telling the PCM the engine is running excessively rich, and first it will drop the short terms to lean it out, and it the short terms stay below 128, it will start dropping the long terms until the engine is fueled correctly, and the short terms are switching back and forth either side of 128.

Could be a true rich condition, could be a "false" rich condition.

 

I am a friend of F550maranello2, i believe the PCM is incorrectly reading a rich condition and leaning the car out to death. With the o2 sensors unplugged, the car not only runs correctly, but the exhaust (no cats on car) does have a smell to it...not a rich smell but a normal exhaust smell....when the o2 sensors are plugged in...the smell goes away and the exhaust feels cold if you stick your hand by the tail pipes...then if you watch the scan tool it keeps going leaner and leaner until it dies.
As for the engine, it is a stock LT1 with a madz28 tune done. The exhaust is a true duel setup. I have read in many places to ONLY use AC Delco o2 sensors....the car currently is running Delphis.....could this be the reason?

 

This is how it behaves.. i turn it on cold.. it will idle just fine for lets say 5 minutes i pull out of the garage and can hear that the idle control valve is trying to keep the engine alive.. it begins to stumble i give it a little gas and it behaves normal.. i drive a bit till its warmed up and all of a sudden the same thing happens... ill get on the gas a little and feel the engine bog and die... .. this is nuts..

 

Delphi is the company that GM spun off at least 10 years ago, including many AC Delco products. Eventually, many of the AC Delco brand names were changed to Delphi. GM repurchased a majority interest in Delphi. So, bottom line, AC Delco and Delphi appear to be basically the same product. However, over the years since our LT1's were built, the design of the O2 sensors, at least the visible external shield, has changed.

Do the short terms drop dramtically on both banks, at roughly the same rate? Have you checked the wiring? Does the O2 wiring include extensions?

 

wiring is to sensors is good, i have no extensions. The do both drop at about the same rate.

 

so i borrowed my buddies bosch oxygen sensors and the car runs great, he had his on his stock tune and made it run rich.. he let me borrow them and so far no problems whats so ever.. i have some ac delco sensors also i have not put them in yet... im hoping that the delphi sensors were the problem..