Engine is 305 TBI with 747 ECM. Symptoms: engine is running very rough, idle is hunting up and down and it's stalling when MAP sensor is connected. If I removed electrical connection or vacuum hose from it, engine ran reasonably good and was drivable, but ran obviously very rich. Connecting the sensor back almost suddenly stalls engine. Replaced the sensor with another from working car, nothing. Vacuum gauge connected to that port, shows -0.8 bars and reading is very stable. Checked for vacuum leaks, found nothing. Checked reference voltage - 4.97 volts, sounds good. Checked MAP sensor with voltmeter, the reading fluctuated between 0.8 and 3.0 volts. Checked datastream and the reading is same. As engine runs so rough and idle speed hunts up and down, fluctuating reading seems quite logical. Any ideas, what to check?

 

check for vacuum leaks,my tbi350 was running the same way until i replaced the vacuum hose for the map sensor.

 

Actually I replaced the vacuum hose to MAP sensor first anyway. So no vacuum leaks there.

 

Any more ideas? I checked fuel pressure, it's 10 psi and stable, double checked vacuum leaks, measured vacuum with gauge again, nothing seems wrong.

 

Hi Sweden calling!

I have exactly the same problem with my 1989 350 TBI with 747 ECM that i have installed in my 1966 Impala!

When MAP is disconnected and ECM is running on default settings it purs like a kitten but when i connect the MAP it starts stumbling, surging and stalling when in closed loop, i think it's going rich...

I am simply not using the EGR (valve still in but not connected) and PCV (plugged), just trying to keep it as simple and clean as possible. ;-)

I have replaced, CTS, MAP and O2 sensors, still the same.
From what i understand the IAC and TPS is working, but i am considering to replace then as well, just in case.

Fuel pressure is 10psi stable.
No vacuum leaks.
No error codes.

I am using WinALDL, but since i am a rookie i have problems understanding it all...
I attached some WinALDL log data and would really appreciate if someone more skilled than i could have a look.

My car in its current state:


The whole Impala build can be seen on my blog at http://www.tomme.se

I don't mean to hijack this thread and will make my own if i cause any problems.

 

An update:

My Impala is running much better now!

I replaced also the IAC and TPS, so i have now replaced all sensors except the knock sensor.
In an attempt to keep the engine room clean i previously relocated the MAP inside the car (under dash) and it was connected with a quite loch rubber hose, i have now changed that so it is mostly hard plasting lines from the TBI-unit to the MAP sensor.
And i re-connected the PCV.

I guess reconnecting the PCV made the biggest change since it affects the MAP situation by introducing a vacuum leak.

After running the car in closed loop for a while it starts behaving much better and i can see in the BLM tables of WinALDL that it is compensating and it gradually runs better.