Severe run issues- 1990 740T

  • Thread starter Thread starter jimb
  • Start date Start date
J

jimb

Good day,

My 740T has started running awful.

Car is 1990 8 valve 740 turbo with 4 speed/overdrive (M46)
transmission.

It is rather cold here.

Car was warmed up and driving normally. Check engine light came on and
it driveability went to crap.

Wife had it so I had to go pick it up as she was afraid to go the last
few miles to home.

It starts and idles OK.

Push accelerator and RPM surges and drops repeatedly and there is no
power to speak of.

I managed to get it rolling and up-shift to keep the RPM low and I was
able to limp home. Good thing there were some downward slopes.

I am suspecting:

Failed AMM (electrical connection, dead AMM)

A clog in airstream

Dirty throttle body

Thoughts?

Side note- amazing that it will chug along in OD at 1000 RPM once it
is moving.

TIA
 
jimb said:
Good day,

My 740T has started running awful.

Car is 1990 8 valve 740 turbo with 4 speed/overdrive (M46)
transmission.

It is rather cold here.

Car was warmed up and driving normally. Check engine light came on and
it driveability went to crap.

Wife had it so I had to go pick it up as she was afraid to go the last
few miles to home.

It starts and idles OK.

Push accelerator and RPM surges and drops repeatedly and there is no
power to speak of.

I managed to get it rolling and up-shift to keep the RPM low and I was
able to limp home. Good thing there were some downward slopes.

I am suspecting:

Failed AMM (electrical connection, dead AMM)

A clog in airstream

Dirty throttle body

Thoughts?
Click to expand...


Sounds exactly like a bad AMM, could also be a large air leak, such as a
hose has come off between the turbo and throttle body. If the check
engine light came on, there should be a stored fault code.
 
Good day,

Car was outside and I needed to get it inside.

Had trouble getting it up the drive.

Disconnected AMM to see if that helped and it didn't.

I assume I introduced an error code by this action.

I have never read error codes before, only seen it done. I am not sure
how to do it.

Took a very brief look on Brickboard, but haven't found anything as of
yet as to the process and readings.

Only have a crappy manual.

Did notice oil around where the hose to the turbo attaches to the
intercooler.

Will open up air cleaner box today hopefully.

TIA

jimB
 
Did notice oil around where the hose to the turbo attaches to the
intercooler.
Click to expand...
I've got a hunch.

Loosen and disconnect the thick hose from the front of the turbo and
put your finger in there to make certain that the turbine spins freely
on the shaft.

If it is frozen: your turbo is toast.
 
I've got a hunch.

Loosen and disconnect the thick hose from the front of the turbo and
put your finger in there to make certain that the turbine spins freely
on the shaft.

If it is frozen: your turbo is toast.
Click to expand...

Turbine spins thank goodness.

jimB
 
jimb said:
Turbine spins thank goodness.

jimB
Click to expand...


Check and see if the fuel pump is running, it's surprising how long an
engine will idle on residual pressure in the line.
 
Check and see if the fuel pump is running, it's surprising how long an
engine will idle on residual pressure in the line.
Click to expand...

Well, I drove (in a fashion) about 3 miles plus and moved it around
the door yard a bit the day after.

The surging under load must be the key.

I need to figure out how to fetch the error codes.

jimB
 
jimb said:
Well, I drove (in a fashion) about 3 miles plus and moved it around
the door yard a bit the day after.

The surging under load must be the key.

I need to figure out how to fetch the error codes.

jimB
Click to expand...


Have you checked carefully for air leaks? I've seen the rubber boot pop
off the throttle body before, as well as oil collect and soften it,
causing a section to blow out the bottom. Coolant temp sensor for the
ECU fails from time to time as well.
 
Finally got to dump the OBD codes.

For the Fuel Injection (in order):

232 Fuel trim (lambda control) too lean or too rich at idle
223 Signal missing to/from idle air control valve
121 Faulty signal to/from Air Mass Meter

The third (and maybe all) I would imagine that I induced by
disconnecting the AMM in order to "limp home"

Cleared the codes & started the car...

Check Engine light went out on it's own, car still runs crappy, light
did not come on, no new codes.

For the ignition (in order):

234 Throttle Position Switch (TPS) idle signal faulty
214 RPM sensor signal absent intermittently

I have not cleared these as of yet to see if they come back.

I am in very unfamiliar territory here. Last car I really worked on
had a carburetor and breaker points.

TIA
 
jimb said:
Finally got to dump the OBD codes.

For the Fuel Injection (in order):

232 Fuel trim (lambda control) too lean or too rich at idle
223 Signal missing to/from idle air control valve
121 Faulty signal to/from Air Mass Meter

The third (and maybe all) I would imagine that I induced by
disconnecting the AMM in order to "limp home"

Cleared the codes & started the car...

Check Engine light went out on it's own, car still runs crappy, light
did not come on, no new codes.

For the ignition (in order):

234 Throttle Position Switch (TPS) idle signal faulty
214 RPM sensor signal absent intermittently

I have not cleared these as of yet to see if they come back.

I am in very unfamiliar territory here. Last car I really worked on
had a carburetor and breaker points.

TIA
Click to expand...

A bad RPM signal could certainly explain poor running. That could be the
crank angle sensor, IIRC this is mounted to the back of the engine block
pointing down in the top of the bellhousing on a '90. TPS switch is easy
enough to check, it may just be out of adjustment.

121 and 232 could certainly be caused by unplugging the AMM. Not sure
about 223.
 
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