740GL: many fuses have lost power!

  • Thread starter Thread starter Geronimo
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Geronimo

The car will not accelerate past 20 MPH, I am sure it is because the
ECM has lost power. Checked fuses with ign on, and car running. Fuse
nos. 11, 25, and 17-22 have no power at all being supplied to them.
These are all 15 amp. There didn't appear to be a common bus, but
almost surely they are all powered from the same source to all be
dead. I do not have a schematic for 89 model, Haynes only covers to
88 model, and I think it is different. Could someone with a correct
schematic check and see wha tis likely to have opened? I figure it
must be an ignition switch or a problem with one of the relays,
perhaps one of them right behind the fuses. However, they are all
seated, and wiggling/tapping them did not fix loss of 12v power to the
fuses. The chk. engine light WAS onfor many days until the engine
suddenly refused to accelerate. Probably a bad o2 sensor....but it's
operationally off now, but still tests when switch is first turned on.
That is why I think the ECM has lost power. Thanks!
 
should have stated it is a 1989 model. And I see from other posts
here that there is another fuse box in the engine compartment, so I
will try to locate that and see if one of those has popped.
 
Geronimo said:
The car will not accelerate past 20 MPH, I am sure it is because the
ECM has lost power. Checked fuses with ign on, and car running. Fuse
nos. 11, 25, and 17-22 have no power at all being supplied to them.
These are all 15 amp. There didn't appear to be a common bus, but
almost surely they are all powered from the same source to all be
dead. I do not have a schematic for 89 model, Haynes only covers to
88 model, and I think it is different. Could someone with a correct
schematic check and see wha tis likely to have opened? I figure it
must be an ignition switch or a problem with one of the relays,
perhaps one of them right behind the fuses. However, they are all
seated, and wiggling/tapping them did not fix loss of 12v power to the
fuses. The chk. engine light WAS onfor many days until the engine
suddenly refused to accelerate. Probably a bad o2 sensor....but it's
operationally off now, but still tests when switch is first turned on.
That is why I think the ECM has lost power. Thanks!
Click to expand...


If the ECM loses power the engine won't run at all, it controls the fuel
injectors.
 
If the ECM lost power your car wouldn't start because the ECU grounds the
fuel pumps through the FP relay.

You need a new air mass meter. The ECM is getting a 'bad' signal from the
AMM and thus reverting to a closed loop 'limp home mode', which results in a
super rich mixture and very little power. You might find that eventually
the car will start and idle, but not accelerate at all.
 
Check all connections inc ecu for corrosion just make sure their clean
disconnect battery before taking ecu connections off .Just a little
electrolysis can play havoc .
 
YOu might be right. I was completely off-track with the
observations about the fuses, I found out all of the fuses that were
not getting power were for the lights..which were all turned off.
(duh!!)
However, shouldn't I have a check eng lite illuminated if the ECM is
getting a "bad" signal from the AMM? It is not coming on now. But in
the days just prior to the car going down for loss of acceleration,
the lite was steady on. Then it ran perfectly, but was sure eating
gas.
As a test to see if the chk engine lite was still working
operationally, I pulled the EMM conn. off, started car, and I got a
chk eng lite right away. Might try pulling the o2 sensor conn. and
verify that brings it on, too. It doesn't make sense....I have a bad
sensor, but the ECM is not sensing it, as shown by the chk engine lite
being on? I am sure a new AMM would cost a lot...is there any way to
check it , like back-probing its output siginal with a DMM? Is there
something else that could cause something like a "limp-home"
condition. The car never stalls, but it just "chokes" when I hit the
accelerator.Its limited to first gear, runs perfectly in park or
neutral. Thanks for the help!
 
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