1989 740GL Running Rough

[John]

Hi all-

I had an episode today with my 740 with ~197K miles. Started fine, but
when I pressed the gas pedal, the engine would rev and drop off
repeatedly. If I feathered the gas, it ran fine, but I had to pull off
to the side of the road to travel up a hill since I couldn't give the
car any gas. After restarting the car for the 3rd time, the car ran
fine, accelerating without a hiccup. Add into the equation that my
mileage has dropped to the high teens the last 2 tankfuls, a check
engine light that will be checked next week, and a new catalytic
converter last month. Any thoughts?

On a positive note, I had no trouble driving in the snow last month
when we got 2+ feet of snow in Buffalo. All my neighbors appreciate
the Brick. Thanks in advance for your replies-

John

 

[jimmy]

Hi all-

I had an episode today with my 740 with ~197K miles. Started fine, but
when I pressed the gas pedal, the engine would rev and drop off
repeatedly. If I feathered the gas, it ran fine, but I had to pull off
to the side of the road to travel up a hill since I couldn't give the
car any gas. After restarting the car for the 3rd time, the car ran
fine, accelerating without a hiccup. Add into the equation that my
mileage has dropped to the high teens the last 2 tankfuls, a check
engine light that will be checked next week, and a new catalytic
converter last month. Any thoughts?

On a positive note, I had no trouble driving in the snow last month
when we got 2+ feet of snow in Buffalo. All my neighbors appreciate
the Brick. Thanks in advance for your replies-

John

Hi John,
Have you checked your fuel filter lately? If you haven't had any
problems since,
maybe you got some bad gas? Hope it has cleared up.
jimmy
1990 740 GL wagon

 

[Tony]

Hi all-

I had an episode today with my 740 with ~197K miles. Started fine, but
when I pressed the gas pedal, the engine would rev and drop off
repeatedly. If I feathered the gas, it ran fine, but I had to pull off
to the side of the road to travel up a hill since I couldn't give the
car any gas. After restarting the car for the 3rd time, the car ran
fine, accelerating without a hiccup. Add into the equation that my
mileage has dropped to the high teens the last 2 tankfuls, a check
engine light that will be checked next week, and a new catalytic
converter last month. Any thoughts?

Don't quite understand 'rev and drop off'. I assume it is
A. Automatic
B. Injection with lambda sensor

I guess it is loosing power because of too much or too little fuel, or
possibly bad ignition.

From the previous bad economy it sounds like its running very rich
(progressively so) or too lean at some points, which may have damaged
the cat and be the reason the check light is on. Air mass meter would be
the first suspicion, maybe lambda sensor.

 

[John]

Hi guys, thanks for your responses. Tony, you're right on both A and
B. And AMM was replaced about 100k miles ago. I dumped in a bottle of
fuel injector treatment and the problem cleared up in 20 miles. I'll
find out more when I get the check engine light checked. Thanks again-

 

[John]

Update on the old girl.

My business trips took me by the Indian Reservation, so I would fill up
there, saving ~25 cents a gallon. When those trips stopped, I went
back to my usual station. Right off the bat, my mileage went from 16
to 23 mpg. Check engine light was for the throttle body, adding a
couple more mpg. I was never a fan of the different station/same gas
theory, but now I'm a believer.

Hi guys, thanks for your responses. Tony, you're right on both A and
B. And AMM was replaced about 100k miles ago. I dumped in a bottle of
fuel injector treatment and the problem cleared up in 20 miles. I'll
find out more when I get the check engine light checked. Thanks again-

A. Automatic
B. Injection with lambda sensor

I guess it is loosing power because of too much or too little fuel, or
possibly bad ignition.

From the previous bad economy it sounds like its running very rich
(progressively so) or too lean at some points, which may have damaged
the cat and be the reason the check light is on. Air mass meter would be
the first suspicion, maybe lambda sensor.