940 Poor running after 100 miles

I have a 940 2.3lpt auto, I have owned it for 2 ? years and its been a great car.

Went on a 200 mile journey at weekend and in the last 20 miles it started to lose acceleration, but would still run smooth if I didnt try to accelerate too hard.

After a 6 hour rest if performed as normal again on the way home until the last 50 miles when it got gradually worse. 10 miles from home it was almost dead so I pulled over and let it rest for 15 minutes then it ran better allowing me to get home.

It feels like a fuel issue rather than a misfire but I dont understand why it does this only after a long run. Its also hard to identify as its fine again now.

I started it up and it ran fine then unplugged each fuel injector in turn and noticed a lumpy idle each time, fuel injection is not something im used to messing with though.

Any pointers what to check, btw the fuel filter is fairly new and I filled up at 2 different garages on the day so think fuel should be ok.

First thing that comes to mind is that your tank lift pump is dead or the pick up hose failed. The pressure pump will suck gas from a full tank but has trouble as fuel level drops. Two hundred miles would have taken the tank to less than half full, you filled up and then ran it down again.

Use a gauge to check the fuel pressure under load. Tape the gauge to the windshield so you can observe while driving.
If the level of fuel in the tank affects the car, look at the tank pump and power supply. But don't ignore the high pressure pump.
Check for a voltage drop across the fuel pump relay.
These tests should be done when the problem is present, if intermittent.

I hooked up a diagnostic lamp to the obd and returned the fault 121 (mass air flow meter fault) which seems as though it could be the problem as symptoms are poor running and heavy fuel consumption.
I did think it was using more fuel but could not be certain, anyway no local suppliers could get one so I have ordered one off ebay which should arrive in a couple of days and fingers crossed it will be a quick and easy fix.

5 gallons down from full tank and my 88 765 Turbo would stall in hot weather. Replacing the intank pump fixed the issue.

Oily said:

I hooked up a diagnostic lamp to the obd and returned the fault 121 (mass air flow meter fault) which seems as though it could be the problem as symptoms are poor running and heavy fuel consumption.
I did think it was using more fuel but could not be certain, anyway no local suppliers could get one so I have ordered one off ebay which should arrive in a couple of days and fingers crossed it will be a quick and easy fix.

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Keep us updated. Having a similar problem on cold starts. Car won?t idle unless I give it gas then after a minute of super rough idling (with my foot on and off the gas) it smooths out but not before the check engine light comes on.

colgate41 said:

Keep us updated. Having a similar problem on cold starts. Car won?t idle unless I give it gas then after a minute of super rough idling (with my foot on and off the gas) it smooths out but not before the check engine light comes on.

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For your issue I'd guess engine coolant sensor.

lummert said:

For your issue I'd guess engine coolant sensor.

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Right, after some asking and digging here that might be my issue. I have the part, just need to install. Thanks for the info.