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Discussion Starter #1
Have had a problem that is unresolvable, 1991 Classic Range Rover 3.9 litre, 132,000 miles.
Historically had a warning light which has been linked to O2 sensor but never caused running issues.
The engine runs, runs well at high or low revs when stationary. Either immediately or after 500yards the engine will stutter & unable to drive at all "normally" have to "feather" the throttle.
We have replaced the coil, ignition module, disconnected & reconnected the throttle position sensor, changed the mass air flow sensor 3 times (used the "bad" one in a running Jag with no issue).
Tested the fuel pressure to be 35 psi during any type of running, good or bad. Used a test light to show that signal for fuel during running goes dim when stuttering starts ( signals that sufficient fuel isn't being sent to the engine??)
Finally replaced the fuel injection ECU with a used one and engine continues to stutter. (14CUX....)
Generally if we change ANYTHING the RR runs well for 500yards or so even if it was running badly before.
We need some inspiration here
Mike
 

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Check the tube from the air box leading to the throttle body.....if theres a rip in the liner on the inside of the tube maybe your not getting enough air in the mixture. something similar happened to my 91 classic and it runs fine except i have to replace a intake manifold gasket. Thats about the only thing i can thinks of for the time being.
 

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My initial thought was also that it sounds like an air leak. Have you tried spraying some WD40 around the air system while the engine is running to see whether you get a change in revs as it gets sucked in through a leak?

When you say about the test light to check the signal for fuel, what exactly are you testing? Current to the fuel pump or signal to the injectors?

Are you only running petrol, or do you have an LPG conversion on the car as well?

What does the spark look like, both when running well and when stuttering?

Have you tried unplugging the air flow meter completely and running on 'get me home' settings?
 

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Discussion Starter #4
We can check the tube from the air box to the throttle body / change it
The "test light" was the signal from one of the injectors.
We can try running with the air flow meter completely unplugged to see how it runs on 'get me home' settings.
I'm not sure the spark was checked when driving - it was checked while stationary; for some reason we lost all spark, which led to the ignition module replacement.

It is petrol only.

One of the other tests used the signal from the MAF sensor and the computer graphic showed at 3.6 MV or so it wasn't reaching the desired 4.3 millivolts in a "Snap throttle response" test. Can't say I understood the test but it convinced the engineer that the MAF was bad - we don't think it is.

If you only rev the engine while stationary it seems absolutely OK so I'm not sure if spraying WD 40 will show anything but we'll try.
 

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The WD40 test will still work at idle - it's testing for air leaks, so works irrespective.

You won't be able to check the spark whilst driving (well you could, but you'd need a daredevil volunteer! :shock: ), but I think you need to check the spark at idle - if you're not getting a crisp, blue spark you could have a problem. Is your ignition amp attached to the distributor or does it sit next to the coil?
 

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Discussion Starter #6
Well, the temporary fix seems to be to short out the "water temp sensor" - then the engine runs normally - just went across Pittsburgh Pa, 50 miles without any stuttering or bad running.
Interestingly if we replace the sensor with others (scrounged from other donor cars, Jag etc.) the stuttering problem reoccurs.
We can also turn the problem back on by removing the jump wire across the water temp sensor.

So we fixed the problem, but there is still a lingering problem because it won't run with a functioning water temp sensor !!

Mike
 

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You have really solved the issue at it's basic point of trouble shooting. It sounds like you have a wiring harness issue. To be more specific you have a wire issue within the harness. From the temp sensor start tracing back/shorting out the temp sensor wire 6 or 8 inches at a time in the harness until you no longer have the issue. From that point run a new wire or repair the short and check operation with the sensor running. You are on the right track, now the PITA is to find the break in the wire.
 
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