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  #1  
Old 05-01-2006, 01:04 AM
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Join Date: Jan 2002
Posts: 177
Why EFI fuel cuts out above 1500 rpm ?

Greeting forum members,

I'm hoping that someone can help me diagnose the problem I have recently been experiencing with the engine in my 1972 350sl not running above 1500 rpms.
The engine starts up and idles properly but I can only rev the engine up to 1500 rpms.
If I attempt to rev the engine over 1500 rpms the engine will cut out and drop down below 1500 rpms.
If I keep my foot down in an over 1500 rpm throttle position the engine will begin to hunt and start to back fire out the manifold air intake.
This wasn't a problem when I parked it last winter.
Per my induction timing light I am getting a continous spark.
Something in the system seems to be cutting the fuel from being injected above 1500 rpm.

Thanks,

Knarf

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  #2  
Old 05-01-2006, 01:42 AM
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Have you replaced the fuel filter recently? The fuel pump? Maybe the system can't deliver over a certain amount without losing pressure.
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  #3  
Old 05-05-2006, 05:50 PM
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don't know about 72

but 87 has a rev limiter, i believe a feature of the fuel pump relay, that shuts fuel down before tach redlines to protect the engine. Symptom of the rev limiter kicking in: Engine dies and comes to life rapidly over and over til you let off the throttle. I didn't like the way my was cutting in too often so i adjusted transmission cable (actually a rod) for a little quicker shift and it solved my problem. But if you're cutting out at 1500 rpm and do have a rev limiter, I would borrow a bud's fuel pump relay to see if your's is bad (even thought it operates properly in all other aspects). Just a thought!
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Old 05-05-2006, 06:52 PM
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Join Date: Jul 2005
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The limiter weren't installed in Mb back in 72.
More like a clogged fuel filter.
If the ignition is out after 1500 RPM then you may hear back fire as the unburnt gas leave the manifold it can ignite when contact the hot exhaust manifold.

OT my Eldorado had that happened once, cannot over 40MPH and hesitating, so we pulled out the mini fuel filter. But threading her back was a big prob, crossed many times. In the end we just took out the filter and glued the screw back in and added a bigger online filter.

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