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runs rough under 2.5k rpms

855 Views 3 Replies 3 Participants Last post by  jmarkiss
Hello i bought a rough running 1990 range rover, it has a 4.2l swapped into it already.

The problem is it runs very rough, stumbling and misfiring under 2500rpms, but once your above that it runs great!! smooth and pulls hard.

Ive done a full tune up, plugs, wires, fuel pump and filter, cap and rotor and even the ignition module on the distributor. Ive sprayed carb cleaner all over the top end looking for vacuum leaks and found none, i removed and cleaned and checked operation of the stepper motor and it seem fine. Also clean MAF, i checked voltage from alternator and even disconnected it to see if it made a difference.

It seems to rev up fairly smooth in park but under load it cant get out of its own way until it gets over 2500rpms

I have a parts 92 rover and tried swapping some sensors one at a time to see if anything would help(fuel temp sensor and engine temp sensor and stepper motor), even swapped the ECU... still no progress.

Any ideas?? im stumped!!

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any codes present? check your fuel delivery pressure should be 30 to 45 psi, replace your fuel filter. if your intake hose is the older style cloth wrapped consider replacing, they leak.

use 14 cux software such as rovergauge to view sensor operation in live time, check your coolant temp sensor and proper operation of your 02 sensors. this page has very good information, http://www.britishv8.org/Articles/Rover-14CUX-EFI.htm
Check timing and both mechanical & vacuum advance.
No codes are present. The fuel filter and fuel pump are new, although i still need to check fuel pressure. Ive been stuck because the battery was dead and two of my battery charges conveniently stopped working this week. So new charger on it today.

Ive never heard of the rover gauge, ill do some looking into that.

Need to recheck timing again also.

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