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finnerty

Primary vs. Secondary fuel pump question

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What is the functionality and operational mode of the 2 separate fuel pumps on the V8 ?

I assume that the primary pump always runs continuously and that the secondary pump cuts in & out only under certain demand conditions ? Or, are they both supposed to run simultaneously (e.g., as a low pressure & high pressure paired system?)---- or, is the secondary pump just a "back-up"?

Currently, when I look at the OBD data while my car is running, only the primary pump is "on" --- secondary pump is "off". Is that normal, or do I have a problem with my secondary pump / relay --- should it also be "on" ?

Car seems to be running a bit rough & stumbling at idle, so I'm looking at possible fuel delivery issues as the cause.....although, strangely enough, I'm getting no error codes at this time. Fuel trim values do look a bit unbalanced though...

Thanks

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The primary pump runs all the time with the secondary pump being used at times of increased fuel demand. At start up the secondary pump is run for a very short time to ensure it is used at least once during every drive cycle.

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Hello,

 

My car is under service right now. Not a Lotus workshop, so I gave to the tech guy the free OBD tool and he could read P1103 Fuel Pump #2 Relay or Circuit Shorted.

He will have a look to the relay and fuse link to fuel pump 2, thanks to parts catalog available on full member area.

And if not enough he will look at the wires...

 

But does anyone had the same code. What is the most common reason ? Only the relay (I hope so) ? Is it really a problem to drive like that for the moment ?

 

Thanks mates.

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David:

sometimes to look into the workshop book is the best way ;)

 

 

 

just as Derek mentions ..the 'two stage' pump system is meant to compensate fuel demands under WOT and 'engine-start' conditions ..as such to deliver fuel for the 8 +2 injectors under full load, and if more fuel injection is required (cold start , fuel condensation on the intake walls)

 

..if you monitor your OBD live data, it should state that under a 'full load condition' (see *load* under OBD parameter list) both pump work.

 

the good thing with this concept is, on an older Esprit V8 ..with a notable 'noisy' and aged primary pump, you simply undo the pump system from the tank, and replace the less used secondary with the former primary  ..so you interchange them in the pump-mounting and don't need to spend much money on replacements :D  (been there, done that..)

Edited by Günter

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The secondary fuel pump relay also controls your after-cooling system. It operates the electric coolant pump and the fans. So, if it is failing, you need to make sure it's replaced or you will likely have head gasket problems in the near future. Now, I should ask, is the car actually stumbling, or is it hunting for idle? If it's hunting, then I would look to cleaning the idle air control motor as they gum up over time.

 

However, if you have drastic trim differences between banks, you will definitely want to check your cam timing. The lotus V8 is VERY sensitive to cam timing and the car will compensate for it with the o2 sensors up to a point. After a certain amount of the cams being out of timing, the computer will set a lean or rich condition on either bank. The most common cam to slip is the right hand side (UK drivers side) intake cam.. which, awkwardly enough is the cam the engine references for TDC.

 

As for the fuel pump system:

 

I usually replace the factory primary pump with a Walbro pump from a mustang. The primary pump, however, is not usually the problem. It's actually the fuel lines themselves. The fuel lines vulcanize horribly and if you are having the famous "warm start" issue that is almost always blamed on injectors.. it isn't usually the injectors.. its the fuel lines in the tank. Pull your fuel pump "hat" out and replace the rubber lines and the clamps. The factory clamps are junk, you need to replace them with stainless steel screw clamps. The reason the warm start and idle usually have issues is that when the lines leak, the pressure does not remain in the fuel system. So, it takes longer for the fuel system to prime without normal fuel pressure.

 

Let me know how it goes...

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