3.9 hotwire on a 3.5 engine

Seight-V8 · Post by **Seight-V8** » Sun Jul 22, 2007 3:01 pm

hiya all,

Having some major problems with a flapper type efi on my 3.5 seight.

Thinking it may be better to replace the whole lot with a hotwire.

I dont mind all the extra work involved, but what i need to know is will the hotwire from a 3.9 engine work ok on a 3.5 engine.

Will i have any issue with the reduction in engine capacity as regards running it on a 3.5.

Hoping the engine would run better than with a flapper type.

Dont really want to change the block as its only done 4K miles.

thanks

scott richmond

Ian Anderson · Post by **Ian Anderson** » Sun Jul 22, 2007 4:56 pm

I don't know re the Efi but would it not be cheaper and easire to go Carb?

Unless you are in cat requirement on emissions due to engine age probably cheapest?? and easiest option

Ian

kiwicar · Post by **kiwicar** » Sun Jul 22, 2007 5:45 pm

thought of a megasquirt?
Mike

Post by **katanaman** » Sun Jul 22, 2007 9:32 pm

Hotwire will work but it will overfuel on a 3.5. I seem to remember there is something you can do to change its map but whether they all have a 3.5 map or not I don't know.

badger · Post by **badger** » Sun Jul 22, 2007 9:42 pm

Use an ecu from an early efi 3.5 discovery (the only hotwire 3.5 that left the factory!) on any hotwire efi system, and the correct tune resistor - no probs.

ramon alban · Post by **ramon alban** » Sun Jul 22, 2007 11:28 pm

Seight-V8 wrote:hiya all,

Having some major problems with a flapper type efi on my 3.5 seight.

Thinking it may be better to replace the whole lot with a hotwire.

I dont mind all the extra work involved, but what i need to know is will the hotwire from a 3.9 engine work ok on a 3.5 engine.

Will i have any issue with the reduction in engine capacity as regards running it on a 3.5.

Hoping the engine would run better than with a flapper type.

Dont really want to change the block as its only done 4K miles.

thanks

scott richmond

Scott, I have been following all your posts on the non working 3.5 flapper system and it is sad that you are not getting anywhere.

This might be because those trying to help you are not getting the whole picture, or more likely, that there are in fact several faults on your current setup which makes simple diagnosis almost impossible.

From your prior post citing the injectors staying open and the resistor pack getting very hot, that almost certainly points to a busted ECU at the very least, somehow due to the ignition being left on, which should not have actually caused such a failure, unless something else was faulty too.

Because of all these problems you now seem to be be searching for an alternative such as hot wire that may be even more difficult to analyse and set-up unless you have expert knowledge or assistance.

It may not be as good or as adjustable or as potent as some alternate systems but the original Rover Efi system has a history of being tried and tested and requires no special mapping or alternative knowledge.

My advice, if you have not already done so, would be to get yourself an appropriate (flapper) efi test manual and go thro the whole diagnostic process from A to Z, because the scattergun approach rarely succeeds.

This will bring your knowledge up to speed, teach you how the system works and instruct you how to performs tests on all the system components using simple equipment (no oscilloscopes required).

If you want to follow this route I can put you in touch with the appropriate documentation.

Seight-V8 · Post by **Seight-V8** » Mon Jul 23, 2007 5:36 pm

ramon,

Thanks for the help.

If you could let me know where i can get my hands on the flapper efi test manual.

Looks like its back to the drawing board.

I've had so much trouble with this engine so far, and its very diffucult to come to the right conclusions first time.

I did have the engine running last weekend, after tracing the problem down to the injectors not flowing enough fuel.

So i thought i had cracked the problem. Then after leaving the ignition on one night thats put me right back where i was.

Just thought i might be able to get a more tuneable engine by changing it over to hotwire, but this may not be the case.

But i am always learning, and everyones opinion/help is much appreciated.

scott

ramon alban · Post by **ramon alban** » Mon Jul 23, 2007 7:02 pm

Seight-V8 wrote:ramon,

Thanks for the help.

If you could let me know where i can get my hands on the flapper efi test manual.

Scott,
I have sent you a PM

Ramon

mikemgbv8 · Post by **mikemgbv8** » Wed Aug 29, 2007 5:12 pm

I converted the Vitesse flapper system to hot-wire on my MGB with no problems.

Although I am using the ECU from a 3.9 it does not over-fuel, I fitted lambda sensors on the exhaust down pipes, it's a much more efficient system than the flapper one, slightly more flexibility at low speeds, and a noticeable improvement in fuel consumption at cruising speeds.......go for it, I'm sure that you will not regret it

kiwicar · Post by **kiwicar** » Wed Aug 29, 2007 6:20 pm

Hi congratulations on the conversion, glad to hear it is working well. Should have a capacity in the fueling system for a bit of tuning now!

best regards
Mike

mikemgbv8 · Post by **mikemgbv8** » Wed Aug 29, 2007 6:51 pm

I did it about 3 years ago, and have slowly improved on it since, it now has larger , 45mm shortened trumpets,and 65mm throttle, have just finished fitting a 123 Ignition distributor, ....can't praise it enough, really smooth idle and nice clean pick-up........can't wait to get it on the rolling road !!!

v84x4 · Post by **v84x4** » Wed Aug 29, 2007 7:06 pm

i did the same on my 3.5 it all went smooth

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3.9 hotwire on a 3.5 engine

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