Rough running 4K+ rpm...now barely idles - Page 2 - LotusTalk - The Lotus Cars Community
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post #21 of 24 (permalink) Old 06-30-2019, 05:47 AM Thread Starter
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Originally Posted by tmusc View Post
Is that connector near the header tank and the TPS sensor? Does this car have the revised harness?
Its near the main coolant tank in the rearmost passenger side of the engine bay. I’m not sure about the revised harness though.
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post #22 of 24 (permalink) Old 06-30-2019, 05:53 AM Thread Starter
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Hi Mike, So glad to hear that the S4s is running the way it should. A coupled of things I question , you said you don't have the service manual? I included it with the sale, also there are a couple of plugs back by the header tank area that went to the deleted exhaust back pressure valve. If you have to replace the fuel pump , it's going to be a real pain in the a$$ because of all the sealer on top of the tank, sorry, on the bright side I did give you a new fuel tank O ring from JAE. Keep up the good work. Dave S4s [IMG class=inlineimg]/forums/images/LotusTalk_2015/smilies/tango_face_smile.png[/IMG]
Dave thanks I realized that after going back through all the materials. Apologize for the misspeak.
Ahhhh glad to know where that plug used to live. I was wondering if that might’ve been it but wasn’t sure.
I’ve got another trip coming up but when I get home I plan to trouble shoot the fuel system. I know the PPPO had the fuel tanks cleaned and sealed to prevent further rust but after checking pressure if its not up to par I’m going to replace the fuel filter first just in case. Then it’ll be decision time from there.
For now I’m just glad to be able to drive!
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post #23 of 24 (permalink) Old 06-30-2019, 06:41 AM
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Big Picture, not sure if you thought about this - keep in mind - dont want to scare you - fuel pressure issues are particularly "dangerous" on turbo cars. If you are driving aggressively on boost and the fuel pump does not deliver the goods (fuel) the cylinder charge can go very lean very quickly. Very lean = detonation and potential damage.

I imagine the computer is smart enough to detect a lean condition very well and quickly but no where near like a modern car.

So be aware of this potential and if its missing or you hear pings or something is not right stay off the boil until you can diagnose.

One issue I have read about here and have experienced on other cars. The fuel pulsation dampener is just above the fuel pump in the tank. This apparently gets old and allows pressure to bleed off. Normally the failure manifests as hard to start because the fuel bleeds off when the car is switched off. Replacement fuel pumps for our cars come with a "pulsation dampener delete" (its a piece of hose). I can imagine that if this plastic bit was really coming apart it might allow pressure to bleed off and cause problems with fuel pressure at high RPMs and boost. Its hard to imagine you would not also have hard start problems but keep it in mind. And if you do end of changing the pump delete the dampener.
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94 Esprit S4 - Silver
Previous - lots of hot rod Air Cooled 911s
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post #24 of 24 (permalink) Old 06-30-2019, 06:56 AM
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Also I thought I was having fuel pump issues and Dave S4s recommended resetting the computer. Made all the difference. Try disconnecting the battery for a bit and reconnecting and let the computer do its relearn on a driving cycle and see if there is any change? cant hurt. My issue was hard start.
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94 Esprit S4 - Silver
Previous - lots of hot rod Air Cooled 911s
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