3k stumble? Exhaust rattle?

[95lotus]

I was googling around trying to find out if anyone else has experienced a hesitation at around 2700RPM during acceleration, and found the reviews of some ECU chip upgrades that mentioned the "3k stumble" in them. I couldn't find any more info on this stumble...can anyone fill me in? I had the 36K C-service done within a month of my purhcase of my S4S, and I didn't remember this hesitation prior to having the service done.

While I'm thinking about it, I also have an annoying rattle that makes the car sound cheap while driving through the parking lots that is coming from a vacuum pulloff that increases the exhaust backpressure after the cat. The linkage has a cable that is enclosed in a metal tube, and it's these two vibrating at certain RPMs that's the culprit. Is there supposed to be some sort of gasket or O-ring between the cable and the tubing? Flipping the valve manually moves them in unison, but I can't tell if they can ever move independently. Anyone know of a fix?

thanks,
Bill

[size13]

Not the same car, but I had similar problem on my 01 Impreza, I disconected the battery overnight to resert the ECU and it ran much better afterwards.

[rob.e]

The "stumble" is a well known issue. I believe the upgraded ecu's available from PUK etc improve on the factory setup.

Ref the exhaust - i think a lot of the 4 cylinder guys remove the ebpv entirely. Again, PUK and others sell a 'spacer' that replaces this.

cheers
Rob

puk site : http://freudhoefer.de/lotus/esprit/index.html

[cnh1990]

Sometimes the EBPV bracket bends and you just grab the vac actuator and just bend it back into place increasing the tension on the spring so the rattle goes away. Also what may appear as a EBPV rattle may actually be the cat core rattling. If you undo the 3 bolts that hold the EBPV on to the exhaust and slip it off isloating the muffler and the cat with a gap. Use a rubber mallet or your hand and tap the cat. If it rattles it's the cat. Tap the muffler if it makes noise it's probably the muffler comming apart. If both are silent it's the EBPV.

Calvin

[d didit]

Hi there 95 S4,

I had the exact same thing happen to me. I do not have the ebpv gate at all and it was still rattling. First check to make sure it is not the valve. Then if it is not, as in my case since I removed mine, bang on the catalytic converter with your hand and listen for rattling. If it does, more than likely, the rear brick of you cat has come loose. When this happens, it just rolls around in there. I got a screw driver and just broke it all out. I plan on purchasing a new performance cat soon.

Dindo

[95lotus]

Hi all,

Thanks for the advice everyone. I watched the valve while my helpful wife stepped on the accelerator, and I can see the valve begin to resonate and rattle. I've set aside some time this weekend to do some other work on her, and I've added this to my list. By the way, the cat. was replaced when I purchased the car back in April. The car wouldn't pass inspection, and I couldn't take posession until it did. The previous owner spent ~$1000 getting one FedEx'd in and installed...better him than me! :^) Now I worry about what the valves might look like. He tended to run some high octane fuel which apparently is what caused the cat. to fail.

And Rob, a very special thanks to you! :^) I told my wife that the experts here told me that the car needs a new ECU chip and she's bought into it...OH YES!! Now, which one(s) to buy for my little S4S, hmmmm.... :^)

thanks again,
Bill

>> Edited by 95lotus on Friday 12th September 06:39

[rob.e]

95lotus said:

And Rob, a very special thanks to you! :^) I told my wife that the experts here told me that the car needs a new ECU chip and she's bought into it...OH YES!! Now, which one(s) to buy for my little S4S, hmmmm.... :^)

Glad to be of service

[95lotus]

Well, I pulled off the EBPV today and, after a couple of hours dremeling the welds off of the butterfly valve, put it back on...rattle be gone! I was toying with several ideas, including the purchase of the spacer, and ended up removing the butterfly plate and putting a kink in the middle of the cross-shaft causing it to bind up. It looks stock, but without the vacuum pull-off (in keeping w/Lotus tradition and making things lighter).

Thanks again all!

regards,
Bill ('95 Esprit S4s)

[Mark91SE]

Regarding 3k stumble. The setting of the wastegate can have a lot to do with this. If you remove the wastegate solenoid connector under the hatch relay cover behind the coolant header tanks. Then drive in several gears at hi-boost... verify you're getting nominally .60 bar. The lower bar the wastegate setting is, the more prone to 3k stumble.... not to exceed .65 bar.
This is my experience anyway and I tired a lot of different settings.
- Mark91SE

[95lotus]

I'll try that. I had it in for the C-service at a Lotus dealer a few weeks after I bought it, and I didn't notice it until I got it back...maybe the mechanic mucked with it and got it wrong (either that, or my high level of enthusiasm after purchasing the car caused me to overlook it). Any pointers to site(s) that I could learn more about wastegates from? This is my first turbo.

thanks,
Bill