Boost control problems

[The Veg]

So last weekend I had a good experienced wrench give my Esprit a thorough once-over to see just what state it's in and assess its mechanical condition. While he gave it a good rating overall, he did express some concern over the boost-adjustment valve that the previous owner had installed. Basically, it's a small knob mounted on the engine side of the relay-box wall that controls a spring-and-diaphragm type thing that is plumbed inline into the small rubber tube that goes from the turbocharger to the intake plenum. He set it at a healthy level of boost (about 8-9 PSI max, plenty enough for good spirited driving) and recommended removing the valve and reconnecting the tube directly.

Today I did just that, taking the adjustable valve out of the loop and reconnecting the hose directly to the plenum. When I drove the car later, I got no farther than a block up the street when I got a surprising jolt of what seemed like over-boost (bucking and bouncing and sever loss of power), except that it was doing it as VERY low boost-levels, around 3 PSI! back to the driveway, put the valve back inline...same thing happens...turn valve up some...same thing happens!

I'm still very much in the learning-curve when it comes to this turbocharger and related system, but I'm wondering if maybe there's some problem with the wastegate or something? Anybody have any thoughts?

[molemot]

Don't think it's overboost...more likely you have an airleak! Any overboost would show on the boost gauge..3 psi isn't going to cause any problems. This might give you valuable info....I can only really speak about the earlier carburetted cars with an external, exhaust maniflod mounted wastegate.

http://www.lotusespritworld.com/EGuides/ETechnical/turbo.html

[The Veg]

Interesting...the bad download I have of a different edition of the manual says that the overboost switch cuts out the ignition...but in any case, it seems to be the switch activating, as pointed out by a factory-wrench who's looked over my car. We had the aftermarket boost adjustment dialed in to prevent it happening, but now something seems to be tripping the switch at very low indicated boost levels. Something in the plumbing must be amiss I think.

[molemot]

As my late father used to pound into me...once you know the basics, you can work out everything else yourself, from first principles...good luck with your plumbing!!

[The Veg]

Thanks John. I've got time to think about it, as I have no garage and it's FRIKKIN' COLD outside!

[The Veg]

Well, I'm full of it...the overboost switch was NOT the mechanism of the problem, as today I bypassed the switch and the problem persisted...back to square 1!

[lotus4s]

Ben,

Sounds like it could be a fueling issue, have you checked the pressure? Don't you have two fuel pumps, are both working?

[esprit3]

Don't forget the DPO's of tomorrow are giving advice today

[The Veg]

As far as I know, both pumps are working.

The problem as it now stands is that everything is fine parked in the driveway- can rev up as much as I want to. But put it in gear and start rolling, and something is making it cut out at about 2800 RPM. Or in other words, it only happens when the engine is under load, and when I say cut out I mean cut out- not a mere stumble or surge or rough-running, but WHAM!- power lost, and the thing bucks and porpoises until I lift my foot. I can accelerate briskly or VERY slowly and gently, doesn't matter- it cuts out at around 2800.

There was no problem before I:

1) changed oil & filter,

2) changed air filter,

3) bypassed the DPO-installed boost-adjustment valve,

4) removed DPO-installed engine bay cooling fans and associated wiring (no other wiring was touched in the process).

Gonna go outside now and tinker with it some more and see if I can't find anything amiss that I may have overlooked before...

Jim, thanks for putting the idea of the pumps into my head!

I think I've got it solved and the short version is that I think that one pump might not have been working, for a really stoopid reason.

The long version has to do with item #4 above. Those fans were powered by a fuse-tap that was on one of the fuel pump fuses...examined the fuse socket contacts and one seemed like it might have been a bit expanded...whether or not it was preventing a pump from running, I'm not really sure. I bent it back to proper tightness and also replaced some rubber tubing to the overboost switch, as I noticed when I did my switch-bypassing experiment that the tubing was getting rather 'past it' as some of our British friends like to say.

Whatever was the problem, it seems to be gone now as I've just driven about 20 trouble-free miles.

[Mesprit87]

Glad for you it runs again, I'm new in the game too and following everything I can!

If in any doubt about the pump again, you can always use the old screwdriver in the ear technique but then again I'm probably a little late...

And by the way John, 86-87 HCI still use the same manifold with the wastegate attached on it, they just added a lot of piping and switches... but still a blast to run!

Cheers

Luc

Edited December 27, 2010 by Mesprit87

[Simon350S]

Don't forget the DPO's of tomorrow are giving advice today

Not understanding that comment?

Glad you've got the old girl running right..