[rkubara]

When I replaced a fuse for my vacuum pump, I did not notice that I dislodged a relay in the same fuse box and later got a check engine light and an engine code error. At that time I only got 0.5 bar boost. I reinstalled the relay and cleared the error code and now get 0.75 bar boost that does start until 6,000RPM, otherwise it sits at 0.5 boost until 6,000. I use to get 1 bar boost at 4200 RPM.

The engine does even sound like it did, otherwise it runs well. While it is cooler outside, I notice the engine is running cooler than normal.
Any ideas what can cause the loss of boost?
Ron

 

[89.5 Esprit SE]

Tell us what model you have.
You should reset your computer, and let it go through the learning process, and then see how it performs.

Randy

 

[Vulcan Grey]

If the engine coolant temp is too low, below 77C iirc, then boost will be restricted to about .65bar.

Replace the thermostat with the correct 82C part.

 

[rkubara]

I have a 95 Esprit S4 Sport with a fresh build and new 82C Thermostat. It definitely is running a bit cooler than normal and I gather that it the problem. I do have an 85C thermostat I can put in.

How do I reset the computer? I do have Sanj's Scan tool and FreeScan.

 

[Vulcan Grey]

With the engine off, ignition on, you can use freescan to reset the blm and error codes. Unless you have a check engine code, this won't do anything for the low boost problem. Generally, as the outside temperatures get lower, the car will boost more.

If you check the water temperature reading in freescan, and it matches the gauge on the dash, and your temperature is below 77C, then that is your problem with boost.

You could still have other issues, but you need to get the coolant temp up to about 82C, where it should be. Otherwise you'll never know what else is causing the boost to be restricted.

 

[lotus4s]

Ron,

Check your turbo hose connections turbo to intercooler and intercooler to plenum.

You shouldn't need to change to an 85 degree thermostat but that is not to say you don't have a problem with the current one.

Jim

 

[carbuff]

You shouldn't need to change to an 85 degree thermostat but that is not to say you don't have a problem with the current one.

Jim

As the THERMOSTAT KING, I can tell you that getting a duff t-stat out of the box is quite possible.

Often they fail to close completely, soon after install. That results in cool running. I've had this problem with at least three different brands of T-stat, too.


BTW, if the thermostat you buy does not have a "jiggle pin", drill a very small hole (1/16th inch) in it's base plate, to expel air pockets.

 

[QuadCam]

check the boost solenoid fuse.

If the fuse blows, you'll only get boost up to the wastegate spring pressure. The boost solenoid pulses, limiting the pressure line to the wastegate (actuator), which allows the turbo to spin higher. if the fuse blows, the solenoid rests in the open position...which results in only the boost pressure the wastegate (or actuator in the case of your S4S) spring pressure can resist.

 

[Lotus Dave]

The THERMOSTAT KING speaks the truth. Installed a Stant 13398 after having problems with OE thermostats. Worked fine, but it shortly started causing the car to run cool. Very slow to warm up. I believe I have caught the dreaded thermostat virus from " Atwell, The Thermostat Queen." Ooops, I mean King.

Dave
90SE

 

[jtrealty]

They also can get stuck closed. It used to be rare to see a problem with them but it seems to happen more and more often. Probably because they are all made in China now! Easy to check with a pot of hot water on a stove and a thermometer. Remember that unless the system is well bled of air they won't work either. They have to be completely immersed in liquid. That is what that check valve is that Atwell referred to. As he said, if you don't have that check valve (and it doesn't have to be a check valve) at least make a small hole so air can pass through so you can bleed the system properly. Also make sure you do not have it in upside down and check the temperature marked on the thermostat with the spec you need.
David Teitelbaum

 

[rkubara]

Problem update, resolved! Sorry for the delay as I have been out of the country. Thanks to all for the input.

FreeScan indicates 82C, I suspect I did not wait until the engine was warm on my first go at this. Water/engine temp is not the problem.

I thought the engine sounded different when this problem first happened, now that I am back in town and at it again, I am certain the engine/turbo sound is not right. When hitting the current maximum boost, I am certain I can hear an air pressure loss. It is a sort of "whoosh" that stops instantly when I back off the throttle. It had more of "pop" before when backing off the throttle. So at first I focused on the dump valve.

I finally noticed a clamp on the air hose between the ChargeCooler and the intake manifold had slipped from position. In fact it slipped off the hose and the hose was not secure on one end. You might think this was easily spotted, but it wasn't. Everything was in position, but the clamp was just off the hose slightly and barely noticeable that it was no longer on the hose. Simply, at high boost the pressurized air leaked out between the Charge Cooler and the manifold. Jim as Lotsu s4s was bang on, it was a turbo hose! Thanks Jim, I re-read all the posts as well as yours and started looking very close.

The car is near mint and the engine bay very clean. I had the car on exhibit at a car show early and had sprayed all the hoses with tire silicone for a high sheen. It made the hose slippery and I gather at high boost the hose pressurized, inflates a wee bit and pushed the clamp off the end. Fluke! The roads are still wet so I can't take it for a test drive, but for sure this was the air leak and the sound of the "swoosh" and lack of "pop" when I back off the throttle. Image below highlights the clamp that slipped.

Next day update, dry today and got the Lotus out to confirm full boost is back. Many hours to determine the cause, minutes to repair. Again, thanks for the input. This forum rocks!
Ron

 

[lotus4s]

:up::up:

 

[Vulcan Grey]

Usually when that house leaks, the person describes a high pitched turbine whine sound... and a severe lack of power... strange that you never described the noise!

 

[rkubara]

:facepalmNo high pitch turbine and the woosh is slight, I thought I imagined it. The clamp slid off one side only so the air leak was minor and I gather only at the highest of pressure, I still hit 3/4 boost! I threw many off because I noted that the engine never came up to full operating temp. Sorry

 

[Vulcan Grey]

That used to happen to my intercooler hose all the time, one twice in one drive. Always immediately knew by the sound. Eventually I fixed it by breaching the hose clamps so they couldn't move closer to each other, or father away.