Where is the high boost cutoff switch????????

Fordiesel69 · Post by **Fordiesel69** » 27 Mar 2004, 15:57

On my 83 240turbo, I hooked up my home made boost controller and when the guage gets into the orange the car cuts off, how do I disable this?

Volvord · Post by **Volvord** » 28 Mar 2004, 08:44

Boost pressure controls a wastegate located on the underside of the turbo, when pressure reaches a set point the wastegate will open allowing the exhaust to bypass the turbine which limits boost. The rod that connects the pressure diaphram to the wastegate can be adjusted to change maximum boost. Don't increase boost too much or engine failure will result

Fordiesel69 · Post by **Fordiesel69** » 28 Mar 2004, 10:24

What I am talking about is that I have increased the boost so it is far more than factory, but now the engine shuts down and the turbo light comes on. My dealer said there is a sensor that if boost is excessive it will cut off the fuel or spark.

Guest · Post by **Guest** » 08 Oct 2005, 18:51

Volvord 784VC wrote:Boost pressure controls a wastegate located on the underside of the turbo, when pressure reaches a set point the wastegate will open allowing the exhaust to bypass the turbine which limits boost. The rod that connects the pressure diaphram to the wastegate can be adjusted to change maximum boost. Don't increase boost too much or engine failure will result

Kmaniac in California USA · Post by **Kmaniac in California USA** » 09 Oct 2005, 00:55

I suspect your turbo does have a high pressure limit switch, as do most turbo charged automobiles. Forcing your turbo to increase it's boost may provide preformance satisfaction in the short term, but may lead to some type of premature mechanical failure in the future if allowed to continue. I have first hand knowledge of this.

My normally aspirated, 1986 740 GLE is driven primarily by my teenage daughter. The car I have driven primarily for 13 years is a 1991 Dodge Shadow with turbo charged 2.5 liter four cylinder and automatic transmission. When I first bought the car in 1993, I found that the turbo was programmed to open the wastegate early, restricting the time interval for maximum boost to just five seconds. About four years ago, I began to notice that the car would cut out, like there was momentary ignition failure, whenever I stood on the throttle at freeway speed. Other times, it would begin to ping under the same circumstance, even though I use premium fuel consistently. After a year of experiencing this from time to time, I began to notice that my turbo boost gauge would peg out to maximum boost and not back off until it either shut down, pinged or I would pull up on the throttle. I suspected the wastegate wasn't working.

After about a year and a half of letting this condition continue, I took the car to the dealer for a 90,000 mile service and asked them to look at the turbo. The mechanic found the vacuum control line to the wastegate was leaking and replaced the vacuum line. The turbo began to work like new again. 50 miles out of the dealer, though, the transmission began to stick in high gear. A local transmission shop disassembled the transmission and found a clutch plate in the front clutch pack had fragmented a the center spline, causing metal to permeate the transmission. I had the transmission flushed and rebuilt. One year and 8,000 miles later, it again began to stick in high gear again. The transmission shop pulled it out and apart under warranty and found nothing visibly wrong. 120 miles later, something went "Bang" under the hood while I was cruising down the freeway at 70 miles per hour. The car continued down the freeway for the next 7 miles, but I lost the function of the speedometer and I kept hearing a scraping sound whenever I accelerated. When I pulled off the freeway, I found the transmission again stuck in high gear. Manually downshifting the transmission lead to a permenant "neutral" condition. The transmission shop found that something had come apart, causing the rear planetary gear set to lock, ripping out the splines between the rear planetary set and the output shaft. The transmission was rebuilt again, under warranty.

What I came to realize is that the automatic transmission in my car was not designed to handle the peak power produced by this engine with full turbo boost. Driving the car for a year and a half with a faulty wastegate caused the over powered engine to overstress the internal components of the transmission, leading to the premature transmission failures in encounted.

So, if you continue to run your engine with higher than designed turbo boost, be prepared to replace either the engine, transmission, other parts of the drive train or all of the above within a couple years. It might not happen, but still, be prepared.