4.1 liter modern and efficient V8, HT4100 the An exciting step towards the driving needs of Cadillac in the early 80’s. The engine got hot with the tail of a very unstable cylinder deactivation experiment V8-6-4. Unfortunately, like the previous cylinder game and the later North Star, HT was plagued by problems that took years to solve. The name HT meant high technology, but it could mean half of it. Let’s go back to the 70’s and talk about cylinders.
The time to launch the HT power plant was a difficult time for domestic automakers. Their lineup was full of huge and inefficient vehicles made of bargain basement parts. They were roughly assembled by workers who may have been drunk on some days of the week. American consumers have become wise with the advent of more efficient and better Japanese cars, and the government has been stirring pots with fuel regulations.
The regulation was the result of the 1973 Arab oil ban, and the Gerald Ford administration took action to improve the fuel economy of the entire market for cars sold in the United States. Cadillac will need a new V8 pretty soon, but HT was still just an idea. GM compromised and Cadillac’s V8 decided to undergo cylinder deactivation.
The idea of cylinder deactivation is not new and was first tested on a multi-cylinder engine in World War II. Cadillac aimed to modernize the technology that was sold as the V8-6-4. GM engineers have worked with Eaton Corporation’s vehicle division to develop an electronically controlled deactivation system. It was the first time they created it, but now it’s found in all cars: engine control units, or ECUs.
The ECU determined the power demand at any moment by executing a program GM called modulation displacement. The system promised to switch the engine to 8, 6, or 4 cylinders properly and automatically. Three modes of execution worked because the ECU turned off the pair of cylinders on the opposite side. For each ad, it was “like three engines in one.” Some of the elaborate ECUs included an on-board diagnostic program that displayed the engine trouble code on the HVAC display. It was so sophisticated at the time that the diagnostic system stored all the error codes, so the mechanic didn’t have to use a separate scanning tool. It also showed the digital number in the new MPG Sentinel. Sentinel provided estimates of the number of cylinders currently in operation, average or instantaneous fuel economy, and the range of vehicles to empty.
With just four cylinders, this technology promises to save a lot of fuel for Cadillac customers. Cadillac wasn’t accepted by American luxury car buyers, so it wasn’t really possible to use a small engine at the time. This feature was standardized in Cadillac in 1981 and was brand-only. Seville used a diesel V8 as the base engine, so this feature could not be standard equipment. The engine was also messed up, but the diesel-based model Seville was the first American car to be sold with a diesel engine as standard equipment.
V8-6-4 has been added to the Cadillac L62V8. The engine was new in 1980 (as the L61) and featured the always-desired throttle body fuel injection. The 368 cubic inch engine with a displacement of 6.0 liters is a boring version of the 1968 472 V8 and was specially designed to comply with CAFE’s fuel economy requirements. During the transition from L61 to L62, the output dropped from 145 horses and 270 lb-ft torque to 140 horses and 265 lb-ft torque.
The new V8-6-4 was immediately praised as a technology landmark, but the praise didn’t last long. Almost immediately, Cadillac owners began complaining that their new car wasn’t working properly. The engine problem was serious and the main cause was a brand new ECU. ECUs were limited in processing speed, programming, and overall computing power, and could not efficiently manage the higher orders required by Modified Displacement. There were too many variables. The ECU could never catch up.
In addition, the L62 required a different type of EGR valve than the regular implant. Engineers chose a positive back pressure type EGR (there was no electronic EGR in these times). This setup works on a normal engine, but on a V8-6-4 I got an engine ping. With four cylinders, the engine had a lower displacement than usual and the pressure to operate the EGR was also lower. General Motors needed to act, so it brought the engine to PROM.
PROM in this case means programmable read-only memory. GM has released a PROM update for the chip for the engine control module. 13 of them. However, customers weren’t very interested in continually returning to the dealership to update their PROMs or actually saving some money on fuel. As a result, the service department often turned off the system. Turning off the modulation displacement feature was easy and required pulling a single wire from the transmission. When completed, the L62 returned to the 8-cylinder business as usual. It is very rare to find a Cadillac with a working cylinder deactivation system later this year.
GM was discontinued in 1982 because it was convinced that it did not want to offer the V8-6-4 again in the next model year. GM went a step further and removed the 368 engine (standard L61 and L62) from almost every Cadillac. Cylinder deactivation holdout was a unique model called the Fleetwood Limousine until 1984. The L61368 was used with Cadillac’s commercial chassis carburetors for hearse and things. This is also until 1984.
The 368 died notoriously, but was the last large block cast iron pushrod V8 offered on a production vehicle. The big block brother died much earlier, and by 1978. Something else died along with the 368 using the legendary THM400 in a factory GM car. The rugged 3-speed was last used in the remaining 368 units in 1984.
As a result of the V8-6-4 turmoil, Cadillac was forced to take decisive action in exchange. Initially, the HT engine was planned to be introduced in the 1983 model as a new front drive Cadillac product. However, the company’s current model couldn’t wait that long, so HT rushed to develop and start production, making its debut in 1982 with a Cadillac rear-wheel drive model. And it worked very well! See Part II for more information.
Become a TTAC Insider. Get the latest news, features, TTAC articles, and everything else to know the truth about your car first. Our subscription Newsletter..
General Motors high-tech engine and other CAFE Foibles (Part I)
Source link General Motors high-tech engine and other CAFE Foibles (Part I)