“Back To the Future” After a Blast from the Past

It was a trip I’d never forget…under the hood of a real piece of automotive history

1981 Delorean

8,459 miles

2.8L Engine

5 Speed Manual Transmission

Rough Idle, Stumbles, Won’t Accelerate

The Delorean: The Delorean seems to look like it’s moving even when standing still, and it certainly stands out in a crowd.

An Amazing Machine

            Of the folks who have never seen a Delorean in “the flesh”, most have at least seen the Michael J. Fox “Back to the Future” films.  I heard somewhere that seventeen Deloreans were destroyed in the making of those films.   According to one source I spoke with while shopping for Delorean parts and information, around 8500 were made, and about 7000 of them are still around.

            John Delorean had been one of General Motors’ most respected engineers, but few people remember that now.  He was charged by the feds with trafficking cocaine, but in spite of the fact that he was later exonerated, his fledgling auto company collapsed as a result.  But what came out of Delorean’s factory in Northern Ireland was a truly amazing automobile that has weathered the test of time with surprising elegance and grace.  One fellow I spoke with restores Deloreans and sells them for around $62,000, and from the experience I had it seems that just about any part a person might need for one of these brushed stainless babies is readily available over the internet.

            In my estimation, you’d have to drive a Delorean to fully appreciate it.  When it’s running right, the rear-mounted Peugeot-Renault-Volvo 2.8-liter V-6 engine drives this heavy little machine with a surprisingly crisp acceleration.  The front wheels are an inch smaller than the rear to minimize over steer and improve handling.

Engine Exploded View: Here’s an exploded view of the Delorean’s Peugeot-Renault-Volvo 2.8-liter V-6 engine.

            The Delorean owes its unique yet functional appearance to Giorgetto Giugiaro, the Italian designer who gave us the speedy look of the Volkswagen Scirocco and the Lotus Esprit, not to mention the simple yet interesting Eagle Premier! 

The body is a peculiar plastic reinforced with glass overlaid with the unusually eye-catching brushed stainless steel skin that sets the Delorean apart from other production vehicles.

            The “gull wing” doors need less than half the swing space required by conventional car doors. Because of the upward swing of the doors, settling into the seat of a Delorean and sliding back out of it can be more easily accomplished than with other low-slung sport models.  And where the Dodge Viper has a couple of externally visible “Gurney blisters” on the roof line for head room, the Delorean contains its head room accommodations within the sleek no-nonsense roofline Guigario gave the exterior.  The result is that the cockpit is surprisingly roomy and comfortable compared to other two-seaters.  

The power window switches are on the console, but don’t expect a hole large enough to engage in much drive-in activity, even when the window is all the way down.  Most of the glass remains stationary with only a small central airspace provided with the “windows” lowered.

The Instrument Cluster:  The brake warning light had a propensity to remain illuminated whenever the ignition was switched on, but that was a different story. The instrument cluster is fairly plain, and the numbers stopped at 85 mph.  Not that I’d want to drive 88 mph on a Delorean anyway!

A Conversation Piece for the Showroom

            The Delorean I personally encountered was acquired several years ago by the dealer where I was employed until January of 2001, and while it had run well enough in the beginning, the Law of Increasing Entropy had taken its toll.  The Delorean had spent more than its share of time in the dealership showroom as a conversation piece.  The fuel system had become clogged with the rusty rottenness of old fuel to the point that the lines and the fuel pump had to be replaced and the tank had to be steamed before the engine would even start. Even when it finally started, the engine ran so sluggishly that the car was practically undriveable.  The job was put on the back burner due to a heavy backlog of customer work.

I was visiting the dealership one Friday a few weeks ago when I discovered that the Delorean was in need of service. Since my old compadre was wrapped up with customer repairs I rolled up my sleeves and prepared to have a look at it. Even though I had walked by the car hundreds of times it was my first trip under the hood. 

What Kind of Fuel Injection?

When I first opened the Delorean’s deck, I saw an engine that closely resembled the 3.0L Eagle Premier powerplant, and I also noticed that it was adorned with braided steel fuel lines and a 1000-dollar K-jetronic fuel distributor, courtesy of Robert Bosch.  I had become acquainted with a very similar Bosch system when I worked at a Volkswagen dealership in the early eighties.

The Powerplant:  This is what I saw when I opened the deck. Notice the Bosch fuel distributor behind the air cleaner plenum.  The “Warmup Regulator is mounted to the left and in front of the A/C compressor, and the ignition distributor is neatly mounted out of sight and at a jaunty angle below and to the left of the fuel distributor.

The injectors are little more than mechanical atomizers, with fuel delivery controlled through the movement of a vertically sliding spool-valve type piston past laser-thin slits in the fuel distributor sleeve. The piston rests on the arm of a mechanical airflow sensor. 

“Control Pressure” is delivered through a special “Warmup Regulator” to a point on the fuel distributor directly above the piston so as to act against the rising force of the airflow sensor.   The regulator reduces control pressure when the engine is cold, working in conjunction with the cold-start injector to provide cold enrichment.  As the engine warms up, the electrically heated bi-metal valve in the regulator lets the control pressure normalize.

Lambda (Oxygen) sensor signals are interpreted by the ECU (mounted in a hidden compartment behind the driver’s seat), which can change the line pressure to the fuel distributor by altering the pulse width to an electrically driven “Frequency Valve” that actually resembles an electronic fuel injector.

Frequency Valve:  Here’s the Frequency Valve the ECU uses to control the line pressure to the Fuel Distributor.

When the Frequency Valve is energized, the line pressure available to the fuel distributor is reduced.  When it is de-energized, the pressure is increased, but increased pressure causes the fuel control piston to resist the upward pressure applied by the airflow sensor lever. 

Adjustments to the Fuel Distributor are made using an exhaust gas analyzer and an Allen head screw beneath a small rubber plug in the airflow meter housing. According to the Delorean Shop manual, the reading is supposed to dial in at about 1.0 percent, exactly the same reading required by Volkswagen. CO is measured at a special exhaust port between the engine and the catalyst.  At Volkswagen we would monitor the duty cycle of the Frequency Valve and shoot for 50 percent.

            The idle air control is a stepper motor that is more sophisticated than the old VW auxiliary air regulator, but very similar to the one found on the Eagle Premier.

Isolating a Problem

            The Delorean’s throttle plate is mounted below and in front of the airflow sensor so that the incoming air forces the round plate down.  With the air cleaner off and the plate exposed, the plate should deflect as the throttle opens.  On the opposite side of the airflow sensor fulcrum the fuel distributor piston rides on a small roller bearing for smooth operation.  As I opened the throttle I noticed that the plate only deflected slightly and the engine was starving for fuel.  Finger pressure on the plate helped a lot, but from the feel of the plate, it seemed evident that there was either a pressure problem or a sticking piston.  Subsequently, I decided to run some fuel injector cleaner through the fuel system to melt any sludge that might have clogged the tight tolerances within the fuel distributor.

            Using a quart of gasoline and a bottle of Ford’s injector-flushing chemical, I tied into the system at the fuel pump supply line with a pressure bottle and killed the power to the pump, running the engine at fast idle while the flush was under way.

            After the fuel system flush, the engine ran slightly better, so I removed the screws holding the fuel distributor to the airflow sensor.  With the fuel distributor raised free of the airflow sensor, gravity pressure should slide the piston slowly and freely out of its bore without sticking, and in this case it did just that.  The injector flush had apparently removed any visible trace of sludge that might have been there, so I reattached the fuel distributor to the airflow sensor. 

Incidentally, it’s not a good idea to disassemble one of these fuel distributors.  In many if not most cases, you won’t be able to stop it from leaking when you reassemble it and it may have to be replaced as a result of your adventure.

The right way to check this system is with a special pressure gauge connected in line with the control pressure port in the center of the fuel distributor, but since the Ford/Jeep dealer had no such gauge, I wound up needlessly replacing the Warmup regulator.

Shifting to Electronics

When I realized I had misfired on my initial diagnosis, I shifted the sights on my shotgun in the direction of the Frequency Valve and hit pay dirt.  With the engine running, there was no power available to the valve, but with the ignition switch in the on position and the engine off, the valve had power.  A quick trip to the wiring schematic in the shop manual revealed an interesting circuit. 

The Schematic:  Notice how component 106 (the Main Relay) appears to be a standard ISO relay.  Component 142 is the Frequency Valve and Component 130 is the ECU.  For anybody who knows the pinout and operation of a standard ISO relay, it becomes apparent that the Frequency Valve will lose power and the ECU will receive power when the Main Relay coil is energized.

Notice item #142, which is labeled by the legend as the Frequency Valve.  Component number 106 is the “Main Fuel Relay”, which supplies power to the Frequency Valve as well as the ECU, but the odd thing was that the relay in question was only supplying power to the Frequency Valve when the engine wasn’t running.  As soon as the engine fired up and the R.P.M. relay energized to drive the fuel pump and wake up the ECU through the Main Relay, the Frequency Valve immediately lost its power, but a dithering ground signal to the control terminal of the Frequency Valve indicated that the ECU was alive and working.  There was something rotten going on in the relay panel and my next step was to find out just where the relay panel was located!

Finding the Guilty Relay

The fuse and relay center on the Delorean is located behind the passenger seat beneath the carpet and a wooden cover.

The third “module” or relay to the right of the red module turned out to be the guilty party.  The relay appeared to be a standard ISO relay of the type Fords have been using since the early nineties. VW and several other automakers have used this same type of relay since the 1960’s.  The label warning against interchanging “modules” was obviously intended for guys like me. 

Important Note: Just because a “module” or relay looks like a standard ISO relay doesn’t mean a standard relay will work in that particular application.

Relay Center:  This fuse and relay center can be found behind the passenger’s seat when you pull the carpet back and remove a ¾ inch specially shaped piece of plywood.  The “DO NOT INTERCHANGE MODULES” label is there for a very good reason, and somebody obviously ignored it on this particular car.

An Easy Mistake to Make…

            The relay in question had been replaced by some previous spark-chaser, since it obviously wasn’t the right part for the job.  Those of us who are familiar with the pinout of a standard ISO relay will expect the voltage entering the relay at the common terminal to switch from the normally closed terminal to the normally open terminal when the coil is energized, and that’s exactly what this relay was doing.  The right relay for this job was wired so that the common terminal fed both the other pins when the relay is energized.  With the proper relay in place, the Frequency Valve and the ECU were powered at the same time and the Delorean ran almost normally.

Main Relay Detail: This is a shot of the Main Relay circuit in detail (above).  And while the pinout on the Main Relay appears virtually the same as a standard ISO relay, the two aren’t interchangeable.

Notice the difference: The common terminal 30 on the Delorean Main Relay (left) closes with both 87 and 87b on the Delorean Main Relay.  The ISO common terminal 30 (right) switches from 87a to 87 when the relay coil is energized. Thus the loss of power to the Frequency valve when the relay operates.

            After replacing the distributor cap, rotor, spark plugs, and wires, and a test drive, the Delorean appeared  practically road-ready.  After a blast from the past, it was time to come back to the future.