1974 450SL d-jet fuel pump alternative/ car starts up and dies..

[rowdie]

I doubt it jumped time. The tolerance is so close that the valves would most likely hit the piston.

You can check cam alignment by removing both valve covers. Line up the right cam (US driver side) mark and compare with the left. They should be close. Ideally they should both align. Then look at the timing marks on the balancer. More than 10 degrees is out of spec. and a sign that the chain guides are worn, chain stretched, cam sprockets worn and weak tensioner.

Removing the timing chain cover requires either removing the engine or supporting the engine and dropping the front subframe.

[lovedieselsd]

Originally Posted by rowdie

I doubt it jumped time. The tolerance is so close that the valves would most likely hit the piston.

You can check cam alignment by removing both valve covers. Line up the right cam (US driver side) mark and compare with the left. They should be close. Ideally they should both align. Then look at the timing marks on the balancer. More than 10 degrees is out of spec. and a sign that the chain guides are worn, chain stretched, cam sprockets worn and weak tensioner.

Removing the timing chain cover requires either removing the engine or supporting the engine and dropping the front subframe.

I have no idea where to look. Where can one find these marks they are supposed to line up with? and on the balancer according to what? I guess I should open her up.
what I really don't understand is why an OM617 can run over 500000 miles with same chain and guide rails and these 450's can't??? I bought the car as most people said "bulletproof engine" but that appears not quite to be the case?

[lovedieselsd]

ok

450 - M117 Timing Chain Replacement

same as my '74 450sl I assume..

[rowdie]

Here: 450 - M117 Timing Chain Replacement

No one here or on BenzWorld 107 forums would say the M116 or M117 are bullet proof so I wonder who the they are that said that. '74 was the first year for the plastic guide rails which is a known issue.
On the other hand the M110 in the 107 does not have the same issue with the chain but it is an I-6 engine.
You keep comparing turnips to kumquats.

[Graham]

Originally Posted by lovedieselsd

I have no idea where to look. Where can one find these marks they are supposed to line up with? and on the balancer according to what? I guess I should open her up.
what I really don't understand is why an OM617 can run over 500000 miles with same chain and guide rails and these 450's can't??? I bought the car as most people said "bulletproof engine" but that appears not quite to be the case?

I have owned one of each for about 25 years.

The 72 M117 engine at 157k miles has not been opened, but it has been maintained, including new timing chain and tensioner at about 130k miles. The djet EFI was a learning experience!

The 85 OM617 engine at 200k miles was becoming hard to start in winter even with new gloplugs and valves adjusted. It did need maintenance like clearing blocked boost lines, finding and curing ongoing oil leaks, ALDA adjustment, failed starter motor and the list goes on. Engine since replaced for other reasons.

I love both cars, but have equally thick binders covering the repairs done over the years!

Location of marks: http://www.benzworld.org/forums/r-c107-sl-slc-class/1639405-timing-chain-slack-cam-gear-replacement.html

Link from PP Vintage Forum: http://www.peachparts.com/Wikka/M117TimingChain

[lovedieselsd]

I really like my w124 250d wagon the best. speaking of bulletproof...

haven't opened the valve covers yet, someone told me it could be the tensioner that has lost hydraulic pressure or the oil pump screen that could be blocked. The oil pressure does go up when starting the car, but rather slow? It did sit for 20 years... Are those reasons for a sloppy chain maybe?
how hard is it to take off oil pan, is the center support in the way?

[rowdie]

Weak tensioner could very well cause loose chain.

Same procedure as timing case cover. Removing the oil pan is why the engine has to be removed or front subframe dropped to remove the timing cover.

[lovedieselsd]

Originally Posted by rowdie

Weak tensioner could very well cause loose chain.

Same procedure as timing case cover. Removing the oil pan is why the engine has to be removed or front subframe dropped to remove the timing cover.

so removing oil pan is not quite as easy as on a 617 I gather?

[meltedpanda]

here you go , all you need to know, not my authorship ---
D Jet explained

Trigger Points

The trigger points are located in the base of the distributor below the ignition point breaker plate.These points are used to produce the signal that synchronizes the injector to the crankshaft.They consist of two low voltage,low current contact points which are driven by a cam located on the distributor shaft.Each set of points initiates the opening of one or two groups of injectors.

Unlike ignition points,the trigger points can last 100,000 miles or more.As the distributor rotates,a pulse is created by the opening and closing of the trigger points.This pulse is sent to the ECU.The ECU uses this signal to open the injectors and will use the inputs from the other sensors to determine when to close them.

Temperature Sensor I

Temperature Sensor I is an ambient air temperature sensor.As the ambient air temperature decreases,the density of the air increases.As a result,the ECU must inject more fuel on a cold day than on a warm day.

Temperature Sensor I is a temperature sensitive resistor known as negative temperature coefficient thermistor (NTC). This sensor has a resistance of between 400 and 500 ohms at 50 degrees F. At 100 degrees F.,the resistance is between 150 to 200 ohms.

Temperature Sensor I actually has little effect on the operation on most D Jetronic equipped vehicles.This is because most of these cars have tens of thousands of miles on the engine and are running very rich due to this wear.The troubleshooting consequence of this is that disconnecting the air temperature sensor during the diagnostic procedure may have little effect on the way the engine runs,and in some cases it may actually improve the way it runs.

Temperature Sensor II

Temperature Sensor II is the coolant temperature sensor on water cooled engines.Like temperature sensor I, it is a NTC thermistor.The temperature of the engine is important because the intake manifold design of fuel injected engine does not permit the use of an air restictive choke.Additionally,restricting the air to enrich the engine during warm up would cause inaccurate readings from the manifold pressure sensor.The warm up choke function is therefore performed by Temperature Sensor II.

When the coolant temperature is about 50 degrees F.,the resistance of Temperature Sensor II is between 3000 and 4500 ohms.As the temperature increases to more that 120 degrees F.,the resistance drops to less than 1000 ohms.Thus the sensors work is done once the engine is warmed up.Also it must be continuously remind the ECU that the engine has warmed up.If damaged,Temperature Sensor II will not continue to partially function( such as the resistance values shifting). It will completely fail,creating an open short or ground.

An open circuit in Temperature Sensor II or the wiring leading to it will cause the engine to run extremely rich once warmed up.Symptoms would be dark smoke from the tailpipe (most noticable at idle),rough idle and poor power.Keep in mind that these same symptoms could also be caused by engine compression problems and ignition.

Should the sensor become shorted or the wiring harness grounded,the effects may not be noticable at all when the engine is warmed up.The symptoms would be more like a carburetor with the choke stuck open-rough or erratic idle,stalling or hesitation when the engine is cold and progressively running better as the engine warms up.


Throttle Switch

The throttle switch tells the ECU when the throttle is closed,when the throttle is wide open and when the throttle is moving toward the open position.The switch consist of twenty two contacts,with a set of wiping contacts that move across them as the throttle progresses from the closed position to the wide open position.

One wiping contact is used to inform the ECU that the throttle is closed.Another makes contact only when the throttle is wide open and a third makes and breaks contact twenty times as the throttle opens.The electrical pulses created by the making and breaking of the contacts signals the ECU to open the injectors more frequently,thereby enriching the mixture for acceleration.This feature behaves much like an accelerator pump on a carburetor.

Symptoms associated with a defective throttle switch include a rich(smoky)idle and hesitation.An intermittent condition at cruise-which feels like you shut off the engine and immediately turned the key back on,can also be caused by the throttle switch.

To test the throttle switch,open the throttle with the key on but the engine not running.The injectors should open exactly twenty times,evidenced by twenty evenly spaced clicks.


Pressure Sensor

The D Jetronic pressure sensor is known as a linear variable displacement transducer (LVDT).It consist of a pair of coils,one with about 150 ohms of resistance and the other with about 85 ohms of resistance.An iron core attached to a diaphragm runs through the center of these coils.As changes in manifold pressure moves the diaphragm,the iron core moves inside the coils,causing ripples in the current flowing through these coils.This signal is used by the ECU to monitor the relationship between barometric pressure and manifold pressure.

The most common symptom from a defective pressure sensor is a rich running condition.Of course rich running can be caused by several other defects as well.

Of all the sensors used on D Jetronic,this one both the easiest and the most difficult to test.Usually a simple resistance test of the coils is enough to determine if the unit is good or bad.On the other hand,the only way to be sure is to replace it with a known good unit.

Electronic Control Unit (ECU)

The ECU receives input signals from the pressure sensor,Temp Sensor I,Temp Sensor II and the throttle switch to determine how long to leave the injectors open.It is only able to respond to air-fuel ratio request from one sensor ata time.As a result,whenever a sensor fails,the tendency will be for the ECU to send the injectors a full rich supply of fuel.

The electronic unit has no servicable components.In the event of a failure,the ECU is replaced as a unit.Failures are extremely rare and usually result in a no start.

D Jetronic that have an adjustable air fuel ratio have a detent potentiometer on the side of the ECU.This potentiometer can be used to fine tune the air-fuel ratio during a tune up.

Pin # 19 and 25 of the ECU are connected to the fuel pump relay.When the ignition switch is turned to the on position,the ECU energizes the fuel pump to ensure that the fuel system is filled for ease of starting.If the engine is not cranked,the ECU will shut off the fuel pump after one or two seconds.If the engine is started,the fuel pump runs continuously until the engine is shut off.



D Jet Components

D Jetronic Fuel Components

In Tank Filter

Located inside the fuel tank is a screen or filter designed to protect the fuel pump from rust,dirt and debris.Although seldom the cause of a drivability problem,the in tank filter should be high on the list of items to check.In many cases these filters have been ignored,even on well maintained vehicles.


Fuel Pump

The fuel pump is a high speed roller vane pump.It is capable of pumping fuel at pressures and volumes much higher than the engine or injection system would ever require.This type of pump is very efficient at pushing fuel bur does not do a good job of pulling fuel.As a rsult,these pumps are located very close to the fuel tank or even inside the fuel tank to reduce the chance to vapor lock.

The fuel pump can react adversely and even fail as a result of using some fuel additives.Use extreme when selecting them to ensure that they do not contain methanol or other corrosive substances.

A defective fuel pump can cause low fuel pressure which would result in symptoms such as hesitation,stalling and poor power.Often a defective fuel pump bypasses the poor running stage and simply stops operating.This causes the engine to die or keeps the engine from starting.

Fuel Filter

The fuel filter is the only real protection the injection system has from internal contamination from dirty fuel.Therefore the filter should be changed every time the spark plugs are changed.

Fuel Pressure Regulator

The fuel pressure regulator used on D Jetronic systems consist of a valve connected to a spring loaded diaphragm.The regulator controls the fuel pressure at 28-32 psi and is adjustable so it can ensure the proper fuel pressure throughout the life of the vehicle.Incorrect fuel pressure can cause a lean running engine if the fuel pressure is too low and a rich running engine if the fuel pressure is too high.

A defective fuel pressure regulator can result in high fuel consumption,rough or erratic idle and poor power.

Injectors

The injectors are solenoid operated,normally closed valves controlled by the ECU.Grounded to the engine block or chassis,each injector is opened by a 3 volt pulse from the ECU.The lenghth of the pulse is only a few milliseconds(2 to 5),and it takes time for the injector to close from the spring tension.Thus the injector is open for a total of about 3 to 6 milliseconds.

Very little goes wrong with the D Jetronic injectors themselves.An occasional burned out solenoid winding or restriction from contamination is the most common problem.Another problem is leaking from the hoses that attach the injector to the fuel rail.

Typical symptoms of injector problems include rough idle and poor power.

Fuel Rail

The injectors and the fuel pressure regulator are attached to steel tubing known as the fuel rail.The inbound fuel lines from the fuel pump and filter feeds fuel to the injectors and the fuel pressure regulator through the fuel rail.

As a passive component of the system,very little can go wrong with it except for leaks and restrictions.

Cold Start Injector

Also attached to the fuel rail is a solenoid operated valve known as the cold start injector.Since the earliest applications of the D Jetronic system were four cylinders,the cold start valve picked up the moniker "fifth injector." It stuck in some circles,even for six and eight cylinder applications.

The cold start injector receives battery voltage whenever the starter is engaged and is grounded through a device known as a thermo-time switch.The thermo-time switch is a temperature sensitive bimetal switch designed to provide a ground for the cold start injector when the temperature of the engine is less than 95 degrees F. A second circuit in the switch is an electric heating element intended to heat the bimetal as the engine is being cranked.

Consequently,the cold start injector should operate only when the engine is being cranked,the temperature of the engine is less than 95 degrees F. and for a maximum of five to twelve seconds.

Two of the most common symptoms of a cold start injector problem are hard starting when cold becuse the cold start valve is not operating and a leaking cold start injector which can cause an extremely rich running condition.

[lovedieselsd]

so, did they actually try to come up with the most prone to failure system ever?? Isn't the whole idea of an automobile to be reliable??

I will never have any classic car aver again that sports a computer in it. Getting rid of my SDL too. Electric components and reliability don't go together imo

[meltedpanda]

depends on which way you look at it . They were ahead of the curve at the time. Now not so much, and with few that understand the issues, hard to keep reliable. I will tell you though , when sorted out they perform very well. The problem as you know is that is very rarely one issue - but for some the journey is more important than the destination

[97 SL320]

Originally Posted by lovedieselsd

so, did they actually try to come up with the most prone to failure system ever?? Isn't the whole idea of an automobile to be reliable??

I will never have any classic car aver again that sports a computer in it. Getting rid of my SDL too. Electric components and reliability don't go together imo

Where do you get that this system was failure prone? Please quote the exact text.

VW started using D jet in 1969 on the Type 3 fastback / squareback / notch back. It was later used by SAAB , Volvo, Jaguar and a few others. These now 40 year old systems are bound to have a bad part now and then.

If you don't like electronics, why do you own a computer?

[lovedieselsd]

Originally Posted by 97 SL320

Where do you get that this system was failure prone? Please quote the exact text.

VW started using D jet in 1969 on the Type 3 fastback / squareback / notch back. It was later used by SAAB , Volvo, Jaguar and a few others. These now 40 year old systems are bound to have a bad part now and then.

If you don't like electronics, why do you own a computer?

Because I need it to use this forum. And, I don't drive my computer... I drive my diesels, buying the 450 was a mistake. Especially as I'm not an elderly lady. I don't mind my 63 and 65 microbusses, they're as reliable as it gets for a gasser. I thought about installing a computer in one of them, that makes sounds every now and then or actuates a servo that makes things pop up but haven't got to that yet.

[lovedieselsd]

where I get that the system is failure prone? That's a quote of myself, based on the sheer multitude of electrical components needed to make the vehicle operate, which are all prone to failure. In comparison to your average 40 year old classic, it's pretty darn prone to failure imo.