I have extensive experience with the D24 so I will try to help you here however you're going to need a supply of GoJo or Fast Orange when this is over.
The tests Im about to outline here are only valid assuming the car ran the day before thus discounting a serious mechanical problem like a broken belt.
Before you do anything open the little screw at the top of the fuel filter and let some seep on a paper towel, carefully sniff it for the smell of gasoline, I was mis-fueled in Portland Oregon once with 92 octane after repeatedly telling the pump jockey that it was a diesel car. All the pumps had the white sleeve on the pump handle and the pump itself was a 2 handle meaning one was for 3 grades of gasoline and 1 for diesel in the same box... At night I could not tell the diffrence until I got down the road... Gasoline does not burn in a diesel engine very well.

First things first, at +36F diesel fuel will not gel unless its Bunker-C and in that case won't flow until its over +125F so we can discount gelling or wax in the fuel system. The D24 has no spark plugs coils or intake injectors, the diesel injection works at 2200+ pounds of pressure spitting fuel into the chambers whos ambiant peak temps are over 1500F with the block at 170F at idle. Enter the glow plug. These little heaters normally come on when the engine is cool or cold and the "on" time varies with block temp. Normally they will run for a few moments and go off allowing you to start the engine. If one or two plugs fail to heat during this cycle the car might start up and be very grumpy for a few minutes. 3 plugs or more failed will not allow the engine to start however you will get the black puffs of smoke as the fuel tries to ignite.

A simple test... With the interior lights on hit the key and allow the glow plugs to cycle, note the intensity of the lights or if you have the cluster volt meter it should drop way down then rise once the plugs have cycled and the interior light should go bright, make sure the heater blower moter is not running or place the climate control in the off position. You will not notice 1 or 2 failed plugs in this manner however it will indicate if all the glow plugs are burned out. Listen for the controller to cycle off and the lights should go back to bright. Wanna get greasy? Grab your safety glasses, you will need them and place a thick towel over the battery vents only leaving the terminals exposed.

Armed with a 5/16 nut driver or wrench remove the copper strap that connects the thick red wire from the glow plug controller and move this strap back to test the glow plugs individually. You will not get at the plug nestled under the injection pump however if you can get behind and remove the connection to the last or #6 plug you can test the other through the strap. Now get yourself a clip lead that is flexible and made of number 16 wire clip it to the brass screw of the glow plug and just touch it to the battery plus terminal, do NOT hold it for more than 5 seconds! If the plug "was" good and you exceed this time it will now be bad and will need to be replaced. When touching to the battery plus terminal you should get a bit of a spark, nominal current draw for each plug is around 10 to 12 amps so you will know if its working. Do this test to every glow plug and when you have finished place the strap back on observing the corners around the water outlet neck to make sure it does not short to ground.

Lets assume at this point all the plugs worked and everything went back together correctly. Now remove the glow plug controller relay from the shock tower by the battery and examine the bottom fuse, if it is blown or melted in any way replace the controller and not the fuse. By the time that fuse blew the relay contacts could have welded themselves together inside the controller or overheated the relay itself, sure it may work again but Ive learned the hard way not to chance it.

Next test is to remove the thick red wire OR use a stout screwdriver and short between the battery red to the glow plug red, have your wife or son in the drivers seat and crank the engine over while you use no more than 5 seconds on and 5 seconds off with the glow plugs. If the engine starts easily let it idle to warm up and once warm go get a new glow plug controller.

Now lets say the car does not start and the plugs have ALL tested good. Using a test light with the clip grounded have your wife or son or whoever cycle the ignition key to the run position while you hold the tip of the test light to the copper strap between the plugs, it must light then go out. If it stays lit after the controller cycles out that means all the glow plugs have burned out because the relay welded the contacts internally and the plugs themselves will have either buldged internally or the tips have burned off inside the engine. Pull 3 plugs out starting with #1 and examine the end. A fat buldge on the side will be hard to remove however wont damage the engine, a missing tip will damage the engine and head once you do get it started as the left over tip is stainless steel and will get mashed into the head, valve or piston and damage your wallet. So you pulled 3 plugs out and found no buldge or burnt tip, then the plugs have failed with age and its time to replace all of them. You have 2 choices here, go with the orig 6 volt fast heat plugs OR convert to the slower 11 volt plugs to heat at a snails pace yet no risk of burn out. The 11 volt conversion however is for someone with electrical experience so if you lack this then just replace with the correct part.
Replacing the plugs is NOT for the faint at heart or the inexperienced, to reinforce the previous warning do NOT and I mean do NOT take the car to a chain like Midas, Sears or any of the other "quick profit" auto care centers, they will make a real mess of the engine without knowing it. They do not have the training or experience to deal with an "exotic" engined car. Instead find an older run down import garage or Mercedes mechanic with long gray whiskers to deal with changing the plugs. He will have to completly remove the injection pump to get at the #5 plug and after that retime the pump. One can do this without the timing gauge however it takes an experienced ear to set it correctly. You can however replace all the plugs you can get at and leave the #5 if you dont mind the extra cranking and the local temps dont drop much below say +15-20F.

Cold start advance device... An easy one to check. Look at the side of the pump for a bar that extends up to the throttle lever and should have a ball stud on the end, engine cold it must rest against the throttle lever as this is the high idle position. If it is not and has more than 1/8" clearance the cold start device is bad and the pump must be removed for service as the settings are done on a test bench under dynamic conditions meaning the pump is run by a motor and timing electronically checked and set. Looking for obvious damage or failures like the steel cable rusting or broken parts there is little the home mechanic can do with these, the pumps however do share parts with the early Dodge/Cummins B59-130 engines until 1994 so parts are available.

Last test and this one will suck if everything goes right...

Remove the fuel return hose from the fuel system and place it in a jar, the return hose is the one that comes from the backside of the pump and has a smaller cloth covered 1/4 OD hose connected to the side of the same fitting, it is also marked OUT on the fitting itself but normally is not visible after the years. With the hose in a jar crank the engine without waiting for the glow plugs, best to have someone crank it while you watch, fuel should flow into the jar after a second or two of cranking meaning the internal transfer pump is working. The Volvo diesel has NO fuel pump in the tank or on the frame, the injection pump has a sucker pump to pull fuel through the filter and into the injection circuits. If by cranking NO fuel flows to the jar or its only a trickle make your way to a Pep Boys, NAPA, Checker or whoever your chain store is and get one of those "universal electric" fuel pumps that is rated for around 2-4 PSI of pressure, another is the Onan electric pump used on the Emerald 4000 generators. Plumb the pump in so the discharge feeds the fuel filter and power it from the blue wire at the top of the injection pump, mount it to the plate next to the cruise control or fabricate a mounting plate to hold the pump to the shock tower.

Another thing to try is get one of those small "cube" ceramic heaters or hair dryer rated at 1000 to 1500 watts and place it inside the air filter box after removing the filter element, power it up and after say 30 to 45 seconds hit the key and see if it starts with the warm air in its face, you can also pull the plastic inlet tube from the top that goes directly to the turbo and stuff the face of the hair dryer directly into the pipe. Do not however use a "heat gun" as these are designed for high discharge temp and low velocity. A 1500 watt heat source will yield around 5200 BTU of heat and with 10 to 15 seconds of cranking it will heat the intake up. If the engine doesnt start at this point and you are sure everything is in good condition go find that old timer Mercedes mechanic or run down import service garage with the tempermental owner and see if he will help you out. The Volvo diesel is not a real complex beast and needs only fuel, oil water and moderate heat to start in the morning. I wont get into the synthetic oil debate again here however it is your engine and you can run what you want. I would not however use anything thicker than a 10-30-CD/DS oil in the moderate winter climates and NEVER ATTEMPT TO USE STARTING FLUID IN THE INTAKE!!! Starting fluid or ether in a volvo or any other pre-chamber diesel is not only hazardous to the engine it can be hazardous to your well being! This stuff is very unstable around heat and pressure and with that 22:1 compression it will set off long before the piston hits TDC and could break the crankshaft or worse. At the very least it will blow the head gasket and maybe rip the timing belt teeth off when the engine fires going in the wrong direction.


I will be watching this thread and awating your reply to see how things are going. I would rather take the time and help a fellow D24 owner and help keep the car on the road as I know what a real pleasure these are to drive.


Have fun and work safely.

Fmr Badge988