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When buying an IDI (Please read)

Ford 83-94 6.9 and 7.3L General Discussion of 83-94 6.9 and 7.3 Liter Ford Diesels

When buying an IDI (Please read)

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Old 01-07-2014, 11:14 PM
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Star When buying an IDI (Please read)

The following is a primer on what to look for in a used Ford truck or van, powered by the 1983 to 1987 6.9 and 1987 to 1994 7.3 IDI (Non-Powerstroke) engine.

Obviously any vehicle purchase should include an inspection for the obvious signs of trouble. Leaks, squeaks, obvious damage, bad smells, and the like should all be investigated to ascertain their origin and if they are a concern. Driveability, road noise, tracking and other such things are all part of the assessment of a vehicles worth and desireability. This discussion is meant to cover the specialized things one must look for on an IDI powered truck, and is not meant to exclude any of the normal things mentioned or not mentioned above. It is up to the prospective new owner to do what is possible to identify early on, any issues that may affect the longevity of the vehicle and satisfaction of the purchase. Make sure the truck you are looking at is an IDI powered truck! Many people mistake a Powerstroke engine for an IDI or the other way around. IDI's are characterized by a beefy V-8 engine with a forward mounted rotary injection pump with individual steel lines radiating outward to individual injection nozzles at each cylinder. It may or may not be turbocharged, and the turbo, if so equipped, may be in one of 3 different locations, depending on the Factory, or aftermarket turbo installed. A Powerstroke looks like a chunk of plastic with a lot of wires attached.

Things to look for on both engines -

Condition of the oil.

These engines require diesel rated oil. Most commonly used are Shell Rotella-T and Chevron Delo 400. Ford sells Motorcraft 15W-40 which is a good oil also. Both engines specify the Motorcraft FL-784 oil filter, although most users have upgraded to the FL-1995 filter which holds an additional quart, and is believed to filter slightly better since it was designed for use with a turbocharged engine. Engine capacity is 10 or 11 quarts depending on which filter your using. Engines in severe service require a 2500 mile oil change. 5000 is the recommended interval for standard duty. Extension of the oil change interval is likely to cause valve guide wear, and result in higher amounts of crankcase gas blow-by. Ford calibrates their dipstick to give readings in hot oil, so the best time to check the oil is a half hour after shuting the engine down. You will find the oil to be black in most cases. New looking oil is just that. New. It probably hasn't been in the engine running for more than 5 minutes. Because of the soot content of these engines, the oil gets black very quickly. Also, the 6.9 and to a lesser extent the 7.3, have a history of oil consumption. It is not uncommon for these engines to require a few quarts between oil changes. The design of the valve guides is the reason. The 6.9 valve guide seals are not as good as the ones on the 7.3, so the oil is consumed there. Again, frequency and quality of oil changes can make the difference. Be sure to ask the previous owner what the oil consumption history is. Take the engine oil fill cap off and look at the bottom of it. If there is any condensed water, this could be a sign of trouble. With the engine running at idle, observe the amount and flow of the blow-by gases coming from the filler neck. A "steaming teapot" effect is the norm. Any severe puffing may indicate a cracked piston, and is an indication that a compression test should be performed on the engine to ascertain its general mechanical health. Run the engine up to around 1800 and observe that the blow-by smoke is no longer eminating from the filler neck. If it is, the engine may have a problem with the CDR valve or it may have excessive blow-by. If possible, obtain an engine oil sample, and send it to Blackstone labs for analysis. This will tell you more about the engine then you could hope to know.

Condition of the coolant.

Both engines require low-silicate standard green antifreeze. Some extended life coolants and "complete" formulated coolants can be used without harm, however by far the standard green coolant is the norm. What IS most important, is that a supplimental coolant additive is present in the coolant. The presence of this additive can be determined by dipping the coolant with a test strip. For more information, see the article on Cavitation. The coolant should be clear, and free of any foam, oil, or sludge. The presence of oil in the coolant is usually an indicator that the oil cooler has failed, but a head gasket problem can cause this as well. See if you can find out when the coolant was last changed, and what the intervals were. The recommended coolant change interval is every 36 months or 50,000 miles. Low coolant may indicate coolant consumption caused by caviation. If there is coolant in the recovery bottle, and the coolant is low, it may be that the recovery bottle hose is leaking or that the radiator cap is bad. In either case, anything other than a full radiator should raise a red flag. These engines are very sensitive to overheating. If the truck has an overheating event in it's history, proceed with caution. Cracked or warped heads often result from such an event. If the truck has been equipped with a coolant filter, this should be taken as a good sign, as they are usually installed by members of this forum!

Condition of the glow plugs.

The engine uses 6 volt glow plugs with a cycling mechanism to aid in starting. Common issues with glow plugs are burned out plugs, bad controllers, and defective wiring. If possible, when going to look at a vehicle, look at it when COLD. Observing the way the engine starts when cold will tell you more about the glow plugs in 10 seconds, then a half hours worth of electrical checks. Many forum posters have made the mistake of buying a truck "hot off the lot" only to find that they couldn't get it started the next day. If there are starting difficulties, find out if the previous owner has used either or starting fluid to get the truck running. Starting fluid should never be used on these engines except in extremely rare instances by knowledgeable people. Engines subjected to starting fluid may have serious mechanical problems. Sometimes owners who have experienced problems with glow plug controllers in the past, will bypass the controller and install a push button system, or some variation. Again, observing the engine on a cold start will tell you if the owner knew what he was doing, and how to use the push button. Examine the wiring for burned or frayed insulation. This may be a sign of impending or past trouble. If the controller was bypassed, make sure you understand how the circuit was re-wired. Generally speaking, these glow plugs cannot take more than 10-15 seconds of on time before they burn out. Take a look at the glow plugs and see if they are Motorcraft or Beru brand plugs. These are the best. Engines with Autolite plugs, Champion or other brands are likely to have swollen tips which may break off upon removal. If you observe an engine that starts hard, misses when running or has known glow plug problems, it is possible that a glow plug tip has broken off, and is buried in the top of a piston. Again, be very cautious around engines with known glow plug problems. Many professional garages have ruined engines by ignoring broken off tips when changing glow plugs.
 
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Old 01-07-2014, 11:16 PM
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Condition of of the fuel system

The fuel system is the fuel tanks, fuel pump, fuel filter and or water seperator, injection pump, injection nozzles, and all lines, hoses and clamps. There should be no fuel leaks from a properly maintained system. Puddles of fuel around the fuel injection nozzles indicate leaky O-rings or cracked return line caps, or possibly a loose injector line. Problems with the return lines (the rubber hoses which run from injector to injector) may cause starting difficulties and are easy to repair in most cases. Fuel injection pumps and injectors are medium wear items and you may find yourself desiring to replace them. Reference THIS article for more details. It is possible for the mechanical fuel pump or fuel injection pump (if it is an old style) to leak fuel into the crankcase. Be wary of engines with oil ABOVE the full mark. The oil may be diluted with diesel fuel from one of these two sources. Check the steel injection lines to make sure they are in good condition. There are 3 or 4 clamps which hold the lines together in groups. These clamps are important to prevent vibration from breaking the lines. Look for fuel in the valley pan which lies under the injection pump and air intake. Shine a flashlight in there to see if it is wet with fuel. This may indicate a leaking injection pump which would need replacement. In some cases, the mechanical fuel pump may have been removed or bypassed by the previous owner, and an electric fuel pump substituted in its place. If this is the case, be sure to ask questions about how the modification was done and how the pump is hooked up. The Holley Red fuel pump is by and large the most popular, but other types may be found as well. As long as they produce 4 to 8 PSI of presure, the truck should run fine. These trucks require a fuel additive to lubricate the injection pump and provide maximium longevity. See if you can ascertain what fuel additives have been run and on what frequency. The fuel filter on the 6.9 filters only fuel. The 6.9 has a seperate water seperator mounted on the firewall from the factory. Many 6.9 owners bypassed or elminated the water filter in favor of the 7.3 system. The 7.3 factory filter has a metal bottom, which is retained when the filter is changed. Sometimes this is discarded in favor of a third party filter which is a one piece design. The 7.3 factory filter with the metal bottom has a hose and wiring going to it. Try to ascertain what type of filter is being used, and if any of the water in fuel warning circuitry is still intact. Lastly, take a look under the vehicle at the lines and tanks. Look for leaks or wet spots that might indicate fuel loss and the entry of air. You might also look at the fuel fills for the tanks. Some owners modified their filler necks to accept the larger dispensing nozzles at truck stops. While this is not an issue, you may wan to ask the previous owner how easy or difficult it was to fill the tanks.

Hard starts

In addition to the glow plug issues mentioned above, hard starts can be caused by air in the fuel system. Again, seeing how the truck starts when cold AND hot are key. A truck which starts right away, runs for a few seconds and dies, has air in the fuel system. This can be repaired inexpensively, but requires time and talent. A truck which requires extensive cranking to get started may have a glow plug problem, or a major air leak. Be wary. A HOT truck which doesn't restart after sitting for 20 minutes or so is suffering from injection pump heat soak, and is probably going to need a new injection pump. So, after that first extensive test drive, come back 20 minutes later and restart it to see! Check the level of fuel in the tanks. Most all trucks run good on a full tank, but only the ones with healthy fuel pickups run down to the E mark. If the tanks on the truck you are looking at are full, it may have a bad pickup sender. After all, who sells a truck with full tanks! Try switching tanks, and make sure the fuel level changes. Maybe the other tank is pretty low, and you can at least ascertain if that tank has a good sender in it.

Electrical.

All years of the IDI sometimes develop problems with the headlight switch. The running lights, especially if more have been added, can tax the capacity of the wire at the switch, and cause it to burn and increase it's resistance, perpetuating a cycle that eventually leads to destruction of the switch and sometimes the wiring. A popular mod is to put relays on the running lights and headlights, to improve their brightness and reliability. If the vehicle your looking at buying has had this mod performed, it's a good thing, but ask questions about the history of the modification, and assess if it was done safely. Make sure it was fused correctly and that the wiring insulation is in good condition. There are a lot of underhood vibrations on these trucks, and a wire left unsecured can rub through and cause a spark, short, or fire. There isn't much you can do to check the switch in a pre-sale situation, but it is something you will want to look at upon obtraining ownership. Take a look at the batteries as well. The IDI's require two large 12 volt batteries with a minimum cold cranking capacity of 850 or so. If you see a pair of 650's in there, figure on replacing them soon. Also look at the battery cables and post clamps. While they are easy to replace, they are not cheap, so keep this in mind when assessing the value of the truck.

---AutoMerged DoublePost---

Road test

When you start an IDI, it should fire within a few revolutions of the crank. Low batteries, bad cabling or a weak starter will not spin the engine fast enough to obtain a quick start. When the IDI's are first started and the water temp is below 130 degrees, the cold idle advance and cold high idle should be on. After starting, depress the pedal slightly untill about 1200 RPM and release. The high idle should maintain around 900-1000 RPM. During this time, the cold advance will be on and the engine will have more clatter than when it is warm. Allow the engine to warm up, and observe that the high idle kicks down. Depending on ambient temperature, this may be 5 to 20 minutes. This would be a good time to walk around the vehicle and check the lights, exhaust system, and look for leaks. Bear in mind that the factory gauges are notoriously bad, and poor indicators of actual engine conditions. Nominal readings for factory gauges are usually mid center position. If the previous owner has installed aftermarket gauges, and they work correctly, your in luck. A pyrometer (exhaust temperature gauge or EGT guage) is an invaluable gauge, and one which you should install as soon as possible, if not so equipped. If the truck has one, idle temps are generally around 260 degrees. Check the parking brake. A lot of owners ignore these, which isn't good. You may want to ask the previous owner if he used it. If he didn't, assume it is bad and it may stick on when you press it down. The brake cables may have rusted up. Applying it now, may render you unable to drive it, so evaluate that at a more appropriate moment. When you are ready to drive the vehicle, adjust the side mirrors so that you can observe the exhaust smoke as you drive. The smoke should appear as follows under the various driving conditions.
Normal cruising should be light haze to no smoke
Lugging should be brown or black
Normal acceleration should be light haze to dark smoke*.
Against compression should be no visible smoke

* If the previous owner has turned up the injection pump, you may have significant black smoke on acceleration. This is normal. However, for a factory calibration, you should see little or no smoke. Also the injection pump timing may be off. It would be appropriate to have the truck timed once you purchase it, to ensure best performance.

The truck should run strong. Unless the truck is extremely heavy, it should feel like it has a lot of pep. Don't expect it to burn rubber and throw you back in your seat though. This is a diesel and not a gas engine. Observe the smoke, and listen for any noises. A properly maintained IDI sounds like a sewing machine with an attitude!


Things specific to the 6.9LD.

Headgasket problems

The 6.9LD uses smaller head bolts than the 7.3LD. As a result, they eventually have problems with head bolts stretching, and loosing their clamping force. This usually results in a water or oil leak to the outside of the engine. One of the first places to look is at the rear of the head. Take a flashlight and lay on the ground under the vehicle, and examine the head to block seal at the rear of the engine on each side. This is where the heads usually lift first. Oil in this area below the block deck indicates an oil leak. If there is oil on the head and the block, it may be from a valve cover gasket, and so if there is a headgasket leak due to oil, you will not be able to tell. If the engine leaks water, there may be a white colored stain from where this has been happening. Look at the Y pipe below this area. Often if there is a water leak, it will make the Y pipe wet from where it has been dripping. This is often more obvious after the truck has run hard for a while. The smell of antifreeze when the truck is at operating temperature is also an indicator that there may be a headgasket leak. Headgasket leaks on 6.9's are common, and it may be realistic to expect to have to change them at least once during the ownership of the vehicle, so a leak of this kind is not a show stopper, but you need to be aware that the gasket change out if required, is not something to put off. Improvements in gasket designs, and the availability of head studs, can make headgasket replacement a once and done deal on many engines.
 

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Old 01-07-2014, 11:16 PM
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Glow plugs.

As previously mentioned, glow plugs are a major concern on the 6.9. The reason - the 83 to 86 glow plug controller design causes the plugs to burn out when it fails. If the glow plugs are Autolight brand, then your probably looking at pulling the heads to get them out. The 1987 6.9 has the 7.3 glow plug system which is not a problem.

Block cracking.

Some unfortunate 6.9 blocks have been known to crack in the vacinity of the block heater, which is located on the passenger side near the center of the lenght of the engine. Some have been sucessfully repaired. Most have not. Take a look at this area to ensure the integrity of the block, and throw away the cord to the block heater if you buy it. You do not want to use the factory block heater on any 6.9. Empirical wisdom on how to identify these blocks...
Block casting........INTERNATIONAL HARVESTER DIESEL ENGINES
6.9L and 7.3L Core Identification
6.9L Old Style Block
Block Casting Number:
On left side of block (beneath oil cooler) 1805440C1
Note: Some 440 blocks are truly new style and must be visually inspected by raised donut around the block heater, frost plug (right rear). Old style below serial number 173828.
Visual Identification: *No counter bored area for block heater
*No defined area on side of block for dip stick
*Thickness of cast iron around block heater 3/8" (.375")
Head Bolts: *7/16, 12 point socket is used to torque head bolts
*Block tapped with 7/16-14 for head bolts

6.9L New Style Block
Block Casting Number: 1807996C1 Note: Some new style blocks have casting
number 440. Above serial number 173828.
Visual Identification: *Has counterbored area for block heater
*Very defined relief area cast in side of block for dip stick tube.
*Thickness of cast iron around block heater 15/32" (.470")
*Latest style (not all new style 6.9) has ribs around head bolts, rear two on left side go from head gasket surface to pan rail - same as 7.3
Head Bolts: *Same as old style 6.9

7.3L Block
Block Casting Number: 1809000 C1
Visual Identification: *Same as 6.9L new style block
*Head bolt ribs on side of block extend from pan rail to head gasket surface or rear two head bolts left side
Head Bolts: *1/2" - 12 point socket is used to torque head bolts
*Block tapped with 1/2 - 13 for head bolts

Trans and clutch.

The 6.9 is typically mated to either a 4 speed manual Borg-Warner T-19B or a 3 speed Ford C6 automatic. Neither have overdrive. The C6 is somewhat bullet proof, and as long as the fluid is good, you should have no problems. The T-19B may have some clutch issues to be aware of. Lubrication of the throw out bearing and the transmission input sleeve on which it rides, is critical to ensureing that the clutch system works as designed. Check for hard pedal effort, difficultiy in engaging and shifting, and cracks in the firewall around the clutch master cylinder. The 1987 6.9 is mated to the 7.3 drivetrain, so reference that section for more info.

Things specific to the 7.3LD.

Cavitation.

Without a doubt, cavitation (The Big C, Block Worm, etc) is the biggest concern on a 7.3. The reason - Ford did not tell the original owners about the need for supplimental coolant additives until way too late, and some owners never found out about it at all. Generally speaking, any 7.3 with over 100K and an unknown SCA history is a big roll of the dice. This is not to say that engines with less than 100K are cavitation free, as they can go with far less miles on them then that. Pay particular attention to the cooling system issues discussed above when shopping for a 7.3. If possible run the engine up to operating temperature with the radiator cap removed and be sure you do not observe any air bubbles in the coolant.

Serpentine belt.

Later 7.3's have a serpentine belt for the accessory drive. Take a look at the hood blanket (stuck to the underside of the hood) and see if it has any big chunks taken out of it by a wayward serp belt. Observe the tensioner pulley and see which of the 3 styles of tensioner it has, and discuss the belt history with the previous owner. If buying from a dealer, and the belt looks brand new, they may be trying to hide the fact that the belt has a hard time staying on, or they may be just really swell guys who put new belts on everything they sell just for fun.

Transmission

The 7.3 is mated to either a ZF Industries ZF-5 or a Ford E4OD Automatic, both of which have overdrive. The ZF is an alluminum transmission with a one piece bell housing built into it. The flywheel for the ZF is the Dual Mass Flywheel (or DMF), which will eventually fail. The springs and things inside them go bad, and then you need to either get a new DMF, or upgrade to a solid flywheel and live with the gear rollover noise. If the 7.3 makes a terrible racket, like a washing machine on a spin cycle, or a can of marbles being dragged down a dirt road, it is likely the DMF is to blame. The clutch pedal also may have issues with failing bushings under the dash. Inspect the clutch pedal linkages for worn or broken parts. The E4OD has it's own set of issues, but the presence of additional fluid coolers and clean fluid is a good indication that the unit is healthy.

copied from Agnem of oilburners (moose pump builder)

This is roughly what you should look for, is a great read and will help with future troubleshooting if needed
 

Last edited by Dortiz; 01-07-2014 at 11:21 PM.
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Old 01-08-2014, 01:39 PM
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wow man .... u shouldda wrote a book .....
 
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Old 01-08-2014, 03:41 PM
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Just trying to help people out
 
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Old 01-17-2014, 12:47 PM
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Dortiz thanks for sharing all that info. I wish I knew all this when I was searching for an idi. Lucky for me I bought my idi with no problems, at least none that I have encountered yet...... Anyways thanks for posting all this great info.
 
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Old 01-28-2014, 11:00 PM
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It was my pleasure, if only we could get this thread a sticky or something of the sort, it's a really useful read
 
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Old 01-30-2014, 01:39 PM
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Up Thanks Soooo Much!!

Just wanted to thank you Dortiz on this post. Very informative and I will definitely be looking into some upgrades for Marge!! Thanks again and great job!!
 
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Old 01-30-2014, 02:19 PM
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Glad you were informed
 
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Old 02-10-2014, 10:23 PM
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BUMP
 

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