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idi died. replace or rebuild?

22K views 15 replies 10 participants last post by  kladd  
#1 ·
my newly acquired '93 7.3 non-turbo idi with 323K miles has trouble cold starting. long story short the diagnosis now is low compression when cold. i could keep messing around but think its time to replace or rebuild this tired beast.

used engines are plentiful at $1k or less.

my question is how difficult are these to rebuild. i've done a few sbc's with success but no diesel experience. kits seem cheap and available. so how easy are these things for a hack mechanic to rebuild? special tools? obviously block would get sent out to machine shop. head too? what cost can i expect from that?

i will probably replace with a cheapo used motor and take my chances. but a rebuild would be educational and maybe cost effective.

kevin
 
#3 ·
you shouldnt have low compression when cold.. Alot of time these engine need new return line kits (40 bucks fleabay) Basically the return lines get old and cracked and let the fuel bleed back to the tank and this causes the hard start.. Id do a little more homework and try to see if you have a fuel problem. I believe there is also a check valve in that system that if malfunctioning will let the fuel bleed back also.. Just my 2 cents.
 
#5 ·
yeah there is a lot more to this story.

i am traveling now with a tiny keyboard so i will keep this short and fill in details later.

motor had other symptoms, some intermittent. like sometimes start then immediately die, classic symptom of air in fuel line. also rearmost tank would get down to 1/4 and motor would start missing (hole in pickup tube?). sometimes conked out while idling, usually requiring starting fluid to restart.

i needed the truck quick for plowing so took to a local mechanic. he swore compression fine and replaced all return lines. then lines around fuel filter etc. stumped. second mech decided it was low compression but i question his desire to really dig into problem.

i've since bought a $500 motor and will continue this saga when life and time and workshop permits. turns out i can't fit a longbed crewcab in my shop without some modification! since there is interest i will keep everyone posted.

btw, all i wanted the first mech to do was a compression test! ended up repairing my existing plowtruck for one more new england winter.

kevin
 
#6 ·
Take it to a diesel shop and tell them all you want done in a compression test. Most auto shop mechs don't even have a compression gauge capable of diesel compression pressures, nor the proper adapter fittings. If the compression is fine the diesel mechs will probably give you helpful pointers on what to look for. One thing you should ALWAYS do first is to replace the fuel filter(s), even if you think they are still fine. I have seen that bite so many people... Also, check yo make sure your glow plugs are working - ALL of them. IDI's need heat in the prechamber or else they will be virtually impossible to start cold. Cranking speed is important too - slow cranking=less compression heat=no start.

I will tell you an easy way to see if you have an upstream air leak. There is a rubber line coming off the top of your Stanadyne IP and going to the return hard line- that is the IP's return line. Temporarily replace the rubber hose with a piece of clear vinyl hose of the same size. Let the truck sit overnight, then have a buddy start it the next day while you watch the clear hose. If you get bubbles in the return hose, you have an upstream air leak. If it's all good, replace the vinyl hose with the rubber hose, and then check your inlet fuel pressure. It should be about the same as a carbed gas engine, somewhere in the 5 to 12 PSI range. IF the compression checks out, glows are working, fuel filters are new, there's no air leaks, and your lift pump is giving good fuel pressure, then you can start suspecting the IP. At 323K you should be on your second IP and ready for a third, not to mention injectors...
 
#7 ·
MaxPF, great info, thanks! its gonna be a month or 2 before i can dig into this again, but i surely will.
thanks again
kevin
 
#8 ·
I know it's an older post my dad's 94 IDI turbo had some starting issues and mising with only 125k on the clock this last year. we replaced the injectors and return lines and it actually made the problem bigger. used the clear line on the far back line to see if the return lines were gettign air and didn't find any. finally we turned the injection pump just a tiny bit figuring the pump was bad if timming wasn't. just a degree or two made it start better, gave it more power and better MGP. very small turns on the rotery pumps can do a lot for the IDI's
 
#9 ·
compression test results

i finally found the time to perform compression test:
all glow plugs removed.
engine stone cold.
40A charger connected with fresh dual batteries in truck - turns over fast.

front
350 460
480 480
460 480
440 430
rear

so, cylinder 1 is marginal but i am concluding compression is not contributing to starting trouble. glow plug system was functioning when i brought truck to mechanic #1. now 2 plugs are out. all return lines were replaced by same mechanic.

not sure what to do about low cylinder. in this warm massachusetts weather truck starts grudgingly with bad glow plugs.

next i'm gonna put 8 new motorcraft zd9's in and make sure relay working properly.
and a new lift pump and fuel filter.
and some clear line in a few spots to check for air intrusion.

i am also suspicious of tank pickups and lines for air intrusion. if truck starts/runs decent i will put back on road. won't really know for sure till cold weather.

kevin
 
#11 ·
With that many Miles or KM's on that engine the quickest way to tell is unscrew the return line from IP and see if you have black plastic bits if there the flex ring is gone it will screw up the timming and the same time the advance piston will be wornout and stay in retarded setting.

You can advance the timming but one stern warning do not go more than 5° advance otherwise you will overheat the engine . to advance move the injector pump toward to passnger side but before you do that make sure you see the notch on the IP and do very little and do this with the engine off otherwise you will damage it.

Replace all the glowplugs the same and see if you have later verison of glow plug controller I know I have TSB related to this engine but left the notes back in USA { I am in France } it did mention the restitor strip on glow plug controller.

And check each glow plug connectors as well.

If you engine start ok when it is cold but hot hard to start a tip grab a ice cube on the IP it will cool off a little and it will run. { I have done that twice before on IHC and few on JD engines }

To get rebuilted injector pump they will run about 500 Euros exhanged you may want to look around a little but do not get a used pump from other engine unless it have very low miles on IP.

As far for your water pump you should be replacing by now most will leak about 150,000 miles range.

Yeah the other thing when you rebuilt them they are free standing block no sleeves in there and also watch out for cavations the 7.3 have them on back two cylinder while the 6.9 are not too bad but the hot spot will be back two cylinders anyway.

Merci.
Marc
 
#12 ·
I'm facing very similar problems with my IDI powered F350 and have opted to start the Cumming 6BT conversion process (bought an engine, collecting other parts now). I've been battling 7.3 IDI Fords on and off for about five years now and never have I ever dealt with anything (gas or diesel) so unreliable and finicky as these engines. Even my Detroit 4-53 powered F250 was more reliable than either of my 7.3s (though decidedly less practical!).

A note on french277's comment on rebuilds, everything I've read and heard indicates that these engines are generally not rebuildable because the cylinder bores cannot be bored out without leaving too thin of a block or bored and sleeved without having problems with the sleeves coming loose. Look up the experiences of buyers of remanufactured engines over on fordtrucks.com in the 6.9/7.3 section and you'll see what I mean.

For me the swap decision was easy after I researched the cost and complexity: I live in a relatively remote area of upstate NY and have an office job a 40 minute commute away, so when it's snowing and 10 degrees and my daily driver just won't cut it the F350 HAS to start and run reliably or I'm hosed. The 7.3 just hasn't proven itself up to the task for me.

That's my $0.02 anyway, let us know how you make out.
 
#13 ·
A note on french277's comment on rebuilds, everything I've read and heard indicates that these engines are generally not rebuildable because the cylinder bores cannot be bored out without leaving too thin of a block or bored and sleeved without having problems with the sleeves coming loose. Look up the experiences of buyers of remanufactured engines over on fordtrucks.com in the 6.9/7.3 section and you'll see what I mean.
I have rebuilt couple of them allready and you have be very carefull how much you can take out of the bore and most of the 7.3 block I have ran into most will have cavation issue once you see it I will not bother to rebore it at all just get a short block or new bare block if possible the 6.9 block do have little leeways but not much at all.

Merci.
Marc
 
#14 ·
Another 2 cents. in the land of diesels if you do not have an engine what incorporates sleeves, well. more than likely it was never ment to be rebuilt. Its dissposible at the end of its service life. Not talking Mercedes here, or older high nickle engines of yore..And 300plus on a 7.3 and yet you really do have good compression, go figure. As for that compression, unless you can do a hot(or at the least a fairly warm) test u are only getting half the picture. Me, i'd stick some systhetic in the oil, dissconnectb the glow plugs and put an either injection set-up on it. Thats what i got on my 6BT. Starts every time. Even in Wisconsin..MM
 
#15 ·
Another 2 cents. in the land of diesels if you do not have an engine what incorporates sleeves, well. more than likely it was never ment to be rebuilt. Its dissposible at the end of its service life.
That is an old falsehood. The reason larger engines are built with sleeves is to allow in frame overhauling. Beyond a certain size it is much easier to in-frame an engine rather than pull it out to rebuild or replace it with a reman. Also, most local shops lack the ability to bore and hone larger engines. Not to mention, it's easier to manufacture large engines with seperate sleeves. If the engines were "disposable", the manufacturers wouldn't offer oversize pistons, sleeves, and factory remans for them.
 
#16 ·
well i figured i should give an update of progress.

after the compression test showed good results, i decided to totally go thru the fuel system. the return lines on the top of the engine had already been gone thru. this is what i found:

return line from tee on back of engine down to hard line at frame rail looked original and highly suspect.

pickups in both tanks had desintigrated as suspected. thats why i got cavitation at 1/4 tank.

fuel supply hardline on front tank had pinhole right before the quick disconnect flare!

all hardlines, disconnects, and rubber lines were replaced but all looked ok.

lift pump was replaced with electric pump which i located just after fuel selector valve.

truck now starts instantly if at all warm. has never again conked out. and cold starts pretty good in freezing temps. i think a new starter may help cold starts. glowplugs are new and working properly. batteries new and cables good.

these motors seem to have a fussy reputation. we'll see how it works out. but hopefully i am ready for snowplow season.

kevin